Australian pork producers are increasingly adopting covered anaerobic lagoons to manage greenhouse gas (GHG) emissions and recover the methane from biogas for energy production, according to research.
Algal biomass produced in high-rate algal ponds (HRAP) treating piggery wastewater can remove CO2 and is also an additional source of energy, which could be released via anaerobic digestion or co-digestion with pig slurry.
While other wastes such as industrial organic wastes, fruit, vegetables and olive wastes are commonly co-digested, there have been limited studies on the digestion of algal biomass as a sole substrate or co-digested with other wastes such as pig slurry.
Dr Ryan Cheng, a higher degree research student at Flinders University, has published a thesis called Exploitation of wastewater grown microalgae for the production of biogas, which investigates the effect of CO2 addition on algal growth and methane production.
In Dr Cheng’s PhD research, a laboratory approach was used to examine the effect of the addition of CO2 on the growth of microalgae in wastewaters of three different strengths determined by their biochemical oxygen demand (BOD).
According to his PhD supervisor, Prof Howard Fallowfield, his results question whether adding CO2 enhances algal production in all types of wastewater.
Co-digestion of pig slurry with algal biomass resulted in a slightly higher methane yield.
“Results demonstrated that adding CO2 did not increase biomass production in wastewaters rich in organic carbon, since the CO2 produced by bacterial mineralisation, adequately supported optimal biomass production,” Dr Cheng said.
“My research ultimately provided a better understanding of how to achieve integration of algae and wastewater treatment by determining if it is necessary to supply external CO2 and evaluating the outcome of anaerobic co-digestion of algal biomass with pig slurry or waste activated sludge.”