Hydraulic Conductivity and Leachate Characteristics of Stabilized Fly Ash

Disposal of fly ash on land amounts to sacrificing precious land space. Recycling of fly ash is one of the methods of solving the disposal problem. Stabilization of a low lime fly ash with lime and gypsum was studied through large scale tests on the stabilized material designed to simulate field recycling conditions as closely as possible, and found to be a very effective means to control hydraulic conductivity and leachate characteristics. The effects of moulding water content, lime content, gypsum content, curing period, and flow period on hydraulic conductivity, and on leachate of metals flowing out of the stabilized fly ash are reported herein. With proper proportioning of the mix, and adequate curing, the values of hydraulic conductivity on the order of 10?7 cm∕s were achieved. The concentrations of As, Cd, Cr, Cu, Fe, Hg, Mg, Ni, Pb, and Zn in the effluent emanating from the hydraulic conductivity specimens of mixes with higher proportions of lime or lime and gypsum were below threshold limits acceptable for contaminants flowing into ground water.     

Environmental Geochemistry of Leachate From Leached Brown Coal Ash

The long-term disposal of ash from brown coal combustion requires a thorough understanding of the geochemical controls on leachate quality. The geochemistry of leachate in ash generated from the combustion of coal in the Latrobe Valley region of Victoria, Australia, has been studied in the field and laboratory. The field studies, conducted over 14 months, showed active leaching and changes in leachate chemistry in the ash with mobilization of some trace elements. A further series of laboratory columns demonstrated similar leaching dynamics. Geochemical modeling indicated that both sulfate and carbonate minerals are the most likely solubility-controlling mineral phases in the ash. For regularly detected trace elements, such as As, Ba, and B but particularly Mo, Se, and Sr, the trends suggest that adsorption and coprecipitation controls are also important. The overall approach adopted in this paper has enabled a more realistic assessment of the controlling processes for solute transport during the active leaching phase of ash disposal, thereby improving long-term environmental management.     

Physical–Chemical Treatment of Groundwater Contaminated by Leachate from Surface Disposal of Uranium Tailings

Leaching of trace elements including heavy metals, nonmetals, and radionuclides from surface impoundments of tailings generated during uranium mining and milling often leads to groundwater contamination. This paper reports results from coagulation and membrane filtration experiments designed to evaluate the capabilities of these processes to remove molybdenum, selenium, uranium, radium, thorium, and other mono- and divalent ions from contaminated groundwater in a shallow unconfined aquifer influenced by uranium tailings. A 10 mg Fe3+/L dose at pH 4 and 10 was found to be very effective for removing radium and thorium that were associated with particles in the raw water. Molybdenum and uranium removals by coagulation are consistent with surface complexation and electrostatic interactions between major coagulant and contaminant complexes in solution. Poor selenium removal suggests that selenate [Se(VI)] was the dominant species in the surficial groundwater. Permeation coefficients (intrinsic transport parameters) for dissolved ions and complexes across three new generation thin-film composite nanofiltration and reverse osmosis membranes evaluated obeyed Gaussian distributions with ionic charge having a mean value of zero. Thus, dissolved solute rejection from brackish multicomponent solutions appears to be only a function of the magnitude of ionic charge and not its sign (positive or negative). Solute permeation coefficients decreased in a power-law fashion with increasing product of molecular weight and absolute ion charge suggesting that both properties determine their removal by nanofiltration and reverse osmosis membranes. Because nanofiltration and reverse osmosis were found to be highly effective for removing a variety of ionic solutes they can be employed in pump and treat operations for groundwater purification prior to reinjection.     

垃圾填埋场渗沥液处理技术发展趋势

综述我国垃圾渗沥液的特性、处理技术的发展和应用情况,并对存在的问题、发展对策进行了分析。     

垃圾填埋场渗沥液处理技术发展趋势

综述我国垃圾渗沥液的特性、处理技术的发展和应用情况，并对存在的问题、发展对策进行了分析。     

危险废物处置场的计算机控制系统

针对工业危险废弃物处置场的生产特点,设计了一套以网络结构和PLC控制站为主的计算机控制系统,并详细介绍了该系统的结构、特点、功能及实施方法.     

