Optimized Gravitational Settling of Hog Manure Solids: Engineering and Design Study

Prepared for:

Manitoba Livestock Manure Management Initiative Inc.

Prepared by:

DGH Engineering Ltd. 12 Aviation Boulevard

St. Andrews, Manitoba R1A 3N5

October 2013 (Revised)

ACKNOWLEDGEMENTS

The project was funded in part by the Canada and Manitoba governments through

Growing Forward, a federal-provincial-territorial initiative and the Manitoba Pork

Council.

Contents

1. Introduction ………………………………………………………………………. 1

2. Solids and Phosphorus in Swine Manure and Their Removal ……………. 2

3. Separation Technologies ………………………………………………............ 5 3.1 Screening and Filtration for Liquid-solid Separation ………….......... 5

3.2 Gravitational Settling for Liquid-solid Separation and Dewatering ... 8

4. Feasibility of Manure Air Drying ………………………………………………. 13

4.1 Feasibility of an Open and Year Round Drying Facility ……………. 13

4.2 Seasonal Drying Facility ……………………………………………….. 14

4.3 Review Existing Solar Drying Facilities ………………………………. 16

5. Literature Review Summary …………………………………………………… 20

6. Primary Conceptual Designs ………………………………………………….. 21

6.1 Air Drying Bed …………………………………………………………… 21

6.2 In-situ Storage Dewatering …………………………………………….. 25

7. Supplementary Conceptual Design .………………………………………….. 28

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1. INTRODUCTION

In recent years, intensive studies have been conducted on liquid-solid separation of livestock

manure for various purposes: odour control, energy recovery, nutrients management, etc.

Different objectives have different separation technology requirements as well as different

requirements for the extent of separation. To employ liquid-solid separation for reducing

phosphorus, there is a need to successfully deal with the two aspects of the separation:

reducing solids content in the separated liquid stream to decrease phosphorus and achieve an

appropriate balance of nitrogen and phosphorus; and reducing the liquid content in the retained

solids stream to facilitate handling.

It is well documented that separation reduces phosphorus and raises the ratio of nitrogen to

phosphorus in the separated liquid stream. The extent of separation required to achieve a ratio

of nitrogen to phosphorus suitable for crops has not been well quantified. In an over-separated

liquid stream of manure, the ratio of nitrogen to phosphorus may be so high that addition of

phosphorus is required for optimum plant growth. This study attempted to determine if

separation via gravitational settling is sufficient to obtain an appropriate ratio of nitrogen to

phosphorus for crop nutrients needs.

Published literature has focused on the effectiveness of liquid-solid separation on reducing

solids content and in turn reducing phosphorus in the separated liquid stream. There is relatively

little practical information on dewatering the retained solids stream. Usually, the retained solids

stream contains a high water content and this has inhibited the employment of liquid-solids

separation in practice. The project sought to identify a practical and economical technology to

address to the high water content in the separated solids stream following gravitational settling.

This study consisted of a review of the literature; an analysis of data in the literature; and the

development of conceptual method to achieve the objectives identified above.

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2. SOLIDS AND PHOSPHORUS IN SWINGE MANURE AND THEIR REMOVAL

Manure contains substantial amount of inorganic phosphorus, most of which is in insoluble

forms (Gerritse and Vriesema, 1984). Luo et al. (2001) reported that insoluble inorganic

phosphorous constituted the major part (73.5%) of total phosphorus in hog manure. Soluble

ortho-phosphorus and organic phosphorus were found to be about 16.2% and 10.3% of the total

phosphorus, respectively.

Vanotti et al. (2002) reported that the soluble reactive phosphorus represented, on average, a

small fraction (17%) of total phosphorus in the flushed manure. Vanotti et al. (2002), however,

classified the rest of phosphorus as organic phosphorus, occupying 83% of total phosphorus.

The percentage of organic phosphorus is equivalent the sum of organic and insoluble inorganic

phosphorus in Luo et al. (2001).

Rice et al. (2005) collected hog manure (faces and urine) from a belt system under a slotted

floor. They reported that 90% of total phosphorus is in the solids fraction of hog waste. Based

on the data they reported, the characteristics of hog manure can be estimated as shown in

Table 2-1.

Table 2-1 Raw Hog Manure Characteristics

TKN TP TS Ratio N : P % mg/L % mg/L % mg/L

Total 100 7,932 100 1,868 7.16 73,298 4.25 : 1

Solids Fraction 39* 15,196 90* 8,553 33 373,000 1.78 : 1

Liquid Fraction 61* 6,144* 10* 235* ----- ----- 26.14 : 1 *Reported by (Rice et al., 2005). The balance of the figures was calculated based on the data in the literature. The volume of solids fraction was estimated based on the density of 1.1147 kg/L using the formula ρ=3.446TS+1001 (Langner and Bibeau, 2009) and TS of 33% (Rice et al., 2005).

Phosphorus is present in manure slurry mainly in insoluble forms (solids), which may explain

why phosphorus can be reduced by separating solids from the slurry. Chastain et al. (2001)

found that the concentration of total phosphorus (TP) in the influent and effluent correlate well

with the total solids content. The reduction in phosphorous due to solid-liquid separation can be

predicted by the decrease in total solids (TS).

Bicudo et al. (1999) investigated 15 anaerobic lagoons operated from 2 to 18 years. They

reported that the sludge typically has a much higher concentration of total phosphorus than the

liquid. It appeared that approximately 91% of the total phosphorus was contained in solids

stream.

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In Manitoba, Racz and Fitzgerald (2001) investigated the manure storages from 38 different hog

operations and confirmed that the highest correlation of percent solids occurred with total

phosphorous (r=0.718, n=145), reflecting an increase in the phosphorous content of the manure

with percent solids.

Chastain and Vanotti (2003) conducted a study and tried to establish correlation equations to

predict solids and nutrients removal by gravitational settling. The swine manure they used

contained TS of 0.5%, 1.0% and 2.0%, respectively. They established regression equations to

describe the nutrient in manure correlating to TS concentration. The equations of the TKN and

TP are expressed as:

TKN=0.112 TS; and TP=0.052 TS.

The equations were reported to be applicable for manure with TS in range of approximately

1,730 to 23,850 mg/L (approximately 0.17% to 2.38%). For the effluent resulting from settling

(supernatant), Chastain and Vanotti (2003) predicted:

TSout=8.12 TS in0.71;

TKNout=1.15 TKN in0.95; and

TPout=7.87 TP in0.52.

