Integrated biological-chemical system for phenol removal from petrochemicals wastewater

Phenol is a highly concerning pollutant in petrochemical industrial wastewater. It is extremely poisonous, carcinogenic, and persistent, therefore, it bioaccumulates in the food chain reaching humans, where it causes acute irritation to the skin, eyes, and respiratory tract, as well as chronic effects on the liver, kidneys, and nervous system. It spills or leaks easily into surface water or groundwater sources, leading to the creation of other harmful substituted compounds. Therefore, the present study aimed to design an integrated biological-chemical system (phenol degrader(s) and nanoparticle assemblage) for the efficient removal of phenolic compounds from wastewater of a poly-vinyl chloride production unit at a petrochemical company in Alexandria. Ten indigenous microbial isolates were obtained from phenol-contaminated wastewater and purified. Two fungal isolates were excluded, and eight bacterial isolates were screened for their efficiency in the degradation and removal of phenol. Three isolates (Stutzerimonas chloritidismutans strain AW-1 (A2), Stutzerimonas stutzeri ATCC 17588 = LMG 11199 (A4), and Arthrobacter ruber strain MDB1-42 (A9)) proved to be the most promising candidate(s) and were investigated as individual and mixed cultures. The mixed culture (A2, A4, and A9) proved to be the most efficient, and could achieve 98.85, 31.08, 45.83, and 45.83% removal of phenol, chemical oxygen demand (COD), biochemical oxygen demand (BOD), and total dissolved solids (TDS), respectively (all below their maximum permissible limits (MPLs)), for discharge or reuse. The bacterial consortium was decorated with the synthesized and characterized Fe₃O₄ Nanoparticles (NPs) at 1:3 (g/g), the optimum ratio for coating and immobilization (94.22%) of the bacterial consortium. Fe₃O₄ NP/bacteria assembly (trial 1) showed the highest RE of 20, 56.66, 47.06, 25.16, and 96.78% for TDS, total suspended solids (TSS), BOD, COD, and phenol, respectively, all after only 1 h except TSS (2 h), compared to the treatment with undecorated bacterial consortium (trial 2) or bacteria-free Fe₃O₄ NPs (trial 3). It is concluded that the proposed treatment system (Fe₃O₄ NP/bacterial assembly) is an extraordinarily effective, practical, quick, clean, renewable, long-lasting, ecologically friendly, and simply implemented technology for remediating phenol-contaminated wastewater compared to other conventional treatment methods. Concerning TSS, COD, and phenol residues that are still higher than their MPLs, it can be easily overcome by increasing the exposure (contact) time or the dose of the Fe₃O₄ NP/bacterial assembly, using multiple units of the proposed treatment in sequence, or fixing the decorated bacteria as a biofilm system and treating the effluent in a continuous mode.