Study On Remediation Of Cadmium And Atrazine Combined Pollution Soil By Biochars

With the continuous development of industry and agriculture, heavy metal polluted and organic polluted soil is increasing. Restoration and comprehensive governance of these polluted soil are imminent, which is also become a environmental researchfocus. Biochar (BC), which has huge specific surface area and rich oxygen containing functional groups, shows a good performace of adsorption and a good reduction of soil heavy metal and organic pollutants activity. In addition, BC could promote the biodegradation of organic pollutants in soils by providing nutrients to microbes. Therefore, BC used widely in the environmental research. This study selected typical organic wastes in Guangxi, sugarcane top、cassava stem、 rice straw and silkworm excrement, as raw materials to preparate biochars at the temperatures of300℃and700℃,respectively(refers as BCst、BCcs、BCrs and BCse). We used different methods, including Scanning Electron Microscope (SEM), Fourier Transform Infrared Spectroscopy (FTIR), Boehm titration and determination of iodine adsorption value, organic carbon and cation exchange capacity, to character the traits of various biochars, thus, to show the difference of biochars by using different materials under different temperatures. BCst and BCse were selected as Cd and AT polluted soil amendments due to their huge difference of characteristics. By doing this, we expect to provide certain theoretical basis to remediate heavy metals and organic compound contaminated soil. The main research results are shown as follows:1、Pyrolysis temperature significantly affects the yield, ash content and the pore structure of the biochars.The same raw material, compared with low pyrolysis temperature(300℃),the yield of the biochars preparated at high pyrolysis temperature(700℃) is reduced and the ash is accumulated. Holes of biochars are richer and the pore structure is more obvious in the biaochars preparated at the higher pyrolysis temperature. At the same pyrolysis temperature, the yield and ash contnent of different biochars are characterized by:BCse>BCrs>BCcs> BCst.2、All the biochars pH value are higher than7, and the high pyrolysis temperature pH value is higher than low temperature biochars. At the same pyrolysis temperature,the pH value of different biochars are characterized by:BCse>BCrs>BCcs>BCst. In addition, biochars have rich oxygen containing functional groups, and the amount of the lower temperature is-more than the higher temperature biochars. Among them, the types and quantities of functional groups on BCse and BCst were more than the others. The biochars preparated at low pyrolysis temperature had more acidic functional groups, and the content of BCst-300, BCcs-300, BCrs-300andBCse-300was3.22,3.00,2.56and1.73mmol/kg respectively. BCst is givent priority tohydroxyl and carboxyl and other BC are given priority to phenolic hydroxyl and lactone base. The proportion of acidic functional groups decreased but the alkaline functional groups rised on the higher temperature biochars.3、Cd and AT can be adsorpted on BCs effectively, especially on BC-700. BCrs and BCse had more powerful adsorption capacity of Cd, while BCrs has more powerful adsorption capacity of AT. The adsorption behavior of BCs was affected with the pH value and the initial concentration of the solution. Partial neutral condition (pH=6) was more conducive to the adsorption of Cd on BCs, and the acidic conditions (pH=4) was more conducive to the adsorption of AT, meanwhile the adsorbing capacity of Cd and AT increased with the increase of concentration. Sorption kinetics of Cd and AT on all the BCs followed Pseudo-second-order kinetics equation.4、The pH, SOC and CEC of contaminated soil rose to some extent after BCs application, thus, reduced the content of soil aci-extractable Cd. Effects of applying BCse to increase soil pH and CEC was better than that of BCst while applying BCst to increase SOC was better than that of BCse. The application of BCs lessened bioavailability of Cd, in which the BCse-300treatment had the best effects. Comparing with CK, the content of Cd decreased significantly after the use of BCse-300, it could make content of Cd in soil decrease42.72%, then, the content of Cd in soil under application of BCse-700, BCst-700and BCst-300which decrease38.55%,31.28%and22.86%respectively.5、The application of BCs can adsorb of AT in the soil effectively, thus lessen the activities of AT and reduced the poison to soil microorganisms. BCs increased the soil microbial carbon and nitrogen content, also promoted digestion of AT in the soil, mainly by increasing the activity of soil microorganisms to promote microbial degradation of AT. Effects of applying BCse were better than that of the BCst and the best was still to apply BCse-300.As mentioned above, the BCs have remarkable remediation effects on Cd-AT compound polluted soil. There is a substantial reduction of soil active Cd contents and soil AT residual by adding different BCs, in which the using of BCse, under the manufacture at300℃, has best reduction effects. By comparing the CK, the contents of active Cd and AT decreased by47.72%and84.51%, respectively.