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12 May 2019

Fossa Alterna

Applicable to

Application level

City

Household

Neighborhood

Management level

Household

Public

Shared

Inputs

Faeces Excreta Organics
+ Dry Cleansing Materials + Anal Cleansing Water

Outputs

Pit Humus
Author/Compiled by
Eawag (Swiss Federal Institute of Aquatic Science and Technology)
Beat Stauffer (seecon international gmbh)
Dorothee Spuhler (seecon international gmbh)
Executive Summary

The Fossa Alterna is a short cycle alternating, waterless (dry) double pit technology. Compared to the double VIP which is just designed to collect, store and partially treat excreta, the Fossa Alterna is designed to make an earth-like product that can be used as a nutrient-rich soil conditioner. The Fossa Alterna is dug to a maximum depth of 1.5 m and requires a constant input of cover material (soil, ash, and/or leaves).

Advantages
Because double pits are used alternately, their life is virtually unlimited
Excavation of humus is easier than faecal sludge
Significant reduction in pathogens
Generates nutrient-rich humus with good potential for use as soil conditioner
Flies and odours are significantly reduced (compared to non-ventilated pits)
Can be built and repaired with locally available materials
Low (but variable) capital costs depending on materials; no or low operating costs if self-emptied
Disadvantages
Requires constant source of cover material
Manual removal of humus is required
Garbage may ruin end-use opportunities of the product
In Out

Faeces, Excreta, Organics, Dry Cleansing Materials, Anal Cleansing Water

Compost/Biosolids

Factsheet Block Title
Introduction
Factsheet Block Body

The fossa alterna toilet system is similar to the Arborloo, but it consists of two pits, which are lined.

Cover material should be added to the pit after defecation (not urination). The soil and leaves introduce a variety of organisms like worms, fungi and bacteria which help in the degradation process. Also, the pore space is increased, which allows for aerobic conditions. Additionally, ash helps to control flies, reduces odours and makes the mix slightly more alkaline.

The full pit degrades while the second pit is filling, which, ideally, should take one year. The material in the full pit will degrade into a dry, earth-like mixture that can be easily removed manually. Because of the added carbonaceous bulking material, the degradation process is accelerated, and the content is ready for excavation and use much faster than in a double VIP.

Factsheet Block Title
Design Considerations
Factsheet Block Body

A Fossa Alterna pit would fill over a period of 12–24 months depending on its size and the number of users. Even though the pits are shallow (1 to 1.5 m), each of them can be used by a family of six for one year. The Fossa Alterna technology will only work properly if the two pits are used sequentially and not concurrently. Therefore, an adequate cover for the out of service pit is required.

The Fossa Alterna should be used for urine, but water should not be added (small amounts of anal cleansing water can be tolerated). Water encourages the development of vectors and pathogens, but it also fills the pore spaces and deprives the aerobic bacteria of the oxygen that is required for degradation. A UDDT can be used with the Fossa Alterna, but only in circumstances when the soil cannot sufficiently absorb the urine or when the urine is highly valued for application. Since cover material is used to continuously cover the excreta, smells are reduced. To reduce the smells even further, a ventilation pipe can be added.

In flood-prone areas and where the groundwater table is too high, the Fossa Alterna could be raised or built entirely above ground to avoid water intrusion and groundwater pollution. Raising the pits could also be an option for rocky ground and compacted soils that are difficult to dig.

If space is abundant and emptying not desired, the Arborloo can be an alternative disposal option. Pits should not be lined if used as an Arborloo.

Factsheet Block Title
Health Aspects/Acceptance
Factsheet Block Body

By covering faeces with soil, ash, and/or leaves, flies and odours are kept to a minimum. Users may not understand the difference between the Fossa Alterna and a double VIP, although if given the opportunity to use one, people should have a good appreciation of the advantages. Demonstration units can be used to show how easily one can empty a Fossa Alterna in comparison to emptying a double pit. Keeping the contents sealed in the pit for the duration of at least one year makes the material safer and easier to handle. The same precautions that are taken when handling compost should be taken with the humus derived from the Fossa Alterna.

