Municipal solid waste available to the Chinese energy sector - Provincial projections to 2050

Intelligent technologies powering clean incineration of municipal solid waste: A system review

Cleanliness has been paramount for municipal solid waste incineration (MSWI) systems. In recent years, the rapid advancement of intelligent technologies has fostered unprecedented opportunities for enhancing the cleanliness of MSWI systems. This paper offers a review and analysis of cutting-edge intelligent technologies in MSWI, which include process monitoring, intelligent algorithms, combustion control, flue gas treatment, and particulate control. The objective is to summarize current applications of these techniques and to forecast future directions. Regarding process monitoring, intelligent image analysis has facilitated real-time tracking of combustion conditions. For intelligent algorithms, machine learning models have shown advantages in accurately forecasting key process parameters and pollutant concentrations. In terms of combustion control, intelligent systems have achieved consistent prediction and regulation of temperature, oxygen content, and other parameters. Intelligent monitoring and forecasting of carbon monoxide and dioxins for flue gas treatment have exhibited satisfactory performance. Concerning particulate control, multi-objective optimization facilitates the sustainable utilization of fly ash. Despite remarkable progress, challenges remain in improving process stability and monitoring instrumentation of intelligent MSWI technologies. By systematically summarizing current applications, this timely review offers valuable insights into the future upgrade of intelligent MSWI systems.

Municipal solid waste management instruments that influence the use of the refuse as fuel in developing countries: A critical review

Landfills are the destination of most of the refuse generated whereas composting, material recycling, and Waste-to-Energy (WtE) technologies are not commonly employed in developing countries. However, the destination for energy purposes could be supplied with this refuse, improving the viability of energy use. Thus, this article raises some questions to identify aspects that could encourage its use as refuse-derived fuel (RDF) in these countries. Among them, does environmental education affect the municipal solid waste (MSW) source separation with emphasis on a destination? Can selective collection and extended producer responsibility (EPR) affect the MSW for energy recovery? Is there competition between the recycling market and the energy market for RDF? A systematic review of the literature was conducted to gather data and provide answers to such questions. This enabled to observe that EPR, selective collect expansion and source separation influence the quantity and quality of waste sent for energy use. Both internal and external factors impact on source separation. Additionally, there is evidence to support that despite several studies showing their technical, economic, environmental and social viability, the methods of energy usage of the refuse still need to improve their deployment in developing countries. In addition to identifying the main research gaps to be filled in future studies, the article also identified the instruments of MSW management that are to be applied in developing countries to divert recyclable and organic waste from landfill.

Characterization and stabilization of incineration fly ash from a new multi-source hazardous waste co-disposal system: field-scale study on solidification and stabilization

The multi-source hazardous waste co-disposal system, a recent innovation in the industry, offers an efficient approach for hazardous waste disposal. The incineration fly ash (HFA) produced by this system exhibits characteristics distinct from those of typical incineration fly ash, necessitating the use of adjusted disposal methods. This study examined the physicochemical properties, heavy metal content, heavy metal leaching concentration, and dioxin content of HFA generated by the new co-disposal system and compared them with those of conventional municipal waste incineration fly ash. This study investigated the solidification and stabilization of HFA disposal using the organic agent sodium diethyl dithiocarbamate combined with cement on a field scale. The findings revealed significant differences in the structure, composition, and dioxin content of HFA and FA; HFA contained substantially lower levels of dioxins than FA did. Concerning the heavy metal content and leaching; HFA exhibited an unusually high concentration of zinc, surpassing the permitted emission limits, making zinc content a critical consideration in HFA disposal. After stabilization and disposal, the heavy metal leaching and dioxin content of HFA can meet landfill disposal emission standards when a 1% concentration of 10% sodium diethyldithiocarbamate (DDTC) and 150% silicate cement were employed. These results offer valuable insights into the disposal of fly ash resulting from incineration of mixed hazardous waste.

