Effects of the basicity on the comelting conditions of municipal solid waste incinerator fly ash and sewage sludge ash

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 + 4.19 CaO - 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.     

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.     

应用神经网络方法优化垃圾焚烧模拟灰渣熔点的预测

采用SiO₂、Al₂O₃、CaO、Na₂CO₃、NaCl和Fe₂O₃等物质来模拟垃圾焚烧的真实灰渣组成,通过实验测定模拟灰渣熔点,建立神经网络模型进行熔点预测,由预测结果来指导进一步实验,得到修正的模型,最终预测出的半球温度（HT）平均误差低于5%。     

Emission characteristics for co-combustion of leather wastes,sewage sludge,and coal in a laboratory-scale entrained flow tube furnace

Four different mixed fuels consisted of leather waste, coal, and sewage sludge were combusted in a lab-scale entrained flow fluidized bed furnace. The influence of blending ratio on emission characteristics of SO₂, NO_x, HCl, particulate matter (PM), heavy metals, and polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) was studied. Results showed that the mixing of coal with sewage sludge had a complex effect on the emission characteristics. On the one hand, with more sewage sludge blending in the mixed fuel, the acid gas pollutant (SO₂, NO_x) decreased a lot, and the recovery of volatile heavy metals (Cd, Pb) increased at the same time. Furthermore, the leaching toxicity of Cr in the fly ash and bottom ash went down below the national standard with the adding of sewage sludge. On the other hand, the mixing of sewage sludge which consisted of more ash content resulted in the increase of the PM emission. Moreover, the high content of Cu and chlorine in the sewage sludge can promote the formation of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) when the fuel 3 and 4 were combusted. Most importantly, the concentration of toxic PCDD/Fs in the flue gas produced from fuel 3 and fuel 4 was successfully controlled down below 0.20 ng I-TEQ/Nm³ by the active carbon.

     

Air-Surface Exchange of Mercury with Soils Amended with Ash Materials

Abstract

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.     

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.     

Nickel Speciation of Residual Oil Fly Ash and Ambient Particulate Matter Using X-ray Absorption Spectroscopy

ABSTRACT

The chemical speciation of Ni in fly ash produced from ~0.85 wt % S residual (no. 6 fuel) oils in laboratory (7 kW)- and utility (400 MW)-scale combustion systems was investigated using X-ray absorption fine structure (XAFS) spectroscopy, X-ray diffraction (XRD), and acetate extraction [1 M NaOAc-0.5 M HOAc (pH 5) at 25 °C]-anodic stripping voltammetry (ASV). XAFS was also used to determine the Ni speciation of ambient particulate matter (PM) sampled near the 400-MW system. Based on XAFS analyses of bulk fly ash and their corresponding acetate extraction residue, it is estimated that >99% of the total Ni (0.38 wt %) in the experimentally produced fly ash occurs as NiSO₄-xH₂O, whereas >95% of the total Ni (1.70 and 2.25 wt %) in two fly ash samples from the 400-MW system occurs as NiSO₄-xH₂O and Ni-bearing spinel, possibly NiFe₂O₄. Spinel was also detected using XRD. Acetate extracts most of the NiSO₄-xH₂O and concentrates insoluble NiFe₂O₄ in extraction residue. Similar to fly ash, ambient PM contains NiSO₄-xH₂O and NiFe₂O₄;

however, the proportion of NiSO₄-xH₂O relative to NiFe₂O₄ is much greater in the PM. Results from this and previous investigations indicate that residual oil ash produced in the 7-kW combustion system lack insoluble Ni (e.g., NiFe₂O₄) but are enriched in soluble NiSO₄-xH₂O relative to fly ash from utility-scale systems. This difference in Ni speciation is most likely related to the lack of additive [e.g., Mg(OH)₂] injection and residence time in the 7-kW combustion system.     

