Study On The Intensified Purification Of River Water Quality In Pre-dam Ecosystem

In recent years,point source pollution has been effectively controlled in watershed water pollution control in China,and the problem of non-point source pollution has gradually replaced point source pollution,which has become the main cause of water pollution in the river basin.As an effective approach to surface source pollution control,pre-dam technology has the advantages of low investment,low operating costs,improved ecological environment,and improved ecosystem diversity.It has been widely used in water pollution control at home and abroad.In this study,it is supported by the National Water Pollution Control and Treatment Science and Technology Major Project with requirements of the topic.Based on the pre-dam system of the Gaopu River inlet at the upstream of the Dongjiang River as the background,the improvement of water quality of the pre-dam ecosystem was studied.By monitoring the water purification effect of the pre-dam ecosystem,a plan to improve the water purification effect of the pre-dam system is proposed for the monitoring results.According to the experimental plan,a small-scale test for the selection of the composite filler packs in the gravel bed and the aquatic plants in the pre-dam purification area was designed.A detailed and detailed feasibility plan for the water quality enhancement purification of the pre-dam ecosystem was designed using composite filler packs and aquatic plants selected from the pilot test.The main conclusions of thesis are shown as follows:?1?The pre-dam system includes two major function areas,that is gravel bed and pre-dam purification.Monitoring of the water purification effect shows that:The pre-dam system has a certain removal effect on CODcr?NH₄⁺-N?TN?TP and SS?rainy weather?in water,and the average removal rate is 42.4%,28%,29.9%,22.8%,62.9%.Among them,the removal effects of CODcr and SS?rainy weather?are obvious and the removal efficiency is stable,but the removal rates of NH₄⁺-N,TN and TP are lower,and the average removal rate is less than 30%.In the different functional areas of the pre-dam ecosystem,the gravel bed has a significant effect on the purification of CODcr,NH₄⁺-N and SS,while the pre-dam purification area has better removal effect on TN and TP.In different hydrological periods,the purification effects of CODcr,NH₄⁺-N,TN,and TP were also significantly different.The purification effect of CODcr was the low water period>the high water period>the level water period;while NH₄⁺-N,TN,and TP were all the level water period>the high water period>the low water period.The concentration of NH₄⁺-N,TN,and TP in the effluent of this pre-dam system did not meet the Class III standard of?Environmental Quality Standards for Surface Water??GB3838-2002?.Therefore,it is necessary to carry out enhanced purification of the water quality in the pre-dam system.?2?When the gravel bed was filled with zeolite-ceramsite-sawdust-iron filings,charcoal-ceramsite-sawdust-iron filings,soil-ceramsite-sawdust-iron filings composite filler packs,the concentrations of CODcr,NH₄⁺-N,TN and TP in the test system all decreased significantly.Among them,the CODcr concentration in the charcoal group system has the largest drop,with an average removal rate of 62%,followed by the zeolite group with an average removal rate of 52.2%.The average removal rates of NH₄⁺-N,TN and TP were all in the zeolite group>charcoal>soil group.The average removal rates of NH₄⁺-N,TN,and TP in the zeolite group are 91.9%,87.37%,and 64.7%,respectively.As the soil fillers are easy to block the system,taking into account the long-term stable operation of the pre-dam system,and the average concentration of CODcr in the effluent at the end of the pre-dam system has been met,the zeolite-ceramsite-sawdust-iron filings composite filler pack is selected as an alternative filler pack for the gravel bed water quality enhancement purification plan.?3?The growth status of the three plants of Lythrum salicaria,Cyperus alternifolius and Ruellia brittoniana are different in the test system.The growth rate,dry biomass increase,and growth height of Cyperus alternifolius and Ruellia brittoniana are all significantly better than those of Lythrum salicaria.Lythrum salicaria is affected by insect pests during the experiment,its chlorophyll content changing is relatively large,and its environmental adaptability is weak.The test group system has a good purification effect on CODcr,NH₄⁺-N,TN,and TP.The Ruellia brittoniana system has the best removal efficiency to CODcr,with an average removal rate of 68.9%.The Cyperus alternifolius system is the second,and the average removal rate is 65.9%.The Lythrum salicaria system is the worst and the average removal rate is only 45.9%.The removal rates of NH₄⁺-N and TN were Ruellia brittoniana>Cyperus alternifolius>Lythrum salicaria.The average removal rates of NH₄⁺-N in the three groups of plants are 76.5%,73.5%and 69.5%.The average removal rate of TN is70.6%,68.7%,and 62.6%.The root system of the plant has a great influence on the removal of N from the system.The root system of Cyperus alternifolius and Ruellia brittoniana are more robust than that of Lythrum salicaria,so the removal efficiency of N is higher.Among the three plant systems,the best removal effect of TP is Cyperus alternifolius,with an average removal rate of 67%,followed by Ruellia brittoniana,with an average removal rate of 61.3%.Lythrum salicaria is the worst and the average removal rate is only 51.2%.When the hydraulic load is increased,the water purification effects of the three plant systems decreasing,but it is always higher than that of the control system,indicating that the three plant systems have strong impact-resistant load capacity.Comprehensively analyze the growth adaptability and water quality purification effects of the three plant systems,and Cyperus alternifolius and Ruellia brittoniana are selected as the preferred plants in the enhanced purification program of the pre-dam ecosystem.?4?According to the results of the pilot test,the zeolite-ceramsite-sawdust-iron filings composite filler pack is added to the gravel bed,and the pre-dam purification area is constructed to build the Heart Island and the ecological floating bed.Arundo donax var,Bulrush-Canna generalis and Iris tectorum in the local wetland park are planted on the Heart Island.Ruellia brittoniana and Cyperus alternifolius are planted on the ecological floating bed.These are the optimal solution for the enhanced purification of river water quality by the pre-dam ecosystem.