Impact of Materials in Multi-Media-Soil-Layer(MSL) System on Sewage Treatment

Multi-media-soil-layering(MSL) is a new type of decentralized domestic wastewater treatment system,especially fit for rural areas.In the experiment four MSL systems were constructed in box(50 cm×10 cm×60 cm) comprising typically soil mixture layers alternated with permeable layers.The soil mixture layer contained sandy soil,sawdust and charcoal/straw,iron scraps/bentonite mixed at a ratio of 7∶2∶1 by dry weight,and the permeable layer was composed of zeolite and gravel.The MSL systems ran continuously for two months at a hydraulic loading rate(HLR) of 500 L·m^-2·d^-1.Results show that the four MSL systems did not differ much in average COD_Cr removal rate,varying in the range of 79.58%-80.22%;and their TP removal rate was in the range of 47.83%-82.60%,and addition of zeolite and bentonite in the permeable layers increased TP removal rate by a large margin;their TN removal rate varied in the range of 29.74%-57.89%.Permeable layers of zeolite were better than those of gravel.The mixture of charcoal and sawdust was more suitable as organic carbon source than straw in the MSL systems.