They reported that gravity settling did not decrease soluble contents, such as total ammonia nitrogen (TAN) and ortho-phosphorus (soluble P).

Whether these equations are suitable for Manitoba hog operations needs to be further verified.

To design a manure settling facility, preliminary bench scale tests should be conducted to

predict the settling efficiency, removal of TS and TP and ratio of N to P.

Vanotti et al. (2002) used flushed hog manure with an average TS of 1.1% (0.4% ~ 2.5%) and

average initial N to P ratio of 4.8 to 1 in their liquid-solids separation experiment. They found

that the removal of organic P and organic N (all insoluble P or N was classified as organic P or

N) correlated to the removal of total suspended solids (TSS). They reported that for 1 gram of

TSS removal, the organic P and organic N removal were 33.2 mg and 72.6 mg. Based on the

data provided in their paper, the required TS removal via liquid-solids separation can be

estimated to be 50% for an N to P ratio of 10 to 1 and 40% for a ratio of 8:1.

Zhang and Westerman (1997) reported that suspended solids (SS) as percentage of total solids

(TS) in fresh swine manure is 45 to 65%. The theoretical maximum TS separation efficiency for

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liquid swine manure by physical separation (sedimentation, screening, filtration and

centrifugation) is therefore in the range of 48 to 70%.

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3. SEPARATION TECHNOLOGIES

There are different technologies for liquid-solid separation which can potentially achieve TS

removal of 50%. Table 3-1 displays the removal efficiencies for TS, TKN and TP for various

separation technologies.

Table 3-1 TS and Nutrients Removal from Hog Manure via Liquid-Solid Separation

Removal from liquid stream Residual in solids stream references

TS % TKN % TP % TS % Volume

pilot scale settling (14~28 days) 50~70 20~30 75 15.5, 17.4 15 Slevinsky et al. 2009

bench scale settling (12 days) 66 ---- 82 11 55* Barrington et al. 2004

geotextile bag (lagoon sludge) 82.0** 76.7** 82.0** 14.7 36.3 Baker et al. 2002 and Cantrell et al. 2008 geotextile bag (fresh manure) 31.3** 26.2** 47.6** 3.4 60.3

screw press screen (0.5 mm) 14.9 9.2 14.8 22.6 ~ 34.4 Chastain et al. 2001

stationary screen (1.0 mm) 6~31 3~6 2~12 5 Piccinini & Cortellini, 1987

vibrating screen (0.516 mm) 21~52 5~32 17~34 9 ~ 17 Holmberg et al.,1983

vibrating screen (0.44 mm) 15~25 2~5 1~15 13 Piccinini & Cortellini, 1987

vibrating screen (0.104 mm) 50~67 33~51 34~59 2~8 Holmberg et al.,1983

rotating screen (0.8 mm) 5~24 5~11 3~9 12 Piccinini & Cortellini, 1987

belt press screen (0.1 mm) 47~59 32-35 18~21 14~18 Fernandes et al., 1988

centrifuge 15~61 3.4~32 58~68 16~27 Piccinini & Cortellini, 1987

* The volume of solids fraction was estimated based on the density of 1.040 kg/L based on formula ρ=3.446TS+1001 (Langner and

Bibeau, 2009); solids stream occupied 58% of initial mass and TS of 11% (Barrington et al. 2004). **Calculated average based on data in Baker et al. 2002.

It is noted that recently reported data for TS removal was close to TP removal in terms of

percentage. The ratio of TP removal to TS removal can be estimated to be 1 to 1. It appears,

however, that in the 1980‟s reports, the TP removal was lower than the TS removal.

3.1 Screening and Filtration for Liquid-solid Separation

The mechanism of screening separation by screening is that solid particles with a size larger

than the opening of the screen are retained by the screen in solids steam. Hill and Toller

(1980) studied the characteristics of flushed swine manure after screening with a set of

standard sieves with the openings of 3.000, 2.000, 1.000, 0.500, 0.250 and 0.105 mm,

respectively. Their results showed that 46% of TS, 70% of TKN and 75% of TP passed the

sieve with 0.105 mm openings. These results imply that the theoretical removal efficiency

cannot be higher than 54% for TS, 30% for TKN and 25% for TP with a 0.105mm screen. In

reality, the removal efficiency can be higher than aforementioned since the particles stopped at

the screen may help to retain even smaller particles.

For vibrating screens, increasing the flow rate may increase removal efficiency; but this also

increases the moisture (water content) of the retained solids stream which in turn increases the

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volume of the retained solids stream. Holmberg et al. (1983) found that for a given screen, such

as the 30 mesh, increasing of the flow rate from 37.5 to 150 L/min increased the total solids

separation from 20.7% to 51.9%, but also increased the moisture content of the separated

solids from 83.8% to 90.5% (Zhang and Westerman, 1997) (see Table 3-1 vibrating screen

0.516 mm opening).

If a screen separation facility were employed in a 4000 pig feeder operation to achieve more

than 50% of TS removal, the annual volume of the separated solids stream would be

approximately 2.3 million litres consisting of with 90% of water (TS of 10%). This figure is based

on a manure generation rate of 6.5 litres per hog per day with 3.5 % solids.

Separation technologies should be evaluated not only by their solids (or phosphorus) removal

from the liquid stream, but also by the moisture content of the solids stream or/and the ratio of

the volume of solids stream to total volume of manure.

Geotextile bag filtering is a technology used for domestic wastewater dewatering. Limited

research with this technology has been undertaken for livestock manure dewatering. Backer et

al. (2002) and Cantrell et al. (2008) used geotextile bags for fresh manure and lagoon sludge

liquid-solid separation. The initial TS of the feed stock was approximately 2.6%, 3.1% and

2.8%. These TS contents are typical for flushed manure from hog barns. It was found that the

dewatering characteristics of fresh hog manure were very poor. For the manure with TS of

2.8%, the TS in the retained solids stream was 3.4%. The retained volume was about 60.3% of

the initial feed stock volume.

It is noted that the dewatering characteristics of the sludge from a hog manure lagoon was

much better than fresh manure. Geotextile bag filtering retained 34.4% of the initial feed

volume in the solids stream and the TS in the solids stream was 14%.