Need more relevant sanitation knowledge?

Read some of our most visited tools on sustainable sanitation such as slow- or rapid sand filtration!

Factsheet Block Title
Operation & Maintenance
Factsheet Block Body

When the first pit is put into use, a layer of leaves should be put onto the bottom of the pit. Periodically, more leaves should be added to increase the porosity and oxygen availability. Following the addition of faeces to the pit, a small amount of soil, ash, and/or leaves should be added. Occasionally, the mounded material beneath the toilet hole should be pushed to the sides of the pit in order to optimise the use of space.

Unlike a simple or ventilated pit which will be covered or emptied, the material in the Fossa Alterna is meant to be used as a soil conditioner. Therefore, it is extremely important that no garbage is put into the pit.

Emptying the Fossa Alterna is easier than emptying other pits; the pits are shallower and the addition of soil, ash, and/or leaves means that the contents are less compact. The material that is removed is not offensive and presents a reduced threat of contamination. Depending on the dimensions of the pits, the contents should not be emptied more often than once a year.

Applicability

The Fossa Alterna is appropriate for rural and peri-urban areas. It is especially suitable to water-scarce environments. It is a useful solution for areas that have poor soil and could benefit from the use of the stabilised humic material as a soil amendment.

The Fossa Alterna is not appropriate for greywater as the pit is shallow and the conditions must remain aerobic for degradation.

The material is manually emptied from the Fossa Alterna (it is dug out, not pumped out); thus, vacuum truck access to the pits is not necessary.

The Fossa Alterna is not suited for rocky or compacted soils (that are difficult to dig) or for areas that flood frequently, except if the pits are raised.

A urine diversion toilet slab can be used with the fossa alterna if the soil cannot sufficiently absorb the urine or urine is needed for agriculture.

The Fossa Alterna technology will only work properly if the two pits are used sequentially and not concurrently. Therefore, an adequate cover for the out of service pit is required.

Library References

Toilets That Make Compost

This book describes in an easy-to-understand and picture-based way how to construct three different low cost sanitation solutions, namely arborloos, fossa alterna and urine diversion toilets.

MORGAN, P. EcoSanRes (2007): Toilets That Make Compost . Stockholm: Stockholm Environment Institute URL [Accessed: 09.05.2019]

Ecological Toilets

This book describes how to construct Arborloo toilets and how it can be upgraded to VIPs at a later stage.

MORGAN, P. EcoSanRes (2009): Ecological Toilets. (pdf presentation). Stockholm: Stockholm Environment Institute URL [Accessed: 09.05.2019]

This module introduces the importance of market-based RRR solutions. At the end of this module you have identified key challenges in your local sanitation and waste management system and a RRR-related business idea.

Cover image Module  1

This module sheds light on the importance of studying the business environment and its components like waste supply, market demand, competition and the institutional framework. At the end of this module you have gained insights to evaluating the potential of your business idea.

Cover image Module  2

This module shows how a business idea can be turned into a business model while putting a specific focus on understanding the customer and designing products that meet their needs. At the end of this module you will have developed a business model and positioned your offer in the market.

Cover image Module  3

This module focusses on planning the operations of a RRR related business. During this part RRR technologies will be introduced for different waste streams and tools for planning the production process. At the end of this module you will have blueprinted your production process and the required technology and production inputs.

Cover image Module  4

This module covers key aspects of financial planning and analysis. At the end of this module you will have forecasted your profits, cash flows, required investment and evaluated the financial viability of your business model.

Cover image Module  5

This module enables you to set objectives and plan activities for the launch of your RRR business and identify potential financing sources. At the end of this module you will have developed an action plan for launch and identified appropriate financing sources.

