Effects of the Basicity on the Comelting Conditions of Municipal Solid Waste Incinerator Fly Ash and Sewage Sludge Ash

Abstract

In this study, the effects of the basicity on the pouring point of the municipal solid waste incinerator fly ash-sewage sludge ash mixture is investigated. Four kinds of sewage sludge ash, which were collected from several primary and secondary sewage treatment plants and were produced by different processes and sludge conditioning alternatives, were used as modifiers. The results indicate that the pouring point of the mixture increased with increasing basicity, within the range of 0.65–1.90. The pouring point is affected by the contents of the mixtures (CaO, SiO₂, Al₂O₃, and the flux). It is suggested that an increase in the CaO content tends to raise the pouring point, whereas an increase in the SiO₂ and/or the Al₂O₃ contents cause as adverse reaction. The prediction equation, obtained by multilinear regression (significant level is 0.05), is as follows: pouring temperature =1189.6 + 4.19CaO-0.96 SiO₂-4.33 Al₂O₃ (R² = 0.91). In general, the pouring point decreased when the basicity was <1. The pouring point apparently increased when the basicity was>1.2. The regression squares for the different basicities were between 0.84 and 0.91. From these relationships, we note that a basicity index of 5 gave the best R² (0.91). From the results of this study, it can be concluded that the modification of the basicity of the fly ash by the addition of sewage sludge ash to lower the pouring point is feasible and leads to a more energy-efficient melting process. In addition, these synthetic slags have a good pozzolanic reactive activity.     

Effect of reducing conditions on sludge melting process

The objective of this study was to compare the effects of CO/CO(2) reducing conditions with those of air oxidizing conditions on the pouring temperature of the sludge melting process and the heavy metal leachability of the resultant sludge slag. Synthetic sludge ash composed of SiO(2), CaO and Al(2)O(3), as well as sewage sludge ash generated from a laboratory incinerator was employed. The experimental results indicated that the pouring temperatures are significantly reduced under the reducing conditions of CO/CO(2), or 24 and 77 degrees C lower than under air conditions for synthetic and sludge ash, respectively. The heavy metal leaching tests further indicate lower heavy metal concentrations present in the leachate under the reducing conditions, notably an order of magnitude lower in Zn. However, X-ray diffractogram indicates similar peaks for these two slags produced under different conditions.     

A comparison between sludge ash and fly ash on the improvement in soft soil

In this study, the strength of soft cohesive subgrade soil was improved by applying sewage sludge ash as a soil stabilizer. Test results obtained were compared with earlier tests conducted on soil samples treated with fly ash. Five different proportions of sludge ash and fly ash were mixed with soft cohesive soil, and tests such as pH value, compaction, California bearing ratio, unconfined compressive strength (UCS), and triaxial compression were performed to understand soil strength improvement because of the addition of both ashes. Results indicate that pH values increase with extending curing age for soil with sludge ash added. The UCS of sludge ash/soil were 1.4-2 times better than untreated soil. However, compressive strength of sludge ash/soil was 20-30 kPa less than fly ash/soil. The bearing capacities for both fly ash/soil and sludge ash/soil were five to six times and four times, respectively, higher than the original capacity. Moreover, the cohesive parameter of shear strength rose with increased amounts of either ash added. Friction angle, however, decreased with increased amounts of either ash. Consequently, results show that sewage sludge ash can potentially replace fly ash in the improvement of the soft cohesive soil.     

污泥焚烧灰固化处理技术研究

研究了硅酸盐水泥、高铝水泥、高岭土和β-萘系减水剂在污泥焚烧灰固化技术中的应用效果。考察了污泥焚烧灰固化块(以下简称固化块)的抗压强度,测定了固化块的重金属浸出毒性,并采用X射线衍射(XRD)和扫描电镜(SEM)分析固化块组成和微观结构。结果表明,4种物质对提高固化块的抗压强度均具有较好的效果,硅酸盐水泥、高铝水泥、高岭土和β-萘系减水剂的适宜掺量分别为10、30、20、1.0g(以100g污泥焚烧灰中掺加的质量计)。XRD和SEM分析结果显示,经固化处理后制得的固化块结构密实,存在石英(SiO2)、水化硅铝酸钙(CaAl2Si2O8)和水化硅酸铝钙(Ca2Al2SiO7)等物质,其中水化硅铝酸钙等凝胶物质有利于提高固化块的抗压强度。     

Immobilization and volume reduction of heavy metals in municipal solid waste fly ash using nano-size calcium and iron-dispersed reagent

