Effect of biochar on petroleum hydrocarbon degradation and energy production in microbial electrochemical treatment

Petroleum and petroleum product exploration, transportation, processing, and burning negatively impact soil ecosystems and cause severe damage. Hence, a study was conducted to evaluate the performance of microbial electrochemical treatment (MET) in terms of biodegradation and electricity generation with petroleum hydrocarbon-polluted soil by adding rice straw biochar pyrolyzed at 600 °C for different doses of 4%, 8%, and 12% w/w. This study confirmed for the first time that increasing the dose of biochar from 8% to 12% w/w in the anodic chamber of MET led to a decrease in its degradation of petroleum hydrocarbons from 87.8% to 49.2% and its current density from 3.5 A/m2 to 0.5 A/m2 in 20 days. Moreover, the relative abundance of Desulfuromonas and Geobacter, which have been reported to participate in inter-species electron transfer as electroactive bacteria, also decreased from 52.32% to 1.5% and 3.47–1.4%, respectively. This apparent change in primary genera further suggested that biochar content was the core factor reshaping the distribution of the bacterial community. The electrochemical investigation also shows that the redox-active quinone in biochar is responsible for extracellular electron transfer. The results of this study showed that the effectiveness of biochar for the degradation of petroleum hydrocarbons using microbial electrochemical treatment depends on the dose of biochar in the soil.