Co-Composting

Co-composting is the controlled aerobic degradation of organics, using more than one feedstock (faecal sludge and organic solid waste). Faecal sludge has a high moisture and nitrogen content, while biodegradable solid waste is high in organic carbon and has good bulking properties (i.e., it allows air to flow and circulate). By combining the two, the benefits of each can be used to optimize the process and the product.

There are two types of co-composting designs: open and in-vessel. In open composting, the mixed material (sludge and solid waste) is piled into long heaps called windrows and left to decompose. Windrow piles are periodically turned to provide oxygen and ensure that all parts of the pile are subjected to the same heat treatment. In-vessel composting requires controlled moisture and air supply, as well as mechanical mixing. Therefore, it is not generally appropriate for decentralized facilities.

Although the composting process seems like a simple, passive technology, a well-working facility requires careful planning and design to avoid failure.

Design Considerations

The facility should be located close to the sources of organic waste and faecal sludge to minimize transport costs, but still at a distance away from homes and businesses to minimize nuisances. Depending on the climate and available space, the facility may be covered to prevent excess evaporation and/or provide protection from rain and wind. For dewatered sludge, a ratio of 1:2 to 1:3 of sludge to solid waste should be used. Liquid sludge should be used at a ratio of 1:5 to 1:10 of sludge to solid waste

Windrow piles should be at least 1 m high and insulated with compost or soil to promote an even distribution of heat inside the pile.

Appropriateness

A co-composting facility is only appropriate when there is an available source of well-sorted biodegradable solid waste. Solid waste containing plastics and garbage must first be sorted. When carefully done, co-composting can produce a clean, pleasant, beneficial soil conditioner.
Since moisture plays an important role in the composting process, covered facilities are especially recommended where there is heavy rainfall.
Apart from technical considerations, composting only makes sense if there is a demand for the product (from paying customers). In order to find buyers, a consistent and good quality compost has to be produced; this depends on good initial sorting and a well-controlled thermophilic process.

Health Aspects/Acceptance

Maintaining the temperature in the pile between 55 and 60°C can reduce the pathogen load in sludge to a level safe to touch and work with. Although the finished compost can be safely handled, care should be taken when dealing with the sludge, regardless of the previous treatment. If the material is found to be dusty, workers should wear protective clothing and use appropriate respiratory equipment. Proper ventilation and dust control are important.

Operation & Maintenance

The mixture must be carefully designed so that it has the proper C:N ratio, moisture and oxygen content. If facilities exist, it would be useful to monitor helminth egg inactivation as a proxy measure of sterilization. 

A well-trained staff is necessary for the operation and maintenance of the facility. Maintenance staff must carefully monitor the quality of the input material, and keep track of the inflows, outflows, turning schedules, and maturing times to ensure a high quality product. Forced aeration systems must be carefully controlled and monitored.

Turning must be periodically done with either a front-end loader or by hand. Robust grinders for shredding large pieces of solid waste (i.e., small branches and coconut shells) and pile turners help to optimize the process, reduce manual labour, and ensure a more homogenous end product.

References

Further Readings

  • Cover image of a reference book or miscellany.

    ECOSAN CLUB (Editor) (2012): Faecal Sludge Management.. Vienna: Ecosan Club. URL [Accessed: 16.10.2012]. PDF

    This issue presents studies from different regions (Bangladesh, Cameroon, Burkina Faso) that mainly show the non-existence of faecal sludge management. Additionally, the last paper describes a new technological solution (LaDePa) for producing hygienically safe organic fertiliser from sludge from ventilated improved pit toilets (VIPs).

  • Cover image of a reference book or miscellany.

    STRANDE, L. (Editor); RONTELTAP, M. (Editor); BRDJANOVIC, D. (Editor) (2014): Faecal Sludge Management. Systems Approach for Implementation and Operation. London: IWA Publishing. URL [Accessed: 16.07.2014]. PDF

    This is the first book to compile the current state of knowledge on faecal sludge management. It addresses the organization of the entire faecal sludge management service chain, from the collection and transport of sludge, to the current state of knowledge of treatment options, and the final end use or disposal of treated sludge. It presents an integrated approach that brings together technology, management, and planning, based on Sandec’s 20 years of experience in the field. It also discusses important factors to consider when evaluating and upscaling new treatment technology options. The book is designed for undergraduate and graduate students, engineers, and practitioners in the field who have some basic knowledge of environmental and/or wastewater engineering.