This study was conducted to examine the synthesis and application of novel nano-size calcium/iron-based composite material as an immobilizing and separation treatment of the heavy metals in fly ash from municipal solid waste incineration. After grinding with nano-Fe/Ca/CaO and with nano-Fe/Ca/CaO/[PO₄], approximately 30 wt% and 25 wt% of magnetic fraction fly ash were separated. The highest amount of entrapped heavy metals was found in the lowest weight of the magnetically separated fly ash fraction (i.e., 91% in 25% of treated fly ash). Heavy metals in the magnetic or nonmagnetic fly ash fractions were about 98% and 100% immobilized, respectively. Additionally, scanning electron microscopy combined with energy-dispersive X-ray spectrometry (SEM-EDS) observations indicate that the main fraction of enclosed/bound materials on treated fly ash includes Ca/PO₄-associated crystalline complexes. After nano-Fe/Ca/CaO/[PO₄] treatment, the heavy metal concentrations in the fly ash leachate were much lower than the Japan standard regulatory limit for hazardous waste landfills. These results appear to be extremely promising. The addition of a nano-Fe/Ca/CaO/PO₄ mixture with simple grinding technique is potentially applicable for the remediation and volume reduction of fly ash contaminated by heavy metals.

Implications: After grinding with nano-Fe/Ca/CaO and nano-Fe/Ca/CaO/[PO₄], approximately 30 wt% and 25 wt% of magnetic fraction fly ash were separated. The highest amount of entrapped heavy metals was found in the lowest weight of the magnetically separated fly ash fraction (i.e., 91% in 25% of treated fly ash), whereas heavy metals either in the magnetic or nonmagnetic fly ash fractions were about 98% and 100% immobilized. These results appear to be very promising, and the addition of nano-Fe/Ca/CaO/PO₄ mixture with simple grinding technique may be considered potentially applicable for the remediation and volume reduction of contaminated fly ash by heavy metals.     

Long-term study of palladium in road tunnel dust and sewage sludge ash

The present work summarizes data about palladium contents of road tunnel dust from 1994 to 2007 and sewage sludge ash from 1972 to 2006. Since palladium is emitted from automotive catalytic converters as elemental particles, road dust is quiet useful to study traffic-related Pd emissions. Very high Pd values of up to 516 μg Pd kg⁻¹ were found in the road dust samples collected in 2007. Heavy metals of all urban emissions, also dental practice effluent, are enriched in sewage sludge ash and thus this matrix is useful for the documentation of palladium emission caused by the use of Pd alloys in dental medicine. In sewage sludge ash highest Pd contents of maximum 460 μg Pd kg⁻¹ were found in the years 1986-1997. In both matrices correlations of Pd content to Pd demand of industry are discussed.     

Air-surface exchange of mercury with soils amended with ash materials

Air-surface exchange of mercury (Hg) was measured from soil low in Hg (0.013 mg/kg) amended with four different ash materials: a wood ash containing -10% coal ash (0.070 mg/kg Hg), a mixture of two subbituminous coal fly ashes (0.075 mg/kg Hg), a subbituminous coal ash containing -10% petroleum coke ash (1.2 mg/kg Hg), and an ash from incinerated municipal sewage sludge (4.3 mg/kg Hg) using a dynamic flux chamber. Ash was added to soil to simulate agricultural supplements, soil stabilization, and pad layers used in livestock areas. For the agricultural amendment, -0.4% ash was well mixed into the soil. To make the stabilized soil that could be used for construction purposes, -20% ash was mixed into soil with water. The pad layer consisted of a wetted 1-cm layer of ash material on the soil surface. Diel trends of Hg flux were observed for all of the substrates with significantly higher Hg emissions during the day and negligible flux or deposition of Hg during the night. Hg fluxes, which were measured in the summer months, were best correlated with solar radiation, temperature, and air O3 concentrations. Mean Hg fluxes measured outdoors for unamended soils ranged from 19 to 140 ng/m2 day, whereas those for soil amended with ash to simulate an agricultural application ranged from 7.2 to 230 ng/m2 day. Fluxes for soil stabilized with ash ranged from 77 to 530 ng/m2 day and for soil with pads constructed of ash ranged from -50 to 90 ng/m2 day. Simple analytical tests (i.e., total Hg content, synthetic precipitation leaching procedure, heating, and indoor gas-exchange experiments) were performed to assess whether algorithms based on these tests could be used to predict Hg fluxes observed outdoors using the flux chamber. Based on this study, no consistent relationships could be developed. More work is needed to assess long-term and seasonal variations in Hg flux from (intact and disturbed) substrates before annual estimates of emissions can be developed.     

