Study On Advanced Treatment Of Urban Sewage By Greenhouse Constructed Wetland

With the continuous growth of population and the expansion of people's activities,water environmental problems have been becaming more severe.Acording to some studies,the biggest test of water environmental problems is how to improve and optimize the wastewater treatment process be better.With less cost,priority should be given to control the contents of pollutants such as organic matter,nitrogen and phosphorus in water,so the water environment quality could be improved effectively.The Surface Flow Constructed Wetland is well applied in engineering owing to the advantages of low construction cost,simple structure,low energy consumption and convenient management.However,it also has some defects,such as:the seasonal variation has great influence on them,the growth state and activity of plants and microorganisms will be affected.Therefore,the purification effect of the wetland system on the sewage will be affected,especially in the northern low temperature conditions,which will cause the plants to die early or enter the dormancy state,thus the capacity of the wetland purification would be decreased obviously.In this experiment,advanced treatment of secondary biochemical treatment effluent from sewage treatment plant by greenhouse constructed wetland,breaks the limitations of traditional constructed wetland which is influenced by seasonal temperature and enables the constructed wetland to operate normally in the four seasons,provides a better way to solve the seasonal effects on constructed wetland in northern China.At the same time,the greenhouse constructed wetland provides more scientific and effective methods to satisfy the emission limit of water pollutants of the sewage treatment plants(stations)and industrial enterprises in the area of Xiao Qing river in Ji'nan.Moreover,it can facilitate the urban sewage discharge to meet the "standard of surface water environmental quality"(GB3838-2002)?.The experiment is combined with two kinds of sewage treatment process.Starting from the quality of greenhouse heat preservation,the growth status of the wetland plants and the decontamination effect of the constructed wetland system on Chemical Oxygen Demand,Ammonia Nitrogen and Total Phosphorus.The operation of greenhouse constructed wetland for urban sewage advanced treatment in northern China is studied and the following conclusions are obtained:(1)According to the purpose and requirements of this test,relying on the powerful local heat preservation conditions of greenhouse,we build the greenhouse constructed wetland.It is feasible to select the locallimestone,quartz sand and soil as the substrate and select wetland plants with good growth of Oenanthe javanica and Water hyacinth in the local natural wetland ecosystem for this test.(2)The research on the quality of greenhouse heat preservation in winter shows that the steel frame plastic greenhouse can guarantee the growth of plants in the four seasons,and delay or break the dormancy state of plants effectively;The greenhouse can effectively improve the indoor temperature and the water temperature of the constructed wetland system in winter,which is beneficial to the stability of the internal environment of the constructed wetland.Winter-greenhouse can effectively improve the indoor temperature and the water temperature in the constructed wetland system,which is beneficial to the stability of the internal environment of the constructed wetland.The temperature difference between day and night is relatively large in the greenhouse,and it is more beneficial to improve the night heat preservation effect of the greenhouse by spreading the heat preservation quilt.(3)In the study of plant growth performance in greenhouse constructed wetland,the adaptability and ramet ability of the two wetland plants(Oenanthe javanica and Water hyacinth)are compared.The results show that the adaptive capacity of Oenanthe javanica is stronger.It has a short dormancy state and the ramets are not obvious under high temperature in summer.However,it grows more vigorously and ramets fast in other seasons;In winter and spring,Water hyacinth has a long stagnant growth,accompanying with leaf blight,but the growth cycle has been prolonged.The growth of wetland plants in the cold regions of the north can be realized through heat preservation in the greenhouse.(4)Through the research and analysis of the effect of the advanced treatment of urban sewage by greenhouse constructed wetland.The results show that greenhouse constructed wetland system under the condition of the best HRT for five days running,the system of the concentrations of water Chemical Oxygen Demand,Ammonia Nitrogen and Total Phosphorus are 20?36 mg/L,1.25?3.25 mg/L and 0.20?0.35 mg/L respectively,under the condition of greenhouse constructed wetland for the removal rates can reach 50%-71%,54%?76%and 45%?76%,the effluent concentration can basically meet the "standard of surface water environmental quality"(GB3838-2002)?.