Study On The Domestic Wastewater Treatment By The Constructed Wetland Through The Intensified Technology

The constructed wetland is widely used in rural and urban sewage treatment because of its low cost, no energy consumption, easy operation and maintenance, but has many shortcomings, such as large covered area needed, easy clogging, and poor treatment performance for nitrogen and phosphorus. In order to realize effective removal of contaminants, various intensified techniques, such as combination process, matrix and plants enhancement, were investigated to purify the wastewater by the constructed wetland. The activated sludge process was widely applied to wastewater treatment with high performance for organic matters and ammonia nitrogen removal. Therefore, activated sludge process can serve as constructed wetland strengthening combination process. The backflow of wastewater is beneficial to oxygen recovery, and to interaction between pollutants and biofilm formed between rizosphere of plant and substrate surface, leading to potential enhanced removal of pollutants, especially for nitrogen abatement, thus, can serve as one of intensified technologies for a constructed wetland. Majority of phosphorus removal was realized by substrate adsorption; so, modification of substrate is one way to obtain the enhanced phosphorus removal. Therefore, the object of this thesis is to evaluate the potential usefulness of the combination process, backflow of wastewater, and substrate modification in enhancing pollutants removal in the constructed wetland, and the main contents are as follows:(1) By analyzing the long-term monitoring data, the removal of organic pollutants, nitrogen and phosphorus in the pilot-scale subsurface constructed wetland combined with the activated sludge process as pretreatment technology was evaluated.(2) By analyzing the monitoring data, the removal of pollutants in the pilot-scale subsurface constructed wetland combined with the backflow process was evaluated, and the factors affecting the removal of pollutants in sewage were also discussed.(3) The potential of using a coal cinder supported iron oxides as a substrate for the removing of phosphate in the constructed wetlands was investigated, and the adsorption kinetics and the isothermal adsorption were also studied.The following results are obtained:(1) Concentration of organic pollutants, nitrogen, and phosphorus in effluent of the combined activated sludge-constructed wetland system can meet the first-class requirement of GB 18918-2002, suggesting that the combined system promises high performance for removal of organics and ammonia, and thus can be used as the intensified technology.(2) The backflow of treatment system effluent can dilute the influent wastewater. The higher the backflow ratio is, the higher the dilution is. The backflow process is benefit to removal of organics and phosphorus, whereas, is insignificant to ammonia removal. The backflow process caused pH value of the effluent of the system, for example, it induced decrease of pH in A1,B2 and D2, probably due to the result of nitrification.(3) The results demonstrate that the as-prepared new substrate could increase phosphate removal significantly by 11 times as compared with the unmodified coal cinder. The removal efficiency of phosphate could reach 90% at 80 g/L of adsorbent dosage. The kinetic phosphate adsorption data of iron oxide-coated coal cinder can be fitted well with the pseudo-second-order kinetic model and the isothermal adsorption data can be modeled well with the Langmuir formula with the estimated maximum phosphate adsorption capacity of 84.74 mg/kg. The factors affecting phosphate removal such as adsorbent dosage, pH of solution, concentration of humic acid and solution temperature were also studied.