Microbial respiration in fly ash/sewage sludge-amended soils

Microbial respiration within a Fox sandy loam and a Blount silt loam was assessed after addition of acidic (pH 3.5) and alkaline (pH 12.2) fly ash (FoxAC, BlountAC, FoxAK and BlountAK, respectively). At the 20% alkaline ash rate, respiration was completely inhibited in the FoxAK and reduced by 97% in the BlountAK. In contrast, the 20% acidic ash rate reduced respiration in the FoxAC by 28% and in the BlountAC by 33%. Co-application of 5% composted sewage sludge to the ash-soil mixtures (FoxSSAC, BlountSSAC, FoxSSAK and BlountSSAK, respectively) improved respiration in both soils except for the 20% alkaline ash rate. Soil electrical conductivity, and concentrations of B, Mo, exchangeable Al and soluble anions were not closely associated with inhibition of respiration. In contrast, high pH appeared associated with decrease in respiration. Ecological Dose 50% (EcD(50)) values of the sewage-amended treatments were greater than for those of the non-sludge treatments for each sampling date as a result of the ameliorating properties of the sludge.     

Phosphorus in waters from sewage sludge amended lysimeters

In surface waters, phosphorus (P) concentrations exceeding 0.05 mg liter(-1) may cause eutrophic conditions. This study was undertaken to measure total P concentrations in runoff and tile drainage waters from land receiving either inorganic fertilizer or anaerobically digested sewage sludge. Total P was measured in runoff and tile drainage waters during 2 years of sample collections from instrumented, large-scale lysimeters planted to corn (Zea mays L.). During the 3 years prior to monitoring P concentrations, six of the lysimeter plots had been amended with anaerobically digested sewage sludge which supplied 5033 kg P per ha. Additional sludge applications supplied 1058 and 1989 kg P per ha during the first and second years of monitoring operations, respectively. Another six lysimeters were annually treated with fertilizer which included P applications amounting to 112 kg ha(-1). For years 1 and 2, respectively, annual losses from lysimeters treated with sewage sludge were 4.27 and 0.35 kg P per ha in runoff and 0.91 from 0.91 and 0.51 kg Per P per ha in drainage waters. Parallel annual losses of P from lysimeters treated with superphosphate were 2.15 and 0.17 kg ha(-1) in runoff and 0.53 and 0.35 kg ha(-1) in tile drainage waters. Sludge applications did not significantly change absolute soil contents of organic P, but did decrease the per cent of total P present in organic forms. Sludge and soil, respectively, contained 21 and 36% of their total P contents in organic forms. In sludge and soil about 85 and 64% of their respective total inorganic P contents were associated with the Al and Fe fractions. Sludge applications significantly increased soil contents of P in the saloid (water-soluble plus P extracted with 1 N NH(4)Cl), Al, Fe and reductant soluble P fractions, but contents of Ca-bound P were not changed. Total P contents of the soil below a depth of 30 cm were not affected by sludge incorporated to a depth of about 15 cm by plowing.     

Effect of thermal processing on the characteristics of incineration fly ash

This work investigated the possibilities of immobilizing incineration fly ash by applying different processing methods. Direct sintering of fly ash at 1050 degrees C produced material with increased resistance to leaching; however, the high content of halides prevented the achievement of appropriate strength. Fly ash melting and casting into metallic moulds resulted in the formation of glass with good chemical resistivity and mechanical properties, which were further improved by devitrification, and the formation of glass-ceramics. The most successful combination of strength and resistance to leaching was obtained by a process consisting of fly ash melting, by pouring the melt into water, then grinding, and sintering without additives at 850-950 degrees C. In this way, a material was produced that cannot only be landfilled as a stabilised and non-reactive waste in landfills for non-hazardous wastes, but can also be utilized as a valuable material for manufacturing useful products. This article provided valuable results for policy-makers in Slovenia, about the handling fly ash from incineration plants. Implications: Fly ash from an incineration plant was thermally treated using several processing routes. Ash-melting, by pouring the melt into water and sintering, produced glass-ceramics having an optimal combination of strength and resistance to leaching that can find applications as useful products. These results provide important data for policy makers in Slovenia regarding the building of incineration plants, and handling the solid-waste products, especially fly ash.     

