Municipal Solid Waste Incineration Bottom Ash Research Articles

Evaluation of reclaimed municipal solid waste incinerator sands in concrete

U.S. municipal solid waste incinerator (MSWI) ash is generally disposed of in landfills, due to the absence of approved avenues to repurpose the material through recycling. This work investigates the utilization of MSWI bottom ash sands in concrete that have been reclaimed from a recycling plant in Central Pennsylvania. Physical and chemical properties of the reclaimed sands are examined for suitability as a partial replacement for fine aggregates in concrete. The performance of raw incinerator ash vs. Reclaimed sands in concrete are compared through microstructure SEM analysis, shrinkage, compression strength, and hydrogen gas production due to metallic aluminum present in incinerator ash. It is found that reclaimed sands satisfy most ASTM requirements to be used as a lightweight concrete aggregate. Despite this, it is currently not recommend to use reclaimed sands in concrete due to the formation of empty holes in the cement matrix microstructure due to hydrogen gas production. These holes cause cracks in the concrete which leads to reduced structural capacity of the material. It is also not recommended that raw ash be used in concrete due to significant amounts of drying shrinkage, leaching concerns, and the unclean nature of the ash.

An algorithm for the use of MSWI bottom ash as a building material in road pavement structural layers

Municipal solid waste incinerator (MSWI) bottom ash (constituting approximately 80–90%) and fly ash are by-products of the incineration of solid waste. In general, MSWI residues are primarily discarded into landfills. To address the continuous growth of landfills and to implement zero waste and circular economy policies, researchers are focusing on more efficient ways of using MSWI bottom ash. To that end, the best practices show that MSWI bottom ash is suitable for civil engineering applications, especially roads. Therefore, the subject of this research was the performance of subgrade and different unbound and bound pavement structural layers containing bottom ash. An algorithm was also introduced to facilitate the use of MSWI bottom ash as a building material. Soil and mineral aggregate mixtures with different percentages (0–100%) of bottom ash were designed and analysed, and more than 10 testing subjects containing a high amount of MSWI bottom ash were tested in the laboratory. The research revealed the suitability of the 0/2 fraction of bottom ash to improve soil and to enhance the performance of asphalt concrete mixture AC 16 PD in which the 0/4 fraction of sand is replaced with the 0/2 fraction of bottom ash. Furthermore, the suitability of mixtures composed of mineral aggregates and MSWI bottom ash or only of MSWI bottom ash (100%) to construct sub-base and base courses was confirmed.

Influence of calcium content on structure and strength of MSWI bottom ash-based geopolymer

This study explored the strength limitations of municipal solid waste incineration (MSWI) bottom ash-based geopolymer, which can limit its use in building materials. The calcium content in MSWI bottom ash was increased by the addition of varying amounts of granulated blast furnace slag (GBFS) and calcium-containing chemicals. The results showed that the low calcium content of MSWI bottom ash in geopolymer was the main cause of insufficient polymerisation. Both GBFS and calcium-containing chemicals improved geopolymer microstructure and enhanced the degree of polymerisation, which clearly improved the compressive strength. However, further increases in geopolymer compressive strength were not significant when the GBFS content was greater than 40%, and the compressive strength decreased sharply when hydrated Ca(OH)2content was greater than 5%.

Cooperative action and compatibility between Portland cement and MSWI bottom ash alkali-activated double gel system materials

Abstract This study investigated the cooperative action and compatibility between Portland cement and municipal solid waste incineration (MSWI) bottom ash alkali-activated double gel system materials, focusing on the two different methods of mixed casting and layered casting. The results show that alkali-activated materials and Portland cement have a severe incompatibility problem when mixed casting is used. However, layered casting completely solves this compatibility problem in double gelled system materials. This is because liquid sodium silicate accelerates the initial setting time in alkali-activated materials and thus eliminates the influence between polymerization and hydration. Furthermore, alkali-activated materials can compensate for the lack of calcium by absorbing the Ca(OH)2 generated by the hydration of Portland cement. In this case, Calcium-Silicate-Hydrate (C-S-H) and Aluminium-Modified Calcium-Silicate-Hydrate (C-A-S-H) gels are formed, which strengthens the interface transition zone.

