Large-scale Municipal Solid Waste Research Articles

Numerical analysis of NOx reduction in large-scale MSW grate furnace through in-bed combustion optimization using multi-section fuel bed model with thermally thick treatment

This study focuses on reducing NOx emissions in large-scale municipal solid waste (MSW) grate furnaces through in-bed combustion control. A multi-section fuel bed model with thermally thick treatment is developed to accommodate the configurations of large-scale MSW grate furnaces. The model incorporates detailed sub-grid models to simulate the intraparticle gradient, and the stochastic mixing is accounted to deal with the multi-section fuel beds with vertical drop-offs. The influences of primary air distribution and average grate velocity on combustion status and NOx emissions are investigated numerically and validated in a 600 t/d MSW grate boiler. The results indicate that combining a relatively low primary air ratio with a thickened fuel bed ensures both reduced NOx emissions and high burnout efficiency. By reducing the excess air ratio of primary air from 1.2 to 0.9 and distributing it through a rear-enhanced air mode, the overall NOx emission decreased from 398.50 mg/Nm3 to 215.05 mg/Nm3, although at the expense of an increased unburned carbon content from 1.995 wt% to 3.063 wt%. Further lowering the grate velocity to thicken the fuel bed allowed for leveraging the heterogeneous reduction effect of the char layer, reducing the NOx emissions to 184.95 mg/Nm3. Additionally, the unburned carbon content was also remarkably reduced to 1.560 wt%. The proposed strategies of delaying the primary air supply and thickening the fuel bed offer a cost-effective alternative to post-combustion measures, with which the MSW grate boilers can achieve lower NOx emissions while maintaining efficient and stable combustion.

Identification and verification of PCDD/Fs indicators from four typical large-scale municipal solid waste incinerations with large sample size in China

Monitoring PCDD/Fs emissions from municipal solid waste incinerations (MSWIs) is of paramount importance, yet it can be time-consuming and labor-intensive. Predictive models offer an alternative approach for estimating their levels. However, robust models specific to PCDD/Fs were lacking. In this study, we collected 190 PCDD/Fs samples from 4 large-scale MSWIs in China, with the average PCDD/Fs levels and TEQ levels of 0.987 ng/m3 and 0.030 ng TEQ/m3, respectively. We developed and evaluated predictive models, including traditional statistical methods, e.g., linear regression (LR) as well as machine learning models such as back propagation-artificial neural networks (BP ANN) and random forest (RF). Correlation analysis identified 2,3,4,7,8-PeCDF, 1,2,3,6,7,8-HxCDF, 2,3,4,6,7,8-HxCDF were better indicator congeners for PCDD/Fs estimation (R2 > 0.9, p < 0.001). The predictive results favored the RF model, exhibiting a high R2 value and low root mean square error (RMSE) and mean absolute error (MAE). Additionally, the RF model showed excellent prediction ability during external validation, with low absolute relative error (ARE) of 10.9 %-12.6 % for the three indicator congeners in the normal PCDD/F TEQ levels group (<0.1 ng TEQ/m3) and slightly higher ARE values (13.8 %-17.9 %) for the high PCDD/F TEQ levels group (>0.1 ng TEQ/m3). In conclusion, our findings strongly support the RF model’s effectiveness in predicting PCDD/Fs TEQ emission from MSWIs.

Occurrence and carcinogenic potential of airborne PBDD/Fs and PCDD/Fs around a large-scale municipal solid waste incinerator: A long-term passive air sampling study