典型危险废物的工程力学特性

掌握填埋废物的工程力学特性是确保危险废物填埋堆体稳定性的重要前提条件,因此,针对6种典型危险废物的工程力学特性开展了调查研究.研究结果表明,污泥类危险废物的含水率和有机质含量远高于非污泥类危险废物,而前者的比重则显著低于后者.污泥类危险废物的渗透系数相对较小,比污染土壤和飞灰炉渣混合物的渗透系数小1个数量级,比滤池填料的渗透系数小2个数量级.不同危险废物的无侧限抗压强度排序为:飞灰炉渣混合物(314.3 kPa)和滤池填料(278.9 kPa)＞污染土壤(124.9 kPa)＞杭州氧气厂污泥(68.6 kPa)、锌铬污泥(71.4 kPa)、油泥(58.4 kPa).不同危险废物的粘聚力排序为:飞灰炉渣混合物(40.8 kPa)、滤池填料(31.1 kPa)＞污染土壤(20.9 kPa)＞杭州氧气厂污泥(1.94kPa)、锌铬污泥(3.10 kPa)、油泥(1.81 kPa).此外,不同危险废物的内摩擦角差异相对较小,其变化范围在18.8°～35.0°之间.综合分析可知,飞灰炉渣混合物和滤池填料的工程力学特性较好,而污泥类危险废物的工程力学特性则较差.     

添加粉煤灰对污泥比阻影响的研究

污泥脱水是污泥处理中重要的一环.本研究采用电厂废弃物粉煤灰对未脱水污泥改性,经过改性的污泥比阻降低,改善污泥脱水性能,并对产生这一现象的机制进行了探讨.     

添加粉煤灰对污泥比阻影响的研究

污泥脱水是污泥处理中重要的一环。本研究采用电厂废弃物粉煤灰对未脱水污泥改性，经过改性的污泥比阻降低，改善污泥脱水性能，并对产生这一现象的机制进行了探讨。     

Low-temperature dechlorination of hexachlorobenzene on solid supports and the pathway hypothesis

The dechlorination of HCB was carried out under low-temperature and oxygen deficient conditions on different solid supports such as SiO(2), CaO, CaSiO(3), cement and treated fly ash (tFA). All the tested supports except SiO(2) showed a HCB dechlorination potential. The dechlorination efficiencies (D(1)) of HCB by CaO, CaSiO(3), tFA and cement reached 64.62%, 76.15%, 79.97% and 32.21% at 350 degrees C for 4h, respectively. It was thought electrons in the vacancies originated from the unsaturated metallic ions and O(2-) on the crystal surfaces made the D(1) different between SiO(2), CaO and CaSiO(3). Comparing the D(1) by tFA and cement, the high dechlorination potential of tFA was due to the more free electrons from the crystal defects and the transition metals, and the more active points for the gas-solid phase reaction, which both had positive effects on dechlorination reaction. The effect of Cu addition (0.2-5.0%) on HCB dechlorination might result from the Ullmann coupling which was not notable in enhancing the dechlorination reaction. From the study, we can draw the conclusion that the dechlorination potential mainly depends on the support characteristic rather than the transition metal content. Based on this study and previous references, the dechlorination/polymerization induced by the electron transfer mode was thought to be the dominant pathway while the hydrogen transfer mode was minor. The electron was originated from the crystal defects or induced by transition metals, and the dissociation of a chloride ion happened forming a radical, and then the polymerization of radicals led to the formation of high-molecular-weight compounds which seemed to cause the material imbalance.     

粉煤灰在水厂污泥处理和处置中的作用研究

在水厂污泥水中加入电厂粉煤灰,不需再添加其他材料,即可以很好地改善水厂污泥的脱水性能.细粉煤灰最佳投加量为20%,粗粉煤灰最佳投加量为30%,不但可以节约能耗,粉煤灰有了新的出路,干化污泥对环境友好,而且还能制成低热值燃料作焚烧处置,回收部分热能.     

Vitrification Process for Treatment of Sewage Sludge and Incineration Ash

ABSTRACT

Vitrification processes, in which the operating temperature is higher than the melting point of the silica compounds contained in sewage sludge that turns into slag, are studied in this paper. The dried sludge and the incineration ash are injected into a furnace with auxiliary fuel and flux. The flux is the material used to control basicity of the ash content. Crushed limestone is used as the flux in this test. Almost all ashes in the sludge are vitrificated into slag. The flow of molten slag from the tap is smooth. After the slag is treated, it can be used as wall tile, interlocking tile, insulating material, and slag wool. This technology conforms to resource recycling.     

