CIWEM calls for:

1. A firm regulatory footing for controls on composting treatment and product quality (as is the case for organic material containing kitchen waste).

2. Regulation of composting that is exempt from waste management licensing, to the same standard as for other centralised composting operations.

3. The delivery of agreed microbiological quality standards for composts.

4. Quantitative monitoring at the district scale to determine the effectiveness of home composting at diverting household waste from landfill disposal.

5. The UK Government to make a case to the European Commission for derogation of composted material from the prescribed nitrogen (N) limits of the Nitrate Directive.  This would resolve the apparent conflict between improving soil organic matter and restricting N additions to soil from composts, so that the full benefit of composted materials on soil quality can be realised. 

6. Further research to develop alternative products from composted biomaterials, that are acceptable to the specialised sector of the horticulture industry, which continues to require peat for use in its growing media.

7. Local authorities to address as a matter of urgency how to tackle segregation of kitchen waste in the context of those living in flats, high-rise apartments and dwellings where home composting is not possible.

The Chartered Institution of Water and Environmental Management (CIWEM) is the leading professional body for the people who plan, protect and care for the environment and its resources, providing educational opportunities, independent information to the public and advice to government. Members in 96 countries include scientists, engineers, ecologists and students.

*This PPS addresses stabilised compost derived from source separated organic wastes.  Partially or fully stabilised materials produced, for example, as an output from Mechanical Biological Treatment (MBT) plants are discussed in a separate PPS.
 
Context

Composting is a well-established natural method for treating, sanitising and stabilising organic materials such as green waste, fruits, vegetables, cardboard and wood found in municipal solid waste (MSW) streams.  It is undertaken on both a large and small scale, ranging from home composting bins to centralised sites that compost thousands of tonnes every year.  Composting is playing a key role in helping local authorities to achieve targets both on diverting waste from landfill and on recycling. 

Composting is generally defined as the controlled biological decomposition of organic material under conditions that are predominantly aerobic and that allow the development of “thermophilic” temperatures because of biologically produced heat.  The composting process produces a final product that is sanitised, stabilised, high in humic substances and can be applied to land.  Applying compost to land is beneficial as it adds valuable organic matter which improves soil structure, adds valuable macro- and micro-nutrients and adds micro-organisms back to the soil to improve its health.

In order to improve the UK’s performance in the management of MSW the Government has imposed a system of recovery and recycling targets on local authorities.  With incremental targets based on each local authority’s individual performance, it is the Government’s intention to reach 33% recycling nationally by 2015.  Biodegradable materials such as paper can either be removed from the MSW stream and recycled as paper, or turned into a compost along with other organic wastes.  Compost is regarded as a recycled product, and therefore counts towards the achievement of the 33% target.  At EU level, the Landfill Directive requires the UK to divert biodegradable MSW away from direct landfilling into alternative forms of treatment – 25% diversion (relative to 1995 levels) by 2010, rising to 65% diversion by 2020.  This equates to up to 33 million tonnes of biodegradable waste being diverted from landfill.

Currently, over 80% of good quality compost (approximately 500,000 tonnes) is obtained from green waste (plant clippings, grass cuttings etc.) collected from civic amenity sites and from parks and civic gardens.  Only 7% of compost is produced from organic waste collected at the kerbside.  Tightening recycling and landfill diversion targets will require ever-larger quantities of compost to be produced, turning the organic fraction of waste into an increasingly significant source of compost, since 63% to 68% of MSW is believed to be biodegradable.

Home composting offers a complementary route to civic amenity collection sites and centralised treatment for garden waste.  Recent estimates indicate that participating households, on average, may divert 400 kg per year of organic waste from landfill⁽¹⁾.

Composting of sewage sludge with green waste or woody wastes is also practised by a number of water companies to make the sludge safe for application to agricultural land.  Methods to improve the management of solid farmyard manures, in order to encourage composting, are also being discussed with respect to controlling microbiological hazards from these livestock-derived organic wastes.

Key Issues

Composting technologies
Many technologies and systems are commercially available for centralised composting of wastes.   Currently the main process type is open-air windrow turning, a lower cost option than other more technologically developed in-vessel methods, or aerated static piles. In 1999, 88% of the waste composted in the UK was by open-air mechanically turned windrow⁽²⁾.  However, open windrows are more susceptible to odour complaints than other methods which are enclosed or not mixed during the initial, active, composting phase.  In-vessel composting takes place in a sealed container where the environment can be carefully controlled and optimised for stabilisation and sanitisation of the product and allows gas scrubbing to prevent odour emissions. The approximate cost of composting in windrows is £15 per tonne of feedstock and is £30 per tonne by in-vessel systems⁽³⁾.