Effect of activated silica on polymerization mechanism and strength development of MSWI bottom ash alkali-activated mortars

This study investigated the effect of activated silica on both the polymerization mechanism and strength development of municipal solid waste incineration (MSWI) bottom ash alkali-activated mortars, with a specific focus on increasing the silica content by adding either solid or liquid sodium silicate. The results show that such additives increase the content of active silicon and improve the resulting compressive strength of mortars, which is more effectively enhanced by liquid solid sodium silicate addition. However, a significant decline of these effects was found with increased addition of sodium silicate. Solid sodium silicate is difficult to dissolve; therefore, increasing its content not only fails to improve the content of active silicon but also causes precipitation. Using liquid sodium silicate could further improve the content of active silicon; however, excessive addition will result in a large surplus of activated silicon and thus, causing sodium and magadiite precipitation.

Soluble Salt in Municipal Solid-Waste Incinerator Bottom Ash and Its Effect on the Performance of Cement-Stabilized Materials

The contents of soluble salts, including chloride and sulfate, were tested to use municipal solid-waste incinerator bottom ash (IBA) in cement-stabilized materials for roadbase. In addition, the effects of soluble salts on the strength properties of cement stabilized IBA and crushed stone mixture were analyzed by applying unconfined compressive and splitting strength tests, respectively. Moreover, the deformation properties of the mixture were analyzed by applying dry and temperature shrink tests, respectively. In addition, the microscopic mechanism of chloride and sulfate on the mixture was analyzed by using micro-test methods. Results show that the average contents of chloride and sulfate in IBA are 0.57% and 1.01%, respectively. The strength of the mixture that contains 30% IBA greatly decreases when the contents of chloride and sulfate in IBA are higher than 1.67% and 2.00%, respectively. The dry and temperature shrinkage deformations of the mixture greatly increase when the contents of chloride and sulfate are higher than 0.67% and 1.00%, respectively. Water treatment reduces the soluble salt content of IBA. Unlike the control mixture, the strength properties of the mixture that contained IBA with water treatment shows no remarkable difference, whereas the short and temperature shrinkage deformations increase and decrease, respectively. Microscopic analysis shows that Cl- reacts with cement hydration products to produce Friedel salts, and the amount of hydration products increases in the mixture due to the addition of chloride and sulfate. However, some cement particles are not hydrated when the Na2SO4 content is 1.0%. The content of soluble salts in IBA should be limited to ensure the performance of the mixture.

Understanding the Behavior of Radioactive Cesium during the Incineration of Contaminated Municipal Solid Waste and Sewage Sludge by Thermodynamic Equilibrium Calculation.

