Chemical speciation and mobility of heavy metals in municipal solid waste incinerator fly ash

Chemical speciation is a significant factor that governs the toxicity and mobility of heavy metals in municipal solid waste incinerator fly ash. Sequential extraction procedure is applied to fractionate heavy metals(Pb, Zn, Cd, Cu, and Cr) into five defined groups: exchangeable, carbonate, Fe-Mn oxide, organic, and residual fractions. The mobility of heavy metals is also investigated with the aid of toxicity characteristic leaching procedure. In the fly ash sample, Pb is primarily presented in the carbonate(51%) and exchangeable(20%) fractions; Cd and Zn mainly exist as the exchangeable(83% and 49% respectively); Cu is mostly contained in the last three fractions(totally 87%); and Cr is mainly contained in the residual fraction(62%). Pb, Zn and Cd showed the high mobility in the investigation, thus might be of risk to the natural environment when municipal solid waste incinerator fly ash is landfilled or reutilized.

Polychlorinated dibenzo-p-dioxins and dibenzofurans in flue gas emissions from municipal solid waste incinerators in China

Polychlorinated dibenzo-p-dioxins and furans （PCDD/Fs） emissions in flue gas from two types of municipal solid waste incinerators （MSWIs） most commonly used in China were investigated in this study. The selected incinerators include two grate-type MSWIs： MSWI-A （350 t/d） and MSWI-B 050 t/d）, and two fluidized bed MSWIs： MSWI-C （400 t/d） and MSWI-D （400 t/d）, which are all equipped with semi-dry lime scrubber and bag filter except MSWI-D equipped with cyclone and wet scrubber （WS） as air pollutant control device （APCD）. Results indicated that the emission concentration and the international toxic equivalents （I-TEQs） of the PCDD/Fs from the stacks were in the range of 1.210-10.273 ng/Nm^3 and 0.019-0.201 ng I-TEQ/Nm^3, respectively. They were greatly lower than the emission regulation standard of PCDD/Fs in China （1.0 ng I-TEQ/Nm^3）. However, only the PCDD/Fs emission level from MSWI-C was below 0.1 ng I-TEQ/Nm^3. Although the homologue profiles were distinct, the contributions of the 2,3,7,8-subsituted congeners to the total I-TEQ were similar among all the investigated MSWIs. Two major 2,3,7,8-substituted congeners, 2,3,4,7,8-PeCDF and 1,2,3,7,8-PeCDD, account for 47% and 9% （average values） of the total I-TEQ values, respectively. The correlation between PCDD/Fs levels and composition of flue gas was also discussed.

Geo-environmental application of municipal solid waste incinerator ash stabilized with cement

The behavior of soluble salts contained in the municipal solid waste incinerator(MSWI) ash significantly affects the strength development and hardening reaction when stabilized with cement.The present study focuses on the compaction and strength behavior of mixed specimens of cement and MSWI ash.A series of indices such as unconfined compressive strength,split tensile strength,California bearing ratio(CBR) and pH value was examined.Prior to this,the specimens were cured for 7 d,14 d,and 28 d.The test results depict that the maximum dry density(MDD) decreases and the optimum moisture content(OMC)increases with the addition of cement.The test results also reveal that the cement increases the strength of the mixed specimens.Thus,the combination of MSWI ash and cement can be used as a lightweight filling material in different structures like embankment and road construction.