Cover image Module  6

Week 1: Identify challenges in your local sanitation & waste management

Download Materials
Further Readings

SDG 6 along the water and nutrient cycles

This AGUASAN publication illustrates how the water and nutrient cycles can be used as a tool for creating a common understanding of a water and sanitation system and aligning it with SDG 6.

BROGAN, J., ERLMANN, T., MUELLER, K. and SOROKOVSKYI, V. (2017): SDG 6 along the water and nutrient cycles. Using the water and nutrient cycles as a tool for creating a common understanding of a water and sanitation system - including workshop material. Bern (Switzerland): AGUASAN and Swiss Agency for Development and Cooperation (SDC) URL [Accessed: 26.03.2019] PDF

Why shit matters [Video File]

TEDX TALKS (2019): https://www.youtube.com/watch?v=d4yD0kz34jg [Accessed: 28.03.2019]

"3 billion people worldwide live in cities without sewers or wastewater treatment plant infrastructure. This forces them to dump their waste into open waters, contaminating the drinking water for others downstream. Imagine if we could harness nutrients in wastewater instead of harming human and environmental health. Christoph Lüthi sees a renewable, locally produced and growing resource where others see only human waste. Watch his talk to learn why shit matters! "

Week 2: Identify RRR products and business opportunities

Download Materials
Further Readings

A public-private partnership linking wastewater treatment and aquaculture (Ghana) - Case Study

AMOAH, P., MUSPRATT, A., DRECHSEL, P. and OTOO, M. (2018): A public-private partnership linking wastewater treatment and aquaculture (Ghana) - Case Study. In: Otoo, M. and Drechsel, P. (Eds.). Resource recovery from waste: business models for energy, nutrient and water reuse in low- and middle-income countries. Oxon (UK): Routledge - Earthscan. Section IV, Chapter 15, pp.617-630. URL [Accessed: 26.03.2019]

Briquettes from agro-waste (Kampala Jellitone Suppliers, Uganda) - Case Study

GEBREZGABHER, S. and MUSISI, A. (2018): Briquettes from agro-waste (Kampala Jellitone Suppliers, Uganda) - Case Study. In: Otoo, M. and Drechsel, P. (Eds.). Resource recovery from waste: business models for energy, nutrient and water reuse in low- and middle-income countries. Oxon (UK): Routledge - Earthscan. Section II, Chapter 3, pp.41-51. URL [Accessed: 26.03.2019]

Cooperative model for financially sustainable municipal solid waste composting (NAWACOM, Kenya) - Case Study

OTOO, M., KARANJA, N., ODERO, J. and HOPE, L. (2018): Cooperative model for financially sustainable municipal solid waste composting (NAWACOM, Kenya) - Case Study. In: Otoo, M. and Drechsel, P. (Eds.). Resource recovery from waste: business models for energy, nutrient and water reuse in low- and middle-income countries. Oxon (UK): Routledge - Earthscan. Section III, Chapter 3, pp.362-370. URL [Accessed: 26.03.2019]

Week 1: Analyse waste supply

Download Materials
Further Readings

Testing the implementation potential of resource recovery and reuse business models: from baseline surveys to feasibility studies and business plans

OTOO, M., DRECHSEL, P., DANSO, G., GEBREZGABHER, S., RAO, K. and MADURANGI G. (2016): Testing the implementation potential of resource recovery and reuse business models: from baseline surveys to feasibility studies and business plans. Colombo (Sri Lanka): International Water Management Institute (IWMI), CGIAR Research Program on Water, Land and Ecosystems (WLE). Resource Recovery and Reuse Series 10. URL [Accessed: 27.03.2019]

Week 2: Analyse market demand

Download Materials
Further Readings

Testing the implementation potential of resource recovery and reuse business models: from baseline surveys to feasibility studies and business plans

