Carbon dioxide addition can improve quality of wastewater

Carbon dioxide addition can improve the quality of wastewater

March 4, 2015

A NIWA scientist undertaking doctoral biological research at the University of Canterbury has been exploring how carbon dioxide can improve the quality of wastewater.

Water quality in New Zealand is deteriorating due to increased nutrient loads from human activities, including urban and agricultural development. As a result there is a need for improved nutrient measures, particularly for nutrient removal from wastewater.

Dr Donna Sutherland says one option for better wastewater treatment and nutrient removal is the use of advanced wastewater treatment ponds that offer immediate solutions to nutrient mitigation.

“These ponds allow microalgae to grow profusely which enhances nutrient removal. They have been shown to be more effective and consistent than conventional wastewater treatment ponds currently used in New Zealand,” Dr Sutherland says.

“Another advantage of the advanced ponds is the ability to recover resources which can be used for fertiliser, animal feed or biofuel production. Current low fossil fuel costs preclude the use of biofuel production alone, but when coupled with wastewater treatment the conversion to biofuel could provide a valuable energy source for communities as an alternative to fossil fuel.

“However, increasing biomass and reducing capital costs is still regarded a top priority to make microalgal biofuel a commercial reality. Microalgal photosynthesis, nutrient uptake and subsequent growth, coupled with aerobic bacteria degradation of organic compounds, are fundamental to the process of wastewater treatment in advanced ponds.

“Understanding how the physio-chemical environment affects microalgal performance is critical to improved wastewater treatment and nutrient recovery. I have been researching how the photosynthetic performance of microalgae and nutrient uptake could be improved through simple modifications such as adding carbon dioxide, influent dilution, pond depth, hydraulic retention time, mixing speed and frequency.”

Dr Sutherland’s study demonstrated that carbon is the primary limiting factor and light is the secondary limiting factor of microalgal performance in full-scale wastewater ponds. The results have demonstrated that the simple addition of carbon dioxide had the greatest influence on light absorption, photosynthetic efficiency and microalgal productivity, while continuous mixing had the greatest effect on nutrient removal efficiency.

Her research was funded as part of the National Institute of Water and Atmospheric Research (NIWA) programme Algal Biofuel Energy from Wastewater and was supervised by the Head of the School of Biological Sciences Professor Matthew Turnbull and Dr Paul Broady.

© Scoop Media