3 5 2 . 1

7 3 M E

METHANE DIGESTERSFOR FUEL GAS AND FERTILIZER

WITH COMPLETE INSTRUCTIONSFOR TWO WORKING MODELS

52. ' 9-3

Price $4.00L JOHN FRY1223 North Nopal StreetSanta Barbara, Calif. 93103

Inspiration: L. John Fry

Contributors: L. John Fry, Richard Merrill

Editors: Richard Merrill, Yedida Merrill

© 1973 L. John Fry Artwork: Beth AmineRichard Merrill

Thanks to: Earl BarnhartTwelfth Printing

Kim M i t c h e l l

METHANE DIGESTERSFor Fuel Gas and Fertilizer

TABLE OF CONTENTS -2>jT2' I

I INTRODUCTION 1

I I BACKGROUND 2

II I HISTORY 7

IV B IOLOGY OF DI GEST ION 8

Bio-Succession in the Digester 8

pH 9

Temperature 10

V RAW MATER IALS 12

Digestible Properties of Organic Matter 12

Manure Production and the Livestock Unit 13

Carbon to Nitrogen Ratio 13

Calculating C/N Ratios 16

VI THE GAS 17

VI I Dl GESTERS 19

Raw Materials and Design 20

Loading Rate, Etc 21

Heating Digesters 22

VIM USING GAS 23

Efficiency of Digestion Process 2k

IX US ING SLUDGE 25

X BUILDING A SUMP DIGESTER 29

XI BUILDING AN INNER TUBE DIGESTER 31

XII NECESSITY IS THE MOTHER OF INVENTION kO

XIII REFERENCES k5

Mr. L. John Fry beside a three digester unit he made in1973- Gas holder center, water-heater on the right. Bucketsin the foreground were for loading raw materials. This unitwas taken down in 1974-

Recently, attention has turned to methanedigesters as a source of fuel gas and fer-tilizer. The interest is understandable inview of the mounting shortages of energysources (whether real or political) and theincreasing desire of many to develop a moreself—sufficient pattern of livingespecially in rural areas.

However, much of the information concern-ing digesters and digester systems has beenmisleading and overly complex. It has avoid-ed basic questions such as: how much raw or-ganic material can be expected from theplant or animal wastes available? How muchgas will they produce? What kind and sizeof digester should be built? (so that itsuits the needs and resources of whoeverbuilds it). And how is the digester started?

The answers to these questions aren'tthat difficult, and we have found that pro-ductive digester operations can be built and

maintained by knowing some things about thebiology of digestion, and the properties ofthe raw materials going into the digester.Of course, this knowledge is useless withoutdirect experience with small-scale models(which can be constructed cheaply from easi-ly available materials). Once the digesteris understood at this level, larger unitscan be built with more sophisticated ways ofusing methane gas energy and recyclingsludge back into the biological systems.

In this newsletter we would like to: (1)present a general background of the raw ma-terials and processes of digestion; (2) dis-cuss some preliminary ideas for using meth-and gas and sludge; (3) describe two designsfor building simple working models of diges-ters; and (4) develop feedback from readerswho are working on digester projects acrossthe country.

1

BACKGROUND

When organic material decays it yieldsuseful by-products. The kind of by-productdepends on the conditions under which decaytakes place. Decay can be aerobic (withoxygen) or anaerobic (without oxygen). Anykind of organic matter can be broken downeither way, but the end products will bequite different (Fig. 1).

It is possible to mimic and hasten thenatural anaerobic process by putting organicwastes (manure and vegetable matter) intoinsulate/i, air-tight containers called di-gesters. Digesters are of two types: XT)Batch-load digesters which are filled all atonce, sealed, and emptied when the raw mate-rial has stopped producing gas; and (2) Con-tinuous-load digesters which are fed a Tvt-tle, regularly, so that: gas and fertilizerare produced continuously.

The digester is fed with a mixture of wa-ter and wastes, called "slurry." Inside thedigester, each daily load of fresh slurryflows in one end and displaces the previousday's load which bacteria and other microbeshave already started to digest.

Each load progresses down the length ofthe digester to'a point where the methanebacteria are active. At this point largebubbles force their way to the surface wherethe gas accumulates. The gas is very similarto natural gas and can be burned directlyfor heat and light, stored for future use,or compressed to power heat engines.

Digestion gradually slows down toward theoutlet end of the digester and the residuebegins to stratify into distinct layers (Fig.2).

ANAEROBIC DECAY(without oxygen)

"NATURAL"/ \

ORGANIC WASTES

AEROBIC DECAY(with oxygen)

/ \"ARTIFICIAL" "NATURAL" "ARTIFICIAL"

Air-tightDigester

BIO-GAS

PEAT MANURE SLUDGE

FIG.l End Products of Organic Decay

Plant Wastes,Animal Bodies,Dung Piles

AMMONIA,CARBON DIOXIDE

AMMONIA,CARBON DIOXIDE

HUMUS SOLIDS

at the bot-

Liquid orfer t i l izer

dryfor

liquids of the

Sand and Inorganic Materialstorn.

Sludge, the spent solids of the originalmanure reduced to about 40% of the volume i toccupied in the raw state,sludge makes an excellentcrops and pond cultures.

Supernatant, the spentoriginal slurry. Note that the fert i l iz ingvalue of the liquid is as great as sludge,since the dissolved solids remain.

Scum, a mixture of coarse fibrous materi-a l , released from the raw manure, gas, andliquid. The accumulation and removal of scumis one of the most serious problems with d i -gesters. In moderate amounts, scum can actas an insulation. But in large amounts i tcan virtually shut down a digester.

PHASES

GAS

LIQUID 1

SOLID

BIO-GAS

SCUM

SUPERNATANT

DIGESTED SLUDGE(SPENT SLURRY)

INORGANIC SOLIDS

USEABLERESOURCE

^.COMBUSTIBL

•> FERTILIZERINSULATOR

•*• BIOLOGICAL LACTIVE

•• FERTILIZER

FIG.2 Layering of By-ProductsIn the Digester

For perspective, consider the total fuelvalue of methane that could be produced fromthe available organic wastes in the UnitedStates.

I. Fuel Value of U.S. Methane Resources (From Ref. 1)

A. Organic wastes in U.S./year 2 billion tons (wet weight)

800 million tons (dry weight)B. Dry organic waste readily collectable 136.3 million tonsX. Methane available from "B" 1.36 trillion ftVyear

(@10,000 ft3/ton)*D. Fuel value of methane from "C" 1,360 trillion BTU/yr

(1000 BTU/ft3)

II. Fuel Consumption of U.S. Farm Equipment (From Ref. 2)A. Total gasoline consumed (1965) 7 billion gallons/yearB. Total energy consumed by "A" 945 trillion BTU/year

(1 gallon gasoline = 135,000 BTU)

III. Total U.S. Natural Gas Consumption (1970) 19,000 trillion BTU

IV. Total U.S. Energy Consumption (1970) 64,000 trillion BTU

*Urban refuse; higher figure for manure and agricultural wastes.

Table 1. Total Fuel Value of U.S. Methane Resources Suppliedby Digestion of Readily Collectable, Dry, Ash-FreeOrganic Wastes.

So, speaking generally, methane gas con-verted from easily available organic wastescould supply about 150% of the gasoline en-ergy used by all U.S. farm equipment (1965),7% of the 1970 natural gas energy, and 2% ofthe total 1970 U.S. energy demands.

Methane-Gas Plant: Synergy at Work

When we consider digesters on a homesteadscale, there are two general questions toask: (1) with the organic wastes and re-sources at hand, what kind of digestershould be built, and how big should it be?and (2) what is the best way of using thegas and sludge produced to satisfy the ener-gy needs of the people involved? (whetherthe sludge should be used to fertilize crops,fish or algae ponds, and whether the gasshould be used directly for heat, and light,or stored, or fed back to the digester toheat it, etc. Fig. 3).

The first question involves the digesteritself, which is just the heart of a wholeenergy system. The second question is syn-ergistic; you can choose which products areto be generated by digestion and how to usethem or feed them back to the digester,"cre-

ating an almost endless cycle if you wished(Fig. 4).

The model in Figure 4 is idealized fromoriental aquaculture systems and other ideas,both old and new. A single pathway can bedeveloped exclusively (have your digesterproduce only sludge to feed an algae pond)or you can develop the potential synergy(many possible systems working together asan integrated whole, Fig. 5).

The small farmer or rural homesteader cantake a step toward ecological self-suffi-cency by producing some of his fuel and fer-tilizer needs using a digester to convertlocal wastes.

Total dependence on conventional fuels,especially in rural areas, is likely to be-come a serious handicap in the years to comeas reserve shortages and specialized tech-nologies hike the costs of fossil and nucle-ar fuels. But by producing energy from localresources, it is possible to be partiallyfreed from remote sources of increasinglyexpensive fuel supplies.

Kinds of AvailableBui lding Materials

Kinds of FreshOrganic Wastes Available

PLANT AN IMAL

DETER IINE

SIZE AND TYPEOF DIGESTER

Needs of Familyor Communi ty

METHANELighting, Heating,Cooking, RunningEngines

SLUDGELiquid Fert i 1 izer

FIG.3 Related Considerations of a Digester Operation

CROPS FISHPOND

FOOD

ALGAEPOND

WATERBOILERHEAT

ENGINE

BIO-GAS

BURNERS

HEAT,LIGHT

ALGAEPOND

ANIMALFEED

FIG.k The Closed Nutrient System of a Complete Digester Operation

ENGINE(RototillerK

HIGH-PRESSURETANK

COMPRESSOR

THERMOSTAT(140* R)

RAW MATERIAL

DIGESTERWATERCOILS

GAS OUTLET

THERMOSTAT (95°E)WATERBOILER(LOWTEMR>

CONDENSATION TRAP

HYDROPONICGRASSES

\ I ]

- i STORAGETANK

FIG.5 Integrated Organic Digester Operation(Using 50 gal lon drums for digester)

HISTORY

In nature, anaerobic decay is probablyone of the earth's oldest processes for de-composing wastes. Organic material coveredby a pool of warm water will first turn acidand smell rank, then slowly over about sixmonths will turn alkali. The methane bacte-ria, always present, will take over and de-compose it, and gas bubbles will rise to thesurface.

Anaerobic decay is one of the few naturalprocesses that hasn't been fully exploiteduntil recent times. Pasteur once discussedthe possibilities of methane production fromfarmyard manure. And (according to a reportissued from China April 26, 1960) the Chin-ese have used "covered lagoons" to supplymethane fuel to communes and factories fordecades. But the first attempt to build adigester to produce methane gas from organicwastes (cow dung) appears to have been inBombay, India in 1900. At about this time,sewage plants started digesting sewagesludge in order to improve its quality. Thisstarted a mass of laboratory and small-scaleexperiments during the 20's and 30's (manyof them summarized by Acharya, Ref. 3).

During World War II, the shortage of fuelin Germany led to the development of methaneplants in rural areas, where the gas wasused to power tractors. The idea spread intoWestern Europe, until fossil fuels onceagain became available (although, today,many farmers in France and Germany continueto use home digesters to produce their ownmethane fuel gas).

Currently the focus of organic digester/bio-gas research is in India. India's impe-tus has been the overwhelming need of a de-veloping country to raise the standard ofliving of the rural poor. Cows in India pro-duce over 800 million tons of manure peryear; over half of this is burned for fueland thus lost as a much needed crop ferti-lizer.1* The problem of how to obtain cheapfuel and fertilizer at a local level led toseveral studies by the Indian AgriculturalResearch Institute in the 1940's to deter-mine the basic chemistry of anaerobic decay.In the 1950's, simple digester models weredeveloped which were suitable for villagehomes. These early models establishedclearly that bio-gas plants could: (1) pro-vide light and heat in rural villages, elim-

inating the need to import fuel, to burn cowdung, or to deforest land; (2) could pro-vide a rich fertilizer from the digestedwastes; and (3) could improve health con-ditions by providing air-tight digester con-tainers, thus reducing disease borne by ex-posed dung.

More ambitious designs were tested by thePlanning Research and Action Institute inthe late 1950's. Successes led to the startof the Gobar Gas Research Station at Ajitmalwhere, with practical experience from theKhadi and Village Industries Commission, twoimportant pamphlets5'6 were published on thedesign of village and homestead "bio-gas"plants in India.

In America, where the problem is wastedisposal, rather than waste use, organic di-gesters have been limited to sewage treat-ment plants.7'8 In some cases sludge is re-cycled on land or sold as fertilizer,9'10

and methane gas is used to power generatorsand pumps in the treatment plants.11 TheHyperion sewage treatment plant in Los An-geles generates enough methane from its pri-mary treatment alone to power its 24-2,000hp. diesel engines. Usually, however, bothsludge and gas are still regarded as wasteproblems.

