A novel system of two-stage partial nitritation/hydroxyapatite (HAP)-anammox treating effluent of anaerobic membrane reactor: Performance, elemental flow and nutrient recovery potentials

As a measure towards achieving carbon neutrality and sustainability in the wastewater treatment industry, an autotrophic PN/HAP-A (airlift reactor/EGSB reactor) system is proposed in this study. The undiluted effluent from an AnMBR digesting municipal organic waste was applied for the practical validation of the system. With continuous feeding mode, the high efficiency, stability and operational simplicity were confirmed. In both reactors, the sludge manifested macro-aggregates and HAP-anammox granules with a satisfactory settling velocity and well-functional microorganisms. The alkalinity/IC consumptions and the buffer capacity were given individually and systematically. The elemental flow and potentials of precipitations indicated the high possibility and viability of phosphorus recovery by the formation of HAP, and in turn, the accumulation of precipitates in the biomass enhanced the settling velocity of the sludge. It is confirmed that the PN/HAP-A system is a promising approach to achieving nitrogen removal and phosphorus recovery from high-strength wastewater.