Integrating chemical precipitation and membrane separation for phosphorus and ammonia recovery from anaerobic digestate

This study focuses on developing and demonstrating feasibility of an integrated chemical precipitation and membrane filtration method for recovering phosphorus (P) and ammonia (NH3‐N) in two separate streams from anaerobic digestate generated from municipal wastewater. Nutrient recovery from waste streams creates alternative raw material sources of fertilizers and offers opportunities for reduced energy usage and CO2 emissions compared with their conventional production processes. Using both synthetic and real anaerobic digestates, the effects of ferrous dosage and precipitation pH on P recovery through vivianite precipitation was examined. Fe/P molar ratio 2.1 at circumneutral pH was found as an optimal condition for ~100% P recovery. The P‐free digestate was further treated with polyelectrolyte‐modified nanofiltration (NF) membranes to separate NH3‐N and the organic constituents as a means of N recovery. The surface‐modified membranes demonstrated ~2X NH3‐N/organic carbon selectivity versus commercial NF membranes. This integrated Fe‐enabled chemical precipitation and membrane‐based process demonstrates a unique approach to sustainably recover critical nutrients from wastewater.