Electrified Nutrient Recovery at Municipal Wastewater Facilities: Sampling, Screening and Multivariate Analyses

Municipal wastewater facilities can contain recycle streams with high nutrient content, that both increase the overall energy consumption in the facility and cause environmental pollution when not properly handled. Reducing the nutrient load of these streams through recovery is a promising solution that enhances the Food-Energy-Water nexus by producing sustainable fertilizer. In this study, the potential for nutrient recovery at municipal wastewater facilities was investigated through a 1-year sampling of nutrient, ionic, organic and heavy metal composition of three wastewater streams influent to or effluent from two types of digesters. Subsequently, electrochemical nutrient recovery was evaluated for these streams through multivariate screening of three groups of variables – operational, stream and design – and the effect of these variables on optimal nutrient recovery in the form of phosphorus. Results showed that Orthophosphate (Ortho-P) and ammonia concentrations do not show significant correlation in any tested streams. On the other hand, major ions exhibited interdependence with Ortho-P concentration, while the stream pH was found to correlate with Ortho-P and Cl- in the anaerobic digester effluent. Screening analyses identified 5 – anode type, cathodic potential, initial P concentration, initial NH4+ concentration and temperature – of the 11 variables evaluated were the variables that most significantly affected P recovery efficiency and specific energy consumed during this recovery. Finally, the optimum conditions for high phosphorus recovery and low energy consumption from the anaerobic digester effluent during a 2-hour experiment were a cathodic potential of -0.805 V vs Ag/AgClsat, an electrode area to electrolyte volume ratio of 0.145 1/cm, and a temperature of 41.3°C, with a solid product that was predominantly struvite. Overall, the demonstrated 95% P recovery efficiency and 0.03 kWh/kg P are characteristic of an emerging process that could be competitive at scale with state-of-the-art synthetic nutrient routes, if applied to the right stream.