Pressure-driven membrane nutrient preconcentration for down-stream electrochemical struvite recovery

Abstract

Nutrient recovery from wastewater is a sustainable solution to combat the harmful release of nutrients to the environment. Here, we investigate nutrient recovery from wastewater by pre-concentration of wastewater nutrients using pressure-driven membranes prior to downstream electrochemical nutrient precipitation. When using electrochemical struvite precipitation, a higher nutrient concentration leads to a higher precipitation efficiency. Therefore, we investigate the performance of commercial nanofiltration (NF) and reverse osmosis (RO) membranes with different polymer chemistry and molecular weight cut-offs (MWCO) and discuss the membrane selection based on design goals and wastewater compositions for maximum nutrient recovery efficiency. Our results indicated that the Alfa membrane, a polyamide thin film composite (PA-TFC) NF membrane with 300 Da MWCO has the highest concentration factor in phosphorus (P) preconcentration among all the membranes studied due to the high flux and removal efficiency. BW30LE (PA-TFC, 100 Da), Synder (PA-TFC, 100–250 Da) and NF90 (PA-TFC, 200–400 Da) achieved a high concentration factor for nitrogen (N) recovery. NF90 and Synder NF membranes are able to achieve a nitrogen concentration factor similar to BW30LE RO membrane at much lower energy consumption. A multistage membrane system design is suggested using the selected membranes for effective nutrient recovery. Life cycle assessment (LCA) was conducted to characterize the environmental impact of the multistage membrane nutrient recovery system. Among the different process configurations of the selected membranes, key trends included: 1) environmental impacts across most categories increased as the number of membranes increased, and 2) as the amount of fertilizer substitute that could be produced in a given configuration increased, total environmental impacts decreased with some exceptions.