Potential Environmental Applications of Pure Zeolitic Material Synthesized from Fly Ash

A pure 4A∕X (60∕40) zeolite product was synthesized from silica extracts of the Meirama fly ash in northwestern Spain. A high cation-exchange capacity (4.7 meq∕g) was obtained for the zeolitic material. The potential application of this coal fly ash conversion product for decontamination of high heavy metal waters was evaluated using three high heavy metal waters from acid mine drainage around the pyrite Huelva belt. The results were compared with those obtained with an equivalent pure commercial synthetic zeolite. A considerable reduction in the heavy metal content was attained (Zn from 174 to <0.1 mg∕L, Cu from 36 to 0.1 mg∕L, Fe from 444 to 0.8 mg∕L, Mn from 74 to <0.1 mg∕L, Pb from 1.5 to <0.1 mg∕L, and Cd from 0.4 to <0.1 mg∕L), even in high Ca and Fe waters using zeolite doses from 5 to 30 mg∕L. Both precipitation and cation-exchange processes accounted for the reduction in the pollutant concentration in the treated waters. Leachable hazardous elements from coal fly ash, such as Mo, B, As, V, and Cr, were not fixed in the synthesis of pure zeolites from the silica extracts. Consequently, they did not restrict the potential applications of this material as an ion exchanger, unlike the zeolitic material obtained from fly ash by direct alkaline conversion.     

Numerical Evaluation of Landfill Stabilization by Leachate Circulation

This study compares various leachate management scenarios using a biologically reactive transport model, which is proposed in this study. The proposed model can be used to predict the contribution of biodegradation to contaminant attenuation and contaminant concentration in leachate over time. It can also be used to assess the extent of landfill stabilization in terms of local mass per bulk volume of remaining refuse available for transfer. A sensitivity analysis shows that landfill stabilization has significant sensitivity to most biokinetic parameters, the fluid-phase saturation constant, and the dissolution rate, in addition to the half-saturation constant and the retardation factor. The proposed model is applied to assess landfill stabilization under two control scenarios: leachate recycling versus continued input of clean water with no recirculation. The simulation results indicate that leachate recirculation provides more favorable conditions for development of an active anaerobic bacterial population and, hence, accelerates landfill stabilization.     

危险废物处置中心厂址选择的环境可行性

文章通过危险废物处置中心的厂址选择,从自然社会环境、厂址环境、工程地质、水文地质、气候条件、应急救援等多方面进行综合分析,对多个厂址进行了比选,确定了推荐厂址和备选厂址,论证了它们的环境可行性。     

Field Evaluation of a Leachate Collection System Constructed with Scrap Tires

Landfilling costs and the potential uses of scrap tires have prompted researchers to investigate beneficial reuses. One important application is the use of tire chips as a leachate collection material in municipal solid waste landfills. Laboratory and field studies were conducted to investigate the performance of tire chips as a drainage medium in landfills. The laboratory portion of the program included a series of hydraulic conductivity and compressibility tests. Two field test cells, one with tire chips and another with gravel as the control, were constructed. The tire-chip cell was instrumented with flowmeters, thermistors, and gas collection devices to evaluate the hydraulic performance as well as the potential for spontaneous combustion. Leachate collected from the two cells was analyzed to determine if tire chips would potentially contaminate the groundwater. The results indicated that adequate drainage conditions were present within the tire-chip layer. The presence of insignificant quantities of carbon monoxide, and the lack of oxygen, and recorded low temperatures suggested that a combustion hazard was not present. The field leachate data indicated that tire chips can be safely used as part of a landfill leachate collection layer, even though it may not be suitable to place them near drinking water sources.     

