introduction to composting mr angus campbell recycled organics unit

Introduction to Composting

Mr Angus Campbellwww.recycledorganics.com

Recycled Organics Unit

www.recycledorganics.com

Lecture Overview

The Composting Industry in Australia1) What is industrial-scale composting?2) Value of recycled organics products

• key to reversing land degradation, ESD and waste management

3) Composting facility process diagram & site layout4) Types of composting technologies & relative performance

Composting Facility Management - Process Control1) Feedstock and receival2) Preparing the mix3) Composting phase4) Curing and screening

5) Final product preparation

6) Quality testing7) Storage / bagging /

sale


The Composting Industry in Australia

What is industrial-scale composting?• Large-scale facilities designed to process organic “wastes” (materials)

into stable, humified and products which can be used in landscaping, horticulture and agriculture and a number of specialised applications

• Controlled decomposition of organic materials with minimum impact on air, soil and water quality

• Hot composting process – achieve pasteurisation of materials (>55°C)• Key infrastructure to recycle organic materials into useful products,

thereby reducing our dependence on landfilling• Facilities designed to process organic materials on a regional basis

from municipal; commercial / industrial; and construction / demolition sources

• Facilities may process up to 150,000 tonnes per annum


The Composting Industry in Australia

Aerial photograph of a typical outdoor windrow composting facility in Australia - SA


Need for ESD

Better resource utilisation and conservation is being demanded by the community, and supported by State and Federal Government ESD policies

Management of the organic fraction of solid waste stream is critical - comprises up to 50% of the waste stream – and also is largely responsible for the negative environmental impacts of landfills

Reprocessing of organic materials into saleable products avoids the impacts of these materials on the environment when disposed of in landfill

Organic materials generate methane in landfill (greenhouse gas, 21x CO2 equivalent), and contribute to high nutrient and BOD in leachate, which can pollute ground- and surface water reserves

Encroaching urban development, and community resistance to poor resource utilisation AND localised urban amenity impacts

Only ~21% of organic “wastes” in Sydney Metropolitan Area are recycled.


Quantities of materials from GSR

* Wright, T. (2000). Report of the Alternative Waste Management Technologies and Practices Inquiry. April 2000.


Value of recycled organics products

OM in soil is key to reversing land degradation More than 70% of NSW is affected by one or more

forms of land degradation from modern agricultural practices (1)

Degradation includes: soil erosion, dry land salinity & sodicity, acidification, nutrient decline & weed invasion (2)

Land degradation costs NSW more than $700 million in lost productivity (2)

Recycled organics products can help stabilise soils, reduce susceptibility to erosion, provide nutrients and reduce fertiliser requirements

Use of organic matter for such applications is considered to be a high-value re-use option (cf waste to energy)

1) NSW EPA (2000). State of the Environment Report. NSW EPA, Sydney.2) NSW Agriculture (1995). NSW Agriculture Annual Report 1994-1995. Orange, NSW.


Composting facility process diagram

Process flow diagram depends on:• type of facility operated,• Type of technology used,• Type of materials processed• Range of products

manufactured This is typical of a large-scale,

outdoor windrow composting facility producing a range of quality products

Majority of facilities in NSW are of this type (~35)

Receival

Preparing the mix

Composting

Curing

Screening

Final product preparation

Quality testing

Feedstock/ raw material

Re-processing

non-conformance

disposal/landfill

SALE

Storage Bagging

oversize


Site layout – Windrow composting facility, Wyong

GateReceival & inspectionMix preparation

Composting

Stockpiledmaterial

Leachate collection

Site officeBiosolidsIncorp’n


Types of composting technologies

At least eight different forms of composting technologies are available for processing a wide range of organic materials.

Turned windrow systems have been the predominant form of composting in Australia, particularly for garden organics material.

Higher technology composting systems are now being implemented for processing materials that have traditionally been difficult to process in outdoor turned windrow systems, such as food organics.

All systems aim to control compost production by manipulating temperature, oxygen and moisture during composting. This varies from technology to technology.


