Process Research On Facultative Biochemical And Partial Aeration Wavy Subsurface-flow Constructed Wetland For Treating Scattered Point Pollution Water

Wastewater treatment must take the way of combining the centralized treatment and decentralized treatment together. According to the characteristics of decentralized sewage treatment, the following three innovations were proposed in this paper: (1) the technology line and structure for handling wastewater in facultative biochemical technology and wavy subsurface-flow constructed wetland (W-SFCW) with partial aeration were proposed and constructed; (2) The best conditions for the operation of facultative biochemical technology were analyzed, and the assumption of partial aeration in wavy subsurface-flow constructed wetland was proposed for the first time, and the removal rates of NH4+-N and TN were improved by the combination of partial-aeration and recirculation, which could go up to higher than 93% and 50%, respectively; (3) Discussion was made on the kinetic model for COD removal in the combined technology and nitrification Monod model in constructed wetland.With regression analysis and matlab curve analysis, the best conditions for facultative biochemical technology could be gained: HRT was 8h,MLSS was 5800mg/L,which was validated in facultative biochemical reactor when influent flux was 1m³/d, and the test also proved that facultative biochemical technology has a certain effect on regulating water quality, enhancing biodegradability and removing COD. However, the effect was not obvious on removing TP, TN and NH4+-N, which showed that further process is needed for the effluent of facultative biochemical technology to achieve the discharge standards.If partial aeration pipe was placed in the front or at the back of W-SFCW, the concentration of dissolved oxygen (DO) in wastewater could be improved partially, besides, nitrification process and the removal of COD can be strengthened. When the hydraulic load of W-SFCW was 0.8m3/m²Â·d, the average removal rate of COD reached 62.12% and 58.09%, and that of NH₄⁺-N reached 93.5% and 96.6%. The effluent COD can maintain at about 30mg/L, and furthermore, the shock resistance capacity of the whole system was sharply improved, effluent quality was quite stable.In the wavy subsurface-flow constructed wetland with aeration in forepart, 50% of effluent was recirculated to the starting part, and raw sewage entered the wetlands at the 1/3 of wetland length, a better removal rate of TN was gained, to about 50%. In wavy subsurface-flow constructed wetland with aeration at the back part, at the same recirculation rate, TN removal rate was higher than 50%. The ratio of length/ width is required about 10 in the design of the latter wetland.The mechanisms for nitrogen and COD removal in partial-aeration constructed wetlands were analyzed in this paper, and so are the factors that affect the performance of partial-aeration constructed wetlands: temperature, dissolved oxygen (DO), pH value, retention time, organic and hydraulic load, oxygen consumption and supply of wetlands.Derivation of Monod kinetic equation for COD removal in the facultative biochemical technology and first-grade kinetic model for COD removal and nitrification in partial-aeration constructed wetlands were performed, and kinetic equation for COD removal of combined technology was also gained. Model parameters were gained from experimental data. It was shown that first-grade kinetic does not suit the nitrification process in partial-aeration constructed wetlands, but nitrification kinetic equation derived from Monod kinetic equation for partial- aeration constructed wetland can perfectly simulate nitrification process in the wetland. Relevant design points and parameters for the combined technology were proposed in this paper, which can guide the engineering design and application of this technology.