Study On Synergistic Effect Of Ferrous Sulfate And Digestate On Co-disposal Of Chromium Containing Soil

In this work,ferrous sulfate and digestate were used to co-dispose the Cr（VI）in simulated soil,and the synergy were verified through co-disposal effect comparison experiments,and the dosage and reaction conditions were briefly optimized by single-factor experiments.Then the synergistic mechanism of ferrous sulfate and digestate co-disposal of Cr（VI）in soil was investigated through ion impact experiments,soil co-disposal effect comparison experiments,X-ray photoelectron spectroscopy（XPS）and microbial community.Finally,the preliminary exploration of the in situ application in this work was carried out by varying the sample agitation to compare the effect of reduction and by analysing the diffusion of the reduction potency of the mixture in the soil through soil simulation column experiments.The main results are as follows:（1）Ferrous sulfate and digestate co-disposal the Cr（VI）in simulated soil,the reduction efficiency is higher than that of the single ferrous sulfate method and the reduction rate is faster than that of the single digestate reduction method,which preliminarily proves that the ferrous sulfate and digestate have a synergistic effect.After adding 3%ferrous sulfate,5%digestate and 2%glucose into the chromium-contaminated simulated soil which the initial concentration is 3000 mg/kg,and adjusting the water content was at about 50%,then the reactor was placed in an anaerobic environment at 30°C（constant temperature）,all Cr（VI）was converted to Cr（III）within 10 d.（2）Both SO₄^2- and Fe（III）alone can promote the reduction of Cr（VI）by digestate,after the addition of an appropriate amount of ferrous sulfate,Fe（II）is completely converted into Fe（III）,the coexistence of SO₄^2-and Fe（III）in the medium has a more obvious promotion effect,and the mixture can also automatically adjust the p H of the soil.The results of XPS analysis showed that Fe（II）,sulfite and sulfide appeared in the chromium-containing soil after co-processing of ferrous sulfate and digestate.The results of microbial community analysis showed that the abundance and diversity of bacterial communities in the co-processing group were higher than those in the digestate treatment alone,not only the relative abundance of chromium-reducing bacteria increased,but also the abundance of iron-reducing bacteria and sulfur-reducing bacteria promote and after co-processing.（3）In the low Cr（VI）concentration environment,the reduction rate of Cr（VI）was slightly faster with the homogenous dosing than the agglomerated dosing,it can convert all Cr（VI）into Cr（III）in a short time.In the high Cr（VI）concentration environment,the reduction rate was faster with the homogenous dosing at the initial stage,but it became gentler and the agglomerated sample continued to reduce Cr（VI）at a slower rate,and the reduction efficiency was higher than that of the homogenous sample.The reducing effect of the mixture of ferrous sulfate and digestate on Cr（VI）in soil is not limited to the surrounding of the drug release point,and it can deeper into the soil,and the reduction effect is inversely proportional to the diffusion distance.The use of ferrous sulphate and digestate for the synergistic disposal of Cr（VI）in soil reduces the use of chemicals and rationally disposes of organic waste digestate.It overcomes the shortcoming of long-single treatment cycles for digestate,and achieves complete reduction of Cr（VI）which is expected to achieve low-cost in situ remediation.This method provides theoretical support and technical support for the low carbon remediation of Cr（VI）contaminated sites.