In-situ Remediation Of Cd Polluted Soil By Organic Amendents

In-situ chemical fixation remediation becomes a research hotspot as its fast andsimple feature. The key is to filter out a low investment, high efficiency and stableamendents. In this paper, two types of amendents were used, the one were producedfrom sewage sludge and food waste through pyrolysis, composting and drying processes,the other is mixture of humic acid and pine biochar. The incubation experiments wereconducted to observe the effects of amendments on Cd fractions and main factors in soilartificially contaminated with Cd after60and330days incubation period. Combinedwith the seed germination test and soil column leaching test, these results indicatedtogether situ remediation effect of several organic amendments on Cd-contaminated soil.Reached the following conclusions(1) The change of Cd fractions after organic amendents added.The pyrolysis and composting of sewage sludge and food waste were added in soil,the dosage is5%, the percentage point of acid extractable Cd were decreased by5.9%-7.6%, the percentage point of residual Cd were increased by10.8%-25.0%, The fixationeffect of pyrolysis and composting is better than other amendents, the fixation effect ofthe pyrolysis is better than compost when from the same raw material. The mobility ofcadmium in the soil were increased with application of dry product. Compared with theCd fractions after60days incubation period, the cadmium in soil subjected to varyingdegrees of activation after330days incubation period, the performances of Cdactivation degree with various products as amendment presented in following order:drying product> composting product> pyrolytic product.Compared with the blank, the percentage point of acid extractable Cd weredecreased by9.3and15.2respectively with application of FT-2(5%humic acid and5%pine biochar) and FT-3(5%humic acid and10%pine biochar); the percentage point ofresidual Cd were increased by12.0and16.8respectively, the unstable fraction of Cdwere increased with application of FT-1(5%humic acid and1%pine biochar). Thefixation effect were increased with the increasing dosage of pyrolysis products.Compared with the Cd fractions after60days incubation period, the performances ofCadmium activity were increased after330days incubation period.(2) The change of physical and chemical properties of soil after organic amendentsadded. The physical and chemical properties of soil were changed with application ofsewage sludge and food waste products after60days incubation period. The pH valueof the soil were increased by0.430.83units compared to the control with applicationof composting product and pyrolytic product derived from sewage sludge and foodwaste, organic matter increased by5.2712.20g/kg. The CEC of the soil were increasedby2.834.53compared to the control with application of pyrolytic product. According tothe result of correlation analysis, it could be speculated that the change of pH in soil is oneof the main factors in charge of Cd forms distributions in soil with application oforganic amendments from sludge and food waste. Compared with the Cd fractions after60days incubation period, the pH value, organic matter and CEC were decreased after330days incubation period, the decreased degree presented in following order: dryingproduct> composting product> pyrolytic product. The effectiveness of soil cadmiumand soil properties has good correspondence relationship.The pH value of the soil were increased from5.29to4.98,5.27and5.46respectively with application of FT-1,FT-2,FT-3after60days incubation period, theorganic matter of the soil were increased from12.52g/kg to42.10g/kg,46.30g/kg and50.78g/kg respectively. The CEC of the soil were increased from18.51cmol/kg to22.98cmol/kg,25.01cmol/kg and29.05cmol/kg respectively. The physical and chemicalproperties of the soil were improved with the increasing dosage of the pyrolysisproducts. and may also decreases the effectiveness of cadmium in the soil. Comparedwith the Cd fractions after60days incubation period, the pH value, organic matter andCEC were decreased with application of FT-1,FT-2,FT-3after330days incubationperiod, the mobility of the soil were increased.(3) The evaluation of the fixation effect by the organic amendments.Compared with the control, the percentage points of the ryegrass seed germinationrate increased by17.322.0. Soil column leaching test assumes that the pH of theleachates are higher than the control with application of composting product andpyrolytic product derived from sludge and food waste, and the concentration ofcadmium and the release accumulation were lower than the blank.Compared with the control, the percentage points of the ryegrass seed germinationrate were increased by7.3,22.0and28.0with application of FT-1,FT-2,FT-3. The pHof the leachates presented in following order: FT-3＞FT-2＞FT-1, and theconcentration of cadmium and the release accumulation presented in following order:FT-1＞FT-2＞FT-3. There is a better correspondence between the pH of the leachates and the release of the Cadium. The fixed effects were increased with the increasingdosage of the pine biochar.