Following the nuclear accident at the Fukushima Daiichi Nuclear Power Plant in 2011, even the municipal solid waste (MSW) and sewage sludge (SS) in northeastern Japan became contaminated by radioactive nuclides such as 137Cs and 134Cs. To understand the state of radioactive cesium (r-Cs) in the incineration residues of the municipal wastes, research groups studied the concentration and the chemical form of r-Cs in the residues, as well as its water-leaching behavior. In the present study, we conducted thermodynamic equilibrium calculations to estimate the possible chemical forms of r-Cs in the incineration residues. Thermodynamic data for cesium oxides and aluminosilicates were collected and compiled into a new database to perform equilibrium calculations for systems that include Cs. The calculation results suggested that Cs (radiocesium and stable cesium) in municipal solid waste was transformed into gaseous CsCl or crystalline aluminosilicate at incineration temperatures and, when a molten aluminosilicate phase (i.e., slag phase) was generated, a proportion of the Cs species was dissolved into the slag phase. In the case of sewage sludge, Cs was calculated to be transformed mostly into crystalline aluminosilicate at incineration temperatures, whereas by analogy with the behaviors of Na and K, Ca,Cs-phosphate double salts were also potential incineration products. These results could account for the high leaching rates of r-Cs from the MSW incineration fly ash and the low leaching rates from the MSW incineration bottom ash and SS incineration fly ash reported in earlier studies. In the case of dewatered SS that included a large amount of slaked lime as a flocculant, it was exceptionally difficult for the calculation to represent the fate of Cs, and we needed to include the contribution of silica sand in a fluidized-bed combustor in the equilibrium calculation to represent the low leaching rates of alkali species from the dewatered SS fly ash. From the results of the thermodynamic equilibrium calculations and also from the calculated standard Gibbs energy of cesium aluminosilicate formation/decomposition reactions, the effects of waste composition and incineration temperature on the fate of Cs were examined: High incineration temperature and large amounts of Ca and Cl in the waste composition increased the fraction of gaseous CsCl in the furnace and thus resulted in the high distribution ratios of Cs in the fly ash of MSW and the high leaching rates of Cs from the fly ash.

MSWIBA-based cellular alkali-activated concrete incorporating waste glass powder

In this study, municipal solid waste incineration bottom ash (MSWIBA) and waste glass were recycled and reused to synthesize aerated or cellular alkali-activated concrete (AAAC) in order to minimize their disposal at landfills and to produce a value-added construction material. The experimental results showed that incorporating 20% waste glass powder (WGP) in the alkali-activated MSWIBA-WGP products would not cause a decrease in strength, and WGP can be considered as a precursor as well as a waste-derived activator to provide the reactive silica for geopolymerization. The MSWIBA as the main precursor contributed to the structure forming of AAAC as well as acting as a source of foaming agent due to the presence of metallic aluminium. The prepared AAAC incorporating 20% WGP exhibited low thermal conductivities ranging from 0.14 to 0.38 W/m·K with compressive strengths ranging from 0.9 to 10.4 MPa, and density values from 494 to 1295 kg/m3. The results obtained by optical photography and Scanning Electron Microscopy-backscattered electrons imaging methods showed that the prepared AAAC had less spherical air voids and wider air-void size distribution from 0.02 to 3.0 mm when compared to traditional aerated cement concrete, and the reactive silica was able to form C(N)-A-S-H which provided the mechanical strength development of AAAC.

Solidification and Stabilization of Sewage Sludge and MSWI Bottom Ash for Beneficial Use as Construction Materials

AbstractThis paper investigates the feasibility of converting municipal sewage sludge and municipal solid waste incineration (MSWI) bottom ash to a construction material for the dikes of a sludge-o...

Evaluation of physicochemical and hydromechanical properties of MSWI bottom ash for road construction

Municipal Solid Waste Incinerator (MSWI) Bottom Ash has been used as a substitute for traditional aggregates in road construction; however, this material is little understood. The work presented in this paper pursues the study on the mechanical performance of bottom ash, proven by Le et al. (2017). Using a coupling technique for the first time, the physicochemical aspects and hydromechanical resistance of bottom ash were evaluated and analyzed. Physicochemical tests were first carried out, followed by oedometer tests under a wetting path. This coupled evaluation underlined the role of principal mineralogical components of the studied bottom ash as well as the link with its hydromechanical properties. Tests results showed that the principal constituent of bottom ash is SiO2, which thus affects the characteristics of bottom ash. Given the physical stability of SiO2 which generated a compacted material being less sensitive to water and chemical reactions, and bottom ash’s other characteristics, this demonstrates why bottom ash could be a viable material in roadworks.

