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Abstract
Multi-soil-layering (MSL) systems permit higher hydraulic load rates (HLR) and pollutant loads than some conventional soil systems by forming the alternating structures inside to enhance the filtration ability of soil. However, the quantitative evaluations of water movement in MSL are insufficient to be understood. Residence time distribution (RTD) is a tool to characterize the mixing and flow within reactors and is useful for troubleshooting existing reactors. In this study, pulse tracer tests were conducted to determine the RTD to investigate the flow patterns of MSL. Results show that the back-mixing extent of MSLs was moderate dispersion under HLR 200, 400, 800, and 1,600 L/(m2 d), and the RTD of them indicate evident flow patterns of CSTR. Residence time shows a significantly negative correlation with the dead zone (p = 0.001). The dead zone ratio of the MSLs were 41.0%, 52.3%, 59.6%, and 38.8% under HLR 200, 400, 800, and 1,600 L/(m2 d), respectively.
Acknowledgements
The work was financially subsidized by scholarship from Demonstration Base of Water Quality Improvement and Ecosystem Restoration at Lakeside Zone of Taihu Xincheng (2012ZX07101-013), National Natural Science Foundation of China (No. 40901257), Priority Academic Program Development of Jiangsu Higher Education Institution (PAPD), Nanjing University of Information & Technology (NJUIST, No. S8111028001), and Undergraduate Teaching Quality Reform Project in 2012 in NJUIST (N1885012079, N1885012180).