Solid waste

1. Composting of
Municipal Solid Waste
(MSW)
Caitriona Gaffney
Deirdre Mulchrone
Teresa Conway

2. Overview
INTRODUCTION - CAITRIONA GAFFNEY
Definition, Sources, Characterisation, End Products
INTERMEDIATE - TERESA CONWAY
Waste Hierarchy, Legislation, Microbiology, Site Selection,
Types of Systems
CONCLUSIONS - DEIRDRE MULCHRONE
Environmental Factors, Problems, Economics

3. Introduction – Caitriona Gaffney
Definition of MSW & Irish Facts
Sources
Composting & Classification
Compost Grades
End Uses
Who Benefits

4. What is Municipal Solid Waste?
Mixed waste from Residential, Commercial & Industrial
sources
Compostable potential of 60-90%
Composition includes: paper, glass, wood, plastics, soils,
chemicals, food waste, plant debris, metals, textiles, street
cleaning & OM
Organic material makes up 50-70% of MSW
The fewer the non-compostable materials in feedstock the
better the finished compost material.

5. Components of MSW
Recycling
Composting
Combustion
Landfilling

6. Municipal Waste Management in EU
Countries

7. Irish Facts 1998-2005
1998 The national recovery rate of MSW was 9% with
91% going to landfill
“Waste Management: Changing our Ways” published
targets to be achieved over 15 year period;
 a diversion of 50% of household waste from landfill,
 recycling of 35% of MW
 rationalisation of municipal waste landfills – 20 state of
the art facilities incorporating energy recovery & enviro
protection
 reduce methane emission from landfill by 80%.

8. Irish Facts 1998-2005
Changes in waste composition between the years 1995, 1998 & 2001

9. Irish Facts 1998-2005
2001 - 2,704,035 tonnes MW produced, 4% of the total waste generated
- 86.7% landfilled & 13.3% recycled
2002 - 2,723,739 tonnes MW produced
- Landfill of MW decreased by 5%
2003 - 3,001,016 tonnes MW produced
- EPA carried out survey on waste generation & management.
- Recycling increased by 46%
- 69% of the recyclable waste was recycled abroad
- Export of hazardous waste increased by 56%
2004 - 72% of municipal waste was consigned to landfill
- Landfill capacity will still be used up within the next 10 years

10. Irish Facts 1998-2005
Provisional data from 6 surveys carried out in Waterford
Coco & Galway City in November 2004 and March 2005

11. Composting & Classification
Definition:- “Composting is the biological decomposition of the
organic constituents of wastes under controlled conditions to a
state sufficiently stable for nuisance-free storage and utilization.”
Performed either by households or in large centralised units
Compost systems can be classified on three general bases:
1. Oxygen usage (aerobic & anaerobic)
2. Temperature (Mesophilic 15-40OC & Thermophilic 45-65 OC)
3. Technological approach (static pile or windrow, and mechanical
or "enclosed" composting)

12. Grades of Compost
Premium Grade
- agricultural and horticultural use
- home use, turf, pot plants
- can be freely traded
- regulations may control the application of nitrogen to land
Regulated Grade
- remediation, restoration, agriculture, forestry and non food crops
- specialist expertise necessary in trading and its use
- regulation of the application
- biological, chemical or physical hazards remain a concern
Engineering Grade
- access to composts is strictly limited
- other risk management measures in place
for e.g. uses such as daily cover, or as engineering fill material - in bunds
and sound barriers, or as pollution control measures such as biofilters.

13. End Uses of Compost
Soil Improvement
- soil structure, condition and fertility
Growing media
- component of mixes used to grow crops in containers
Mulches
- suppress weed growth, conserves water and also to maintain soil
temperatures. Mulching also protects plants from frost.
Restoration
- used for soil “forming” and soil improvement
Landfill Applications
- improvement of landfill covers – soil formation

14. Local Authorities
Landfill companies
Waste and sewage companies
Those Who Benefit from the End Uses

15. Overview – Teresa Conway
Waste Hierarchy
Process Options for Organic Waste
Why Biologically Treat Waste
Legislation & Targets
Physical Processing of MSW
Biological Process of Composting
 Biology
 Site Selection
 Types of Systems

16. Waste Hierarchy
Composting can be considered a component of
Integrated Waste Management (IWM)
Options near top
are more desirable than
those at the bottom

17. Process Options for Organic Waste
Process Options
Landfill Incineration Biological Processing Direct Land Disposal
Anaerobic Digestion Specialised Methods
Composting
Marketable Products

