From Treatment to Platform: Coupling Anaerobic Carbon Conversion with Nitrogen Removal and Phosphorus Recovery toward Circular Urban Biorefineries

Abstract

Resource recovery and nutrient management from organic waste streams are receiving more attention. Water and resource recovery facilities (WRRFs) are expected to support need-driven resource recovery at practical scale, with acceptable costs and reduced greenhouse gas (GHG) emissions. In many WRRFs, anaerobic digestion (AD) is widely implemented along the solids line for energy recovery and is frequently coupled with sidestream deammonification processes, such as partial nitritation/anammox (PN/A), to treat ammonium-rich flows from sludge dewatering. (1) In addition, phosphorus recovery is becoming an important component of resource recovery, with physicochemical units commonly installed for phosphorus precipitation and biological oxygen demand reduction before sidestream treatment. This configuration has enabled progress in resource recovery, but it remains largely fragmented and sidestream-centric. Carbon, nitrogen, and phosphorus removal and recovery are still optimized primarily in separate process units, with limited design attention given to how the quality of the anaerobic effluent affects subsequent nitrogen removal, phosphorus recovery, and emissions control. As a result, energy costs and GHG emissions are determined by not only biological conversion but also the energy demands for the thermal hydrolysis process (THP), aeration, chemical conditioning, and sidestream operation. The central challenge is therefore no longer simply to improve isolated unit operations, but to couple upstream carbon valorization with downstream low-carbon nutrient management within a coherent treatment framework.