Effective removal of naphthalene from water using bacteria and bacteria-load carrier materials

The volatilization of naphthalene unavoidably poses significant risks to health, the environment, and safety. Traditional remediation approaches have been criticized for their inefficiency in removing naphthalene and transforming its toxicity. This study proposed a bacteria-loaded carrier material and evaluated its degradation efficiency compared to that of free bacteria. High concentrations made it more challenging for Microbacterium paraoxydans (ms) to achieve effective degradation of naphthalene. Additionally, the degradation process was not timely, thereby exacerbating the risks associated with the volatilization of naphthalene. Three carrier materials-activated carbon (AC), calcium alginate (CA), and composite gel beads (CO)-were evaluated for their adsorption, biocompatibility, and thermal stability. CO's adsorption of naphthalene occurred mainly through chemisorption, with π-π conjugation and Ca-π interaction enhancing the adsorption process. The adsorption peaks did not exhibit any shifts after the involvement of bacteria, indicating the best biocompatibility among the carrier materials, despite having the second lowest total weight loss (CA > CO > AC) during the heating process. The salicylic acid pathway and the phthalic acid pathway were involved in the degradation of naphthalene. No signs of naphthalene were seen in the samples from confocal laser scanning microscope (CLSM) tests, indicating that ms fully degraded naphthalene after its adsorption. While ms degraded naphthalene on day 4 for 50 mg/L and 100 mg/L concentrations, 31.2 mg/L remained for the 200 mg/L concentration. In contrast, ms-loaded CO degraded most of the naphthalene on day 1, with only 2.8 mg/L remaining from the initial 200 mg/L concentration. This study underscored the relative merits of applying ms-loaded CO to the degradation of naphthalene.