Municipal solid waste incinerator (MSWI) not only is deemed one of the uppermost sources of polychlorinated dibenzo-p-dioxins/furans (PCDD/Fs), but also produces substantial amount of polybrominated dibenzo-p-dioxins/furans (PBDD/Fs) owing to the existence of brominated flame retardants (BFRs) in the waste. So far, however, PBDD/Fs in the vicinal environments of MSWI and their associated risks remain rarely studied. Based on a one-year passive air sampling (PAS) scheme, we investigated airborne PBDD/Fs and PCDD/Fs around a large-scale MSWI that has been operated for multi-years. Both the concentrations of PBDD/Fs and PCDD/Fs showed spatially decreasing trends with the distance away from the MSWI, confirming the influence of the MSWI on the dioxin levels in its ambient air. But its influence on PBDD/Fs was less because PBDD/Fs exhibit lower volatility and therefore lower gaseous concentrations than PCDD/Fs. Compared to the existing global data of airborne PCDD/Fs and PBDD/Fs, our data of the MSWI vicinity were at medium levels, despite PAS samples only represent the concentrations of gaseous dioxins in theory. The seasonal data suggest that meteorological conditions exerted apparent influences over the concentrations and sources of airborne dioxins around the MSWI. As for PCDD/Fs, the MSWI was diagnosed as their uppermost source, followed by local traffic and volatilization/deposition. Whereas the top three PBDD/F sources were related to PBDEs, bromophenol/bromobenzene, and traffic vehicles, respectively. The bioassay-derived TEQs based on the aryl hydrocarbon receptor activation of airborne dioxins around the MSWI were one or two orders of magnitudes higher than their concentration-based TEQs, and the corresponding carcinogenic risks at some MSWI-vicinal sites exceeded the acceptable threshold proposed by the U. S. EPA (10−6 ∼ 10−4) and deserve continuous attention.

Field investigation of temporal variation and diffusion of hydrogen sulfide on waste working face and intermediate landfill cover

This paper presents the study on the variation, influencing factors and diffusion regularity of hydrogen sulfide (H2S) concentration and surface flux on the working face and intermediate geomembrane cover of a landfill. Field investigations were conducted using static chambers at a large-scale municipal solid waste landfill in Hangzhou, China, from January 2019 to June 2021. The analytical models of H2S transport in the working face and intermediate cover were developed to investigate the surface flux under various conditions. The CALPUFF model was used to demonstrate the diffusion path. The H2S surface flux on the working face ranged from 7.1 × 10−3 to 1.7 mg/m2/h, whereas the range was found to be 1.5 × 10−4 to 0.9 mg/m2/h on the intermediate geomembrane cover. This observation indicated that the geomembrane can reduce H2S emissions. In addition, the H2S surface fluxes at the HDPE GMB seams and near the gas collecting wells were generally 1–2 orders of magnitude larger than that in the intact GMB. The analytical model estimates that the intact GMB exhibits a diffusion coefficient of H2S ranging from 2.7 × 10−11 to 2.2 × 10−10 m2/s. However, the diffusion coefficient increases significantly to a range of 3.3 × 10−11–9.8 × 10−7 m2/s on the GMB seams. According to CALPUFF results, only the H2S diffusion from the working face had areas exceeding the standard concentration.

Microbial mercury methylation potential in a large-scale municipal solid waste landfill, China

Landfills harbor ideal conditions for microbial mercury methylation. However, the levels and distribution of mercury (Hg) and methylmercury (MeHg), potential microbial Hg methylation, and their linkage within landfills are largely unknown. In the present study, total mercury (THg), MeHg, the Hg methylation gene (hgcA) and mer operon were quantified in 30 waste samples from different depths (0–30 m) at 5 locations within a large-scale landfill in China. The average concentrations of THg and MeHg in the solid waste samples were 1422.91 ng/g and 3.15 ng/g, respectively. THg (up to 14405.29 ng/g) and MeHg (up to 10.42 ng/g) have high concentrations in the middle part (10–15 m) along the depth profiles. The concentration of THg was strongly positively (both p < 0.05) correlated with the MeHg concentration and the relative abundance of hgcA, indicating that the THg concentration can play an important role in microbial Hg methylation. The hgcA genes were detected in most samples and mer operon were detected in all samples. Combined hgcA qPCR and metagenomics data showed that Archaea Methanofollis may mainly account for Hg methylation within landfills. These findings provide fundamental knowledge on Hg cycles in landfills.