Much information on digestion and small-scale digester operations comes from exper-iences in India, Western Europe and SouthAfrica and journals such as: Compost Sci-ence, Water Sewage Work, Soils and FertilT-zer, Waste Engineering, Sewage and Industri-al Wastes and recent publications of theU.S. Environmental Protection Agency andSolid Waste Conferences (see Bibliography atend). An excellent book to learn from iscalled:Plant

Manual of Instruction for SewageOperators,put out by t h e N e w Y o r k

State Dept. of Health and available from theHealth Education Service, P.O. Box 7283,Albany, New York 12224.

A great deal of information can be foundin pre-WW II sewage journals, especiallySewage Works Journal. After WW II, as withmost other kinds of science and technology,waste treatment research became a victim ofthe trend to make machines ever bigger, andinformation increasingly incomprehensible.

BIOLOGY OFDIGESTION

Bio-Succession In The Digester

Perhaps the most important thing to re-member is that digestion is a biologicalprocess.

The "anaerobic" bacteria responsible fordigestion can't survive with even the slight-est trace of oxygen. So, because of the ox-ygen in the manure mixture fed to the diges-ter, there is a long period after loadingbefore actual digestion takes place. Duringthis initial "aerobic" period, traces of ox-ygen are used up by oxygen-loving bacteria,and large amounts of carbon dioxide (C02)are released.

When oxygen disappears, the digestionprocess can begin. That process involves aseries of reactions by several kinds of an-aerobic bacteria feeding on the raw organic

matter. As different kinds of these bacteriabecome active, the by-products of the firstkind of bacteria provide the food for theother kind (Fig. 6). In the first stages ofdigestion, organic material which is digest-ible (fats, proteins and most starches) arebroken down by acid producing bacteria intosimple compounds. The acid bacteria are ca-pable of rapid reproduction and are not verysensitive to changes in their environment.Their role is to excrete enzymes, liquefythe raw materials and convert the complexmaterials into simpler substances (especial-ly volatile acids, which are low molecularweight organic acids - See Raw MaterialsSection). The most important volatile acidis acetic acid (table vinegar is dilute ace-tic acid), a ̂ ery common by-product of allfat, starch and protein digestion. About70% of the methane produced during fermenta-tion comes from acetic acid.12

Once the raw material has been liquefiedby the acid producing bacteria, methane pro-ducing bacteria convert the volatile acids

RAW ORGANIC WASTES

INORGANICPORTION

IORGANICPORTION

\

INDIGESTIBLE DIGESTIBLE

ACID PRODUCINGBACTERIA

SIMPLE COMPOUNDS

VOLATILE SOLIDS

METHANE PRODUCINGBACTERIA

I IMINERALCOMPOUNDS

FIBER,LIGNIN

1METHANE CARBON

DIOXIDEWATER,AND GASES

FIG.6 The Biological Breakdown of Wastes in the Digester

into methane gas. Unlike the acid bacteria,methane bacteria reproduce slowly and arevery sensitive to changes in the conditionsof their environment. (More information onthe biology of methane fermentation can befound in Ref. 13 and 14.)

Biologically, then, successful digestiondepends upon achieving and (for continuous-load digesters) maintaining a balance be-tween those bacteria whicf. produce organicacids and those bacteria wi:"^ produce meth-ane gas from the organic acids. This bal-ance is achieved by a regi ar feeding withenough liquid (see Feeding Section) and bythe proper pH, temperature i thz qualityof raw materials in the digest

acidity during which volatile acids and ni-trogen compounds are digested, and ammoniacompounds are formed (this ammonia becomesimportant when we consider the fertilizervalue of sludge). As digestion proceeds,less C02 and more methane is produced andthe pH rises slowly to about 7. As the mix-ture becomes less acid, methane fermentationtakes over. The pH then rises above theneutral point (pH = 7), to between pH 7.5and 8.5. After this point, the mixture be-comes well buffered; that is, even whenlarge amounts of acid or alkali are added,the mixture will adjust to stabilize itselfat pH 7.5 to 8.5.

ACID

THE WELL BUFFERED DIGESTERI

10

BeerSoft drinks

.VinegarStomach acid

EU

%m f* I « 1 •

11 12

BASIC

Sodium bicarbonateBlood

H/ATERI-Cow's milk

Sali va Ammoni a

FIG.7 The pH Scale

pH and the Well-Buffered Digester

To measure the acid or alkaline conditionof a material, the symbol "pH" is used. Aneutral solution has pH = 7; an acid solu-tion has pH below 7; and an alkaline solu-tion has pH above 7. The pH has a profoundeffect on biological activity, and the main-tenance of a stable pH is essential to alllife. Most living processes take place inthe range of pH 5 to 9. The pH requirementsof a digester are more strict (pH 7.5-8.5,Fig. 7).

During the initial acid phase of diges-tion, which may last about two weeks, the pHmay drop to 6 or lower, while a great dealof C02 is given off. This is followed byabout three months of a slow decrease in

Once the mixture has become well buffer-ed, it is possible to add small amounts ofraw material periodically and maintain aconstant supply of gas and sludge (continu-ous load digesters). If you don't feed adigester regularly (batch-load digesters),enzymes begin to accumulate, organic solidsbecome exhausted and methane productionceases.

After digestion hasshould remain around 8pH values of effluentplants is 7 to 7.5,usually given as the

stabilized, the pH0 to 8.5. The idealin sewage treatment

and these values arebest pH range for di-

gesters in general. From our experience, aslightly more alkaline mixture is best fordigesters using raw animal or plant wastes.

You can measure the pH of your digesterwith "litmus" or pH paper which can be boughtat most drug stores. Dip the pH paper intothe effluent as it is drawn off. Litmus pa-per turns red in acid solutions (pH 1 to 7)and blue in alkaline solutions (pH 7 to 14).You can get more precise measurements usingpH paper which changes colors within a nar-row range of pH values.

ter, (3) the sludge they produce is of poorfertilizer quality, and (4) because it isdifficult to maintain such a high tempera-ture, especially in temperate climates.

The bacteria that produce methane in the"normal range" 90°-95°F are more stable andproduce a high quality sludge. It is notdifficult to maintain a digester temperatureof 95°F (See Digester Heating Section).

Condition

Too acid

(pH 6 or less)

Too Alkaline

(pH 9 or more)

Possible Reasons

1) Adding raw materials too fast

2) Wide temperature fluctuation

3) Toxic Substances

4) Build-up of scum

1) Initial raw materialtoo alkaline

"Cure"

Reduce feeding rate;Ammonia

Stabilize temperature

Remove scum

Patience

Never put acid intodigester

Table 2. Problems with pH.

If the pH in the continuous-load digesterbecomes too acidic (Table 2), you can bringit up to normal again by adding fresh efflu-ent to the inlet end, or by reducing theamount of raw material fed to the digester,or as a last resort, by adding a little am-monia. If the effluent becomes too alkaline,a great deal of C02 will be produced, whichwill have the effect of making the mixturemore acidic, thus correcting itself. Pa-tience is the best "cure" in both cases.NEVER add acid to your digester. This willonly increase the production of hydrogensulfide.Temperature

For the digesting bacteria to work at thegreatest efficiency, a temperature of 95°F(36°C) is best. Gas production can proceedin two ranges of temperature: 85°-105° and120°-140°F. Different sets of acid-producingand methane bacteria thrive in each of thesedifferent ranges. Those active in the high-er range are called heat-loving or "thermo-philic" bacteria (Fig. 8). Some raw materi-als, like algae, require this higher rangefor digestion. But digesters are not com-monly operated at this higher range because:(1) most materials digest well at the lowerrange, (2) the Thermophilic Bacteria arevery sensitive to any changes in the diges-

4-1

*a>DC

LU

Z

o

STI

IGE

o

\\

\

V\

NORMALRANGE

THERMOPHILICRANGE

-

50 Co 7o 90 9o too no zo 5

TEMPERATURE, F°

FIG.8 Digestion Time and Temperature

(af ter Ref. 7)

10

75'

CTO

CO

50'0)Q.

"a0)o

Oa.

25

13x

73

a>ena>

-aOO

g

40 50 60 68 77 86 95 ^

Temperature

FIG.9 Gas Production and Temperature(after Ref. 15)

The same mass of manure will digest twiceas fast at 95° than it will at 60° (Fig. 8)and it produces nearly 15 times more gas inthe same amount of time!(Fig. 9)i(See how theamount of gas produced improves with temper-ature to 80°-100°F, where production is op-timum.) In Fig. 10 it can be seen how adi^terent amount of gas is produced when thedigester is kept at 60° than when it is keptat ;5°.

•olOO 1

70

o<a; 35

0)

10 20 30

TIME (Days)

50 60 70

FIG. 10 Comparison of Gas Production Rates at 60°F and 95°F

(Measured from time new sludge addedto buffered digester).

11

RAW MATERIALS

The amount and characteristics of organicmaterial's (both plant and animal wastes)available for digestion vary widely. In ru-ral areas, the digestible material will de-pend upon the climate, the type of agricul-ture practiced, the animals used and theirdegree of confinement, the methods of col-lecting wastes, etc. There are also degreesof quality and availability unique to urbanwastes. Because of all these things, it ispractically impossible to devise or use anyformula or rule-of-thumb method for deter-mining the amount and quality of organicwastes to be expected from any given source.There is, however, some basic informationwhich is useful when you start wondering howmuch waste you can feed your digester.

Digestible Properties of Organic Matter

When raw materials are digested in a con-tainer, only part of the waste is actuallyconverted into methane and sludge. Some ofit is indigestible to varying degrees, andaccumulates in the digester or passes outwith the effluent and scum. The "digesti-bility" and other basic properties of organ-ic matter are usually expressed in the fol-lowing terms (see Ref. 16):

MOISTURE: The weight of water lost upondrying at 220°F until no more weightis lost.

TOTAL SOLIDS (TS): The weight of drymaterial remaining after drying asabove. TS weight is usually equiva-lent to "dry weight." (However, ifyou dry your material in the sun,assume that it will still containaround 30% moisture.) TS is composedof digestible organic or "VolatileSolids" (VS), and indigestible resi-dues or "Fixed Solids."

Volatile Solids(VS): The weight oforganic solids burned off when drymaterial is "ignited" (heated toaround 1000°F). This is a handyproperty of organic matter to know,since VS can be considered as theamount of solids actually convert-ed by the bacteria.

Fixed Solids (FS): Weight remainingafter ignition. This is biologi-cally inert material.

As an example, consider the make-up offresh chicken manure.17

So if we had 100 pounds of fresh chickenmanure, 72-80 pounds of this would be water,and only 15-24 pounds (75-80?Volatile Solidsof the 20-28% Total Solids) would be avail-able for actual digestion (Fig. 11).

72 - 802WATER

20TOTAL

- 28%SOLIDS

-VOLATILE SOLIDS

nFIXED SOLIDS

75 - 801

20 - 25%

Composition ofChicken Manure

Composi tion ofTotal Soli ds inChicken Manure

FIG.11 Properties of Chicken Manure

Amount of Manure Collectable

When you see a table which shows theamount of manure produced by different kindsof livestock, it's important to know thatthe amount on the table may not be theamount that is actually available from youranimals. There are three major reasons forthis:

1) The Size (Age) Of The Animal

Consider the total wet manure productionof different sized pigs:

Total RatioHog Manure Manure/Weight Lbs/Day Feces Urine Hog Wt.

40-80

80-120

120-160

160-200

(From

5.6

11.5

14.6

17.6

37)

2.7

5.4

6.5

8.5

2.9

6.1

8.1

9.1

1:11

1:9

1:10

1:10

Table 3

12

So the size (age) of your livestock has alot to do with the amount of manure produced.Notice that the ratio of total wet manureproduction to the weight of the pig is fairlyconstant. It is likely that similar ratioscould be worked out for other kinds of live-stock, enabling you to estimate the produc-tion of manure from the size of livestock.2) The Degree of Livestock Confinement

Often the values given for manure produc-tion are for commercial animals which aretotally confined. All of their manure canbe collected. On the homestead or smallfarm, total confinement of the livestock isnot always possible or even desirable. (For-'aging and uncrowded livestock are less like-ly to contact diseases and more likely toincrease the quality of their diet with nat-urally occurring foods.) Because of this, alarge proportion of the manure is depositedin fields and thus hard to collect. For ex-ample, the fresh manure production of com-merical chickens in total confinement isabout 0.4 lbs. per chicken per day. 1 7» 2 8

However, for small-scale operations likehomesteads and smali farms, where preferencetends to favor the well-being of the chick-ens rather than the economics of egg produc-tion, chickens are often allowed to forageall day and confined only at, night. In suchcases, only manure dropped during the nightfrom roosts can be conveniently collected.In our experience, this may amount to onlyabout 0.1 to 0.2 pounds of fresh manure perday per adult chicken. Similar reasoningholds for other livestock.

