Unplanted Drying Beds

An unplanted drying bed is a simple, permeable bed that, when loaded with sludge, collects percolated leachate and allows the sludge to dry by evaporation. Approximately 50% to 80% of the sludge volume drains off as liquid or evaporates. The sludge, however, is not effectively stabilized or sanitized.

The bottom of the drying bed is lined with perforated pipes to drain the leachate away that percolates through the bed. On top of the pipes are layers of gravel and sand that support the sludge and allow the liquid to infiltrate and collect in the pipe. It should not be applied in layers that are too thick (maximum 20 cm), or the sludge will not dry effectively. The final moisture content after 10 to 15 days of drying should be approximately 60%. When the sludge is dried, it must be separated from the sand layer and transported for further treatment, end-use or final disposal. The leachate that is collected in the drainage pipes must also be treated properly, depending on where it is discharged.

Design Considerations

The drainage pipes are covered by 3-5 graded layers of gravel and sand. The bottom layer should be coarse gravel and the top fine sand (0.1 to 0.5 mm effective grain size). The top sand layer should be 250 to 300 mm thick because some sand will be lost each time the sludge is removed To improve drying and percolation, sludge application can alternate between two or more beds. The inlet should be equipped with a splash plate to prevent erosion of the sand layer and to allow for even distribution of the sludge.

Designing unplanted drying beds has to consider future maintenance because ensuring access to people and trucks for pumping in the sludge and removing the dried sludge is essential.

If installed in wet climates, the facility should be covered by a roof and special caution should be given to prevent the inflow of surface runoff.

Appropriateness

Sludge drying is an effective way to decrease the volume of sludge, which is especially important when it has to be transported elsewhere for further treatment, end-use or disposal. The technology is not effective at stabilizing the organic fraction or decreasing the pathogenic content. Further storage or treatment (e.g., Co-Composting) of the dried sludge might be required.

Unplanted drying beds are appropriate for small to medium communities with populations up to 100,000 people, but larger ones also exist for huge urban agglomerations. They are best suited for rural and peri-urban areas where there is inexpensive, available space situated far from homes and businesses. If designed to service urban areas, unplanted drying beds should be at the border of the community, but within economic reach for motorized emptying operators.

This is a low-cost option that can be installed in most hot and temperate climates. Excessive rain may prevent the sludge from properly drying.

Health Aspects/Acceptance

Both the incoming and dried sludge are pathogenic; therefore, workers should be equipped with proper protection (boots, gloves, and clothing). The dried sludge and effluent are not sanitized and may require further treatment or storage, depending on the desired end-use.

The drying bed may cause a nuisance for nearby residents due to bad odours and the presence of flies. Thus, it should be located sufficiently away from residential areas.

Operation and Maintenance

Trained staff for operation and maintenance is required to ensure proper functioning.

Dried sludge can be removed after 10 to 15 days, but this depends on the climate conditions. Because some sand is lost with every removal of sludge, the top layer must be replaced when it gets thin. The discharge area must be kept clean and the effluent drains should be regularly flushed.

References

Further Readings

  • Cover image of a reference book or miscellany.

    ANDREOLI, C.V. (Editor); SPERLING, M. von (Editor); FERNANDES, F. (Editor) (2007): Sludge Treatment and Disposal. London: International Water Association (IWA) Publishing. URL [Accessed: 01.11.2013]. PDF

    Sludge Treatment and Disposal is the sixth volume in the series Biological Wastewater Treatment. The book covers in a clear and informative way the sludge characteristics, production, treatment (thickening, dewatering, stabilisation, pathogens removal) and disposal (land application for agricultural purposes, sanitary landfills, landfarming and other methods). Environmental and public health issues are also fully described.

  • Cover image of a reference book or miscellany.

    VERHAGEN, J.; CARRASCO, M. (2013): Full-Chain Sanitation Services That Last. Non-Sewered Sanitation Services. The Hague: International Water and Sanitation Center (IRC). URL [Accessed: 07.08.2013]. PDF

    This paper sets out a framework for the delivery of non-sewered sanitation services that last, are accessible to all and are at scale. The framework is based on IRC International Water and Sanitation’s (IRC) experience and lessons learnt from its engagement in non-sewered sanitation service at scale.

  • Cover image of a reference book or miscellany.

    HEINSS, U.; LARMIE, S.A.; STRAUSS, M. (1998): Solids Separation and Pond Systems for the Treatment of Faecal Sludges in the Tropics . Lessons Learnt and Recommendations for Preliminary Design . Duebendorf: Swiss Federal Institute of Aquatic Science (EAWAG), Department of Water and Sanitation in Developing Countries (SANDEC). URL [Accessed: 12.04.2010]. PDF

    The report sets out to provide guidelines for the preliminary design of faecal sludge treatment schemes comprising solids-liquid separation and stabilisation ponds. The document is based on the results of collaborative field research conducted by the Ghana Water Research Institute and SANDEC on full and pilot-scale faecal sludge (FS) treatment plants located in Accra, Ghana.