PCDD/Fs from a large-scale municipal solid waste incinerator under transient operations: Insight formation pathways and optimal reduction strategies

Polychlorinated dibenzo-p-dioxin and dibenzofurans (PCDD/Fs) emissions from the transient operation of municipal solid waste incinerators can reach up to 690 ng/Nm3, as measured in this study. To control the extreme emissions to meet the national standard, the formation pathways of PCDD/F were investigated under transient operations (cold start-up, hot start-up, and after start-up) and normal operations. Compared with normal operations, transient operations facilitate the formation of low-chlorinated congeners rather than highly chlorinated congeners. Statistically, for transient operations, strong correlations were found among tetrachlorodibenzo-p-dioxin or tetrachlorodibenzofuran isomers. An abundant carbon matrix is an important carbon source for PCDD formation. Moreover, the comprehensive study revealed that the oxidation of deposited soot is the main source of PCDD/F emissions, relative to de novo synthesis, chlorobenzene-route synthesis, chlorophenol-route synthesis, and chlorination of dibenzo-p-dioxin/dibenzofuran. In addition, the optimal start-up procedure was constructed by analyzing main formation pathways and operating conditions. The relationship between the international toxic quantity (I-TEQ) values (CI-TEQ) and the reaction time can be assigned as CI-TEQ = 11.72t−0.65 (R2 = 0.97) for the circulating fluidized bed. The relationship of CI-TEQ = 4.61t−0.59 (R2 = 0.85) was also proven on the dataset with a grate furnace. Then, the optimal feeding rate of activated carbon was further proposed by the relationship between the reaction time and I-TEQ, and the semi-empirical equation for PCDD/Fs adsorption. Finally, the PCDD/Fs emissions can be reduced to 0.1 ng I-TEQ/Nm3 under transient operations according to the time since start-up.

Analysis of Current Status and Regulatory Promotion for Incineration Bottom Ash Recycling in Taiwan

Incineration is the most important technology for treating municipal solid waste (MSW) and industrial waste in Taiwan. Currently, there are 24 large-scale MSW incineration plants operated to generate about 1.2 million metric tons of residual ash (mostly bottom ash) based on approximately 6.5 million metric tons of waste incinerated yearly. To reduce the depletion of non-renewable resources under the circular economy principle, the recycling of MSW incineration bottom ash (IBA) as recycled aggregate in concrete and construction applications has been progressed in recent years around the world. According to the official database, the trend analysis of MSW generation and treatment, electricity power and IBA generation from the MSW incineration plants over the past decade (2010–2019) was performed in this work. It showed an increased power generation, growing from 0.485 kWh/kg in 2010 to 0.530 kWh/kg in 2019. In 2019, 2738 GWh of power was sold to Taipower (one of the state-owned companies in Taiwan) for electricity grid connection, gaining income of about NT$ 5,089,383,000 (≈US$ 172,520,000) at an average rate of 1.86 NT$/kWh (0.063 US$/kWh). On the other hand, the ratios of incineration bottom ash (IBA) generation to refuse incinerated indicated a decreasing trend due to the increased operation efficiencies of MSW incineration plants. Based on the revised regulations implemented on 18 May 2020, the regulatory measures for promoting IBA recycling in Taiwan were promulgated to valorize it for the production of recycled aggregate under rigorous requirements for prevent it from polluting the environment.

Problems of municipal solid waste recycling in Irkutsk region

The aim of the article is to predict economic and social consequences of possible solutions to the problem of municipal solid waste (MSW) recycling in Irkutsk region, describe technologies aimed at reducing cost and optimizing business processes of Irkutsk company “Spetsautokhozystvo” which is the most typical enterprise dealing with MSW recycling. The authors used the methods of system, integrated, functional, statistical, structural and comparative analyses, expert and statistical forecasts. The article says that Irkutsk region was divided into two zones - southern and northern ones. The article identified standards of MSW production per resident depending on settlements and MSW transportation and recycling fares. Irkutsk region is not ready to implement a large-scale MSW recycling project. The solutions to the MSW recycling for Irkutsk and Irkutsk region, implementation of technologies aimed at reducing costs and optimizing business processes of “Spetsautokhozystvo” were described. The need for developing a target MSW recycling project in Irkutsk and Irkutsk region was substantiated.

