Composting of Municipal Solid Waste

(MSW)

Caitriona Gaffney Deirdre Mulchrone Teresa Conway

Overview

INTRODUCTION - CAITRIONA GAFFNEYDefinition, Sources, Characterisation, End Products

INTERMEDIATE - TERESA CONWAYWaste Hierarchy, Legislation, Microbiology, Site Selection, Types of Systems

CONCLUSIONS - DEIRDRE MULCHRONEEnvironmental Factors, Problems, Economics

Introduction – Caitriona GaffneyDefinition of MSW & Irish FactsSourcesComposting & ClassificationCompost Grades End UsesWho Benefits

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

Components of MSW

RecyclingCompostingCombustionLandfilling

Municipal Waste Management in EU Countries

Irish Facts 1998-20051998 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%.

Irish Facts 1998-2005

Changes in waste composition between the years 1995, 1998 & 2001

Irish Facts 1998-20052001 - 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

Irish Facts 1998-2005

Provisional data from 6 surveys carried out in Waterford Coco & Galway City in November 2004 and March 2005

Composting & ClassificationDefinition:- “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)

Grades of CompostPremium Grade

- agricultural and horticultural use- home use, turf, pot plants - can be freely traded - regulations may control the application of nitrogen to landRegulated 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.

End Uses of CompostSoil 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 improvementLandfill Applications- improvement of landfill covers – soil formation

Local AuthoritiesLandfill companiesWaste and sewage companies

Those Who Benefit from the End Uses

Overview – Teresa ConwayWaste Hierarchy Process Options for Organic WasteWhy Biologically Treat WasteLegislation & Targets Physical Processing of MSWBiological Process of Composting

Biology Site Selection Types of Systems

Waste HierarchyComposting can be considered a component of Integrated Waste Management (IWM)

Options near top are more desirable than those at the bottom

Process Options for Organic Waste

Process Options

Landfill Incineration Biological Processing Direct Land Disposal

Anaerobic Digestion Specialised MethodsComposting

Marketable Products

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

% MSW that is biodegradable

25%

35%

60%

0%

10%

20%

30%

40%

50%

60%

70%

80%

Paper &Cardboard

Food & GardenWaste

TotalBiodegradable

MSW (EEA,2003 )

Number of authorised Landfills remaining in Ireland

126

92

34

0

20

40

60

80

100

120

140

1998 2001 2002

No. of Landfills

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

a diversion of 50% of household waste from landfill by 2013a minimum 65% reduction in biodegradable waste consigned to landfillthe 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

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 ActRegulations made under the European Communities Act, 1972 in relation to waste managementLandfill Directive 99/31/EC

Legislation & Targets

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

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)ActinomycetesFungiProtozaRotifers

Biological Process of Composting

Food Web of a Compost pile

Organic Residue

Primary Consumersbacteria, fungi, actinomycetes

Secondary Consumersnematodes, protozoa, rotifera,

Tertiary Consumerscentipedes, mites, beetles

Site Selection for MW ProcessingLarge enough to receive projected waste volumes & for technology usedAdequate 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

A low water table to prevent site floodingA central accessible location with good traffic flowA water source for wetting compost piles & fire protectionArrangements for leachate to be collected and treated Windrows need shelter in regions of moderate to heavy rainfall

Site Selection for MW 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

Physical Processing

1) Turned Windrow2) Static Aerated Pile3) 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

Turned Windrows

Windrows Composting

Sites

Natural Air Circulation in a Compost Windrow

Most preferred method used in IrelandCommonly used for rapid composting of yard wastesWindrows 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 freezingFinished compost can be made between 3 mts - 2 yrs Rate of composting is generally directly proportional to frequency of turning

Turned Windrow Systems

Typical 18 month schedule using Turned Windrow system

SummerWindrows turned

monthly

AutumnWindrows dismantledRoom made for newincoming material

AutumnWindrows formed Using a front end

loader

SpringWindrows turned

monthly

WinterWindrows turned

monthly

Next 6 MonthsCompost screened

Moved to curing pileStabilised & yields N

March/AprilFinished Compost

Peak Demand

Static Aerated PileDoes not employ turning – ‘static’Air is drawn or blown through a network of perforated plastic pipes under the windrowsFaster than windrow systemsUsed 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)

This blower forces air into a static compost pile.

Forced aeration in a bin type system

Passively Aerated Windrow System (PAWS)

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

In-Vessel SystemsAlso 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

In-Vessel SystemsProtected from severe weather and odour containmentLow retention time (RT) (often <14 days)Requires further compost processing - low RT is insufficient for thermophilic composting stageExpensive to build and operate

Types of In-Vessel SystemsHorizontal UnitsVertical UnitsRotating Drums

Horizontal UnitsMaterial contained and aerated in a long, horizontal reactor, usually build of concreteMaterial may be moved in and out by:

A front end loader or conveyor systemPlug flow system – hydraulic ramMoving floor system

Horizontal Bed Reactor

Vertical Units

Small land areaEnclosed and aerated in a vertical reactor known as “silos” or “towers”.Compaction of material at the base reactor - impedes aeration - anaerobic regions developingGood for Sludge composting industry but not MSW

A vertical in-reactor composting system

Rotating Drums

Most common in-vessel composting approachCombined with aeration in static piles or turned windrow Feedstock introduced into one end of slowly rotating drum, inclined at about 5 degrees from horizontalRT varies from 4-6 hours to 2-3 daysDrum allows homogenisation and screening of materials

A large-scale, Rotating Drum Composting Vessel

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 OrganicsIn-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 1,000Household 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

Problems associated with Composting of

Municipal Waste 1. 1. LeachateLeachate

OdoursVector for organisms supports the proliferation of insects

2. Odour & VOC’sOdour & VOC’sFeedstockEnhanced under anaerobic conditions

3. DustDustAgitation of composting materialsBioaerosols

Problems associated with Composting of Municipal Waste

4. Vermin, Birds & InsectsVermin, Birds & Insects-Nuisance Problems-Pathogens in Final Product

5. BioaerosolsBioaerosols and other Health RisksHazard – pathogenic organisms in feedstock.

Pathway – ingestion of materials (for example from unwashed hands). Receptor – compost site workers.

6. FireFire-Stored in bulk

1. TemperatureThermophilic (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

2. pHAnaerobic 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

3. Aeration (Anaerobic & Aerobic)Anaerobic:

Advantagesa) minimisation of the loss of nitrogenb) less costlyDisadvantages include:a) Slowness of decompositionb) Absence of high temperaturesc) The presence of un-decomposed intermediatesd) The un-pre-processed appearance of the product

Environmental Factors Affecting Composting

AerobicAerobic composting benefits from:a) A rapid rate of degradationb) Elevated temperature levelsc) 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

4. Moisture ContentMoisture 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

Factors affecting Composting

5. SubstrateThe 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)

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.

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.

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 theexperience of the operative -Food waste is estimated at a C: N ratio of15:1. -Woodchip is added at the assessment ofthe operative- Less woodchip is required if there isadequate shrub prunings in the incomingwaste.-More woodchip is added if there is a lot ofgrass in the incoming material as there isin 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”

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

ConclusionFrom 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.

Questions?