Experimental Study On Chemical Washing Treatment For Urban River Contaminated Sediment

Contaminated sediment treatment is an important part for river aqueousenvironment improvement and restoration. This study chose actual contaminatedsediment in a Shenzhen urban river as treatment target. To solve the problems ofsediment blackish color and malodor, and heavy metal and organic pollution, sedimentwashing technology was studied to achieve contaminated sediment detoxification.Through experimental study, operation procedures for simultaneous treatment oforganic and heavy metal pollutants were optimized, wastewater, gas and solid wastedischarge during sediment washing process were monitored, and finally, a completesediment washing process for simultaneously treating sediment blackish color, malodorand organic and heavy metal pollution was proposed, which is expected to providereference and technical supporting for similar contaminated sediment cases.Total organic carbon （TOC） and acid volatile sulfides （AVS） are set ascharacteristic parameters of investigation on the effect of chemical oxidants on organicpollutant, blackish color and malodor treatment. As shown by the results, KMnO4andFenton’s reagent can be used as washing agents to effectively treat TOC and AVS insediment. If apply operating parameters orienting ideal treatment target, sediment TOCcontent can be treated to <2%, AVS can be treated to <40mg-S/kg dry sediment; ifapply operating parameters orienting practical treatment target, sediment TOC contentcan be treated to <3%, AVS can be treated to <90mg-S/kg dry sediment.This study set idal treatment target and practical treatment target for sedimentheavy metal pollution, repectively, based on sediment heavy metal concentration andheavy metal leaching toxicity. Results show that washing treatment cannot achieve idealtreatment target for multiple heavy metal pollution. When using Fenton’s reagent aswashing agents, heavy metals in contaminated sediment can be treated to meet practicaltreatment target. The results of sediment heavy metal distribution study show thatwashing treatment has good treatment effectiveness for heavy metals present in weaklybound fractions, and poor treatment effectiveness for heavy metal existing in residualfraction.For practical treatment target, washing operation parameters can be formed to beable to simultaneously treating sediment blackish color, malodor and organic and heavymetal pollution: concentration of washing pharmacy H₂O₂50mM, concentration ofFeSO₄0.5mM, solid-liquid ratio1:6, initial pH3, washing time4h. Sediment meetingwashing treatment standards can be considered as filling material and road accessoriesfor comprehensive utilization which also effectively solves the ultimate consumptiveproblem of dredging sediment. This study adopts combination method with neutralization-precipitation, oxidationreaction and flocculation sedimentation to treat washing wastewater containingpollutants which can achieve Integrated Wastewater Discharge Standard （GB8978-1996）II standard. Chemical sludge after washing wastewater treatment is identified asnon-hazardous waste through leaching toxicity identification and can be used forlandfill. Exhaust generated in the washing process also meets Air Pollutant DischargeStandard （GB16297-1996） II standard and can be safely emitted.In this thesis, after cost estimating to contaminated sediments washing treatmentprocess containing sediment washing and washing wastewater treatment, the entirewashing treatment process costs about254CNY/m³.