Recovery of Zn and Cu from municipal solid waste incineration fly ash by integrating ammonium leaching and ammonia removal.

This study introduces an environmentally friendly process for recovering zinc (Zn) and copper (Cu) from municipal solid waste incineration (MSWI) fly ash using ammonium chloride leaching and ammonia removal. The leaching rates for Zn and Cu were 54.39% and 86.23%, respectively, with total recovery rates reaching 52.21% and 85.28%, respectively. The recovered precipitate demonstrated significant Zn (33.62%) and Cu (14.19%) contents, making it ideal for metal smelting. The ammonium leaching process also showcased effective reduction and dechlorination effects on the fly ash. The treated fly ash had a reduced mass of only 30.63% of the original, and chlorine content decreased from 26.23% to 0.84%. The results of this study support the sustainable utilization of MSWI fly ash by facilitating valuable resource recovery and promoting its conversion into construction materials.

A novel and sustainable technique to immobilize lead and zinc in MSW incineration fly ash by using pozzolanic bottom ash.

Fly ash (FA) generated from Municipal Solid Waste (MSW) incineration contains high leaching potential of toxic metals. Calcium silicate hydrate (C-S-H) is the main hydration product of cement and can immobilize the leaching of toxic metals, formed by the reaction of Ca with pozzolanic Si in a highly alkaline environment. Toxic metals can be immobilized by the addition of pozzolan to FA residues (in lieu of cement), which is a source of Ca and provides an alkaline condition. The current study proposed a new approach of reusing the fine-fraction of MSW incineration bottom ash (BA), which contains amorphous silica, known as pozzolan for immobilization of lead (Pb) and zinc (Zn) in FA. The dissolved amorphous silica and alumina emerged from the BA, with available Ca ions and in an extremely alkaline condition owing by FA, stimulate the pozzolanic reaction, resulting the formation of cementitious compounds of C-S-H gel and calcium aluminate hydrates (C-A-H) that can immobilize the heavy metals leaching from FA. The existence of calcium hydroxide promotes the carbonation process, reducing pH, and consequently immobilizing heavy metals. The method involves the simple mixing of BA and FA with water. The mixture was settled for 1, 4, 16, and 30 days at room temperature and annealed (120 °C) conditions. The leaching concentrations of Pb and Zn significantly reduced in the stabilized FA samples followed by standard Japanese leaching test (JLT- 46). Pb stabilization efficiency was reached >99.9% after 16-days of settling periods with 10% dosage of BA at room temperature. The added BA to FA residues reacted with Ca(OH)2 and CaClOH produced the C-S-H gel. pH, XRD, and SEM-EDX analyses evaluated the carbonation and pozzolanic reactions that promoted the immobilization of Pb and Zn. Immobilization of heavy metals by using fine-fraction of BA seems to be very effective and technically feasible. The technology can save original material, produce inert material and avoids landfilling of incineration residues. More advanced and detailed experiments have been designed to promote the optimization of the proposed technology for application in industries.

Removal of harmful components from MSWI fly ash as a pretreatment approach to enhance waste recycling.

Municipal solid waste incineration (MSWI) fly ash contains many harmful components that may limit its potential for recycling. An effective pretreatment is therefore required before any recycling can be implemented. In this study, the effects of four pretreatment methods (water washing, CO2-aided washing, CO32--aided washing, and CO2 and CO32--aided washing) on the extraction behavior of chloride, sulfate, and heavy metals were evaluated. Water washing was found to be effective for the extraction of all easily and moderately soluble Cl-bearing salts, achieving Cl extraction ratios of 88%, 90%, and 96% for ash from Chongqing (CQ), Qingdao (QD), and Tianjin (TJ), respectively. Injection of CO2 during washing facilitated decomposition of the hardly soluble Cl-bearing salts, increasing the Cl extraction efficiency by 6% for CQ ash and 9% for QD ash. However, for the TJ ash that contained few insoluble Cl-bearing minerals, CO2 injection decreased the Cl extraction rate. The addition of CO32- had a negative influence on Cl extraction for all ashes, but it slightly promoted sulfate extraction. Despite the high Cl removal rate, only 23-37% of the sulfate and 0.1-12% of heavy metals were removed. Overall, water-based pretreatment, especially CO2-aided washing, significantly altered the physical, chemical, and mineralogical characteristics of the fly ash, making it more suitable for recycling. Consequently, the blending ratio of the fly ash for cement clinker manufacture increased from 0.2 to 0.3% in the raw ash to 3.5-5.5% in the treated ash, enabling the extensive use of ash materials.

