| CW as an ecological wastewater treatment, become more widely used with its advantages of cheap, easy to administer and good environmental performance, the current main problem of CW is the low nitrification ability. BAF technology has been applied widely for wastewater treatment with high volume load, hydraulic loading large, short hydraulic retention time, and low energy consumption and operating costs, meanwhile the process removal the organic matter and ammonia nitrogen effectively. BAF mainly used for micro-polluted source water, sewage and water preconditioning treatment. In this study, the BAF enhanced constructed wetland technology was used and the GDS as phosphorus matrix in wetland substrate was studied, in order to improve the removal efficiency for nitrogen and phosphorus, and provide technical support for the wider use of wetlands.Research topics include the following elements:①CW treatment of domestic sewage alone;②BAF treatment of sewage separatly;③domestic sewage treatment by the enhanced technology;④pollutants removal kinetics of the enhanced technology. Through the research reach to the following conclusions:1) The removal efficiency of pollutants in CW increase with the water level rises and the level of 65cm should be better than the other water level in the experimental conditions. The hydraulic loading suitable for this study was 0.8×10-2m3/(m2·h). Under the same conditions, vertical flow constructed wetland contaminant removal levels were 10% higher than horizontal flow wetland, indicating the advantage of vertical flow CW.2) pH is an important parameter for nitrification, pH around 9.0 is the best conditions for this strudy. COD/N ratio effect COD removal slightly, while the removal of ammonia is affected by it heavely. COD removal rate of the combined wetland is stable and the average rememal rate was 75.93%, average ammonia removal rate was 25.05%, the total nitrogen removal rate was 26.44% and was 74.14% of the TP.3) Langmuir isotherm equation fit better than Freudlich isotherm equation in substrate phosphorus adsorption isotherms, the theory adsorption capacity of GDS (G0) was 688.18mg/kg, which of the slag (G0) is 521.58mg/kg. P adsorption increased with the increasing of solution pH, the adsorption amount of phosphate matrix increase slowly in acidic conditions, but in alkaline environment, substrate adsorption of phosphorus increased with increasing pH value rapidly. Meanwhile, the presence of anions weaken on phosphorus adsorption but there may be increased by presence of cation.4) Gas-water ratio and hydraulic loading affect the removal effeciency of BAF, at gas-water ratio of 3:1 and hydraulic loading of 1.28m3/(m2.h), BAF removal the organic matter and ammonia effecively and without a waste of power consumption. BAF as a separate processing unit can realize the effective removal of organic matter and ammonia, and the removal rate reached 65.4% and 69.25% respectively, but the removal efficiency of TN and TP is not ideal, was 9.97% for TN and 10.41% for TP only.5) The enhanced process on the removal efficiency of pollutants were improved than the BAF and wetland processes alone, the improvement of ammonia and total nitrogen rate was largely due to enhanced technology play in addressing each individual process different forms of nitrogen pollutants on the edge, and use a reasonable combination to achieve the advantages of two complementary treatment process for the realization of the effective removal of pollutants.6) Change of pollutants along the enhanced technology study shows the variation varies between pollutants. COD present in the wetlands along the ladder in the law of diminishing, and the removal of organic pollutants in preceding wetland is dominant. The top 1/2 of the wetland play the dominant role of nitrogen removal, but the ammonia concentration raise in the later section in horizontal wetland, which may be due to the kind of flow in the wetland, the vertical flow wetland can transfer pollutants downward outflow easier, while the horizontal subsurface flow constructed wetland is not easy to direct outflow, resulting in the release of decomposition of organic nitrogen, and ammonia concentration led to recovery.7) Contaminant removal dynamic model was also established. Compared with the measured data, the established model of the system effluent COD, ammonia nitrogen and total nitrogen simulation are efficient, the ideal simulation were 65%,80% and 100% respectively. The model of the system simulated effluent COD and total nitrogen is better than the dynamic model, but the model still has the engineering design functions, needs further study.In conclusion, BAF enhanced wetland treatment process is characterized in that the composition of the nitrifying BAF segment and the subsurface flow constructed wetland denitrification section. Wastewater distribution into the BAF firstly, organic matter removal by aeration and enhanced nitrification, then flows through the wetland for denitrification and nitrogen removaled efficiently. |
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