Petrochemical wastewater treatment in a full-scale biological aerated filter system: Insight into the mechanism of performance deterioration

Advanced petrochemical wastewater treatment using a biological aerated filter (BAF) system occasionally deteriorates in practical application, and the underlying mechanism is not fully understood. In this study, a full-scale BAF reactor treating petrochemical wastewater exhibited an expected decrease in chemical oxygen demand (COD) removal efficiency, from 50.1 % to 30.0 %. To investigate the deterioration mechanism, the physical and chemical characteristics of the granular activated carbon (GAC) filler were analyzed, along with the microbial community in the attached biofilm. It was observed that the surface area and pore volume of GAC decreased by 25 %–51 % and 38 %–42 %, respectively, due to calcium carbonate, suspended solids, and salinity deposition, indicating severe scaling and blockage of the GAC. Furthermore, laboratory-scale BAF experiments further confirmed the above conjecture. Metagenomic analysis demonstrated that functional pathways related to regulating organic matter degradation (from 5.40 % to 4.93 %), biofilm synthesis (from 3.39 % to 3.10 %), and bacterial proliferation (from 6.62 % to 5.82 %) were all downregulated. Additionally, the abundance of functional microorganisms, including Rhodococcus (5.7 %), Acidovorax (3.3 %), Hydrogenophaga (2.2 %), and Pseudomonas (1.7 %), dramatically dropped to below 0.1 %. The imbalance in the microbial community and functions caused the declining organic removal in the full-scale BAF system. Overall, these findings are useful to understand the mechanism of BAF performance deterioration and propose advice for the practical application of BAF.