Research On Activated Sludge Process-Constructed Wetland Combinative Technology Treating Municipal Wastewater

There are some difficulties in treating municipal wastewater in Southern Chinabecause of the weak carbon concentration, comparative strong nitrogen andphosphorus concentration, seasonal changing quality and quantity. To solve theproblem the activated sludge process-constructed wetland combinative technologywas invented. The research focus on real municipal wastewater treatment in a pilotscale system with capacity of 100m³/d and a demonstrating plant with capacity of10000m³/d. In the pilot scale experiment the study involves the influent quality andquantity, the pollutant form and removal efficiency, the COD distribution in differentprocesses. With these studies the operating modes of the interactive reactor indifferent seasons were confirmed. Meanwhile the pollutant removal efficiency andkinetic constants in different types of constructed wetland were investigated and theeffecting factors such as packing medium, load, temperature and plant species werealso researched. Thereout the appropriate type and load of constructed wetland can beconfirmed. Further more the bidirectional input/output adjusting mode forbiological-ecological comnination based on q-t figure was proposed as well as theload distribution. In the full scale experiment the demonstrating reactor was adjustedwith the fluctuating influent quality and the polluent removal efficiency wasinvestigated.The influent concentratons of COD, NH₄⁺-N, TN and TP of pilot system were129mg/L,25.6mg/L,31.5mg/L,3.38mg/L respectly. The needed carbon for nitrogenand phosphorus removal was lacking because of the low C/N and C/P ratios. Theinfluent quality fluctuates with the alternation of season and the pollutantconcentration in rainy weather was about 60% of that in dry weather. Even thepollutant concentration was so weak that close to the discharge standard in rainy dayin spring and summer. So the biological reactor must be adjusted accoding to thechanges of temperature, influent quality and precipitation for making the most ofnitrogen and phosphorus removal with the limited carbon resource. By comparing different processes in the same period, following operting modeof interactive reactor was recommend: enhanced A²/O process fits on spring period,pre-anoxic inverted A²/O process was recommend in dry/mizzle weather in summerperiod, step aeration process was adopted in rainy weather in summer period,alternating oxygen concentration inverted A²/O process was appropriate in autumnperiod, and normal inverted A²/O process was better in winter period. The analysis ofthe organic matter, nitrogen and phosphorus removal rule and the carbon resourcedistribution shows that the preferable process can betterly distribute and utilize thelimited carbon resource.The removal efficiencies of COD, NH₄⁺-N, TN and TP in constructed wetlandwrer remarkably affected by loading. The removal efficiencies were decreased withthe increasing hydraulic loading and areal loading. The increment of areal removalmass was reduced with the increasing areal loading. Otherwise the removalefficiencies of NH₄⁺-N and TN were observably increased with the climbingtemperature. The lab-scale experiment shows that the TN areal removal mass waslinearly related to the NO_x^--N/TN ratio. So increasing the NO_x^--N/TN ratio canimprove the TN removal. The aquatic plants with bigger biomass have strongercapacity to assimilating the pollutant so the concentrations of nitrogen andphosphorus in dry plant should not be the exponent for evaluating assimilatedpollutant by plant. On the condition of low influent concentration the pollutantremoval rules in constructed wetland can be simulated by first-order K-C model.The removal efficiencies of COD and TP in subsurface flow wetland (SSFW)were higher than that in surface flow wetland (SFW) and SSFW/SFW combinedwetland with the same loading. Using shale and slag as medium can enhance theremoval of phosphorus. The removal efficiency of NH₄⁺-N in SFW was higher thanthat in SSFW and SSFW/SFW combined wetland. When the NO_x^--N/TN ratio wasmore than 0.25 the removal efficiencies of TN in SSFW was higher than that in SFW.The advantage of SSFW/SFW combined wetland was less infection by lowtemperature. Eventually the shale/slag filled SSFW was recommended for advancedtreating municipal wastewater and the first-order areal rate constants of COD,NH₄⁺-N, TN and TP were 0.32m/d, 0.065m/d, 0.176m/d and 0.29m/d respectly. Accoding to the pilot experiment results the guidelines of biological-ecologicalcombination was proposed for managing the demonstrating plant. And thebidirectional input/output adjusting mode for biological-ecological comnination basedon q-t figure was builted. A case for the adjusting mode focus on the pilot scalesystem was analyzed. The operation modes of demonstrating reactor were switchedby using enhanced A²/O process, pre-anoxic inverted A²/O process and partialy lowoxygen concentration inverted A²/O process. The effluence quality of demonstratinginteractive reactor can reach the standard of grade B, class one in Discharge Standardof Pollutants for Municipal Wastewater Treatment Plant. Some of them can reach thegrade A standard. When the hydraulic loading of demonstrating SSFW was about0.3m/d to 0.35m/d the effluence concentration of COD, BOD, NH₄⁺-N and TP canreach the Environmental quality standards for surface water, the effluenceconcentration of TN can be declined to 7mg/L.