TECHNICAL UNIVERSITY OF GABROVO

Department of Chemistry and Ecology

The prototype of the waste separation system…

“Waste, rubbish, trash, garbage, or junk”

is any unwanted or undesired material!

Any substance or object which the producer or the person in possession of it, discards or intends or is required to

discard.

Waste can exist as:

solid; liquid; gas; waste heat.

The waste hierarchy refers to the "3 Rs“: Reduce Reuse Recycle

They classify waste management strategies according to their desirability.

Plastics Metals Glass Paper Green waste

Food waste Paper Biodegradable

plastics Human waste Manure Sewage Slaughterhouse

waste

Recycling is a key concept of modern waste management and

the third component of the waste hierarchy

WASTE HAS TO GO SOMEWHERE ! BUT WHERE ?

INSTEAD OF HERE …

Landfill. Unsightly. Unpopular. Unsustainable.Generating bio aerosols, offensive odor and landfillgas (methane). 21 times more powerful thancarbon dioxide in terms of climate change effects!

.

Incineration. There’s a place for it. But what place wants it? ‘Not in my backyard’. More gases. More odor. More public distress.HERE …

Untreated waste spread on land. Imagine blood, guts and similar – spread or sprayed on fields – untreated. Since 2003, illegal. But it does happen

OR HERE …

TREATED ORGANIC WASTE CAN SAFELY GO HERE …

Agriculture. To enrich the earth…

HERE … Sport. To improve our recreational environment…

Horticulture. To give us pleasure…

OR HERE…

July 2003 EU Landfill Directive and Animal By-Products (ABP) Regulation came into force

Now Most organic waste is currently landfilled untreated

In the close future the revised EU Sludge Directive and the new Bio Waste Directive will both require organic waste to be treated!!!

What is the answer?

Anaerobic digestion:

Aerobic decomposition (composting)

Landfilling

Methane (greenhouse gas)

Composting is the process of controlled aerobic decomposition of biodegradable organic matter

During composting, microorganisms break down organic matter into carbon dioxide, water, heat, and compost:

Organic matter + O2

Compost + CO2 + H2O + NO3- + SO4

2- + heat

Materials for composting: Food and drink industry waste; Paper, card, timber and other

biodegradable waste; Household waste; Organic sludge including sewage; Agricultural waste.

: Wastes from meat, dairy products, and eggs should not be used in household compost:

they attract unwanted vermin;they do not appropriately

decompose in the time required.

Main composting agents Main composting agents (decomposers)(decomposers)

1.1. Classification according to the O2 consuming:

Aerobic – use oxygen for their metabolism

Anaerobic– they are active in environment without oxygen

Microorganisms are key to composting !I. Microorganisms

1.2. Classification according to the thermal living conditions:

Microorganisms

Temperature range of activity,

оС

Psychrophiles Mesophiles Thermophiles

0 - 3030 – 45 45 – 50

1.3. Microorganisms growth during the composting process:

Microorganisms Populations according to the thermal conditions

<40 оС 40 - 70 оС

BACTERIA Mesophiles Thermophiles

ACTINOMICETES Thermophiles

FUNGI MesophilesThermophiles

108

104

104

106

106

106

109

108

103

107

A. A. Bacteria

Heterotrophic Autotrophic Aerobic Anaerobic

strong ability of growth in moist medium

large spectrum of activity active in a large range of pH values difficult to adapt in acid medium

B. Fungi

ability to live in medium with low moisture;

competitors of heterotrophic bacteria active in a large range of pH: 2 – 9; low requirements considering the

nitrogen content

Fermenting fungi

Yeast

C. Actinomycetes

Aerobic and thermophilic;They are assimilated by bacteria

and fungi; use organic nitrogen;Active in neutral and slightly

alkaline media;Act in the ending phase of the

composting process.

II. Other agents:

Duckweeds (algae)

Cyanophytes Prothozoe Enzymes

performed by aerobic microorganisms;

decomposition of organic matter; (organic acids, aminoacids, saharides) occurs;

consuming of O2 and release of CO2 and energy;

high rate of composting process; temperature - up to 55-60° С.

I. First stage: active (thermophilic)

Temperature changing during the first stage for biomass with low and

high degree of fermentation:

Decomposing of more complicated organic molecules;

Most of the microorganisms die from lаck of “food”;

Lower rate of the process; Temperature - up to 40 - 45° С; Duration – few weeks : humification!

Waste appearance before and after composting process

II. Second stage: cooling

III. Third stage: maturation Temperature is equal to the

ambient; A completely disinfected high

quality compost is formed as a result

Composting Control parameters1.Porosity of substrate (free volume) –

defined by the spaces inside the biomass occupied by air and water.