OTOO, M., DRECHSEL, P., DANSO, G., GEBREZGABHER, S., RAO, K. and MADURANGI G. (2016): Testing the implementation potential of resource recovery and reuse business models: from baseline surveys to feasibility studies and business plans. Colombo (Sri Lanka): International Water Management Institute (IWMI), CGIAR Research Program on Water, Land and Ecosystems (WLE). Resource Recovery and Reuse Series 10. URL [Accessed: 27.03.2019]

Week 3: Analyse your competition

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Further Readings

Testing the implementation potential of resource recovery and reuse business models: from baseline surveys to feasibility studies and business plans

OTOO, M., DRECHSEL, P., DANSO, G., GEBREZGABHER, S., RAO, K. and MADURANGI G. (2016): Testing the implementation potential of resource recovery and reuse business models: from baseline surveys to feasibility studies and business plans. Colombo (Sri Lanka): International Water Management Institute (IWMI), CGIAR Research Program on Water, Land and Ecosystems (WLE). Resource Recovery and Reuse Series 10. URL [Accessed: 27.03.2019]

Week 4: Analyse the institutional environment

Download Materials
Further Readings

Testing the implementation potential of resource recovery and reuse business models: from baseline surveys to feasibility studies and business plans

OTOO, M., DRECHSEL, P., DANSO, G., GEBREZGABHER, S., RAO, K. and MADURANGI G. (2016): Testing the implementation potential of resource recovery and reuse business models: from baseline surveys to feasibility studies and business plans. Colombo (Sri Lanka): International Water Management Institute (IWMI), CGIAR Research Program on Water, Land and Ecosystems (WLE). Resource Recovery and Reuse Series 10. URL [Accessed: 27.03.2019]

Week 1: Meet the Business Model Canvas

Download Materials
Further Readings

A public-private partnership linking wastewater treatment and aquaculture (Ghana) - Case Study

AMOAH, P., MUSPRATT, A., DRECHSEL, P. and OTOO, M. (2018): A public-private partnership linking wastewater treatment and aquaculture (Ghana) - Case Study. In: Otoo, M. and Drechsel, P. (Eds.). Resource recovery from waste: business models for energy, nutrient and water reuse in low- and middle-income countries. Oxon (UK): Routledge - Earthscan. Section IV, Chapter 15, pp.617-630. URL [Accessed: 26.03.2019]

Briquettes from agro-waste (Kampala Jellitone Suppliers, Uganda) - Case Study

GEBREZGABHER, S. and MUSISI, A. (2018): Briquettes from agro-waste (Kampala Jellitone Suppliers, Uganda) - Case Study. In: Otoo, M. and Drechsel, P. (Eds.). Resource recovery from waste: business models for energy, nutrient and water reuse in low- and middle-income countries. Oxon (UK): Routledge - Earthscan. Section II, Chapter 3, pp.41-51. URL [Accessed: 26.03.2019]

Cooperative model for financially sustainable municipal solid waste composting (NAWACOM, Kenya) - Case Study

OTOO, M., KARANJA, N., ODERO, J. and HOPE, L. (2018): Cooperative model for financially sustainable municipal solid waste composting (NAWACOM, Kenya) - Case Study. In: Otoo, M. and Drechsel, P. (Eds.). Resource recovery from waste: business models for energy, nutrient and water reuse in low- and middle-income countries. Oxon (UK): Routledge - Earthscan. Section III, Chapter 3, pp.362-370. URL [Accessed: 26.03.2019]

Week 1: Plan your production process

Download Materials
Further Readings

Compendium of Sanitation Systems and Technologies. 2nd Revised Edition

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

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

Week 2: Understand the treatment process

Further Readings

Treatment technologies for urban solid biowaste to create value products: a review with focus on low- and middle-income settings

LOHRI, C. R., DIENER, S., ZABALETA, I. MERTENAT, A. and ZURBRÜGG, C. (2017): Treatment technologies for urban solid biowaste to create value products: a review with focus on low- and middle-income settings. In: Reviews in Environmental Science and Bio/Technology, Volume 16, Issue 1, pp 81–130. URL [Accessed: 26.03.2019] PDF