Unconfined Compressive Strength of Municipal Solid Waste Incineration Bottom Ashes

The prospects for the beneficial use of municipal solid waste incineration (MSWI) bottom ash mainly lie in the field of road construction, as a substitute for the traditional filling materials. Nevertheless, the unconfined compressive strength (UCS) characteristics of MSWI bottom ashes are still little known, that are particularly essential to the roadway stability. The main purpose of this paper is to study the UCS and its affected factors of MSWI bottom ashes. A large experimental campaign of unconfined compression tests is presented to describe the UCS characteristics of MSWI bottom ashes. The UCS and initial elastic modulus of MSWI bottom ashes increase with the curing age. There are linear relations between the UCS and initial elastic modulus. In addition, the wave velocity of compacted samples is measured, and the relations of the UCS and initial elastic modulus to the ultrasonic wave velocity are presented.

Engineering Properties of Controlled Low-Strength Materials Containing Bottom Ash of Municipal Solid Waste Incinerator and Water Filter Silt

The bottom ash of a municipal solid waste incinerator (MSWI) and water filter silt (WFS) were applied to a controlled low-strength material (CLSM) in the present study. The CLSM of the control group was composed of cement, water, and fine aggregates. WFS was first used as a fill material to replace 10% of the volume of natural fine aggregates in the CLSM. MSWI bottom ash was used to replace 0%, 25%, 50%, 75%, and 100% of the volume of the remaining natural fine aggregates with a water-cement ratio of 1.6. The engineering properties of freshness, hardening, and durability were examined. The results revealed that the slump flows of all of the mixture proportions ranged between 50 and 70 cm. The tube flow ranged between 20 and 30 cm, conforming to ASTM D6103 and construction regulations regarding CLSMs stipulated by the Water Resources Agency of the Ministry of Economic Affairs in Taiwan. Increases in the replacement amount of MSWI bottom ash prolonged the time required to achieve a resistance to penetration of 2.74 MPa. The diameter of the drop test ball was less than 7.6 cm, indicating that the mixture proportions had sufficient bearing capacity for successive construction. At an age of 28 d, the compressive strength did not exceed the 8.4 MPa prescribed in ASTM D4832. The ultrasonic pulse velocity and water absorption exhibited identical growth tendencies. In summary, using MSWI bottom ash to create CLSMs is feasible on the condition that the appropriate amount of WFS should be added.

Characteristics of geotextile clogging in MSW landfills co-disposed with MSWI bottom ash

As a main byproduct of municipal solid waste incineration (MSWI), bottom ash (BA) has become a big challenge in operating MSWI plants. The most common method for BA treatment is co-disposal with MSW in landfills, which may cause clogging in the leachate collection system (LCS). This research investigated the characteristics of geotextile clogging in landfills with BA co-disposal. The co-disposal of BA changed the characteristics of leachate, especially increasing the concentration of Ca2+. During the experiment, 0.14 g CaCO3 was precipitated in the MSW geotextile, while it increased to 0.52 g CaCO3 in the BA co-disposed geotextile. Based on mass balance of calcium and thermogravimetric (TG) analysis, the formation of biofilm was the main contributor to the mass increment, accounting for about 82% and 57% mass increment in the MSW and BA co-disposed geotextile, respectively. Moreover, CO2 in landfill gas played an important role in the clogging process, including CaCO3 precipitation and biofilm formation. The results suggested that the co-disposal of BA with MSW can increase the risk of geotextile clogging in landfills.

Utilization of municipal solid waste incineration bottom ash in autoclaved aerated concrete

The objective of this study was to assess the feasibility of application of municipal solid waste incineration (MSWI) bottom ash as a substitute of quartz sand for the preparation of autoclaved aerated concrete (AAC). Influence of substitution mass ratio and fineness of MSWI bottom ash on the physical-mechanical properties and microstructure of AAC was investigated. Leaching toxicity was also determined to ensure the environmental safety of AAC with MSWI bottom ash. The results demonstrated that the incorporation of MSWI bottom ash can reduce the gas-foaming time, compressive strength, density and thermal conductivity. Moreover, compressive strength and density of AAC increase with the increasing of fineness of MSWI bottom ash. The reactive silica in the bottom ash strongly affected the formation of tobermorite. The needle-like tobermorite in the control sample was transformed into plate-like tobermorite with the increase of bottom ash up to 40% and the crumbled foiled tobermorite and grass-like C-S-H structure formed in ACC with 100% bottom ash. It is also evident that heavy metal concentrations in the leachates of AAC and autoclaved water are far lower than recommended in the GB5085.3-2007.

