Advanced energy and phosphorus recovery of organic sludge by the integration of a high-solid AnMBR and HAP-based PN/A process

Conventional treatment systems are strained by increasingly complex organic residues. A paradigm shift is needed to transform wastes into feedstocks for integrated biorefineries by coupling anaerobic carbon capture, autotrophic nitrogen conversion, and mineral-based phosphorus recovery under low-carbon conditions. 

My research aimed to establish an energy-generating, low-carbon resource recovery system suitable for the reclamation of concentrated organic sludge. The system consisted of (1) high-efficiency anaerobic digestion using a high-solid anaerobic membrane bioreactor (AnMBR) and (2) nitrogen removal and phosphorus recovery using a hydroxyapatite (HAP)-based one-stage partial nitritation and anammox (PN/A) process. The high-solid AnMBR was continuously operated to investigate bioenergy production, and digestion efficiency was enhanced by optimizing the solid retention time (SRT). The degradation efficiency of the substrate improved from 36 % to 52 %, and the biogas yield increased from 0.37 to 0.51 L/g-VS when the SRT was extended from 30 to 60 d. The HAP-based one-stage PN/A reactor operated at a nitrogen loading rate of 0.73 kg-N/m3/d, achieving a nitrogen removal efficiency of 81.6 %. Phosphorus removal efficiency was significantly enhanced by calcium addition, and a maximum value of 73.2 % was achieved when the influent Ca/P ratio was 2.7. The energy recovery rate reached 100.2 kWh/m3, and the system’s energy self-sufficiency rate was 173 %. This research advances the development of an innovative "AnMBR+" technology, addresses existing challenges, and promotes the decarbonization of sludge treatment plants and promising resources production.