Quality control
The UK has seen the introduction of BSI PAS 100 standard for composts and the commercially derived Apex standard.  In association with European legislation such as the Animal By-Products Order 2003, legal requirements and quality control are playing an increasingly significant role in determining  materials to be composted and the methods that can be used.
 
Declining organic matter in soils – compost as the answer?
The proportion of agricultural soils in England and Wales containing less than 3.6% organic matter has increased from 31% in 1979-81 to 41% in 1995.  Declining organic matter status is identified in the Draft Soil Protection Strategy for England⁽⁴⁾ as a key issue for the sustainable management of soil and has important implications for the physical condition of agricultural soils.

Waste-derived composts, as well as other manures and organic materials, can provide a good source of organic matter for soil improvement.  The Waste Management Licensing Regulations⁽⁵⁾ stipulate that a maximum application of 250 tonnes per ha of waste-derived compost may be spread on the land in any 12-month period.

Composts provide effective replacements for mineral phosphate and potassium fertilisers for crop production, but are generally poor sources of N as the organic N in the product is not readily released.   However, this makes composts ideal substrates for building soil organic matter because the risk of nitrate leaching into groundwater is low. The Code of Good Agricultural Practice for the Protection of Water⁽⁶⁾ for England and Wales sets an application limit of 250 kg N/ha/year from organic wastes and compost (which usually contains 1-2% N). In Nitrate Vulnerable Zones, which represent significant areas of intensively managed agricultural land in England where soil organic matter is in decline, the Nitrates Directive (91/676/EEC) sets a limit of 170 kg/ha/year as total N with the intention of protecting groundwater from nitrate contamination.  Unfortunately, these limits restrict the potential benefits to be gained from applying high rates of composts to soil to raise organic matter values.  No specific limits on N inputs are stipulated in the Scottish Code of Practice for the Prevention of Environmental Pollution from Agricultural Activity⁽⁷⁾, but the matching of nutrient applications to crop needs is required; CIWEM considers this more pragmatic approach preferable. 

A substitute for peat
A further advantage of waste-derived composts is peat substitution and reducing the destruction of unique peatland habitats. Total horticultural peat consumption in the UK is estimated at 3.4 million m3 per year, the majority of which (96%) is used in growing media formulation⁽⁸⁾. Mindful of the environmental measures introduced by peat producers in the UK and the industry’s role as a source of employment, composted biomaterials are accepted as effective alternatives to peat for general soil conditioning purposes and this is likely to be the main outlet for composted wastes in the domestic and commercial landscaping markets. Indeed, significant progress has been made in exploiting alternatives to peat for use as soil conditioners and recent statistics⁽⁸⁾ indicate that peat substitutes already represent 92% of the horticultural market for soil improvers.  This indicates that horticultural demand for soil improvers derived from composts is close to saturation. Therefore, market development activities may now be most effectively targeted on the agriculture sector. 

With considerable refinement and blending, composted wastes can also replace peat to some extent in growing media, but the variability and limitations of biowaste composts, together with high processing costs, do not favour this.

Land reclamation, brownfield development and urban situations
Compost is an ideal material for soil building in reclamation and brownfield development situations. Self-sustaining soils need to have adequate organic matter to provide a reserve of nutrients, water and biological diversity.  The microbial activity that organic matter stimulates can also degrade some of the pollutants found in brownfield situations.  Composted materials are also valuable for soil improvement and mulching in urban areas.