Turned windrows

Turned windrow

Most common system for waste of low odour generating potential

Low capital costs unless concrete pads are installed

High operating costs

Very flexible system - a range of organic materials can be composted and adjustments can be made within a composting cycle

Aeration by turning with front-end loader or specialised machine

Slow rate of decomposition due to varying conditions in pile

Stable compost in 3-12 months

Windrows can be outdoors or formed under a roof (no sides)

Great care needed for effective odour and leachate control


Aerated static pile

Aerated static pile

Medium capital costs

Medium operating costs

Forced aeration

Reduced flexibility - careful preparation of feedstock is essential

Space efficient

Piles usually must be covered (e.g. with compost) to reduce odours

Some control of temperature and aeration resulting in faster composting (6-12 weeks); further curing usually required


Aerated covered windrow

Aerated covered windrow

Medium capital costs Medium operating costs Cover for windrows reusable Forced aeration; computer control of composting possible Reduced flexibility - careful preparation of feedstock essential Space efficient Improved control of temperature and aeration resulting in faster

composting (3-6 weeks); further curing usually required


Rotating drums

Rotating drum

High capital cost

Medium operating costs

Less preparation of starting materials required due to constant mixing and size reduction

Rapid initial decomposition in drum (up to seven days)

Further decomposition required in windrows or aerated static piles

Provides mixing and aeration by means of drum rotation and forced aeration


Agitated bed or channel

Agitated bed or channel

High capital cost Medium operating costs Flexible system – both forced aeration and mechanical mixing used Space efficient Beds are covered in a fully enclosed building or roof Good capacity for odour and leachate control Rapid composting: 2-4 weeks; further curing usually required


In-vessel (horizontal configuration)

In-vessel (horizontal configuration)

High capital cost

Automated system

Uniform temperature and oxygen profile throughout contents of vessel

Composting vessels can be housed in a building or outdoors

Excellent control of odours and leachate

Can be located with minimal buffer distances

Very fast composting (7-14 days)

Further curing in windrows or in-vessel usually required


In-vessel (vertical configuration)

In-vessel (vertical configuration)

High capital cost Automated system Uniform temperature and oxygen profile throughout contents of

vessel Composting vessels can be housed in a building or outdoors Excellent control of odours and leachate Can be located with minimal buffer distances Very fast composting (7-14 days) Further curing in windrows or in-vessel usually required


Composting technology – relative performance


Composting Facility Mgmt – Process Control

Feedstock selection1. Feedstock quality is of paramount

importance to composting because poor quality feedstock produces poor quality composts.

2. Chemical and physical characteristics such as C:N ratio, moisture content and porosity are also important since they determine whether a feedstock can be safely composted by a given composting system at a specific site.

3. Materials such as garden organics, wood chips, bark, food organics, manure, biosoilds, grease trap waste, animal mortalities are often composted.

Clean, uncontaminated garden organics from a municipal

collection to be composted in windrows

Poor source separation can lead to high contamination

levels (e.g. plastic) and poor product quality



Receival1. At the point of receival on site, all

incoming raw feedstock material must be verified, weighed and documented, preferably into a computer database at the main gate.

2. Every raw material load must be inspected on arrival for contaminants such as glass, plastics and metals.

3. Depending on putrescibility of material received, material may be stockpiled (e.g. woody garden organics) or processed immediately (e.g. food organics)

Materials dropped off must be weighed and documentation

prepared to track batch

Inspection is important, facilities may reject batches with high

physical contam-ination or charge increased gate fee



Preparing the mix1. Careful feedstock preparation is

crucial to successful composting in all types of composting systems

2. Matching the type of feedstocks that are processed to an appropriate composting technology is a critical step in the planning process for new facilities

3. Preparing feedstock for thermophilic composting involves: size reduction (i.e. grinding or chipping); achieving the optimum carbon to nitrogen ratio (C:N ratio); achieving the optimum moisture content; and determining the best possible mix of feedstock.

