Study On Terrace-filter Constructed Wetland Purification Technology For Wastewater

A terrace-filter constructed wetland system adapted to terrain features ofmountainous city was built, which possesses the capacity for strengthing naturalreoxygenation multiplicating. The terrace-filter constructed wetland research focused onthe removal effort and migration and transformation discipline of contamination indifferent operation condition, obtaining the optimal factor combination mode and thebest operation condition, establishing a first-order kinetic equation, studying thediversity of the population and distribution characteristics of bacteria in different seasonand by different factor combination, obtaining the relativity of macro runningperformance and microcosmic bacterial population, meanwhile, Investigating the reasonof the optimum purification capability of the recommended operation process. Thesearching achievement is of great significance to the application of the terrace-filterconstructed wetland system in mountainous areas.The main conclusions are listed as follow:1) Through the test of several substrate absorpting nitrogen and phosphorus,compare ammonia nitrogen and phosphorus adsorption capacity of different substrates.Phosphorus adsorption volume is: steel slag> limestone> ceramic, rough sand> gravel,and ammonia nitrogen adsorption volume is: steel slag> ceramic, limestone, sand>gravel. Steel slag has higher adsorption volume and stronger stability. Select gravel andrough sand for wetland structures torquay mass, and steel slag, limestone and ceramicwhich have good adsorption performance as body filler.2) To settle the shortcoming of lacking oxygen of the traditional wetland system, aterrace-filter constructed wetland system adapted to mountainous city terrain featureswas built, which possessing the capacity for strengthing natural reoxygenation. Thecharacteristic of this new system is that by changing the wetland structure and waterdistribution mode, the new system possesses the capacity for strengthing naturalreoxygenation many times, and divides the wetland into three region in seriesconnection: aerobic-anoxic-aerobic, establishing an environment that favors nitration bytesting different substrate combination, thus increases the organic matter removal abilityand nitration ability. The terrace-filter constructed wetland is the ideal process fortreating small-scale urban wastewater and ecological landscape water in mountainousand hilly areas. 3) Investigating the running performance of eight different combination mode ofthe terrace-filter constructed wetland system. The result shows that the B wetlandcombination mode is dominant in the integrated purification effect of pollutant, thusrecommends the B wetland combination mode as the optimum mode, that is: thewaterfall and distribution perforated pipe; the first wetland step substrate-steel slag;clinopodiumpolycephalum; airway; the second wetland step substrate-porcelain granule;canna; the third wetland step substrate-porcelain granule, limestone and calamus. Thereason why the recommended combination process has a better purification includefactors as follow: substrate type and how it is configured provides suitable pHenvironment for nitrobacteria and denitrifying bacteria; special reoxygenation waymeans a substantial increase in the concentration of dissolved oxygen in wetland bed,and builds a suitable oxygen environment for nitrification and organic matter removing.4) Concluding from the orthogonal test, hydraulic load and inlet CODconcentration are the two most important influence factor to the terrace-filterconstructed wetland system (mode B). The recommended optimum operation parameteris: I--0.5m/d’s hydraulic load,150mg/L’s inlet COD concentration,3days’ operationspacing interval,0m’s outlet height; II--1m/d’s hydraulic load,100mg/L’s inlet CODconcentration,3days’ operation spacing interval,0.6m’s outlet height. The inlet CODload is75g/m2.d and100g/m2.d separately, TN load is15.77g/m2.d and21.72g/m2.dseparately, TP load is1.26g/m2.d and1.72g/m2.d separately.5) By statistical data fitting method, study the effect of inlet contamination load topollutant removal load in the recommended combination technology. The COD removalload has the best positive linear relationship with the inlet contamination load; itrecommends that the operation COD load should better lower than the highest capacity.When TN load surpasses22.4g/m2.d, TP load surpasses1.81g/m2.d, it will lead to lowerremoval rate, thus recommends the TN and TP load should accord with the highestpermissible value. The first-order kinetic model are suitable for simulating the COD,TN, TP removal discipline of the recommended mode B process, the simulationequation is separately:1/ln(C o/Ce)=-0.5157q-0.0668(R2=0.9417)，1/ln(C o/Ce)=-0.668q-1.9168(R2=0.833)，1/ln(C o/Ce)=-0.4326q-0.5617(R2=0.8148).6) Investigating the treatment effect of recommended process under the tworecommended conditions, the outlet COD and ammonia concentration is separately10mg/L,9.67mg/L and1.62mg/L,1.53mg/L, meeting the discharge limits of primary Astandard of GB18918-2002steadily; the average outlet TN concentration is separately 16.32mg/L and11.12mg/L, separately closing to the discharge limits of primary Astandard and meeting the standard. The average outlet TP concentration is separately0.48mg/L and0.74mg/L, separately meeting the discharge limits of primary A standardand closing to the standard. Comparing with other comestic wetland, it concludes thatthe recommended mode of terrace-filter constructed wetland is better than thesubsurface-horizontal flow wetland in contaminant removal, and bears a comparisonwith the vertical wetland.7) The Shannon indexs of microorganism TGGE map of each step substrates arelower in winter than summer, the similarity clustering results of different samples arebetter in winter than summer,it shows that with the temperature increasing in summer,the microorganism population breed rapidly, and the diversity increases. The similarityclustering coefficent of mode B are less than mode A both in winter and summer, thegap is larger in summer, it indicates that microorganism population diversity of mode Bis larger than mode A, the rapid growth of microorganism and plant contributes to thediversity of these two wetland in summer. Each step of mode B has different amount,different kind, and different function of particular microorganism to participate indegradation, which makes it better than mode A. The COD concentration of mode A haslower correlation with the Shannon index in winter; it indicates that the microorganismis small in quantity and low in activity. When the temperature stays low in winter, andthat the assimilation of microorganism to organic matter is not in the lead place in modeA. The contamination removal rate of mode B has positive relationship with the totalbacteria shannon index, and the ammonia and TP removal rate have significantcorrelation with shannon index in summer, while the COD removal rate has significantcorrelation with shannon index in winter, these all shows that the assimilation ofmicroorganism to each kind of contamination in mode B plays an important role in thewetland purifacation system in different season, thus make it more stable and better thanmode A in purification.