3) The Kind of Manure that is Collecteda) All the fresh excretement (feces and

urine).b) All the fresh excretement plus the

bedding material•-. —.c) Wet feces only.d) Dry feces only.

Manure Production and the Livestock Unit

Keeping in mind all these factors that canaffect the type and amount of manure that canbe collected, we can assemble a general ma-nure production table. The table only showsrough average values obtained for manysources.15>17»21~39 Values are expressed asthe amount in pounds of wet manure, dry ma-nure and volatile solids that could be ex-pected from various adult livestock per day.For the table, an adult animal is: cow -

1000 lbs; horse - 850 lbs; swine - 160 lbs;human - 150 lbs; sheep - 67 lbs; turkey - 15lbs; duck - 6 lbs; chicken - 3% lbs. (Weneed information on goats and rabbits.)

Table 4 enables us to get some idea of theproduction of readily digestible material(volatile solids) from different animals.Only the feces is considered for cows,horses, swine, and sheep, since their urineis difficult to collect. However, for humansand fowl, both urine and feces are given,since they are conveniently collected togeth-er.

The relative values of digestible wastesproduced are not given in pounds of manureper animal per day,.but in a more convenientrelative unit called the "Livestock Unit."The table shows that on the average one me-dium horse would produce as much digestiblemanure as 4 large pigs, 12% ewes, 20 adulthumans or 100 chickens.

Carbon to Nitrogen Ratio (C/N)

From a biological point of view, digesterscan be considered as a culture of bacteriafeeding upon and converting organic wastes.The elements carbon (in the form of carbohy-drates) and nitrogen (as protein, nitrates,ammonia, etc.) are the chief foods of anaero-bic bacteria. Carbon is utilized for energyand the nitrogen for building cell struc-tures. These bacteria use up carbon about30 times faster than they use nitrogen.

Anaerobic digestion proceeds best whenraw material fed to the bacteria contains acertain amount of carbon and_ nitrogen togeth-er"! TRe carbon to nitrogen ratio (C/N) rep-resents the proportion of the two elements.A material with 15 times more carbon thannitrogen would have a C/N ratio of 15 to 1(written C/N = 15/1, or simply 15).

A C/N ratio of 30 (C/N = 30/1, 30 timesas much carbon as nitrogen) will permit di-gestion to proceed at an optimum rate, ifother conditions are favorable, of course.If there is too much carbon (high C/N ratio;60/1 for example) in the raw wastes, nitro-gen will be used up first, with carbon leftover. This will make the digester slow down.On the other hand, if there is too much ni-trogen (low C/N ratio; 30/15 for example, orsimply 2), the carbon soon becomes exhaustedand fermentation stops. The remaining ni-trogen will be lost as ammonia gas (NH3).This loss of nitrogen decreases the fertilityof the effluent sludge.

AverageAdultAnimal

BOVINE

HORSES

SWINE

SHEEP

HUMANS150 lbs.

FOWL

(1000 lbs.)

BullsDairy cowUnder 2 yrsCalves

(850 lbs.)

HeavyMediumPony

(160 lbs.)Boar, sowPig >160 lbsPig <160 lbsWeaners

(67 lbs.)

Ewes, ramsLambs

Portion

Urine)FecesBoth

Geese,Turkey(15Ducks (6 lb.)Layer Chicken(3iBroiler Chicken

lbs/day/animalUrine Feces

20

8

4.0

1.5

Amount

2 pints, 2.0.5 lbs2.7 lbs

lb.)0.5

lb.)0.30.1

52

36

7.5

3

,2 lbs

Total Solids/Day

20% ofFeces

%TS

6%27%11%

35%

10

7

1.5

0.5

TS/Day

.13

.14

.3

.1

VolatileSolids/Day80% of TS -85% for Swine

8.0

5.5

1.3

0.4

%VS

75%92%84%

65%

VS/Day

.10

.13

.25

.06

LivestockUnits

130-1501205010

130-15010050-70

2520102

84

5

21.51

TABLE 4. Manure and the Livestock Unit

There are many standard tables listing theC/N ratios of various organic materials, butthey can be very misleading for at least tworeasons:

1) The ratio of carbon to nitrogen measur-ed chemically in the laboratory is of-ten not the same as the ratio of car-bon and nitrogen available to the bac-

teria as food (some of the food couldbe indigestible to the bacteria; straw,lignin, etc.).

2) The nitrogen and carbon content of evena specific kind of plant or animalwaste can vary tremendously accordingto the age and growing conditions ofthe plant; and the diet, age, degreeof confinement, etc., of the animal.

Nitrogen: Because nitrogen exists in somany chemical forms in nature (ammonia, NH3;nitrates, N0?; proteins, etc.), there are noreliable "quick" tests for measuring the to-tal amount of nitrogen in a given material.One kind of test might measure the organicand ammonia nitrogen (the Kjeldahl test),another might measure the nitrate/nitritenitrogen, etc. Also, nitrogen can be mea-sured in terms of wet weight, dry weight orvolatile solids content of the material; allof which will give different values for theproportion of nitrogen. ' Finally, the nitro-gen content of a specific kind of manure orplant waste can vary, depending on the grow-ing conditions, age, diet, and so forth.

For example, one study reported a fieldof barley which contained 39% protein on the21st day of growth, 12% protein on the 49thday (bloom stage), and only 4% protein onthe 86th day.15 You can see how much theprotein nitrogen depends on the age of theplant.

The nitrogen content of manure also variesa great deal. Generally, manures consist offeces, urine and any bedding material (straw,corn stalks, hay, etc.) that may be used inthe livestock shelters. Because urine is theanimal's way of getting rid of excess nitro-gen, the nitrogen content of manures isstrongly affected by how much urine is col-lected with the feces.

For example, birds naturally excretefeces and urine in the same load, so that thenitrogen content of chickens, turkeys, ducks,and pigeons are highest of the animal ma-nures in nitrogen content. Next in nitrogencontent, because of their varied diets orgrazing habits are humans, pigs, sheep, andthen horses. Cattle and other ruminants(cud chewers) which rely on bacteria in theirgut to digest plant foods, have a low con-tent of manure nitrogen because much of theavailable nitrogen is used to feed their in-testinal bacteria. (Fig.12)

Even with the same kind of animal thereare big differences in the amount of manure-nitrogen. For example, stable manure ofhorses may have more nitrogen than pasturemanure because feces and urine are excretedand collected in the' same small place.

Since there are so many variables, andbecause anaerobic bacteria can use most formsof nitrogen, the available nitrogen contentof organic materials can best be generalizedand presented as total nitrogen (% of dryweight)..

Carbon: Unlike nitrogen, carbon exists inmany forms which are not directly useable bybacteria. The most common indigestible formof carbon is lignin, a complex plant com-pound which makes land plants rigid and de-cay-resistant. Lignin can enter a digestereither directly with plant wastes themselvesor indirectly as bedding or undigested plantfood in manure. Thus, a more accurate pic-ture of the C part of the C/N ratio is ob-tained when we consider the "non-lignin"carbon content of plant wastes.

100

50

Org-an-ic

MMMI

Amm-oni a(NH3

COW

) r g .

• • • •

NH3

PIG

NH3

CHICKEN •

FIG.12 Types of NitrogenFound in Different Kindsof Manure

15

Calculating C/N Ratios

Table 5 can be used to calculate roughlythe C/N ratios of mixed raw materials. Con-sider the following examples:

Example 1: Calculate the C/N ratio of 50 lbshorse manure (C/N=25) and 50 lbs dry wheatstraw (C/N=150).

Nitrogen in 50 lbs horse manure = 2.3% x50 = 1.2 lbs

Carbon in 50 lbs horse manure = 25 timesmore than nitrogen = 25 x 1.2 = 30 lbs

Nitrogen in 50 lbs wheat straw = 0.5% x50 = .25 lbs

Carbon in 50 lbs wheat straw = 150 timesmore than nitrogen = 150 x .25 = 37.5lbs

Carbon

Nitrogen

Manure

30

1.2

Straw

37.5

.25

Total

67.5

1.45

lbs

lbs

C/N ratio = 67.5/1.45 = 46.5

Although a bit high, this would be asatisfactory ratio for most digestion pur-poses.

Example 2: Calculate the C/N ratio of 8 lbsgrass clippings (C/N=12) and 2 lbs ofchicken manure (C/N=15).

Nitrogen in 8 lbs grass clippings = 4% x8 = .32 lbs

Carbon in 8 lbs grass clippings = 12 timesmore than nitrogen = 3.8 lbs

Nitrogen in 2 lbs chicken manure = 6.3% x2 = .13 lbs

Carbon in 2 lbs chicken manure = 15 timesmore than nitrogen = 1.9 lbs

Carbon

Nitrogen

Manure

3.8

.32

Grass

1.9

.13

Total

5.7

.45

C/N ratio = 5.7/.45 = 12.6

The C/N ratio of this mixture is low. Wemight want to add a higher proportion ofchicken manure since it contains more carbonper weight than the grass.

The following table is a summary of theimportant chemical properties of organic ma-terials. Values are averages derived frommany sources11*»16'18"33 and should be usedonly for approximation.

ANIMAL WASTESUrineBloodBone MealAnimal TankageDry Fish Scraps

MANUREHuman, feces

, urineChickenSheepPigHorseCow

SLUDGEMilorganiteActivatedFresh Sewage

PLANT MEALSSoybeanCottonseedPeanut Hull

PLANT WASTESHay, Young GrassHay, AlfalfaHay, Blue GrassSeaweedNon-Legume

VegetablesRed CloverStraw, OatStraw, WheatSawdust

TotalNitrogen% Dry

1612

6186.3.3.2.1.

5

42.2.1.2.

1.1.0.0.

Weight

38837

8595-4

8151

C/N Ratio

0.83.53.54.1*5.1*

6-10

15

25*18*

5.4*611*

55*

36*

1217*191911-19

2748150200-500

Nitrogen is total nitrogen dry weight andcarbon is either total carbon (dry weight)or (*) non-lignin carbon (dry weight).

Table 5. Carbon & NitrogenValues of Wastes

THE GASComposition

The gas produced by digestion, known asmarsh gas, sewage gas, dungas, or bio-gas,is about 70% methane (CHO and 29% carbondioxide (C02) with insignificant traces ofoxygen and sulfurated hydrogen (H2S) whichgives the gas a distinct odor. (Although itsmells like rotten eggs, this odor has theadvantage of being able to trace leaks easi-ly.)

The basic gas producing reaction in thedigester is: carbon plus water = methaneplus carbon dioxide (2C + 2H20 = ChU + C0 2).The methane has a specific gravity of .55 inrelation to air. In other words, it is abouthalf the weight of air and so rises when re-leased to the atmosphere. Carbon dioxide ismore than twice the weight of air, so theresultant combination of gases, or simplybio-gas, when released to atmosphere, willrise slowly and dissipate.

CHCO

NHCO

0

H2

<•

2

2

2

2

s

methane 54carbon dioxide 27

nitrogen .5

hydrogen 1

carbon monoxide

oxygen

hydrogen sulfide

- 70%- 45%

- 3%

- 10%

0.1%

0.1%

trace

Table 6. General Composition ofBio-Gas Produced FromFarm Wastes

Fuel Value

The fuel value of bio-gas is directly pro-portional to the amount of methane it con-tains (the more methane, the more combusti-ble the bio-gas). This is because the gases,other than methane, are either non-combusti-ble, or occur in quantities so small thatthey are insignificant. Since tables of"Fuel Values of Bio-Gas" may not show howmuch combustible methane is in the gas, dif-ferent tables show a wide variety of fuelvalues for the same kind of gas, dependingon the amount of methane in the gas of eachindividual table.

As a general rule, pure methane gas has aheat value of about 1,000 British ThermalUnits (BTU) per cubic foot (ft3). One BTU isthe amount of heat required to raise onepound (one pint) of water by 1°F. Five ft3,or 5000 BTU of gas is enough to bring h gal-lon of water to the boil and keep it there20 minutes. If you have, a volume of bio-gaswhich is 60% methane, it will have a fuelvalue of about 600 BTU/ft3, etc.

Fuel Gas

Coal (town) gas

Bio-gas

Methane

Natural gas(methane or pro-pane-based)

Propane

Butane

Table 7. Fuel Value

Fuel Value(BTU/ft3)

450-500

540-700

896-1069

1050-2200

2200-2600

2900-3400

of Bio-Gas aOther Major Fuel Gases

The composition and fuel value of bio-gasfrom different kinds of organic wastes de-pends on several things:

1) The temperature at which digestiontakes place. This has already beendiscussed.

