Hematite-facilitated anaerobic oxidation of organics: Novel strategy to alleviate bioclogging in constructed wetlands.

Bioclogging from organic accumulation significantly limits efficiency and longevity of constructed wetlands (CWs). In this study, hematite was introduced to enhance the oxidation of organics by dissimilatory iron reduction (DIR). Compared to gravel CWs (G-CWs), hematite CWs (H-CWs) enhanced the removal of COD, ammonium, and phosphate by 12 %, 46 %, and 72 %, while reducing CH4 and N2O emissions by 69 % and 36 %. The increase in extracellular polymers on G-CWs substrate surface was 5.96 times of H-CWs. This increase was the main reason for the significant reductions in porosity and hydraulic conductivity of G-CWs after 36 months, decreasing by 41 % and 91 %, respectively. However, H-CWs decreased by only 11 % and 52 %. This was attributed to H-CWs promoting the enrichment of DIR bacteria like Geobacter. These anaerobic microorganisms oxidized 55 % of the influent COD, preventing bioclogging from organics accumulation. Our findings provide useful guidance for alleviating bioclogging and enhancing long-term efficiency of CWs.