Updated on January 20, 2024


Created on June 6, 2016

Flexigester V10

Upcoming Update

The Flexigester is an anaerobic digestion system used to produce both biogas and biofertilizer.

Tested By
  • Kite International
  • Sustainable OneWorld Technologies C.I.C. (SOWTech)
  • University of Malawi
Content Partners


Product Description

The Flexigester System is an anaerobic digestion system developed by Sustainable OneWorld Technologies C.I.C. (SOWTech), that can take materials such as animal manures, waste food, human waste and plants and convert them, over a period of several weeks, into natural Biofertiliser and Biogas. The system is delivered in a box, it is small and light, yet it has a capacity of 10 tonnes and above, with V10 in the name indicating 10 tonnes.


Target SDGs

SDG 7: Affordable and Clean Energy

SDG 8: Decent Work and Economic Growth

Market Suggested Retail Price


Target Users (Target Impact Group)

Small and Medium-sized Enterprises, NGOs

Distributors / Implementing Organizations

Flexigester systems have been designed and developed by Sustainable OneWorld Technologies C.I.C. (SOWTech) in joint partnership with Butyl Products Ltd who manufacture and distribute the systems.

Competitive Landscape

Manufacturing/Building Method

The Flexigester V10 is manufactured and delivered on a per demand basis by Butyl Products Ltd.

Intellectural Property Type


User Provision Model

Users purchase the product for delivery by air from Butyl Products Ltd, the sole manufacturer.

Distributions to Date Status

12 Interview with representative

Output energy product


Average daily biogas production (m3/day)

8 m3/day

Description of waste source(s)

Kitchen waste, animal manure, human sewage

Waste input requirements (kg per hour or day)

Up to 280 L/day

Description of other input requirements

None required but can blend waste with water

Other input requirements (amount per hour)


System dimensions (m)

12 x 1.5 x 0.75 m

Design Specifications

The Flexigester is made from butyl rubber which is impervious to both liquids and gases. This stops waste water soaking into the ground and polluting soil and water courses and controls odours from rotting waste. An area of 16 x 3 m is required within which to dig the 12 x 1.5 x 0.75 m hole for the Flexigester V10. Technical specifications:  

Product Schematics

Technical Support

All technical support is provided by the manufacturer, and each item is supplied with an instruction manual.Interview with representative

Replacement Components

Some parts of the system are replaceable, and the Flexigester can be repaired if it becomes damaged.Interview with representative


The manufacturer expects the Flexigester to remain operational for 10 years.Interview with representative The Flexigester is made from Butyl, which is a resilient and robust material, and which can be maintained with simple hand tools. Butyl products have been in use for periods well in excess of 10 years in tropical and subtropical climates. The Flexigester comes with a 12 month warranty.Interview with representative

Manufacturer Specified Performance Parameters

Manufacturers specify a minimum retention time of 30 days, biofertiliser output up to 101 t/yr. An estimate of the value of biofertiliser and biogas output up to 8 m3/day, equivalent to up to 9-17 kg wood/day.

Vetted Performance Status

Kite International conducted a program called SimpliSafi in which Flexigesters were used. The project was supposed to be the world's first simplified sewerage and biogas system - a community-centred sanitation and clean energy solution. During the three year couse of the project, the following impacts were observed:

  • Construction of three simplified sewerage networks, providing sustainable sanitation to over 450 community members of the informal settlements in Dar Es Salaam.
  • Development of an effective method to empower the local community, organising local Sanitation User Associations to manage each network.
  • Installation of a Flexigester, adapting it to function as part of the world’s first integrated simplified sewerage and biogas network– including evidence of proof of concept with the successful production and testing of burnable gas in the community.
  • Build and trial designs from the University of Cambridge that aimed to concentrate solar power to process the flexigester output to create biofertiliser and greywater, closing the loop and achieving zero waste sanitation.
Academics from University of Malawi also vetted the performance of the flexigester installed in Malawi, finding it is generally successful and effective for community and disaster relief contexts, though in winter post-treatment of the biofertilizer is required to reduce pathogen concentration.


There are some potential dangers to running the biogas plant: noise, hazardous waste material disposal, etc. Adequate ventilation, appropriate precautions, good work practices, and adequate personal protective equipment will minimize the dangers associated with biogas.

Complementary Technical Systems

Gas stoves (not manufactured by Butyl Ltd.) can enable use of biogas for cooking.

Academic Research and References

Brown, V.J., 2006, Biogas: a bright idea for Africa. Environmental Health Perspectives, 114(5).

Clemens, H., Bailis, R., Nyambane, A. and Ndung’u, V., 2018, Africa Biogas Partnership Program: A review of clean cooking implementation through market development in East Africa. Energy for Sustainable Development, 46, pp. 23-31.

Freeman, K.K. and Seppala, J.A.K., 2019, The Power of Dung: Lessons Learned from On-Farm Biodigester Programs in Africa. The World Bank, Working Paper No. 136895, pp. 1-108.

Kamwani, F., Thole, B., Anderson, K., Mamani Casilla, G.H., Spit, J. and Gaisford, A., 2015, Investigating the process efficiency of flexigester as an on-site anaerobic faecal sludge sanitation system for application in emergency situations. Malawi Journal of Applied Sciences and Innovation, 1(2).

Rupf, G.V., Bahri, P.A., de Boer, K. and McHenry, M.P., 2017, Development of an optimal biogas system design model for Sub-Saharan Africa with case studies from Kenya and Cameroon. Renewable energy, 109, pp. 586-601.

Zalm, J.E., 2017, Performance of domestic biodigesters in Kenya Towards the development of a comparative method for measuring the performance of different biodigester types in Sub?Saharan Africa. Master’s Thesis, Utrecht University.

Flexigester. n.d. www.sowtech.com.

Homepage. n.d. Butyl Products Ltd.

Flexigester® Anaerobic Digestion System. n.d. Butyl Products Ltd.

Contact Butyl Products Ltd. n.d. Butyl Products Ltd.

Kite International | LinkedIn. n.d. www.linkedin.com.

Anaerobic Digesters and Biogas Safety – Farm Energy. n.d. Farm-Energy.extension.org.


Compliance with regulations

The original Flexigester was designed with input from the International Foundation of Red Cross and Red Crescent Societies (IFRC) and the first version was funded by the IFRC in Malawi.Interview with representative

Evaluation methods

Field Trials

Other Information

The Flexigester is available in a variety of sizes from 10 to 80 m3 allowing it to be used in a variety of different situations. Flexigester distributes another product, Flexigester Sewage Isolation Bag (SIB). There is a series of resources providing additional information about the product on the Flexigester site, including the Flexigester V10 brochure. Some additional resources on the role of biogas globally are also available through SOWTech's site.

Comments from the Community


  1. E4C.COMMENTS says:

    David Fulford says:

    Butyl rubber digesters have been used in USA, but the price is seen as high compared to other types. The proce of the Flexidigester system is not defined.
    It has the advantage that is can be set up quickly for places such as refugeee camps

  2. E4C.COMMENTS says:

    Emily says:

    Treatment method: anaerobic digestion, with bacteria activated in cow dung

Leave a Reply

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