Mixotrophic algal system for centrate treatment and resource recovery

Abstract In traditional activated sludge-based wastewater treatment plants equipped with anaerobic digesters, the nutrient-rich centrate from the digester is typically recirculated to the headworks of the plant exerting a parasitic load. As an alternative, mixotrophic algal cultivation in a blend of the centrate and primary effluent is proposed to yield energy- and nutrient-rich biomass from which, liquid biofuel and fertilizers could be recovered. Core components in the proposed sewage treatment and resource recovery (STaRR) system include i) algal sewage treatment/biomass cultivation; ii) hydrothermal liquefaction of algal biomass for energy recovery, and iii) recovery of struvite and concentrated ammonia from the hydrothermal liquefaction byproducts. Results from a 700 l pilot-scale STaRR system run with four different blends of centrate and primary effluent are presented to validate the proposed approach. A 20: 80 centrate-to-primary effluent blend enabled discharge standards for ammoniacal‑nitrogen, phosphate phosphorus, and biochemical oxygen demand to be met in