Effects of Using Municipal Solid Waste Incineration Tailings as Lightweight Aggregate on the Mechanical Properties of Specified Density Concrete

Municipal solid waste incineration tailings were used as lightweight aggregate(MSWIT-LA)in the preparation of specified density concrete to study the effects on compressive strength,axial compressive strength,flexural strength,microhardness,total number of pores,pore area,and pore spacing.The results showed that the internal curing and morphological effects induced by an appropriate quantity of MSWIT-LA improved the compressive response of specified density concrete specimens,whereas an excessive quantity of MSWIT-LA significantly reduced their mechanical properties.An analysis of pore structure indicated that the addition of MSWIT-LA increased the total quantity of pores and promoted cement hydration,resulting in a denser microstructure than that of ordinary concrete.The results of a principal component analysis showed that the mechanical response of specified density concrete prepared with 25%MSWIT-LA was superior to that of an equivalent ordinary concrete.It was therefore concluded that MSWIT-LA can be feasibly applied to achieve excellent specified density concrete properties while utilising municipal solid waste incineration tailings to protect the environment and alleviate shortages of sand and gravel resources.

Model Prediction and Optimal Control of Gas Oxygen Content for A Municipal Solid Waste Incineration Process

In the municipal solid waste incineration process,it is difficult to effectively control the gas oxygen content by setting the air flow according to artificial experience.To address this problem,this paper proposes an optimization control method of gas oxygen content based on model predictive control.First,a stochastic configuration network is utilized to establish a prediction model of gas oxygen content.Second,an improved differential evolution algorithm that is based on parameter adaptive and t-distribution strategy is employed to address the set value of air flow.Finally,model predictive control is combined with the event triggering strategy to reduce the amount of computation and the controller's frequent actions.The experimental results show that the optimization control method proposed in this paper obtains a smaller degree of fluctuation in the air flow set value,which can ensure the tracking control performance of the gas oxygen content while reducing the amount of calculation.

Influence of SO_2 in incineration flue gas on the sequestration of CO_2 by municipal solid waste incinerator fly ash

The influence of CO2 content and presence of SO2 on the sequestration of CO2 by municipal solid waste incinerator （MSWI） fly ash was studied by investigating the carbonation reaction of MSWI fly ash with different combinations of simulated flue gas. The reaction between fly ash and 100% CO2 was relatively fast; the uptake of CO2 reached 87 g CO2/kg ash, and the sequestered CO2 could be entirely released at high temperatures. When CO2 content was reduced to 12%, the reaction rate decreased; the uptake fell to 41 g CO2/kg ash, and 70.7% of the sequestered CO2 could be released. With 12% CO2 in the presence of SO2, the reaction rate significantly decreased; the uptake was just 17 g CO2/kg ash, and only 52.9% of the sequestered CO2 could be released. SO2 in the simulated gas restricted the ability of fly ash to sequester CO2 because it blocked the pores of the ash.

Prediction of NO_(x)concentration using modular long short-term memory neural network for municipal solid waste incineration

Air pollution control poses a major problem in the implementation of municipal solid waste incineration(MSWI).Accurate prediction of nitrogen oxides(NO_(x))concentration plays an important role in efficient NO_(x)emission controlling.In this study,a modular long short-term memory(M-LSTM)network is developed to design an efficient prediction model for NO_(x)concentration.First,the fuzzy C means(FCM)algorithm is utilized to divide the task into several sub-tasks,aiming to realize the divide-and-conquer ability for complex task.Second,long short-term memory(LSTM)neural networks are applied to tackle corresponding sub-tasks,which can improve the prediction accuracy of the sub-networks.Third,a cooperative decision strategy is designed to guarantee the generalization performance during the testing or application stage.Finally,after being evaluated by a benchmark simulation,the proposed method is applied to a real MSWI process.And the experimental results demonstrate the considerable prediction ability of the M-LSTM network.

