RECYCLING TREATMENT OF CONCENTRATED JOHKASOU SLUDGE BY INTEGRATING HIGH-SOLID ANMBR WITH ONE-STAGE HAP-PNA PROCESS

Abstract

 This research aimed to establish an energy-creating, low-carbon resource recovery system suitable for the reclamation of concentrated Johkasou sludge. The system consists of (1) high-efficiency anaerobic digestion using a high-solid anaerobic membrane bioreactor (AnMBR) for energy recovery and (2) nitrogen removal and phosphorus recovery using the HAP based one-stage partial nitritation and anammox (PNA) process. The high-solid AnMBR was continuously operated throughout a year to investigate the bioenergy production, material flow and seasonal impacts of concentrated Johkasou sludge. The greatest biogas production rate was observed during summer (0.63 L/L/d), owing to the high total organic and solid content. The material flow results revealed that 46.5–52.4% total COD and 50.2–58.0% carbon was converted to biogas. A hydroxyapatite-based one-stage partial nitritation/anammox (HAP-PNA) process was combined with an AnMBR treating concentrated organic sludge for permeate polishing, focusing on the enhancement of phosphorus recovery by influent Ca/P ratio optimization, alkalinity control and the effect of HAP formation on nitrogen removal. The reactor operated at the nitrogen loading rate of 0.73 kg-N/m³/d and realized 81.6% nitrogen removal efficiency (NRE) and 0.6 kg-N/m³/d nitrogen removal rate. The phosphorus removal efficiency (PRE) and sludge settleability were significantly enhanced by the addition of calcium, and a maximum PRE of 73.2% was achieved when the influent Ca/P ratio was 2.7. The reactor showed high stability and nitrogen removal performance, even when the phosphorus removal rate/nitrogen removal rate ratio was as high as 0.12. This study demonstrates the excellent capability of the one-stage HAP-PNA process for permeate treatment with high phosphorus content. The energy recovery rates ranged from 8.69 to 9.96 kJ/g-VSfed and the system energy self-sufficiency rates ranged from 149-203%. The results demonstrated that the innovative system yielded high energy conversion efficiency and could realize energy positive.