Fate of radiocesium in sewage treatment process released by the nuclear accident at Fukushima

The nuclear accident at the Fukushima Daiichi Nuclear Power Plant (FDNPP) which occurred after the Great East Japan Earthquake on March 11, 2011 resulted in releases of radionuclides such as ¹³⁴Cs (half-life:T_1/2 = 2.06 yr), ¹³⁷Cs (T_1/2 = 30.04 yr) and ¹³¹I (T_1/2 = 8.05 d) to the environment. For this paper, we observed the monthly variations of radiocesium (¹³⁴Cs and ¹³⁷Cs) and stable Cs concentrations in influent, effluent, sewage sludge, and sludge ash collected from a sewage treatment plant 280 km north of the FDNPP from July to December, 2011. Using the stable Cs results, we concluded the mass balance of Cs in the sewage treatment plant showed that about 10% of the Cs entering the sewage treatment plant would be transferred to the sewage sludge, and then Cs in the sewage sludge was totally recovered in the sludge ash. The behavior of Cs was similar to that of Rb, but it was not similar to that of K in the sewage treatment process.     

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.     

Urban energy mining from sewage sludge

This work showed that sewage sludge could be a strong candidate for biodiesel production. High lipid content (18–20%) with C_16?18-carbon range was experimentally identified and measured. These lipids from sewage sludge were converted into biodiesel via the transesterification reaction with MgO–CaO/Al₂O₃ derived from magnesium slag, and biodiesel conversion was ～98%. The experimental work enabled explaining that temperature is the main driving force for the transesterification reaction, which can be enhanced in the presence of CO₂. This also enables combination of esterification of free fatty acids and transesterification of triglycerides into a single process within 1 min in the temperature range of 350–500 °C. Sewage sludge residue after extracting lipids was also a good feedstock for recovering energy via thermo-chemical processes. The impact of CO₂ co-feed on the pyrolysis/gasification process of SS residue was also investigated in this work. The CO₂ injected into the thermo-chemical process remarkably increased the generation of CO by a factor of 2. Moreover, the introduction of CO₂ into the pyrolysis/gasification process enabled reducing condensable hydrocarbons (tar) by expediting cracking; thus, utilizing CO₂ as chemical feedstock for the gasification process not only leads to higher thermal efficiency but also has environmental benefits.     

不同污泥源条件下ANAMMOX启动及其与反硝化协同脱氮对比

采用城市生活污水配水同时启动两组ASBR,R1接种好氧硝化污泥,R2按2∶1混合接种短程硝化和厌氧氨氧化污泥,研究2个ANAMMOX反应器启动的可行性及其差异。实验结果表明,R1和R2均可成功启动ANAMMOX,R1需130 d,R2仅需73 d;稳定期R1和R2反应器NH4+-N、NO2--N和TN去除率分别达95.30%、91.30%、76.28%和96.2%、98.3%、90.1%,且周期内NH4+-N、NO2--N和NO3--N降解规律相似;R1和R2反应器发生的主要反应为厌氧氨氧化,但同时存在反硝化作用;2组反应器稳定运行后污泥颜色、形态及微生物组成相似,经SEM观察多为球状菌。     

Medium-Sulfur Coal and Fly Ash Resistivity

Electric generating plants burning medium-sulfur coal need a way to predict when ESP performance will be limited by high electrical resistivity of the collected fly ash. The main uncertainty in mathematical predictions of fly ash resistivity lies in the marginal effect of naturally occurring SO₃ vapor in the flue gas. This paper results from a project to expand the data base of SO₃/SO₂ concentrations and fly ash resistivities measured in utility fly ash precipitators. Complete data sets are presented from three plants in the Southern Company electric system. In situ resistivity data are compared with laboratory measurements and with two different mathematical predictions of resistivity based on coal and ash analyses. The revised version of the resistivity predictor gives results in good agreement with resistivity values measured both in situ and in the laboratory.     

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.     

粉煤灰制备混凝剂及其对黄河水的处理效果

以粉煤灰和铁泥为原料、加入一定量NaCl作助溶剂室温下制备粉煤灰混凝剂,考察酸灰比与酸浓度对Fe3+、Al3+溶出率及混凝剂对黄河水处理效果的影响。结果表明,Fe3+、Al3+的最佳溶出条件为酸灰比3 mL/g、HCl浓度4 mol/L,此时Fe3+溶出率为28.1%,浓度为11.81 g/L;Al3+溶出率为5.2%,浓度为1.86 g/L。粉煤灰混凝剂对黄河水的处理效果在投加量2.38 mL/L、沉降时间30 min、pH 6.2～7.5时最佳,对浊度、SS和CODMn平均去除率分别为89.7%、83.6%和62.3%,优于传统市售混凝剂PAC和FC,Fe3+、Al3+同时存在有利于各自优势的发挥从而提高混凝效果。     

