Effect mechanisms of hematite and goethite on naphthalene biodegradation, insight from electron transfer and microbial gene expression

Polycyclic aromatic hydrocarbons (PAHs), particularly naphthalene (Nap), are persistent and hazardous pollutants, posing significant risks to both the environment and human health. Consequently, remediation strategies are urgently sought to mitigate Nap contamination, with bioremediation emerging as a promising approach. However, the efficacy of bioremediation, reliant on biodegradation, is hindered by various factors, prompting exploration into enhancing technologies. This study explored the potential of iron minerals, specifically hematite (α-Fe₂O₃) and goethite (α-FeO(OH)), in modulating Nap biodegradation from the perspectives of electron transfer and microbial gene expression. The results revealed that α-Fe₂O₃ promoted Nap biodegradation, while α-FeO(OH) inhibited it, and the promoting effect of α-Fe₂O₃ on the biodegradation of Nap increased with the increase in the α-Fe₂O₃ content, and the optimal content of α-Fe₂O₃ for promoting Nap biodegradation was approximately 7.5%, and the inhibitory effect of α-FeO(OH) on the biodegradation of Nap also increased with the increase in α-FeO(OH) content. Mechanistically, α-Fe₂O₃ facilitated microbial growth, accelerated electron transfer efficiency, enriched microbial diversity, and maintained enzyme activity, thus promoting Nap biodegradation. Conversely, α-FeO(OH) inhibited microbial growth, altered microbial communities, and reduced enzyme activity, leading to diminished Nap biodegradation. Therefore, the presence of α-Fe₂O₃ in the environment had a certain positive effect on the remediation of Nap contamination in groundwater. These findings underscore the complex interplay between iron minerals and microbial-mediated Nap biodegradation, offering insights into effective remediation strategies.