Pg = Vv / Vt , %1.2. Free air space (FAS), VfVf - the biomass volume, which is occupied by the air:

(Vv –Va) / Vt

Va – volume, occupied by water

Porosity depends on: Particle size

distribution; Level of humidity; Height of the pail.

1.1. General porosity Pg - the relation of empty spaces volume Vv and the whole biomass volume Vt:

Effective cross sectional area as a function of particle size distribution, shape, and packing

density

1. The particle size distribution, bulk density, and porosity of a compost mixture are group of factors that can lead to anaerobic conditions. 2. These physical characteristics of the compost mixture can interact with high moisture levels to reduce oxygen transport.

2. Moisture

is necessary for the nutrient substances exchange through the cell membrane; forms transport medium for extracellular enzymes; creates medium for soluble substances; is important for chemical reactions performance

Optimal m

oisture:

50 – 60%

< 40% moisture – degradation will proceed at a slow rate (under 25 -30% it stops);> 65% moisture - О2 distributes very difficult in the biomass (anaerobic conditions established)

Water is one of the important elements for the microorganisms’ activity because:

The effect of aqueous film thickness on anaerobic odor production

Metabolic Regions as a function of moisture content

In a properly moist compost matrix, the particles (brown) are

surrounded by aqueous films (blue), but are separated by

air filled pores (white)

Anaerobic zones (purple dots) are

created as increasing water content fills

small pores, so oxygen must diffuse

farther through water.

3. Quantity of oxygen C6H12O6 + 6O2 → 6CO2 + 6H2O + 2 800 KJ/molTo treat 1kg organic matter 1,6 kg of O2 are required !

Oxygen requirement during the composting

process: First stage – 5 - 15% Second stage – 1 -

5% Air: 10 – 100 N.m3/h

O2 could be supplied by means of:

Mechanical mixing;

Forced ventilation (aeration )

Complete mineralization? Humification?

Result:

4. Temperature:

: t > 70C kills also bacteria responsible for composting process!

Defines the thermophilic stage of the composting process;

Easy to monitor Provides disinfection of the product - at 55C almost all

pathogenic are killed; Kills the weeds’ seeds at 65C and more

First stage: 55-65CSecond stage: 35 - 45Ct< 25C end of the composting process

Values of released energy for Values of released energy for main substances:main substances:Glucosis 19 kJ/gGlucosis 19 kJ/gLipides 39 kJ/gLipides 39 kJ/gProteines 23 kJ/gProteines 23 kJ/g

Temperature is a key parameter determining the success of composting process!

Heat is produced as a by-product of the microbial breakdown of organic material

M. Koleva ERASMUS’07

Temperature and pH profiles during composting

5. Ratio C/N, C/P and 5. Ratio C/N, C/P and C/SC/S naturally existing in naturally existing in

biomassbiomass

C C – source of energy for heterotrophic – source of energy for heterotrophic microorganisms;microorganisms;

NN – important for syntesis of protheins – important for syntesis of protheins C

1/3 used by microorganisms2/3 converted to CO2

30 atoms 30 atoms C C : 1 atom : 1 atom NN

C/N > 30

•Inhibited decomposing process;

•Increased

composting time

C/N < 30 •Excess of N that leads to release of NH3

•NH3 is stimulated by: t , N, pH

4.1. C/N:

ImportantImportant: balanced ratio : balanced ratio C/NC/N

4.2. C/P:P acts as a catalyst of biochemical reactions!

Optimal ratio: 100 < C/P< 2004.3.

C/S:Optimal ratio: 100 < C/S< 300

Optimal ratio C/N: •at the start 25 -30•At the end < 20 (10:1)

Carbon-to-nitrogen ratios may need to be adjusted

depending on the bioavailability of these elements !!!

Materials High in Carbon C/N*autumn leaves 30-80:1straw 40-100:1

wood chips or sawdust 100-500:1

bark 100-130:1

mixed paper 150-200:1

newspaper or corrugated cardboard 560:1

Materials High in Nitrogen C:N*vegetable scraps 15-20:1coffee grounds 20:1grass clippings 15-25:1manure 5-25:1

Typical C/N ratios for common compost materials

Source: Dickson, N., T. Richard, and R. Kozlowski. 1991. Composting to Reduce the Waste Stream: A Guide to Small Scale Food and Yard Waste Composting

6. 6. pHpH

I st period:: pH value decreases

The reason: generation of CO2

II nd period: pH value increases up to 8-9

The reason: generation of NH3

Optimal values of pH are: at the beginning pH 5.5

8 at the end: pH 7pH max 8.5

56

7

8

9pH

0 Time

I II

Compost microorganisms operate best under neutral to acidic conditions!

