Quantifying Pentachlorophenol Inhibition in an Aerobic Sequential Batch Reactor: Microbial Toxicity and Process Performance Decay

Across the world, pentachlorophenol (PCP) is used as a pesticide in agriculture and is considered one of the worst environmental pollutants. In this study, an Aerobic Sludge Sequential Batch Reactor (ASSBR) has been utilized to investigate the possibility of the biological removal of Pentachlorophenol. A 10 L reactor with different concentrations of PCP (100 and 130 mg/L) was considered for the experiment. After establishing stable conditions in 8 months, sampling and testing of parameters such as pH, COD, BOD, MLSS, and TSS, as well as the effect of pentachlorophenol on them, were performed. The results showed that in 100 mg/L of PCP, the COD removal efficiency was approximately 75% (772 to 193 mg/L), and in 130 mg/L of PCP, the COD removal efficiency was 56% (824 to 360 mg/L). Additionally, the influence of pH on PCP toxicity was assessed in batch tests at pH 5–5.5. By increasing PCP, the MLSS decreased from 2390 mg/L to 1125 mg/L. On the other hand, with the addition of pentachlorophenol, the specific oxygen uptake rate (SOUR) and SVI have also been measured. These results show that although SBR can remove pentachlorophenol compounds, increasing the amount of pentachlorophenol in the sewage system results in the loss of activated bacteria, leading to a decrease in the SOUR, a reduction in sludge mass, and a decline in the removal efficiencies of both COD and BOD. • Effective biological removal of PCP using an ASSBR, achieving up to 75% COD removal efficiency. • Higher PCP concentrations lead to decreased removal efficiencies for COD, BOD, and TSS in a reactor. • Optimization of pH and retention time enhances microbial activity and treatment performance in ASSBR. • PCP concentration negatively affects microbial populations, reducing MLSS. • Dual impact of PCP on removal efficiency and microbial toxicity informs future wastewater strategies.