2) The nature of the raw material. Ac-cording to Ram Bux Singh:2 "pound forpound, vegetable waste results in theproduction of 7 times more gas thananimal waste." In our experience,pressed plant fluids from succulentplants (cactus), greatly increasesthe amount of gas produced, but cer-tainly not by a factor of 7. HaroldBates (the chicken manure car) hasnoted that more gas is produced frommanure with a little straw added.But, we are more interested in theproduction of methane than bio-gas.Laboratory experiments 1>0.'*1 haveshown that plant materials producebio-gas with a high proportion of car-bon dioxide. So, the extra gas pro-duced by plants may be less valuablefor our purposes of fuel production.

17

The general quality of bio-gas can be es-timated from the C/N ratio of the raw mate-rials used. (Table 8)

With good temperature and raw materials,50 to 70% of the raw materials fed into thedigester will be converted to bio-gas.

Amount of Gas From Different Wastes

The actual amount of gas produced fromdifferent raw materials is extremely variabledepending upon the properties of the raw ma-terial, the temperature, the amount of mate-rial added regularly, etc. Again, for gen-eral rule-of-thumb purposes, the followingcombinations of wastes from a laboratory ex-periment can be considered as minimum values:(Table 9)

C/N Low(high nitrogen)

C/N High(low nitrogen)

C/N Balanced(C/N = near 30)

blood, urine

sawdust, straw,sugar andstarches suchas potatoes,corn, sugar beetwastes

manures,garbage

Methane

little

little

much

C02much

much

some

Hydrogen

little

much

little

Nitrogen

much

little

little

Table 8. Gas Production According toC/N Ratios of Raw Wastes

Material

Chicken Manure

Chicken Manure& Paper Pulp

Chicken Manure& Newspaper

Chicken Manure& Grass Clippings

Steer Manure

Steer Manure& Grass Clippings

Table

Proportion

100%

31%69%

50%50%

50%50%

100%

50%50%

Ft3 Gas Perlb VS Added

5.0

7.8.

4.1

5.9

1.4

4.3

9. Cubic Feet of Gas Producedby Volatile Solids ofCombined Wastes (Ref. 40)

18

CH* Contentof Gas**)

59.8

60.0

66.1

68.1

65.2

51.1

Other values for gas production are fromworking digester operations. These are shownas cubic feet of gas produced by the TotalSolids and are more liberal values than inTable 9.

ManureFtVlb of

Dry Matter (TS)

Pig 6.0 - 8.0Cow (India) 3.1 - 4.7Chicken 6.0 - 13.2Conventional Sewage 6.0 - 9.0

From Ref. 5, 7, 8, 17, 42

Table 10. Gas Produced By TotalSolids of Wastes

As an example, suppose we had 100 chick-ens which were allowed to forage during theday, but were cooped at night, so that onlyabout half of their manure was collectable.At 0.1 lb/chicken/day this would amount toabout 10 lbs of wet or 3.5 lbs dry (Table 4)manure per day. Other conditions beingequal, this could be equivalent to about 20-40 ft3 of bio-gas (assuming 60% methane) 12-24 ft3 of methane gas per day.

DIGESTERS

Basic Digester Design

Digesters can be designed for batch-feed-ing or for continuous feeding. With batchdigesters a full charge of raw material isplaced into the digester which is then seal-ed off and left to ferment as long as gas isproduced. When gas production has ceased,the digester is emptied and refilled with anew batch of raw materials.

Batch digesters have advantages where theavailability of raw materials is sporadic orlimited to coarse plant wastes (which containundigestible materials that can be conve-niently removed when batch digesters are re-loaded). Also, batch digesters require lit-tle daily attention. Batch digesters havedisadvantages, however, in that a great dealof energy is required to empty and load them;also gas and sludge production tend to bequite sporadic. You can get around thisproblem by constructing multiple batch di-gesters connected to the seme gas storage.In this way individual digesters can be re-filled in staggered sequence to ensure a rel-atively constant supply of gas. Most earlydigesters were of the batch type.

With continuous-load digesters, a smallquantity of raw material is added to the di-gester every day or so. In this way the rateof production of both gas and sludge is moreor less continuous and reliable. Continuous-load digesters are especially efficient whenraw materials consist of a regular supply ofeasily digestible wastes from nearby sourcessuch as livestock manures, seaweed, river orlake flotsam or algae from production sludge-ponds. The first continuous-load digesterseems to have been built in India by Patelin 1950.*3

Continuous-feeding digesters can be oftwo basic designs: vertical-mixing or dis-placement (Fig. 12) Vertical-mixing diges-ters consist of vertical chambers into whichraw materials are added. The slurry risesthrough the digester and overflows at thetop. In single-chamber designs the digestedor "spent" slurry can be withdrawn directlyfrom effluent pipes. In double-chamber de-signs the spent slurry, as it overflows thetop, flows into a second chamber where di-gestion continues to a greater degree ofcompletion.

Displacement digesters consist of a longcylinder lying parallel to the ground (e.g.,inner tubes, oil drums welded end on end,tank cars, etc.). As it is digested theslurry is gradually displaced toward theopposite end, passing a point of maximumfermentation on the way.

The displacement digester design seems tohave distinct advantages over vertical-mix-ing designs popularized in India: (1) In

Single

Chamber

\

VERTICAL

cumulate to the point where it inhibits di-gestion. A prone cylinder has a larger sur-face area than an upright one. (4) Any con-tinuous-load digester will eventually accu-mulate enough scum and undigested solid par-ticles so that it will have to be cleaned.The periodical washing out of displacementdigesters is considerably easier than verti-cal-mixing digesters.

The first large-scale displacement diges-

Double

DISPLACEMENT

\GAS

FIG.13 Types of Continuous-Feeding Digesters

vertical-mixing digesters raw material issubject to a vertical pumping motion and of-ten escapes the localized action of digestingbacteria. Slurry introduced at one time caneasily be withdrawn soon afterwards as in-completely digested material. In displacementdigesters slurry must pass an area of maximumfermentation activity so that all raw mate-rials are effectively digested (much likethe intestines of an animal). (2) From apractical point of view, displacement diges-ters are easier to operate. If digester con-tents begin to sour for one reason or anoth-er, strongly buffered material at the farend can be recirculated efficiently by sim-ply reversing the flow of material along theline of the cylinder. In addition, raw ma-terials can be digested to any desired degreewithout the need for constructing additionalchambers or digesters. (3) The problem ofscum accumulation is reduced in displacementdigesters. Since scum forms evenly on thesurface of the digesting slurry, the largerthe surface area, the longer it takes to ac-

ter was designed and built by L. John Fryduring the late 1950's on his pig farm inSouth Africa.1>2''*'* Mr. Fry, now a residentof Santa Barbara, is acting consultant forthe New Alchemy digester project which iscurrently focusing attention on the designand utilization of small-scale displacementdigesters.

Raw Materials and Digester Design

Plant Wastes: The primary advantage toplant wastes is their availability. Theirdisadvantage for a small farm operation isthat plant wastes can often be put to betteruse as livestock feed or compost. Also,plants tend to be bulky and to accumulatelignin and other indigestible materials thatmust be regularly removed from digesters.This severely limits the use of plant wastesin continuous-feeding digesters.

There seem to be three possible ways totake advantage of plant wastes in continuousdigesters: (1) Press plant fluids out of

20

succulent plants (e.g., cacti, iceplant,etc.) and digest juices directly, or usethem as a diluter for swill. (2) Culturealgae for digestion. (3) Digest plants notcontaining lignin (e.g., seaweed).

Animal Manures: The main advantage toanimal manure, with respect to continuousdigesters, is that it is easy to collect(with proper design of livestock shelters)and easy to mix as slurry and load into di-gesters. Successful continuous digestershave been set up using pig manure, J1*2*'1'1

cow dung3»s»6 and chicken manure.17 Thegeneral consensus seems to be that, amonganimal manures, chicken manure "is easilydigested, produces large quantities of gasand makes a fertilizer very high in nitro-gen.1"15

Human Waste: Human waste or "night soil"has long been used as a fertilizer, espe-cially in the Orient.l*6»'17 However, thereseems to be little information on using hu-man wastes as raw materials for anaerobicdigesters. A few ideas involving outhousesand latrines are described by Gotaas15in hischapter, Manure and Night Soil Digesters forMethane Recovery on Farms and in Villages.It seems possible, also, that digesters couldbe incorporated into aerobic dry toilet de-signs of the "Clivus" type.1*8 This may beespecially fruitful since the main drawbackto using human wastes from flush toilets isthe excess water that is carried with itwhich inhibits digestion. A well-designedprivy digester which paid special attentionto the transmission of diseases peculiar tohumans would be a real asset to homesteadtechnology. A solution to this problem wouldbe welcomed. One suggestion is a seat witha clip-on plastic bag. When filled it couldbe dropped into a digester intact. The plas-tic would have to be a material which woulddecompose only in the presence of methanebacteria, or liquids generally after so manyhours.

Loading Rate, Detention Time andDigester Size

In calculating the size of a continuous-load digester the most important factors areloading rate and detention time.

Loading Rate: Is defined as the amount ofraw material (usually pounds of volatile sol-ids) fed to the digester per day per ft3 ofdigester space. Most municipal sewage plantsoperate at a loading rate of .06-.15 lb VS/day/ft3. With good conditions, much higher

rates are possible (up to .4 lbs VS/day/ft3).Again, as with most aspects of digesters,the optimum situation is a compromise. Ifyou load too much raw material into the di-gester at a time, acids will accumulate andfermentation will stop. The main advantageto a higher loading rate is that by stuffinga lot into a little space, the size (andtherefore cost) of the digester can be re-duced.

Example: Suppose you had 10 lbsof fresh chicken manure (totalmanure from about 30 chickens)available for digestion everyday: 10 lbs fresh chicken ma-nure = 2.3 volatile solids (Ta-ble 4). At a loading rate of .2lbs VS/day/ft3 this would requirea digester 2.3/.2 = 12 ft3 in vol-ume (about the size of 2-50-gal-lon drums). At a loading rateof .1 lb VS/day/ft3, this woulddouble the necessary size of thedigester with the same amount ofmanure.

Detention Time: Is the number of daysthat a given mass of raw material remains ina digester. Since it is wery difficult toload straight manure into a digester it isusually necessary to dilute it with waterinto a slurry. If too much water is added,the mixture will become physically unstableand settle quickly into separate layers with-in the digester, thus inhibiting good fer-mentation. The general rule-of-thumb is aslurry about the consistency of cream. Theimportant point here is that as you dilutethe raw material you reduce its detentiontime.

Example: The volume of 10 lbs offresh chicken manure is about.2 ft3. If this is diluted 1:1with water the volume becomesabout .4 ft3. With the 12 ft3digester described above, thiswould mean a detention period of.4/12 = 36 days. If the manurewere diluted more, say 2:1, thevolume would be .6 ft3 and the -detention period would be reduc-ed to .6/12 = 20 days.

21

Up to a point, then (usually no less than6% solids), diluting raw materials will pro-duce the same amount of gas in a shorterperiod of time.

These relationships between loading rate,detention time and digester size reveal them-selves more clearly after direct experiencewith continuous-load digesters. However,generalities can be of some use in the be-ginning.

gester. The water can be heated by solarcollectors or by water boilers heated withmethane.

Gas-heated water boilers are a good ideasince they allow u>ie digestion process tofeed back on itse.., thus increasing effi-ciency. One practical gas-heater design wehave used is shown in Figure 5. The thermo-stat in the water boiler is set at 14l)°F be-cause slurry will cake < surfaces (e.g., thewater coils) warmer thd.i this. The digester

FIG. Solar Water Heaters (Built by Irving Thomas of Santa Barbara)

Heating Digesters

For the most efficient operation, es-pecially in temperate climates, digestersshould be supplied with an external supplyof heat to keep them around 95°F; there areseveral ways to do this. Methods which heatthe outside of digesters (e.g., compostpiles, light bulbs, and water jackets) couldbe more effectively used as insulation sincemuch of their heat dissipates to the sur-roundings. (Since digesters should be con-stantly warmed rather than sporadically heat-ed, compost "blankets" are not wery practicalunless you coordinate a regular program ofcomposting with digestion.) Similarly, greenhouses built over digesters tend to overheatthe digester during the day and cool it downat night.

The most effective method of keeping di-gesters warm is to circulate heated waterthrough pipes or coils placed within the di-

thermostat is set at the optimum 95°F. Untilthe digester begins producing methane, pro-pane can be used as a fuel source for thewater boiler.

