Transcript WASTE HAS TO GO SOMEWHERE ! BUT WHERE

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.
Recycling is a key concept of modern
waste management and the third
component of the waste hierarchy
Plastics
Metals
Glass
Paper
Green waste
Food waste
Paper
Biodegradable plastics
Human waste
Manure
Sewage
Slaughterhouse waste
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!
HERE …
Incineration. There’s a place for it. But what
place wants it? ‘Not in my backyard’. More
gases. More odor. More public distress.
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…
OR HERE…
Horticulture. To give us pleasure…
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!!!
Landfilling
Anaerobic digestion:
What is
the
answer?
Methane (greenhouse gas)
Aerobic
decomposition
(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:
Organic matter + O2
Compost + CO2 + H2O + NO3- + SO42- + 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
(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
1.2. Classification according to the
thermal living conditions:
Microorganisms
 Psychrophiles
 Mesophiles
 Thermophiles
Temperature range
of activity, оС
0 - 30
30 – 45
45 – 50
1.3. Microorganisms growth during the
composting process:
Microorganisms
BACTERIA
Mesophiles
Thermophiles
ACTINOMICETES
Thermophiles
FUNGI
Mesophiles
Thermophiles
Populations according to the
thermal conditions
<40 оС
40 - 70 оС
108
104
106
109
104
108
106
106
103
107
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
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
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
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° С.
Temperature changing during the first
stage for biomass with low and high degree
of fermentation:
II. Second stage: cooling
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
III. Third stage: maturation
Temperature is equal to the ambient;
A completely disinfected high quality
compost is formed as a result
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:
(Vv –Va) / Vt
Particle size distribution;
Va – volume,
Level of humidity;
occupied by water
Height of the pail.
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
2. Moisture
Water is one of the important elements for the
microorganisms’ activity because:
 is necessary for the nutrient substances
through the cell membrane;
exchange
 forms transport medium for extracellular
enzymes;
 creates medium for soluble substances;
 is important for chemical reactions performance
< 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)
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/mol
To treat 1kg organic matter 1,6 kg of O2 are required !
Oxygen requirement during
O2 could be supplied
the composting process:
First stage – 5 - 15%
Second stage – 1 - 5%
Air: 10 – 100 N.m3/h
by means of:
Mechanical mixing;
Forced ventilation
(aeration )
Result:
Complete mineralization?
Humification?
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 > 70C kills also bacteria
First stage: 55-65C
responsible for composting process!
Second stage: 35 - 45C
Values of released energy for
main substances:
t< 25C
end of the
composting process
M. Koleva ERASMUS’07
Glucosis
19 kJ/g
Lipides
39 kJ/g
Proteines
23 kJ/g
Temperature and pH profiles during composting
5. Ratio C/N, C/P and C/S
 naturally existing in biomass
4.1. C/N:
30 atoms C : 1 atom N
C – source of energy for heterotrophic microorganisms;
N – important for syntesis of protheins
C
1/3 used by microorganisms
2/3 converted to CO2
•Excess of N that
leads to release of
NH3
C/N < 30
•NH3 is stimulated
by:  t ,  N, pH
Optimal ratio C/N:
C/N > 30
•at the start 25 -30
Carbon-to-nitrogen ratios may need to be adjusted
•At the end < 20 (10:1)
depending on the bioavailability of these elements !!!
4.2. C/P: P acts as a catalyst of biochemical reactions! Optimal ratio: 100 < C/P< 200
4.3. C/S:
Optimal ratio: 100 < C/S< 300
Typical C/N ratios for common compost materials
Materials High in Carbon
C/N*
autumn leaves
30-80:1
straw
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
15-20:1
coffee grounds
20:1
grass clippings
15-25:1
manure
5-25:1
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. pH
pH
I st period: pH value decreases
9
The reason: generation of CO2
8
II nd period: pH value increases
up to 8-9
7
The reason: generation of NH3
6
I
5
0
II
Time
Compost microorganisms
operate best under neutral to
acidic conditions!
Optimal values of pH are:
pH max  8.5
at the beginning pH 5.5  8
at the end: pH  7
Factors Leading to Anaerobic Conditions
1. Inadequate
porosity
oxygen
cannot move
into a pile
2. Excessive
pile size
the correct pile size
balances the heat
generated by
microbial
decomposition
3. Excess
moisture
reduces
oxygen
penetration
Oxygen is
consumed
much more
rapidly
4. Rapidly
degrading
substrate
Compost is the aerobically decomposed 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
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.
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:
FINISHED COMPOST PRODUCT
Humification index (HI):
the higher the RI, the lower the
compost stability;
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 - cool
composting
Maturation
Separation
Packing
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 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:
A. Enclosed:
home container composting;
industrial in-vessel composting)
B. In exposed piles
industrial windrow composting
Home container composting
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
BioChamber™
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
•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
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
Containerized in-vessel drum compost systems (Willcam Inc., USA)
daily output volumes: 16, 35 or 50 cubic yards
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
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.
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.
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.
WT-3000 Water Trailer
(Midwest Bio-Systems, USA)
PT-120 10 foot Pull-type Compost Turner
(Midwest Bio-Systems, USA)
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.
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 !