Danaher (2009) reported that by adding a of polymer the removal of total suspended solids

(TSS) could be improved to 99%. No information about the TS removal was available. Usually,

the TS removal is slightly lower than TSS removal. The TS removal can be estimated to be at

least 90%. The TS retained in geotextile bag were reported as 13% and 11.2%, respectively in

the two tests. It appeared that the separation characteristics of manure can be improved by

polymer addition to produce a product that matches lagoon sludge characteristics.

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Geotextile bag suppliers (Granite Environmental, Blue River Technologies) were contacted for

the TS content of the retained solids stream, which they were reported as between 12% to 16%

for sludge. These are consistent with the above reported results.

It appears that all of the technologies discussed above have a potential of reducing TS by 50%

from the separated liquid stream with moisture contents in the retained solids stream is higher

than 80% (TS less than 20%).

Photo 3-1 Press Screen Separated Hog Manure (source: DGH Engineering Ltd.)

Photo 3-2 Press Screen Separator (Source: DGH Engineering Ltd.)

Centrifuge and press screening can achieve TS of above 30%. For instance, centrifuged

wastewater sludge from the Winnipeg North End Wastewater Control Centre may achieve TS

as high as 36%. Chastain et al. (2001) reported they achieved TS of 22.6% to 34.4% in the

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retained solids stream with a press screen. Photo 3-1 shows retained hog manure solids from a

press screen.

3.2 Gravitational Settling for Liquid-Solid Separation and Dewatering

Burton (2007) developed a profile of solids in a settling tank (Figure 3-1). Only large/heavy

particles can settle in manure slurry. Dissolved solids and colloidal particles cannot be removed

by settling. The volume of the settled solids portion depends on the original TS.

Figure 3-1 The division of the solid matter of animal manure into fractions that can be removed by the main

categories of separator or separation process. (from Burton, 2007)

The recovery of solids by settling is greater than that of mechanical screens. Employing

gravitational settling, total solids (TS) removal was reported to be as much as 60% (Lorimore et

al. 1995; Zhang and Westerman 1997).

Currently, in Manitoba, the predominant method of manure management is the storage of liquid

manure in outdoor earthen basins, followed by manure spreading on crop land. The storage

period is typically a year. During storage, gravitational liquid-solid separation takes place.

Phosphorus settles with the solids as the same time. Racz and Fitzgerald (2001) reported that

38% of 145 manure samples collected from lagoons had N : P ratios higher than 8 : 1. Among

them, 22 samples had N : P ratios higher than 12 : 1. In many instances, the samples with very

high N : P ratios were obtained from the top of storage facilities and/or from the secondary

storage cells.

Slevinsky et al. (2009) conducted a pilot scale test of liquid-solid separation via gravitational

settling and achieved TS removal of 50 to 70% using hog manure with initial TS of 3.5 to 5.6%.

The volume of the settled portion was reported as 15% of the total volume of manure. The

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solids concentrations of the settled portion were reported as 15.5% and 17.4%. The N:P ratio in

the liquid separated liquid stream was 30:1.

Slevinsky et al. (2009) also found that solids settling efficiency is related the initial solids content

in manure. They concluded that solids settled out from liquid hog manure quite rapidly and

completed when the solids content in the manure was below 5%. When manure contained a

high percentage of solids (solids of 6.6% in their study), both the rate of settling and

completeness of separation were poor. They suggested further studies to elucidate the

reason(s) for the poor of separation by settling in high solids content manure.

Chastain (2011) described the characteristics of manure settling and concluded that hindered

settling is the primary type that occurs. Hindered settling is the process where solid particles

move down though the liquid by gravity. This process settling carries on fairly quickly; as the

solids concentration increases, the settling type changes from hindered to compression.

The type of that settling takes place in concentrated manure solids is compression settling.

Unlike hindered settling where the solids particles move down through the liquid by gravity,

compression settling is a process in which the mechanical support of lower solids to upper

solids push liquid out the space between the particles.

Figure 3-2. The three hindered settling zones for liquid animal manure (TS ≥ 0.5%) (Chastain,

2011)

In Figure 3-2, the surface of the compression layer is formed at approximately of 60% below the

total depth after two hours of settling. As the compression settling carries on, this surface will

occur deeper. Based on the data in Slevinsky et al. (2009), the surface compression layer

settled to below 85% of total depth in four weeks.

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Langner and Bibeau (2009) investigated two hog manure EMS in Manitoba. One of the EMS

was located in Grunthal and the other was located in Niverville. They concluded that (for the

Grunthal EMS) “the solids concentration increased slowly with depth until a certain depth; past

this depth, the increase in TS was much greater. This is evidence of stratification within the

lagoon” (EMS). They quantified the surface layer at 0.45 m with the transaction layer from 0.45

to 1.5 m. The total solids contents in the surface samples ranged from 0.7% to 3.6%. Three

samples collected at the depth of 1.5 m in the sludge zone at the bottom of lagoon, contained

TS of 14.5% (figure reading), 16% (figure reading) and 37.1% (reported), respectively. The

sampling points were 3 m, 12 m and 30 m from lagoon bank, respectively.

Table 3-2 Solids Content in Settled Solids Stream (Manitoba Investigation)

Reported by Initial TS TS in settled Settling period Operation Settling facility

Slevinsky et al, 2009

3.5% 15.8% 28 days grower/finisher 40‟X8‟X4‟ tank

6.6% 17.4% 14 days

Langner & Bibeau, 2009

14.5% * 16.0% * 37.1%

farrow/nursery 200‟ wide lagoon

12.9% 13.2% *

grower/finisher 200‟ wide lagoon

*read data from the reported figure (Langner and Bibeau, 2009)

Photo 3-3 High Solids Content Manure at Bottom of Lagoon (source: DGH Engineering Ltd.)

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Photo 3-4 Solids Residue in Lagoon after Pump-out (source: DGH Engineering Ltd.)

No manure storage duration was reported in the previously discussed research. In Manitoba,

lagoons are normally emptied every year. It appears that TS of between 13% and 17% should

be achieved after one year storage. The TS of 37.1% might have been caused by long term

storage (insufficient agitation at the sample point). Photo 3-3 was taken on a DGH Engineering

project site. Long term uneven agitation while pumping out caused extended compression

settling in the settled manure. The manure solids can be excavated by a backhoe and

transported by a truck. This demonstrates that gravitational settling can potentially achieve high

solids content due to compression settling if sufficient settling time is allowed.

