| The overgrowth of algae due to eutrophication has caused severe environmental problems. Decreasing the concentration of phosphate and nitrogen in the water bodies is an effective way to control eutrophication, thus preventing the overgrowth of algae. Various methods and a variety of materials have been studied to remove phosphate during the past decades, in which coagulation with Al-and Fe-salt (sulfate) phases is the usually applied method. For technical and economical reasons, however, these technological schemes are not applicable at rural areas and small town. For small-scale domestic water treatment, the constructed wetland systems can be used. Although constructed wetlands have proven to be effective for removing organics and total suspended solid, the nitrogen and phosphorus removal capacity is usually problematic. In recent years, worldwide studies have shown the effectiveness of adsorption through natural minerals, by-products, synthetic adsorbents and so on for the removal of phosphorus. In addition, their abilities for removal of ammonium is limited due to lacking dissolved oxygen, especially in horizontal flow subsurface constructed wetlands, and which can through ion exchange. Therefore, looking for the nutrient-loaded filter material as nitrogen and phosphorus adsorbent is urgently necessary.This study was mainly investigated removal of phosphorus in constructed wetlands and the research contents were as follows:(1) By analyzing the long-term monitoring data, the removal of nitrogen and phosphorus of different design and operating parameters in the pilot-scale subsurface constructed wetland (an area of 150m2) was evaluate, and the factors affecting the removal of phosphorus in sewage were also discussed.(2) The removal performance of cinder for phosphorus by different modification methods such as metal salts(calcium and magnesium) and hydrochloric acid(HCl) to modified the coal cinder was compared. (3) The iron oxides loaded zeolite was used to remove nitrogen and phosphorus simultaneously. Firstly, modified materials were characterized by XRD and BET, then the effects of adsorbent dose, pH, contact time, temperature, the initial concentration of target, ionic strength and humic acid on equilibrium adsorption capacity have been investigated. Finally, the adsorption performance of nitrogen and phosphorus by iron oxide modified zeolites was assessed from adsorption isotherms, adsorption kinetics and adsorption thermodynamics point of view.The following results are obtained:(1) Substrates, plants, water level, temperature, as well as influent organic loading rate show influence on the removal of phosphorus in wetlands system. However, substrates and influent organic loading rate were the most important two factors. Constructed wetland which filled cinder and planted Cyperus alternifolius is more conductive to removal phosphorus.(2) The removing capacity of phosphorus has been improved by different modification methods and followed the order of HCl>CaCl2>MgCl2, and the adsorption capacities for phosphorus were 47.24 mg/kg,19.58 mg/kg and 14.50 mg/kg, respectively. HCl modified coal cinder for phosphorus adsorption has reached equilibrium in 24 h. And the adsorption for phosphorus was well fitted with Langmuir isotherm.(3) Compared with the unmodified zeolites, the adsorption capacity of phosphorus was improved 4.6 times by iron-oxides modified zeolites, and the AN adsorption keeps uneffected, therefore the iron-oxides modified zeolites can effectively remove AN and P, simultaneously. It was found that the adsorption equilibrium can be reached within 1h and 24h for AN and P, respectively. The experimental data of AN and P were well described by both the Langmuir and Freundlich isotherm models at room temperature, and the maximum adsorption capacity for AN and P were 71.94 mg/g,1.69 mg/g, respectively. In pH range of 6 to 9, removal of AN and P by iron-oxides modified zeolites can be realized, and the presence of humic acids can inhibit the adsorption of AN and P by iron-oxides modified zeolites.
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