  • Cover image of a reference book or miscellany.

    HEINSS, U.; KOOTAATEP, T. (1998): Use of Reed Beds for Faecal Sludge Dewatering. A Synopsis of Reviewed Literature and Interim Results of Pilot Investigations with Septage Treatment in Bangkok, Thailand. Duebendorf and Bangkok: Swiss Federal Institute of Aquatic Science (Eawag), Department of Water and Sanitation in Developing Countries (Sandec) and Asian Institute of Technology (AIT). PDF

    This study project tested reed beds for their ability to treat septage.

  • Cover image of a reference book or miscellany.

    HEINSS, U.; LARMIE, S.A.; STRAUSS, M. (1999): SOS - Management of Sludges from On-Site Sanitation. Characteristics of Faecal Sludges and their Solids-Liquid Separation. Duebendorf and Accra: Swiss Federal Institute of Aquatic Science (EAWAG). PDF

    This document gives an overview on the characteristics of different sludges as well as monitoring results and recommendations for design of solid-liquid separation. It is based on a field report.

  • Cover image of a reference book or miscellany.

    HEINSS, U.; STRAUSS, M. (1999): SOS - Management of Sludges from On-Site Sanitation. Co-treatment of Faecal Sludge and Wastewater in Tropical Climates. Duebendorf and Accra: Swiss Federal Institute of Aquatic Science (EAWAG). URL [Accessed: 21.04.2010]. PDF

    This article provides operational and design guidance for the co-treatment of faecal sludge in waste stabilisation ponds and in activated sludge sewage treatment plants. Problems which may arise when highly concentrated faecal sludge is not properly included in the design of the co-treatment system are also discussed.

  • Cover image of a reference book or miscellany.

    MONTANGERO, A.; STRAUSS, M. (2004): Faecal Sludge Treatment. Duebendorf: Swiss Federal Institute of Aquatic Science (EAWAG), Department of Water and Sanitation in Developing Countries (SANDEC). URL [Accessed: 10.06.2010]. PDF

    This document reviews current practices of faecal sludge management and treatment.

  • Cover image of a reference book or miscellany.

    MONVOIS, J.; GABERT, J.; FRENOUX, C.; GUILLAUME, M. (2010): How to Select Appropriate Technical Solutions for Sanitation. Cotonou and Paris: Partenariat pour le Développement Municipal (PDM) and Programme Solidarité Eau (pS-Eau). URL [Accessed: 19.10.2011]. PDF

    The purpose of this guide is to assist local contracting authorities and their partners in identifying those sanitation technologies best suited to the different contexts that exist within their town. The first part of the guide contains a planning process and a set of criteria to be completed; these assist you in characterizing each area of intervention so that you are then in a position to identify the most appropriate technical solutions. The second part of the guide consists of technical factsheets which give a practical overview of the technical and economic characteristics, the operating principle and the pros and cons of the 29 sanitation technology options most commonly used in sub-Saharan Africa.

  • 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.

    STRAUSS, M.; DRESCHER, S.; ZURBRUEGG, C.; MONTANGERO, A.; OLUFUNKE, C.; DRECHSEL, P. (2003): Co-composting of Faecal Sludge and Municipal Organic 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: 23.06.2010]. PDF

    The document gives an overview on the combined composting of (faecal) sludges and organic solid waste based on a pilot project in Kumasi, Ghana. Results of the investigation should help the city’s waste management department to develop its biosolids management strategy and enable the project team to develop guidelines for planners and engineers on the option of co-composting.

  • Cover image of a reference book or miscellany.

    TILLEY, E.; ULRICH, L.; LUETHI, C.; REYMOND, P.; ZURBRUEGG, C. (2014): Compendium of Sanitation Systems and Technologies. 2nd Revised Edition. Duebendorf, Switzerland: Swiss Federal Institute of Aquatic Science and Technology (Eawag). URL [Accessed: 28.07.2014]. PDF

    This compendium gives a systematic overview on different sanitation systems and technologies and describes a wide range of available low-cost sanitation technologies.

Case Studies

  • Cover image of a reference journal article.

    KONE, D.; KENGE, I. (2008): Technology Transfer – Forage Plants Used in Faecal Sludge Dewatering Beds in Sub-Saharan Africa. In: Sandec News 9. PDF

    In collaboration with the Asian Institute of Technology (AIT), Bangkok, Eawag has previously demonstrated that constructed wetlands, especially in Thailand, offer a viable solution for the treatment of faecal sludge. However, since the characteristics of sludge vary widely from one region to another, appropriate indigenous plants had to be identified so as to ensure successful operation of these facilities.

  • Cover image of a reference book or miscellany.

    KONE, D.; STRAUSS, M. (2004): Low-cost Options for Treating Faecal Sludges (FS) in Developing Countries - Challenges and Performance. Duebendorf: Water and Sanitation in Developing Countries (SANDEC), Swiss Federal Institute for Environmental Science (EAWAG). URL [Accessed: 23.06.2010]. PDF

    This article analyses and discusses the performances of low-cost technology for treating faecal sludges in developing countries. It shows that where septic tanks are the predominant type of on-site sanitation installations, septage is the only or predominant type of faecal sludge generated. It also shows that constructed wetlands, settling tanks/ponds, or unplanted drying beds might prove suitable as a pre-treatment.

