Comparative life cycle assessment of landfill sludge treatment technologies in China.

Reasonable treatment of large amounts of sludge excavated from landfills has gained increasing attention due to the diminishing availability of landfill space in China. In this study, five landfill sludge (LS) treatment technologies using life cycle assessment (LCA) and life cycle cost (LCC) were investigated, i.e., co-incineration in coal-fired power plants (CFPP) and waste incineration power plant (WIPP), co-processing in cement kiln, bricks production, and sintering ceramsite. The LCA results demonstrate that sintering ceramsite outperforms other technologies and LCC results indicate sintering ceramsite also provides the highest economic benefit ($869.94). To further enhance environmental and economic performances of the LS treatment, the substitution of coal with natural gas and biomass can reduce Energy Conservation and Emission Reduction (ECER) index by 74% and 98%, respectively. This substitution can increase economic returns by 24% and 26%, respectively. Furthermore, national-level economic benefit and carbon emission reduction potential of different LS treatment technology alternative scenarios were assessed. Results display that a combination of 50% CFPP, 25% bricks, and 25% ceramsite (biomass) offers the highest economic gain, which is 3.02 times that of 50% CFPP and 50% cement (original case). Conversely, the replacement of 25% brick with 25% cement in the above combination result in the lowest carbon reduction, which is 9.35 times that of the original case.

Environmental and economic analysis of the transformation of paper mill sludge treatment technologies in China.

Paper mill sludge (PMS) is featured with a high content of cellulose and hemicellulose, and using its characteristics to make paperboard can achieve a high-value utilization of PMS, which has attracted growing interest. In this study, currently prevalent landfill, incineration technologies (generating heat and electricity by incineration), and three paperboard technologies (medium density fiberboard, pulp board, and corrugated paper) were evaluated and compared via life cycle assessment (LCA) and life cycle costing (LCC) methods. LCA results show that the PMS-to-pulp board outperforms others with an energy conservation and emission reduction (ECER) value of - 2.86 × 10-8, while the landfill exhibits the highest overall environmental impact with an ECER value of 4.80 × 10-9. LCC results reveal that the PMS-to-pulp board delivers the highest economic profit with $257.357, while the landfill is the lowest with $ - 35.63. The PMS paperboard technologies are more economically friendly than the incineration technologies due to additional electricity/steam consumption during the PMS pre-drying process in incineration. In addition, different scenarios were set up to explore national GHG emission reduction potential by increasing paperboard technologies application rate and reducing the proportion of landfill and incineration. The scenario analysis suggests that replacing 90% of landfill and incineration ratio with PMS paperboard technologies could tremendously improve the overall emission reduction performance with - 9.08 × 1010 kg CO2 eq. This result indicates that the PMS treatment technology transformation has a significant favorable impact on the achievement of the "carbon neutrality" target.

Comparative study of electroplating sludge reutilization in China: environmental and economic performances.

Harmless disposal and reutilization of electroplating sludge (ES) attract growing interests due to the high content of heavy metals, which requires economical-affordable and environmentally friendly processing technologies. Main reutilization alternatives in China, i.e., acid leaching, bioleaching, smelting, ironmaking blast furnace co-processing (IBFC), and cement kiln co-processing (CKC), were evaluated and compared via life cycle assessment (LCA) and life cycle costing (LCC) methods. In addition, the heavy metal recovery potential of these scenarios was also evaluated to focus on the sustainable use of metal resources. LCA results show that acid leaching outperforms other scenarios due to the environmental benefits originating from recovering heavy metals, while smelting exhibits the worst due to high energy consumption. The environmental contribution analysis reveals that the product nickel sulfate has a significant positive impact on acid leaching and bioleaching scenarios, and energy consumption is the key factor for smelting, IBFC, and CKC. LCC results show that bioleaching outperforms others, while CKC performs the worst because only inorganic materials are utilized. Bioleaching has the lowest externality cost while CKC has the highest. The heavy metal recovery assessment indicates that bioleaching exhibits the greatest potential with recovery rates of 99%, 99%, 93%, 96%, and 95% for Cu, Cr, Ni, Zn, and Fe, respectively. In contrast, the target heavy metal recovery rate for both acid leaching and smelting is 93%. Acid leaching and bioleaching scenarios are more advantageous from a comprehensive comparison.

