Composting of Municipal Solid Waste (MSW)

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

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

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 (EEA,2003 )

20. Number of authorised Landfills remaining in Ireland

21. Legislation & Targets • 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:

22. Legislation & Targets • 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

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

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. Biological Process of Composting • 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

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

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. Site Selection for MW Processing • 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

29. Physical Processing • 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

30. Biological Processing Options 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

31. Turned Windrows

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

33. Turned Windrow Systems • 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

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

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. 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 RisksHazard – pathogenic organisms in feedstock. Pathway – ingestion of materials (for example from unwashed hands). Receptor – compost site workers. 6. Fire -Stored in bulk