Preparation And Performance Of Granular Agents For In-situ Remediation Of Sediments Polluted By Electronic Wastewater

The sediment polluted by electronic wastewater often contains heavy metals（HMs）,nitrogen（N）and phosphorus（P）,acid volatile sulfide（AVS）and other pollutants,and then presented black and odorous.In-situ chemical remediation is an effective method to remediate this type of contaminated sediment.However,this method always has to apply chemical powder or liquid agents,which is not suitable for applied with overlying water.One of the effective ways to solve the problems was prepared the powder chemical agents to granules.While,the existing granules agents have a single composition,which can only solve the problem of black and odor of sediment,but has limited ability to stabilize heavy metals,and control N and P releasing.In this study,we screened the chemical agents to comprehensive control of sediment pollutants,and optimized the preparation conditions of the granule agent.Then,we prepared a type of granules that suitable for remediation of electronic wastewater contaminated sediment,and finally observed the long-term efficiency.It might have been provided a reference for in-situ remediation of contaminated sediment in the practical project case.Form lab-scale study,the type and proportion of compound of remediation agents for electronic wastewater polluted sediment were optimized.The results showed that the most suitable compound composition includes calcium peroxide,hydroxyapatite and zeolite powder,and the best compound mass ratio was 4:4:5.After the compound agents put into the contaminated sediment with the dosage of 13%,the AVS was almost completely removed,the proportion of stable form pollutants such as insoluble-P and residual fraction of HMs were significantly increased,and compared with contaminated sediment,the total releasing concentration of ammonia nitrogen（NH₄⁺-N）and total nitrogen（TN）were reduced after a period remediation.In addition,the remediation thickness was 3cm,which can effectively isolate the pollutants released from un-remediated sediment of lower layer into the overlying water body.Based on the determined types and proportions of compound agents,granules were prepared by optimizing the concentration and preparation conditions of the embedding agent PVA,and then the remediation performance and sedimentation properties of the granules were studied.The study determined that the mass concentration of the embedding agent PVA solution was 3%,the preparation drying temperature was 100℃,and the drying time was 3 h.The best shape of the granule was sphere,and the radiated remediation range was 30mm when the diameter of the granules was 10 mm.Moreover,by adding the inner core to change the density of the granules,which can enter the appropriate position of the sediment layer and play a better effect.Finally,the prepared granules were added to the black-odorous sediment to observe the long-term remediation efficiency for 60 days.The results showed that under the condition of adding the granules at an interval of 30 mm,the black-odor sediment can be effectively remediated.After 10 days,the sediment turned from black to earth yellow,and the AVS removal rate can reach more than 95%.At the same time,P and HMs were effectively stabilized,the proportion of calcium-bound-P increased by about 35%,and they were almost no release.The proportion of HMs residue fractions increased by 3%-30%,and the total release of Cr,Ni,Cu,and Zn were reduced by about 23.1%,15.2%,0.8%,and 65.2%,respectively,and the equilibrium concentrations decreased by 28.1%,53.9%,41.1%,and 72.6%,respectively.Moreover,the total NH₄⁺-N releasing concentration decreased by about 21.6%,the equilibrium concentration decreased by 45.8%.