| China is one of major country to produce chromate. The discharge of chromium(Cr)-containing salg resulted in serious pollution for the deposition site and ambient environment. Nowadays, the traditional treatment methods for the remediating the Cr-contaminated soils all have the disadvantages, such as high cost and secondary pollution. The biological remediation was paid more attentions in recent years due to the low investment and low function fees.In our previous researches, one indigenous microbial strain with high Cr(â…¥) reduction efficiency was isolated and screened from the soils contaminated by chromium containing slag. Based on the previous research, a novel technique "crashing-heaping-leaching-chromium recovery" for the remediation of soils contaminated by chromium-containing slag was proposed. The optimal parameters of technique was obtained using column leaching experiment. A pilot scale experiment was further carried out. Moreover, the obstrauct technology was preminary studied using absorption experiment and attended to further optimize technique for in-situ microbial remediation of chromium-contaminated soils. The results were obtained as follows:1) The result of the column experiment showed the addition of culture medium could stimulate the remediation of water soluble Cr(â…¥), exchangeable Cr(â…¥) and carbonate-bonded Cr(â…¥) in soils contaminated by chromium-containing slag. Particle size, spray intensity, initial Cr(â…¥) concentration and process systems were crucial parameters. The preferable result was obtained when the partical size was less than 20mm and the spray intensity was in the range of 29.6-59.2 ml/min. With the increasing of initial Cr(â…¥) concentration, the time for Cr(â…¥) remediation in soils increased. The cyclic spray revealed better efficiency of Cr(â…¥) remediation than a single spray cycle. The column experiment verified that it is feasible to remedate chromium contaminated soils using indigenous microorgainism. The result can provide the technique parameters for pilot experiment.2) A pilot experiment was further explored to optimize condition and a demonstration project of 25 tons/batch was run. The result revealed that the soils contaminated by chromium containing slag is completely remediated after 7-10 days run. The Cr(â…¥) leacing concentration declined from 53.8 mg/L of the initial concentration to 0.41 mg/L (HJ/T299-2007) at 10 days, which was lower than the Cr(â…¥) limited value of chromium-containing slag used as roadbed material and concrete according to the Environmental Protection Technical Specifications for Pollution Treatment of the Chromium Residue ((HJ/T301-2007). It was verified that the microbial remediation of the soils contaminated by chromium-containing slag was feasible in pilot experiment. The result provides an innovative way for the remediation of chromium contaminated soils.3) Langmuir adsorption isotherm can well describe the adsorption of Cr(â…¥) and Cr(â…¢) by sugarcane pulp residue and Cr(â…¥) by Fe(â…¡)-loaded biochar, while the adsorption of Cr(â…¢) by biochar fitted to Freundlich adsorption isotherm. The maximum adsorption capacity of Cr(â…¢) by biochar was 21.57mg/L, which was much higher than that of sugarcane pulp residue (3.38 mg/L); The maximum adsorption capacity of Cr(â…¥) by Fe(â…¡)-loaded biochar was 22.92mg/L, which was much higher than that of sugarcane pulp residue (0.57 mg/L). Therefore, Fe(â…¡)-loaded biochar was used as obstacle material of pollutants and applied to the micrpbial remediation technique of chromium contaminated soils. The revealed that the maximum adsorption capacity of Cr(â…¥) by Fe(â…¡)-loaded biochar can reach up to 860mg/g. |
