Electrokinetic remediation of bottom ash from municipal solid waste incinerator

The electrokinetic remediation was studied to verify the possibility to reclaim the bottom ash from municipal solid waste incineration (MSWI). In Italy, a production of 1 million tons per year of this kind of residue has been estimated, 90% of which is still landfilled. This work shows the results of four electrokinetic remediation tests for the removal of Pb, Cu, Zn, Cd and chlorides, using an open cell with graphite electrodes and without enhancing agents. The four tests have, respectively, been performed at a constant current density of 0.89, 1.67, 2.04 and 2.48 mA cm⁻², with duration of 42, 68, 47 and 40 h. Heavy metals occur in ashes in various forms, such as exchangeable, adsorbed, precipitated, organically complexed and residual phases. In order to determine the nature of any given system, in terms of specific chemical species and pertaining mobilities, sequential extraction analyses have been performed. The release of pollutants was investigated for treated and untreated ash. After treatment, the concentration of pollutants in the leachate was reduced by 31-83%, better results being obtained for chlorides. Both the low amount of heavy metal extracted and the increase of ash pH during the electrokinetic tests, suggest to use enhancing agents or a cation exchange membrane at the cathode, to prevent the precipitation of metals as hydroxides.     

Use of municipal solid waste incineration fly ash in concrete

With a view of reducing the quantities to be landfilled, the Solvay Company has been working on the development of a new physicochemical treatment for municipal solid waste incineration (MSWI) fly ashes: the Revasol process. This process allows reducing the soluble fraction, fixing heavy metals and eliminating dioxins. This article reports on the characteristics of a treated ash and on its use in concrete. For the latter point, three characteristics were chosen: the compressive strength and the durability of the hardened concrete and its behavior to leaching. From mechanical and durable points of view, the ash incorporated in the concrete behaves like ordinary sand. The leaching tests carried out on the concrete confirm that the process makes it possible to obtain materials without major risks for the environment. Also, these results as a whole suggest that the use of waste in concrete constitutes a potential means of adding value.     

Analysis and optimization of municipal solid waste combustion in a reciprocating incinerator

A mathematical model is presented for the combustion of municipal solid waste in a reciprocating incinerator. The most preferable incinerator is determined by detailed simulation and analysis of different incinerator shapes. Furthermore, the optimal design and operating parameters are obtained by analyzing the injection angle and velocity of the secondary air. Both the results of numerical simulation and practical operation show favorable combustion state, low contaminants emission, and suitability for the combustion characteristics of Chinese municipal waste and the treating requirements. This study provides an important reference for the optimizing design and operation of municipal solid waste incinerator.     

Preparation of low melting temperature glass-ceramics from municipal waste incineration fly ash

Glass-ceramics have been prepared from air pollution control residues (fly ash) of a municipal solid waste incineration (MSWI) plant in southern China. The use of additives was investigated in order to decrease the melting temperature of the waste and thus to reduce the costs of production of glass-ceramics from the vitrified waste. Results showed that the melting temperature can be decreased significantly from 1500 to 1200 °C, which was achieved by combining the MSWI fly ash with silica sand powder and a Fe₂O₃-rich and CaO-rich iron slag to form a glass in the SiO₂-CaO-Al₂O₃-Fe₂O₃ quaternary phase system. Sodium carbonate and borax were used as fluxing agents and TiO₂ of chemical grade was added as a nucleation agent. The main crystalline phase in both high and low melting temperature glass-ceramics was found to be diopside (Fe-bearing), and the microstructure exhibited the presence of fine crystals of size in the range 100-200 nm which developed at crystallization temperatures in the range 800-900 °C for 1-2 h. The leaching behaviour of the glass-ceramic materials was tested, and it was found to be lower than that of a cement-stabilized body that was fabricated using the same waste for comparison. The results demonstrate the feasibility of reusing MSWI fly ash for glass-ceramic production at relatively low melting temperature, e.g. in a less energy-intensive process, as a viable approach for tackling the problem of hazardous MSWI residues.     