Enhanced Pb and Zn stabilization in municipal solid waste incineration fly ash using waste fishbone hydroxyapatite.

The present research focused on evaluating the role of waste fishbone hydroxyapatite (FB-HAP) in stabilizing heavy metals, particularly Pb and Zn, in incineration fly ash (IFA). Bones were collected from various fish species and processed for batch experiments. A commercial apatite product (Apatite II™) was also obtained for a comparative analysis. The experiments were performed at fishbone/fly ash ratios of 0.0 (control group) and 1:10 (by weight), settling times of 6, 12, 24, and 672 h (28 days), and W/S ratios of 1.0 and 1.5 mL/g. The highest Pb removal efficiency reached 86.39% at 28 days settling periods, when the FB-HAP dose was only 10% at W/S 1.5 mL/g. FB-HAP was found noticeably more effective (approximately 1.5 to 2 times) than Apatite II™, particularly at shorter settling periods. Stabilization of Zn was efficient at longer settling period (28 days) using FB-HAP. The highest stabilization rate of Zn was 62.67% at W/S 1.0 mL/g. The results indicated that settling time and W/S ratio were the most important factors to enhance the stabilization of Pb and Zn in IFA. Utilization of waste fishbone is expected to be a low-cost and eco-friendly technology.

Comparative study on inorganic Cl removal of municipal solid waste fly ash using different types and concentrations of organic acids.

In this study, different organic acids-such as citric, acetic, lactic, propionic, and butyric acid-were evaluated to ascertain the optimum leaching solvent for dechlorinating fly ash. Results suggest that the acid type, concentration, and interactions between both parameters contributed significantly to the variations in the efficiency of fly ash dechlorination. Simple main-effect analysis suggested that a higher acid concentration yields better dechlorination efficiency. However, improvements in dechlorination efficiency did not necessarily yield a low chlorine content leaching residue because in a specific acid concentration region, the increased acid concentration may also accelerate the mass reduction rate of the leaching residue. Experimental results also demonstrate that citric and acetic acid yield the highest dechlorination efficiency, followed by propionic and butyric acid. The least dechlorination efficiency of lactic acid could be attributed to the formation of precipitate (i.e. calcium lactate) which might cover the chlorides and reduce the contact area of intimal chlorides with the leaching solvent. Therefore, a specific concentration of organic matter fermentation broth rich in citric and acetic radicals may present itself as an ideal water substitute for fly ash dechlorination.

Simulating the impact of heavy rain on leaching behavior of municipal solid waste incineration bottom ash (MSWI BA) in semi-aerobic landfill.

In Japan, approximately 64% of municipal solid waste incineration bottom ash (MSWI BA) is landfilled. Because landfills in Japan are operated without capping, the landfill body is directly exposed to climatic events. Increased frequency of heavy rain is predicted to affect the chemical stabilization of bottom ash (BA) landfill, as rainwater seeps into and interacts with landfill components. This study examined the effect of normal rainfall (15 mm/h) and heavy rainfall (25, 50, and 100 mm/h) events on the leaching behavior of ions (Cl-, Na+, K+, and Ca2+) and total organic carbon (TOC) in BA (<10 mm particle size) using a percolation column test. The results showed the decreased leaching of leachate components after heavy rainfall and increased leaching after normal rainfall. In addition, the pH fluctuated around 11-12 after heavy rainfall but decreased to 7-9 after normal rainfall. The carbonation of the leachate and BA layers appears to be the main factor in lowering the pH value. Changes in the TOC and ion concentrations can be explained by dissolution, dilution, and the contact time of water molecules and BA particles. The data showed that the cumulative TOC and ion release rates were not affected by heavy rain intensities. The release rate of leachate components during normal rainfall was higher than that in heavy rainfall in all the scenarios. Significant correlations were found between the leachate components (TOC, Cl-, Na+, K+, and Ca2+ concentrations) and rainfall variation.

