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"Incineration"
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Use of municipal waste incineration fly ashes (MSWI FA) in metakaolin-based geopolymer
The solidification/stabilization (S/S) through geopolymer is regarded as the ideal approach for the disposal of municipal waste incineration fly ashes (MSWI FA). This work aims to investigate the S/S behaviors of MSWI FA (up to 20 wt.% incorporations) in metakaolin-based geopolymer (MKG), with a focus on the effect of MSWI FA dosage on the performance of geopolymer. Results show that MSWI FA participates in the geopolymerization and alters the reaction products of geopolymer. MSWI FA imposes a dual effect on the performance of geopolymers. A dosage of MSWI FA lower than 5 wt.% can enhance the strength development of geopolymer, mainly due to the formation of C-A-S–H gels in the framework. However, an MSWI FA addition higher than 5 wt.% significantly decreases the strength of geopolymer. The efficiency of immobilization increases with the ionic radius of heavy metals, following the order of Pb > Zn > Cr > Cu. Heavy metals are immobilized in geopolymer framework through ions exchange and coordination to the nonbridging Si–O
−
and Al-O
−
. These results help to further understand the use of metakaolin-based geopolymer as an MSWI FA S/S binder.
Graphical abstract
Journal Article
Creep characterisation and microstructural analysis of municipal solid waste incineration fly ash geopolymer backfill
In this work, an alkali-activated municipal solid waste incineration (MSWI) fly ash-based filling material was prepared with MSWI fly ash as the raw material and slag as the auxiliary material. The filling body experiences long-term creep, which may have a direct effect on the stability of the overlying strata of the mine goaf. The long-term mechanical properties of the fly ash-based filling materials were tested with a triaxial rheological apparatus. First, uniaxial creep testing was carried out at five levels of axial stress: 50%, 60%, 70%, 80% and 90% of the uniaxial compressive strength (UCS). Then, triaxial creep testing was carried out by considering the geological environment of the goaf. The creep characteristics of fly ash-based filling materials under a three-dimensional stress state were explored. The results indicate that (1) under different stress levels, the creep curves of fly ash-based filling materials can be divided into three types: decelerated creep‒stable creep, decelerated creep‒constant creep, and decelerated creep‒constant creep‒accelerated creep. (2) The total creep deformation of the fly ash-based filling material is 0.46 ~ 0.78%, which is similar to the creep deformation of soft rock. The instantaneous deformation during loading contributes most of the total deformation. (3) The polymerization products generated in the fly ash-based filling material system can effectively cement the raw material particles, and the presence of gel can effectively delay the accelerating creep process of the material. (4) A nonlinear fractional-order model composed of an Abel dashpot can fully describe the complete process of decelerating creep-constant creep-accelerating creep.
Journal Article
Characteristics of incineration ash for sustainable treatment and reutilization
Municipal solid waste incineration (MSWI) generates bottom ash, fly ash (FA), and air pollution control (APC) residues as by-products. FA and APC residues are considered hazardous due to the presence of soluble salts and a high concentration of heavy metals, and they should be appropriately treated before disposal. Physicochemical characterization using inductively coupled plasma mass spectroscopy (ICP-MS), X-ray diffraction (XRD), and X-ray fluorescence (XRF) have shown that FA and APC have potential for reuse after treatment as these contain CaO, SiO
2
, and Al
2
O
3
. Studies conducted on treatment of FA and APC are categorized into three groups: (i) separation processes, (ii) solidification/stabilization (S/S) processes, and (iii) thermal processes. Separation processes such as washing, leaching, and electrochemical treatment improve the quality and homogeneity of the ash. S/S processes such as chemical stabilization, accelerate carbonation, and cement solidification modify hazardous species into less toxic constituents. Thermal processes such as sintering, vitrification, and melting are effective at reducing volume and producing a more stable product. In this review paper, the treatment processes are analyzed in relation to ash characteristics. Issues concerning mixing FA and APC residues before treatment, true treatment costs, and challenges are also discussed to provide further insights on the implications and possibilities of utilizing FA and APC as secondary materials.
