Study On The Removed Rate Of Cd In Irrigation Water By Artificial Wetland And Adsoption Technology

In order to cut off the exogenous Cd into the paddy fields, through cutting irrigation channels water into the rice fields, explore ways to control Cd in irrigation water,searching for the suitable purification process system, the article through comparing the adsorption performance of the adsorption material (charcoal, artificial zeolite, clinoptilolite, diatomaceous earth) under the proposed low concentration,analysis of pH, temperature, adsorption time, initial concentration and other factors on charcoal, synthetic zeolite, clinoptilolite, adsorption properties of diatomite Effect; compare the merits of four kinds of adsorbent adsorption properties of the adsorbent material,and then pick out the most suitable treatment of the irrigation water Cd, applied to the process system of Grit Chamber+Surface wetland+adsorption pool. And then by running the outdoor process system, analysis the removal efficiency of the process system. While wetlands are running according along the set collection points, collected cattail and sediment the front flow wetland; to explore the wetland removal Cd in irrigation waterl of the mechanism, and distribution law and accumulation law of Cd in wetland sediment and cattails in. The main results are as follows:(1) This test simulates field irrigation water and investigated the effects of adsorbent material(charcoal, synthetic zeolite, clinoptilolite) of adsorptption effect facors, for example particle size, different pH, different adsorption time, different temperatures, different initial concentrations. With increasing the mesh, reaction time, temperature, the initial concentration, the four kinds of adsorbent material in Cd2+removal rates are rising, charcoal, artificial zeolite, clinoptilolite, diatomaceous earth, have different effects on removal of Cd2+, the test optimum pH of charcoal was 6, the optimum pH of artificial zeolite was 5.5, the optimum pH of clinoptilolite was 6.5, the optimum pH of diatomite was 7.By examining the isotherm adsorption of Cd2+ adsorption about that charcoal, synthetic zeolite, clinoptilolite, diatomite. The study found the four adsorbent can fit the theoretical model are Langmuir and Freundlich theoretical model, charcoal, artificial zeolite, clinoptilolite and diatom of the maximum adsorption capacity of Cd2+ were 19.71 mg·g-1,0.76 mg·g-1,10.28 mg·g-1,10.55 mg·g-1. diatomite and clinoptilolite of performance were almost the same, but limited to the defects physical and chemical structure of diatomite, such as diatomaceous earth during the test friable, when it used to the field can cause the loss of the adsorbent material with the water migration, also may cause there secondary pollution risk, which limits to some extent the play its adsorption properties, the need for some modification, such as firing into the ceramic. when Charcoal dealing with low concentrations of cadmium contaminated water, the removal rate is relatively low, and is also easily broken. After comparing of date, four kinds of adsorbent materls for processing such low cadmium polluted water, clinoptilolite advantages:a smaller influence on the adsorption effect of particle size, pH, temperature, adsorption time, and can quickly remove water in Cd2+; and when the water in the Cd2+concentration is less than 200 ?g·L-1, adding 20 g·L-1 particle size of clinoptilolite 0.850-0.42 mm of the treated water can make Cd2+concentration fall to 10?g·L-1, reached irrigation water quality standards (GB 5084-2005).(2) through irrigation canal irrigation water inlet continuous monitoring, concentration of cadmium floating large, environmentally sensitive, up to 19.15 ?g·L-1, the minimum is only 3.02 ?g·L-1; while the influent flow variations were Great, maximum instantaneous flow rate of up to 60.48 m3·h-1. Surface flow constructed wetland water flow paths to the surface push mainly in the sewage treatment process, mainly based on natural filtration and sedimentation of pollutants to achieve the purpose of removing contaminants through the plant stems and leaves interception, soil adsorption. Grit+artificial surface flow wetland adsorption process system, the total irrigation water cadmium removal between 86.12% -100.00% and the average removal rate is as high as 94.32%, and stable operating results, b, flow rate little effect, the final effluent are below 2.00 ?g·L-1, the average effluent concentration of cadmium only 0.50 ?g·L-1.(3) Cattail is a excellent aquatic plant which can purify theCd2+in water of irrigation, which also has excellent enrichment capability.The Cd contents in underground and aboveground parts of the typha were127.39 mg·kg-1 and 14.65 mg·kg-1 corresponding to a enrichment coefficient and transfer coefficient were 6.58-41.26 and 0.037-0.107, respectively, indicating that the typha has a high capacity for purifying irrigation water. The Cd contents within the typha and in the sediment decreased gradually with the distance of water flow but increased with time. The percentage of various forms of Cd in sediment following the order: B2>B1>B3>B4 and a high potential effectiveness was determined.