Struvite recovery from microbial fuel cells treating different nutrient-rich wastewaters

Wastewater is an abundant renewable source of nutrients such as nitrogen and phosphorus. However, current recovery methods require substantial amounts of energy and chemicals, which pose various economic and environmental burdens. Microbial fuel cells (MFCs) represent a feasible alternative for nutrient recovery from wastewater as they reduce the cost of chemicals and energy input while producing electricity from treated organics. Despite the promising benefits of MFCs, there is limited knowledge of the effect of substrate type on their operation and nutrient recovery. Therefore, this study investigates the efficiency of struvite formation for nutrient recovery in 700-ml-volume dual-chamber MFCs using various wastewaters: urine, centrate, and greywater (laundry and dishwasher wastewater). The performance was assessed based on electricity output, organics removal in terms of soluble chemical oxygen demand (SCOD), and struvite recovery. The highest SCOD removal efficiency of over 95 % was achieved with the centrate-fed cell. Moreover, the highest maximum power densities generated from the urine, centrate, and greywater-fed MFCs were 1.7, 1.5, and 0.95 mW/cm², respectively. In terms of struvite recovery, the urine-fed cell produced the highest struvite precipitate quantity (2.1 g/l), followed by the centrate (1.8 g/l) and the greywater (0.4 g/l). The phosphate recovery efficiencies were 55, 36, and 48 % for the MFCs treating urine, centrate, and greywater, respectively. Morphological and chemical analyses of the formed precipitates confirmed that the nutrients were recovered primarily as struvite. Overall, the results and conclusions of the present study support the potential for utilizing MFCs for nutrient recovery and energy generation.