Science Centres: Energy

Giving biogas a good scrub

We are currently investigating biogas generation for energy production, using anaerobic ponds at Ruakura. In one recent experiment, with the University of Auckland, we tested ways to 'scrub' the gas.

The biogas produced in the anaerobic digestion phase of sewage treatment contains 50-70% methane. If you want to use biogas as a fuel, however, you generally need to remove corrosive impurities such as hydrogen sulphide and reduce carbon dioxide to improve engine efficiency.

Scrubbing usually involves expensive chemical methods, but we tested simple technologies that can be easily added to wastewater stabilisation pond systems with aerobic ponds, and particularly High Rate Ponds. The highly oxidising, alkaline pond water does the scrubbing. The most successful approach was a 'counter current pit' – a new approach to biogas scrubbing. At gas flow rates of up 1500 ml/min, the pit consistently reduced carbon dioxide levels from 40% to less than 5% (the detection limit of the method used).

Our experiments on biogas generation are continuing, funded by the Foundation for Research, Science & Technology. We will investigate how biogas scrubbing affects wastewater treatment efficiency, particularly ammonia removal, and the use of High Rate Ponds to scrub CO₂-rich exhaust gases from industry.