Dioxin emission prediction from a full-scale municipal solid waste incinerator: Deep learning model in time-series input

The immeasurability of real-time dioxin emissions is the principal limitation to controlling and reducing dioxin emissions in municipal solid waste incineration (MSWI). Existing methods for dioxin emissions prediction are based on machine learning with inadequate dioxin datasets. In this study, the deep learning models are trained through larger online dioxin emissions data from a waste incinerator to predict real-time dioxin emissions. First, data are collected and the operating data are preprocessed. Then, the dioxin emission prediction performance of the machine learning and deep learning models, including long short-term memory (LSTM) and convolutional neural networks (CNN), with normal input and time-series input are compared. We evaluate the applicability of each model and find that the performance of the deep learning models (LSTM and CNN) has improved by 36.5% and 30.4%, respectively, in terms of the mean square error (MSE) with the time-series input. Moreover, through feature analysis, we find that temperature, airflow, and time dimension are considerable for dioxin prediction. The results are meaningful for optimizing the control of dioxins from MSWI.

Quantifying the effect of socio-economic-geo drivers on the change of municipal waste disposal in China by an integrated TWFE-PRF-SDM methodology

Municipal solid waste management and disposal in China have significantly evolved since 2000. Due to China's vast land area and significant socioeconomic and geographic disparities, nationwide waste management strategies need to be further evaluated. This study quantified the effect of social, economic, and geographic drivers on municipal waste disposal activities in 31 provincial-level administrative regions from 2003 to 2020, by establishing a methodology integrated by two-way fixed effects regression model, panel random forest, and spatial Durbin model. The results showed, in the past two decades, socio-economic-geo indicators significantly co-decided the landfill and incineration activities. In particular, the explanatory ability of GDP per capita was above 45%, while land resources and city size also showed great significance. Spatial autocorrelation analysis showed that the relationship between landfill/incineration rates and socio-economic-geo drivers changed notably from unobvious to significant with economic growth. Furthermore, the local economy and land resources displayed more impact than those of the neighboring regions, while sci-tech and education showed clear spatial spillover effects. Chinese government would carefully assess the full-scale promotion policy of incineration plants, landfill is still hold as a reasonable option for regions with specific socio-economic-geo conditions.

Low Temperature Thermal Treatment of Incineration Fly Ash under Different Atmospheres and Its Recovery as Cement Admixture

Municipal solid waste incineration fly ash is classified as hazardous waste because it contains dioxins and a variety of heavy metals. It is not allowed to be directly landfilled without curing pretreatment, but the increasing production of fly ash and scarce land resources has triggered consideration of the rational disposal of fly ash. In this study, solidification treatment and resource utilization were combined, and the detoxified fly ash was used as cement admixture. The effects of thermal treatment in different atmospheres on the physical and chemical properties of fly ash and the effects of fly ash as admixture on cement properties were investigated. The results indicated that the mass of fly ash increased due to the capture of CO₂ after thermal treatment in CO₂ atmosphere. When the temperature was 500 °C, the weight gain reached the maximum. After thermal treatment (500 °C + 1 h) in air, CO₂, and N₂ atmospheres, the toxic equivalent quantities of dioxins in fly ash decreased to 17.12 ng TEQ/kg, 0.25 ng TEQ/kg, and 0.14 ng TEQ/kg, and the degradation rates were 69.95%, 99.56%, and 99.75%, respectively. The direct use of fly ash as admixture would increase the water consumption of standard consistency of cement and reduce the fluidity and 28 d strength of mortar. Thermal treatment in three atmospheres could inhibit the negative effect of fly ash, and the inhibition effect of thermal treatment in CO₂ atmosphere was the best. The fly ash after thermal treatment in CO₂ atmosphere had the possibility of being used as admixture for resource utilization. Because the dioxins in the fly ash were effectively degraded, the prepared cement did not have the risk of heavy metal leaching, and the performance of the cement also met the requirements.