Resource recycling through artificial lightweight aggregates from sewage sludge and derived ash using boric acid flux to lower co-melting temperature

This study focuses on artificial lightweight aggregates (ALWAs) formed from sewage sludge and ash at lowered co-melting temperatures using boric acid as the fluxing agent. The weight percentages of boric acid in the conditioned mixtures of sludge and ash were 13% and 22%, respectively. The ALWA derived from sewage sludge was synthesized under the following conditions: preheating at 400 °C 0.5 hr and a sintering temperature of 850 °C 1 hr. The analytical results of water adsorption, bulk density, apparent porosity, and compressive strength were 3.88%, 1.05 g/cm³, 3.93%, and 29.7 MPa, respectively. Scanning electron microscope (SEM) images of the ALWA show that the trends in water adsorption and apparent porosity were opposite to those of bulk density. This was due to the inner pores being sealed off by lower-melting-point material at the aggregates' surface. In the case of ash-derived aggregates, water adsorption, bulk density, apparent porosity, and compressive strength were 0.82%, 0.91 g/cm³, 0.82%, and 28.0 MPa, respectively. Both the sludge- and ash-derived aggregates meet the legal standards for ignition loss and soundness in Taiwan for construction or heat insulation materials.

Implications Artificial lightweight aggregates (ALWAs) could be synthesized from sewage sludge and derived ash. In this study, co-melting technology of low temperature was applied with boric acid as a fluxing agent and the formation temperature of glass phase was decreased to 900 °C. Both aggregates derived from sludge and ash meet regulatory standards of ignition loss and soundness in Taiwan for construction or heat insulation material.     

Preliminary study on removing Cs+/Sr2+ by activated porous calcium silicate—A by-product from high-alumina fly ash recycling industry

¹³⁷Cs⁺/⁹⁰Sr²⁺-containing radioactive wastewater is one of the most important problems that the world has been facing with. A by-product, activated porous calcium silicate, is generated at high levels by the pre-desiliconizing and soda-lime-sintering processes for producing Al₂O₃ from high-alumina fly ash. In order to examine if this by-product could be used as an absorbent for removal of ¹³⁷Cs⁺/⁹⁰Sr²⁺ from radioactive wastewater, various parameters, such as pH, adsorbent dose, contact time, and initial concentration, were discussed. Results indicated that the equilibrium reached in about 2 hr. Activated porous calcium silicate was highly pH sensitive and able to remove Cs⁺/Sr²⁺ in a near-neutral environment. The adsorption equilibrium was best described by Freundlich isotherm equations, and the adsorption of Cs⁺/Sr²⁺ was a physical process. The adsorption kinetic data could be better fitted by the pseudo-second-order model, and the adsorption was controlled by multidiffusion. Current study showed that activated porous calcium silicate has a good adsorption of Cs⁺/Sr²⁺ for their removal. However, other characteristics, such as selectivity because of coexisting cations, elution and regeneration, thermal stability, and acid resistance, should be discussed carefully before using it in an actual field.

Implications:Removing ¹³⁷Cs⁺/⁹⁰Sr²⁺ from radioactive wastewater is one of the tough issues that has been attracting more and more attention world widely, which is the same as fly ash. For recycling high-alumina fly ash, in which Al is extracted to produce Al₂O₃, a huge amount of activated porous calcium silicate is generated year by year. In this paper, this by-product was successfully used as an absorbent to remove ¹³⁷Cs⁺/⁹⁰Sr²⁺ from radioactive wastewater for the first time. Factors that affect the absorbability and the mechanisms were discussed in details, providing a possible choice for disposal of ¹³⁷Cs⁺/⁹⁰Sr²⁺-containing radioactive wastewater.     