Analysis of municipal solid waste incineration plants for promoting power generation efficiency in Taiwan

Taiwan is a developed nation with approximately 98 % of its energy supplied by imported fuels. In this regard, the efficient energy utilization of municipal solid waste (MSW) is thus becoming attractive in Taiwan because the production of electricity from this source in 2012 has increased to 3,057 GWh, of which 2,350 GWh, or 76.8 %, was connected to the public grid system with the revenues of US$ 154 million. According to the official statistics on the operation status of MSW incineration plants with design capacity of over 300 ton/day in Taiwan, a preliminary analysis of power generation efficiencies for 24 large-scale MSW incineration plants was carried out in the paper. It showed that the energy efficiencies of MSW incineration plants in Taiwan were relatively low with a gross value of 16.2 % in recent years (2008–2012). This meant that a majority of produced heat was discharged into the atmosphere without efficient recovery. As a consequence, the central competent authority in Taiwan is currently planning a promotion policy for combining the district heating and cooling system with waste heat from all MSW incineration plants, which aims at a 30 % increase in the overall energy efficiency.

Municipal solid waste: alternative source of energy to the cement kilns in the state of Madhya Pradesh, India

Rapid urbanisation has resulted in large-scale municipal solid waste (MSW) generation in India. Scientific and environment friendly disposal of MSW is a challenge for the municipal local bodies. A survey has been conducted regarding municipal solid waste generation from 342 local bodies in the State of Madhya Pradesh. Total generation of the MSW in the State is estimated around 4,500 MT/day containing around 55% incinerable waste with around 45% moisture content. There are nine major cement industries in the State, with clinker production capacity of more than 20 million MT/year. Coal is a primary fuel for clinker production and the process takes place at 1,400 to 1,450°C. The MSW is being practiced as alternative fuel and raw material (AFR) in the form of refuse derived fuel (RDF) by the cement industries. The stack emission and the engineering properties of the clinker are found unaffected after the use of refuse derive fuel (RDF) as a co-fuel. Hence, the MSW to RDF may be considered as environmentally safe option for its disposal and the better alternative source of energy, for the cement industries.

Biodegradation Behavior of Municipal Solid Waste with Liquid Aspects: Experiment and Verification

AbstractA specially designed, large-scale municipal solid waste (MSW) settlement apparatus was used to conduct experiments in this study. The suction for unsaturated waste in different layers also was measured. The test results show that the deeper the sample, the more saturated it will become during testing, although the initial state of the overall sample is almost the same. The pore gas pressure was measured for different depths of the sample. It is shown that the pore gas pressure varies in different layers. Two sets of experiments were conducted to make the comparisons. For one test, water was added to the sample; for the other test, no water was added. Significant differences were observed in the quantity of gas and leachate produced during contrastive tests. A previous theoretical model was updated and extended to be suitable to new boundary conditions with a liquid supply.

Content Analysis of Heavy Metals in Fly Ash from One Shanghai Municipal Solid Waste Incineration (MSWI) Plant

The presence of heavy metals in municipal solid waste incineration (MSWI) fly ash is of environmental concern due to their leaching potential in landfill environments. Heavy metal content was performed on fly ash samples from a large-scale municipal solid waste incineration plant in Shanghai China. Content of heavy metals followed the decreasing sequence of Ni &gt; Zn &gt; Pb &gt; Cu &gt; Cd. As pollution of heavy metals is related to not only the content but also their leaching toxicity, further experiment of leaching concentrations of the metals is required to determine the seriousness of pollution caused by the heavy metals.

Characterization and mass balance of dioxin from a large-scale municipal solid waste incinerator in China

The input and output samples from existing large-scale municipal solid waste incinerator (MSWI) were collected and analyzed for polychlorinated dibenzo-р-dioxins and dibenzofurans (PCDD/Fs) in this study, aiming to evaluate PCDD/F characteristic and the corresponding mass balance through the whole system. The grate-type MSWI is equipped with semi-dry scrubber, activated carbon injection, and bag filter as air pollutant control devices (APCDs). Results showed that on the output side, the stack gas, bottom ash and fly ash presented their mean dioxin levels of 0.078ng I-TEQ/Nm3, 12.94ng I-TEQ/kg and 858ng I-TEQ/kg, respectively, and showed large similarities in congener profiles. Instead, on the input side, the municipal solid waste (MSW) presented a mean dioxin level of 15.56ng I-TEQ/kg and a remarkable difference in congener profiles compared with those of the output. The dioxin mass balance demonstrated that the annual dioxin input value was around 5.38g I-TEQ/yr, lower than the total output value (7.62g I-TEQ/yr), signifying a positive dioxin balance of about 2.25g I-TEQ/yr.

