CO2 improves the anaerobic biodegradation intensity and selectivity of heterocyclic hydrocarbons in heavy oil

Heterocyclic hydrocarbons pollution generated by oil spills and oilfield wastewater discharges threatens the ecological environment and human health. Here we described a strategy that combines the greenhouse gas CO2 reduction with microbial remediation. In the presence of nitrate, CO2 can improve the biodegradation efficiency of the resins and asphaltenes in heavy oil, particularly the biodegradation selectivity of the polar heterocyclic compounds by the newly isolated Klebsiella michiganensis. This strain encoded 80 genes for the xenobiotic biodegradation and metabolism, and can efficiently utilize CO2 when degrading heavy oil. The total abundance of resins and asphaltenes decreased significantly with CO2 , from 40.816% to 26.909%, to 28.873% with O2 , and to 36.985% with N2. The transcripts per million (TPM) value of accA gene was 57.81 under CO2 condition, while respectively 8.86 and 21.23 under O2 and N2 conditions. Under CO2 condition, the total relative percentage of N1-type heterocyclic compounds was selectively decreased from 32.25% to 22.78%, resulting in the heavy oil viscosity decreased by 46.29%. These results demonstrated a novel anaerobic degradation mechanism that CO2 can promote the anaerobic biodegradation of heterocyclic hydrocarbons in heavy oil, which provides a prom-ising biotreatment technology for the oil-contaminated water.

Automated summary

Heterocyclic hydrocarbon pollution from oil spills and oilfield wastewater poses a threat to the environment and human health. A strategy combining CO2 reduction and microbial remediation was described, utilizing the isolated Klebsiella michiganensis bacteria's ability to selectively biodegrade polar heterocyclic compounds in heavy oil. The presence of CO2 improved the biodegradation efficiency, reducing the abundance of resins and asphaltenes and decreasing heavy oil viscosity. These findings highlight a promising biotreatment technology for oil-contaminated water.