  • Cover image of a reference book or miscellany.

    ROTHENBERGER, S.; ZURBRUGG, C.; ENAYETULLAH, I.; SINHA, A.H.M. (2006): Decentralized Composting for Cities of Low-and Middle-Income Countries A Users’ Manual. Water and Sanitation in Developing Countries (SANDEC) at the Swiss Federal Institute for Environmental Science (EAWAG) and Waste Concern. URL [Accessed: 11.08.2010]. PDF

    Based on the experiences of Waste Concern on implementing decentralized composting facilities in Dhaka and other Asian Cities, this manual provides step-by-step guidelines on how to initiate and operate small-scale composting facilities in developing countries so as to turn waste into jobs and food security.

  • Cover image of a reference book or miscellany.

    ROUSE; ROTHENBERGER, S.; ZURBRUEGG, C. (2008): Marketing Compost. A Guide for Compost Producers in Low and Middle-Income Countries. Duebendorf: Water and Sanitation in Developing Countries (SANDEC), Swiss Federal Institute for Environmental Science (EAWAG). URL [Accessed: 05.05.2010]. PDF

    This guide describes a marketing approach to composting, and is intended to help compost producers run more viable initiatives by unlocking the value of their product. The handbook does not cover everything there is to know about marketing, but starts with the basics and introduces the key principles and techniques. These include understanding the ‘marketing environment’, identifying appropriate target customer groups, and developing and promoting products to suit the market.

  • Cover image of a reference book or miscellany.

    IWMI (Editor); SANDEC (Editor) (2002): Co-composting of Faecal Sludge and Solid Waste. Swiss Federal Institute of Aquatic Science (EAWAG), Department of Water and Sanitation in Developing Countries (SANDEC) and International Water Management Institute (IWMI). URL [Accessed: 11.08.2010]. PDF

    This report summarises the technical and operational aspects of the co-composting process (design and mode of operation) that were investigated at a pilot plant in Kumasi (Ghana) between February and June 2002.

  • Cover image of a reference book or miscellany.

    ALI, M. (Editor) (2004): Sustainable Composting Case Studies and Guidelines for Developing Countries. Leicestershire: Water Engineering and Development Centre, Loughborough University. URL [Accessed: 05.08.2010]. PDF

    This publication presents the findings of a research on “Promoting Composting as a Business for the Urban Poor” in the form of guidelines based on case studies from India, Bangladesh, Sri Lanka, Pakistan and Ethiopia.

  • Cover image of a reference book or miscellany.

    UNEP (Editor) (2002): A Directory of Environmentally Sound Technologies for the Integrated Management of Solid, Liquid and Hazardous Waste for Small Island Developing States (SIDS) in the Pacific Region. The Hague: United Nations Environment Programme (UNEP). URL [Accessed: 28.03.2012]. PDF

    This directory is part of UNEP collaboration with SIDS on the implementation of the Waste Management chapter of the Barbados Programme of Action. It focuses primarily on proven sound environmental technologies for solid, liquid and hazardous waste management plus those currently successfully being used in SIDS within the Pacific Region.

  • Cover image of a reference book or miscellany.

    UNHABITAT (Editor) (2010): Solid Waste Management in the World’s Cities . London and Washington DC: Earthscan. PDF

    This third publication in the series aims to capture the current trends in waste management with the assistance of 20 case studies from around the world.

  • Cover image of a reference book or miscellany.

    ZURBRUGG, C.; DRESCHER, S.; PATEL, A.H.; SHARATCHANDRA S.C. (2002): Decentralised Composting in India – Lessons Learnt. Leicestershire: Water Engineering and Development Centre, Loughborough University. URL [Accessed: 05.08.2010]. PDF

    The paper discusses the findings of a study of 20 compost plants, ranging in size from household composting to large centralised composting facilities, in Bangalore, Chennai, Pune and Mumbai.

Case Studies

Awareness Material

  • Cover image of a reference book or miscellany.

    ENPHO (Editor) (n.y.): Vermi-Composting advertisement. Kathmandu: Environment and Public Health Organization. PDF

    This poster illustrates use of vermi-composting for Solid Waste Management at household level.

  • Cover image of a reference book or miscellany.

    WASTE CONCERN (Editor) (n.y.): Community based Composting. Dhaka: Waste Concern. PDF

    This brochure describes composting and the “Community-based Waste Management and Composting Pilot Program,” implemented in urban slum and suburban areas of Bangladesh by Waste Concern, with support from Government of Bangladesh and UNICEF.

