MSWI Bottom Ash Research Articles

Analysis of MSWI Bottom Ash Reused as Alternative Material for Cement Production

The bottom ash sample was obtained from one of three stably running municipal solid waste incineration plants in Beijing. The major components of bottom ash, i.e. CaO, SiO2, Al2O3, Fe2O3, were similar to that of ordinary Portoland cement, suggesting that bottom ash had the potential for reuse as cement material. In this paper, the smaple was sieved into 8 fractions according to the particle size distirbution. The content of CaO and chloride in the bottom ash almost decreased with the increase of particle size of bottom ash, contrary to the SiO2 content variation in the bottom ash. The Al2O3 and Fe2O3 content were relatively stable in the bottom ash with different particle size. The chloride, which could cause serious corrosion in the cement kiln, in 8 portion of bottom ash were all higher than its allowable limit in raw material for cement production and clinker quality, the dosage of bottom ash used as alternative material for cement production must be stringently controled, and some proper treatment must be used to reduce the corrion caused by chloride. The heavy metals concentration in the bottom ash were relatively high, but met standard requirements for heavy metals concentration in raw meterial. The content of alkaline oxide (K2O, Na2O) and sulphur, also affected cement production, in bottom ash with differernt particle size were all relative high. The bottom ash had the potential to be recycled as alternative material for cement production, but proper treatment measures, such as by-pass system, must be taken to satisfy the cement production, clinker quality and environmental safety.

Adsorption of Ammonia on Municipal Solid Waste Incinerator Bottom Ash Under the Landfill Circumstance

− The adsorption characteristics of ammonia on MSWI bottom ash were investigated. The effect of the variation of the landfill environmental parameters including pH, anions and organic matter on the adsorption process was discussed. Results showed that the adsorption could be well described by pseudo-second-order kinetics and Langmuir model, with a maximum adsorption capacity of 156.2 mg/g. The optimum adsorption of ammonia was observed when the pH was 6.0. High level of ion and organic matter could restrict the adsorption to a low level. The above results suggested that MSWI bottom ash could affect the migration of ammonia in the landfill, which is related to the variation of the landfill circumstance.

Influence of MSWI bottom ash used as unbound granular material on the corrosion behaviour of reinforced concrete

The reutilisation of MSWI natural weathered bottom ash (WBA) in many applications such as road and underground constructions, embankments or as an aggregate replacement is a common practice in many developed countries. Its potential environmental risk has regularly been evaluated from the point of view of the leaching of heavy metals and metalloids. Nevertheless, the influence over steel rebar when reinforced concrete is exposed to the contact with WBA has been poorly assessed before. In this study, it has been possible to evaluate in terms of days the probability of corrosion in a common case of WBA reutilisation, which is in contact with reinforced concrete formulated with conventional Portland cement. The corrosion monitoring indicates that the probability of corrosion of steel rebar is higher than 90 % with a corrosion rate (CI) estimated to be 11.6 µm year−1. The aggressive conditions imposed by WBA suppose an important withdrawal if the application of reutilisation involves contact with steel rebar.

Effect of the Alkali-Activation on the Mechanical Property of Geopolymer Composite

In this work, pastes were prepared from slag and MSWI bottom ash by geopolymer technique. And its physical property was evaluated with mixing ratio of sodium silicate and potassium silicate. The amounts of leaching products, such as silica, alumina and calcium ions were changed for mixing ratio of raw materials. The compressive strength was increased with the increment of leaching amount of silica, alumina and calcium ions.

Occurrence and Significance of Secondary Iron-rich Products in Landfilled MSWI Bottom Ash

Incineration is one of the most effective techniques for the treatment of both municipal and hazardous wastes. Via this technique, the majority of toxic substances are expected to be stabilized in the durable matrix of the end-ofprocess bottom ash products. These products consist of a variety of glassy/crystalline components including primary Fe-rich phases that may undergo alterations when exposed to natural environment. In the present research, the impact of natural weathering on the behavior of primary Fe-rich phases, their alteration, and the formation of the relevant secondary products in the weathered bottom ash samples of a (mono) landfill site was systematically investigated. Samples of various ages (1-20 yrs) were collected from four locations of the landfill in 2009. Optical microscopy, SEM-EDX, XRD and XRF examinations were applied in order to document the footprints of weathering processes. Using these techniques, we understood that several secondary (newly-formed) products (amorphous or crystalline) have been developed, including goethite (α-FeOOH), lepidocrocite (γ-FeOOH), hematite (Fe2O3), magnetite (Fe3O4), iron oxide (FeO), and Fe-rich Ca-Si and Ca-Al-Si gel phases. They occurred under variable environmental conditions as the weathering products of the primary iron-rich phases. The strong affinity of these secondary phases with heavy metals of environmental significance such as Zn, Cu, Pb, and Ni was also identified. This suggests that the development of secondary Fe-rich products can partially contribute to the reduction of heavy metals release to the surrounding environments. However such phenomena may have inhibitory effect on the utilization of bottom ash as recycled aggregates.