Week 3A: Design technology systems for nutrient recovery

Further Readings

Co-composting of Solid Waste and Fecal Sludge for Nutrient and Organic Matter Recovery

COFIE, O., NIKIEMA, J., IMPRAIM, R., ADAMTEY, N., PAUL, J. and KONÉ, D. (2016): Co-composting of Solid Waste and Fecal Sludge for Nutrient and Organic Matter Recovery. Colombo (Sri Lanka): International Water Management Institute (IWMI), CGIAR Research Program on Water, Land and Ecosystems (WLE). Resource Recovery and Reuse Series 3. URL [Accessed: 27.03.2019]

Decentralized composting in India

DRESCHER, S. and ZURBRÜGG, C. (2004): Decentralized composting in India. In: Harper et al. Sustainable Composting: Case Studies in Guidelines for Developing Countries. Loughborough (UK): Water Engineering and Development Centre (WEDC), Loughborough University, Part2: Case Studies, Chapter 3, pp.15-27. URL [Accessed: 27.03.2019] PDF

Low Cost Composting Training Manual: techniques based on the UN-Habitat/Urban Harvest-CIP community based waste management initiatives

KARANJA, N., KWACH, H. and NJENGA, M. (2005): Low Cost Composting Training Manual: techniques based on the UN-Habitat/Urban Harvest-CIP community based waste management initiatives. Nairobi (Kenya): UN-Habitat. URL [Accessed: 27.03.2019]

Testing the implementation potential of resource recovery and reuse business models: from baseline surveys to feasibility studies and business plans

OTOO, M., DRECHSEL, P., DANSO, G., GEBREZGABHER, S., RAO, K. and MADURANGI G. (2016): Testing the implementation potential of resource recovery and reuse business models: from baseline surveys to feasibility studies and business plans. Colombo (Sri Lanka): International Water Management Institute (IWMI), CGIAR Research Program on Water, Land and Ecosystems (WLE). Resource Recovery and Reuse Series 10. URL [Accessed: 27.03.2019]

Week 3B: Design technology systems for energy recovery

Further Readings

Briquette Businesses in Uganda. The potential for briquette enterprises to address the sustainability of the Ugandan biomass fuel market

FERGUSON, H. (2012): Briquette Businesses in Uganda. The potential for briquette enterprises to address the sustainability of the Ugandan biomass fuel market. London (UK): Global Village Energy Partnership (GVEP) International. URL [Accessed: 27.03.2019] PDF

Testing the implementation potential of resource recovery and reuse business models: from baseline surveys to feasibility studies and business plans

OTOO, M., DRECHSEL, P., DANSO, G., GEBREZGABHER, S., RAO, K. and MADURANGI G. (2016): Testing the implementation potential of resource recovery and reuse business models: from baseline surveys to feasibility studies and business plans. Colombo (Sri Lanka): International Water Management Institute (IWMI), CGIAR Research Program on Water, Land and Ecosystems (WLE). Resource Recovery and Reuse Series 10. URL [Accessed: 27.03.2019]

Week 3C: Design technology systems for water recovery

Further Readings

Testing the implementation potential of resource recovery and reuse business models: from baseline surveys to feasibility studies and business plans

OTOO, M., DRECHSEL, P., DANSO, G., GEBREZGABHER, S., RAO, K. and MADURANGI G. (2016): Testing the implementation potential of resource recovery and reuse business models: from baseline surveys to feasibility studies and business plans. Colombo (Sri Lanka): International Water Management Institute (IWMI), CGIAR Research Program on Water, Land and Ecosystems (WLE). Resource Recovery and Reuse Series 10. URL [Accessed: 27.03.2019]