For optimum heat exchange within the di-gester, a ratio of 1 ft* coil area per 100ft3 of digester volume is recommended.8

Insulating Digesters

A word of caution if you insulate your di-gester. Methane is not only combustible buthighly explosive* when it makes up more than9% of the surrounding air in confinedspaces. If you use synthetic insulation,avoid porous materials such as spun glasswhich can trap gas mixtures. It's easy toscrounge styrofoam sheets since they are socommonly used as packing material and regu-larly discarded. Styrofoam is one of thebest insulating materials, although it isslightly flammable.

22

USING GAS;

Properties of Methane

Specific Gravity (air = 1.0)Dry Weight, lb / f t 3

Liquid Weight, l b / ^1Fuel Value, BTU/ft3

Air for Combustion, f t 3 / f t 3

Flammability in Air,% Methane

Uses of Methane

.55

.04 (gas)3.5 (liquid)950-10509.55-14

General: Methane can of course be used inany appliance or utility that uses naturalgas. The natural gas requirements of anaverage person with a U.S. standard of livingis about 60 ft3/day. This is equivalent to10 lbs of chicken or pig manure per day (7pigs and 100 chickens) or 20 lbs of horsemanure (about 2 horses). Other uses andmethane requirements are listed in Table 11.

UseLighting

Cooking

Incubator

Ft!2.5

8-16

12-15

.5-.7

Gas Refrigerator 1.2

Gasoline Engine*CH«, 11

Bio-Gas

For GasolineCH*Bio-Gas

For Diesel OilCH-Bio-Gas.

*25% efficiency

16

135-160180-250

150-188200-278

Rateper mantle perhourper hour per2-4" burnerper person perday

ft3 per hour perft3 incubatorft3 per hour perft3 refrigerator

per brake horse-power per hourper brake horse-power per hour

per gallonper gallon

per gallonper gallon

Heat Engines: Methane, the lightest or-ganic gas, has two fundamental drawbacks toits use in heat engines: it has a relativelylow fuel value (Table 7), and it takes nearly5,000 psi to liquefy it for easy storage.(87.7 ft3 methane gas = 1 gallon of liquidmethane or 1 ft3 methane gas = 9 tablespoonsliquid methane.) So a great deal of storageis required of methane for a given amount ofwork. For comparison, propane liquefiesaround 250 psi. Consider the following ex-ample where methane is compressed to just1,000 psi in a small bottle and used to powera rototiiler of 6 brake horsepower

Example:1 horsepower hr = 2540 BTUFuel value of methane = 950 BTU/ft3

TV (tank vol.) = 2' x 6" cylinder =678 in3 = 0.39 ft3

TP (tank pressure) = 1000 psi = 68 atmosEV (effective vol.) = (TP) (TV) =

26.7 ft3 = 25,300 BTUhp = brake horsepower of enginehr = hours of runningx = heat value of gas (BTU/ft3)y = efficiency of engine (25% for con-

ventional gas engines

Methane Gas Consumption (G) (ft3)

of general heat engine:

r - (hp) (2540) (hr)U " (x) (y)

of gasoline engine on methane:

r = (hp) (2540) (hr) = ,13 (0.25) (9.50) '

for a 6 hp ro to t i l le r

G = (hp)(hr)(10.7 units)

Operating Time (OT)

).7 ft3/hp-hr)

(64.2 ft3/hr)(hr)

FV0T = I 1 = 0.414 hr = 25 minutes/tank

UsefulWorkSupplied

2.5 hp hr = 6,350 BTU =

(25,300 BTU/tank) (25% eff)

Table 11. Uses for Methane

At 25% compressor efficiency it would take.52 hp-hr to compress the gas (1320 BTU).In other words, it would take 1320 BTU tocompress 25,300 BTU worth of gas that pro-vides 6,350 BTU worth of work. Clearly thesystem is not very "efficient" in the sensethat 21% of the resulting work energy isneeded for compression while 75% of theavailable energy is lost as heat.

23

Methane has been used in tractors'*9»50 andautomobiles.51 The gas bottles carried bysuch vehicles are often about 5 ft long by9 in diameter (1.9 ft3) charged to 2800 psiso that about 420 ft3 of methane is carried(about Z\ gal. gasoline). However, it seemsthat the most efficient use of methane wouldbe in stationary heat engines located nearthe digester (e.g., compressors and genera-tors). There are two reasons for this: (1)The engine's waste heat can be recirculatedin digester coils instead of dissipating inthe open. (2) Gas can be used directly asit is produced, without the need of com-pressors. For example, bio-gas produced frompig manure was used at ordinary pressures byJohn Fry to power a Crossley Diesel engine.The diesel ran an electric generator and thewaste heat was recirculated directly backinto the digesters.52 It is likely that bio-gas produced from mixed wastes would have tobe "scrubbed" of corrosive hydrogen sulfide(by passing through iron filings), and pos-sibly C02 (by passing through lime water).

EFFICIENCY OF DIGESTION

The efficiency of anaerobic digestion canbe estimated by comparing the energy avail-able in a specific amount of raw material tothe energy of the methane produced from thatmaterial. Four such estimates are given be-low. (Fig. 15)

It seems fair to conclude that anaerobicdigestion is about 60-70% "efficient" in con-verting organic waste to methane. However,it would probably be more accurate to callthis a conversion rate since, like all bio-logical processes, a great deal of energy isrequired to maintain the system, and most ofthis extra energy is not included in the con-version. For example, consider how muchenergy is needed just to keep a digesterwarm in a general temperate climate.

Example: Direct-heating hot water boilershave an efficiency of about 70%. Gasengines have a power efficiency of 20-25%and a water heating efficiency of about50%.7 As hot water heaters, then, heatengines are about as efficient as waterboilers. In either case about 20-30% ofthe gas energy derived from digestionmust be put back into the system to heatdigesters. Without even considering theenergy needed to collect raw materials orload and clean the digesters, the conver-sion efficiency of digestion should becloser to 50%

2k

1 Lb.Sedim.

8.000

6,320

P r i ma rySludge

BTU

79%Conversion

BTU

1Al

10

4,

Lb. Drygae

,000 BTU

42-69%Conversion

200-6950 BTU

(Ref. 7) (Ref. 53)

1SI

8

Lb. Dry Rawudge (70% VS)

7,

f t

5,

800 BTU

67%Conversi

3 (65% CHk)

200 BTU

1 Lb. Fresh, DryChicken Manure

BTU

Conversion

7.5 ft3 (50% CH/,)

2,800 BTU

(Ref. 8) (Ref. 17,22)

FIG.15 Efficiency of MethaneProduction from DifferentMaterials

USING SLUDGE

Sludge as a Fertilizer

Most solids not converted into methanesettle out in the digester as a liquidsludge. Although varying with the raw ma-terials used and the conditions of digestion,this sludge contains many elements essentialto plant life: . nitrogen, phosphorous, po-tassium plus small amounts of metallic salts(trace elements) indispensible for. plantgrowth such as boron, calcium, copper, iron,magnesium, sulfur, zinc, etc.

Nitrogen is considered especially impor-tant because of its vital role in plant nu-trition and growth. Digested sludge containsnitrogen mainly in the form of ammonium(NhU), whereas nitrogen in aerobic organicwastes (activated sludge, compost) is mostlyin oxidized forms (nitrates, nitrites). In-creasing evidence suggests that for many landand water plants ammonium may be more valu-able as a nitrogen source than oxidized ni-trogen; in the soil it is much less apt toleach away and more apt to become fixed toexchange particles (clay and humus). 'Like-wise, important water algae appear to beable to utilize ammonium easier than ni-trates.51* Generally speaking, this is a re-versal from the earlier belief by fertilizerscientists that oxidized nitrogen always pre-sented the most available form of nitrogenfor plants. Because of these things, it hasbeen suggested that liquid digested sludgeproduces an increase of nitrogen comparablewith those of inorganic fertilizers in equiv-alent amounts.5S

Most of the information showing the poorfertilizer value of sludge has been based onmunicipal sewage sludge. It is a bad measureof the fertilizer value of digested sludgein general. (Municipal treatment flushesaway all the fertilizer rich liquid efflu-ent.) In one case7 digested sewage sludgewas found to contain only about h the amountof nitrogen in fresh sewage, whereas else-where26 digested pig manure was found to be1.4 times richer in nitrogen content thanraw pig manure. Similar results have beenfound with digested'chicken manure.

Sludge from your digester can be recycledin a wide variety of ways, both on land and.in water and pond cultures. The possibili-ties are many and only brief descriptions ofpotentials can be given here.

RAW SEWAGE

DIGESTED SLUDGE10 municipalitites12 Ohio munici-

palities51 samples,

21 cities• General averageGeneral average

ACTIVATED SLUDGE

(% dry wt.)

1.0-3.5

- 1.8-3.1

0.9-3.0

1.8-2.32.0

1.0-4.0

5 municipalities 4.3-6.4General average 4.0-6.0General average 4.0-7.0

DIGESTED MANURE SLUDGE

HogChickenCow

FINISHED COMPOST

6.1-9.15.3-9.02.7-4.9

Municipal .4-1.6Garbage .4-4.0Garden 1.4-3.5

fable 12. Nitrogen Fertilizerof Various SludgesFinished Compost

Sludge Gardening and Farming

Reference

56

9

9

10,57956

99

56

262323

585858

Valueand

The application of digested sludge tocrops serves a double purpose since it isboth a soil conditioner and fertilizer. Thesludge humus, besides furnishing plant foods,benefits the soil by - increasing the water-holding capacity and improving its structure.In some preliminary experiments with gardenand house plants we have obtained astoundingresults with the use of sludge from ourchicken manure digester. However, there aresome things to consider first: (1) Freshdigested sludge, especially from manures,contains high amounts of ammonia, and in thisstate may act like a chemical fertilizer byforce-feeding large amounts of nitrogen intothe plant and increasing the accumulation oftoxic nitrogen compounds.59*60 There is nodirect evidence for this, but the possibilityexists. For this reason it is probably best

25

to let your sludge "age" for a few weeks inan open area (oil drums, plastic swimmingpools, etc.), or in a closed container for afew months before using it on crops. Thefresher it is the more you should dilute itwith water before application. (2) The con-tinued use of digested sludge in any one areatends to make soils acidic. You should prob-ably add a little dolomite or limestone atregular intervals to your sludge plots,allowing at least 2 weeks interval betweenapplications to avoid excess nitrogen loss.Unfortunately, limestone tends to evaporateammonia so you may experience a temporarynitrogen loss when you apply it on yoursludge plots. (3) Unlike digested municipalsludge, sludge from farm wastes does notcontain large amounts of heavy metals orsalts so there is little danger of applyingit too heavily over a period of time. How-ever, you should pay attention to the struc-ture of your soil. If it contains a lot ofclay, the sludge will tend to accumulate andpossibly present problems in the root areaof your plants. In general, keep close tabson your sludge plots in the beginning untilyou become familiar with its behavior inyour own particular soil.

Sludge-Pond Cultures

There are at least three general ways tointegrate pond cultures with organic diges-ters: hydroponic crops, sludge-algae-fishand sludge-algae-methane systems. All havetheir advantages depending on local needsand resources.

Sludge Hydroponics: Hydroponics is theprocess of growing plants directly in nu-trient solution rather than soil. The nu-trients may consist of soluble salts (i.e.,chemical fertilizers) or liquid organicwastes like digested sludge and effluent.Plants grown hydroponically in sludge-en-riched solutions can serve a variety of pur-poses for organic digester operations: (1)They can do away with the cost and energy oftransporting liquid fertilizer to crop landssince they can be grown conveniently near todigesters. (2) They tend to be more produc-tive than conventional soil crops, and thuscan serve as a high-yield source of fodder,compost, mulch or silage. (3) They can serveas convenient high-yield sources of raw ma-terials for the digester itself.

Overhead Supply^ Tank Wy

Dome

Constant HeadOverflow Line^'

/

[Valve /

>^y HIW y y w% V-V^YYVMPlastic Lining.

\\V\\\\\\\\\\\\\\\\\\\\\\\\N

' Grass Cover In TankSludge

-Sand

- Pea Gravel

Sludge Pond

FIG. 16 Hydroponic Sludge Culture of Pasture Grasses

26

Information about the use of sludge tofertilize water plants comes from projectsto treat waste water in run-off areas or"sewage lagoons."61'62 Some plants, for ex-ample water hyacinth, Ipornoea repens andsome cool season pasture grasses such as rye.fescue and canary grass, have the ability togrow well in waste water and to take up greatamounts of nutrients efficiently, thus help-ing to control polluted waters. These cropshave the added advantage that they are easyto harvest for livestock feed, thus givingan efficient method of converting sludge nu-trients into animal protein.