Pilot-scale road subbase made with granular material formulated with MSWI bottom ash and stabilized APC fly ash: Environmental impact assessment

A granular material (GM) to be used as road sub-base was formulated using 80% of weathered bottom ash (WBA) and 20% of mortar. The mortar was prepared separately and consisted in 50% APC and 50% of Portland cement. A pilot-scale study was carried on by constructing three roads in order to environmentally evaluate the performance of GM in a real scenario. By comparing the field results with those of the column experiments, the overestimations observed at laboratory scale can be explained by the potential mechanisms in which water enters into the road body and the pH of the media. An exception was observed in the case of Cu, whose concentration release at the test road was higher. The long-time of exposure at atmospheric conditions might have favoured oxidation of organic matter and therefore the leaching of this element. The results obtained showed that immobilization of all heavy metals and metalloids from APC is achieved by the pozzolanic effect of the cement mortar. This is, to the knowledge of the authors, the only pilot scale study that is considering reutilization of APC as a safe way to disposal.

Pilot scale evaluation of the BABIU process – Upgrading of landfill gas or biogas with the use of MSWI bottom ash

Biogas or landfill gas can be converted to a high-grade gas rich in methane with the use of municipal solid waste incineration bottom ash as a reactant for fixation of CO2 and H2S. In order to verify results previously obtained at a laboratory scale with 65–90kg of bottom ash (BA), several test runs were performed at a pilot scale, using 500–1000kg of bottom ash and up to 9.2Nm3/h real landfill gas from a landfill in the Tuscany region (Italy). The input flow rate was altered. The best process performance was observed at a input flow rate of 3.7Nm3/(htBA). At this flow rate, the removal efficiencies for H2S were approximately 99.5–99%.

Effect of Temperature of Exposure on Properties of Cement Mortar with MSWI Bottom Ash

Effect of Temperature of Exposure on Properties of Cement Mortar with MSWI Bottom Ash

Upgraded MSWI Bottom Ash as Aggregate in Concrete

The objective of this research was to examine the technical feasibility of upgraded bottom ash from municipal solid waste incinerators as fine and coarse aggregate in concrete. The effect of partial replacement of natural sand and gravel by such bottom ash on all relevant properties of concrete (technological, structural as well as durability and reuse as recycled aggregate) has been determined. Based on these findings a guideline has been formulated for the use of upgraded incinerator bottom ash in ready-mixed as well as precast concrete. Although the upgraded bottom ash is of better quality then the original bottom ash, some properties still need special attention (i.e. must meet additional requirements): particle density, metallic aluminium content, loss on ignition, chloride, sulphate and alkali content and, finally, constituents which alter the setting and hardening of the cement. Upgraded incinerator bottom ash can replace up to 20 %V/V sand and/or gravel in reinforced concrete and up to 50 %V/V in plain concrete (non-structural concrete). Application in prestressed concrete is not recommended because of the possibly higher risk of stress corrosion in the prestressed steel.

Reuse of MSWI bottom ash mixed with natural sodium bentonite as landfill cover material

The research described in this study had the aim of evaluating the reuse of incinerator slag, mixed with sodium bentonite, for landfill capping system components. A characterization was performed on pure bottom ash (BA) samples from an incinerator in the north of Italy. The results show that the BA samples had appropriate properties as covers. The compacted dry unit weight of the studied BA (16.2 kN m(-3)) was lower than the average value that characterizes most conventional fill materials and this can be considered advantageous for landfill cover systems, since the fill has to be placed on low bearing capacity ground or where long-term settlement is possible. Moreover, direct shear tests showed a friction angle of 43°, corresponding to excellent mechanical characteristics that can be considered an advantage against failure. The hydraulic conductivity tests indicated a steady-state value of 8 × 10(-10) m s(-1) for a mixture characterized by a bentonite content by weight of 10%, which was a factor 10 better than required by Italian legislation on landfill covers. The results from a swell index test indicated that fine bentonite swelled, even when divalent cations were released by the BA. The leaching behaviour of the mixture did not show any contamination issues and was far better than obtained for the pure BA. Thus, the BA-bentonite mixture qualified as a suitable material for landfill cover in Italy. Moreover, owing to the low release of toxic compounds, the proposed cover system would have no effect on the leachate quality in the landfill.

