Sustainable management of urban waste is a major challenge for municipal authorities. Much urban waste is biodegradable and recyclable. A large proportion consists of organic matter that can be recycled into compost for urban agriculture. Promising new composting techniques are available but planners must learn why previous projects have failed.

Research from the International Water Management Institute explores the benefits and constraints to composting for agriculture in cities in developing countries.

Municipal authorities lack capacity to collect, transport and safely treat waste. In many cities household waste collection is restricted to wealthy neighbourhoods and most waste is dumped along road sides, in illegal dumps and in storm water drains.

Solid waste is a collection of different materials including organic material, plastics, metal and textiles. These can be handled in different ways to maximise recovery. Over half the waste generated in cities in low- and middle-income countries is bio-degradable. In African cities there is a very high proportion of organic matter. In the Rwandan capital, Kigali, this reaches 94 per cent. It includes vegetable and fruit peelings, charcoal ash, garden refuse, leaf litter, animal dung, human faecal matter, sludge from septic tanks and waste generated by abattoirs, breweries and agro-industries.

Composting involves breaking down organic waste materials by micro-organisms such as bacteria, protozoans, fungi and invertebrates. Composting complements chemical fertilisers for crop production and reduces the need for large imports of fertilizer. It reduces amount of waste for landfill and methane generation at landfills. When urban organic waste recycling is decentralised there is reduced need for external inputs like equipment, fuel and transportation. Centralised composting has not proved sustainable.

When human excreta is included in composting materials, extra care is required in agricultural application. If compost piles are badly managed dangerous organisms like nematodes and parasite eggs may survive the decomposition process. They may then be carried to farmers’ fields when composts are applied to soils.

Urban composting projects have often failed because of:

• insufficient knowledge and care in carrying out composting, resulting in unacceptable odours, attraction of rodents and heavy metal contamination
• lack of markets for compost where customers have been put off by low quality compost
• limited support by municipal authorities who prioritise centralised waste collection services rather than promoting local recycling
• lack of coordination between the various institutions and sectors  concerned
• over-dependence on external funding.

Many urban and peri-urban areas are potential users of recyclable nutrients from municipal waste. In order to reap the potential benefits of composting and restore the natural nutrient recycling loop, planners must:

• do much more than simply choose the right locally appropriate technology
• focus on institutional and management issues, delivery of feedstock (raw organic material), distribution of compost products and extension and education services
• invest in improved segregation and sorting procedures to ensure purer organic waste for composting
• reduce health risks through provision of protective clothing and first aid facilities for compost workers, training in waste management and recycling.

Source(s):
‘Recycling of Urban Organic Waste for Urban Agriculture’ by Olufunke Cofie, A. Adam-Bradford and Pay Drechsel in ‘Cities Farming for the Future – Urban Agriculture for Green and Productive Cities’, edited by René van Veenhuizen, RUAF Foundation, August 2006. Full document.

Funded by: International Water Management Institute

id21 Research Highlight: 24 November 2006

Further Information:
Olufunke O. Cofie and Pay Drechsel
West Africa Office
International Water Management Institute
PMB CT 112 Cantonments
Accra
Ghana

Tel: +233 (0)21 784752
Fax: +233 (0)21 784752
Contact the contributor: o.cofie@cgiar.org ; p.drechsel@cgiar.org

International Water Management Institute

A. Adam-Bradford
Centre for Developing Areas Research,
Department of Geography
University of London, Royal Holloway
Egham TW20 0EX
UK

Tel: 44 (0)1784 443563
Fax: +44 (0) 1784 472836
Contact the contributor: adambradford68@hotmail.com

Other related links:
'Composting – a business for the urban poor?'

'A solid case for improving waste reuse in Mali and Burkino Faso'

'Not wasting waste: improving the livelihoods of poor urban waste pickers'

'Waste not: ecological sanitation breaks new ground in Africa'

Working with urban farmers for food security