Photo 3-4 shows solids left in a HDPE lined lagoon after manure pump-out. It was found that the

dewatering characteristics of the residual manure are fairly good. It can be seen in the photo

that water can drain relatively quickly from the solids with very little slope. Two factors may have

contributed to this. One is the smooth impermeable liner made drainage easy. And another is

the characteristics of dewatering changed while the manure is stored. So far, we have not found

any research on this phenomenon.

US EPA (1987) reported that freeze/thaw cycles help with wastewater sludge dewatering. It was

found to be beneficial for sludge with solids content of 3% to 7%. The solids concentration

would rapidly approach 25% as soon as the frozen mass is completely thawed, due to very

rapid drainage. The data showed that the freeze/thawed sludge reached 26% solids with in

approximately one week. The sludge without freeze/thaw reached 9% in a period of more than a

month. It has been frequently reported that the sludge in a manure lagoon has much better

dewatering characteristics than fresh manure. This observation is possibly due to the same

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freeze/thaw effect. Manitoba has a long winter that provides a natural freeze/thaw process and

this would be beneficial for manure dewatering.

The U.S. EPA Design Manual for Dewatering Municipal Wastewater Sludges (1987) provides

design methods and criteria for air drying facilities, such as sludge dewatering beds (sand beds,

wedgewire beds, paved beds) and sludge drying lagoons. Among them, a sludge lagoon

appears to be feasible for Manitoba‟s climate.

Photo 3-5 Conception of Sludge Lagoon

Photo 3-5 shows the first cell of hog manure lagoon with a concrete floor. The cell can hold

settled solids for 3 years if gravitational settling efficiency is 45 to 50%. At the present time, this

cell is emptied every year by incorporating secondary cell liquid manure and pumping out the

mixture. The concept of a sludge lagoon is to keep the settled solids in the cell to enhance

dewatering. After three cycles of freeze/thaw, the characteristics of dewatering of manure solids

will be improved and compression settling has apparently occurred to a certain extent. Floor

drainage will be conducted periodically through a filter pipe (far end in Photo 3-5). The filter pipe

leads to a pump out well. Prior to cleaning the cell, the supernatant will be pump out. The target

average solids content is 30% for this type of sludge lagoon.

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4. FEASIBILITY OF MANURE AIR DRYING

4.1 Feasibility of an Open and Year Round Drying Facility

The evaporation from open water bodies and precipitation in south Manitoba can be found in

Photo 4-1. It shows that in the vicinity of Winnipeg, the average annual values of evaporation

(from open water bodies) and precipitation are 700 mm and 600 mm, respectively.

Figure 4-1 Annual Precipitation and Evaporation in South Manitoba (source: U of Manitoba, http://home.cc.umanitoba.ca/~mlast/lakelevel/page3/page3.html)

Wiki (http://en.wikipedia.org/wiki/Lake_Manitoba) reported that annual average evaporation of

Lake Manitoba is 2.49 km3. The surface area of the lake is 4,624 km2. The annual evaporation

rate can be calculated as 538 mm (equivalent to 1.47 mm/day).

Berry and Stichling (1954) employed A.F. Meyer‟s evaporation formula to estimate the water

evaporation from large lakes and reservoirs in the Northern Plains Region of North America.

Their calculations showed that the average (1901-1950) annual evaporation from Lake of

Winnipeg was 25.3 inches (642.6 mm, equivalent to 1.76 mm/day). For smaller water bodies

(dugouts) in south Manitoba, the evaporation rate calculation needs to be multiplied by a factor

of 0.781. Based on the method provided by Berry and Stichling (1954), the evaporation rate

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from a small area can be estimated as 500 mm/per year (1.37 mm/day) in the vicinity of

Winnipeg.

The annual evaporation and precipitation in the Winnipeg area are basically balance. This

suggests that an open, year round drying facility cannot be expected to preform reliably.

4.2 Seasonal Drying Facility

Data shown in Berry and Stichling (1954) indicate that the evaporation takes place

predominantly in four months at Lake Winnipeg: June, July, August and September. The

evaporation in these months covers 74 percent of the annual evaporation. Using this

information, the evaporation rate from a lagoon located near the Winnipeg area can be

estimated as 370 mm in the period from June to September (3.0 mm/day).

Table 4-1 Winnipeg Solar Energy and Surface Meteorology (http://www.gaisma.com/en/location/Winnipeg.html)

The statistical precipitation in the Winnipeg area is shown in Table 4-1. The precipitation in the

period from June to September is 280 mm, which accounts for approximately 55 percent of

annual precipitation. This precipitation is significant --- 75.7% of the evaporation potential (370

mm). Reliable air drying facilities therefore need to be covered to prevent precipitation from

entering.

The energy driving an air drying facility is provided by the sun. Approximately 0.68 KWh is

needed to evaporate one kilogram of water at 20oC. In an ideal situation where all solar energy

received is applied to evaporation, the maximum evaporation rate will be 8.5 mm/day in July.

The theoretical maximum evaporation in the period from June to September is 880 mm.

15

The actual evaporation rate is much less than this calculated ideal value. Some of the main

factors that impact evaporation rate are

Temperature of air and water: higher temperature helps evaporation;

Relative humidity: lower relative humidity helps evaporation;

Wind speed: higher wind speed helps evaporation; and

Cloud levels, direct sunshine helps evaporation.

Figure 4-2 Winnipeg Climate (source: http://www.winnipeg.climatemps.com/)

Figure 4-2 provides information about Winnipeg‟s climate similar to Table 4-1. Figure 4-2

showed that the lowest relative humidity occurs in May. The insolation in May is much higher

than in September. The temperature and wind speed in May are similar to September. The

evaporation rate in May may be similar to that in September in Winnipeg area. If this is the case,

the proposed manure drying facility can probably operate for one additional month (5 months

total).

In an evaporation pan observation monitored by DGH Engineering one mm evaporation was

observed in a period of 9 hours on April 1st, 2013. The ambient temperature varied from -12 oC

to -2 oC; relative humidity varied from 44% to 71%; wind speed varied from 3.3 m/s to 4.7 m/s.

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Although it was a short term observation, an evaporation rate of 2 mm/day may be expected

with favourable weather in late April and early October.

4.3 Review Existing Solar Drying Facilities

Relatively little literature is available on solar drying hog manure. Air drying for municipal

wastewater sludge, however, has a long history.