18. Why Biologically Treat MSW?
Reduces waste going to landfill
Estimated to be 10 years’ remaining landfill
capacity available for municipal waste
(Nationally in 2004)
Could be the first step in Ireland meeting its
waste challenge

19. % MSW that is biodegradable
25%
35%
60%
0%
10%
20%
30%
40%
50%
60%
70%
80%
Paper &
Cardboard
Food & Garden
Waste
Total
Biodegradable
MSW
(EEA,2003 )

20. Number of authorised Landfills
remaining in Ireland
126
92
34
0
20
40
60
80
100
120
140
1998 2001 2002
No. of Landfills

21. Taking the Landfill Directive as a framework the
following National Landfill Diversion targets were
outlined in 1998 in the Policy statement
“Changing Our Ways”.
-The statement includes a number of targets to be
achieved over a 15 year time period. Some of these
include:
Legislation & Targets

22. a diversion of 50% of household waste from
landfill by 2013
a minimum 65% reduction in biodegradable
waste consigned to landfill
the development of waste recovery facilities,
including the development of composting
and other feasible biological treatment facilities
capable of treating up to 300,000 tonnes/year
Legislation & Targets

23. The primary statute law on waste management is
contained in –
Waste Management Act, 1996 & 2001 and
Regulations made under the Act
EPAAct 1992 and Regulations under the Act
Regulations made under the European Communities
Act, 1972 in relation to waste management
Landfill Directive 99/31/EC
Legislation & Targets

24. Biological Process of Composting
Microorganisms + OM -------> H2O + CO2 + Heat + Humus
3 phases under optimal conditions
(1) Mesophilic - lasts couple of days (~40oC)
(2) Thermophilic can last a few dys to several mts ( 55oC–65oC)
(3) Several-month cooling and maturation phase

25. Abundance and variety of microbes indigenous to
wastes are sufficient to compost the wastes
Microbes active in the compost process are:
Bacteria (mesophyllic and thermophyllic)
Actinomycetes
Fungi
Protoza
Rotifers
Biological Process of Composting

26. Food Web of a Compost pile
Organic Residue
Primary Consumers
bacteria, fungi, actinomycetes
Secondary Consumers
nematodes, protozoa, rotifera,
Tertiary Consumers
centipedes, mites, beetles

27. Site Selection for MW Processing
Large enough to receive projected waste volumes
& for technology used
Adequate buffer zone from neighbours with a
prevailing wind that blows away from neighbours
A nearly level surface, 2-3% grade
A high soil percolation rate to avoid standing water
but an impermeable surface as a base

28. A low water table to prevent site flooding
A central accessible location with good traffic flow
A water source for wetting compost piles & fire
protection
Arrangements for leachate to be collected and
treated
Windrows need shelter in regions of moderate to
heavy rainfall
Site Selection for MW Processing

29. Quantity and characteristics of the feedstock is collected and
determined – MSW differs from other feedstocks
Nonbiodegradable and biodegradable separated through:
Separation (Recovery)
 Manual Separation
 Mechanical Separation
• Size Reduction
• Air Classification
• Screening
• Trommel
• Magnetic Separation
Drying and Densification
Physical Processing

30. 1) Turned Windrow
2) Static Aerated Pile
3) In-Vessel
-Horizontal Units
-Vertical Units
-Rotating Drums
NOTE:
Design and management of technical options must
be based on the needs of microorganisms
Biological Processing Options

31. Turned Windrows

32. Windrows
Composting
Sites
Natural Air Circulation
in a Compost Windrow

33. Most preferred method used in Ireland
Commonly used for rapid composting of yard wastes
Windrows are aerated regularly by turning
Constructed to be 6 to 10 ft high, 10 to 20 ft wide
The center of the pile insulated so that composting can
continue when outdoor temperatures are below freezing
Finished compost can be made between 3 mts - 2 yrs
Rate of composting is generally directly proportional to
frequency of turning
Turned Windrow Systems

34. Typical 18 month schedule using Turned Windrow system
Summer
Windrows turned
monthly
Autumn
Windrows dismantled
Room made for new
incoming material
Autumn
Windrows formed
Using a front end
loader
Spring
Windrows turned
monthly
Winter
Windrows turned
monthly
Next 6 Months
Compost screened
Moved to curing pile
Stabilised & yields N
March/April
Finished Compost
Peak Demand