Comprehensive assessment of food waste treatment emission reduction in China: a life cycle perspective.

Food waste (FW) treatment has attracted increasing attention since waste classification occurred in China. Analyzing the environmental and economic impacts of different FW treatment technologies is required. In this study, four FW treatments, i.e., anaerobic digestion, black soldier fly (BSF) bioconversion, composting, and landfill, were evaluated using life cycle assessment (LCA) and life cycle cost (LCC). LCA results show that anaerobic digestion outperforms the other technologies, while LCC results indicate anaerobic digestion has the lowest economic benefits ($5.16) and landfill has the highest ($14.22). Bioconversion has the highest product revenue ($37.98). FW anaerobic digestion followed by treating digestate and waste crude oil was employed to investigate the environmental differences between waste classification and mixed incineration. Digestate gasification and conversion of waste crude oil to biodiesel are found to be environmentally friendly, and waste classification outperforms mixed incineration. Furthermore, we explored national-level environmental emission reduction with anaerobic digestion as the dominant technology via increasing resource utilization rate and applying household FW disposers. Results display that a 60% resource utilization rate decreases the overall environmental impact by 36.68% compared with current situation, and treating household FW separately at the source can further lead to emission reduction. This study provides a reference for selecting FW technologies for countries worldwide from environmental and economic perspectives, as well as a direction of resource utilization for how to reduce environmental emissions from treating the total FW produced by all humanity.

Environmental and economic assessment of rural domestic waste gasification models in China.

The dispersed sources and inconvenient transportation of rural domestic waste (RDW) lead to difficult centralized treatment. Gasification is suitable for decentralized waste treatment, which can effectively avoid RDW long-distance transportation and reduce dioxin emissions compared with small-scale incineration. Hence, economically-affordable and environmentally-friendly RDW treatment models with different gasification scales are required, and village, town and county models were compared via life cycle assessment (LCA) and life cycle cost (LCC) methods in this study. Furthermore, scenario analysis investigated waste sorting based on two food waste (FW) treatment technologies, different FW separate collection efficiency, and electricity recovery to explore the environmental and economic improvement potentials of three models. LCA results show that electricity consumption and direct emissions are significant contributors to environmental impacts, and the county model outperforms village and town models. Moreover, transportation accounts for 6% of the overall environmental impact in the county model. Scenario analysis reveals that waste sorting and electricity recovery can reduce the overall environmental impact by 29% to 146% for three models. LCC results demonstrate that the town model delivers the lowest economic cost, while the village model is the highest. In scenario analysis, resource utilization of FW and electricity recovery of other waste exhibit promising economic benefits. The findings provide comprehensive references for sustainable RDW treatment.

A review on emergency disposal and management of medical waste during the COVID-19 pandemic in China.

The surge of medical waste (MW) generated during the COVID-19 pandemic has exceeded the disposal capacity of existing facilities. The timely, safe, and efficient emergency disposal of MW is critical to prevent the epidemic spread. Therefore, this review presents the current status of MW generation and disposal in China and analyzes the characteristics and applicability of emergency disposal technologies. The results show that movable disposal facilities can dispose of infectious MW on site, even though most of their disposal capacity is at a low level (<5 t/day). Co-disposal facilities need to be reformed completely for emergency MW disposal, in which separate feeding systems should be taken seriously. Specifically, municipal solid waste (MSW) incineration facilities have great potential to improve emergency MW disposal capacities. For hazardous waste incineration facilities, compatibility of the wastes must be matched to the composition and calorific value of the waste. As for cement kiln, MW can only be used as an alternative fuel instead of a raw material for cement. Based on the environmental risk and technical adaptability, the six emergency MW disposal technologies are recommended to be prioritized as follows: movable microwave sterilization, movable steam sterilization, movable incineration, co-incineration with hazardous waste, co-incineration with MSW and co-disposal in cement kilns. Infectious MW, especially COVID-19 MW, should be prioritized for disposal by centralized and movable disposal facilities, while non-infectious MW can be disposed of using co-disposal facilities. All stakeholders should strengthen the delicacy management of the end-of-life stage of MW, including collection, classification, packaging identification, transportation, and disposal. Currently, it is necessary for centralized disposal enterprises to follow the emergency disposal operation flowchart. From a long-term strategic perspective, making full use of regional movable and co-disposal facilities in the megacities can effectively enhance the emergency MW disposal capacity.