Leachate from Land Disposed Residential Construction Waste

Solid waste from construction and demolition (C&D) activities is often disposed in unlined landfills. Leachate from unlined landfills poses a potential risk to groundwater quality. An understanding of the types of chemical constituents likely to be encountered in C&D waste landfill leachate and the concentrations at which they occur help assess this risk. An experiment was performed to characterize leachate from land-disposed residential construction waste. Four 54 m2 (580 ft2) test cells were excavated, lined, and filled with waste. Leachate samples were collected and analyzed for a number of water quality parameters over a 6 month period. No volatile or semivolatile organic compounds were detected at elevated constituent levels in the leachate. Inorganic ions were found to account for the bulk of the pollutant mass leached. Calcium and sulfate were the predominant ions in the leachate, resulting from the dissolution of gypsum drywall. The concentrations of several leachate constituents were found to exceed water quality standards. These constituents included aluminum, arsenic, copper, manganese, iron, sulfate, and total dissolved solids. Arsenic was the only primary water quality standard exceeded. The arsenic was concluded to result from chromated copper arsenate (CCA)-treated wood. The potential risk of impacting groundwater was examined by comparing the measured constituent concentrations with the water quality standards to assess the amount of dilution and attenuation needed in the groundwater so that a water quality standard would not be exceeded. The water quality standard exceeded by the greatest magnitude was manganese, followed by iron.     

Evaluation of Legal Risks for E-Commerce in Construction

E-commerce is steadily becoming a reality in the construction industry. However, despite the increasing rate of utilization by owners and contractors alike, the legal implications of using e-commerce in construction have not been studied in depth. This paper fills this gap in literature. It identifies and analyzes the different types of legal risks involved in the use of e-commerce in construction. It also outlines the risk that contractors and professionals may face in their e-commerce implementations. A classification of e-commerce legal risks is also introduced. The legal risks discussed include agency, jurisdiction, contract formation, validity and errors, authentication, attribution, nonrepudiation, privacy, conflict of laws, and conflict between law and technology.     

Swell Potential of Pulverized Coal Combustion Bottom Ash Amended with Sodium Bentonite

Within the last decade several studies have been conducted to evaluate the geotechnical properties of bottom ash obtained from electric utilities burning pulverized coal amended with admixtures such as clay, bentonite, and lime. Most of these studies concentrated on evaluating strength and stiffness characteristics of the mixtures. Because of the high volume change characteristics of bentonite and clay, improper and/or excessive use of these admixtures can impart significant swelling characteristics to the mixtures. This study was conducted to evaluate the swelling properties of two bottom ash-bentonite mixtures compacted at various initial moisture contents. Results from this detailed investigation show that the swelling potential increased with the increase in bentonite content and decreased with the increase in initial moisture content. Mixtures with 20% bentonite were observed to have volume change characteristics that may not be suitable for some lightly loaded structures. Mixtures with 15% bentonite; compacted at initial moisture contents of 18% or higher; were observed to have less than 4% free swell, whereas for mixtures compacted at an initial moisture content of 16% or lower, the percent increase in free swell was observed to be greater than 7%.     

Fenton Process for Landfill Leachate Treatment: Evaluation of Biodegradability and Toxicity

The single Fenton or the Fenton process implemented in combined scheme as a posttreatment after the ferric chloride coagulation was applied for leachate collected from a real waste disposal site. Depending on the ratios of H2O2/chemical oxygen demand, H2O2/Fe2+, and pH, the Fenton oxidation or both the Fenton oxidation and the Fenton coagulation were involved in chemical oxygen demand reduction. The implementation of ferric chloride coagulation as a pretreatment stage or acidification of raw leachate did not result in the improvement of chemical oxygen demand reduction efficacy of the following Fenton process comparing with that obtained by the direct Fenton treatment of raw leachate. The direct Fenton treatment with a higher (3/1) H2O2/chemical oxygen demand ratio applied to raw leachate without pH preadjustment (H2O2/Fe2+ = 10/1), produced more oxidized organic compounds (measured as dissolved organic carbon/chemical oxygen demand ratio), more biodegradable by-products (measured as a 7-day biological oxygen demand/chemical oxygen demand ratio), and required a considerably lower dosage of NaOH for neutralization, making it preferable for the leachate treatment. Although up to a twofold reduction in the toxicity was observed after the overall Fenton process application, the treated leachate remained extremely toxic to Daphnia magna.     