On the fate of heavy metals in municipal solid waste combustion Part I: devolatilisation of heavy metals on the grate

The aim of this study has been to investigate the chemistry and volatility of the heavy metals As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn on the grate of a MSW fired furnace, using equilibrium calculations. Focus has been on the influence of varying MSW composition and operational parameters such as air/fuel ratio and temperature. Equilibrium distributions at 950–1600 K, under reducing and oxidising conditions on the grate, showed that Cd, Hg and Pb are fully volatilised. However, Cr is found to be stable in solid phase, in the entire temperature range. The volatile behaviour of Cd, Cr, Hg and Pb show no significant influence, while As, Cu, Ni and Zn are strongly influenced by one or more of the parameters; temperature, fuel/air and chlorine/metal ratios.     

掺烧生活垃圾焚烧飞灰和炉渣对水泥熟料矿物组成的影响

分别对掺烧20%生活垃圾焚烧炉渣的熟料和掺烧10%生活垃圾焚烧飞灰的熟料进行化学成分分析、相萃取、XRD分析与岩相分析,并与用化学纯试剂配料煅烧的基准样熟料进行对比研究。研究结果发现,受灰渣中较高含量的硫、氯等阴离子的影响,熟料KH值会降低;受灰渣当中微量重金属元素的影响,掺烧灰渣熟料的铁相中有少量C2F存在,并且其C4AF特征峰的d值增大。     

电化学氧化法处理垃圾焚烧发电厂沥滤液生化出水

垃圾焚烧发电厂储坑沥滤液是一种高污染、高氯离子和高胶体含量的废水,经过传统生化处理后仍难达标排放。根据生化出水中氯离子浓度较高的特点,面向实际工程应用,设计了板框式电化学反应器,以钛基氧化钌-氧化铱涂层电极(Ti/RuO₂-IrO₂)作为阳极,304钢板作为阴极,开展了电化学氧化去除废水中难生物降解有机物的研究。重点考察了电流密度、表观流速、氯离子浓度、电极极距等因素对去除废水COD的影响。结果表明:当电流密度为65.35 mA·cm^-2,反应器内表观流速为2.72 cm·s^-1,初始氯离子浓度为5000 mg·L^-1时,废水中COD的去除具有良好的效果。研究了COD去除的动力学过程,提出了反应体系中活性氯的减少可能是第二阶段COD去除速率降低的主要机理。对几种结构电化学反应器的能耗进行了对比分析表明,极距减小50%,去除COD的平均能耗可节约25%以上,紧凑多通道小电极极距结构在设计工业电化学反应器时值得考虑。     

垃圾焚烧厂渗滤液生化出水混凝处理及其模型的建立

对采用聚合氯化铝、硫酸铝和氯化铁等混凝剂处理焚烧厂垃圾渗滤液生化出水的混凝效果及其模型进行了研究.结果表明:聚合氯化铝对焚烧厂垃圾渗滤液中CODCr、色度和浊度的去除效果比硫酸铝和氯化铁要好,且投加量相对也较少.在投加量500 mg/L、中性条件下,CODCr、浊度和色度的去除率可分别达到28.9%、91.6%和77.6%.在不同投药量、pH和搅拌速度下,PAC保持了良好的污染物去除效果,而对硫酸铝和氯化铁的处理效果影响较大.各种混凝剂的最佳投药量与起始CODCr浓度之间的关系可采用指数关系式表达.通过对PAC在各条件下混凝效果的统计分析,采用Matlab优化工具软件,建立了垃圾焚烧厂垃圾渗滤液PAC混凝处理的处理效果数学模式方程,其与试验结果的相关系数可达到0.982,表明建立的模型与混凝处理效果较为一致.     

上海城市生活垃圾焚烧飞灰的性质分析

垃圾焚烧飞灰是我国城市垃圾焚烧新技术发展过程中产生的一个新问题,飞灰中有大量有害物质。必须予以安全处置。而飞灰的性质对如何处置以及处置的效果非常重要。飞灰的性质有很大的地域性差异。我们对上海浦东御桥垃圾焚烧厂产生的飞灰的相关性质如化学组成、重金属浸出率、重金属挥发特性等进行了检测。并对结果进行了分析。结果表明：上海市飞灰中SiO2含量较高。有利于进行熔融固化。但飞灰在熔融过程中。重金属的挥发量较大,需要引起注意。     

Characterisation of bottom ash from municipal solid waste incineration in Catalonia

