Advanced algal-osmosis membrane system for resource recovery of municipal wastewater: technical, economic and life cycle assessments

Abstract:

A dual algal-osmosis membrane treatment system was studied for the recovery of biomass, fertilizer, and potable-quality water from primary effluent. The core components of the integrated system include a mixotrophic algal process for removal of organic carbon (in terms of biochemical oxygen demand, BOD) and nutrients (measured as ammoniacal nitrogen, N; and phosphates, P) from the primary effluent, followed by a hybrid forward osmosis (FO)-reverse osmosis (RO) system for separation of biomass from the algal effluent and production of potable-quality water. In contrast to traditional wastewater treatment systems, mixotrophic metabolism of the algal system removes BOD and nutrients from the primary effluent through a single-step treatment and eliminates the input of aeration energy and supplemental carbon for denitrification. The field experiment demonstrated consistent performance of the algal system in meeting surface discharge standards for 5-day BOD, and nutrients in a fed-batch processing time of 2 to 3 days. Overall, the advanced algal-osmosis membrane system achieved complete removal of ammonia, fluoride, and phosphate; over 90% removal for calcium, sulfate, and organic carbon; 86-89% removal for potassium and magnesium. High resolution mass spectrometry and fluorescence excitation-emission matrix (FEEM) spectrophotometry were used to study the transport and fate of the organic contaminants in the algal and membrane processes. Broadband characterization using the high resolution mass spectrometry revealed broad removal of organic compounds, particularly wastewater surfactants upon algal treatment. The technical, economic, and life cycle assessments of the algal-osmosis membrane system in comparison with conventional secondary wastewater treatment and advanced membrane treatment processes demonstrated the algal-membrane system is highly attractive regarding technical viability, economic benefits, energy demand, and greenhouse gas emissions.