The co-removal of PCDD/Fs by SCR system in a full-scale municipal solid waste incinerator:Migration-transformation and decomposition pathways

Polychlorinated dibenzo-p-dioxins and furans(PCDD/Fs)generated from municipal solid waste(MSW)incineration are considered as the key pollutants,which could pose serious risks to the environment and ecology.This study comprehensively investigated the effect of selective catalytic reduction(SCR)system on PCDD/F removal,phase distributions,and migrationtransformation characteristics of 17 congeners in a full-scale MSW incinerator.The three flue gas samples and two fly ash samples were separately collected for PCDD/F analysis.The results showed that the SCR system reduced the I-TEQ concentration of PCDD/Fs from 0.135 to 0.010 ng I-TEQ Nm^(−3)with a remarkable toxicity removal efficiency of 92.6%,through oxidation decomposition over V_(2)O_(5)-WO_(3)/TiO_(2)catalysts and chlorination process of low-chlorinated congeners.In addition,the de novo synthesis observed along the flue between SCR system and stack regenerated unexpected PCDD/Fs,which might enhance the PCDD/F emission level.This study verified the three pathways of SCR system on PCDD/F removal and inspired operating suggestions for SCR system,i.e.,keeping SCR system operated in stable and consistent conditions,regularly replacing V_(2)O_(5)-WO_(3)/TiO_(2)catalysts,and timely cleaning the dusts and inlet materials of SCR system,which would be beneficial for achieving the ultra-low emission of PCDD/Fs in full-scale MSW incinerators.

Microstructures and thermal properties of municipal solid waste incineration fly ash

To analyze the feasibility of utilization of thermal technology in fly ash treatment, thermal properties and microstructures of municipal solid waste incineration （MSW1） fly ash were studied by measuring the chemical element composition, specific surface area, pore sizes, functional groups, TEM image, mineralogy and DSC-TG curves of raw and sintered fly ash specimens. The results show that MSWI fly ash particles mostly have irregular shapes and non-typical pore structure, and the supersonic treatment improves the pore structure; MSWI fly ash consists of Such crystals as SiO2, CaSO4 and silica-aluminates, and some soluble salts like KCl and NaCl. During the sintering process, mineralogy changes largely and novel solid solutions are produced gradually with the rise of temperature. Therefore, the utilization of a proper thermal technology not only destructs those persistent organic toxicants but also stabilizes hazardous heavy metals in MSWI fly ash.

Mechanism of high concentration phosphorus wastewater treated by municipal solid waste incineration fly ash

The mechanism of removing phosphate by MSWI(municipal solid waste incineration)fly ash was investigated by SEM(scanning electron microscopy)with EDS(energy dispersion spectrum),XRD(X-ray diffraction),FT-IR(Fourier transform infrared spectroscopy),BET(specific surface area),and BJH(pore size distribution).The results indicate that the removal rate of phosphate(100 mg/L)in 50 mL phosphorus wastewater reaches at 99.9% as the dosage of MSWI fly ash being 0.9000 g under room temperature.The specific surface area of MSWI fly ash is less than 6.1 m2/g and the total pore volume is below 0.021 cm3/g,suggesting that the absorption capacity of calcite is too weak to play an important role in phosphate removal.SEM images show that drastic changes had taken place on its specific surface shape after reaction,and EDS tests indicate that some phosphate precipitates are formed and attached onto MSWI fly ash particles.Chemical precipitation is the main manner of phosphate removal and the main reaction is: 3Ca2++2 PO4 3-+xH2O→Ca3(PO4)2↓·xH2O.Besides,XRD tests show that the composition of MSWI fly ash is complex,but CaSO4 is likely to be the main source of Ca2+.The soluble heavy metals in MSWI fly ash are stabilized by phosphate.

Effect of oxide interactions on chromium speciation transformation during simulated municipal solid waste incineration

