Abstract: The wastewater generated from tomato sauce processing in Xinjiang exhibits high concentration, challenging treatment, and potential for surface water pollution. Therefore, studying the degradation technology for tomato sauce wastewater treatment is of significant importance. In this study, floc sludge was inoculated into two sequencing batch reactors (SBR), R1 and R2, at room temperature. Artificially prepared tomato sauce wastewater was used as the influent substrate to cultivate aerobic granular sludge (AGS) under varying influent chemical oxygen demand (COD) concentrations. The aim was to investigate the effects of influent COD concentration on AGS morphology, physicochemical characteristics of the sludge, and pollutant removal efficiency. The results demonstrate that with a fixed COD concentration of 350 mg/L in the gradient influent, the particle diameters of the sludge in R1 and R2 after complete granulation were measured as 780 μm and 1 060 μm, respectively. The average removal rates of COD, NH₃-N, TN, and PO^3-₄-P in the tomato sauce wastewater were as follows: R1 (95.2%, 96.03%, 85%, 92.07%) and R2 (93%, 89.54%, 78%, 89%). For influent COD concentrations ranging from 346 to 750 mg/L, 750 to 900 mg/L, and 900 to 1 200 mg/L, the granular morphology consisted of filamentous bacterial skeletons, porous structures, and agglomerates. Ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) predominantly existed in the outer and subouter layers of small-sized AGS particles, while polyphosphate-accumulating organisms (PAOs) and glycogen-accumulating organisms (GAOs) were mainly found in larger particles at the bottom of the reactor.Under constant gradient influent COD concentration, a high influent COD concentration contributed to the rapid formation of AGS and the enrichment of microbial communities responsible for nitrogen and phosphorus removal, consequently enhancing the system’s nitrogen and phosphorus removal performance.

Key words: aerobic granular sludge, gradient inflow, decontamination performance, sequencing batch reactor, tomato sauce processing wastewater