A Primary Design Using Artificial Wetland Composite Process To Treat Arsenic Polluted Acid Water From Mining Area

Xinzhou gold mine, in Qingxin county, Qingyuan city, experienced20years disorderedmining and gold extracted using indigenous method, generates a large mount of poisonousand harmful slag in the residual mining area. And with the erosion of mountain stream andrainwater, a large quantity of acidic mining waste water is produced. It flows together, thenruns to the debris intercepted dam, and lastly overflows to Leigongbei River, causing seriouspollution to Leigongbei River, which is important irrigation water source.Based on the study of related materials about acid arsenic mine wastewater in and abroad,investigation of Xinzhou gold mine, sampling and analyzing of Leigongbei Revier waterwhich is polluted by discharge water of mine zone, we determine the pollutant is acidicarsenic. The situation is especially serious, exceeding6.5to36.4times with reference to theirrigation water quality standard when the river pH is between2.88and4.11.In study, wecarry out arsenic removal flocculation precipitation test of water sample, select pH, coagulanttype and dosage to conduct three levels of orthogonal experiments. Finally find the optimumconditions, pH value is9, coagulant type is polymerization ferric sulfate, and coagulantdosage is20ppm. With the above method, the removal rate of arsenic in raw water can be upto80%. Through consult literatures, design “lime neutralization+poly iron coagulation+surface flow artificial wetland combination process" system to treat Leigongbei River water,the river water quality can meet the irrigation water quality standard (GB5084-2005)requirements.This paper finishes preliminary design of flocculation precipitation system, includingregulating reservoir, neutralization tank, coagulation tank, flocculation tank, andsedimentation basin, determines the optimum operation parameters. It also makes preliminarydesign of wetland system, determines the type, site, scale, the matrix and plants of screenedwetlands, even the matrix grain size and the plant configuration. Finally, determines thewetland area is4600m2, processing capacity is900m3/d, hydraulic retention time is about3.5d. The design reaches its target when forecasted with “Pollutant Removal Estimates forWetlands”. Furthermore, this paper prepares maintenance management project according to the design plan, makes investment budget on the basis of quantities and material, also takestechnical and economic feasibility analysis.