Usually, the plants are grown in shallowponds filled with a diluted sludge solution.The process consists of slowly adding sludgeunder a gravel bed lining the pond and cover-ed with a layer of fine sand. Over the sand,plants are sprouted in containers floatingon the effluent that percolates up throughthe gravel and sand layers. After sproutingthe grasses then root and anchor in the sanddnd aravpi .

Sludge-Algae-Fish: The essence of thesludge-algae-fish or "aquaculture" systemconsists of placing sludge into ponds andstimulating the growth of algae. The algaeare then used as feed for small invertebratesor fish growing in the pond. The idea ismodeled after Oriental aquaculture systems.

During the last two years, under the direc-tion of Bill McLarney, New Alchemy has es-tablished preliminary models for experimentalfish cultures (Tilapia). A general descrip-tion of small-scale fish farming methodsusing organic fertilizers and invertebratefish food cultures has been presented else-where.63"65

Sludge-Algae-Methane: In the Sludge-al-gae-metnanesystem gTeen algae is grown indiluted sludge, then harvested, dried anddigested to produce methane for power andsludge for recycling. This procedure oftransforming solar energy and sludge nutri-ents into the chemical energy of methane ispotentially a very efficient and rapid bio-logical process: (1) It is a closed nutri-tional system and (2) the rate of turnoveris extremely high; organic matter is decom-posed relatively quickly by anaerobic bac-teria in the pond while it is most rapidlymade by green algae. The complete sludge-algae-methane system involves a series ofprocesses. The principle features of thesystem are integration of the algae culturewith the gas in such a manner that nutrientsand water are recycled from one process tothe other (Fig. 17). Most of the informa-tion concerning this system has been develop-ed by researchers at Berkeley in a manner

CHICKENMANURE

MANURE/SLUDGESETTLING

TANK

DIGESTEREFFLUENT

NUTRIENT CARBONATED

SUPERNATANT WATER

POND

CULTURE

WATERCARBONATIONTANK

WATER FLOCCULATIONTANK

BIOGAS

ALGAE

CONCENTRATEDEWATERING

BEDS

FIG.17 Flow Diagram of Sludge-Algae-Methane Conversion System

27

that has real potential for the homestead orsmall farm.53*66-69 Space does not permiteven a brief discussion of the considera-tions: (1) cultivated algae, (2) pond de-sign and operation, (3) harvesting of algae,(4) digestion of algae, (5) efficiency andyield. Hopefully, with experience, we canbegin to develop practical aspects of theseideas in future Newsletters.

(From Upper Left.Clockwise)Chinese Bamboo Trellis with Lathe House inBackground; Drum Digester Heater; DrumDigesters; Solar Water Heater.

28

BUILDING ASUMP DIGESTER

FIG.18 Original Sump Digester. Upper Drums Have Been Forced Up by Methane

This is the simplest type of methane di-gester, since gas is stored in a coverfloating over the digester. It can be madevery cheaply and it demonstrates that manuredoes decompose ahaerobically (without air),and that it generates a surprising amount ofgas.

Sump digesters can be made of any two cy-linders which fit inside one another, suchas drums, buckets, coffee cans, etc. Thesump digester described below is made of a30 gallon drum fit into a 50 gallon drum.

Making Starter Brew

Before starting, read the Safety Pre-cautions WARNING (#11 below).

One of the first steps in the constructionof any sized unit is the brewing up of abatch of starter material. (Unless you'relucky enough to have an operating digesterin your area, from which you can get somebacteria.)

It takes weeks and even months to culti-vate the strain of bacteria that functionsbest on the manure being used locally. Onceyou have your starter going, though, like asourdough bread or yogurt culture, you canhave it for a long time.

Starter brew can be generated in a 1 or 5gallon glass bottle. Care must be taken tofill the bottle only about h full with either(a) active supernatant from a local sewageworks or (b) the runoff from the low pointon the land of any intensive stock farm inyour district. Fill % more with fresh dung.Leave the other h of the bottle for freshmanure additions at weekly intervals. Neverfill to near the screw cap, since foamingcould block off the opening and burst thebottle. Of course, the screw cap must beleft loose to keep the bottle from exploding,except when agitating the bottle. It is apecularity of methane brews that a slightagitation when adding material is beneficial,but that continuous agitation has an adverseeffect.

1) Get two metal drums, one 30 gallon withan outlet on top and one 50 gallon.(Fig. 19a.)

2) Remove the top of the 50 gallon drumand the bottom of the 30 gallon drum.

3) Fit a valve into the small outlet inthe top of the 30 gallon drum. Solderor weld it securely. This will be thegas outlet.

4) Firmly tape a hose to the outlet pipewith polyvinyl chloride tape (adhesiveon one side only).

5) The hose can be led to an inner tubeto be filled with gas for storage(Inner Tube Digester, Section 10); orlead directly to a simple burner (In-ner Tube Digester, Section 11).

6)The 50 gallon drum is ready to be filled.It should be filled only to the height ofthe 30 gallon drum with a mixture of halfslurry and half starter "brew," Fig. 19a.

7) Make a slurry the thickness of creamby mixing fresh, raw manure with warmor hot water, 90° to 95°F.

8) To this, add an equal amount of start-er "brew."

9) With the valve open, sink the 30 gal-lon drum all the way down into theslurry and starter mixture (Figure 19).This must exclude all the air from the30 gallon drum. Then close the valve.

10) In cool climates, active compost canbe packed around the outer drum, tomaintain a steady temperature of be-tween 80° and 95°F. After about threeweeks, gas should begin to generate.The smaller drum will fill slowly withgas and rise above the surface of theslurry (Figures 18, 19b).

11) SAFETY PRECAUTIONS: A NOTE OF WARNING.When the small drum rises the firsttime, do not attempt to burn the gas.Rather, let it escape to atmosphere,push the 30 gallon gas holder com-

L J x ^ ^ — Valve

pletely down into the slurry again,shut off the valve and allow it torise a second time. This is to insurethat no air is mixed with the gas. Agas and air mixture is highly explosivebetween the range of 1 part in 4, to 1in 14. Even outside this range itcould be dangerous. Also, the firstgas yield probably will not light any-way due to a high proportion of carbondioxide when fermentation first starts.When burning the gas, open the valveonly slightly, press down lightly onthe 30 gal Ion drum to create a positivepressure on the gas. Close the valvebefore releasing the pressure.

In rare cases there occurs an abundanceof gray foamy bubbles at about the time whenfermentation starts. If this happens leavethe digester alone for a few days. Do notfeed any raw material. If the digester isheated, reduce the heat.

12) Periodic supplies of fresh raw mate-rial should be "fed" in to keep thedigestion going. This can vary fromdaily to once every three months de-pending on the requirements of theuser and the digester design.

To feed this digester it is necessary toremove the 30 gallon drum, take out about 5gallons of material and replace it withfresh slurry. Again press down the smalldrum to exclude air.

Sump designs are particularly good unitsto learn from since they are so easy tobuild and maintain.

STARTERBREW

SLURRY

JO Gal. Drum(no bottom)

50 Gal. Drum(no top)

19A (Before) 1 9 B ( A f t e r )

FIG.19A & B Sump Digester Before and Af ter Methane Production

30

INNER TUBE DIGESTER

J hope that in these times ofever increasing pressures in theenergy crisis, that this innertube unit will be made availableto the millions on millions ofpeople around the world who couldbenefit from it. To those on theland eking out an . existence, Idedicate this unit. As a morselof technology, it might well bene-fit them more than a man standingon the moon.

L. John Fry

The following inner tube unit was made ata cost of about $20. If it could be producedin quantity, the cost might be as low as $2using cheaper material.

The unit has no working parts and shouldlast the normal life of the materials used.

This inner tube digester has been testedcut in Santa Barbara for over 18 months,auring which all the "bugs" have been elim-inated. It is a thoroughly reliable device.

NOTE: Read "SAFETY PRECAUTIONS" (#16below) and "STARTING THE BACTERIAL BREW"(Sump Digester) before beginning construc-tion.

1415

16171819

I.

. 1/4" rubber or latex hose

. 1 gallon jug with cork with 2 1/4-inchholes

. Bottle

. T pieces

. Truck inner

. Screw type

Main Chamber

tubes (storage)pinch clamp.

of the Digester

Inner Tube Digester Parts List

1. Truck or tractor sized inner tube2. Plexiglass (1/8" thick) 7" x 28" (or

circumference of inner tube).Plexiglass 10" x 10".

* 3. Methyl chloride liquid (hobby shop)4. Plexiglass tubes (2" x 3')5. 2 2-inch diameter bicycle inner tubes6. Polyvinyl-chloride (PVC) tape7. 3 5-gallon polyethylene buckets8. 5-gallon container - metal or plastic -

for scum collector9. Epoxy resin

10. Rubber sealing compound11. Rubber cement

. 12. Wire13. Pipe adapter (kind that goes from

steel to plastic)•* Methylene dichloride

(correction) 31

This consists of a discarded truck-sized(or better still, a tractor-sized) innertube.

1. Test carefully for leaks. (Bear inmind that e^jery part going into thedigester should be carefully testedfor leaks. Any gas escaping, out ofeven a pinhole, is a potential causeof explosion.)

2. Patch over, if necessary. If there isa large gash or hole, cut that portioncompletely out of the tube.

3. Make a clean cut at right angles tothe long circumference of the tube.This is where the plastic cylinderwill be inserted (Fig. 21).

4. Thoroughly wash and dry the inside ofthe tube. The inner tube is now readyfor the plastic insert.

Polyethylene Bucket

2" Bicycle Tubes

1/V Latex orPlast ic Tub!ng

(2)

Variable Weiqhtl

D

(in

(1) Main Chamber of Digester

(2) The Plastic Cylinder

(3) Inlet, Gas, and Effluent Pipes

(k) Inlet Feeding Bucket

(5) The Effluent Outlet

(6) The Gas and Scum Outlet

(7) Scum Col lector

(8) Gas Yield Indicator

(9) Pressure Reieaser

(10) Inner Tube Storage

(11) Burner

FIG.20 DIAGRAM OF INNER TUBE DIGESTER

*•> ̂ ;?'f S # j &*^z»rz^Wy:l

ro

FIG.21 Attachment of Pipes and Buckets

FIG.22 Preparation of theInner Tube

II. The Plastic Insert

A. The Plastic Cylinder

1. Heat a 1/8" thick x 7" wide x about28" long (length should be the circum-ference around the opening of the innertube, picture 2) piece of plexiglassin a 400° oven, until it will bend(about 5 minutes).

2. Bend it around a saucepan or other cy-lindrical object which has the samecircumference as your inner tube. Makethe ends of the plexiglass meet toform a cylinder.

3. Glue the ends together by generouslyapplying methyl-chloride glue. Theglue can be made by melting someacrylic scraps in methyl-chloride.

4. Cut a round flat piece of plexiglassto fit inside the cylinder, and gluethis plate with methyl-chloride gluemidway inside the cylinder (Figures23,24). This will make a central di-viding wall to keep the manure fromcircling around and around the innertube.

5. The lip. Heat a 1/4" x 29" strip in a400° oven for 5 or 10 minutes. Wraparound the outside edge of the plasticcylinder to form a rim. (This willhelp keep the inner tube from slidingoff the cylinder.) Hold the hot plas-

tic strip in place with clothespinsuntil cold. Eyedrop straight methyl-chloride between the two surfaces.Keep the clothespins on until surfacesare securely stuck together. Repeatfor other cylinder edge.

B. The Inlet, Gas and Effluent Pipes

These are constructed of 2" diameter,heavy-duty plexiglass tubes. The inlet pipewill be inserted on one side of the centraldividing wall of the cylinder and the gasand effluent tubes on the other side, asfollows (Figures 23,24). .

1. Make 3, 2" diameter holes, one on oneside of the center divider, two on theother side (Figures 23, 24). Exactplacement is not important, but mustbe so close to the baffle as to touchit and in the general area shown inFigure 3. Apply a little glue at thetouching point for added strength.Allow at least 1" between the tubes tothe lip of the cylinder (Figure 2).We made the holes by burning aroundthe outside edge of the hole with asimple soldering iron. A FRET sawwould do a better job.

EFFLUENT->

rii

iGAS

TiIIIi

i"

«-INLET

4"

v

FIG.23 Cross Section of thePlastic Insert

Inlet Pipe:2. Ream out the inlet pipe hole to allow

the inlet pipe to go in at a slightangle (Figure 24). This angle helpsthe mixing in the inner tube, by tend-ing to make the incoming raw slurryrevolve in the tube.