The calcination process in a system for washing, calcinating, and converting treated municipal solid waste incinerator fly ash into raw material for the cement industry

Calcination is the second step in a washing-calcination-conversion system in which treated municipal solid waste incinerator fly ash and bottom ash can be reused as raw material in the cement industry and can decompose or stabilize hazardous compounds, reduce residue amounts, and alter residue characteristics. In this research, only fly ash is discussed. Chloride reduction is important if treated fly ash is to be reused in cement; however, the relationship between washed fly ash properties and chloride reduction by calcination is not well understood. This study used washed residues of three types of fly ash-raw fly ash (RFA) from the boiler or economizer of an incineration system, fly ash collected in a bag filter injected with calcium hydroxide (Ca(OH)2) for acid removal (CaFA), and fly ash collected in a bag filter injected with sodium bicarbonate (NaHCO3) for acid removal (NaFA)-in calcination experiments with varying temperature (400-1100 degrees C) and atmosphere (100% nitrogen [N2] at 25 mL/min or 10% oxygen [O2] [90% N2] at fluxes of 25, 50, and 75 mL/min). From the perspective of chloride reduction, heating to 1000 degrees C with 1-hr heating time, 1-hr holding time, and an atmosphere of 10% O2/90% N2 was most suitable for calcination. Under these conditions, chloride levels were reduced by 91, 52, and 96% in washed residues of RFA, CaFA, and NaFA, respectively. Among the washed residues, the weight of the washed residue of NaFA decreased the most.     

Digested sewage sludge solidification by converter slag for landfill cover

A new technology for solidification of digested sewage sludge referred to as converter slag solidification (CSS) has been developed using converter slag as the solidifying agent and quick lime as the solidifying aid. The CSS technology was investigated by analyzing the physicochemical properties of solidified sludge and determining its microstructural characteristics. The feasibility of using solidified sludge as a landfill cover material was considered in the context of the economical recycling of waste. Sludge solidified using the CSS technology exhibited geotechnical properties that are appropriate for replacing currently used cover soil. Microscopic analyses using XRD, SEM and EDS revealed that the main hydrated product of solidification was CSH (CaO . SiO2 . nH2O), which may play an important role in the effective setting process. Negligible leaching of heavy metals from the solidified sludge was observed. The solidification process of the hydrated sludge, slag and quicklime eliminated the coliform bacteria. Recycled sewage sludge solidified using CCS technology could be used as an effective landfill cover.     

SGA对垃圾焚烧飞灰中重金属的固化性能研究简

根据EPA 1311、HJ/T 299-2007、HJ/T 300-2007和HJ 557-2009等国内外不同标准,研究了深圳某垃圾焚烧发电厂垃圾焚烧飞灰的浸出毒性,探讨了六硫代胍基甲酸（sixthio guanidine acid,SGA）、二甲基二硫代氨基甲酸盐（sodium dimethyl dithio carbamate,SDD）和Ca（OH）₂浓度对垃圾焚烧飞灰中重金属的固定性能的影响。研究结果表明,随着浸提液pH的降低,该厂焚烧飞灰中大部分金属元素的浸出量增大,焚烧飞灰浸出液中的Cd、Ni、Pb和Zn浓度分别超过国家危险废物鉴别标准（GB5085.3-2007）规定值的4.75倍、1.47倍、6.72倍和2.20倍,属于危险废弃物,必须进行稳定化处理。当固化剂SGA加入量为0.1 mol/kg时,稳定化后的重金属浸出浓度已经低于危险废物鉴别标准,且对Cd、Cr、Cu和Pb的固化性能优于SDD和Ca（OH）₂;当固化剂SGA、SDD和Ca（OH）₂加入量为0.5 mol/kg时,稳定化后的焚烧飞灰重金属浸出浓度均低于国家危险废物鉴别标准（GB 5085.3-2007）中的规定值。与SDD和Ca（OH）₂相比,SGA对垃圾焚烧飞灰中重金属的固化处理更具有优势。     

The behaviour of phosphorus and heavy metals in sewage sludge ashes

The effect of the combustion atmosphere and the additives (CaO and HCl) on the behaviour of phosphorus and heavy metals during sewage sludge combustion was investigated. The results demonstrated that the reduction combustion promoted the vapourisation of phosphorus and heavy metals during sewage sludge combustion. Moreover, the concentrations of phosphorus and heavy metals in the bottom ash decreased with increasing HCl ratio, and the addition of CaO can stabilise heavy metals and phosphorus. It was also observed that phosphorus and heavy metals increased with increasing CaO ratio. Lastly, the difference of the TG-DTA curves with and without additives is discussed.