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Building up gas for good

Building up gas for good

5 engineers have joined forces to harness the energy from biogas to use in remote island situations in the South Pacific. The Engineers Without Borders (EWB) team led by Anita Walbran, PhD student at the University of Auckland Engineering School and Roy Elliot, Masters of Engineering (Civil) Student and part-time water resources engineer at URS Ltd, has been working on a feasibility study for biogas digesters in the Pacific Islands for the past 3 months. The other members of the team include project mentor Peter Trafford, Senior Process Engineer at WaterCare Services Ltd, and Civil Engineering students at the University of Auckland; Alan Collins and James Russell.

Biodigesters harness useful biogases via anaerobic processes. The gas produced provides a valuable renewable energy source that can be used for cooking, lighting, running generators and refrigeration. The digesters offer a cleaner solution and simple treatment option for the disposal of human/animal excrement and waste vegetation, offering a significant reduction in disease-causing microorganisms in the final effluent. Using wastes as inputs into the digesters also reduces the impact of wastes upon potable water supplies, as well as reducing the need for infrastructure for waste disposal. Small scale biogas digesters have been used extensively and successfully throughout rural areas in China, India, South East Asia, and Central and South America.

The biodigester project was sourced for EWB by the Pacific Islands Trade and Investment Commission (PITIC). The project proposal came from Waste Management Ltd (WML) based in Tonga. WML called upon the skills of Engineers Without Borders to assist in evaluating the technical, environmental and social feasibility of using biogas digesters in Tonga. The aim of the project was to analyse the feasibility of using biogas digester technology, and subsequently design a biodigester suitable for environments in Tonga. Likely inputs to the biodigester in the smaller island communities were identified as human, pig and vegetation wastes and the likely uses for the gas are cooking, lighting and providing supplementary electricity generation. This technology is heavily needed in areas of Tonga, not only as a solution to waste problems, but also to supplement the high cost of electricity in the island nation.

The team developed two designs, a polyethylene bag biodigester and a modified Chinese design digester. WML subsequently requested the Chinese design to be implemented for a farm in Tongatapu, the main island in the Kingdom of Tonga. This unit will serve as a demonstration unit for similar biodigesters in schools and on smaller islands.

The team will travel to Tonga from the 4-18th Dec to implement the biodigester design and educate the people who will be looking after it on the operations and maintenance principles. They will be preparing educational material with which to engage local people, to ensure the effectiveness and manageability of the designs. This is an important component of the project, ensuring that local people are enabled with the skills required to sustain the developed technology.

Engineers Without Borders provides engineering aid to partner project organizations in countries within the South Pacific region. The biodigester project has been an invaluable experience for all those involved, giving the engineers the opportunity to use their skills to benefit schools, families and the wider community in Tonga. The team is currently raising funds towards this trip, and donations or enquiries can be made at

“Working on this project has been a very rewarding experience and will hopefully be the first step towards seeing many more biodigesters aiding communities in Tonga.“

Anita Walbran (EWB NZ Treasurer, Tonga Project Leader 08)


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