Discussion

1. The environmental, operational and regulatory pressures influencing composting are dynamic and finely balanced.  Composting is a key way to reduce the amount of organic waste sent to landfill.  However, this is balanced by the need to protect the natural environment from pollution when compost is used on land.  EU legislative trends are moving in the direction of increased regulation, and cleaner composts derived from source separated waste streams.
2. A key issue is the requirement for controls on composting treatment and product quality.  CIWEM considers this should have a firm regulatory footing, as is the case for biosolids and organic material containing kitchen waste, and that standards should be set according to risk.
3. CIWEM recognises that whilst composting undertaken through the use of exemptions (from waste management licensing, under The Waste Management Licensing Regulations 1994) is useful in helping to recycle organic material, these operations need to operate to the same standard as other centralised composting operations.
4. CIWEM recognises that standards are necessary to provide quality assurance for composted materials and supports the efforts of both Government and the commercial sector to develop and implement these.  However, effective co-ordination of this effort is required to avoid duplication and confusion.
5. Proposed microbiological quality standards for composts require measurement of numbers of pathogenic and indicator bacteria. This type of analysis is inherently difficult and results from different laboratories are likely to be highly variable because of the lack of standardisation of methods used.  Therefore, further work is necessary to develop and validate, through inter-laboratory comparison, agreed standard protocols for detecting and counting specified indicator and pathogenic organisms in composted residuals.
6. Home composting has the potential to divert significant amounts of biodegradable household waste from landfill disposal and fulfils the proximity principle for waste management. Many local authorities in the UK have distributed home compost bins to the public.  A continued commitment to promoting home composting is important to expand waste diversion in this way.  So far, only qualitative information on the diversion of waste by home composting has been collected based on questionnaire surveys, so there is uncertainty about its actual contribution. Therefore,  quantitative monitoring work is needed at the district scale to determine the contribution of home composting to diverting household waste away from landfill disposal. 
7. In areas where home composting is not possible or is not desired, food waste disposers⁽⁹⁾ can play a useful role in managing kitchen waste safely and diverting it from the municipal solid waste stream.
8. UK agriculture requires significant inputs of biomaterials to correct the declining organic matter in soil used for food production. Composts provide an ideal substrate for this purpose as they contain significant amounts of organic matter.  Their low N availabilities also have the advantage of minimal risk of nitrate leaching to groundwater. Large rates of addition are necessary to increase soil organic matter reserves, but there is a conflict apparent between the need to raise soil organic matter and the current restrictions on N additions via organic manures. CIWEM recommends that these conflicts be resolved so that the full agronomic benefit of these materials on soil quality can be realised.
9. The market for alternatives to peat as horticultural soil conditioners is approaching saturation. Therefore the agricultural sector, land reclamation, soil improvement in urban areas, etc. are likely to be the main outlets for recycling bulk quantities of composted biowastes to land.
10. Considerable progress has occurred in the substitution of peat with alternative biomaterials for general soil conditioning purposes in the domestic and commercial horticultural markets.  The main use of peat is now in growing media formulation.  CIWEM is fundamentally against the extraction of peat and considers that the UK Government should take a proactive role in promoting wider use of alternatives which are of a consistent standard and acceptable to this specialised sector of the horticulture industry.

References

(1) Smith, S.R. and Jasim, S. (2002) Small-scale composting of biodegradable household waste: Process, diversion and end-use. 7th European Biosolids Organic residuals Conference, 17 – 20 November, Wakefield.

(3) Slater, R.A., Frederickson, J. and Gilbert, E.J. (2001) The State of Composting 1999: Results of The Composting Association’s Survey of UK Composting Facilities and Collection Systems 1999. The Composting Association, Wellingborough.

 (3) Hogg, D. (2002) Costs for Municipal Waste Management in the EU. Final Report to Directorate General Environment, European Commission. Eunomia Research & Consulting, Bristol.

(4) Department of the Environment, Transport and the Regions (2001) The Draft Soil Strategy for England – A Consultation Paper. DETR, London.

(5) UK Statutory Instrument (1994) The Waste Management Licensing Regulations 1994. SI No 1056. The Stationery Office, London.

(6) Ministry of Agriculture, Fisheries and Food/Welsh Office Agriculture Department (1998) Code of Good Agricultural Practice for the Protection of Water. PB 0585. MAFF Publications, London.

(7) The Scottish Office Agriculture, Environment and Fisheries Department (1997) Prevention of Environmental Pollution from Agricultural Activity: A Code of Good Practice. SOAEFD, Edinburgh.

(8) Department of the Environment, Transport and the Regions (1999) Monitoring and Assessment of Products for Growing Media and Soil Improvers in the UK. DETR, London (available on website: http://www.peatproducers.co.uk/useuk.html).

(9) CIWEM PPS on Food Waste Disposers

March 2005
Note: CIWEM Policy Position Statements (PPS) represents the Institution’s views on issues at a particular point in time.  It is accepted that situations change as research provides new evidence.  It should be understood, therefore, that CIWEM PPS’s are under constant review, that previously held views may alter and lead to revised PPS’s.