Air pollutant emissions and reduction potentials from municipal solid waste incineration in China

China fully implemented the new emission standards in 2016 to further reduce the emissions of air pollutants from the municipal solid waste (MSW) incineration industry; however, the implementation effect of the new standards remains unknown. This study developed the first nationwide air pollutant emission inventory of MSW incineration plants in China based on the measured concentration data from China's continuous emissions monitoring systems (CEMS) network, and activity level data from the China Urban Construction Statistical Yearbook, to evaluate the effectiveness of implementing the new emission standards and estimate the future reduction potentials. Our results demonstrated that the overall standard-reaching proportions of particulate matter (PM), sulfur dioxide (SO₂), nitrogen oxide (NO_X), hydrogen chloride (HCl) and carbon monoxide (CO) were 98.8%, 99.3%, 99.4%, 99.4% and 97.6%, respectively, by comparing with the corresponding concentration limits of new emission standards. The total emissions of PM, SO₂, NO_X, HCl and CO from 412 MSW incineration plants in 2019 were 1.9, 6.2, 50.8, 4.3 and 6.6 kt yr^-1, respectively, which is 33.6-75.8% lower than those in 2015, mainly due to the sharp decrease in emission factors. Pollutant emission hotspots were mainly concentrated in eastern and central and southern regions with large populations and well-developed economies. The analysis of future scenario results shows that despite the continuous increase of MSW incineration amount in the future, if the government strengthens pollutant emission standards and comprehensively implements waste sorting, total emissions and emission factors of air pollutants could be further reduced by 25.8-72.7% and 59.8-81.2%, respectively, by 2050. These findings provide helpful insights into future policymaking and technology selection for China and other countries seeking to reduce pollutant emissions from the MSW incineration industry.

Safe disposal of hazardous waste incineration fly ash: Stabilization/solidification of heavy metals and removal of soluble salts

Hazardous waste incineration fly ash (HFA) is considered a hazardous waste owing to the high associated concentrations of heavy metals and soluble salts. Hence, cost effective methods are urgently needed to properly dispose HFA. In this study, geopolymers were prepared by alkali-activation technology to stabilize and solidify heavy metals in HFA. In addition, the effects of three different aluminosilicates (metakaolin, fly ash, and glass powder) on the heavy metal immobilization efficiency were investigated. Because the soluble salt content of HFA is too high for their direct placement in flexible landfill sites and water washing can lead to heavy metal leaching, water-washing experiments were conducted after alkali-activation treatment to remove soluble salts. The results suggest that the concentrations of heavy metals leached from geopolymers can satisfy the Chinese Standard limits (GB18598-2019) when the addition of aluminosilicates exceeds 20 wt%. More than 77% of Cl^- and >64% of SO₄^2- in geopolymers could be removed via water-washing treatment. The Zn leaching concentration was maintained below approximately 0.52 ppm. After alkali-activation treatment, the water-washing process could efficiently remove soluble salts while inhibiting heavy metal leaching. Sodium-aluminosilicate-hydrate (N-A-S-H) gel, a product of the geopolymerization process in this study, was demonstrated to act as a protective shell that inhibited heavy metal leaching. Hence, HFA-based geopolymers are considered suitable for disposal in flexible landfills.

Curbing dioxin emissions from municipal solid waste incineration: China's action and global share

China generates the world's second-largest amount of municipal solid waste (MSW) and incinerates the largest quantity of MSW. However, data on the latest dioxin emissions from MSW incineration (MSWI) and the related global share were lacking. In the context of MSW classification, distinguishing the long-term MSW generation and incineration quantity, and dioxin emissions was necessary for macro-control and policy-making by the Chinese Government. By considering population size and GDP per capita, China's MSW generation toward 2050 was projected based on Monte Carlo simulation. Moreover, dioxin emission factors were also assumed based on the diffusion rate of four grades of air pollution control devices (APCDs). Finally, we show that the quantity of China's MSW generation in 2050 will be 363.50 million tonnes (Mt) with 341.06-382.45 Mt of 75% certainty. China's dioxin emissions from MSWI were approximately 15.46 g I-TEQ in 2019, which accounted for 26.1% of total emissions from global MSWI. We discuss dioxin emission reduction scenarios depending on MSW diversion and APCD upgrades. China's dioxin emissions will be 70.38 g I-TEQ for the business-as-usual scenario, and the dioxin emissions will be 9.29 g I-TEQ (within the range of 8.88-9.64 g I-TEQ) for the optimal scenario in 2050. Moreover, in 2050, the APCD diffusion rate will account for 98.8% of the sensitivity of dioxin emissions from China's MSWI. According to the assumed scenarios, there is a dioxin emission reduction potential of 18.6% and 86.8% in 2050 by MSW diversion alone and maximum APCD upgrades combined with food waste diversion, respectively.

