Effectiveness and mechanism of using PBS-ZVI carriers to enhance granulation in UASB reactors for coking wastewater treatment.

Slow anaerobic granulation and poor shock load resistance in up-flow anaerobic sludge blanket (UASB) reactors present significant challenges in treating difficult-to-degrade coking wastewater. In this study, we developed a novel poly(butylene succinate)-zero-valent iron (PBS-ZVI) carrier (KT) and examined its effects on anaerobic granulation and shock load resistance. The addition of KT increased the quantity of anaerobic granular sludge (AGS) larger than 1 mm in the UASB by a factor of 2.33, which enhanced its shock resistance and enabled rapid recovery within 8 days following shock loading. During shock events, the KT reactor's COD removal rate, methane conversion rate, and methane production rate were 0.78 times, 3.12 times, and 6.32 times higher than those of the control reactor, respectively. PBS and ZVI acted synergistically to accelerate the anaerobic granulation process. The PBS in the KT carriers improved the affinity of microorganisms for iron, leading to enhanced microbial retention and a 33 % increase in electron transfer system activity compared to the control. Furthermore, ZVI promoted the secretion of proteins and extracellular polymeric substances from AGS. During shock events, the key functional microorganisms in the KT system were identified as Gaiellales, whose relative abundance was 3 times higher than that in the control reactor, effectively resisting shock loading. The AGS in the KT system secreted lactate dehydrogenase at 27.5 % of the control level and higher levels of ABC transporter proteins, indicating that the KT system is effective in mitigating the toxicity of coking wastewater on cells.