Environmental performance evaluation of large-scale municipal solid waste incinerators using data envelopment analysis

Limited to insufficient land resources, incinerators are considered in many countries such as Japan and Germany as the major technology for a waste management scheme capable of dealing with the increasing demand for municipal and industrial solid waste treatment in urban regions. The evaluation of these municipal incinerators in terms of secondary pollution potential, cost-effectiveness, and operational efficiency has become a new focus in the highly interdisciplinary area of production economics, systems analysis, and waste management. This paper aims to demonstrate the application of data envelopment analysis (DEA) – a production economics tool – to evaluate performance-based efficiencies of 19 large-scale municipal incinerators in Taiwan with different operational conditions. A 4-year operational data set from 2002 to 2005 was collected in support of DEA modeling using Monte Carlo simulation to outline the possibility distributions of operational efficiency of these incinerators. Uncertainty analysis using the Monte Carlo simulation provides a balance between simplifications of our analysis and the soundness of capturing the essential random features that complicate solid waste management systems. To cope with future challenges, efforts in the DEA modeling, systems analysis, and prediction of the performance of large-scale municipal solid waste incinerators under normal operation and special conditions were directed toward generating a compromised assessment procedure. Our research findings will eventually lead to the identification of the optimal management strategies for promoting the quality of solid waste incineration, not only in Taiwan, but also elsewhere in the world.

Characterization of Persistent Organic Pollutants in Ash Collected from Different Facilities of a Municipal Solid Waste Incinerator

This study investigated five persistent organic pollutants (polychlorinated and polybrominated dibenzo-p-dioxins (PCDDs/PBDDs), dibenzofurans (PCDFs/PBDFs), biphenyls (PCBs/PBBs), and diphenyl ethers (PBDEs)) in ash collected from several units (super heater (SH), heat economizer (HE), semi-dryer absorber (SDA), bag-house filter (BF), and fly ash pit (FAP), and bottom ash (BA) discharger) of a large-scale municipal solid waste incinerator (MSWI). Data on levels and emission factors of the five target compounds in the different units of the MSWI were first reported. The PCDD/Fs were found in high content in the HE, mainly because of the operating temperature range (250–400°C) which is favorable for PCDD/F formation through de novo synthesis. High concentrations PCBs and PBBs were detected in the BF. The highest concentrations of PBDD/Fs and PBDEs were observed in the BA. A significant correlation existed between content of PCDD/F and PCB in individual ash and corresponding operating temperature, while the content of ash-bound PBDD/Fs and PBDEs chiefly related to feeding wastes that contained brominated flame retardants. The emission of the five pollutants in the MSWI was primarily from fly ash. Further treatment is necessary for ash collected from the HE and BF because the ash had total-PCDD/F content exceeding the regulation limit (1 ng I-TEQ/g) in Taiwan.

Minimum feeding rate of activated carbon to control dioxin emissions from a large-scale municipal solid waste incinerator

To obtain a minimum feeding rate ( F min) of activated carbon (AC), a series of measurements on dioxin emission concentration were carried out in a large-scale municipal solid waste incinerator. It was found that dioxin removal efficiency ( η) increased with an increase in AC feeding concentration. This had an almost linear function to F/ Q when F/ Q was less than 65 mg/Nm 3, where F was the AC feeding rate (mg/min), and Q was the volumetric flow rate of flue gas (Nm 3/min). However, it did not seem to be affected by F/ Q, when F/ Q was larger than 150 mg/Nm 3. On the basis of the experimental data obtained in this study, the removal efficiency of dioxins by the application of AC could be correlated as η (%) = 100/[1.0 + (40.2/( F/ Q) 3)]. It is valid in appropriate conditions ( F/ Q = 10–300 mg/Nm 3) suggested by the study with a statistical error of ±18%. The correlation would be applied to estimate the dioxin removal efficiency ( η) using the F/ Q value. For engineering applications, the ( F/ Q) min could be solved using a graphic illustration method, by which the minimum feeding rate ( F) was obtained if the flue gas volumetric flow rate ( Q) was known.

