Electrolysis-integrated constructed wetland with pyrite filler for simultaneous enhanced phosphorus and nitrogen removal

Abstract

Constructed wetlands (CWs) have been widely applied for tail water treatment. However, conventional CWs usually encounter poor phosphorus and nitrogen removal performance due to limited adsorption capacity of fillers and insufficient electron donors. In this study, an electrolysis-integrated CW using pyrite as filler surrounding electrodes (e-PCW) was developed. After around 140 days’ operation with various voltages (5, 10 and 15 V), synergistic effects of pyrite filler and electrolysis process were observed. The optimal removal efficiencies of NH4+-N, TN and TP achieved at 5 V were 42.6 ± 3.5%, 68.2 ± 1.8% and 75.8 ± 2.5%, respectively. O2 generated at anode in e-PCW promoted oxidation of FeS2 in pyrite to release Fe3+, which could form FePO4 for phosphorus removal. At cathode, the produced H2 together with FeS2 could serve as electron donors, driving autotrophic denitrification to improve nitrogen removal. The results also showed that inputting 10 and 15 V voltages caused acidification in anodic area due to water electrolysis. Although minerals like CaMg(CO3)2 in pyrite could partially neutralize acidification, low pH (5–6) still inhibited nitrification process and led to desorption of phosphorus from fillers. Based on microbial community analysis, main functional bacteria were Desulfomicrobium (13.43%) and Thauera (4.66%) in cathodic area of e-PCW, which could reduce SO42− to S2− and afterwards drive sulfur-based autotrophic denitrification respectively. This work provided a novel and competitive technology for advanced wastewater treatment.