Journal Article
Leaching characteristics of chlorine from municipal solid waste incineration fly ash by up-flow percolation column tests
To determine the potential release of chlorine from municipal solid waste incineration (MSWI) fly ash, the leaching behaviors of MSWI fly ash from Likeng waste incineration power plant in China were characterized according to the US EPA method 1314. Chlorine leaching characteristics were investigated over a wide range of liquid-to-solid ratios (L/S 0.2–10 mL/g-dry) and different pH conditions (2, 4 and 6). The test results revealed that the pH of eluate increased with increasing L/S ratio due to the increased release of CaO in fly ash. An initial fast early chlorine release followed by a slower, final release period was obtained. Chlorine release widely exceeds the limit of 2500 mg/L at initial stage. A maximum extractable amount (43–48 %) was obtained when the cumulative L/S ratio is about 2. The leachability of chlorine was almost pH independent due to the strong solubility. The leaching of chlorine is controlled by solution followed by diffusion of capillary. Exponential decay equation could well fit the cumulative chlorine release curves. X-ray diffraction results showed that the water-soluble chlorides, such as sodium chloride (NaCl), potassium chloride (KCl) and calcium chloride (CaCl
2
·2H
2
O), were easy to leach out, while calcium chloride hydroxide [Ca(OH)Cl] was hard to release.
Journal Article
The Resource Utilization and Environmental Assessment of MSWI Fly Ash with Solidification and Stabilization: A Review
Municipal solid waste incineration fly ash, containing heavy metals and dioxins with strong toxicity and carcinogenicity, would pose severe harm to human health and the environment. This review details the chemical composition of MSWI fly ash, summarizes the sources and pollution characteristics of heavy metals and dioxins. In this paper, various solidification/stabilization (S/S) methods and the resource utilization of MSWI fly ash with S/S, such as cement solidification, geopolymer solidification, chemical stabilization and hydrothermal treatment are comprehensively discussed. Besides, the principle of heavy metals stabilization and the mechanism of dioxins degradation are analyzed in detail. Moreover, an overall comparison of these approaches for the harmless treatment of MSWI fly ash, including pollutants solidification/decomposition, advantages, disadvantages and resource utilization approach, is carried out. The risk assessment methods of solidified and stabilized products for heavy metals were discussed. Finally, studying on degradation of dioxin and enrichment of heavy metals in MSWI fly ash by multi-synergistic treatment, inhibiting the leaching of pollutants into aqueous solution during solidification are proposed. This paper is expected to provide some reasonable development directions for the environmentally safer treatment and resource utilization of MSWI fly ash.
Graphical Abstract
Journal Article
Strategies for heavy metals immobilization in municipal solid waste incineration bottom ash: a critical review
Incineration is an integral part of the waste management process to reduce the enormous volumes of municipal solid waste generated daily. Of the various incineration products, bottom ash makes up a major portion, which subsequently needs to be disposed or reused. Unavoidably, trace amounts of heavy metal content present in incineration bottom ash (IBA) can be leached out over time, ending up in water bodies and eventually entering the food chain. This can lead to toxic bioaccumulation of heavy metals in animals and humans. To minimize leaching, it is essential for heavy metals in IBA to be effectively immobilized. In this review, we critically evaluate the effectiveness of various heavy metal immobilization strategies to treat IBA in terms of their suppression of heavy metal leaching based on past research examples. Furthermore, these strategies are assessed for their medium to long term stabilities, potential impact on the environment, as well as challenges that may be faced in their successful implementation. Finally, some future directions in heavy metal immobilization efforts are proposed in light of the present climate crisis.
Journal Article
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.
Journal Article
Life cycle assessment of environmental impact on municipal solid waste incineration power generation
Municipal solid waste (MSW) incineration power generation is an important treatment technology, which has been widely concerned in recent years. It is of great significance to evaluate the environmental impact. This study conducted the environmental life cycle assessment of MSW incineration power plant in Yongcheng city, Henan province, China. After that, the comprehensive environmental impacts of MSW incineration power plant, landfill, and coal-fired power plant are compared. Furthermore, the energy conservation and emission reduction benefits brought by MSW incineration power plant in Yongcheng city are quantitatively analyzed. The results show that (1) the main environmental impact categories of MSW incineration power plant are human toxicity potential and acidification potential, which together account for 72.8% of the total comprehensive environmental impact. In addition, incineration is the main process of pollutant generation, which contributes 94.1% to the comprehensive environmental impact. (2) As an effective supplement to landfill and coal-fired power generation, MSW incineration power generation produces lower environmental impact. (3) Significant energy-saving and emission reduction benefits can be brought by MSW incineration power plant. Particularly, it could save energy 2.75×10
4
tce, reduce greenhouse gas emissions 3.43×10
5
t CO
2
-eq, and effectively reduce the emissions of various air pollutants for the local area annually.
Journal Article