Bioenhancement mechanism of PVA-SA immobilized composite strains Alishewanella fetalis and Exiguobacterium profundum in pyridine degradation

Coal chemical wastewater (CCW) represents a type of recalcitrant organic wastewater characterized by its intricate composition and high concentration of pollutants, posing a severe threat to global aquatic environments and public health. This study focuses on the degradation of pyridine, a notoriously persistent organic pollutant in CCW, through the identification and application of two highly efficient pyridine-degrading bacterial strains: Alishewanella fetalis (Al-f3) and Exiguobacterium profundum (Ex-p). These strains were immobilized using a polyvinyl alcohol-sodium alginate (PVA-SA) matrix to investigate their bioaugmentation mechanisms in the pyridine degradation process. The findings indicate that strains Al-f3 and Ex-p achieved degradation rates of 95.94 % and 97.83 %, respectively, for an initial pyridine concentration of 200 mg/L at 96 hours. When strains Al-f3 and Ex-p were mixed in equal proportions and immobilized within PVA/SA beads, a degradation rate of 81.06 % was reached within 48 hours, with the efficiency increasing significantly by 96 hours. This enhancement is attributed primarily to the marked increase in enzymatic activity post-immobilization, achieving 17.13 μmol/mg·min, and the elevated secretion of extracellular proteins and polysaccharides, measured at 3.47 mg/L and 1.03 mg/L respectively within 48 hours. Notably, in the immobilized mixed culture system, the total organic carbon (TOC) was reduced to a mere 0.03 mg/L within 72 hours, with a removal rate of 92.31 %. These outcomes not only demonstrate the bioaugmentation role of the immobilized mixed strains in degrading pyridine but also offer novel solutions for the biodegradation of other organic contaminants in CCW, thereby enhancing the treatment efficiency of such wastewater. Given their large specific surface area and cost-effectiveness, PVA/SA immobilization matrices serve as efficient biocarriers in the biodegradation processes for treating CCW. This research provides innovative strategies and methods for the biotreatment of recalcitrant industrial wastewater.