Chapter 3 - Technology Selection

VEENSTRA, S., ALAERTS, G. and BIJLSMA, M. (1997): Chapter 3 - Technology Selection. In: Helmer, R. and Hespanhol, I. (Eds). Water Pollution Control - A Guide to the Use of Water Quality Management Principles. London (UK): World Health Organization (WHO)/United Nations Environment Programme (UNEP). URL [Accessed: 27.03.2019]

Guidelines for the safe use of wastewater excreta and greywater. Volume I. Policy and Regulatory Aspects

Volume I of the Guidelines for the Safe Use of Wastewater, Excreta and Greywater focuses on policy, regulation and institutional arrangements. Accordingly, its intended readership is made up of policy-makers and those with regulatory responsibilities. It provides guidance on policy formulation, harmonisation and mainstreaming, on regulatory mechanisms and on establishing institutional links between the various interested sectors and parties. It also presents a synthesis of the key issues from Volumes II, III, and IV and the index for all four volumes as well as a glossary of terms used in all four volumes is presented in Annex 1.

WHO (2006): Guidelines for the safe use of wastewater excreta and greywater. Volume I. Policy and Regulatory Aspects. Geneva: World Health Organisation URL [Accessed: 10.04.2019]

Guidelines for the safe use of wastewater excreta and greywater. Volume II. Wastewater Use in Agriculture

Volume II of the Guidelines for the safe use of wastewater, excreta and greywater provides information on the assessment and management of risks associated with microbial hazards and toxic chemicals. It explains requirements to promote the safe use of wastewater in agriculture, including minimum procedures and specific health-based targets, and how those requirements are intended to be used. It also describes the approaches used in deriving the guidelines, including health-based targets, and includes a substantive revision of approaches to ensuring microbial safety.

WHO (2006): Guidelines for the safe use of wastewater excreta and greywater. Volume II. Wastewater Use in Agriculture. Geneva: World Health Organisation URL [Accessed: 05.06.2019] PDF

Guidelines for the safe use of wastewater excreta and greywater. Volume III. Wastewater and Excreta Use in Aquaculture

Volume III of the Guidelines for the Safe Use of Wastewater, Excreta and Greywater deals with wastewater and excreta use in aquaculture and describes the present state of knowledge regarding the impact of wastewater-fed aquaculture on the health of producers, product consumers and local communities. It assesses the associated health risks and provides an integrated preventive management framework.

WHO (2006): Guidelines for the safe use of wastewater excreta and greywater. Volume III. Wastewater and Excreta Use in Aquaculture. Geneva: World Health Organisation URL [Accessed: 08.05.2019]

Guidelines for the safe use of wastewater excreta and greywater. Volume IV. Excreta and Greywater Use in Agriculture

Volume IV of the Guidelines for the Safe Use of Wastewater, Excreta and Greywater recognizes the reuse potential of wastewater and excreta (including urine) in agriculture and describes the present state of knowledge as regards potential health risks associated with the reuse as well as measures to manage these health risks following a multi-barrier approach.

WHO (2006): Guidelines for the safe use of wastewater excreta and greywater. Volume IV. Excreta and Greywater Use in Agriculture. Geneva: World Health Organisation (WHO) URL [Accessed: 09.05.2019] PDF

Week 3: Analyse financial viability

Further Readings

Testing the implementation potential of resource recovery and reuse business models: from baseline surveys to feasibility studies and business plans

OTOO, M., DRECHSEL, P., DANSO, G., GEBREZGABHER, S., RAO, K. and MADURANGI G. (2016): Testing the implementation potential of resource recovery and reuse business models: from baseline surveys to feasibility studies and business plans. Colombo (Sri Lanka): International Water Management Institute (IWMI), CGIAR Research Program on Water, Land and Ecosystems (WLE). Resource Recovery and Reuse Series 10. URL [Accessed: 27.03.2019]

Week 1: Set objectives and plan activities for launch

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Further Readings

Week 2: Finance the launch

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Further Readings

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