Chromium released during municipal solid waste incineration(MSWI)is toxic and carcinogenic.The removal of chromium from simulated MSWI flue gas by four sorbents(CaO,bamboo charcoal(BC),powdered activated carbon(PAC),and Al_(2)O_(3))and the effects of four oxides(SiO_(2),Al_(2)O_(3),Fe_(2)O_(3),and CaO)on chromium speciation transformationwere investigated.The results showed that the removal rates of total Cr by the four sorbents were Al_(2)O_(3)<CaO<PAC<BC,while the removal rates of Cr(Ⅵ)by the four sorbents were Al_(2)O_(3)<PAC<BC<CaO.CaO had a strong oxidizing effect on Cr(Ⅲ),while BC and PAC had a better-reducing effect on Cr(Ⅵ).SiO_(2)was better for the reduction of Na_(2)CrO_(4)and K_(2)CrO_(4)above 1000℃due to its strong acidity,and the addition of CaO significantly inhibited the reduction of Cr(Ⅵ).MgCrO_(4)decomposed above 700℃to form MgCr_(2)O_(4),and the reaction between MgCrO_(4)and oxides also existed in the form of a more stable trivalent spinel.Furthermore,when investigating the effect of oxides on the oxidation of Cr(Ⅲ)in CrC_(l3),it was discovered that CaO promoted the conversion of Cr(Ⅲ)to Cr(Ⅵ),while the presence of chlorine caused chromium to exist in the form of Cr(V),and increasing the content of CaO and extending the heating time facilitated the oxidation of Cr(Ⅲ).In addition,silicate,aluminate,and ferrite were generated after the addition of SiO_(2),Al_(2)O_(3),and Fe_(2)O_(3),which reduced the alkalinity of CaO and had an important role in inhibiting the oxidation of Cr(Ⅲ).The acidic oxides can not only promote the reduction of Cr(Ⅵ)but also have an inhibitory effect on the oxidation of Cr(Ⅲ)ascribed to alkali metals/alkaline earth metals,and the proportion of acidic oxides can be increased moderately to reduce the generation of harmful substances in the hazardous solid waste heat treatment.

Event-triggered-based self-organizing fuzzy neural network control for the municipal solid waste incineration process

Due to the large uncertainty in the municipal solid waste incineration(MSWI)process,the furnace temperature of the MSWI process is difficult to control and the controller is updated frequently.To improve the accuracy and reduce the number of controller updates,a novel event-triggered control method based correntropy self-organizing TS fuzzy neural network(ETCSTSFNN)is proposed.Firstly,the neurons of the rule layer are grown or pruned adaptively based on activation intensity and control error to meet the dynamic change of the actual operating condition.Meanwhile,the performance index is designed based on the correntropy of tracking errors,and the parameters of the controller are adjusted by gradient descent algorithm.Secondly,a fixed threshold event-triggered condition is designed to determine whether the current controller is updated or not.The stability of the control system is proved based on the Lyapunov stability theory.Finally,the furnace temperature control experiments are conducted based on the actual data of a municipal solid waste incineration plant in Beijing.The experimental results show that the proposed ET-CSTSFNN controller shows a better control performance,which can reduce the number of the controller update significantly while achieving accurate furnace temperature control compared with other traditional control methods.

Event-triggered fuzzy neural multivariable control for a municipal solid waste incineration process

Because of coupling,nonlinearity,and uncertainty in a municipal solid waste incineration(MSWI)process,a suitable multivariable controller is difficult to establish under strong disturbance.Additionally,the problems of reducing mechanical wear and energy consumption in the control process should also be considered.To solve these problems,an event-triggered fuzzy neural multivariable controller is proposed in this paper.First,the MSWI object model based on the multiinput multioutput TakagiSugeno fuzzy neural network is established using a data-driven method.Second,a fuzzy neural multivariable controller is designed to control the furnace temperature and flue gas oxygen content synchronously under external disturbance.Third,an event-triggered mechanism is constructed to update the control rate online while ensuring control effects.Then,the stability of the proposed control strategy is proven through the LyapunovⅡtheorem to guide its practical application.Finally,the effectiveness of the controller is verified using the real industrial data of an MSWI factory in Beijing,China.The experimental results show that the proposed control strategy greatly improves the control efficiency,reduces energy consumption by 66.23%,and improves the multivariable tracking control accuracy.