35. Static Aerated Pile
Does not employ turning – ‘static’
Air is drawn or blown through a network of perforated
plastic pipes under the windrows
Faster than windrow systems
Used where aeration and temperature control are
crucial, (i.e. sludge or food processing wastes)
Works best with a material that is relatively uniform in
particle size ( not > 1.5 to 2 in. in any dimension)

36. This blower forces air
into a static compost pile.

37. Forced aeration in a
bin type system
Passively Aerated Windrow
System (PAWS)

38. Permanent air outlets
in the pad for an aerated
static pile at a site in
Washington

39. In-Vessel Systems
Also referred to as
-Contained systems
-Reactor
-Bioreactor
Computer provides greater control of composting
process
Raw waste is placed in a large container, with built-
in aeration and mechanical mixing equipment

40. In-Vessel Systems
Protected from severe weather and odour
containment
Low retention time (RT) (often <14 days)
Requires further compost processing - low RT is
insufficient for thermophilic composting stage
Expensive to build and operate

41. Types of In-Vessel Systems
Horizontal Units
Vertical Units
Rotating Drums

42. Horizontal Units
Material contained and aerated in a long, horizontal
reactor, usually build of concrete
Material may be moved in and out by:
A front end loader or conveyor system
Plug flow system – hydraulic ram
Moving floor system

43. Horizontal Bed Reactor

44. Vertical Units
Small land area
Enclosed and aerated in a vertical
reactor known as “silos” or “towers”.
Compaction of material at the base reactor -
impedes aeration - anaerobic regions developing
Good for Sludge composting industry but not MSW

45. A vertical in-reactor
composting system

46. Rotating Drums
Most common in-vessel composting approach
Combined with aeration in static piles or turned
windrow
Feedstock introduced into one end of slowly rotating
drum, inclined at about 5 degrees from horizontal
RT varies from 4-6 hours to 2-3 days
Drum allows homogenisation and screening of
materials

47. A large-scale, Rotating Drum Composting Vessel

48. Facility Capacity Feedstock Technology
Tralee Composting site 3,000 Household Organics Windrow
Limerick Composting Site 2,000 Household Organics In-Vessel and Windrow
Galway Corporation Depot 5,000 Household Organics Aerated Pile (VAR System)
Lucan Green Waste Composting 5,000 Green Waste Windrow
Aran Island Recycling Scheme 500 Household Organics In-Vessel (Biosal Unit)
Ballinasloe Composting Site 4,000 Household Organics
In-Vessel and Aerated Pile (Celtic
Composting)
Silliot Hill, Kildare 5,200 Commercial and Green Waste VCU In-Vessel
Kildare Sludge Plant 5,200 Municipal Sludge TEG In-Vessel
CTO Middleton 3,000 Commercial Organics Windrow
Kinsale Road Facility 2,000 Green Waste Windrow
Keady Composting Facility (Armagh) 65,000 Organic and Green Waste Enclosed Aerated and Windrows
McGill Facility (Cork) 10,000 Commercial Sludges Enclosed Aerated
Enviro Grind Ltd. 3,000 Green Waste Windrow
Shannon Vermicomposting 1,000
Household Organics/ Municipal
Sludge Windrow
Robert Delaney 10,000 Green Waste Windrow
Down District Council Composting
Site 1,800 Household Organics Windrow
SimproIreland Ltd. 4,000 Green Waste Windrow
Organic Gold 3,000 Municipal Sludge, Cattle Manure Windrow
Some Biological Treatment Locations in Ireland

49. Problems associated with Composting of
Municipal Waste
1. Leachate
Odours
Vector for organisms
supports the proliferation of insects
2. Odour & VOC’s
Feedstock
Enhanced under anaerobic conditions
3. Dust
Agitation of composting materials
Bioaerosols

50. Problems associated with Composting of
Municipal Waste
4. Vermin, Birds & Insects
-Nuisance Problems
-Pathogens in Final Product
5. Bioaerosols and other Health Risks
Hazard – pathogenic organisms in feedstock.
Pathway – ingestion of materials (for example from unwashed hands).
Receptor – compost site workers.
6. Fire
-Stored in bulk

51. 1. Temperature
Thermophilic (45 –650C) and Mesophillic (15-400C).
Above this temperature spores produced (Resting Stage).
Microorganisms inactivated or die off.
Affected by its climatic surroundings and method of aeration.
In a windrow highest temperature reached in centre, lower at
edges.
Environmental Factors Affecting
Composting

