Watercare Biogas Cogeneration Plant
Maunsell Ltd

The existing cogeneration plant at New Zealand’s largest wastewater treatment plant in Mangere produced electricity and heat from biogas for use in the sewage treatment process but greater benefits were anticipated from an improved process design.
The upgraded plant produces up to 6.7 megawatts of electricity and 8 megawatts of hot water from methane extracted from the digestion process.

The process design for the new plant was complex and the project required considerable creativity and ingenuity. Some of the process technologies had not previously been utilised in New Zealand or had not been used in combination on such a scale anywhere else. The use of iron sponge filters, for example, is cutting edge in
world terms.

The methane production system now reliably provides cleaned biogas to the gas engines in an energy efficient way and there is minimal flaring of digester gas.

The treatment plant is now almost self sufficient in electricity, significantly reducing operating costs.

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