Aerobic granular sludge treating tannery wastewater and particle size control

Aerobic granulation of tannery wastewater was successfully accomplished in sequencing batch reactors, with R1 employing a conventional aeration head and R2 utilizing a spiky-type aeration head. The brief settling time of five minutes, along with the influent’s high concentrations of elements such as calcium, magnesium, phosphorus, and iron, were critical factors influencing the formation of aerobic granules. The findings indicated that granules were successfully cultivated in reactors R1 and R2 by day 36 and day 40, respectively. By the 60th day of operation, the mean particle sizes for R1 and R2 were 469.6 ± 31.4 and 390.3 ± 22.8 μm, respectively, with corresponding SVI5 values of 43.6 and 46.2 ml/g. The implementation of a spiky-type aeration head proved effective in mitigating the increase in particle size by continuously shearing the granular sludge. During the entire granulation process, both systems demonstrated enhanced pollutant degradation capabilities, achieving removal efficiencies of ∼85% for COD, 80% for NH4+–N, 70% for TN, and 60% for TP after 60 days of operation. Notable alterations were observed in extracellular polymeric substances and microbial communities, with a substantial increase in the relative abundance of Proteobacteria, rising from 46.45% in the inoculum sludge to 80.98% in R1 and 75.86% in R2. This increase played a pivotal role in the granulation process.