Experimental Study On Wastewater Treatment Of Service Areas In Expressway By Biological-ecological Treatment

With the construction of expressway in our country, the service areas get rapiddevelopment, but issues of sewage treatment in service area are becoming increasingly revealedat the same time. Most service areas are far away from the city, and the sewage could not bedirectly discharged into the urban sewage systems, so independent sewage treatment units areused, however, kinds of the problem existing in the operation of the traditional process alwayslead to the direct emission of the sewage into the environment, which creates pollution. On thebasis of the research and data collecting of the sewage characters, the text tried a certainrelatively simple device to make an research on the sewage treatment with the combinedprocess of composite biofilter and constructed wetland in order to provide a new type oftreatment for the sewage in service areas. In the text, ability and effect of the compositebiofilter、constructed wetland and combined process was studied, optimization parameters ofstable operation for the system could be found out through the study, the major contents andconclusions have been drawed as follows：The process loading、hydraulic loading、period of water distribution and other aspectsaffect the removal efficiency of the composite biofilter. The biofilter could obtain the best resultwhen the volume loading、hydraulic loading、period of water distribution and ventilation ratioare controlled at0.3~0.5kgCOD·m-3·d-1、4.46~5.02m3·m-2·d-1、20~22.5min and8%respectively. With the study of nitrification and denitrification in the biofiter, the averageremoval rates of COD、NH4+-N and TN could be80%、87%and63%respectively with theC/N ratio of5to8,which shows well simultaneous nitrification denitrifying effect. In the text,Eckenfelder model was used to fit the biodegradable model in the biofilter on the basis of theremoval efficiency of organic matter, which could provide the calculation formula of theorganic matter removal efficiency.It could be found through the absorption of the nitrogen and phosphorus in the plants that,among the selected plants, cyperus alternifolius had strong ability to absorb both nitrogen andphosphorus in the sewage while canna lily absorbed phosphorus strongly. The whole nitrogenabsorbed almost distributed in the leaf and stem while the whole phosphorus mainly focused onthe part above the earth. Harvesting the ground parts of the plants is an effective way of croprotation to remove the nitrogen and phosphorus from the sewage in autumn and winter.The removal of pollutants in biofilter mainly relies on biodegradation while carbonoxidation and nitration reaction mainly effects in the stage, nitration effect went the same trend on increase or decrease with the temperature. Better effects of the nitrogen removal wasobtained with the underpart of biofilter in the submerged state while the nitrogen removal ratioreached61%; the phosphorus was removed by physical adsorption、chemical reaction and theplants in the wetland, the removal of phosphorus did not stop when absorbed to the surface offilter material, phosphorus was further removed by the hydrophyte. Suspended solid was almostcompletely removed in the system.The combined process of biofilter and constructed wetland obtained satisfactory removalefficiency of pollutants, the average concentrations of COD、NH4+-N、TP、SS in the effluentwere19mg/L、1.44mg/L、0.38mg/L、0.98mg/L respectively. The effluent quality indexes couldmeet the requirements of Water Quality Standard for Urban Miscellaneous WaterConsumption(GB/T18920-2002). The operating cost of the combined process in treatingsewage of service areas in expressway for reuse was low.Biological-ecological combined process could not only purify the sewage and green thesurroundings in the service area, but also reduce the dust pollution by using fly ash as filtermaterial which could realize the recycle of the waste. The combined process could achieve theenvironmental effectiveness while obtain certain economic benefits and social benefits whichshows certain theoretical significance and application value.