国内铝工业全行业铝灰特性和利用处置技术研究进展

为对我国铝工业全行业铝灰的特性进行总结归纳,通过收集国内24家大型铝行业企业的不同类型铝灰样品进行pH、含盐量、元素含量、重金属等测试分析,梳理了各行业铝灰的来源特性、成分特性及污染特性;针对当前国内铝灰利用处置市场的活跃需求,归纳总结了铝灰规模化利用处置技术实践进展及发展方向,以期为全行业铝灰的利用处置提供借鉴和指导。     

Hydrological Evaluation of Septic Disposal Field Design in Sloping Terrains

The most common form of onsite domestic wastewater treatment in the United States is the septic system. Although the design of these systems has been well established, no systematic evaluation of septic system performance exists for sloping hardpan soils. In this paper, we develop a simple hydrologic model for assessing the probability of failure for a set of hydrologic conditions, septic loading rates, and soil and landscape parameters that are readily available for sloping soils. To demonstrate the model capabilities, input data for a septic field of a two-person residence in the New York City drinking water basin in the Catskills was utilized. Our analysis showed that the saturated hydraulic conductivity, depth to the impermeable layer, and slope of the drain field are critical parameters to assess in the design and siting of these systems. We concluded that septic systems perform poorly in undulating landscapes where the hydraulic conductivity is low and the impermeable layer is close to the surface. Under prolonged rainfall conditions on these soils, the septic field and downslope field saturate, causing hydraulic failure of the septic system and saturation in the downslope field; as a result, effluent may be routed directly to streams via overland runoff.     

化学镀铜废水的处理

本文探讨了用水解中和沉淀、氧化－水解中和沉淀、取代及化学还原法处理化学镀铜废水的可行性。试验结果表明，用水解中和沉淀法，铜的去除率在１４～２０％，用氧化－水解中和沉淀法和取代处理法，铜的去除率约为４０％。化学还原法的关键在于还原剂的选择。用连二亚硫酸钠处理，效果显著。在最佳操作条件下，出水能稳定达到排放标准，产物沉降性能好，便于回收再利用，是一种简便、实用的方法。     

从氯化烟尘酸浸液中萃取提纯钪的实验研究

用萃取法对氯化烟尘酸浸液中钪的提纯进行了实验研究。萃取体系采用P204＋改质剂＋磺化煤油。结果表明：钪的萃取率为99．7％，铁、锰的去除率最高分别达到98．1％和99．3％。有机相用NaOH溶液反萃，反萃率可达99．6％，有效地实现了钪与铁、锰杂质的分离。     

Evaluation and Management of Political Risks in China's BOT Projects

The potential slowdown of the economic growth in China has led the government to increase spending in basic infrastructure such as roads, ports, and power generation facilities. There are opportunities in the infrastructure sectors for foreign investors. It is important however to identify and manage the unique or critical risks associated with investments in China's infrastructure projects. Such issues have received special attention with the closure of the Guangdong International Trust and Investment Corporation in 1998 and the subsequent confusion over government support and guarantees. This paper is based on the findings from an international survey on risk management of build-operate-transfer (BOT) projects in developing countries, with emphasis on infrastructure projects in China. It discusses specifically the criticality of the political and force majeure risks. Based on the survey, the following critical risks, in descending order of criticality, are identified: Chinese Parties' reliability and creditworthiness, change in law, force majeure, delay in approval, expropriation, and corruption. The measures for mitigating each of these risks are also discussed.     

铝生产过程中固体废物的处置

叙述了铝生产过程中所产固体废物的种类、性质及处置方法。指出固体废物综合利用是一举多得的措施,符合国家的环境保护政策和可持续发展的战略要求。