FeO_x@GAC catalyzed microbubble ozonation coupled with biological process for industrial phenolic wastewater treatment: Catalytic performance, biological process screening and microbial characteristics

Phenolic compounds are common ccontaminants in industrial effluents. In this study, a combined catalytic microbubble ozonation and biological process was developed and applied for efficient industrial phenolic wastewater (PWW) treatment. Catalytic activity of an iron-oxides (FeO_x) doped granular activated carbon (GAC) catalyst (FeO_x@GAC) in microbubble ozonation for PWW treatment was investigated. The results demonstrated that the FeO_x@GAC catalyzed microbubble ozonation (O₃/FeO_x@GAC) obtained significantly higher reaction rate constant (k₁ = 0.023 min^-1) in TOC removal compared to the bare GAC catalyzed microbubble ozonation (O₃/GAC, k₁ = 0.013 min^-1) and ordinary microbubble ozonation (k₁ = 0.008 min^-1). Destruction rate constant of phenolic compounds (k₂) was improved from 0.014 min^-1 (ordinary microbubble ozonation) to 0.025 min^-1 (O₃/FeO_x@GAC). The 60-min pretreatment of PWW by O₃/FeO_x@GAC process enhanced BOD₅/COD ratio from 0.31 to 0.76 and reduced the acute bio-toxicity by 79.2%. Screening and characterization of biological post-treatment processes were conducted among activated sludge process (ASP), up-flow anaerobic sludge blanket (UASB) and membrane bioreactor (MBR). UASB and ASP showed limited phenolic compounds removal of 35.4% and 57.0% with lower bio-toxicity resistance than MBR (94.9% phenolic compounds removal). The combined process O₃/FeO_x@GAC-MBR was thus developed and achieved high COD removal (98.0%) and phenolic compounds degradation (99.4%). PWW pretreatment by O₃/FeO_x@GAC process decreased membrane fouling rate of MBR by 88.2% by reducing proteins/polysaccharides accumulation in both extracellular polymeric substances and soluble microbial products. 16S rRNA high-throughput sequencing revealed the predominance of phylum Proteobacteria, class Alphaproteobacteria and genera Mycobacterium, Gordonia, Pedomicrobium & Defluviimonas in biological PWW treatment bio-systems. Pearson correlation coefficient and ANOVA analysis verified that Mycobacterium possessed high bio-toxicity resistance and was the main contributor to the biodegradation of phenolic compounds.