Dechlorination of fly ash by hydrolysate of municipal solid waste leachate.

Municipal solid waste incineration fly ash (referred to as the fly ash) presents an important environmental problem in China today, but strategies for its treatment have yet to be widely studied and implemented. The currently available methods for the dechlorination of fly ash are not sufficient, given the amounts of fly ash produced each year. To increase the reuse fraction of fly ash as raw material for cement production, we propose an improved dechlorination method. Specifically, fly ash was leached with the hydrolysate of municipal solid waste leachate (HMSWL) to remove the water-insoluble chlorine. Three-step HMSWL leaching removed 94.3% of the total chlorine in fly ash, much more than the 82.7% that was removed through three-step ultrapure water (UW) leaching. X-ray diffraction indicated that three-step UW leaching could remove Cl mainly in the forms of KCl, NaCl, CaClOH and AlOCl, whereas three-step HMSWL leaching could further remove more water-insoluble Cl in the forms of AlOCl. In addition, the experimental results further suggested that the low pH of HMSWL (4.9) contributed little to the water-insoluble Cl removal, whereas the displacement of organic acid radicals (especially by the butyrate radical) was the major cause of water-insoluble Cl removal. Therefore, HMSWL rich in butyrate radical could be an ideal water substitute for fly ash dechlorination.

Evaluation of chemical speciation and environmental risk levels of heavy metals during varied acid corrosion conditions for raw and solidified/stabilized MSWI fly ash.

In this work, the leaching pattern, chemical speciation, and environmental risks of various heavy metals (Pb, Zn, Cu, Cd, Cr, and Ni) were investigated synchronously under different acid corrosion conditions through end-point pH leaching experiments. The heavy metals were present in raw, stabilized (phosphoric acid; chelating agent), and solidified (Portland cement) municipal solid waste incineration (MSWI) fly ash. The results showed that the stabilization and solidification pre-treatment could effectively decrease the leaching of most heavy metals. However, phosphoric acid stabilization and Portland cement solidification increased the solubility of Ni and Pb/Cu/Cd under low end-point pH conditions, while that of Cr and Pb increased under high end-point pH conditions. Overall, the leaching pattern of heavy metals was not affected by the addition of binders/additives. The results from speciation analysis showed that the bioavailable fractions (exchangeable and carbonate-bound) were leached out from initial raw or solidified/stabilized fly ash after distilled water leaching. However, with the decrease in end-point pH levels, the bioavailable fractions increased again due to the increase in acid corrosion on metal-bearing mineral matrixes. The risk assessment results indicated that, after exposing the raw or solidified/stabilized fly ash to highly acidic conditions, not only the high-content Pb/Zn/Cu, but also some low-content Cd posed potential risks to the environment. During the leaching process, under extremely acidic conditions, the increased environmental risks posed by Pb/Zn/Cu/Cd in residual fly ash solids were greatly ascribed to the increase in bioavailable fractions, which might result in the re-leaching of some heavy metals to the environment.

Impact of secondary generated minerals on toxic element immobilization for air pollution control fly ash of a municipal solid waste incinerator.

Impacts of secondary generated minerals on mineralogical and physical immobilization of toxic elements were investigated for chelate-treated air pollution control (APC) fly ash of a municipal solid waste incinerator. Scanning electron microscope (SEM) observation showed that ettringite was generated after the moistening treatment with/without chelate. Although ettringite can incorporate toxic elements into its structure, elemental analysis by energy dispersive X-ray could not find concentrated points of toxic elements in ettringite structure. This implies that mineralogical immobilization of toxic element by the encapsulation to ettringite structure seems to be limited. Physical immobilization was also investigated by SEM observation of the same APC fly ash particles before and after the moistening treatment. The transfer of soluble elements was inhibited only when insoluble minerals such as gypsum were generated and covered the surface of fly ash particles. Neoformed insoluble minerals prevented soluble elements from leaching and transfer. However, such physical immobilization seems to be limited because insoluble mineral formation with surface coverage was monitored only one time of more than 20 observations. Although uncertainty owing to limited samples with limited observations should be considered, this study concludes that mineralogical and physical immobilization of toxic elements by secondary minerals is limited although secondary minerals are always generated on the surface of APC fly ash particles during chelate treatment.

