Abstract
Multi-soil-layering (MSL) wastewater treatment systems consist of soil units (soil mixture blocks, SMB) arranged in a brick-like pattern surrounded by permeable layers of zeolite or alternating particles of homogeneous sizes that allow for a high hydraulic loading rate. This study evaluated the performances of MSL systems that have been operating for 17 to 20 years in small rural communities. Even though 20 years had passed since this system was installed, high organic matter treatment performance continued. Nitrogen removal was higher than with conventional soil systems. Two of the MSL systems continued to show high phosphorus removal performances, whereas in the third system, the adsorbing capacity was relatively low, requiring further investigation. Treatment performances were largely dependent upon the structure of the MSL systems. It appeared that improving the structure to enhance the contact efficiency between the wastewater and the soil in SMB was important for enhancing treatment performances. The combined use of existing wastewater treatment systems with the MSL system was effective for preventing environmental pollution over a long period.
Highlights
Water treatment systems incorporating soil have been widely used as on-site wastewater treatment systems in the U.S [1], Australia [2], and Europe [3]
MSL systems consist of soil units arranged in a brick-like pattern surrounded by permeable layers (PL) of zeolite or alternating particles of homogeneous sizes that allow for a high hydraulic loading rate (HLR)
Several basic and applied studies on MSL systems have been undertaken in Japan, ailand, Morocco, China, Taiwan, and the U.S Basic studies of water movement inside the system [10, 11], wastewater treatment mechanisms [9], material composition of Soil mixture block (SMB) and PL [7,12,13,14], aeration effects [13], horizontal flow MSL system [15], and the relationship between treatment capacities, HLR, and contamination levels [16, 17] have been conducted on these systems
Summary
Water treatment systems incorporating soil have been widely used as on-site wastewater treatment systems in the U.S [1], Australia [2], and Europe [3]. E MSL system has the added advantage that its performance does not depend strongly on soil properties at the site because the water purification function of the SMB can be enhanced by mixing materials such as sawdust, jute, iron metal, and charcoal with the soil [7]. Several basic and applied studies on MSL systems have been undertaken in Japan, ailand, Morocco, China, Taiwan, and the U.S Basic studies of water movement inside the system [10, 11], wastewater treatment mechanisms [9], material composition of SMB and PL [7,12,13,14], aeration effects [13], horizontal flow MSL system [15], and the relationship between treatment capacities, HLR, and contamination levels [16, 17] have been conducted on these systems. We calculated the mass balances of BOD, nitrogen, and phosphorus and evaluated the effects of the structural differences between the three MSL systems on wastewater treatment efficiencies
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