Size reduction of woody garden organics prior to

composting

Mixing of materials to achieve an optimum composting mix

before placement into windrows



Composting phase1. Composting process management

varies with type of composting technology

2. For outdoor turned windrows, key process management steps are: Maintenance of thermophilic (55-

60°C) conditions to ensure rapid decomposition

Turning to aerate mass, improve oxygen levels, alleviate compaction and avoid odour formation

Addition of water to ensure optimum moisture content for microbial decomposition, and to avoid dust and aerosol production

Turning of a biosolids windrow with a Scarab® windrow turner

Checking of oxygen levels with a Galvanic cell oxygen

meter



Curing1. A period of curing of between 3 and 6

weeks may be required for a stable and mature product suitable for unrestricted application

2. Immature composts can be toxic to plants (if inappropriately / over applied):• Oxygen depletion; metabolites such

as organic acids – root damage; ammonia release (high N materials);

N drawdown (low N materials)3. Curing should be performed in a

separate functional area of the composting facility

4. The site should be well-drained to prevent excess water accumulating at the base of piles after rainfall (if not under cover)

Curing of compost in an open-sided building based

on a concrete pad



Screening1. Screening separates compost

particles of different size and/or shapes.

2. In a composting operation, screening serves one or more of the following purposes:• removes a physical contaminants

from the finished compost including: rocks, metal, glass, plastic etc.;

• recovers bulking agent from the compost for re-use; and

• Separates to meet required particle size specifications for a range of different products (eg. mulch, soil conditioner, top dressing, potting mix)

Photograph of a mobile screening plant. This plant is capable of separating a range of particle size fractions from

cured compost



Final product preparation1. After screening, the base compost

product can be blended with a range of additives to form a range of value-added products – e.g. engineered soils, coloured mulches, potting mixes, customised products etc.

2. Additives may include: fertiliser; wetting agents; sand; gravel; vermiculite; perlite; ash; rock dust; natural soil; dolomite; lime; gypsum etc.

3. Compost blends must have predictable and uniform characteristics to meet market demands

Photograph of a compost screening and batch mixing

plant used to manufacture an ‘engineered soil product’



Quality testing1. In-process testing and final product

testing are used are critical to reduce the amount of non-conforming or defective product produced, and can guarantee its products to its customers with confidence

2. An inspection and testing plan is often used to test product at key critical control points during the manufacturing process

3. Conformance to a relevant Australian Standard (e.g. AS 4454, AS 3743, AS 4419), or to a performance based industry specification may be required by some customers

Composting facilities often have basic on-site testing for

characterising product quality. Very few have laboratories

with equipment such as ICP’s for nutrient and metal

analysis, most use commercial laboratories.



Storage / bagging / sale1. Storage is the last step in the

compost manufacturing process.2. Final products should be stored in a

separate functional area of the composting facility.

3. The conditions of storage should be adequate to prevent a degeneration in product quality through: re-contamination of the final product with untreated materials; dust and odour generation; waterlogging and nutrient leaching; re-commencement of thermophilic composting; and risk of fire.

4. Some products bagged prior to sale

Photograph of a fully automatic bagging machine manufactured by Hamer™. This machine forms, fills and seals bags.


Conclusions

Conversion of organic materials into quality composted products that can improve soils and the environment is a central component of the NSW Government’s strategy to reduce waste disposal to landfill.

An understanding of the basic principles of composting science and process management will allow solid waste managers to select and implement appropriate composting solutions.


Further reading

Haug, R.T. (1993). The Practical Handbook of Compost Engineering. Lewis Publishers, Boca Raton, USA.

Recycled Organics Unit (2001). Establishing a Licensed Composting Facility: A guide to siting, designing, gaining approval and a licence to develop and operate a composting facility in New South Wales. Recycled Organics Unit, internet publication: www.recycledorganics.com

Recycled Organics Unit (2001). Producing Quality Compost: Operation and management guide to support the consistent production of quality compost and products containing recycled organics. Recycled Organics Unit, internet publication: www.recycledorganics.com

Recycled Organics Unit (2001). Composting Science for Industry: An overview of the scientific principles of composting processes. Recycled Organics Unit, internet publication: www.recycledorganics.com

NSW EPA (2002). Draft Environmental Guidelines for Composting and Related Organics Processing Facilities. http://www.epa.nsw.gov.au/publications/composting_draft_egs.pdf

http://www.recycledorganics.com/




Further information

Recycled Organics Unit publications available from www.recycledorganics.com

introduction to composting mr angus campbell recycled organics unit

Documents

organic wastes materials

composting phase

industrialscale composting

pasteurisation of materials

quantities of materials

landfill zorganic materials

australia sa slide

organics unit slide