Biogas Production from Algae Biomass Harvested at Wastewater Treatment Ponds

Waste-grown microalgae are a potentially important biomass for biofuel production. However, most of the 7,000 wastewater treatment ponds systems in the US do not use algae harvesting. Those that do, typically return the biomass to the ponds, where it decomposes on the pond floor, releasing methane to the atmosphere and degrading water quality. Instead, the algae biomass could be processed in anaerobic digesters. Algae typically yield less methane than wastewater sludge (~0.3 vs. 0.40 L CH4/g volatile solids introduced). Ammonia toxicity and recalcitrant cell walls are commonly cited causes of the lower yields. Ammonia toxicity might be counteracted by co-digesting algae with high-carbon organic wastes. This paper describes the state of the current literature on algae digestion and presents new data on co-digestion with organic wastes. The focus of the project is to identify the essential information required for full-scale implementation of algae co-digestion at wastewater treatment plants, including the optimal conditions to maximize the methane yield, the volumetric methane productivity, and net energy production