[Screening of the Reduction/Stabilization Reagent for Cr(â ¥) Contaminated Soil in a Planting Site and Reaction Process Monitoring].

There are lots of problems in the domestic remediation of Cr (Ⅵ) contaminated soil field,such as lack of the key processing parameters,poor long-term effect and so on.The Cr (Ⅵ) heavy polluted surface soil was sampled from an electroplating site in North-China,and then treated with five different reducing reagents.At the same time,the on-line ORP probes and interval sampling test were chosen to monitor the reaction process,and to explore the reaction rate and effect.The results showed that No.4 reagent had the highest Cr (Ⅵ) reduction effect,reaching up to 99.5%,and the minimum soil Cr (Ⅵ) concentration could reach 2.4 mg·kg-1.The No.1 and No.4 reagents had relatively faster reducing rates.There were obvious difference in ORP and pH monitoring values between different reductants,for example,the No.1 reagent kept the ORP value stable at around -400 mV.The No.4 reagent gradually increased the value from -200 mV to 100 mV since 30h,and then kept stable.According to the pH difference among different reductants,the No.4 reagent was the best and kept the pH value at around 7.Taking together the final effect and process key parameters,the No.4 reagent was the best.The scale-up experiment was operated with process monitoring,and the ORP and conductivity values showed that the reduction reaction took about 160 h.This work would provide theoretical basis for controlling the maintenance condition and reaction process in soil Cr (Ⅵ) remediation.

Application of nitrate to enhance biodegradation of gasoline components in soil by indigenous microorganisms under anoxic condition.

Anaerobic/anoxic biodegradation of hydrocarbons offers an attractive approach to the removal of these compounds from polluted environments such as aquifers, aquatic sediments, submerged soils and subsurface soils. The application of nitrate was investigated to accelerate the degradation of gasoline components such as mono-aromatic hydrocarbons and total petroleum hydrocarbons (TPH) in soil by indigenous microorganisms under anoxic condition. The addition of nitrate had little effect on the degradation of mono-aromatic hydrocarbons m- & p-xylene, o-xylene, sec-butylbenzene and 1,2,4-trimethylbenzene, but facilitated the degradation of TPH (C6-C12) and mono-aromatic hydrocarbons toluene and ethylbenzene markedly. Furthermore, the more nitrate added, the higher the percentage of toluene, ethylbenzene and TPH (C6-C12) degraded after 180 days of anoxic incubation. Microorganisms capable of degrading toluene, ethylbenzene and TPH (C6-C12) with nitrate as the electron acceptor under anaerobic/anoxic condition are composed predominantly of Alpha-, Beta-, Gamma- or Delta-proteobacteria. Beta- and Gamma-proteobacteria were the main components of indigenous microorganisms, and accounted for 83-100% of the total amount of indigenous microorganisms in soil used in this study. Furthermore, the total amount of indigenous microorganisms increased with nitrate added. The addition of nitrate stimulated the growth of indigenous microorganisms, and therefore facilitated the degradation of toluene, ethylbenzene and TPH (C6-C12).

Application of zerovalent iron (Fe(0)) to enhance degradation of HCHs and DDX in soil from a former organochlorine pesticides manufacturing plant.

Remediation of pesticide-polluted soil is particularly challenging when pesticides in soil are aged and a mixture of pesticides is present. Application of zerovalent iron (Fe(0)) was investigated to accelerate the degradation of HCHs (alpha-, beta-, gamma- and delta-hexachlorocyclohexane) and DDX (DDT, DDE and DDD) in the soil from a former organochlorine pesticide manufacturing plant. Ultrasonic extraction was used extract the organochlorine pesticides from soil. The identification and quantification of organochlorine pesticides in the extracts were accomplished by gas chromatograph. The addition of Fe(0) facilitated the degradation of the beta-HCH isomer, but had little effect on the degradation of alpha-HCH, gamma-HCH and delta-HCH. Zerovalent iron significantly increased the degradation of p,p'-DDT and o,p'-DDT in soil, and the percentage degradation of p,p'-DDT and o,p'-DDT increased with increased Fe(0) concentration during the first period of incubation. However, the amount of p,p'-DDD, the main dechlorinated product of p,p'-DDT, basically kept increased except in the unamended soil. The addition of Fe(0) therefore did not increased the percent degradation of summation SigmaDDT (p,p'-DDT+p,p'-DDD+p,p'-DDE) markedly.