A novel anoxic/aerobic process coupled with micro-aerobic/anaerobic side-stream reactor filled with packing carriers for in-situ sludge reduction

Activated sludge process with anaerobic side-stream reactors (SR) in the sludge recirculation line can achieve in-situ sludge reduction. But sludge reduction efficiency (SRE) is limited with low cell lysis and particle organic matter hydrolysis rates under short hydraulic retention time of SR for practical application. This study firstly inserted alternating micro-aerobic/anaerobic conditions (AMAC) and packing carriers into SR with low hydraulic retention time for improving SRE. The effects of AMAC and packing carriers on sludge rheology properties, molecular characteristics of dissolved organic matter (DOM) and microbial communities were investigated. Results showed that AMAC coupled packing carriers achieved SRE by 51.09% with efficient effluent pollutant removal. AMAC specialized inactive particle organic matter hydrolysis and active cell lysis in the micro-aerobic and anaerobic SR, respectively. Packing carriers intensified this function division effect. This effect weakened colloidal entanglement of flocs. It intensified the cell lysis in mainstream aerobic tank, causing the accumulation of refractory lignins in DOM. The higher utilization of released bioavailable DOM decreased microbial activity. Overall, the improved SRE favored the declined DOM bioavailability by inserting AMAC and packing carriers in SR. The sludge reduction-related bacteria like slow growing (Dechloromonas), predatory (Norank_Saprospiraceae), and hydrolytic/fermentative bacteria (Chelatococcus, Pseudomonas, Tolumonas, and Unclassified_Bacteroidia) were involved in decreasing DOM bioavailability. This study advanced our knowledge about the effects of AMAC and packing carriers on in-situ sludge reduction systems. This research also showed how AMAC and packing carriers enhanced the sludge lysis/hydrolysis for sludge reduction.