Performance and mechanism of SMX removal in an electrolysis-integrated tidal flow constructed wetland at low temperature

Constructed wetlands are a well-established technique to degrade wastewater contained antibiotics. And its removal at low temperature (<15 °C) has baffled researchers and engineers for decades. Electrochemical process has been increasingly valued as a promising approach to enhance antibiotics removal by both electrocatalytic oxidation–reduction and electrocoagulation. A pilot study was conducted using an electrolysis-integrated tidal flow constructed wetland (E-TFCW) to intensity sulfamethoxazole (SMX) under 4, 8 and 12℃ temperature regimes. E-TFCW have shown the better SMX removal efficiency (16.38% ∼ 31.45%) at low temperature, which was nearly 14.10% ∼ 25.31% higher than that of TFCW. It was no significant difference between 4℃, 8℃ and 12℃ in E-TFCW, which was attributed to electrocatalysis of iron electrode. Temperature had no effect on the degradation path of SMX, where SMX was removed with hydroxylation, nitration and S-N hydrolysis. Proteobacteria contributed to higher SMX removal efficiency at low temperature. The response speed of microorganisms to external environment (<8 ℃) was accelerated owing to electrolysis, where the populations with same functions can be gathered together to resist the change of the extreme environment. However, the cooperative relationship among microorganisms in E-TFCW was weakened at 4 ± 1 ℃. PICRUSt analysis results further demonstrated that the abundance of extracellular electron transfer related functional genes was increased. This study provides new insights into electrolysis-integrated constructed wetland functioning stability for accelerating antibiotics removal in cold environment.