52. 2. pH
Anaerobic digestion the pH level covers a narrow range (pH 6.5 to 7.5)
Aerobic- pH so broad difficulties rarely encountered with too high or too low pH
in composting.
During the early stages the pH usually drops (down to about pH 5.0) because
of organic acid formation.
An exception which can reduce the pH is fruit wastes which can reduce the
pH to 4.5.
calcium hydroxide (lime) can be used as a buffer but it also lead to a loss in
ammonium nitrogen.
Environmental Factors Affecting
Composting

53. 3. Aeration (Anaerobic & Aerobic)
Anaerobic:
Advantages
a) minimisation of the loss of nitrogen
b) less costly
Disadvantages include:
a) Slowness of decomposition
b) Absence of high temperatures
c) The presence of un-decomposed intermediates
d) The un-pre-processed appearance of the product
Environmental Factors Affecting
Composting

54. Aerobic
Aerobic composting benefits from:
a) A rapid rate of degradation
b) Elevated temperature levels
c) Absence of putrefactive
Oxygen uptake reflects intensity of microbial activity. Theoretically
the amount of oxygen required is determined by the amount of
carbon to be oxidised (Chrometzka, 1968).
Environmental Factors Affecting
Composting

55. 4. Moisture Content
Moisture content and oxygen availability are closely related
If the moisture content of the mass is so high as to displace the
air from the interstices (voids between particles) anaerobic
conditions will develop within the mass .
The maximum permissible moisture content is a function of the
structural strength of the particles of the material to be
composted i.e. the degree of resistance of individual particles to
compression.
Woodchips, straw and hay can be as high as 75 to 80% whereas
paper (upon becoming wet, collapses and forms mats) has a
permissible moisture content of 55 to 60%.
Environmental Factors Affecting
Composting

56. Factors affecting Composting
5. Substrate
The waste (referred to as the substrate) should contain all
necessary nutrients.
Macronutrients Micronutrients
Carbon (C) Cobalt (Co)
Nitrogen (N) Manganese (Mn)
Phosphorous (P) Manganese (Mg)
Potassium (K) Copper (Cu)

57. Factors affecting Composting
Substrate (cont.)
only available if they are in a form that can be assimilated by the
microbes.
Certain groups of microbes have an enzymatic complex that
permits them to attack, degrade and utilise the organic matter
found in freshly generated waste.
Others can only utilize decomposition products (intermediates)
as a source of nutrients.

58. Factors affecting Composting
Carbon: Nitrogen Ratio (C: N)
The C: N ratio of the waste to be composted is the most important
factor that requires attention.
A large percentage of the carbon is oxidised to carbon dioxide by the
microbes in their metabolic activities .
The major consumption of nitrogen is in the synthesis of protoplasm
consequently much more carbon is required.
The C: N of the substrate should fall within the range of 20-25:1.
Mmicroorganisms such as bacteria and fungi grow best with the
proper level of Carbon and Nitrogen.

59. C: N (continued) (CAST STUDIES)
Galway City Council
At the Galway City Council composting site
-no clear cut method of establishing a
C: N ratio for the material.
-done by visual assessment and the
experience of the operative
-Food waste is estimated at a C: N ratio of
15:1.
-Woodchip is added at the assessment of
the operative
- Less woodchip is required if there is
adequate shrub prunings in the incoming
waste.
-More woodchip is added if there is a lot of
grass in the incoming material as there is
in summer
Celtic Composting
-The C: N of source separated bio-
waste is typically measured using the
total nitrogen and volatile solids content
of a sample screened to <10mm.
-Inclusion of large amounts of
unavailable carbon from woody bulking
materials will give a false high carbon
reading.
- Normally bio-waste with high green
waste content is fine.
-However, winter deliveries with little
green waste needs nitrogen
supplementation.
-In the UK, it is typical to include a lot of
paper and cardboard in the bio-bins
and this needs nitrogen additions also.
Similarly mixed waste composting often
suffers from low nitrogen”

60. The costs of a composting facility include land, labour and
equipment.
It will divert waste that would otherwise need costly disposal. If
the compost site is closer than the other disposal site, there will
be savings in transport costs.
The finished compost can be used as a substitute for purchased
mulch or topsoil in municipal landscaping.
If sold commercially, compost can generate revenues, which help
defray processing costs.
Economic Factors

61. Conclusion
From an environmental perspective, composting
not only reduces the problems associated with
landfills and incinerators, but the finished
compost adds beneficial humus and nutrients to
soil. Composting is a waste management
solution, which can benefit municipalities and
benefit the environment at the same time.

62. Questions?