A solar drying technology was assessed for sludge dewatering in 1994. It consisted of a

greenhouse with concrete floor and walls; with a ventilation system and a solids mixer. The

greenhouse prevents precipitation from entering the sludge while taking advantage of solar

heat. Ventilation exhausts humid air and draws dry air in. The mixer breaks up the dry crust to

expose wet sludge to air. Greenhouse solar drying may not be economical for drying manure,

but it provides an optimised condition to study evaporation rates.

Mangat et al. (2009) used an evaporation rate of 2.2 kg water per m2 per day (mm/day) in a

design for Trinidad and Tobago. Their target was to dry sludge of 16% ~ 18% TS to 70% ~ 90%

TS. The local conditions are solar radiation of 1886 kWh/m2/year (5.17 KWh/m2/day), annual

average temperature of 30oC and relative humidity level of 80%. These designers anticipated

that in the dry season in Trinidad, the evaporation rate would be greater than 2.2 kg water per

m2 per day (mm/day). No actual operation data was available for this drying facility. It provided a

reference for evaporation rate design.

Meyer-Scharenberg and Pöppke (2010) reported the results of tests on a solar drying system

located in Managua. In a 3-week cycle test, sludge of 28% TS was dried to of 70% TS. The

dewatering rate was reported as 4,300 kg water per m2 per year (11.78 mm/day). The test was

conducted during the rainy season. This dewatering rate exceeded all expectations. They

concluded that ventilation fans were not required to operate continuously. In Managua, solar

radiation and temperature are relatively constant throughout the year with average values of 20

MJ/m2/day (5.44 kWh/m2/day) and 28 oC. The relative humidity varies from 60% to 80%. The

unit of “kg water per m2 per day” can be interpreted as “mm per day”. Using the “ideal

evaporation rate” calculation discussed above, the maximum evaporation rate that can be

reached should be 8 mm per day (5.44 kWh/m2/day÷0.68 kWh/kg water). It is noted that the

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actual evaporation rate is higher than the calculated “ideal” value. No information of test

conditions (ambient temperature, sunlight hours, etc.) was available.

A solar drying facility (Photo 4-1) was tested in Discovery Bay, California in 2009 (Hill and Bux,

2011). The test results are listed in Table 4-2.

Table 4-2 Discovery Bay Data Analyses

Start Date Original TS Reach 75% TS Evaporation rate* Monthly average T#

April 23, 2009 17.8% 18 days 8.15kg/m2/day 10 to 23

oC

June 17, 2009 14.7% 13 days 12.37 kg/m2/day 15 to 31

oC

*calculated on basis of dimensions of drying system and reported original volume of sludge. #source: http://www.weather.com/weather/wxclimatology/monthly/graph/94505

It appeared that the evaporation rate in the tests was higher in June than in April. No information

on the test conditions (ambient temperature, sunlight hours, etc.) was available. Comparing

statistical data for the three months (Table 4-3), more insolation, higher temperature and less

wet days in June might contribute to the higher evaporation rate.

Using reported information, the “ideal” evaporation rates of the two tests are calculated as 9.2

mm/day and 11.4 mm/day.

Photo 4-1 Solar Drying Facility in Discovery Bay, CA (source: Hill 2013)

Comparing the April and May information of Brentwood, California with the June and July

information of Winnipeg (Table 4-2), Winnipeg has similar insolation, higher temperature

(advantage) and more wet days (disadvantage). An evaporation rate of 8.15 kg water/m2/day

should be achieved in Winnipeg in June and July, based on the California results.

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Table 4-3 Brentwood* Solar Energy and Surface Meteorology (http://www.gaisma.com/en/location/brentwood-

california.html)

*Brentwood is approximate 8 km from Discovery Bay, California.

Zweifel et al. (2001) reported some results for of a solar drying facility in Europe. The facility is

located in Glarnerland, Switzerland. It was reported that the initial TS and final TS were 25%

and 40%~50%, respectively. The facility occupies 1440 m2 and 1224 m2 were used for drying.

Total water evaporated was reported as 1,600 tons in a year. Based on the data provided in the

article, we can derive the evaporation rate as 3.52 kg/m2/day (mm/day).

Unlike previously mentioned drying facilities which are located at lower latitudes, Glarnerland is

much higher, similar to North Dakota. No information on solar energy and surface meteorology

for Glarnerland was available. The information for Bern, Switzerland, is shown below. Bern is

approximately 120 km west of Glarnerland.

Table 4-4 Bern Solar Energy and Surface Meteorology (http://www.gaisma.com/en/location/Bern.html)

Table 4-5 Comparison between Winnipeg and Bern in April to Sept

location Insolation Kwh/ m

2/day

Temperature (oC) Wind speed

(m/s) Wet days in 6 months

Winnipeg 4.36 to 5.77 2.49 to 19.95 4.46 to 5.01 58.7

Bern 4.11 to 5.59 6.29 to 17.28 3.71 to 4.84 94.5

19

It appears that in the months between April and September, the evaporation conditions are

similar in Winnipeg and in Bern except that the wind speed is higher and the number of wet

days is less in Winnipeg. Figures 4-2 and 4-3 provided evidence that the relative humidity is

between 50% and 60% in Winnipeg during April to September and the relative humidity is above

70% in Bern during same period. It can be estimated that the evaporation conditions in southern

Manitoba are better than in Glarnerand, Switzerland. The optimum evaporation rate in

Manitoba can therefore be expected to be higher than the 3.52 kg/ m2/day (mm/day) achieved in

Glarnerand.

Figure 4-3 Bern (Glarnerland) Climate

In a period of 3.5 months (June, July, August and early September), an evaporation of 0.35

metres to 0.4 metres can be expected to be achieved with a covered air drying bed in Manitoba.

The target solids content for this type of drying bed is 40%.

20

5. LITERATURE REVIEW SUMMARY

The following conclusions have been drawn from the literature review:

a. The sedimention that occurs in existing two cell earthen manure storage is sufficent to

reduce phosphorus in the liquid fraction to achieve a N:P ratio that nearly meets crop

nutrient uptake. The reduction in total solids (TS) required to meet this objective is

approximately 40%.

b. The total solids content in the settled manure fraction is approximately 13% to 17%. This

low solids content results in a product that is difficult to handle and expensive to

transport. The challenge is to develop a cost-effctive method to dewater this high

moisture solid fraction.

