植物塘+人工湿地+吸附池系统对灌溉水中痕量Cd的去除效果

为了降低灌溉水中Cd向农田输入,减轻农田土壤Cd污染,试验选取梭鱼草、狐尾藻、野茭白为材料,构建“植物塘+人工湿地+吸附池”系统,研究其对湖南典型矿区Cd超标灌溉水净化效果,并分析Cd在系统中的分布规律。结果表明:在2018年11月—2019年9月监测期间,进水全量Cd平均浓度为6.35μg·L^-1,经系统净化后灌溉水中可溶态Cd、悬浮态Cd及悬浮颗粒物平均去除率分别为86.58%、90.37%和81.54%,构建的人工系统可有效降低灌溉水中Cd含量。进水口悬浮态Cd与悬浮颗粒物呈极显著正相关,悬浮颗粒物与进水流速呈显著正相关。灌溉水Cd输入总量为859.61 g,大气沉降Cd输入总量为95.34 g,处理系统拦截为865.52 g,各个单元拦截量从高到低依次为一级植物塘(544.64 g)>三级人工湿地+吸附池(167.62 g)>二级植物塘(156.26 g)。3种湿地植物对Cd均有较好的富集效果,富集浓度随水流方向下降。一、二级植物塘底泥最大Cd浓度分别为11.05、4.75 mg·kg^-1,底泥中Cd弱酸可溶态比值较大,存在向水体解吸释放的风险。所构建的“植物塘+人工湿地+吸附池”净化系统可有效降低湖南典型矿区灌溉水中超标Cd含量,降低农田土壤Cd的灌溉输入通量。

Removal of Cd from irrigation water by plant pond + wetland + adsorption pond systems

A field experiment was conducted in order to reduce the input of Cd into farmland from irrigation water and reduce Cd pollution in farmland soil.A multistage constructed wetland planted with Pontederia cordata,Myriophyllum verticillatum,and wild Zizania was evaluated for Cd removal ability when dealing with irrigation water in a mining area containing Cd exceeding standard values and the distribution of Cd in wetlands was analyzed.The results showed that during October 2018 to September 2019,the total Cd average inflow was 6.35μg·L^-1.After purification by the wetland systems,a removal efficiency of 86.58%,90.37%,and 81.54%was achieved for the dissolved Cd,particulate Cd,and total suspended solids,respectively.The particulate Cd inflow had a significant positive correlation with suspended solids,and suspended solids had a significant positive correlation with the inflow velocity.The total inputs of Cd from irrigation water and atmospheric sedimentation were 859.61 g and 95.34 g,respectively,and the interception by the wetland systems was 865.52 g.Specifically,the interception of Cd from high to low by each system was as follows:first plant pond(544.64 g)>third free wetland with an adsorption tank(167.62 g)>second plant pond(156.26 g).All three wetland plants had a considerable enrichment effect on Cd,and the concentration decreased with the direction of water flow.The maximum Cd concentrations in the first and second plant pond sediments reached 11.05 mg·kg^-1 and 4.75 mg·kg^-1,respectively.However,weak acid-soluble Cd occupied a large proportion in the sediment which had a risk of release into water.In general,the multistage constructed wetland system can effectively reduce Cd concentration in irrigation water from typical mining areas and reduce the irrigation input flux of Cd to farmland soil.