Biodegradation of Heterogeneous Pollutants in Hybrid MBBR System: Resilience Assessment under Different Shock Stress Conditions

The sudden increase in phenol concentrations is frequently observed in coke-oven, petrochemical, and petroleum refinery waste streams due to changes in process parameters, posing challenges for the biological treatment processes due to the combined toxic effects of phenol with other inorganic pollutants present in the same wastewater. Owing to that fact, the versatility of the designed biological treatment system against multiple shock loading conditions needs to be analyzed before field-scale implementation. Therefore, this study aims to investigate the stability of a continuous hybrid moving bed biofilm reactor (MBBR) system against multiple and extreme phenol shock stress conditions and its impacts on the degradation of each pollutant (phenol, NH₄–N, ${\mathrm{SO}}_4^{2-}$, and NO₃–N) present in the wastewater under different metabolic conditions. The continuous hybrid system comprises three different MBBR units, such as anaerobic (CM₁), anoxic (CM₂), and aerobic (CM₃) units, connected in series and operated at 2.11 days. The system was exposed to 3,500, 4,000, and 5,000 mg/L of phenol shock loads in the presence of NH₄–N (300 mg/L) and ${\mathrm{SO}}_4^{2-}$ (200 mg/L) during Shock Phases I, II, and III, respectively. In Phase IV, the degradation performance of the system was further analyzed with 5,000 mg/L of phenol and two subsequent doses of NH₄–N (350 and 400 mg/L) to assess the system’s stability under multiple pollutant stress conditions. The system was completely recovered from the 3,500 and 4,000 mg/L of phenol stress conditions within a recovery period of 14 days, in Phases I and II. However, the ${\mathrm{SO}}_4^{2-}$ and NH₄–N removal was inhibited in CM₁ and CM₃ reactors, respectively, due to the exposure of the high concentration of phenol (5,000 mg/L). The performance of CM₁ and CM₂ was severely affected in Phase IV, even after stopping the feed. Nonetheless, CM₃ removed all the phenol from the wastewater in Phase IV, which reflects the dominance of heterotrophs. The hybrid MBBR system could withstand up to 4,000 mg/L of phenol shock load and achieved 100%, 97%, 69%, 93.51% of phenol, NH₄–N, ${\mathrm{SO}}_4^{2-}$, and NO₃–N removal during the recovery period, respectively.

An abrupt change in pollutant concentration in waste streams is often observed, which becomes a stumbling block for secondary biological treatment processes due to the toxic effect. However, studies related to the treatment of multiple pollutants and achieving stable removal efficiency using a biological treatment system under multiple shock loading conditions are limited. This study shows the potential of a continuously operated hybrid MBBR system for simultaneous removal of heterogeneous pollutants (phenol, NH₄–N, NO₃–N, and ${\mathrm{SO}}_4^{2-}$) under various phenol and ammonia shock loading conditions. The results obtained from this lab-scale study could be helpful for the practitioners in designing integrated treatment systems to treat the real coke-oven and petroleum refinery effluent. The system achieved stable and higher removal efficiency for the multiple pollutants-bearing wastewater under various shock loading conditions.