3.. Insert the pipe in at an angle, 4"down into the cylinder (Figure 23).The distance the pipe sticks out thetop of the cylinder is not important.

4. To eliminate leaks, seal the seamaround the pipe and hole with: (1) alayer of melted plexiglass and methyl-chloride and then (2) a layer of rub-ber sealing compound available in hard-ware stores.

Gas Outlet Pipe:

5. This pipe is glued to the top of thecylinder (Figure 23). Again, thelength of the pipe sticking out thetop of the cylinder should be about 6inches. Length in Fig. 23 is aboutright.

6. Seal as above.

Effluent Pipe:

7. Insert the effluent pipe straight downinto the cylinder to 1" from the bot-tom. (Figure 23.) Again 6" above top.

8. Seal seams as above. Where the inletand outlet pipes touch the center baf-fle, apply a little glue to give addedstrength to them, as mentioned above.

Inlet

FIG.2k Placement of PipesIn Plastic Cylinder (NoteAngle of Pipes)

FIG.25 Placing Cylinder inThe Inner Tube

III. Attaching the Cylinder to theInner Tube

Paint the inside of each open end ofthe inner tube to a depth of about 2"with any kind of rubber cement (Fig.22).Insert the cylinder into the innertube, past the lip, to a distance farenough to ensure a good seal (Fig. 25).Tape in place with polyvinyl-chloride(PVC) tape to hold cylinder and innertube securely in position (Fig. 26).Then wind wire twice around on thetape. Twist the ends of the wire tomake a very tight hold. (The wire andthe tape are never removed.)

35

IV.

FIG.26 Fastening Tube toPlexiglass Cylinder

Inlet Fittings and Attachment ofthe Slurry (Feeding) Bucket

1

2.3.

Cut a 2" diameter balloon bicycleinner tube to a length of about 3',after checking for leaks.Place it on the inlet pipe (Fig. 21).Tape with PVC tape which is adhesiveon one side only, by stretching thetape very tightly around the pipe andinner tube. Make sure it is tapedfirmly.

Attachment of Bucket:

4. Burn a hole in the polyethylene slurrybucket, 1" from the bottom of thebucket. (Figures 20 and 22.) When thehose is attached to this hole off thebottom, it will allow sand, feathersand other heavy indigestible materialto settle to the bottom of the bucketand . be left behind when feeding theslurry to the digester.

5. Attach an adapter in the hole of thetype used to go between steel andplastic pipe

6. Attach a length of 2" bicycle innertube to the adapter in the slurrybucket with PVC tape. The tube shouldbe long enough to allow the bucket tobe held up for gravity feeding theslurry into the digester (Figure 20).

V. Fitting the Effluent Pipe

1. Simply tape another length of 2" bi-cycle inner tube to the effluent pipe(Fig. 2 1 ) .

2. Hang the tube in a bucket.

VI. Fitting the Gas Outlet

1. Attach a 21 or 31 length of the 2" bi-cycle tire tubing to the gas outletwith PVC tape.

2. Lead it to the scum collector.

VII. The Scum Collector

If you remember, scum is a mixture of (1)floating material (bedding, straw, feathers,etc.) and (2) liquid interspersed with (3)gas bubbles. Scum rises up with the gas outof the gas outlet. Scum formation is a majorproblem in any sized digester. On thisscale, though, it is simple to eliminate.

1. Select a metal or firm polyethylenecontainer with at least a 2" wide fill-er cap. We used a 5 gallon, plasticmilk container. It is much easier toattach the pipes to a metal container,though.

2. Turn the container upside-down (fillercap underneath) and make a 2" hole inthe top. Solder or weld a short lengthof 2" wide metal pipe to the top (thiswas the bottom of the container origi-nally) (Fig. 27).

3. Firmly tape the inner tube coming fromthe gas outlet to the short length ofpipe. Scum will be forced through thegas outlet, through the cycle tube anddrop in the container. Gas will con-tinue on its way to storage via:

Gas Outlet Continuation:

4. Solder or weld a second pipe at anotherpoint on the top of the container.The hole should be k" in diameter (Fig.27).

5. Tape a length of V rubber or latexhose to the V' pipe. This will go tothe gas yield indicator bottle (Figure20).

36

From Digester v

\ \ \

To Gas Yield

Gas andScum

t

SCUM

Remove Scum

FIG.27 SCum Collector

VIII. Gas Yield Indicator

This is a jug of water, through which thegas from the digester bubbles. It is a niceway to see that your digester is producinggas. (Also, if the water is changed fre-quently, it will filter out some of the car-bon dioxide in the gas.)

1. Take a 1 gallon jug and place a corkwith two V holes in the bottle'smouth (Fig. 28).

2. Place between the scum accumulator andpressure release bottle (Figure 20).

3. Fill the jug with about 6" of water.4. Run the hose from the scum accumulator,

through one cork hole and to 4" belowthe level of water in the bottle.

5. Run another piece of V1 rubber or la-tex tubing out of the other cork hole,to the pressure release (overflow)bottle.

From "*~\i»kScum \ \Col lector \ \

\ \ \

/

tfJo PressurejL Release/ ^ Bott le

/ CORK

FIG.28 Gas Yield Indicator

IX. Pressure Release Bottle

This bottle is placed between the gasyield indicator and inner tube storage (Fig.20). It allows the release of extra pressurein the inner tube storage, or overflow ofgas to escape through the water in the bot-tle, rise to the atmosphere, and disperseharmlessly.

1. A 12" or so deep bottle is fitted witha "T" piece (Fig. 29).

2. The tubing from the gas yield indica-tor is attached to one arm of the "T"and a tubing to storage is attached tothe other anru

3. A plastic tubing is attached to theleg of the MT" piece and immersed in8" of water.

4. In the event that the gas pressure ismore than 8" water gauge, the gas willescape through the water, to the at-mosphere.

"T" Piece

From Gas YieldIndicator

FIG. 2Q Pressure Release

37

X. Inner Tube Storage

1. Gas can be stored in one or a numberof truck inner tubes, stacked on eachother and interconnected with "T"pieces (Figure 20). Check for leaksand patch if necessary.

2. A weight, such as pieces of lumber,are placed on the topmost tube tocreate pressure.

XI. Burner

The gas produced by this digester is about700 BTU per cubic foot at sea level (585 BTUat 6000 ft. altitude). The average dailyproduction of this system is 5 cubic feet;enough to bring % gallon of water to theboil and keep it there 20 minutes. THIS ISENOUGH TO COOK A MEAL.

1. The simplest burner can be a piece of%" metal pipe 18" to 2' long.

2. Place on a reducer to V totubing from storage.

3. Place some sort of on/off clamp on thetubing, plus a pinch screw to regulatethe amount of gas (Fig. 30).

4. The h" pipe is laid between 2 bricksand a third brick is placed on thepipe to hold it in position.

fit the

, - i " Pipe

FIG.30 Simple Burner

Reducer AkO

XI I . Temperature

Methane bacteria only work their best whenkept warm. The best temperature is 95°F.Without artificial heating the only areas inwhich a digester will function is in or nearthe tropics. Thus, without supplementalheat, this unit is limited to the tropics.Alternatively, if placed in an insulated boxand heated by two 100 watt light bulbs inseries (this takes very little electricityand the bulbs last a long time), with athermostat set to 95° in the circuit, it canbe operated almost anywhere.

XIII The Bacterial Brew

Add to Manure Contents (See Sump Digester)

XIV. Feeding

1. The daily routine consists of collect-ing three 1-pound coffee cans full ofdry chicken manure. (Almost any kindof manure is suitable, but to avoidexcessive scum formation, a finer tex-ture manure is better. Chicken or pigmanure is probably the most suitable.)

2. Stir in the slurry bucket with 3/4gallon of water or urine to form aslurry. If you can use urine insteadof water, it will aid fermentation andmake the effluent a better fertilizerafter digestion.

3. Now raise the bucket high so that theslurry will gravity feed into the di-gester. It will mix with yesterday'sload, which by now has been "seeded"with active, hungry bacteria. The in-let pipe (set at an angle) helps themixing, by tending to make the incomingraw slurry revolve in the inner tube.

4. Dispose of the feathers, fiber, sand,etc., left in the bottom of the bucket.

The action inside the digester is the sameon any scale. The raw material, heavilyseeded, tends to skulk along the floor ofthe digester but as the bacteria work on it,gas is formed and lightens it in relation tosurrounding material. Vertical motion be-gins, throwing up chunks of dung and bubblesof gas. Each load displaces the last, aroundthe circuit round the inner tube. At somestage each and every particle has to pass apoint of maximum fermentation where the wholemass seethes and bubbles furiously. Up anddown currents mix the contents thoroughly.From there the fermentation slows and strat-ification begins into the layers of gas,scum, supernatant and sludge...the spentportion of the original solids. Through di-gestion this sludge will have contractedconsiderably from the original raw state.

Failureof the bacterial "brew" will occurif excessive loads of manure are used. Keepto 3-1 pound coffee cans daily. If not feddaily for one reason or another and the unitis left without "food" for a week for in-stance, start it up again with four and one-half coffee cans full the first day and con-tinue as usual afterwards. Do not feed in

38

back coffee cans full for each missed day(21 cans for 7 missed days).

A second reason of failure of the brew isan excess of water, particularly cold water.

XV. Removing Scum and EffluentA. Scum

1. When the scum collector containerfeels heavy, remove the filler cap.from the bottom of the scum containerand let the scum out.

2. Care must be taken that air is notallowed to enter the container at thisDoint.

B. Effluent3. Effluent is drawn off daily or so to

the extent of approximately half ofvolume of daily input at feeding. Theother half of daily input is accountedfor as (1) gas and (2) contractionduring fermentation.

4. The superior fertilizing value of theeffluent is discussed elsewhere. Thisinner tube digester will produce enoughto improve growth of plants on an areaof 2,152 sq. ft. per year - a goodsized vegetable patch.

XVI. Safety Precautions

PRECAUTIONS IN GAS USAGEGas will burn with a hot flame when ig-

nited as it leaves the burner (in contactwith air). But if gas and air are mixed to-ge.ther in proportions of 1 part in 4 to 1 in14 and then ignited in a closed area or con-tainer, a violent explosion will ensue.

To avoid any possibility of explosion inthis sized unit, the first time the digesterproduces enough gas to fill the pipes, scumaccumulator and storage tanks, this gasshould be allowed to disperse to the atmo-sphere. The second time it fills up will berelatively - almost certainly - safe tolight. The flame is so clean and blue thatit will be difficult to see in sunlight butclearly visible at night.

The second safety factor is to keep apositive (however slight) pressure of gas inthe pipelines and storage, so that air isnever drawn into any part of the unit.(Weights on the storage inner tubes, pressureon the main tube when emptying the scum, sothe pipes won't collapse).

The third safety factor is to check theunit daily for leaks; there will be a dis-coloration of the tubing in places where thegas has leaked out.

Finally, smell is important in safetyhandling. Never light a match in a roomwith a strong smell of gas - or even a slightsmell. Air out the room first.

XVII. Lighting the Flame

1. A small gas flame can be lit at theopen end, provided the gas flow is heldlow. If the flow is too strong, theflame will burn inches away from theopen end and be difficult to controlThe adapter on the burner decreasesthe flow.

XVIII. pH

To keep track of pH values, narrow rangelitmus paper with a range from. 6.5 to 8.5 or9 can be used to check effluent. In my ex-perience of digesting animal manures, ahealthy brew, working at top efficiency willhave an effluent pH of around 8.5. This isin contrast to all published literature ondigestion of sewage plant solids in which aworking range of 7 to 7.6 is considered av-erage. If it should drop to 7.6 or so inthis unit, reduce feeding to miss the firstday, then half, feed until the pH of theeffluent rises to 8 at least.

Should the pH drop as low as 7 or 7.2,add a cup of ammonia (the ordinary ammoniabought in a store) to the raw slurry at thenext feed in. Reduce the feed in (or load-ing) slightly from then on.

39

NECESSITY IS THEMOTHER OF INVENTION

A Brief Personal Account of TheFirst Large-Scale Displace-ment Digester

by L. John Fry

FIG.31 Where it All Began. L.J.Fry's South Africa Farm

I owned and operated a hog farm outsideJohannesburg. The average standing popu-lation was 1000. It was a model farm on25 acres and ran most efficiently exceptfor one considerable problem: the two tons(wet weight) of manure produced daily.

For years I composted it and spread itinches thick over the farm and used a ro-tary hoe to chop it into the soil. Thisrequired scraping it up9 piling it, water-ing it, and turning the piles twice, atleast, then loading it on a truck and fi-

naily spreading it more or less evenly.Heavy rains played havoc with it at times.Often drought required using precious wa-ter to dampen the compost. It required alot of labor.