Simultaneous study of the interaction effect of chemical and hydrothermal pretreatment on the yield of methane produced from municipal waste

Municipal waste has the potential to be a significant source of energy production. This study investigated pretreatment methods such as NaOH, hydrothermal, and ozonation to increase biomethane production from municipal waste. In addition, these pretreatments were further evaluated using ultrasonic pretreatment after achieving optimal conditions by RSM CCD methods. The optimum pretreatment conditions were observed to be 8% NaOH concentration, 132 °C hydrothermal temperature, and O₃ equal to 0.19 g/g TS. The maximum biomethane produced and achieved during the tests was 394 mL/kg TS, which increased to 410 mL/kg TS after ultrasonic pretreatment. The best sCOD reduction in the optimal pretreatment conditions and after the ultrasonic pretreatment was 87% and 91%, respectively. Also, in the absence of ozone pretreatment, the highest yields of biomethane and biogas occurred at a 6.4% concentration of NaOH and a temperature of 135 °C; however, in the presence of ozone, the yield of biomethane and biogas produced was greater and the inhibitory effect of sodium hydroxide also occurs in higher amounts. Experiments have shown that ozonation increases biomethane production rather than increasing biogas production (hence the ratio of methane to biogas).

Dioxin emission prediction based on improved deep forest regression for municipal solid waste incineration process

Dioxin (DXN) emission concentration is an important environmental indicator in the municipal solid waste incineration (MSWI) process. The prediction model of DXN emission can be used for pollution control to realize actual requirements of operation optimization. Therefore, a DXN emission concentration prediction model based on improved deep forest regression (ImDFR) is proposed in this study. A feature reduction layer based on out-of-bagging error is first introduced into the ImDFR to eliminate redundant variables and feed all confidence information on DXN emission into the feature enhancement layer of the MSWI process. A deep ensemble stacking model is subsequently built to depict deep features and increase diversity and accuracy using random forests, completely random forests, GBDT, and XGBoost as subforests. Finally, the predicted value of the DXN prediction model is determined in the decision layer. The DXN emission prediction model is verified using actual historical data of two incinerators operated with a daily processing capacity of 800 tons. The experimental results showed that the proposed prediction model presents higher accuracy and better generalization ability than state-of-the-art models.

The influence of internal motivation and external publicity on consumers' waste sorting behaviour

Waste sorting is an important aspect of environmental protection, which is now being enforced on a large scale in China. More broadly, it is beneficial to improve the implementation strategies for waste sorting policy and programmes. This study analyses the psychology of consumers that influences the mechanisms of consumer waste sorting and the governmental policies influencing consumers' attitudes and behaviours. About 295 validated participants were collected from four regions of China. Regression analysis was used to examine the relationship among consumers' internal motivation, government's external publicity and consumer behaviour, and the Hayes' PROCESS macro was used to test mediating effect and moderating effect. The results show that consumers' internal motivation and government's external publicity have a positive effect on consumer behaviour. Consumer attitude played a complete mediating role between consumers' internal motivation and consumer behaviour. Between the government's external publicity and consumer behaviour, consumer attitude played a complementary mediating role. Consumers with self-transcendence values, positive motivation of waste sorting and the government's external publicity had a greater positive impact on their attitudes than consumers with self-enhancement values. The greater the material benefits and psychic income consumers received from waste sorting, the more it promoted a positive attitude to consumer behaviour. The article puts forward some management suggestions to improve the government's implementation of its waste sorting policy.

