WASTE HAS TO GO SOMEWHERE ! BUT WHERE ?

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TECHNICAL UNIVERSITY OF GABROVO Department of
Chemistry and Ecology
AEROBIC BIODEGRADATION OF WASTE
(COMPOSTING)
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The prototype of the waste separation system
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Waste
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.

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Waste hierarchy

• The waste hierarchy refers to the "3 Rs
• Reduce
• Reuse
• Recycle
• They classify waste management strategies
  according to their desirability.

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Recycling is a key concept of modern waste
management and the third component of the waste
hierarchy

• Plastics
• Metals
• Glass
• Paper

RECYCLED WASTE

• Green waste
• Food waste
• Paper
• Biodegradable plastics
• Human waste
• Manure
• Sewage
• Slaughterhouse waste

BIODEGRADABLE WASTE
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WASTE HAS TO GO SOMEWHERE ! BUT WHERE ?
INSTEAD OF HERE
Landfill. Unsightly. Unpopular.
Unsustainable. Generating bio aerosols, offensive
odor and landfill gas (methane). 21 times more
powerful than carbon dioxide in terms of climate
change effects!
.
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Incineration. Theres a place for it. But what
place wants it? Not in my backyard. More gases.
More odor. More public distress.
HERE
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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
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TREATED ORGANIC WASTE CAN SAFELY GO HERE
Agriculture. To enrich the earth
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HERE
Sport. To improve our recreational environment
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Horticulture. To give us pleasure
OR HERE
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• 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!!!

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Landfilling
Anaerobic digestion
What is the answer?
Methane (greenhouse gas)
Aerobic decomposition (composting)
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COMPOSTING

• 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

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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.

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• Main composting agents (decomposers)

Microorganisms are key to composting !
I. Microorganisms
1.1. Classification according to the O2 consuming

• Aerobic use oxygen for their metabolism
• Anaerobic they are active in environment
  without oxygen

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1.2. Classification according to the thermal
living conditions
Microorganisms Temperature range of activity, ??
Psychrophiles Mesophiles Thermophiles 0 - 30 30 45 45 50
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1.3. Microorganisms growth during the composting
process
Microorganisms Populations according to the thermal conditions Populations according to the thermal conditions
lt40 ?? 40 - 70 ??
BACTERIA Mesophiles Thermophiles ACTINOMICETES Thermophiles FUNGI Mesophiles Thermophiles 108 104 104 106 106 106 109 108 103 107
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• 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

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B. Fungi

• Fermenting fungi
• Yeast

• 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

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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.

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II. Other agents

• Duckweeds (algae)
• Cyanophytes
• Prothozoe
• Enzymes

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Stages of the composting process
I. First stage active (thermophilic)

• 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 ?.

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Temperature changing during the first stage for
biomass with low and high degree of fermentation
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II. Second stage cooling

• Decomposing of more complicated organic
  molecules
• Most of the microorganisms die from l?ck of
  food
• Lower rate of the process
• Temperature - up to 40 - 45 ?
• Duration few weeks

? humification!
Waste appearance before and after composting
process
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III. Third stage maturation

• Temperature is equal to the ambient
• A completely disinfected high quality compost is
  formed as a result

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Composting Control parameters

1. Porosity of substrate (free volume) defined by
   the spaces inside the biomass occupied by air and
   water.

1.1. General porosity Pg - the relation of empty
spaces volume Vv and the whole biomass volume Vt
Pg Vv / Vt ,
1.2. Free air space (FAS), Vf - the biomass
volume, which is occupied by the air

• Porosity depends on
• Particle size distribution
• Level of humidity
• Height of the pail.

(Vv Va) / Vt Va volume, occupied by
water
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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.
Effective cross sectional area as a function of
particle size distribution, shape, and packing
density
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2. Moisture
Water is one of the important elements for the
microorganisms activity because

• 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

lt 40 moisture degradation will proceed at a
slow rate (under 25 -30 it stops) gt 65
moisture - ?2 distributes very difficult in the
biomass (anaerobic conditions established)
Optimal moisture 50 60
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The effect of aqueous film thickness on anaerobic
odor production
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Metabolic Regions as a function of moisture
content
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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.
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3. Quantity of oxygen
C6H12O6 6O2 ? 6CO2 6H2O 2 800 KJ/mol
To 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 )

Result
Complete mineralization?
Humification?
yes
no
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4. Temperature
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

