Forward osmosis with an algal draw solution for wastewater concentrating and polishing
Forward osmosis (FO) is an emerging wastewater treatment technology capable of high solute rejection by separating water from wastewater across a semi-permeable membrane. However, there is always leaking of ammonium from the feed solution (FS) to the draw solution (DS). Parallel bench-scale FO systems were operated with synthetic municipal wastewater as an FS. Both systems had a synthetic seawater DS with one system also inoculated by an algal species (Chlorella Vulgaris) to act as an absorbent (polishing agent). At the completion of three consecutive trials (lasting a total of three days), ammonium removal efficiency in the algae-based FO system improved by 35.4 ± 4.6%. Throughout the fed-batch operation in the DS chamber, the algal biomass concentration was maintained at 606 ± 29 mg/L due to simultaneous algal growth and dilution. The water flux gradually decreased from an average initial flux of 16.5 LMH to an average of 8.2 LMH after each trial operation, with an average water flux of 11.63 ± 0.49 LMH compared to 12.05 ± 0.35 LMH in the system without algae. Meanwhile, organic matter and phosphorus were completely retained in the FS in both systems. At the completion of each trial operation, the concentrations of chemical oxygen demand (COD) and phosphorus in the synthetic wastewater increased by an average of 44%. This work highlights the dual-benefit applications of algae-based FO with improved effluent water quality and concentrated wastewater COD and phosphorus for potential water resource recovery and water reuse.