Influence of operations on leachate characteristics in the Aerobic-Anaerobic Landfill Method.

Landfill aeration is an effective technique for the controlled and sustainable conversion of conventional anaerobic landfills into a biologically stabilized state associated with a significantly lowered or the near elimination of the landfill gas emission potential. For in-situ leachate treatment recycling back the generated leachate in the bioreactor is also a promising technique for reducing pollutants and cost of ex-situ treatment as well. This research has been conducted to ascertain the in-situ treatment of leachate in Aerobic Anaerobic Landfill Method (AALM) compared with aerobic landfill and evaluated the impacts of various leachate recirculation regimes on MSW degradation and to provide data for successful operation in landfill sites. The experiment was conducted using six Plexiglass® landfill simulation reactors with a height of 100 cm and a diameter of 15 cm. Air was injected at the rates of 1.6 l/kg DM/h (Low aeration rate) for reactors R-LA, R-LAA (recirculatory) and LAA (non-recirculatory) and 4.8 l/kg DM/h (High aeration rate) in R-HA, R-HAA (recirculatory), and HAA (non-recirculatory) until day 242. It has been evaluated that R-HAA at high aeration rate achieved higher leachate quantity reduction (36.9%) than low aeration rate reactor R-LAA (19.6%) and AALM provides a better solution to control the temperature within the landfill body. The final NH4+-N concentration in R-HA (214.5 mg/l) was eight times lower than in the R-LA (1741.0 mg/l) reactor, and R-HAA (842.5 mg/l) was about three times lower than R-LAA (2315.4 mg/l) reactor on day 242. The change in leachate recirculation amount at varying moisture content positively affected the stabilization process and in-situ leachate treatment efficiency. The combination of both technologies (intermittent aeration and leachate recirculation) is a feasible way for in-situ leachate treatment, decrease the cost of further ex-situ leachate treatment as well as a viable and cost-saving alternative to continuous aeration.

Hydrogen gas generation from metal aluminum-water interaction in municipal solid waste incineration (MSWI) bottom ash.

In the present research, municipal solid waste incineration (MSWI) bottom ash (BA) residues from three incinerators (N, K, and R) in Japan were collected for hydrogen gas generation purpose. The samples were split into four particle size fractions: (1) d≤0.6, (2) 0.6≤d≤1.0, (3) 1.0≤d≤2.0, and (4) 2.0≤d≤4.75mm for the characterization of metal aluminum, the relationship between the present metal aluminum and hydrogen gas production, and the influence of external metal aluminum on the enhancement of hydrogen gas. The batch experiments were performed for each BA fraction under agitated (200rpm) and non-agitated conditions at 40°C for 20days. The highest amount of hydrogen gas (cumulative) was collected under agitation condition that was 39.4, 10.0, and 8.4 L/kg of dry ash for N2, R2, and K2 (all fraction 2), respectively. To take the benefit of the BA high alkalinity (with initial pH over 12), 0.1 and 1g of household aluminum foil were added to the fractions 2 and 3. A Significantly larger amount of hydrogen gas was collected from each test. For 0.1g of aluminum foil, the cumulative amount of gas was in the range of 62 to 78 L/kg of dry ash and for 1g of aluminum foil the cumulative amount of hydrogen was in the range of 119-126 L/kg of dry ash. This indicated that the hydrogen gas yield was significantly a function of supplementary aluminum and the intrinsic alkaline environment of the BA residues rather than ash source or particle size.

Separation and characterization of magnetic fractions from waste-to-energy bottom ash with an emphasis on the leachability of heavy metals.