Determinants of municipal solid waste: a global analysis by countries' income level

The generation of municipal solid waste (MSW) is an environmental problem worldwide. A high rate of MSW produces pollution and diseases and affects the economic development of countries. This study analyzes the effect that GDP, population density, urbanization, and tourists' flow have on the generation of MSW in 173 countries worldwide. We grouped countries according to their income levels to control for heterogeneity between regions. The results show that, during 2016, solid waste generation increased along with GDP increments, mainly in high-income countries. We show that the increase in MSW is also due to the rise in population and urbanization. Tourism also has a positive and significant impact on the generation of waste. Our results allow us to recommend some public policy actions.

Behavioral change in waste separation at source in an international community: An application of the theory of planned behavior

Analysing and understanding the factors that influence the behavior of waste separation is critical to improved waste management. This study identified the factors behind behavioral change in waste separation at source in an international community. The theory of planned Behavior (TPB) was adopted to conduct a self-report questionnaire survey twice, in which 354 residents participated at Time1 and 331 at Time 2, with a retention rate of 93.5%. The questionnaires were designed based on TPB with additional questions regarding waste separation rules in the community, experience of waste separation, and environmental knowledge. With the questionnaire data and follow-up qualitative interviews, factors related to waste separation through factor analysis and structural equation modelling and text mining were specified. The panel data collected over three months demonstrated the changes in attitudes, subjective norms, and perceived behavioral control that affect behavioral intention in the process of behavior adaption. Combined with interview data, the reasons for these changes can be further attributed to individuals' environmental knowledge and community guidelines. The findings imply that policies targeting environmental education and rulemaking are effective to help residents form more positive intentions towards waste separation.

Demand gap analysis of municipal solid waste landfill in Beijing: Based on the municipal solid waste generation

Achieving accurate prediction of the Municipal Solid Waste (MSW) generation is essential for the sustainable development of the city. This paper selects Beijing as the research object, building a neural network model based on Grey Relational Analysis and Long and Short-Term Memory (GRA-LSTM), and choosing 14 influencing factors of MSW generation as the input indicators, to realize the effective prediction of MSW generation. Then this study obtains the landfill area in Beijing by using the aforementioned prediction results and the calculation formula of the landfill. Firstly, the GRA method is used to sort the influencing factors of the MSW generation for obtain the key influencing indexes. Secondly, the LSTM model is used to learn features of the key influencing indexes. Finally, the area of Beijing landfill is estimated by the calculation formula of landfill area. The results show that, first of all, the MAPE value of the GRA-LSTM combined model established in this paper is 7.3, and the prediction performance of this model is better than the other seven structural methods. Secondly, the area demand for landfills in Beijing shows an upward trend. At last, this paper put forward relevant suggestions to achieve sustainable urban development and deal with the increase in the MSW generation and the demand for landfills.

Characterization of hydrogen production and microbial community shifts in microbial electrolysis cells with L-cysteine

L-cysteine is used to improve efficiency in anaerobic biological systems as an oxygen scavenger, electron shuttle and substrate source. The performance of MEC by addition of L-cysteine was investigated during start-up and operation phases, respectively. Results showed that the maximum current density of 6.36 ± 0.14 A/m², hydrogen yield of 1.08 ± 0.05 m³/m³ and energy efficiency of 130% were achieved with L-cysteine adding during operation phase. By contrast, the addition of L-cysteine during the start-up phase reduced the energy efficiency by more than 30%. The microbial community analysis revealed that a higher microbial community richness and diversity were achieved, the enrichment of Sulfuricurvum, Sulfurospirillum, Desulfovibrio and other electroactive microorganisms indicated their relative abundance could be regulated by L-cysteine during start-up phase when L-cysteine was added. This study provided an alternative method to enhanced hydrogen production and a better understanding of the mechanism of L-cysteine action in MEC performance.