Microbial mechanism of organic contaminant removal of sodium bentonite/clay (BC) mixtures in high-permeability regions utilizing reclaimed wastewater

Abstract

In high-permeability regions, utilizing reclaimed wastewater, sodium bentonite/natural clay (BC) mixes may be used to effectively reduce reclaimed wastewater riverbed infiltration; however, the removal efficiency of pollutants in riverbed media dramatically reduced. Microorganisms play vital roles in contamination transportation and transformation. Accordingly, the current study sought to investigate the microbial community of a riverbed medium and the removal of contamination using phospholipid fatty acid (PLFA) biomarkers. Results indicate that the local hydrological condition of the riverbed medium significantly changed after infiltration reduction using a mixture of sodium bentonite and clay (BC): saturation and non-saturation regions. It was difficult for nutrients and microorganisms to penetrate the infiltration reduction layer due to the high densification of the infiltration reduction layer, and the concentration of PLFA on the lower surface of the infiltration reduction layer was 82.0% less than that on the upper surface, and the species number of PLFA decreased by 6. The number and diversity of microorganisms also reduced in the riverbed medium due to the above reasons. Comparing with natural riverbed, in the non-saturation region of BC riverbed, the amount of PLFA and nitrifying bacteria was decreased by 49.0%, 19.1%, respectively. As to the saturation region of BC riverbed, the amount of PLFA and nitrifying bacteria was decreased by 39.8%, 31.4%, respectively. Besides, the amount of PLFA in both the non-saturation and saturation regions of the BC riverbed decreased in concurrence with an increasing sodium bentonite ratio. The findings may be used to explain the effect mechanism of infiltration reduction materials on the contamination removal efficiency of riverbed media.