Hematite-Facilitated Anaerobic Oxidation of Organics: A Novel Strategy to Alleviate Bioclogging in Constructed Wetlands

Abstract

Constructed wetlands (CWs) are recognized as effective treatments for domestic sewage. However, bioclogging from organic accumulation significantly limits both long-term efficiency and longevity. In this study, we introduced hematite as an alternative substrate in CWs to enhance the anaerobic 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 11.69%, 45.69%, and 72.02%, respectively, while reducing global warming potential by 51.80%. After 1096 days of operation, the porosity and hydraulic conductivity of G-CWs declined by 41.19% and 91.45%, respectively, while those of H-CWs decreased by only 10.95% and 51.60%. This demonstrates a substantial alleviation of bioclogging in H-CWs. In addition, H-CWs were enriched with the typical DIR bacterium Geobacter. DIR potential tests confirmed that these anaerobic microorganisms oxidised 55.14% of the influent COD. Correlation analysis between primary microorganisms and environmental factors further confirmed that Geobacter-mediated DIR is the principal driver for reducing the deposition of organic and alleviating bioclogging. Our findings validate the considerable potential of hematite in alleviating bioclogging within the anaerobic zone and decreasing greenhouse gas emissions, which is crucial for improving CW treatment efficiency and prolonging the operational lifespan.

Keywords: Constructed wetlands, Clogging, Hematite, Dissimilatory iron reduction, Global warming potential