Copper stimulation on methane-supported perchlorate reduction in a membrane biofilm reactor

The present study demonstrated that the perchlorate reduction rate in a methane-based membrane biofilm reactor was significantly enhanced from 14.4 to 25.6 mg-Cl/L/d by increasing copper concentration in the feeding medium from 1 to 10 μM, indicating a stimulatory effect of copper on the methane-supported perchlorate reduction process. Batch tests further confirmed that the increased copper concentration enhanced both methane oxidation and perchlorate reduction rates, which was supported by an increasing trend of functional genes (pmoA for methanotrophs and pcrA for specific perchlorate reducers) abundances through quantitative polymerase chain reaction (qPCR). Both 16S rRNA gene sequencing and functional genes (pmoA and pcrA) sequencing jointly revealed that the biofilm supplied with a higher copper concentration exhibited a more diverse microbial community. The methane-supported perchlorate reduction was accomplished through a synergistic association of methanotrophs (Methylocystis, Methylomonas, and Methylocystaceae) and perchlorate reducers (Dechloromonas, Azospira, Magnetospirillum, and Denitratisoma). Acetate may function as the key syntrophic linkage between methanotrophs and perchlorate reducers. It was proposed that the increased copper concentration improved the activity of particulate methane monooxygenase (pMMO) for methane oxidation or promoted the biosynthesis of intracellular carbon storage compounds polyhydroxybutyrate (PHB) in methanotrophs for generating more acetate available for perchlorate reduction.