Bottom ash from municipal solid waste incinerator plants in Catalonia was characterised to investigate some alternatives for its utilisation and their potential environmental impact. After a detailed chemical and mineralogical characterisation, physical and geotechnical properties were investigated. The study focused on the use of bottom ash as an aggregate substitute in pavement applications. The results show that this material may be successfully used as a compacted material in unbound road sub‐bases. According to Spanish Specifications for road construction, bottom ash complies with the technical requirements for sub‐bases. Data obtained from the leaching test satisfy the limit values established by Catalan Specifications for bottom ash utilisation. The use of bottom ash in the envisaged application should therefore not result in any environmental impact. © 2002 Society of Chemical Industry     

垃圾焚烧飞灰处置技术研究进展

系统介绍了垃圾焚烧飞灰处理技术和最新研究成果,阐述了垃圾焚烧飞灰处理技术一般可分为固化/稳定化技术和分离萃取技术两大类。其中固化/稳定化技术主要为水泥固化、热处理、化学药剂稳定化及水热处理技术;分离萃取技术主要为生物/化学提取和超临界流体萃取技术。分析了各项技术的优缺点,认为:水泥固化技术成本低,但增容过大;热处理技术有一定的减容效果,但能耗成本过高;化学药剂稳定化技术稳定化程度高,但较难实现多种重金属的同步固化;生物/化学提取技术反应条件温和,但成本较高;超临界流体萃取技术虽能有效实现重金属的回收利用,但其对设备要求过高;而水热处理技术的反应条件虽对设备有一定要求,但其无害化程度高,而且反应产物可以再利用。最后指出,水热法应该是未来具有较大应用潜力的飞灰处理方法。     

Characterization of solid residues from municipal solid waste incinerator

In China, the generation of municipal solid waste (MSW) incineration solid residues is expected to increase significantly in the future. Because of ever-increasing generation rates and the concentrations of potentially hazardous heavy metals, which may endanger the ambient environment, these solid residues are of particular concern. Thus, such issues have necessitated the study of the characterization of these solid residues. A detailed characterization of five samples of different type of ashes, collected from two types of MSW incinerators located in Shenzhen (southern China), was carried out in terms of chemical composition, morphology, mineralogy and leaching behavior. Results of chemical analysis and leaching tests suggest that the MSW incineration fly ash must be classified as hazardous waste and should be properly managed. Therefore, the results of this characterization would contribute to the development of adequate waste management strategies.     

水热法稳定垃圾焚烧飞灰中重金属研究进展

随着社会经济的发展和垃圾焚烧的应用,产生了大量属于危险废物的垃圾焚烧飞灰。其无害化处理技术的研发变得日益迫切,而水热处理技术是最具潜力的垃圾焚烧飞灰无害化技术之一。本文综述了水热法处理垃圾焚烧飞灰稳定重金属的研究进展。首先阐述了垃圾焚烧飞灰的理化性质;然后系统介绍了针对垃圾焚烧飞灰的水热处理方法,将其细分为传统水热法、添加剂辅助水热法和微波水热法,并分别总结了各类水热处理方法影响重金属稳定效果的因素,包括反应时间和温度、碱性激发剂及其浓度、液固比等;最后探讨了水热法稳定垃圾焚烧飞灰中重金属技术的优化途径,为后续的研究提供了研究思路,其中探究水热过程中硅铝酸盐矿物的合成及其稳定重金属机理极具发展潜力。     

A particle scale model for municipal solid waste and refuse-derived fuels pyrolysis

The solid phase decomposition during pyrolysis of municipal solid waste (MSW) and refuse-derived fuels (RDF) is modelled on particle scale accounting for heat and mass transfer. Waste pyrolysis is expressed as a linear combination of pyrolysis of its components. The novel characterization method used expresses waste composition in terms of three reference species. The selected species are a mixture of cellulose and hemicellulose, a mixture of polystyrene and polyethylene terephthalate, and a mixture of polyethylene and polypropylene. The pyrolysis kinetics models for these components are taken from the literature. The fractions of the components in the mixtures are optimized to fit the model to non-isothermal mass loss curves from selected experimental reports. The particle scale model has been evaluated against experimental transient temperature profiles at the centre of a large waste pellet during pyrolysis. The model is able to predict the main trend, but shows a more fluctuating temperature curve.     