Factors Leading to Anaerobic Conditions

1. Inadequate porosity 3. Excess

moisture

4. Rapidly degrading substrate

2. Excessive pile size

oxygen cannot

move into a pile

the correct pile size balances the heat generated

by microbial decomposition

reduces oxygen

penetration

Oxygen is consumed much more

rapidly

Compost is the aerobically decompo-sed remnants of organic materials

in gardening and agriculture as a soil amendment;

for erosion control, land/stream reclamation, wetland construction, and as landfill cover;

as a seed starting medium generally mixed with a small portion of sand for improved drainage

Compost is used:

There are several ways to determine the degree of

compost’s stability achieved:

•Oxygen uptake rate.•Low degree of reheating in curing piles.•Organic content of the compost.•Presence of nitrates and the absence of ammonia and starch in the compost.

FINISHED COMPOST PRODUCT

Indexes of compost stability:

Germination index (GI): shows the presence of phytotoxic substances in compost:Compost is phytotoxic if GI > 30%

Nitrogen mineralization index (NMI): Based on the valuation of organic nitrogen biodegradation: For mature compost NMI < 3.5%!

Respiration index (RI): Based on the consumption of O2:

the higher the RI, the lower the compost stability;

Humification index (HI): HI = NH/ (HA+FA)NH- non humified fraction; HA – humic acids; FA – fulvic acids

M. Koleva ERASMUS’07

Organic matter

A B C

Grinding

Mixing

First stage -active composting

Second stage - coolcomposting

Maturation

Separation

Packing

1. According to the method of aerobic composting: A. Active (or hot) composting B. Passive (or cold) composting

allows aerobic bacteria to thrive

kills most pathogens and seeds

Aerobic bacteria produce less odour and fewer destructive greenhouse gases than their anaerobic ;

temperature reaches above 55°C (131°F)

more slow than the hot one;

many pathogens and seeds dormant in the pile;

done in most domestic garden;

temperatures never reach above 30°C (86°F)

2. According to the technical performance:

home container composting;

industrial in-vessel composting)

industrial windrow composting

A. Enclosed: B. In exposed piles

Home container composting

Flow diagram of a typical in-vessel composting facility

vertical plug-flow horizontal plug-flow agitated bin

Types of in-vessel composting reactors:Industrial In-vessel

composting

A self-contained, automated, in-vessel thermophilic composting system designed to convert food waste (including meat, dairy & fish waste), animal manure, sewage sludge (biosolids) and other biodegradable waste

BioChamber™•Fully-enclosed, automated, thermophilic composting •Capable of processing between 1 and 800 or more* tons/day •Modular, scalable, stackable design•Accelerates waste conversion through effective monitoring of temperature, oxygen  and moisture levels • Programmable 7 - 21 day waste stabilization time • Advanced remote monitoring and control•Strict odor control and captures 100% of all leachate for beneficial reuse • Effective elimination of pathogens and weed seeds • Elimination of vectors (rats, bugs, birds, etc.) as required by law • Smallest footprint and lowest cost per/ton processing capacity in the industry •Ideal for both urban and rural settings

•Advanced "Smart-Silo" Thermophilic Vertical Composting System

BioTower™ (BioSystem Solutions,

•Utilizing less space per processing

•provides automated loading, turning and compost discharge to reduce labor cost and increase worker safety

Containerized in-vessel drum compost systems (Willcam Inc., USA)

daily output volumes: 16, 35 or 50 cubic yards

Stationary and containerized in-vessel compost systems (Engineered Compost Systems, USA)

processing 1 to 200 tons per day ; computer controlled aeration system minimized odor generation

Containerized

Stationary

Advantages The composting process can

be more closely controlled. The effects of weather are

diminished. Less bulking agent may be

required. The quality of the resulting

product is more consistent. Less manpower is required

to operate the system and staff is less exposed to the composting material.

Process air can be more easily collected for treatment to reduce odor emissions.

Less land area is required. Public acceptance of the

facility may be better.

Disadvantages In-vessel composting is

generally more costly than other composting methods.

More equipment maintenance is necessary.

The large amount of carbonaceous material creates the potential for fires in storage areas as well as in the active composting mass.

or ?

Benefits: Compost reduces the amount

of waste to be disposed. Easy to use and operate. Can handle a large volume of

material. Low operating costs. Less equipment and

maintenance needed than other methods.

Disadvantages: Large amount of land for

composting. May attracts scavengers. Odors may be produced. Requires large adjacent

areas due to odor and vectors. Rainwater runoff

maintenance. Compost can become

anaerobic under rainy conditions.

PT-120 10 foot Pull-type Compost Turner (Midwest Bio-Systems, USA)

WT-3000 Water Trailer (Midwest Bio-Systems, USA)

Industrial Windrow composting

Increases water holding capacity. Increases aeration and drainage

for clay soils. Provides organic nitrogen,

phosphorus, and potassium. Provides essential plant

micronutrients. Can reduce the need for

pesticides.Composting is an environmentally beneficial activity !