Efficient nitrate removal from synthetic groundwater via in situ utilization of short-chain fatty acids from methane bioconversion

Nitrate (NO₃⁻) removal from groundwater is of great importance since it has posed a major risk to human health. Although methane-based denitrification processes have been developed, the practical application of methane as a carbon source for denitrification is constrained by either a long start-up time or a relatively low nitrate removal rate. This study investigated nitrate removal capacity by using a methane-based membrane biofilm reactor (MBfR) feeding with synthetic groundwater. A high nitrate removal rate of 706 mg-N L⁻¹ d⁻¹ was achieved, which is by far the highest rate reported for methane-based denitrification reactors. Short-chain fatty acids (SCFAs) were detected as products of methane bioconversion, with concentrations of acetic and propionic acid up to 168.8 mg L⁻¹ and 50.2 mg L⁻¹, respectively. Long-term operation and batch test results revealed that the SCFAs generated from methane bioconversion were in situ utilized for supporting nitrate removal as carbon and electron sources, thus leading to a practically useful removal rate. The findings suggest that it is promising to apply the methane-based MBfR to remove nitrate from nitrate contaminated groundwater.