The research indicated that manure that has been stored for an extended period of time

is easier to dewater than fresh manure.

c. Freeze/thaw cycles appear to improve the dewatering characteristics of settled manure

solids. Further research, starting with bench scale testing is recommended to better

understand and utilize the full potential of this natural phenomenon.

d. Long term stored manure sediments may potentially achieve a TS content above 30%,

primarily due to compression settling. Providing drainage from the bottom of the storage

and applying pressure on top of the sediment should accelerate compression settling.

The supernatant needs to be pumped off the solids.

e. An air drying bed, in conjunction with solar input should achieve the high TS content

required for efficient handling and transportation. A TS content of approximatly 30 to

40% is considered necessary to achieve this. The drying bed must be covered to

exclude precipitation in order to reliably achieve these target TS levels.

21

6. PRIMARY CONCEPTUAL DESIGNS

Based upon the literature review and the conclusions summarized in the previous section, two

conceptual designs have been developed to achieve the level of dewatering/drying necessary to

achieve a total solids (TS) content of 30 to 40 percent in the solid manure fraction.

The objective of the following designs is to build on the existing two cell earthen manure storage

model that has been the standard for liquid hog manure storage for several decades. This

model results in a N : P ratio in the liquid fraction stored in the secondary cell that closely

matches crop nutrient requirements, therefore, no further solids (P) removal is considered

warranted for the liquid fraction.

The objective is to dewater the manure now stored in the primary cell. After draining or pumping

off the supernatant liquid in the primary cell, the solids content is estimated to be 13 to 17%,

which is too low to efficiently handle and efficiently transport off site.

All conceptual options are based on a 4000 head finisher hog operation.

6.1 Air Drying Bed

The air drying option is illustrated in the following figure that details two concrete surfaced drying

beds 75 ft. wide by 150 ft. long.

Two smaller beds are proposed roofed over with a fabric covered steel arch building, of which

Manitoba has several manufacturers. A fabric that is semi-transparent is commercially available

and would be used to enhance solar energy capture.

Two sub-options are considered here related to manure handling:

Option A – manure solids pumped from conventional earthen basin Primary Cell.

This option is particularly suited to adopting the new concept to existing farms. The drying beds

would be located adjacent to the Primary Cell of a conventional two cell earthen manure

storage. During clean-out, some of the supernatant in the Primary Cell would be pumped over to

the Secondary Cell. Sufficient liquid must be left which would then be agitated into the solids to

22

permit pumping the solids to the drying beds. Manure with TS up to 10% may be pumped with

conventional centrifugal manure pumps.

The drying bed performs two functions. Some of the free water drains through a filter and flows

back to the manure storage. A subsurface drainage system also collects percolated water for

return to the storage. The remaining water that is not removed by gravitational methods must be

removed by drying (evaporation).

The optimum period for drying in Manitoba is late May to early September. The removal of the

solids from the Primary Cell should therefore occur in mid-May. The drying process will be

completed by late September.

Option B – Downsized Primary Cell.

This option is amenable to new installations and offers an improvement over the traditional 2-

cell earthen basin. This option is a variation of Option A, described above. The objective here is

to improve and simplify agitation and removal of solids from the Primary Cell by using a settling

tank that has a volume one-third of that normally used. Agitation and pump-out would occur

three times per year, which would still allow four months for summer dewatering and drying. The

Primary Cell could be more efficiently constructed as a concrete or steel tank to facilitate better

agitation and pump-out.

Following are the design assumptions and costs for the Air Drying Bed. Design criteria:

finisher hog at 6.5 L/hog/day X 3% solids = 0.196 kg solids/hog/day

4000 hogs = 285,000 kg solids/year

50% of total solids settled = 142,000 kg solids/year

Solids content in settled manure = 13% ~ 37%

Volume of the settled manure (10% TS) = 1,420,000 L (1,420 m3) = 313,000 Imp gallons

Bed area for decant and drying 2000 m2 (150‟ X150‟)

Depth of sludge (10%TS): 0.71 m (2‟-4”)

Decant period: 15 days

Decant target: TS of 15%

Depth of decanted manure: 0.48 m (1‟-7”)

Drying target: TS of 40%

Depth of dried manure: 0.18 m (7”)

Evaporation period (summer, 4 mm/day): 75 days

23

Cost estimate:

Earthwork & concrete $420,000

Roof $215,000

Filter & drainage system $25,000

Total $660,000

24

25

6.2 In-situ Storage Dewatering The in-situ storage dewatering system seeks to capture maximum benefit from compression

dewatering as discussed earlier.

The manure storage would have two Primary Cells that can be modified to each receive manure

from the barn. Each cell would be sized with a 3 year capacity for settled solids. The Primary

Cell in conventional two-cell earthen storages is usually sized for one year capacity.

The Primary Cells would work in turns. Primary Cell One would receive manure for three years

with no agitation or pump-out. The solids will accumulate, enhancing compression settling and

dewatering.

After three years, Primary Cell Two would begin receiving manure, which would last for an

additional three years.

At the end of the 3 year filling cycle, Primary Cell One would be pumped down to remove as

much supernatant as possible. A floating plastic cover would be installed on Cell One while Cell

Two is receiving manure. During this second three year period, the cover would exclude

precipitation from the manure. Accumulated precipitation would be left on the cover to allow the

weight of the water to enhance the dewatering of the sludge below. A drainage system would

continuously remove drainage water from the manure solids and return it to the Secondary Cell

of the storage.

At the end of six years, the cover as well as the solids would be removed. The TS of the solids

would be expected to be approximately 30 percent. The sludge should be compacted to the

extent that the depth would be expected to be five feet, 50% of the original depth. The Primary

Cells will be provided with a concrete floor to facilitate solids removal.

Design criteria:

finisher hog 6.5 L/hog/day, 4000 hogs

daily manure generation = 26 m3 /day

minimum hydraulic retention time = 1 hour

solids (TS) removal from liquid stream = 50%

surface of settled solids

1st year (TS 13%) depth: 1.4 m below transfer channel

26

2nd year (TS 17%) depth: 0.8 m below transfer channel

3rd year (TS 21%) depth: 0.5 m below transfer channel

5th year (TS 30%) depth: 1.4 m below transfer channel

Drying storage design:

number of cells: 2

dimensions of a cell:

Top: 150‟X150‟

Floor: 70‟X70‟

Effective depth: 10‟

Bank slope: 4 (hori.) : 1 (vert.)

capacity of a cell: receive 3-year solids sediments

Bottom drain system:

Concrete floor with slope of 0.5%

Perforated weeping pipe: 4”Φ with sock

Solid PVC pipe: 6”Φ, SDR35

Drain pump out well: 24”Φ PE culvert

Precipitation prevention: 30 mil HDPE cover

Cost Estimate:

Earthwork $109,000

Concrete $158,000

Negative pressure cover $114,000

Drain system $19,000

Total $400,000

The proposed alternative systems both carry significant capital cost, but unlike the systems

relying on mechanical separators, these systems have no day to day operating requirements

and very low maintenance and operating costs. For this reason, it is expected that these

systems are of interest and potentially useful to swine producers.