Investigation of heavy metal partitioning influenced by flue gas moisture and chlorine content during waste incineration

The impact of moisture on the partitioning of the heavy metals including Pb,Zn,Cu and Cd in municipal solid waste （MSW） was studied in a laboratory tubular furnace.A thermodynamic investigation using CHEMKIN software was performed to compare the experimental results.Simulated waste,representative of typical MSW with and without chlorine compounds,was burned at the background temperature of 700 and 950°C,respectively.In the absence of chlorine,the moisture content has no evident effect on the volatility of Pb,Zn and Cu at either 700 or 950°C,however,as flue gas moisture increasing the Cd distribution in the bottom ash increased at 700°C and reduced at 950°C,respectively.In the presence of chlorine,the flue gas moisture reduced the volatility of Pb,Zn and Cu due to the transformation of the more volatile metal chlorides into less volatile metal oxides,and the reduction became significant as chlorine content increase.For Cd,the chlorine promotes its volatility through the formation of more volatile CdCl 2.As a result,the increased moisture content increases the Pb,Zn,Cu and Cd concentrations in the bottom ash,which limits the utilization of the bottom ash as a construction material.Therefore,in order to accumulate heavy metals into the fly ash,MSW should be dried before incineration.

Modeling and motion control simulation of tendon based parallel manipulator translation mechanism for sensor based high value waste processing

A novel sorting system based on one degree of freedom (DOF) tendon based parallel manipulator (TBPM) for high value waste processing was presented and designed. In order to control the motion of loads, nonlinear state feed forward control algorithm in the tendon length coordinate was used. Considering the system redundancy and actuation behavior, algorithms of optimal tension distribution and forward kinematics were designed. Then, the simulation experiments of motion control were implemented. The results demonstrate that the proposed TBPM translation system performs robust capacities. It can transfer the loads 1 m away within 1.5 s. With further optimization, the translation duration can be further reduced to be about 1 s and the optimized translation is followed with 43.59 m/s2 maximum acceleration. The translation errors at the aim position remain below 0.4 mm.

面向城市固废焚烧过程的缺失数据填充及应用

针对城市固废焚烧(municipal solid waste incineration, MSWI)过程中存在的随机和连续数据缺失问题,提出了一种基于专家经验和约简特征集成模型的填充方法.首先,将过程数据缺失情况识别为随机分布、时间维度和特征维度缺失3种类型.接着,基于专家经验对前2种类型进行缺失填充后,面向第3种类型基于分布相似性和互信息相关性为缺失特征预测模型选择建模数据集和约简特征,建立具有互补特性的随机森林、梯度提升决策树和反向传播神经网络子模型对缺失值进行初步预测,利用贝叶斯线性回归(Bayesian linear regression, BLR)构建集成模型以获得最终填充值.最后,利用填充后的MSWI数据建立基于跨层全连接深度森林回归的二噁英排放浓度软测量模型.实验结果表明所提方法提高了MSWI过程数据的质量.

Leaching toxicity characteristics of municipal solid waste incineration bottom ash

The continuously increasing production of municipal solid waste incineration bottom ash （MSWIBA） has promoted its utilization as construction material and raised environmental concern. The physico-chemical properties and leaching behavior of MSWIBA were studied, and ecotoxicological testing using a luminescent bacterium bioassay was performed to assess the ecological pollution risks associated with its leached constituents. The MSWIBA was leached by two types of leachants, H2SO4/HNO3 and HAc solution, at different liquid to solid ratios and contact times. The concentrations of heavy metals and anions in the leachates were analyzed. Multi- variate statistical analyses, including principle component analysis, Pearson＇s correlation analysis and hierarchical cluster analysis, were used to evaluate the contributions of the constituents to the toxicity （ECso） of the MSWIBA leachate. The statistical analyses of the ecotoxicological results showed that the Ba, Cr, Cu, Pb, F and total organic carbon （TOC） concentrations were closely correlated with the ECso value, and these substances were the main contributors to the ecotoxicity of the MSWIBA leachate. In addition, the cluster of these variables indicated similar leaching behaviors. Overall, the research demonstrated that the ecotoxicological risks resulting from MSWIBA leaching could be assessed before its utilization, which provides crucial information for the adaptation of MSWIBA as alternative materials.

