Sustainable OneWorld Technologies C.I.C. (SOWTech)
The Flexigester is an anaerobic digestion system used to produce both biogas and biofertilizer.
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.
Africa. To date projects in Uganda, Sierra Leone, Malawi and Tanzania.
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.
5000 USD Interview with representative
Systems distributed in Africa include Flexi Biogas BG5, MBSA Biogas Plant, Human Waste Bioreactor, Biodome.sarl, and Simgas GesiShamba (now discontinued).
Goal 7: Affordable and clean energy
The Flexigester is designed for use in emergency aid situations, temporary camps and medium sized communities or institutions.
The Flexigester V10 is manufactured and delivered on a per demand basis by Butyl Products Ltd.
Users purchase the product for delivery by air from Butyl Products Ltd, the sole manufacturer.
12 Interview with representative
The form of energy that is created by this system
Types of input waste
Manufacturer-specified system capacity
Description of other consumables required for energy production
Quanity of consumables required per hour
The size of this system
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.
All technical support is provided by the manufacturer, and each item is supplied with an instruction manual.Interview with representative
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
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.
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.
University of Malawi, Kite International and the designer: Sustainable OneWorld Technologies C.I.C.
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.
Gas stoves (not manufactured by Butyl Ltd.) can enable use of biogas for cooking.
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.
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
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.
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