27

28

7. SUPPLEMENTARY CONCEPTUAL DESIGN

In response to a request from MLMMI, we have also provided a conceptual design for a lower

cost, multi-cell settling design.

The objective of this design is to propose a system which offers lower capital cost (than Options

1 and 2) with the trade-off being a reduction in capability to dewater manure. This reduction in

dewatering capability is caused by:

The relatively short time available to dewater; and

Precipitation is not excluded from the manure storage.

This system uses gravity for dewatering. This structure would be sited adjacent to a

conventional “secondary” earthen manure basin which would store the liquid fraction of the

manure. The manure storage would have two „side-by-side‟ Primary Chambers that can receive

manure from the barn. Each chamber would be sized with a 6 month capacity for settled solids,

and receive manure from the barn for six months without agitation or pump-out. The two

Primary Chambers would both function as a conventional “primary” cell, allowing solids to settle

by gravity over a six month period.

Liquids would pass from the Primary Chamber into the secondary cell of the earthen basin

through one of two methods:

1) As manure is added from the barn into the Primary Chamber, the level of liquids will rise and approach the top of the Chamber. Once the level of liquids in the Primary Chamber approaches the top, liquids will flow through an opening near the top of the rear wall of the Primary chamber into the secondary cell of the earthen basin. Since most of the solids will have settled and accumulated in the lower levels of the Primary Chamber, this liquid will have low solids content.

At the end of six months, the incoming manure from the barn will be directed to flow into Chamber Two and the settling process will re-commence.

2) A vertical perforated pipe and pump out well will be incorporated in the back wall of each

chamber. The inside wall of the pipe will be covered with geo textile, to prevent solids from entering the perforated pipe and pump out well. Dewatering will occur for six months while Chamber Two is functioning as the Primary settling chamber. A pump will periodically move the liquids that have accumulated in the perforated pipe into the secondary storage.

The final TS of the solids would be expected to be approximately 15 percent. The Primary

Chamber will be constructed with a concrete floor to facilitate solids removal with a front end

loader.

A schematic design for the supplementary design follows this section.

29

System limitations:

1. Effectiveness of screening/settling The efficiency of screening on fresh manure is low (refer 3.1 of the report) and compression

settling carries on for a very limited time due to the short storage period (refer 3.2 of the

report). The final solid content can be expected to be 15%. It will still be hard to handle.

2. Impact of precipitation The impact of precipitation on the final solids content will be significant (refer 4.1 of the

report*). Adding a cover system to the design concept would improve effectiveness and

provide predictable performance.

Design criteria:

finisher hog at 6.5 L/hog/day X 3% solids = 0.195 kg solids/hog/day

4000 hogs = 285,000 kg solids/year

Hold capacity =365 days

50% of total solids settled/screened = 142,500 kg solids/year

Solids content in settled/screened manure = 15%

Volume of the settled/screened manure = 950 m3

Dimensions: (one chamber)

Width: 36 ft

Length: 80 ft (including 40 ft ramp)

Height of wall: 8 ft

Slope of ramp: 5 (horizontal.) to 1 (vertical.)

Thickness of wall: 12”

Thickness of floor: 5” with 10” footing Two chambers are required. The chambers share a common wall (80 ft). Operation:

Total holding capacity: 365 days (solids with 85% moisture); and

One chamber is being filled while the other is settling. Cost estimate:

Earthwork: $100,000

Concrete chamber: $180,000

Total $280,000

MLMMI .

DETAIL CALLOUT, SECTION

ITEM SYMBOL REMARKS

GENERAL ANNOTATION

"A" DENOTES DETAIL No.,

"B" DENOTES DETAIL LOCATION

ELEVATION CALLOUT

"A" DENOTES DETAIL No.,

"B" DENOTES DETAIL LOCATION

DETAIL CALLOUT

"A" DENOTES DETAIL No.,

"B" DENOTES DETAIL LOCATION

AB

WALL SECTION CALLOUT

"A" DENOTES DETAIL No.,

"B" DENOTES DETAIL LOCATION

AB

BUILDING SECTION CALLOUT

"A" DENOTES DETAIL No.,

"B" DENOTES DETAIL LOCATION

AB

ROOM NUMBER CALLOUT101

DOOR NUMBER CALLOUTD101

WINDOW NUMBER CALLOUTW101

01REVISION NUMBER CALLOUT

2 CHAMBER SETTLING TANK (72'X80')

CLIE

NT

PR

OJE

CT

ABBREVIATIONS LEGEND

ARCH ARCHITECTURAL CONC CONCRETE EQ EQUIVALENT INT INTERIOR PTD PAINTED T.U.L. TOP UPPER LEVEL

B.U. BUILT-UP CONST CONSTRUCTION EXT EXTERIOR LG LONG P.L. PROPERTY LINE T&G TONGUE & GROOVE

B.L.L. BOTTOM LOWER LAYER CONT CONTINUOUS F/H FULL HEIGHT LOC LOCATION R/W REINFORCED WITH T&B TOP & BOTTOM

B.U.L. BOTTOM UPPER LAYER CORR CORRIDOR F/O FACE OF MACH MACHINE ROOM REINF REINFORCING THKG THICKENING

BD BOARD CWN COMMON WIRE NAIL FD FLOOR DRAIN MAX MAXIMUM RWL RAIN WATER LEADER THRU THROUGH

BLDG BUILDING DIA DIAMETER FND FOUNDATION MFR MANUFACTURER REQD REQUIRED TJ TIE JOIST

BLKG BLOCKING DIAG DIAGONAL FLR FLOOR MID MIDDLE SCH SCHEDULE T/O TOP OF

BOT BOTTOM DS DOWNSPOUT FTG FOOTING min

MINUTE (TIME)

