Start-up and microbial mechanisms of low-voltage electrochemically integrated constructed wetlands: Effect of inoculated source

Nitrogen (N) and phosphorus (P) species in wastewater treatment plants (WWTPs) effluents are important sources of nutrient input to water bodies, resulting in deteriorated eutrophication. The combination of electrochemical technology and constructed wetland provides emerging prospects for tertiary treatment of WWTPs effluents. In this work, three bench-scale electrochemically integrated vertical flow constructed wetlands (E-VFCWs) were established in parallel with different inoculated sources. Among them, the E-VFCW inoculated with anaerobic sludge (AN) of a swine wastewater treatment plant exhibited significantly shorter start-up period (9 d), followed by anoxic sludge (A) from a municipal WWTP (18 d), and no inoculum (NI) exhibited the longest startup duration (30 d). In addition, AN group allowed the highest removal efficiencies (NO3--N (97.0 & PLUSMN; 1.6 %), TN (83.3 & PLUSMN; 4.6 %), and PO43--P (93.3 & PLUSMN; 3.3 %)) in tertiary wastewater treatment, and lower concentrations of SO42--S and total Fe in effluents. Results of microbial structure and Tax4Fun suggested that multi-path metabolisms including H-2-, Fe(II)-, and FemSn-dependent denitrification might facilitate NO3--N reduction in E-VFCWs. The microbial mechanisms that AN exhibited the highest denitrification efficiency in the E-VFCWs may include the highest bacterial copies number and the more abundant denitrifying genes. Moreover, it should be noted that electron transfers mediated by sulfur (S) cycle might significantly enhance NO3--N reduction in E-VFCWs, especially in AN group. To conclude, the study offers new microbial insights into N conversion and S cycling patterns in electrochemically integrated systems in response to inoculated source.

Automated summary

This study investigates the performance and microbial mechanisms of electrochemically integrated vertical flow constructed wetlands (E-VFCWs) with different inoculated sources. The results show that the E-VFCW inoculated with anaerobic sludge (AN) from a swine wastewater treatment plant exhibited the shortest start-up period and the highest removal efficiencies in tertiary wastewater treatment. Microbial analysis suggests that AN group may have higher denitrification efficiency due to higher bacterial copies number and more abundant denitrifying genes. The electron transfers mediated by sulfur cycle may significantly enhance nitrate reduction in E-VFCWs, especially in AN group.