Removal efficiency of organic substances in effluent from a municipal sewage plant by a subsurface constructed wetland

Abstract:

Removal process and efficiency of organic substances in effluent from a municipal sewage plant were investigated and compared in a horizontal subsurface constructed wetland with different substrates by application of gel filtration chromatography (GFC) and three-Dimensional Excitation Emission Matrix Fluorescence Spectroscopy (3D-EEM). The results show that weight average molecular weight (Mw) of dissolved organic matter (DOM) in the outflow of the constructed wetland was significantly decreased, as compared to the inflow. After sewage plant effluent was treated by the subsurface wetlands, the percentage of the larger molecules > 50 kDa declined by 33.5%, while the percentage of the smaller molecules below 50 kDa showed a significant increase. Four different types of peaks such as aromatic protein-like compounds, soluble microbial byproducts, fulvic acid-like compounds, visible fulviclike and UV fulvic-like compounds in DOM from the infow significantly decreased in the effluent during purification by the subsurface constructed wetland. Especially, the biorefractory humic-like compounds can be effectively removed by the subsurface constructed wetland. Aromatic structures of humic-like compounds were weakened and organic compounds with benzene rings were decreased in the outflow of the subsurface constructed wetland. By comparison, organic matter transformations from larger molecular weight to smaller molecular weight were completed in the 1/4 front of the constructed wetland filled with ceramisites, while for the constructed wetland with zeolite substrate, the transformations were completed after the middle of the wetland bed. As compared to zeolite substrate constructed wetland system, ceramisite wetland was more effective to transform the organic matter from larger molecular weight to smaller molecular weight and remove the organic substances from the sewage plant effluent.