Investigation of algal cultivation and anaerobic co-digestion of sewage sludge and algae at wastewater treatment plant (WWTP)

Micractinium and Chlorella, harvested from local WWTP, were cultivated in primary effluent, sludge centrate, and their combination. Continuous light condition (24hr light) and periodic light (16hr light/8hr dark) were provided to investigate the behavior of these two algal species in different growth media. Primary effluent supported better growth of both algal species, and also led to higher soluble nitrogen (84-92%) and phosphorous (59-74%) removal. The specific growth rates in all media were low due to the phosphorous-limited condition. Microalgae posed different growth characteristics in real wastewater and resulted in different amount of extracellular polymeric substances (EPS). High amount of EPS helps algal aggregation. Co-digestion study showed that addition of microalgae did not bring negative effects on anaerobic digestion of sewage sludge. These results indicated that microalgae-based process has potential to decrease nutrient loads along with bioenergy production by coupling algae cultivation into wastewater treatment systems with anaerobic digesters.