title: Impact of influent COD/N ratio on disintegration of aerobic granular sludge.
abstract: Disintegration of aerobic granular sludge (AGS) is a challenging issue in the long-term operation of an AGS system. Chemical oxygen demand (COD)-to-nitrogen (N) ratio (COD/N), often variable in industrial wastewaters, could be a destabilizing factor causing granule disintegration. This study investigates the impact of this ratio on AGS disintegration and identifies the key causes, through close monitoring of AGS changes in its physical and chemical characteristics, microbial community and treatment performance. For specific comparison, two lab-scale air-lift type sequencing batch reactors, one for aerobic granular and the other for flocculent sludge, were operated in parallel with three COD/N ratios (4, 2, 1) applied in the influent of each reactor. The decreased COD/N ratios of 2 and 1 strongly influenced the stability of AGS with regard to physical properties and nitrification efficiency, leading to AGS disintegration when the ratio was decreased to 1. Comparatively the flocculent sludge maintained relatively stable structure and nitrification efficiency under all tested COD/N ratios. The lowest COD/N ratio resulted in a large microbial community shift and extracellular polymeric substances (EPS) reduction in both flocculent and granular sludges. The disintegration of AGS was associated with two possible causes: 1) reduction in net tyrosine production in the EPS and 2) a major microbial community shift including reduction in filamentous bacteria leading to the collapse of granule structure.
authors.affiliation: Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China.
authors.forename: Jinghai
authors.initials: J
authors.lastname: Luo
authors.affiliation: Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China.
authors.forename: Tianwei
authors.initials: T
authors.lastname: Hao
authors.affiliation: Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China.
authors.forename: Li
authors.initials: L
authors.lastname: Wei
authors.affiliation: Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China.
authors.forename: Hamish R
authors.initials: HR
authors.lastname: Mackey
authors.affiliation: Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China.
authors.forename: Ziqiao
authors.initials: Z
authors.lastname: Lin
authors.affiliation: Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China; SYSU-HKUST Research Centre for Innovative Environmental Technology, Sun Yat-sen University, Guangzhou, China. Electronic address: ceghchen@ust.hk.
authors.forename: Guang-Hao
authors.initials: GH
authors.lastname: Chen
mesh_terms: D000332:Aerobiosis; D064751:Ammonium Compounds / Q000302:isolation & purification; D001419:Bacteria / Q000235:genetics / Q000254:growth & development; D001673:Biodegradation, Environmental; D057919:Biological Oxygen Demand Analysis; D001704:Biopolymers / Q000032:analysis; D019149:Bioreactors / Q000382:microbiology; D004275:DNA, Ribosomal / Q000235:genetics; D005427:Flocculation; D058465:Nitrification; D009584:Nitrogen / Q000737:chemistry*; D010316:Particle Size; D012722:Sewage / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D014865:Waste Disposal, Fluid
chemical_list: D064751:Ammonium Compounds; D001704:Biopolymers; D004275:DNA, Ribosomal; D012722:Sewage; D009584:Nitrogen
keywords: Aerobic granulation; Extracellular polymeric substances; Granule stability; Substrate COD/N ratio impact; Tyrosine