Advanced Materials Research Vol. 414

Abstract: Chromium-containing slag is one of the most hazardous solid waste because of the high content of dissolvable Cr (VI). Bacterial strains which can remove Cr (VI) efficiently were isolated from chromium-containing slag. The effect of processing parameters, such as quantity of chromium-containing slag, initial pH, temperature and agitation speed on the detoxification of chromium-containing slag were detected in the experiment. The results shows that the detoxification effect is reduced along with the quantity of chromium-containing slag is increased, and the optimized parameters for removing Cr (VI) from chromium-containing slag using the mixed strains are as follows: temperature = 30°C, pH = 7.0, agitation speed = 150 rpm. The detoxification experiments of the mixed strains indicated that the detoxification of chromium-containing slag is related to the growth law of the microorganisms, and the removal of Cr (VI) occurred primarily in the first 24h which is the exponential growth period of the mixed strains. At the same time, the bacterial strains can efficiently accelerate Cr (VI) leaching rate and remove it.

Abstract: With the accumulation of solid waste in developing countries, sites of closed landfills have attracted attentions, which can be sorted as one typical brown field in urban area. Taking closed municipal solid waste landfills as examples, case study for turning brown land into green space in Europe and USA was carried out, based on which, suggestions on the ecological regeneration of brown land in China were put forward. It was put forward that for closed landfill constructed in the earlier days, the reliable procedure for the site generation should be reclamation. If it is not possible to carry out the reclamation engineer at present, establishment of trees on the top soil of closed landfill, in other words, eco-regeneration can reduce the negative effects of landfill as far as possible. For the developing countries, reduction, stabilization and recycling of solid waste should be the final solution for solid waste.

Abstract: The contaminated soil remediation standard formulation's aim is under the premise of ensuring the reuse of contaminated land, to reduce or cut the contaminants which cause to receive in the more serious contaminated soil environment is insufficient to lead to greater ecological damage and health risks. In this paper, some suggestions on the establishment of remediation standards for contaminated soils such as clean technology factors, factors of soil background values, standards and regulations to control pollution of ecological factors and assessment of toxicological risks were put forward, based on the analysis of the disadvantages of soil environmental quality standard research on evaluation methods for remediation effectiveness of contaminated soil, commonly used evaluation methods, such as phytotoxicity testing, terrestrial invertebrate toxicity testing, soil microorganism toxicity testing and biomarker assessment methods were described. Furthermore, future research directions were also discussed.

Abstract: Ancient pyrometallurgical zinc generated large amounts of slags. Natural leaching from ancient pyrometallurgical zinc sites has contaminated the soil closed to the deposits. Electrokinetic removal technology was adopted to treat this slags. But the generation of metal hydroxide precipitation near the cathode during the electrokinetic removal process could be the most serious factor that influenced the removal rate. In this study, cation exchange membrane was used in electrokinetic removal process to overcome this major drawbacks. The final results showed that cation exchange membrane could effectively condition pH of the whole electrokinetic removal system resulted in the dissolution of the precipitated heavy metals near the cathode. In other words, the enhanced treatment have achieved positive effect to some extent. But the leak tightness of experiment setup might not be perfect. Moreover，some operation parameters of the electrokinetic removal technique must be further optimized.

Abstract: This paper includes the analysis of total content of Cd element of 102 samples in the surface soil of farmland around the slag field. We evaluated the contamination of Cd of each samples and the space distribution with the potential ecological risk index method based on ArcGIS soft. The results showed that: average of potential ecological risk index of Cd is 241.4, Moderate ecological risk area accounted for 2.7% of the study area, strong ecological risk area of the region accounted for 30.1% of the study area, 22.2% of the study area had the considerable ecological risk, and the rest 39% of the study area had the extremely strong ecological risk.

Abstract: Petroleum contamination has become one of the major soil contaminations. Aiming at petroleum hydrocarbon contamination, the multi-group opposite experiments is set; this paper use some petroleum hydrocarbon-decomposing bacteria to remedy the soil contaminated by different carbon chain petroleum hydrocarbons. Compare and study the remedial results, and study the growth of the bacteria in the decomposing process. The Study shows that the degradation rate of the bacteria to short-chain petroleum hydrocarbons is relatively high; Within 40 days without nutrient substance, degradation rate of bacteria to gasoline and diesel is 80%, degradation rate of bacteria to aromatics and lubricants is 50%, the trend of bacteria’s growth curve and the degradation rate curve of each component are approximate.

Abstract: This paper describes the model of heavy metal-Cu contaminated soil remediation standard value based on risk assessment. In the Cu contamination risk assessment model, the main exposure methods are oral ingestion and inhalation through breathing, which not only simplifies the calculation but also make people get a clearer understanding of the way of Cu contamination. We get the simplified formula, calculate and discuss Cu contaminated soil remediation target value in specific parameters to provide reference and basis for the remediation of Cu contaminated soil.

Abstract: To investigate the effects of straw ash and sewage sludge on the quality and production of pakchoi grown in cadmium contaminated soil, the present experiment was designed to study the change of quality, production and Cd content of pakchoi for applying different amounts of straw ash and sewage sludge. The results showed that with increase of manure amount, pakchoi production , height ,leaf area and leaf number significantly increase,The Vc and soluble sugar content is a significant trend of rise; On the Cd2Cd4 pakchoi with contrast chlorophyll maximum increased 1.5-1.4 times, Vc increased 1.4-1.3 times, soluble sugar maximum increased 1.7-1.8 times; The pakchoi’ over ground and roots Cd content was significantly lower in the Cd2Cd4 decreased 70.8%-65.6% ,54.5%- 48.3%; The best recommended amount of manure is 40 g·kg^-1 for pakchoi in cadmium contaminated soil.

Abstract: In the electrokinetic (EK) remediation of contaminated soils, the ions in porous fluid move out of soil and meanwhile the ions in electrolytes move in, resulting in the changes of soil conductance and remediation efficiency. This paper investigated the influence of different cations on the power efficiency of EK remediation of chromium-contaminated soils with Fe²⁺, Ca²⁺, H⁺, K⁺, and Na⁺ ions. Results showed that the cations of low equivalent ionic conductance can effectively decrease the power consumption meanwhile not deteriorating the removal rate of total chromium.

Abstract: The produced and extraction process of pyritic would generate a large amount of pyritic mineral processing solid waste. This kind of waste can lead to land occupation, and contaminate the local water, air and soil. Therefore, in this paper, Thiobacillus ferrooxidans and Thiobacillus thiooxidans are used to deal with the pyritic mineral processing solid waste. The particles, catalysts and bioleaching products between microorganism and pyritic mineral processing solid wast were studied. It is indicated that the microorganism growth and the heavy metals leaching efficiency involve biological and chemical interactions. The experimental results suggested that the T.t was best to bioleach the pyritic mineral processing solid waste, and the efficiency of T.f was worse than that of T.t. The leaching effect of mixed bacterias of T.t and T.f fell in between, the leaching rate would decrease when the pulp density increased. The micro-morphology of bacteria was observed by SEM detector, the single cellular dimension of bioleaching bactreia was about (1~2) μm × (0.2~0.5) μm.