Review of harmless treatment of municipal solid waste incineration fly ash

Incineration is widely adopted in municipal solid waste management,which produces large amounts of municipal solid waste incineration(MSWI)fly ash.The harmless treatment of MSWI fly ash requires the appropriate disposal of heavy metals and dioxins that are enriched in fly ash.This review summarizes recently developed harmless disposal methods for MSWI fly ash including solidification/stabilization,thermal treatment,and separation/extraction.In addition,we discuss heavy metal and dioxin fixation,and the removal capacity of fly ash via solidification/stabilization(including cement solidification,chemical stabilization,hydrothermal processes,and mechano-chemical methods),thermal treatment(including sintering,fuel-burning,or electric melting/vitrification),and separation/extraction(including water-washing,chemical reagent leaching,biological leaching,electrodialysis separation,chemical reagent extraction,and nanomaterials extraction).The advantages and disadvantages of different harmless treatment methods are compared and future research prospects and suggestions are summarized.This review provides general guidelines for the harmless treatment of MSWI fly ash in the future.

Characteristics of the stabilized/solidified municipal solid wastes incineration fly ash and the leaching behavior of Cr and Pb

Fly ash is a hazardous byproduct of municipal solid wastes incineration （MSWI）. An alkali activated blast fumace slag-based cementifious material was used to stabilize/solidify the fly ash at experimental level. The characteristics of the stabilized/solidified fly ash, including metal leachability, mineralogical characteristics and the distributions of metals in matrices, were tested by toxic characteristic leaching procedure （TCLP）, X-ray diffrac- tion （XRD） and scanning electron microscopy-energy dispersive spectrometer （SEM-EDS） respectively. Contin- uous acid extraction was utilized to extract metal ions and characterize their leaching behavior. The stabilization/ solidification procedure for MSWI fly ash demonstrates a strong fixing capacity for the metals by the formation of C- S-H phase, hydrated calcium aluminosilicate and ettringite. The stabilized/solidified fly ash shows a dense and homogeneous microstructure. Cr is mainly solidified in hydrated calcium aluminosilicate, C-S-H and ettringite phase through physical encapsulation, precipitation, adsorption or substitution mechanisms, and Pb is mainly solidified in C-S-H phase and absorbed in the Si-O structure.

Analysis of the Relationship between Mechanical Properties and Pore Structure of MSW Incineration Bottom Ash Fine Aggregate Concrete after Freeze-Thaw Cycles Based on the Gray Theory

The destruction of concrete building materials in severely cold regions of the north is more severely affected by freeze-thaw cycles,and the relationship between the mechanical properties and pore structure of concrete with fine aggregate from municipal solid waste(MSW)incineration bottom ash after freeze-thaw cycles is analyzed under the degree of freeze-thaw hazard variation.In this paper,the gray correlation method is used to calculate the correlation between the relative dynamic elastic modulus,compressive strength,and microscopic porosity parameters to speculate on the most important factors affecting their changes.The GM(1,1)model was established based on the compressive strength of the waste incineration ash aggregate concrete,the relative error between the simulated and actual values in the model was less than 5%,and the accuracy of the model was level 1,indicating that the GM(1,1)model can well reflect the change in the compressive strength of the MSW incineration bottom ash aggregate concrete during freeze-thaw cycles.Using the gray correlation method,the correlation between the relative dynamic elastic modulus,compressive strength,air content,specific surface area,pore spacing coefficient,and pore average chord length was calculated,and the pore spacing coefficient and pore average chord length were determined to be highly correlated with each other.This determination can help analyze and infer the deterioration mechanism of concrete subject to freeze-thaw cycles.These results can provide a theoretical basis for guiding the engineering practice of concrete with fine aggregates of household bottom ash in the northern cold region.