Research For The Demonstration Project Of Integrated Vertical Flow Constructed Wetlands

In order to improve the water quality of West Lake and to reduce the totalnitrogen content of Qiantang river, so measures to local conditions which are aimed atthe characteristics of the Qiantang river and be combined with the traits of the typicalsouthern city Hangzhou should be adjusted to treat the Qiantang river to drop thenitrogen. The Qiantang River water nitrogen reduction engineering demonstration hasbeen an important part of the technical subjects which are related to the typicalsouthern city landscape lake, the subjects aimes at improving the water quality andbuilding the aquatic vegetation. The demonstration projects use the ecologicaltechnology such as integrated multi-Tong-construced wetlands, by means of technicalintegraton, the nitrogen content of water can be reduced by40percent, which reachesthe Class Ⅳ surface water environmental quality standards.In this subject,3integrated vertical flow constructed wetlands in thedemonstration projects had been choosen as the research objects, the main researchcontents contain the operational states of the wetlands in the long run,the waterquality index had been monitored, which includes: pH、 conductivity、 DO、temperature、total nitrogen、total phosphorus、ammonia nitrogen、nitrate nitrogen、COD;the removal rates of main pollutants were made correlation analysis with theDO; The main reasons such as the substrate composition, the substrate enzyme andthe botanic ecological characteristics that cause the differences of processing capacityamong different wetlands and the factors which influence the normal operation wereanalyzed. The main conclusions are as follows:1. In the aspects of purifying capacity of the key pollutants from the wetlandunits in the demonstration project:Number1,2and3wetlands have a preferable phosphorus removal ability, in thisperiod of time, the average phosphorus removal rate repectively reaches to64.0%,56.8%and52.5%.The main reasons that influence the differences of phosphorusremoval rates among the wetlands lie in the types of the substrates and the plants.Choosing the anthracites and the gravels as the substrates in the downward pool caneffectively enhance the phosphorus adsorption of the substrates. The roots of the canna are too long, which goes against the phosphorus removal.the denitrification capacity of the system is affected by the temperature obviously,among the3systems, the denitrification capacity is3>2>1,the average values are20.1%、19.3%and9.3%respectively, the denitrification capacity of1system isinferior to the2and3systems remarkably. The main causes which lead to thedifferences of the wetlands are affected by the plants and substrates. The anthracitesand zeolites are fit to be used as the substrates of the downward pool. The aquaticplants which have well-developed roots are not suitable to be used in the downwardpool, the plants which have the characteristics that the ratios of above-ground biomassand underground biomass should be considered as the object of priority selection. Theplants in the uplink pool rarely influence the denitrification.Number1,2and3wetlands systems have preferable removal efficiency ofammonia nitrogen, the average removal rates reaches to63%、63.4%and61.6%respectively. The main reasons which result in the preferable removal rates are thezeolites’ filling.The average removal rates of nitrate nitrogen reaches to0.84%、13.4%and13.6%respectively.The average removal rates of COD in three systems are34.5%、37.6%and39.5%respectively.By means of the correlation analysis between the average DO difference value ofthe inflow and the effluent and the average removal rates of different pollutants, theDO difference value has the maximal relevancy with the COD、total nitrogen andnitrate nitrogen removal rates, which reach to0.9921、0.948and0.922respectively,but the relevancy with the removal rates of total phosphorus and ammonia nitrogen isnot high, this result explains that the removal of ammonia nitrogen and phosphorusdosen’t consume the DO in the effluent.2.The arundo donax、thalia dealbate and camalus in2and3constructed wetlandshave different growth velocity and morphological traits, the mature period of calamusis ahead of time when compared with the arundo donax and the thalia dealbate, afterthe September, the arundo donax can maintain the growth. As to the ratios of theplant’s above-ground biomass and underground biomass, the ratio is arundo donax>thalia dealbate> camalus.The main root biomass of three plants exist in thesuperstratum (0-30cm).3.In the aspects of substrates enzyme and the nitrogen、phosphorus removal fromthe wetland units in the demonstration project: To the supernatant dehydrogenase、urease and phosphatase activities have similarspace and time varying pattern: in the horizontal direction, the activities in thedownward pool are higher than the uplink pool; in the vertical direction, thesuperficial lawyer activities are higher than the middle layer and the bottm lawyer;with the lowering of the temperature, the enzymatic activities increase accordingly.The activity of nitrate reductase shows that with the increasing of depth, the activityenhances in the vertical direction, and when the temperature descends, the activityalso reduces. The enzymatic activity can be used as a index to evaluate the treatmentcapacity of the wetlands.To the nitrogen and phosphorus contents of the substrates in the2and3wetlands,there exists definite regularities of distribution, the contents in the superficial lawyerare higher than the middle and bottom lawyers, the contents in the downward pool arehigher than the uplink pool. In the downward pools of two systems, the accumulativecontents of the nitrogen in the gravels reaches to0.472μg/g and0.479μg/g, thedifferences of nitrogen accumulative contents in the zeolites and the gravels in thetwo uplink pool are not high, but the differences of phosphorus accumulative contentsin two kinds of substrates are high, which reaches to0.095-0.132μg/g and0.030-0.055μg/g. From the perspective of the substrates, the differences of treatmentcapacity can be analyzed under the same flow states.4.The main causes that bring the abnormal operation to the demonstration projectand the wetlands include the carbon source、low temperature、typhoon、the watersupply’s cutting off and the outside nitrogen source pollution, etc. The lowtemperature and the low carbon source affect the nitrogen and phosphorus removaleffects of the wetlands, the typhoon、outside nitrogen source contamination and watersupply’s cutting off affect the normal operation of the whole wetland systems, in linewith the way and degree of influence from each factor, the indispensableprecautionary measures should be carried out to minimize the abnormal operationeven the damage.