Comparative life cycle assessment of emergency disposal scenarios for medical waste during the COVID-19 pandemic in China.

The COVID-19 pandemic attracts concerns globally and leads to an exponential increase in medical waste generation, and disposal of medical waste is an urgent need for preventing the epidemic spread. Emergency disposal scenarios of medical waste generated during the COVID-19 pandemic require a systematic assessment to quantify their potential environmental impacts. The environmental impacts and key factors of three movable disposal scenarios (i.e. incineration disposal vehicle, movable steam and microwave sterilization equipment both followed by co-incineration with municipal solid waste) were quantified via life cycle assessment approach. Furthermore, the environmental impacts of three movable disposal and two co-incineration scenarios were compared via life cycle assessment by expanding system boundaries. The results show that co-incineration with municipal solid waste has the lowest environmental impacts due to environmental benefits produced by power generation, while co-incineration with hazardous waste is the highest due to the high energy consumption. Energy consumption (i.e. kerosene, electricity and diesel) are the key factors for three movable disposal scenarios. For movable steam and microwave sterilization equipment followed by co-incineration with municipal solid waste, power generation from incinerating disinfected medical waste has significant beneficial environmental impacts due to avoided impacts of electricity consumption. The recommendations for improvement of the emergency disposal and management of medical waste during the COVID-19 pandemic globally and other serious epidemic in the future are provided.

Application of microwave energy in the destruction of dioxins in the froth product after flotation of hospital solid waste incinerator fly ash.

Most of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) and powder-activated carbon (PAC) in hospital solid waste incinerator fly ash are enriched in the froths produced through flotation. Because PAC is an excellent microwave absorber, microwave treatment was performed on the froths in this study to decompose PCDD/Fs. The results showed that the destruction efficiency of PCDD/Fs increased with increasing microwave incident power and processing time, particularly for highly chlorinated PCDD/Fs. With a microwave incident power of 2100W at 7min, the total mass destruction efficiency of the PCDD/Fs in the froths reached 99.6wt.% and the total toxic equivalent (TEQ) of PCDD/F was substantially reduced from 29.0 to 0.08 ng-I-TEQ/g. PCDD/Fs in the froths were mostly decomposed and evaporated very little into exhaust gas under microwave treatment, especially at 2100W. The treated froths displayed good porous structures, enabling the potential recovery of PAC for reuse. Microwave treatment of the froths could promote the rapid decomposition of PCDD/Fs and the recovery of a typical waste resource; also it could present a viable alternative to combustion treatment for the froths.

Removal of carbon constituents from hospital solid waste incinerator fly ash by column flotation.

Hospital solid waste incinerator (HSWI) fly ash contains a large number of carbon constituents including powder activated carbon and unburned carbon, which are the major source of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in fly ash. Therefore, the removal of carbon constituents could reduce PCDD/Fs in fly ash greatly. In this study, the effects of the main flotation parameters on the removal of carbon constituents were investigated, and the characteristics of the final product were evaluated. The results showed that loss on ignition (LOI) of fly ash increased from 11.1% to 31.6% during conditioning process. By optimizing the flotation parameters at slurry concentration 0.05 kg/l, kerosene dosage 12 kg/t, frother dosage 3 kg/t and air flow rate 0.06 m(3)/h, 92.7% of the carbon constituents were removed from the raw fly ash. Under these conditions, the froth product has LOI of 56.35% and calorific values of 12.5 MJ/kg, LOI in the tailings was below 5%, and the total toxic equivalent (TEQ) of PCDD/Fs decreased from 5.61 ng-TEQ/g in the raw fly ash to 1.47 ng-TEQ/g in the tailings. The results show that column flotation is a potential technology for simultaneous separation of carbon constituents and PCDD/Fs from HSWI fly ash.