Aluminium recovery vs. hydrogen production as resource recovery options for fine MSWI bottom ash fraction

Waste incineration bottom ash fine fraction contains a significant amount of aluminium, but previous works have shown that current recovery options based on standard on-step Eddy Current Separation (ECS) have limited efficiency. In this paper, we evaluated the improvement in the efficiency of ECS by using an additional step of crushing and sieving. The efficiency of metallic Al recovery was quantified by measuring hydrogen gas production. The ash samples were also tested for total aluminium content with X-ray fluorescence spectroscopy (XRF). As an alternative to material recovery, we also investigated the possibility to convert residual metallic Al into useful energy, promoting H2 gas production by reacting metallic Al with water at high pH. The results show that the total aluminium concentration in the <4mm bottom ash fraction is on average 8% of the weight of the dry ash, with less than 15% of it being present in the metallic form. Of this latter, only 21% can be potentially recovered with ECS combined with crushing and sieving stages and subsequently recycled. For hydrogen production, using 10MNaOH at 1L/S ratio results in the release of 6–11l of H2 gas for each kilogram of fine dry ash, equivalent to an energy potential of 118kJ.

Dielectric properties of MSWI bottom ash for non-invasive monitoring of moisture

The dielectric procperties of MSWI bottom ash as a function of volumetric water content (VWC) are reported in this paper. The objective was to aid the development of microwave based non-invasive emission monitoring and control system for various bottom ash applications. The dielectric measurements were made, on a 1.5-year-old bottom ash, with an electrical network analyzer in microwave range (300MHz-1.5GHz). The VWC of the samples ranged between 0.05 and 0.40m(3) m(-3). The relationship between the dielectric permittivity and the VWC was modeled with an empirical model and a physically based Birchak model (BM). The results showed that a linear relationship existed between the permittivity and the VWC at higher water contents (>0.25m(3) m(-3)). However, at lower water contents (<0.25m(3) m(-3)), the relationship between the permittivity and the WVC was affected by the composition of the bottom ash. The permittivity measurement, with the current method, was not affected by high salt concentrations (10 and 20 dS/m). The empirical model, as compared to BM, provided the best fit between the actual and the predicted water content. The root mean square error (RMSE) values were 0.008-0.010 and 0.06-0.09m(3) m(-3) for the empirical and the Birchak model, respectively.

Energy and Environment: Challenges and Achievements in Rapid Urbanization

Energy and Environment: Challenges and Achievements in Rapid Urbanization

Formation of Secondary Products under Natural Weathering and their Affinity with Heavy Metals in Landfilled MSWI Bottom Ash

Formation of Secondary Products under Natural Weathering and their Affinity with Heavy Metals in Landfilled MSWI Bottom Ash

Effect of short-term natural weathering on MSWI and wood waste bottom ash leaching behaviour

Short term natural weathering was applied on municipal solid waste (MSW) and wood waste incinerator bottom ash (BA). The materials were analysed at different steps of treatment and characterized for chemical and mineralogical composition. Both short and long term leaching behaviour of main elements and heavy metals were investigated as well. Lead, zinc and copper were the main heavy metals to be released. After 12 weeks of treatment the concentration of leached zinc decreased. Lead concentration was not found to be influenced by pH and decreased only for the biomass samples. Weathering did not have beneficial effects on copper leaching, which was well described by complexation processes with DOC. The findings from the experimental campaign indicated that weathering reactions improved the mineral stability of the analysed materials but, in contrast with previous works, the treatment was not sufficient to guarantee pH stability and to comply with leaching law limits.

Procedural uncertainties of Proctor compaction tests applied on MSWI bottom ash

MSWI bottom ash is a well-graded highly compactable material that can be used as a road material in unbound pavements. Achieving the compactness assumed in the design of the pavement is of primary concern to ensure long term structural stability. Regulations on road construction in a number of EU countries rely on standard tests originally developed for natural aggregates, which may not be appropriate to accurately assess MSWI bottom ash. This study is intended to assist in consistently assessing MSWI bottom ash compaction by means of the Proctor method. This test is routinely applied to address unbound road materials and suggests two methods. Compaction parameters show a marked procedural dependency due to the particle morphology and weak particle strength of ash. Re-compacting a single batch sample to determine Proctor curves is a common practise that turns out to overvalue optimum moisture contents and maximum dry densities. This could result in wet-side compactions not meeting stiffness requirements. Inaccurate moisture content measurements during testing may also induce erroneous determinations of compaction parameters. The role of a number of physical properties of MSWI bottom ash in compaction is also investigated.