Distribution of Mono to Octa-chlorinated PCDD/Fs in Fly Ash from a Municipal Solid-Waste Incinerator

We have estimated the concentration and distribution of the mono to octa-chlorinated congeners of polychlorinated dibenzo-p-dioxins (PCDD) and dibenzofurans (PCDF) in fly ashes at various sampling points in a large-scale municipal solid waste incinerator at Umeå, Sweden, as they cooled from 700 to 170 degrees C. Differences between the ashes were observed, the PCDD homologue profile was found to vary with temperature. The total amount of PCDD and PCDF increased as the temperature decreased in the postcombustion zone. The increase was due to both adsorption to the fly ash and formation of PCDD and PCDF. Mono-to trichlorinated PCDD predominated at high temperatures, whereas hepta- and octachlorinated PCDD predominated at temperatures below 400 degrees C. PCDF predominated over PCDD in the whole temperature range. However,the changes in homologue profile for PCDFwere minor. The isomer distribution within the homologue groups was not changed asthetemperature decreased in the postcombustion zone.

A study on the chemical and mineralogical characterization of MSWI fly ash using a sequential extraction procedure

The presence of heavy metals in municipal solid waste incineration (MSWI) fly ash is of environmental concern due to their leaching potential in landfill environments. Sequential chemical extraction was performed on fly ash samples from a large-scale municipal solid waste incineration plant in East China. The transformation of the mineralogical species of fly ash during the sequential extraction was studied using X-ray fluorescence (XRF) and X-ray powder diffraction (XRD). The leaching behavior of heavy metals such as zinc, lead, cadmium and copper in MSWI fly ash was considered to have a dependency relationship with the components of calcium, such as aphthitalite, calcite, anhydrite and calcium aluminate or calcium aluminosilicate.

Model predictive control as a tool for improving the process operation of MSW combustion plants

In this paper a feasibility study is presented on the application of the advanced control strategy called model predictive control (MPC) as a tool for obtaining improved process operation performance for municipal solid waste (MSW) combustion plants. The paper starts with a discussion of the operational objectives and control of such plants, from which a motivation follows for applying MPC to them. This is followed by a discussion on the basic idea behind this advanced control strategy. After that, an MPC-based combustion control system is proposed aimed at tackling a typical MSW combustion control problem and, using this proposed control system, an assessment is made of the improvement in performance that an MPC-based MSW combustion control system can provide in comparison to conventional MSW combustion control systems. This assessment is based on simulations using an experimentally obtained process and disturbance model of a real-life large-scale MSW combustion plant.

Removal of carbon dioxide by a spray dryer

With the global warming due to greenhouse effects becoming serious, many efforts are carried out to decrease the emissions of CO 2 from the combustion of carbonaceous materials. In Taiwan, there are 19 large-scale municipal solid waste incinerators running and their total emission of CO 2 is about 16 950 kton y −1. Spray dryer is the most prevailing air pollution control devise for removing acid gas in waste incineration; however, the performance of spray dryer on the removal of CO 2 is seldom studied. This study employs a laboratory-scale spray dryer to investigate the removal efficiency of CO 2 under different operating conditions. The evaluated parameters include different absorbents mixed with Ca(OH) 2, operating temperature, the concentration of absorbent, and the inlet concentration of CO 2. Experimental results show that the best removal efficiency of CO 2 by a spray dryer is 48% as the absorbent is 10%NaOH + 5%Ca(OH) 2 and the operating temperature is 150 °C. Comparing this result with previous study shows that the performance of spray dryer is better than traditional NaOH wet scrubber. For NaOH + Ca(OH) 2 spray dryer, the removal efficiency of CO 2 is decreased with the inlet concentration of CO 2 increased and the optimum operating temperature is 150 °C. Except NaOH + Ca(OH) 2, absorbents DEA + Ca(OH) 2, TEA + Ca(OH) 2, and single Ca(OH) 2 are not effective in removing CO 2 by a spray dryer.