Potential contributers of the wastewater sector to New Zealand's energy supply

Wastewater treatment can either be energy intensive, or provide an energy resour ce. A small shift in the selection of treatment technologies can significantly affect the energy profile of the NZ wastewater sector. Based largely on analysis undertaken by the EnergyScape programme, a model was developed to test the upper limits of the potential energy contributions of the wastewater sector from currently available technologies, such as: anaerobic digestion, fermentation and algal production. The model identified that the upper limit of technologically feasible energy resource potential from current wastewater flows was: 0.91 PJ/y (~253 million kWh/y) electricity; 1.09 PJ/y boiler fuel / heat; 1.04 PJ/y (~27 million litres diesel equivalent) gaseous transport fuel (compressed bio-methane), and 0.70 PJ/y (~32 million litres) liquid transport fuel (bio-ethanol). This study suggests that New Zealand has much to benefit from a better understanding of available wastewater treatment options – be that in the form of energy self-reliance, energy storage or economic return. Increased uptake of energy yielding wastewater treatment technologies is likely to be dependent upon either: high fossil fuel prices; sustained government incentives for the use of alternative energy; or regulatory requirements for improved control of odour, GHG emission and nutrient discharge.