粉煤灰协同微波-Fenton氧化法处理活性艳蓝KN-R染料废水

以粉煤灰联合微波-Fenton氧化工艺处理活性艳蓝KN-R生产废水,考察了粉煤灰投加量及吸附时间对处理效果的影响,并通过正交实验对微波-Fenton工艺参数进行了优化。实验结果表明,粉煤灰絮凝吸附与微波-Fenton氧化具有协同效应;在粉煤灰投加量为40 g/L,搅拌吸附时间为20 min,滤液pH值为4,Fe2＋和H2O2投加量分别为3.6 mmol/L和0.15 mol/L,微波功率为200 W,辐射反应时间为4 min的优化条件下,染料废水的处理效果最好,COD和色度的去除率分别达到90.90%和99.98%。     

采用配方均匀设计法利用脱水污泥制备陶粒的研究

长期以来,对城市污水处理后产生的污泥处置一直是环保的难题,传统的处理处置方法均存在诸多问题,寻求一种好的处理处置污泥方法迫在眉睫。针对目前的问题运用带约束条件的配方均匀设计方法对粉煤灰-脱水污泥陶粒配方进行实验设计,运用三叶回转窑进行小试。研究了陶粒组分中粉煤灰、污泥、黏土的比例对烧成陶粒堆积密度、颗粒强度的影响;确定了最佳物料配比,使陶粒的性能测试指标均符合GB/17431.2-1998标准的规定。实验结果表明:烧制陶粒湿比例下脱水污泥用量达45%,干比例污泥用量15.2%,污泥减量化和资源化效果显著;陶粒浸出毒性实验结果表明各项指标均低于浸出液中危害成分浓度限值,达到了污泥无害化的效果;粉煤灰、污泥和黏土的优化质量(干)比例为79%,15.2%,5.8%;陶粒的堆积密度为600 kg/m3,筒压强度2.2 MPa,1 h吸水率10.2%,粒型系数1.3。     

Comparison of CaO’s effect on the fate of heavy metals during thermal treatment of two typical types of MSWI fly ashes in China

Both grate and fluidized bed incinerators are widely used for MSW incineration in China. CaO addition for removing hazardous emissions from MSWI flue gas changes the characteristics of fly ash and affects the thermal behavior of heavy metals when the ash is reheated. In the present work, two types of MSWI fly ashes, sampled from both grate and fluidized bed incinerators respectively, were thermal treated at 1023–1323 K and the fate of heavy metals was observed. The results show that both of the fly ashes were rich in Ca and Ca-compounds were the main alkaline matter which strongly affected the leaching behavior of heavy metals. Ca was mostly in the forms of Ca(OH)₂ and CaCO₃ in the fly ash from grate incinerator in which nascent fly ash particles were covered by Ca-compounds. In contrast, the content of Ca was lower in the fly ash from fluidized bed incinerator and Ca was mostly in the form of CaSO₄. Chemical reactions among Ca-compounds caused particle agglomeration in thermal treated fly ash from grate incinerator, restraining the heavy metals volatilization. In thermal treated fly ash from fluidized bed incinerator, Ca was converted into aluminosilicates especially at 1323 K which enhanced heavy metals immobilization, decreasing their volatile fractions as well as leaching concentrations. Particle agglomeration hardly affected the leaching behavior of heavy metals. However, it suppressed the leachable-CaCrO₄ formation and lowered Cr leaching concentration.     

Hydration Properties of Eco-Cement Pastes from Waste Sludge Ash Clinkers

Abstract

Three types of hydraulic cements have been developed by incorporating sludge ash from a primary sewage treatment plant and a water purification plant, as well as slag from steelworks (ferrate), as a partial replacement for clay, silica, alumina, and iron oxide in raw cement meal. The raw meal for the pre-determined recipes was prepared by heating it to 1400 °C for 6 hr in a clinkerization process, using a simulated incinerator and smelter. The major components of ordinary Portland cement, C₃S, C₂S, C₃A, and C₄AF, were all found in the clinkers. Of the three types of eco-cements, the eco-cement A paste was most similar to ordinary Portland cement in terms of composition and compressive strength development, while the eco-cement B paste showed early strength development. The differential thermal analysis species analyses indicated that the hydrates in the eco-cement pastes were mainly calcium hydroxide and CSH gels, like those found in ordinary Portland cement paste. Moreover, the degree of hydration, as determined by nuclear magnetic resonance, increased in all eco-cement pastes with an increasing curing age. The results indicate that it indeed is feasible to use sludge ash and ferrate to replace up to 20% of the mineral components of raw materials for cement.