Sludge reduction and microbial community structure in an anaerobic/anoxic/oxic process coupled with potassium ferrate disintegration.

An anaerobic/anoxic/oxic (AAO) wastewater treatment system combining with a potassium ferrate (KFeO) oxidation side-stream reactor (SSR) was proposed for sludge reduction. Batch experiments showed that optimal KFeO dosage and reaction time for sludge disintegration was 100mg/g suspended solids (SS) and 24h, respectively. Subsequently, an AAO-SSR and a conventional AAO were operated in parallel to investigate effects of KFeO oxidation on process performance, sludge characteristics and microbial community structures. The AAO-SSR process operated under the optimized condition achieved efficient COD and NH-N removal, and reduced sludge by 47.5% with observed yield coefficient of 0.21gSS/g COD. KFeO addition broke sludge particles, increased dissolved organic matters in the mixed liquor, and improved sludge dewaterability. Illumina-MiSeq sequencing results showed that KFeO oxidation in the AAO-SSR decreased microbial richness and diversity, enriched slow growers (Dechloromonas), anaerobic fermentative bacteria (Azospira) and Fe(III)-reducing bacteria (Ferribacterium), but limited the growth of phosphate-accumulating organisms.