  • Cover image of a reference chapter of a book/miscellany.

    WAFLER, M. (2006): Chapter 3. Pilot Project "Navsarjan Vocational Training Institute Dalit Shakti Kendra". In: WAFLER, M.; HEEB, J. (2006): Report on Case Studies of ecosan Pilot Projects in India. Eschborn. URL [Accessed: 26.04.2010]. PDF

    The main aim of the project was to avoid manual scavenging of excreta and to improve the sanitation situation at the Navsarjan Vocational Training Institute. The technical solution proposed was source separation (grey-/blackwater) and reuse. Greywater is separately treated and reused in the garden while the urine and faeces (blackwater) are directly introduced into a biogas plant. Digested sludge is dried on basic drying beds and used as compost for the garden. UDDT were also installed. The concept was implemented and evaluated for its social and cultural acceptability, sustainable and hygienic safety.

  • Cover image of a reference book or miscellany.

    ZIMMERMANN, N.; WAFLER, M. (2009): Decentralized Wastewater Mgmt at Adarsh College, Badalapur, Maharashtra, India. Eschborn: Sustainable Sanitation Alliance (SuSanA). URL [Accessed: 22.05.2012]. PDF

    This case study reports the development of an ecologically sound sanitation concept at Adarsh Bidyaprasarak Sanstha's College of Arts & Commerce. It comprises separate urine collection and a DEWATS system for the treatment of black- and greywater consisting of biogas settler, an anaerobic baffled reactor, and anaerobic filter, a horizontal flow wetland and a polishing pond.

Awareness Material

  • Cover image of a reference journal article.

    STRAUSS, M.; BARREIRO, W.C.; STEINER, M.; MENSAH, A.; JEULAND, M.; BOLOMEY, S.; MONTANGERO, A.; KONE, D. (2003): Urban Excreta Management - Situation, Challenges, and Promising Solutions. In: IWA Asia-Pacific Regional Conference Bangkok, Thailand.URL [Accessed: 23.06.2010]. PDF

    The objective of this paper is to render planners, decision makers, and consultants aware that faecal sludge management (FSM) should form an integral part of the urban development planning process. For this, three illustrative cases are presented, based on which an array of measures or tools, as well as institutional/regulatory, financial/economic, and technical aspects are discussed.

Training Material

  • Cover image of a reference book or miscellany.

    EAWAG/SANDEC (Editor) (2008): Faecal Sludge Management. Lecture Notes. Duebendorf: Swiss Federal Institute of Aquatic Science (EAWAG), Department of Water and Sanitation in Developing Countries (SANDEC). URL [Accessed: 23.05.2012]. PDF

    This module pays special attention to the haulage, treatment and reuse or disposal of faecal sludge. It covers both technical and non-technical (socio-cultural, economic, political etc.) aspects and provides practical information on design, financing and planning of faecal sludge treatment plants.

  • Cover image of a reference book or miscellany.

    EAWAG (Editor); SANDEC (Editor) (2008): Faecal Sludge Management. Pdf Presentation. Duebendorf: Swiss Federal Institute of Aquatic Science (Eawag), Department of Water and Sanitation in Developing Countries (Sandec). URL [Accessed: 23.05.2012]. PDF

    A presentation about faecal sludge management in developing countries.

  • Cover image of a reference book or miscellany.

    MONTANGERO, A.; STRAUSS, M. (2004): Faecal Sludge Treatment. Duebendorf: Swiss Federal Institute of Aquatic Science (EAWAG), Department of Water and Sanitation in Developing Countries (SANDEC). URL [Accessed: 10.06.2010]. PDF

    This document reviews current practices of faecal sludge management and treatment.

  • Cover image of a reference book or miscellany.

    SASSE, L. ; BORDA (Editor) (1998): DEWATS. Decentralised Wastewater Treatment in Developing Countries. Bremen: Bremen Overseas Research and Development Association (BORDA). PDF

    Exhaustive report on technological, operational and economic aspects of decentralised waste water treatment systems. Spreadsheet examples support the reader in designing and planning waste water treatment systems components.

  • Cover image of a reference book or miscellany.

    UNEP (Editor); MURDOCH UNIVERSITY (Editor) (2004): Environmentally sound technologies in wastewater treatment for the implementation of the UNEP/GPA "Guidelines on Municipal Wastewater Management". The Hague: United Nations Environment Programme Global Programme of Action (UNEP/GPA), Coordination Office. PDF

    Technical information on environmentally sound technologies in wastewater treatment.

Important Weblinks

  • http://www.unep.or.jp/ [Accessed: 23.06.2010]

    Link to the online version of the “International Source Book On Environmentally Sound Technologies for Wastewater and Stormwater Management” from the United Nations Environmental Programme. This section is about drying beds.