Optimum Dose Of Lime And Fly Ash For Treatment Of Hexavalent Chromium–Contaminated Soil

The presence of hexavalent chromium, Cr(VI), in soil is an environmental concern due to its effect on human health. The concern arises from the leaching and the seepage of Cr(VI) from soil to groundwater. In this paper, a stabilization technology to prevent this problem was simulated on an artificial soil contaminated with hexavalent chromium. The process is a physico-chemical treatment in which the toxic pollutant is physically entrapped within a solid matrix formed by the pozzolanic reactions of lime and fly ash to reduce its leachability and, therefore, its toxicity. This paper presents the optimum ratio of fly ash and lime in order to stabilize artificial soils contaminated with 0.4 wt.% of Cr (VI) in a brief term process. The degree of chromium released from the soil was evaluated using a modified Toxicity Characteristic Leaching Procedure (TCLP) by US Environmental Protection Agency (EPA). Overall, experimental results showed reduced leachability of total and hexavalent chromium from soils treated with both fly ash and quicklime, and that leachability reduction was more effective with increasing amount of fly ash and quicklime. Stabilization percentages between 97.3% and 99.7% of the initial chromium content were achieved, with Cr(VI) concentration in the TCLP leachates below the US EPA limit for chromium of 5 mg/l. Adequate treatment was obtained after 1 day of curing with just 25% fly ash and 10% quicklime.     

APPLICATION OF THE HEC-4 MONTHLY STREAM FLOW SIMULATION MODEL1

ABSTRACT: The HEC-4 monthly stream flow simulation model, developed by the Hydrologic Engineering Center, Davis, California, is used to extend the available historical stream flow records in the Central Ohio area. The principal objective of this paper is to examine the effectiveness of the HEC-4 model in generating synthetic monthly flows. Important statistical parameters are evaluated in order to relate the statistical properties of the historical and generated flows. In doing so, it is observed that the mean, standard deviation, and skewness of the generated flows are consistently larger than the corresponding estimates based on historical flows. However, results show that these statistics, as well as the lag-1 serial correlation, are generally well maintained by the generated sequences. The degree to which any statistical dissimilarities would be critical, from an engineering design point of view, is demonstrated by utilizing their low flow characteristics. Estimates of reservoir safe-yields, based on a nonsequential mass-curve analysis of the historical and generated low flows, indicate a nominal difference in this particular study.     

对中国排污收费制度改革的思考

排污收费制度是中国环境政策中一个核心的管理手段。它是我国为强化环境管理，运用经济手段，促进工业企业污染防治的一个独特的制度。在新的市场经济体制下和环境目标下，这项制度已不能适应社会主义市场经济发展的需要，因而在必要进行改革以适应新形势下环境保护工作的需要。在分析现行排污收费制度基础上，对我国现行的收费制度、政策和标准等的改革提出见解。     

云南潞西上芒岗红色粘土型金矿地质特征

潞西上芒岗红色粘土型金矿赋存于下二叠统岩溶面之上的第三、第四系红色粘土层中 ,矿体形态受地形控制明显 ,呈似层状。品位较高 ,规模中等 ,适合于露天开采。矿体的红土化作用不彻底 ,去硅富铁铝能力低 ,常见高岭石与伊利石共生。矿石中石英、褐铁矿、粘土矿物为主要载金矿物。成矿物质来自燕山中晚期形成的中侏罗勐嘎组中段与二叠系的沙子坡组的断层接触破碎带内的卡林型金矿。在湿热条件下 ,金发生活化、迁移、富集 ,在潜水面附近成矿。     

Interference of three weed extracts on uptake of nutrient in three different varieties of paddy through radio tracer techniques

Interference of three dominant weed extracts viz., Ageratum conyzoides L., Melilotus indica All. and Parthenium hysterophorus L. were examined on seed germination, seedling growth, and nutrient uptake (32P and 65Zn) in three different varieties (PD-10, PD-12 and PB) of paddy (Oryza sativa L.). Among the three different varieties irrespective of weed extracts, PD-10 and PD-12 were resistant and PB was susceptible in terms of seed germination, radicle length and plumule dry weight; and PD-12 and PB were resistant and susceptible, respectively, in terms of plumule length and total seedling dry weight. A. conyzoides caused maximum reduction in seed germination and M. indica in seedling growth in different varieties of paddy. The weed extracts interfered in uptake of both 32P and 65Zn and there was a gradual decrease in uptake of both nutrients with increasing concentration of extracts in both root and shoot. The uptake of 32P and 65Zn was more inhibitory with the extracts of A. conyzoides and M. indica, respectively in different varieties. The inhibition in seed germination, seedling growth and nutrient uptake may be due to the presence of phenolics and other secondary metabolities. The phenolics such as gallic, vanillic, protocatechuic and p-hydroxybenzoic acids were identified from these weed extracts.     

湖南耐寒桉树优良单株组培研究

本研究以湖南省林业技术推广总站在湖南选育的17个耐寒桉树优良单株为试验材料,进行组培繁殖,有14个优良单株成功地诱导出了愈伤组织或芽。结果表明,以一年生扦插苗的当年生嫩枝作为外植体来源,污染率低且愈伤组织和芽的诱导率高;0.25％氯化汞消毒15—20分钟,可将污染率控制在70％以下,且对外植体的损害最小;按树最佳的诱导培养基为:1/2MS+BA_(1.0)+IBA_(0.25),最佳的继代培基为:MS+BA_(1.0)+KT_(1.0)+VB2_(10)。     

污水土地处理试验工程慢速渗滤系统对优先有机污染物的净化

本文通过模拟实验及现场考察,研究了天津污水土地处理试验工程中慢速渗滤系统对优先有机污染物的净化效率以及该系统经处理污水后对土壤及作物的影响进行了探讨.