Insights into the biodegradation of diesel oil and changes in bacterial communities in diesel-contaminated soil as a consequence of various soil amendments.

Soil amendment is a promising strategy to enhance biodegradation capacity of indigenous bacteria. To assess the consequences of various soil amendments before large-scale implementation, a microcosm study was employed to investigate the effects of nutrients (TN), surfactants (TS), oxidants (TO), biochar (TB), and zero-valent iron nanoparticles (nZVI; TNP) on diesel degradation, bacterial communities, and community-level physiological profiles (CLPPs) of legacy field contaminated soil. The results showed that the TN, TB, TNP, TS, and TO, reduced 75.8%, 63.9%, 62.8%, 49.3%, and 40.1% of total petroleum hydrocarbons (TPH), respectively, within 120 days, while control (TW) reduced only 33.8%. In all soil amendments, TPH reduction was positively correlated with oxidation-reduction potential and heterotrophic and TPH-degrading bacteria, while negatively correlated with total nitrogen and available phosphate. Furthermore, in TW, TB, and TNP microcosms, TPH reduction showed positive association with pH, whereas in TN, TS, and TO, TPH reduction was negatively associated with pH. The bacterial diversity was reduced in all treatments as a function of the soil amendment and remediation time: the enriched potential TPH-degrading bacteria were Dyella, Paraburkholderia, Clavibacter, Arthrobacter, Rhodanobacter, Methylobacterium, and Pandoraea. The average well colour development (AWCD) values in CLPPs were higher in TB, sustained and improved in TN, and markedly lower in TNP, TS, and TO microcosms. Overall, these data demonstrate that nutrients and biochar amendments may be helpful in boosting biodegradation, increasing diesel-degrading bacteria, and improving soil physiological functions. In conclusion, diesel degradation efficiency and bacterial communities are widely affected by both type and duration of soil amendments.