Study On Removal Performance Of Multi-soil-layering System For Simulated Domestic Wastewater Treatment

Multi-soil-layering system（MSL）is a technology for decentralized wastewater treatment,which is widely used around the world.The matrix of MSL system is important for removing pollutants from wastewater.The types,properties and filling methods of matrix affect removal performance of the MSL.Two sets of MSL-1（single packing structure）and MSL-2（mixed packing structure）with the same ratio of matrices but different structures were constructed to explore nitrogen,phosphorus and organic matter removal performanc with different operating parameters.In addition,removal performance of MSL for bisphenol A（BPA）wastewater was also investigated.The results are as follows:（1）The sequence of adsorption capacity of experimental materials as MSL system matrices for nitrogen and phosphorus was mixed matrices>soil>charcoal.The adsorption capacity of rice husk for nitrogen was very small,and a small amount of phosphorus was released.The isothermal adsorption of nitrogen and phosphorus by soil,charcoal and mixed matrices accorded with Langmuir and Freundlich equations.The Pseudo-first order kinetic models and Pseudo-second order kinetic model could describe the adsorption kinetics of nitrogen and phosphorus by soil,charcoal and mixed matrices.（2）When the optimal hydraulic load was 0.10 m~3/（m~2·d）,average removal efficiencies of COD,NH₄⁺-N and TP were 91.63%,97.60%and 96.27%in MSL-1,and were 93.06%,96.23%and 92.11%in MSL-2,respectively.Under hydraulic loads of 0.05 m~3/（m~2·d）,0.10 m~3/（m~2·d）,0.20 m~3/（m~2·d）and 0.50 m~3/（m~2·d）,the removal efficiencies of COD,NH₄⁺-N and TP in MSL-1were better than those in MSL-2.Hydraulic load had no significant effect on NO₃^--N and NO₂^--N concentrations in the effluents（P>0.05）.When C/N was 5:1,COD removal efficiencies of two MSLs were the highest,which were92.45%and 91.55%,respectively.When C/N increased from 5:1 to 10:1,COD removal efficiencies decreased gradually.When the C/N ratio was 5:1,the NH₄⁺-N removal efficiencies of the two systems reached the highest,with removal efficiencies of 98.13%and 97.38%,respectively.Under different C/N conditions,the TP removal efficiencies of the two systems were above 90%.The optimal C/N was 5:1 in two MSLs.When the dry-wet ratio was 2:1,COD removal efficiencies of the two systems reached the highest.When the dry-wet ratio was 1:1,2:1 and 5:1,average removal efficiencies of NH₄⁺-N were 92.07%,93.93%and 89.38%in MSL-1,respectively.Average removal efficiencies of NH₄⁺-N were 91.96%,92.35%and 88.74%in MSL-2,respectively.Average TP removal efficiencies of MSL-1 were 90.06%,89.87%and 88.69%,respectively.Average TP removal efficiencies of MSL-2 were 89.78%,88.30%and 87.24%,respectively.COD,NH₄⁺-N and TP removal perfrmances of MSL-1 were better than those of MSL-2.The optimal dry-wet ratio of the two systems was 2:1.Single packing structure of matrices was recommended for MSLs.（3）BPA removal efficiencies in two systems were more than 85%,while COD,NH₄⁺-N and TP removals were not affected.