SECT SECTION TYP TYPICAL

B/W BOTH WAYS DTL DETAIL GALV GALVANIZED MIN MINIMUM SHTG SHEATHING U/S UNDERSIDE

BRG BEARING DP DEEP G.L. GRID LINE NIC NOT IN CONTRACT SIM SIMILAR UNO UNLESS NOTED OTHERWISE

C.L. CENTERLINE DWG DRAWING H/C HANDICAPPED NO. NUMBER SQFT SQUARE FOOT VERT VERTICAL

C/W COMPLETE WITH E/F EACH FACE HORIZ HORIZONTAL O/C ON CENTRE SQM SQUARE METER W/ WITH

CANT CANTILEVER E/S EACH SIDE hr

HOUR (TIME)

OD OUTSIDE DIAMETER STD STANDARD WP WEATHERPROOF

C.J. CONTROL JOINT E/W EACH WAY HT HEIGHT PRE-ENG PRE-ENGINEERED STOR STORAGE W/R WASHROOM

COL COLUMN EL ELEVATION INSUL INSULATION PREFIN PREFINISHED STRL STRUCTURAL

COMP COMPACTED ELEV ELEVATION ID INSIDE DIAMETER PROJ PROJECTION T.L.L. TOP LOWER LEVEL

Sheet List TableSHEETNUMBER

REVISIONNO

SHEET TITLE

S1 R01 OVERALL VIEW

S2 R01 FOUNDATION PLAN

S3 R01 SECTIONS

S4 R00 STRUCTURAL DETAILS

REV.

DWG. SCALE:

SHEET:PROJECT No.:

SHEET TITLE:

PROJECT:

CLIENT:

DESIGNED BY:

DRAWN BY:

REV. DATE:

DATE:

812-401 YORK AVE,

AS NOTED

TSS

CL

AUG/2013

OCT./01/2013 S1 R01

OVERALL VIEW

2 CHAMBER SETTLING TANK (72'X80')

MLMMI .

PLAN VIEW - OVERALLSCALE: N.T.S.

EARTHEN SECONDARYBASIN

2 CHAMBERSETTLING TANK

SECTION - OVERALLSCALE: N.T.S.

1S1

SHEET REF. S1

SEE SHEET S2

1S1

EARTHEN SECONDARYBASIN

2 CHAMBERSETTLING TANK

INDICATES LEVEL OFSURROUNDING GRADE

1 2 3

A

B

C

36'-0"

36'-0"

72'-0"

40'-0" 40'-0"

80'-0"

16'-0"

4'-0"

32'-0"

4'-0"

16'-0"

SLOPE

SLOPECHAMBER 1

CHAMBER 2

DISCHARGE/PUMP-OUT PIT (TYP)

OVERFLOW CHANNEL TOEARTHEN SECONDARY BASIN

REV.

DWG. SCALE:

SHEET:PROJECT No.:

SHEET TITLE:

PROJECT:

CLIENT:

DESIGNED BY:

DRAWN BY:

REV. DATE:

DATE:

812-401 YORK AVE,

AS NOTED

TSS

CL

AUG/2013

OCT./01/2013 S2 R01

FOUNDATION PLAN

2 CHAMBER SETTLING TANK (72'X80')

MLMMI .

PLAN VIEW - OVERALLSCALE: 1/16" = 1'-0"

1S3

2S3

1S4

2S4

1S4

1S3

1 2 3

EL.

TOP OFFLOOR

100'-0"

EL.

TOPOF WALL

108'-0"

1

5CHAMBER 1

OVERFLOW CHANNEL TOEARTHEN SECONDARY BASIN

C B A

TOP OFFLOOR

100'-0"

TOP OF WALL

108'-0"

PUMP-OUT WELL

CHAMBER 2 CHAMBER 1

REV.

DWG. SCALE:

SHEET:PROJECT No.:

SHEET TITLE:

PROJECT:

CLIENT:

DESIGNED BY:

DRAWN BY:

REV. DATE:

DATE:

812-401 YORK AVE,

AS NOTED

TSS

CL

AUG/2013

OCT./01/2013 S3 R01

SECTIONS

2 CHAMBER SETTLING TANK (72'X80')

MLMMI .

SECTIONSCALE: 3/32" = 1'-0"

1S3

SHEET REF. S2

SECTIONSCALE: 3/32" = 1'-0"

2S3

SHEET REF. S2

PUMP-OUT DETAILSCALE: 3/16" = 1'-0"

1S3

SHEET REF. S2

4'-0"Ø PE PUMP-OUTWELL, PERFORATEFACE ON INSIDE OFCHAMBER w/ 1"ØHOLES

LINE FACE ONINSIDE OF CHAMBERw/ GEOTEXTILE

EL.

TOP OF WALL

108'-0"

TOP OFFLOOR

100'-0"

INTERIOR FACE WALLSTEEL, TYP. B/S:

2x4 KEYWAY

TYP. FLOOR CONST:

5" CONC. SLAB MIN 6" OF COMPACTED

GRANULAR FILL

NOTE:PROVIDE MINIMUM 2" COVERFOR ALL REINFORCING

12"x96" CONCRETE WALL

10"

2'-0" 4'-0"

2"2"

TOP OF WALL

108'-0"

4'-0"

4'-0"

2'-0"

EL.

TOP OF WALL

108'-0"

10"

3

4"

TOP OFFLOOR

100'-0"

INTERIOR FACE WALL STEEL:

2x4 KEYWAY

CONCRETE FLOOR:

EXTERIOR FACE WALL STEEL:NOTE:PROVIDE MINIMUM 2" COVERFOR ALL REINFORCING

12"x96" CONCRETE WALL

10"

2'-0" 4'-0"

2"2"

SLOPE GRADE AT WALL MIN.12" TO SURROUNDING GRADETOP OF WALL

108'-0"

REV.

DWG. SCALE:

SHEET:PROJECT No.:

SHEET TITLE:

PROJECT:

CLIENT:

DESIGNED BY:

DRAWN BY:

REV. DATE:

DATE:

812-401 YORK AVE,

AS NOTED

TSS

CL

AUG/2013

. S4 R00

STRUCTURAL DETAILS

2 CHAMBER SETTLING TANK (72'X80')

MLMMI .

EXTERIOR WALL DETAILSCALE: 3/8" = 1'-0"

1S4

SHEET REF. S2

DIVIDING WALL DETAILSCALE: 3/8" = 1'-0"

2S4

SHEET REF. S2

FOOTINGDETAILSCALE: 3/8" = 1'-0"

1S4

SHEET REF. S2

35

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