Effect of casting methods and SCMs on properties of mortars prepared with fine MSW incineration bottom ash

Fine municipal solid waste incineration bottom ash (MSWIBA) contains more contaminants (e.g. metallic aluminium, glass and gypsum) that cannot be effectively removed by current recycling techniques and this thus limits its engineering application in concrete products. Instead of removing these contaminants, the objective of this research was to investigate the influences of using different casting methods and various supplementary cementitious materials (SCMs) on improving the properties of cement mortar prepared with the fine MSWIBA. In this study, the mortar bar specimens incorporating 100% fine MSWIBA as sand were prepared using the conventional wet-mixed method and a dry-mixed method. The SCMs applied were fly ash (FA), ground-granulated blast-furnace slag (GGBS) and waste glass powder (GP), with a replacement ratio of 30 wt% of ordinary cement in the mortar. The curing conditions of the specimens were in the 20 °C water, in the 80 °C water and in an 80 °C NaOH solution for 28 days, respectively. The experimental results showed that the dry-mixed method was an effective method to mitigate the expansion of the mortar prepared with MSWIBA as well as to enhance its mechanical properties after being subjected to the NaOH solution. The order of effectiveness of SCMs on the reduction in the expansion of the mortar prepared with MSWIBA was FA, GGBS and GP. It was indicated that FA was the most effective in mitigating the alkali-silica expansion as well as the alkaline-Al reaction.

Recycling of municipal solid waste incineration by-product for cement composites preparation

In this study, the feasibility of application of municipal solid waste incineration (MSWI) fly ash and bottom ash as a supplementary cementitious material for the preparation of blended cement was evaluated. For this purpose, the cement composites with 10–50 wt% of cement replaced by the equivalent amount of washed MSWI fly ash and bottom ash were prepared, together with water needed for normal consistency, setting time for the blend, strength and hydration characteristics of MSWI ash-cement composites were investigated. The results show that the washed MSWI fly ash and bottom ash have some cementitious activity, but the activity is relatively lower than Portland cement. The behavior of the addition of composites of washed MSWI fly ash and bottom ash were observed to be different with respect to water demand and setting time. Addition of washed fly ash and bottom ash were found to have a deleterious effect on the mechanical strength of cement composites and the maximum replacement by washed MSWI fly ash and bottom ash should be limited to the range of 40 wt% and 20 wt%, respectively to ensure the mechanical properties of composites. Besides, the hydration characteristic of cement blended with washed MSWI fly ash and bottom ash was also measured by using X-ray powder diffraction (XRD) and scanning electron microscope (SEM). Finally, the environmental and economic impact of the as-derived cementitious materials was also evaluated. It was found that the recycling of MSWI fly ash and bottom ash for the cement production can achieve a significant economic and environmental benefit at the same time.

Removal of metallic Al and Al/Zn alloys in MSWI bottom ash by alkaline treatment

In order to reduce the leaching of pollutants and remove the Al and Zn/Al alloy from municipal solid waste incineration bottom ash (MSWIBA), an optimized alkaline pre-treatment procedure was developed in this study. The influences of alkaline conditions on the removal rate of Al and Zn/Al alloy were investigated, including [OH]− concentration, temperature, particle size, liquid/solid ratio and treatment duration. The experimental results showed that the optimized alkaline pre-treatment conditions to efficiently remove the Al and Zn/Al alloy was by using a minimum of 1.0mol/l [OH]−, at 55°C and with a minimal liquid/solid ratio of 5. The removal rate of Al and Zn/Al alloy followed an S-shape curve, in which the slow beginning stage was attributed to the protection of the oxidation layer and the quenched product around the Al and Al/Zn alloy. After 3h of the optimized alkaline pre-treatment, the leaching of Cr, Cu, Pb and Zn of the treated MSWIBA was reduced by more than 90% of that of the original MSWIBA. The alkali-silica reaction test further indicated that the expansion of concrete prepared with the pre-treated MSWIBA was significantly reduced and there was no macro-crack or spalling damage on the surface of the tested specimens.