MSWI bottom ash used as basement at two pilot-scale roads: Comparison of leachate chemistry and reactive transport modeling

The recycling of municipal solid waste incineration bottom ash as aggregates for road basement requires assessing the long-term evolution of leachate chemistry. The Dåva (Sweden) and Hérouville (France) pilot-scale roads were monitored during 6 and 10 years, respectively. Calculated saturation indices were combined to batch test modeling to set a simplified geochemical model of the bottom ash materials. A common reactive transport model was then applied to both sites. At Hérouville, pH and the concentration of most elements quickly drop during the first two years to reach a set of minimum values over 10 years. The decrease is less pronounced at Dåva. The evolutions of pH and major element concentrations are fairly well related to the following pH-buffering sequence: portlandite, C–S–H phases or pseudo-wollastonite and, finally, calcite in equilibrium with atmospheric CO 2. Al(OH) 3, barite, ettringite and monohydrocalcite may also control leachate chemistry. Cu release is correctly modeled by DOM complexation and tenorite equilibrium. Temperature has no significant effect on the modeling of leachate chemistry in the range 5–30 °C, except at high pH. Effects at road edges and roadside slopes are important for the release of the less reactive elements and, possibly, for carbonation processes.

Manufacture of artificial aggregate using MSWI bottom ash

This paper reports the results of an investigation on material recovery by stabilization/solidification of bottom ash coming from a municipal solid waste incineration plant. Stabilization/solidification was carried out to produce artificial aggregate in a rotary plate granulator by adding hydraulic binders based on cement, lime and coal fly ash. Different mixes were tested in which the bottom ash content ranged between 60% and 90%. To avoid undesirable swelling in hardened products, the ash was previously milled and then granulated at room temperature. The granules were tested to assess their suitability to be used as artificial aggregate through the measurement of the following properties: density, water absorption capacity, compressive strength and heavy metals release upon leaching. It was demonstrated that the granules can be classified as lightweight aggregate with mechanical strength strongly dependent on the type of binder. Concrete mixes were prepared with the granulated artificial aggregate and tested for in-service performance, proving to be suitable for the manufacture of standard concrete blocks in all the cases investigated.

Understanding the chemical and mineralogical properties of the inorganic portion of MSWI bottom ash

This paper investigates the changes of mineralogical composition of bottom ash in the environment. The chemical and mineralogical bulk composition was determined by X-ray fluorescence (XRF) and X-ray powder diffraction (XRPD) Rietveld method. Single bottom ash particles were investigated by optical microscopy, scanning electron microscopy with quantitative energy-dispersive X-ray microanalysis (SEM/EDX) and electron probe micro analysis (EPMA). SEM/EDX and EPMA are valuable complement to bulk analysis and provide means for rapid and sensitive multi-elemental analysis of ash particles. The fresh bottom ash consists of amorphous (>30 wt.%) and major crystalline phases (>1 wt.%) such as silicates, oxides and carbonates. The mineral assemblage of the fresh bottom ash is clearly unstable and an aging process occurs by reaction towards an equilibrium mineral phase composition in the environmental conditions. The significant decrease of anhydrite and amorphous contents was observed in the aged bottom ash, leading to the formation of ettringite, hydrocalumite and rosenhahnite under atmospheric conditions. In the water-treated sample, the calcite contents increased significantly, but ettringite was altered by the dissolution and precipitation processes in part, to produce gypsum, while the remaining part reacted with chloride to form hydrocalumite. Gypsum and other Ca based minerals may take up substantial amounts of heavy metals and subsequently control leaching behaviour of bottom ash.

Effect of carbonation on the leaching of organic carbon and of copper from MSWI bottom ash

In Flanders, the northern part of Belgium, about 31% of the produced amount of MSWI bottom ash is recycled as secondary raw material. In view of recycling a higher percentage of bottom ash, a particular bottom ash fraction ( Ø 0.1–2 mm) was studied. As the leaching of this bottom ash fraction exceeds some of the Flemish limit values for heavy metals (with Cu being the most critical), treatment is required. Natural weathering and accelerated carbonation resulted in a significant decrease of the Cu leaching. Natural weathering during 3 months caused a decrease of Cu leaching to <50% of its original value, whereas accelerated carbonation resulted in an even larger decrease (to ca. 13% of its initial value) after 2 weeks, with the main decrease taking place within the first 48 h. Total organic carbon decreased to ca. 70% and 55% of the initial concentration in the solid phase, and to 40% and 25% in the leachate after natural weathering and after accelerated carbonation, respectively. In the solid material the decrease of the Hy fraction was the largest, the FA concentration remained essentially constant. The decrease of FA in the leachate can be attributed partly to an enhanced adsorption of FA to Fe/Al (hydr)oxides, due to the combined effect of a pH decrease and the neoformation of Al (hydr)oxides (both due to carbonation). A detailed study of adsorption of FA to Fe/Al (hydr)oxides showed that significant adsorption of FA occurs, that it increases with decreasing pH and started above pH 12 for Fe (hydr)oxides and around 10 for Al (hydr)oxides. Depending whether FA or Hy are considered the controlling factor in enhanced Cu leaching, the decreasing FA or Hy in the leachate explains the decrease in the Cu leaching during carbonation.