Formation and Characterization of Aerobic Granular Sludge in the Treatment of Tempering Lubricant Wastewater by Hydrolysis Acidification-Aerobic Process

Tempering lubricant is widely used for the surface treatment of cold rolled strip in steel industry. The used tempering lubricant, along with the process rinse water, was referred to as tempering lubricant wastewater (TLW). TLW is characterized as high concentration of organic matter and total nitrogen (TN), and poor biodegradability, which is rarely treated independently. In this study, the performance of combined hydrolysis acidification-aerobic process for treating real TLW was assessed. A thorough investigation was undertaken to explore the formation process and characteristics of aerobic granular sludge (AGS) in the aerobic reactor. In addition, the characteristics of microbial community were analyzed. The results of 210 days monitoring showed that the hydrolysis acidification-aerobic process had a good effect on the treatment of TLW, with final Total organic carbon (TOC) and TN removal efficiencies reaching 84.8% and 86%, respectively. Meanwhile, AGS was formed in the aerobic reactor, with the proportion in the sludge of 86%. It was also found that higher organic loading rate contributed to AGS formation, while a shorter settling time enhanced the formation of compact and stable AGS. In addition, continuous increase in the consumption of Ca2+ and Mg2+ also promoted the granulation process of AGS. Proteobacteria, Bacteroidota, and Firmicutes were enriched in the hydrolysis acidification reactor, which were beneficial for refractory organic substances degradation. The abundance of Comamonadaceae increased in the aerobic reactor and contributed to TN removal.