Mechanistic Insights into Biochar@PVA-SA Composite Fillers for Enhanced Biopurification of Isohexane in Biotrickling Filters
Biotrickling filtration (BTF) is a promising technology for treating volatile organic compounds (VOCs), but its application to hydrophobic alkanes like isohexane is hindered by mass transfer limitations, low degradation efficiency, and high operational costs. To address these bottlenecks, this study developed composite fillers by incorporating biochars derived from coffee grounds (CG), coconut shells (CS), corn cobs (CC), and activated carbon (AC) into a polyvinyl alcohol-sodium alginate (PVA-SA) hydrogel matrix. The fillers were systematically characterized for water retention, pore structure, surface functional groups, crystalline phase, and acid-base resistance. Adsorption capacity, biofilm formation, and isohexane degradation were evaluated using the strain Rhodococcus ruber ZYH-ZY. Among the composites, CG@PVA-SA exhibited superior performance: water retention of 358 mg·g−1 (vs. 280 mg·g−1 for control), enhanced mesoporosity (specific surface area 4.77 m2·g−1, pore volume 11.46 cm3·kg−1, 10–30% higher than control), and robust acid-base stability (mass loss 21.37% at pH 2 and 31.98% at pH 10). Its saturated adsorption capacity reached 201.02 mg·kg−1 (vs. 114.24 mg·kg−1 for control), and it promoted bacterial colonization with a survival rate of 79.0% (vs. 37.2% for control). Static degradation tests showed 96.59% removal of 10 μL isohexane within 24 h. The abundant polar functional groups and suitable mesoporous structure of coffee ground biochar synergized with the PVA-SA matrix, enhancing water retention, mass transfer, and microbial colonization, thereby significantly improving isohexane purification. CG@PVA-SA is an ideal filler for BTF treatment of alkane VOCs, offering a cost-effective and efficient solution for industrial VOC control.