城市生活垃圾焚烧炉渣用于制备无熟料砌筑水泥的探讨

依照GB/T3183—2003砌筑水泥标准规定的试验方法,对以城市生活垃圾焚烧炉渣、矿渣为主要原料制备的无熟料砌筑水泥的各项性能进行了研究。结果表明,城市生活垃圾焚烧炉渣对激发矿渣的活性具有一定作用,以炉渣、矿渣为主要原料,掺入水玻璃作为补充激发剂能制备出性能满足要求的无熟料砌筑水泥。     

Electrodialytic extraction of Cu,Pb and Cl from municipal solid waste incineration fly ash suspended in water

The possibility of using fly ash from municipal solid waste incineration (MSWI) in, for example, concrete is considered. MSWI fly ash, however, has too high a concentration of heavy metals, which may cause leaching problems during use or problems with waste handling at the end of the lifetime of the concrete. The Cl content in MSWI fly ash is also too high and will cause corrosion problems in reinforced concrete. The possibility of removing some of the unwanted heavy metals (Cu and Pb) together with Cl from an MSWI fly ash suspended in water using an electrodialytic separation method was investigated. The removal of Pb and Cu was found to be highly pH dependent and the highest contents removed were 41 and 90%, respectively. The Cu concentration of the ash decreased from 2200 to 860 mg kg^?1 but the Pb concentration increased from 8560 to 16 800 mg kg^?1, showing that Pb is mainly found in the ash fraction that is least soluble. Hence electrodialytic treatment of the ash suspended in water is not a solution to improve the ash quality in terms of Pb. The water‐soluble Cl content per unit weight of the original ash was 12.4%. The removal of water‐soluble Cl was efficient and >98% of Cl was removed (calculated on the basis of mean initial and final concentrations). This result indicates that electrodialytic extraction may be a method that can be used for the removal of Cl from ash prior to its utilization in concrete. Copyright © 2006 Society of Chemical Industry     

A correlation for calculating HHV from proximate analysis of solid fuels

Higher heating value (HHV) and composition of biomass, coal and other solid fuels, are important properties which define the energy content and determine the clean and efficient use of these fuels. There exists a variety of correlations for predicting HHV from ultimate analysis of fuels. However, the ultimate analysis requires very expensive equipments and highly trained analysts. The proximate analysis on the other hand only requires standard laboratory equipments and can be run by any competent scientist or engineer. A few number of correlations of HHV with proximate analysis have appeared in the solid fuel literature in the past but were focused on one fuel or dependent on the country of origin. This work introduces a general correlation, based on proximate analysis of solid fuels, to calculate HHV, using 450 data points and validated further for additional 100 data points. The entire spectrum of solid carbonaceous materials like coals, lignite, all types of biomass material, and char to residue-derived fuels have been considered in derivation of present correlation which is given as below: HHV=0.3536FC+0.1559VM−0.0078ASH (MJ/kg) (where FC 1.0-91.5% fixed carbon, VM 0.92-90.6% volatile matter and Ash 0.12-77.7% ash content in wt% on a dry basis). The average absolute error of this correlation is 3.74% and bias error is 0.12% with respect to the measured value of HHV, which is much less than that of previous correlations of the similar kind. The major advantage of this correlation is its capability to compute HHV of any fuel simply from its proximate analysis and thereby provides a useful tool for modeling of combustion, gasification and pyrolysis processes. It can also be used in examining old/new data for probable errors when results lie much outside the predicted results.     

Vitrification of municipal solid waste incineration fly ash: An approach to find the successful batch compositions

Incineration is the most common way to reduce the mass and the volume of municipal solid wastes. One of the most dangerous by-products of the incineration process is fly ash that contains a considerable amount of heavy metals. Therefore, its treatment is crucial to prevent the leaching of heavy metals into the environment. In the present work, two different sources of municipal solid waste incinerator fly ash have been vitrified in order to inhibit the release of potentially toxic heavy metals. Two different sources of silica, i.e. silica sand and glass cullet, have been added to each type of fly ash in an attempt to obtain vitrifiable batches. The standard leaching test on vitrified products was performed according to EN12457-2 confirming no heavy metal leaching and, therefore, they all pass waste acceptance criteria to be classified as an inert material. Furthermore, the previously reported data for vitrification of fly ash was combined with the present work and their compositions were presented in the SiO₂–Al₂O₃–CaO, and SiO₂-ΣM₂O₃-Σ(MO + M₂O) ternary phase diagrams to identify the region in which successful compositions are concentrated. This analysis could facilitate the attempt to find the right composition for vitrification of fly ash.