Biological Removal of Phenol from Synthetic Wastewater Using Free and Immobilized Biomass

Biological treatment is a sustainable approach for phenolic wastewater remediation; however, its efficiency is often limited by substrate toxicity and the structural instability of microbial carriers. In this study, alginate beads (changing biochar concentrations) with starch filler were used to investigate the properties and removal kinetics of phenol in synthetic wastewater utilizing free and immobilized mixed cultures of bacteria. A phenol removal efficiency of 99.1% was obtained using alginate-immobilized biomass supplemented with 20% starch and 0.7% biochar, whereas free biomass achieved only 31.23% removal at an initial concentration of 1,000 mg/L within 24 h. The 20% starch concentration was found to optimize the micropore structure, improving mass transfer and microbial growth. Control tests showed that biochar alone removed 40% of the pollutant, indicating a synergistic mechanism in which biochar reduces initial toxicity through adsorption. Furthermore, the system successfully eliminated concentrations up to ∼1,250 mg/L within 48 h, with kinetics shifting from first order to zero order as concentrations increased. The beads remained stable for several days in minimal salt medium and retained 85% efficiency during initial reusability trials. Incorporating starch and biochar into the beads enhanced their mechanical strength.