Training Material

  • Cover image of a reference book or miscellany.

    DRESCHER, S.; ZURBRUEGG, C.; ENAYETULLAH, I.; SINGHA, M.A.D. (2006): Decentralised Composting for Cities of Low- and Middle-Income Countries – A User’s Manual. Dhaka: Swiss Federal Institute of Aquatic Science (EAWAG), Department of Water and Sanitation in Developing Countries (SANDEC) and Waste Concern. URL [Accessed: 16.08.2010]. PDF

    This book describes approaches and methods of composting on neighbourhood level in small-and middle-scale plants. It considers issues of waste collection, composting technologies, management systems, occupational health concerns, product quality, marketing and end-user demands.

  • Cover image of a reference book or miscellany.

    EAWAG (Editor); SANDEC (Editor) (2008): Solid Waste Management. Lecture notes. Duebendorf: Swiss Federal Institute of Aquatic Science (EAWAG), Department of Water and Sanitation in Developing Countries (SANDEC). URL [Accessed: 08.04.2010]. PDF

    This document provides an overview of the present state-of-the-art of solid waste production and management. It contains the characteristics of municipal solid waste and describes current waste treatment systems and technologies, as well as non-technical aspects like private sector involvement and financial arrangements.

  • Cover image of a reference journal article.

    ENAYETULLAH, I. (2010): Innovations in Organic Waste Management. In: Workshop on Innovations for Scaling Up Organic Waste Management in South Asia, April 2-3, 2010. PDF

    This presentation with 76 slides includes details on the community composting plants established and operated by Waste Concern in Bangladesh.

  • Cover image of a reference book or miscellany.

    UNEP (Editor) (2009): Developing Integrated Solid Waste Management Plan – Training Manual . Osaka/Shiga, Japan: UNEP. URL [Accessed: 29.10.2012]. PDF

    This document is the fourth and last of the four sets of guidelines on ISWM. It focuses on how to develop an ISWM Plan by utilizing the information collected and generated with the help of the previous three sets of the guidelines. This document could also be used as a standalone document to build the capacity of experts and policy makers on planning for ISWM.

  • Cover image of a reference book or miscellany.

    UNEP (Editor); IETC (Editor) (1996): International Source Book on Environmentally Sound Technologies for Municipal Solid Waste Management. United Nations Environment Programme (UNEP) and International Environmental Technology Centre Japan (IETC). URL [Accessed: 28.04.2010]. PDF

    This Source Book is directed towards municipal solid waste management decision makers of developing countries and countries in transition, non-governmental organisations and community-based organizations involved in waste management. The book serves as a general reference guide to researchers, scientists, science and technology institutions and private industries on a global state-of-the-art on environmentally sound technologies for municipal solid waste management. It provides a list of information sources and overviews of practices in the world regions relating to environmentally sound management of municipal solid waste (waste reduction, collection and transfer, composting, incineration, landfills, special wastes, waste characterization, management and planning, training, public education and financing). Parts of the book can be viewed within this website.

Important Weblinks

  • http://www.waste.nl [Accessed: 24.07.2010]

    This official site of WASTE Advisers on Urban Environment and Development, an organization based in Netherlands that specializes in solid waste management in ecological sanitation, has several documents on organic waste management and composting.

  • http://www.wasteconcern.org [Accessed: 24.07.2010]

    This site describes the work of Waste Concern, an NGO based in Bangladesh, which has designed and implemented decentralized composting projects in several Asian Cities. It contains lots of information on how to do decentralised composting, as well as publications.

  • http://www.borda-net.org [Accessed: 26.04.2010]

    This is the homepage of the Bremen Overseas Research and Development Association (BORDA), which has contributed strongly to the development of decentralized wastewater treatment (i.e. DEWATS) the past decades.

  • enpho.org [Accessed: 24.07.2010]

    This is the official site of Environment and Public Health Organization (ENPHO), which has some information on home compost bins that are promoted in Nepal as well as other information on ENPHO.

  • http://cwmi.css.cornell.edu/ [Accessed: 24.07.2010]

    This is the official site of the Cornell Waste Management Institute, which serves the public through research, outreach, training, and technical assistance, with a focus on organic residuals.

  • http://www.howtocompost.org/ [Accessed: 24.07.2010]

    This site is a mine of information on composting, for beginners as well as experts. Although most of the information is based on experiences from developed countries, it can be useful for developing countries as well.