Research On The Removal Effect And Mechanism Of Acidic Heavy Metals In Waste Water By Man-made Wetland System

Hindering economic development and causing damage to human health, water pollution has developed into a worldwide environmental problem. Acid wastewater containing heavy metals is mainly resulted from mining, metal processing industries and has been seriously harmed the environment and human survival.Man-made wetlands as an ecological wastewater treatment technology can not only efficiently remove nitrogen and phosphorus in waste water with heavy metals, but also is of stable water quality, simple operation and maintenance, as well as low cost without secondary pollution. Therefore, it has attacted more and more attention in industrial wastewater treatment. In man-made wetland system, aquatic plants play an important role in the process of the removal of heavy metals. Not only can they directly absorb heavy metals, but also secret organic to complex heavy metals generated in the absorption process.Therefore it can provide habitat for microbes and enhance heavy metal removal capacity in wetland system. With different residence time and under different pollution load and acidic condition, through study on the heavy metals removal effect of shuicong, cattail, reeds, rushes, wild rice stem, and arundo donax in the six simulated wetland system, we find out the best plant most suitable for removal of heavy metals and the perfect match between each plant and heavy metals. Also, we study on the content and distribution of heavy metals in wetland plants. The results are as follows:(1) The higher the concentration of heavy metals on the plant, the greater the toxicity is. And with time passing by, plants toxicity becomes more serious.(2) With hydraulic retention time passing by, pH value of the simulation system gradually increased in liquid phase, as compared with the control system, the liquid pH value increases faster. The phenomenon indicates that except for the neutralization among gravel substrate, some basic material and microbial metabolites in soil, plants are endowed with regulation ability, which has little difference among different kinds of wetland plants.Accordingly the change rate of pH valuein liquid phase is closely related with the initial dosing concentration of each heavy metals.When the initial dosing concentration is comparatively low, the change rate of pH valuein liquid phase is more significant.(3)The concentration of copper,zinc,lead,cadmium, and have decreased with time in the six simulated wetland system, which indicates that the six simulated wetland system has a good effect on lead,copper, cadmium and zinc removal.The study finally indicates that with different concentrations of initial dosing, the best purification system for wastewater with copper and lead is Shuicong, rush and arundo donax system, for copper and zinc is typha and reed system and for zinc is wild rice stem system.(4)Six roots,stems,leaves the same effect of absorption and accumulation of heavy metals vary. Copper,zinc,lead,cadmium are accumulated in the roots of other plants except reeds,much less in the stems and leaves.(5) 0f cadmium and lead in the rushes, the major cell binding site is part of the cell wall and cytosolic, nuclear and chloroplast and mitochondrial part of some lead and cadmium were lower.(6) In the initial dosage of three different concentrations, lead and cadmium in the body in the rush to extract state of deionized water, sodium chloride and acetic acid extractable extractable mainly lead and cadmium in the rush that is the main protein in vivo , pectate binding, or insoluble in water, the formation of phosphate adsorption on the root system, the sewage will be purified.