The effect of the origin of MSWI bottom ash on the H2S elimination from landfill biogas

Municipal Solid Waste Incineration (MSWI) Bottom Ash (BA) is a potential alternative adsorbent for biogas treatment due to its reactivity with hydrogen sulfide (H2S). The quality of BA depends however on the nature of the waste and the process technology of the waste incineration facility. To determine whether the origin of the BA could have an influence on its H2S elimination efficiency, comparative experimental tests were conducted in a landfill site with six bottom ashes from different MSW incinerators. Results showed that one of the BAs (A) had a much higher adsorption capacity than the rest (B–F), with 37g H2S/kg dry BA, compared to 11–16g H2S/kg dry BA for the other bottom ashes. Detailed physico-chemical analyses of the six BA were performed and complemented by principal component analysis to understand the different behaviors. BA iron content and specific surface area provided by the quench product stood out as key factors that promote the elimination of H2S.

Effects of two different accelerated carbonation processes on MSWI bottom ash

Abstract This study investigated two different reaction modes with wet and submerged particles for accelerated carbonation of municipal solid waste incinerator (MSWI) bottom ash generated in the Republic of Korea. Additionally, the effects of the two reaction modes were examined in terms of the mineralogical change and leaching behavior of heavy metals during accelerated carbonation. The reaction modes were controlled with water-to-solid ratios of 0.3 and 10 L/kg for the wet and submerged particles, respectively. The CO 2 concentration was kept constant at 30%. The reaction temperature was held at 25 °C. The new, resulting compounds formed by the carbonation reaction in the wet condition precipitated as a thin coating around the bottom ash particles in what is called the carbonated-layer effect. The submerged condition resulted in the formation of only a negligible carbonated-layer. Moreover, the wet condition, due to the carbonated-layer effect, more effectively stabilized the leaching behavior of heavy metals than that of the submerged condition. However, unlike the submerged condition, this carbonated-layer effect did not result in the maximum value of CO 2 reacted with the bottom ash because it prevented the internal diffusion of CO 2 into the particles. The experimental data were fitted with theoretical functions derived from [1 − (1 − X t ) 1/3 ] n = k t. Here, k is the rate constant (h −1 ) of the carbonation reaction and X t is the carbonated fraction vs. time t .

Recovery of copper from small grain size fractions of municipal solid waste incineration bottom ash by means of density separation

ABSTRACTSmall grain size fractions of municipal solid waste incineration (MSWI) bottom ash (BA) contain elemental and chemically bonded metals in appreciable amounts, especially copper. Investigations with a centrifugal concentrator were carried out using samples, which had been treated with different impact devices. Partly the impacts of single devices were visible in outlines, but mostly the surfaces of the metals were still covered with mineral residues. To generate copper rich fractions, parameters of the separation process should ensure mass yields <2%, best between 0.5 and 1%. The density of the concentrates is then generally >3.2 g/cm3. Best results were achieved with material from a special treatment train which is adapted to grain sizes <2 mm. Reliable copper contents between 20 and 40% (single runs >50%) could be realised. However, considering the required mass yields, referred to this subset only 150–170 g copper would be recovered from 1 Mg MSWI BA. Furthermore, this copper is only in parts present in elemental form. A dependable added value of such treatment step seems to be given only, if that enables a recycling of the mineral aggregates (tailings) in parallel to avoid landfill costs.