Experimental Study On The Treatment Of Polluted River Water By Multi-soil-layering System

Dianchi lake was composed primarily by29river, which discharged into Dianchiwith centripetal shape eventually. All the Into-lake rivers in Dianchi lake formed anintegral "composite ecologic system". The Into-lake rivers in Dianchi lake is not asupply for the environmental flows of the Dian lake, but a deliver to the pollutant. Itspeculiar transpertation, tansformation, influxion and sedimentation have a specialstatus and function in urban water environment. Presently, the river channelsfollowing to Dianchi lake mostly belongs to heavily polluted urban rivers. The mainreason of the urban river heavily polluted due to the fast developing economy inDianchi lake basin, the city’s rapid expansion and pollution control measures lag.Hightly urbanization has led to a complete loss of the natural attributes. Some riverseven had been transformed into sewage ditch. The pollution control of the Into-lakerivers in Dianchi lake has become the key and difficult points of the lake pollutioncontrol.Since the1970s, especially in the past10years, a new concept of river treatmentby ecological have been put forward by many countries, such as Japan, U.S., Germany,Switzerland, South Korea, et al. The characteristic of this concept included followingpoints: abandoning the concept of river management "efficiency doctrine" formed inthe period of rapid economic development, building "artificial strengthening riparianzone", respecting the laws of nature of the river systems, focusing on recovery andprotection of the natural ecology of rivers and the natural environment, and givingfull play to the comprehensive service functions of the river. The ecological techniqueis a new idea of lateral treatment of polluted rivers. Combined with the pollutioncharacteristics of the Xinyunliang river which flowing into Dianchi lake, theecological technique "Multi soil layering system（MSL）", was employed in our studyto remove nitrogen and phosphorus of the rivers flowing into Dianchi lake in order toreduce its pollution load and then to improve water quality of urban river.To the polluted river water flowing into the dianchi lake，we carried out theresearch aiming at strengthening nitrogen and phosphorus removal through addingPBS particles-a kind of water-insoluble biodegradable polymers pellets （BDPs） toanoxic phase，using two-stage MSL system with aeration phase and anoxic phase。Inaddition, we investigated the influence of different hydraulic loading rates on the removal effect of MSL system. These studies would provide scientific foundations forthe demonstration project of MSL system and the reformation of river waterenvironment.The results indicated：the adjunction of PBS carbon resource can effectivelysolve the poor removal of nitrogen in traditional MSL system for the lack of carbonresource. In the condition of seriously and light pollution，the average removal rate ofTN were78%and85%， the reduction loads are9.09g.m^-2.d^-1、24.55g.m^-2.d^-1，respectively。The average removal rate of TP are92%and98%，the reduction loadsare0.76g.m^-2.d^-1、2.02g.m^-2.d^-1，respectively. In addtion，the average removal rateof COD are up75%。The different hydraulic loading rates has little influence on theeffluent NH₄⁺and Org-P. The average removal rate of NH₄⁺are up to95%, while theaverage removal rate of Org-P are up to90%. However, The different hydraulicloading rates has great influence on the effluent COD、TN and PO₄^3-. The effluentCOD removal rate degraded from75%to63%, the TN removal rate degraded from85%to61%, while the PO₄^3-removal rate degraded from95%to60%.In conclusion, two-stage MSL system with aeration phase and anoxic phaseshowed excellent effects on the treatment of the river pollution. From the results, wecan see that the system does not show lack of carbon source after using PBS as thecarbon source of the soil mixing module replacing traditional sawdust carbon sourceand the removal efficiency of TN remains high level. Also, we can see that MSLsystem have a great impact on the removal of TN and PO₄^3-under different hydraulicloading. The contributing factor to this phenomenon may be that the short of thehydraulic retention time resulted by the enhanced HLRs will affect the metabolicprocesses of internal microbial of the system which play an important role in theremoval of TN and PO₄^3-.