Whangarei waste water treatment plant cogeneration unit
Whangarei District Council’s waste water treatment plant is relatively small, treating the wastewater of some 55,000 residents.
Methane – a by-product of the waste water treatment process known as biogas – was being flared off but is now used to simultaneously generate electricity and hot water – a process known as cogeneration.
Cogeneration is an underused technology in New Zealand.
The technology demonstration project
Larger waste water treatment plants commonly use cogeneration systems, but this project aimed to show the technology successfully working on a small scale.
Methane biogas was used to generate electricity and heat water with a spark ignited internal combustion engine developed by Shaw Diesel.
This engine, known as a cogeneration unit, demonstrates the commercial viability of a small-scale waste-to-energy unit at the treatment plant.
The engine is a General Motors 540 cubic inch V8 imported new from America and optimised to run on biogas by Shaw Diesels.
Waste methane is now used to generate electricity, supplying around 20-30% of the plant’s requirements, and heat water used as part of the sewage treatment process.
EECA helped fund the project to test an underused technology on behalf of New Zealand, with a lower investment risk.
Key benefits achieved through the project:
- Energy Savings: $60,000 worth of electricity a year.
- Finding value for methane that had previously been flared off, releasing a harmful gas to the atmosphere.
- Water heating through the unit’s heat recovery process has enabled the plant to shut down a biogas boiler.
- If not needed on site, electricity generated can be fed back into the grid.
- The plant will purchase a second cogeneration unit.
Four and six-cylinder engines are available for situations with lower methane volumes.