I then read of a suggestion that manuremight decompose in the same manner as sol-ids do in most sewage works, namely decom-position in a liquid form by methane bac-teria. Would it work on pig manure also?

I went to the main sewage treatmentplant in Johannesburg, and was taken roundthe entire unit. I found the decomposi-tion of solids (called digestion) most in-teresting. If such solids could undergo acomplete metamorphosis as to be unrecog-nizable from the raw product, then manuresolids would presumably do the same. Therewas one big difference. Municipal wasteis washed down the sewer lines with largequantities of water. On the other hand,manure was collected by shovel and cartedby wheelbarrow. Water had to be added toturn it into a slurry.

After many months, frequent visits tothe sewage works, and long hours in thelocal University library, I took back tothe farm a sample of actively working bac-teria in a sealed container as a "starter"to try out on pig manure. I used a seriesof 50 gallon oil drums, cut the tops offand poured in a slurry of pig manure. Intoeach drum I then added a measured quantityof "starter," some from the sewage worksand some from a sump located at the lowestpoint below the piggery. Next I fitted 30gallon drums into the slurry. Some threeweeks later the drum with the "sump start-er" began to generate gas. The smallerdrum filled slowly with gas and rose abovethe surface of the slurry.

It was then the summer of 1956-1957,days in the low 80°F, nights 20° cooler.It was surprising that the sharp varia-tions of 20°F did not kill the bacterial"brew." The first drum to rise was theone half fresh raw pig slurry and half"brew" from the sump. All the others fol-lowed eventually, some weeks later, proba-bly due to insufficient starter "brew."

DESIGN OF THE FIRST FULL SCALEDISPLACEMENT METHANE PLANT

After my success with the sump digesterand a great deal of "weighing the options"I decided on a plan of twin digesters withfixed roofs and a series of gas holders tostore some of the gas .generated. Havingtwin digesters side by side had the advan-tages of:

1) Using one as a primary and the otheras a secondary digester.

2) Should the primary be overloaded andhave a bacterial breakdown, the sec-ondary would then be available toreceive at least part of the load.The primary digester would eventual-ly be brought back to use by split-ting the load between the two.

3) Different manures could be used forexperimentation.

Digester Description

Outside the digester a basin was made12' x 8' x 2' deep with the floor slopingto a grid made of angle iron 31 x 61 witha steel screen of 3/8" rod with 1" mesh.The very heavy 3/8" rod was found neces-sary to withstand the suction pull of thesludge pump and for preventing corrosion.A short ramp up to the basin allowed forwheelbarrows of manure to be run up andtipped into the basin. This was done dailyand amounted to about 26 wheelbarrow loadsof about 2 cubic feet each.

Water (about 250 gallons) was then hos-ed in and the whole mass raked with a gar-den rake. When mixed to a slurry, the pumpwas started and the mass moved to a sandtrap. A simple but efficient system wasused.

A drum with a tight fitting lid andsturdy clamp had an inlet half way downand an outlet near the top. Sand settledto the bottom. I was inefficient in thatthe sand had to be cleaned out daily andthis could be done only after the top halfwas cleaned out first.

From there the raw slurry entered thedigester through a short straight pipe,the outside portion being 21 above thelevel of the inside of the digester andthe digester end down to I1 from the floor.Thus no air entered the digester.

The digesters were each 50' long and11' wide, concrete floor flat at the inletend and sloping down sharply to the farend.

FIG.32 Digester with Storage Tank in Background

At the lowest point was another straightpipe as a digester outlet made of 3" pipewith a gate valve. It is important to notethat all pipes in a digester be straightto allow for rodding out. It is necessaryfrom time to time.

Vital statistics to digester design andloading were brought to light by thisfirst unit and will be discussed in detailunder the heading of 1) loading rates, 2)displacement 3) scum accumulation and 4)gas yields.

In anticipation of having a seriousproblem with scum accumulation I set shortlengths of pipe into the concrete roof atvarious angles pointing down to the diges-ter contents, in line with the long sidesof the digester. The intention was to re-circulate supernatant under pressure witha sludge pump to break the scum layer bygetting the whole digester contents to ro-tate. The scum would then be broken upand forced into the more liquid mass.

In practice all that happened was thatthe jet of supernatant made a neat hole inthe scum and the mass did not move.

As a second measure, I let in a seriesof pipes through the floor of the diges-ters and recirculated gas through a com-pressor to bubble up and crack the scum.This might have been effective if useddaily or weekly with absolute regularity.But once the scum became a foot thick itwould no longer break up. Also the ventholes in the floor became clogged withsand. Both methods were failures. Scumremained a major problem.

I suspect that many have encounteredsimilar difficulties and have abandonedmethane digestion in favor of other meth-ods of treatment, solely because of it.In a small digester it is not too diffi-cult to handle (Inner Tube Digester). Ina large scale unit it can build up to 1foot depth in a year. Scum consists oftightly knit scraps of straw from beddingor animal feed, held together by a darkcolored sticky substance thrown up throughthe supernatant levels in the bubblingzone. It covers the entire surface moreor less evenly. Here we come to anotheradvantage of the displacement digester.

Since the scum forms evenly, the largerthe surface area it has to form on, thelonger it takes before it becomes a thickmat. It takes up so much digester spacethat the whole digester becomes overloadeddue to the slurry being forced through tooquickly. It then has to be either brokenup and mixed back into the fermentation orphysically removed. It is my experiencethat when it is broken up it merely re-forms again within a short time. Little,if any, is decomposed and withdrawn withthe effluent. The problem, therefore, re-solves itself to a question of physicalremoval at intervals.

In order to make room in the digesterto load in the daily quota of slurry,withdrawals were made from the outlet endfrom the lowest point, that is, the sludgeoutlet. I withdrew 3 or 4 days' worth ofeffluent at a time, of 500 gallons each.To do this I backed my tank truck into ashort excavation so that the top of thetanker was about 2 feet below the digesterroof level. A 3" plastic connection andtwo 3" valves completed the withdrawalcircuit. On the top of the tank truck wasan opening to vent out air when the tankerwas being filled. Into this I fitted atennis ball in a cage so that when sludgerose to the vent joint, the tennis ballshut off when the tank filled. This pre-vented messy overflows.

The effluent was then spread on fieldsas a fertilizer. There was also a strongdemand for it in Johannesburg where it wasused in winter to bring up the grass fast-er in the spring than any other knownmethod.

Gas yield from the two digesters aver-aged 8,000 cubic feet per day. The gas wasanalyzed at the City Gas Works at 711 BTUper cubic foot (sea level value). Some-times the gas yield went as high as 12,000ft3 for weeks at a time, after a digesterhad recently been returned to work. It wasa matter of delayed action of the brew.From the time the digester was half fullto the time it was full (about 3 weeks),the bacteria did not generate much gas. Atabout the time it filled up, the backlogwould surge gas production.

To provide the heat to the first dis-placement digester, I built an engine roomadjacent to the digester outlet end. Theengine was fueled by 6000 cubic feet ofgas daily and the cooling water and ex-haust gases were returned to the digesterto maintain the optimum temperature. Theexhaust gas was led through a series ofboulders against one digester wall. Theboulders were packed with dry earth cover-ed, in turn, by a layer of conceret asweatherproof!ng.

33 Spreading the Effluent

The engine design called for a maximumcooling water temperature of 140°F. Thiscoincided exactly with the maximum temper-ature for pipes laid on the digester floor.If a higher temperature had been used, thesludge would have "caked" on the pipes andprevented the transfer of the heat.

So a small 3/4" pump was installed,driven directly by the engine, and run atslow speed (to improve endurance) to cir-culate water. In the circuit there wasalso a 200 gallon header tank to keep thelines full at all times. In winter it wasbypassed and in summer the 200 gallon tankwas taken into the circuit as a means ofcooling the water to prevent the digestertemperature from rising over 95°F. Theengine and digester combination ran dayand night for 6 years, except for occa-sional stoppages and for repairs.

We are taking the experiencegained from this major experiment to drawplans for a series of projects in methanedigestion, in a range of sizes. However,it is worth mentioning that the wholemethane plant including engine cost about$10,000 and produced 8000 ft3 gas daily.At the altitude of 5500 ft above sea levelthe B.T.U. value was 585 per ft3. Thus,4,680 B.T.U.* per day or 46.8 Therms. Atthe present 1973 price in Santa Barbarathis amounts to $7.57 per day or $16,578over the 6 years, in gas alone. The sav-ing in labor in the loading and spreadingof manure made for a far faster return oncapital. By far the greatest return wasneither in gas nor labor saving, but inthe value to the soil of the effluent re-turned as a fertilizing material.

*xlO 3

FIG.34 13 HP Diesel Engine Converted to Run on Methane Gas

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13. Boswell, A. M. 1947. Microbiology and Theoryof Anaerobic Digestion. Sewage Works Journal

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14. Barker, H. 1956. Bacterial Fermentations. JohnWiley & Sons, New York.

15. G otaas, H. 1956. Composting: Sanitary Disposaland Reclamation of Organic Wastes. World HealthOrganizations, Geneva.

16. American Public Health Association. 1960.Standard Methods for the Examination of Waterand Wastewater. 11 ed. New York.

17. Dugan, Gordon L. et. ai. 1970. PhotosyntheticReclamation of Agricultural Solid & LiquidWastes. Sanitary Engineering'Research Laboratory,University of California at Berkeley SERL Reportno. 70-1.

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Waksman, S. 1938. Humus: Origin, ChemicalComposition and Importance in Nature. Williams& Wilkins Co., Baltimore.

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Hart, S. 1963. Fowl Fecal Facts: NationalSymposium on Poultry Foul Wastes, Lincoln American.Society Agricultural Engineers, University ofNebraska.

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Eby, H. 1961. Design Criteria for ManureLagoons. Amer. Society of Agricult. Engineers.Paper 61-935.

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Engine room, summer cooling tank and digester on thefirst full scale methane power plant to operate, on thelinear displacement principle. Water heating tower onright was abandonned in the first year.

•TV-,'

One day's manure production from 1000 pigs, oncedigested, spread on crops in 5 minutes.

PR ACTBUILDI

CALNG OF METHANE

POWER PLANTSFOR POWER and ELECTRICITY

NATURAL FERTILIZER • LABOR SAVING

RURAL ENERGY INDEPENDENCE*ANNOUNCING THE PUBLICATION OF THE FIRST PRACTICAL BOOK ON HOW TO DESIGNAND BUILD YOUR OWN DISPLACEMENT-TYPE METHANE-GENERATING PLANT, COMPLETEWITH CHARTS, DIAGRAMS AND PHOTOS.

• AUTHORED by the pioneer and innovator of thefirst, continuously-operated displacement digestermethane plant.

• SHOWING how you can produce and use your ownsupply of free energy and fertilizing material re-taining nature's full nutrient value, and how youcan save labor while reducing the risk of epi-demics.

• DISCLOSING a never-before-revealed solution tothe scum removal problem before it becomes aproblem.

• TELLING how it all started — and why.• RECOUNTING successes and failures over 6 years

of continuous operation.• INTENDED for small and large farms, homesteads,

feedlots, canneries, dairies, etc.• REVEALING plans for a "Power Plant of the

Future", 100 feet long, 25 feet in diameter andyielding 50,000 cubic feet of gas daily from 5 tons(dry weight) of manure.

• FEATURING a question and answer section devot-ed to most-commonly posed queries.

• BROACHING the subject of human excrement asa raw material for methane power plants.

• DEALING clearly and succinctly with technicalaspects of the biological process and the rawmaterials used.

• DESCRIBING the three main types of methanepower plants: Batch-load, vertical and horizontal,from inexpensive working models to farm-inte-grated power plants.

• ANALYZING the economics of methane powerplant operation.

• PROMOTING a new-age technology wherein wasteorganic matter is recycled to produce fuel andfertilizer (hence food) while helping clean up theenvironment.

FIGURES:FIGURES (onCapital costGas per dayValue, as gas

Value, aselectricity

PLUS savings

my S. African farm):= $10,000= 8,000 fts= $7.57/day or

$16,578 oversix years

= $7.43/day or$16,271 oversix years

down from 8 man/days per week to 1 man/day.PLUS 5 tons Nitrogen, AV2 tonsPhosphates and 1 ton Potash peryear in liquid end products.

SELLING for $12. (California residents add salestax of 6%)NORMALLY sent book rate, or add $1 towardsextra (1st class) mailing costs.$2 additional for overseas airmail.YOUR cancelled check is your receipt.SEND a money order or check to:

L. JOHN FRY1223 North Nopal StreetSanta Barbara, Calif. 93103