• Defines the thermophilic stage of the
  composting process
• Easy to monitor
• Provides disinfection of the product - at 55?C
  almost all pathogenic are killed
• Kills the weeds seeds at 65?C and more

? t gt 70?C kills also bacteria responsible for
composting process!
First stage 55-65?C Second stage 35 - 45?C tlt
25?C end of the composting process
Values of released energy for main
substances Glucosis 19
kJ/g Lipides 39
kJ/g Proteines 23 kJ/g
M. Koleva ERASMUS07
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Temperature and pH profiles during composting
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5. Ratio C/N, C/P and C/S
? naturally existing in biomass
C,N,P,K
30 atoms C 1 atom N
4.1. C/N
Important balanced ratio C/N
C source of energy for heterotrophic
microorganisms N important for syntesis of
protheins

• Excess of N that leads to release of NH3
• NH3 is stimulated by ? t , ? N, ?pH

C/N lt 30
1/3 used by microorganisms
C
2/3 converted to CO2

• Inhibited decomposing process
• Increased composting time

• Optimal ratio C/N
• at the start 25 -30
• At the end lt 20 (101)

C/N gt 30
Carbon-to-nitrogen ratios may need to be adjusted
depending on the bioavailability of these
elements !!!
4.2. C/P
P acts as a catalyst of biochemical reactions!
Optimal ratio 100 lt C/Plt 200
4.3. C/S
Optimal ratio 100 lt C/Slt 300
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Typical C/N ratios for common compost materials
Materials High in Carbon C/N
autumn leaves 30-801
straw 40-1001
wood chips or sawdust 100-5001
bark 100-1301
mixed paper 150-2001
newspaper or corrugated cardboard 5601
Materials High in Nitrogen CN
vegetable scraps 15-201
coffee grounds 201
grass clippings 15-251
manure 5-251
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
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6. pH
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 ? 7

Compost microorganisms operate best under neutral
to acidic conditions!
pH max ? 8.5
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Lets summarize
Factors Leading to Anaerobic Conditions
1. Inadequate porosity
Oxygen is consumed much more rapidly
3. Excess moisture
oxygen cannot move into a pile
2. Excessive pile size
the correct pile size balances the heat generated
by microbial decomposition
4. Rapidly degrading substrate
reduces oxygen penetration
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Compost
Compost is the aerobically decompo-sed remnants
of organic materials
Compost is used

• 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

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• There are several ways to determine the degree of
  composts 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.

• Indexes of compost stability
• Germination index (GI) shows the presence of
  phytotoxic substances in compost
• Compost is phytotoxic if GI gt 30
• Nitrogen mineralization index (NMI) Based on
  the valuation of organic nitrogen biodegradation
  
• For mature compost NMI lt 3.5!
• Respiration index (RI) Based on the consumption
  of O2
• the higher the RI, the lower the compost
  stability

FINISHED COMPOST PRODUCT

• Humification index (HI) HI
  NH/ (HAFA)
• NH- non humified fraction HA humic acids FA
  fulvic acids

M. Koleva ERASMUS07
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Composting technics and equipment
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Types of composting
1. According to the method of aerobic composting
B. Passive (or cold) composting
A. Active (or hot) 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 55C (131F)

• more slow than the hot one
• many pathogens and seeds dormant in the pile
• done in most domestic garden
• temperatures never reach above 30C (86F)

2. According to the technical performance
A. Enclosed
B. In exposed piles

• home container composting
• industrial in-vessel composting)

• industrial windrow composting

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Home container composting
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Industrial In-vessel composting
Types of in-vessel composting reactors

• vertical plug-flow
• horizontal plug-flow
• agitated bin

Flow diagram of a typical in-vessel composting
facility
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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

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
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BioTower (BioSystem Solutions,

• Advanced "Smart-Silo" Thermophilic Vertical
  Composting System

• Utilizing less space per processing

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

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• Containerized in-vessel drum compost systems
  (Willcam Inc., USA)
• daily output volumes 16, 35 or 50 cubic yards

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Containerized
Stationary

• 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

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In-vessel composting

• 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.

?
Yes
not
or

• 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.

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Industrial Windrow composting

• 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.

WT-3000 Water Trailer (Midwest Bio-Systems, USA)
PT-120 10 foot Pull-type Compost Turner (Midwest
Bio-Systems, USA)
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Use of biosolids compost
The use of biosolids compost as a soil
conditioner results in the following

• 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 !