Magnetic fractions were extracted from pulverized waste-to-energy (WTE) bottom ashes using a combined wet-dry extraction method. The resulting magnetic and non-magnetic fractions were subjected to compositional, mineralogical, and redox state analyses by X-ray diffraction (XRD), X-ray fluorescence, and X-ray photoelectron spectroscopy (XPS), respectively. The distribution and leaching toxicity of heavy metals were assessed to evaluate potential effects on the environment. Compositional analyses revealed that Fe accounted for 35% of the magnetic fraction of pulverized ashes, which was approximately seven times that of the raw ash. In addition to Fe, elemental Ni, Mn, and Cr were also significantly enriched in the magnetic fractions. The mineralogical analysis determined that Fe was primarily present as hematite and magnetite, and metallic iron was also identified in the magnetic fraction samples. The XPS analysis further proved the existence of zero-valence Fe. However, a significant amount of Fe remained in the non-magnetic fractions, which could partially be ascribed to the intergrowth structure of the various minerals. The elevated concentrations of toxicity characteristic leaching procedure (TCLP)-extracted Mn, Ni, Cr, Cu, Pb, and Zn were primarily ascribed to the lower buffering capability of the magnetic fractions, with the enrichment of Mn, Ni, and Cr in the magnetic fractions also contributing to this elevation.

Influence of ignition process on mineral phase transformation in municipal solid waste incineration (MSWI) fly ash: Implications for estimating loss-on-ignition (LOI).

This research focused on the mineral phase transformation under varied ignition conditions with the objective of estimating loss-on-ignition (LOI) parameter in municipal solid waste incineration (MSWI) fly ash residues. LOI is commonly used to measure the volatile species, unburned carbon and moisture in the solid materials. There are criteria for LOI measurement in some research fields, while there is no standard protocol for LOI measurement in MSWI fly ash. Using thermogravimetry technique, the ignition condition candidates were proposed at 440/700/900°C for 1 and 2h. Based on X-ray diffractometry results, obvious mineral phase transformation occurred as a function of ignition temperature variation rather than ignition time. Until 440°C, only some minor phases disappeared comparing with the original state. Significant mineral phase transformations of major phases (Ca- and Cl-based minerals) occurred between 440 and 700°C. The mineral phase transformation and the occurrence of newly-formed phases were determined not only by the ignition condition but also by the content of the co-existing components. Mineral phase components rarely changed when ignition temperature rose from 700 to 900°C. Consequently, in order to prevent critical damages to the original mineralogical composition of fly ash, the lowest ignition temperature (440°C) for 2h was suggested as an ideal measurement condition of LOI in MSWI fly ash.

Application of portable gas detector in point and scanning method to estimate spatial distribution of methane emission in landfill.

Methane from landfills contributes to global warming and can pose an explosion hazard. To minimize these effects emissions must be monitored. This study proposed application of portable gas detector (PGD) in point and scanning measurements to estimate spatial distribution of methane emissions in landfills. The aims of this study were to discover the advantages and disadvantages of point and scanning methods in measuring methane concentrations, discover spatial distribution of methane emissions, cognize the correlation between ambient methane concentration and methane flux, and estimate methane flux and emissions in landfills. This study was carried out in Tamangapa landfill, Makassar city-Indonesia. Measurement areas were divided into basic and expanded area. In the point method, PGD was held one meter above the landfill surface, whereas scanning method used a PGD with a data logger mounted on a wire drawn between two poles. Point method was efficient in time, only needed one person and eight minutes in measuring 400m2 areas, whereas scanning method could capture a lot of hot spots location and needed 20min. The results from basic area showed that ambient methane concentration and flux had a significant (p<0.01) positive correlation with R2=0.7109 and y=0.1544 x. This correlation equation was used to describe spatial distribution of methane emissions in the expanded area by using Kriging method. The average of estimated flux from scanning method was 71.2gm-2d-1 higher than 38.3gm-2d-1 from point method. Further, scanning method could capture the lower and higher value, which could be useful to evaluate and estimate the possible effects of the uncontrolled emissions in landfill.

Stimulation of waste decomposition in an old landfill by air injection.

Three pilot-scale lysimeters were operated for 4.5years to quantify the change in the carbon and nitrogen pool in an old landfill under various air injection conditions. The results indicate that air injection at the bottom layer facilitated homogeneous distribution of oxygen in the waste matrix. Substantial total organic carbon (TOC) decomposition and methane generation reduction were achieved. Considerable amount of nitrogen was removed, suggesting that in situ nitrogen removal via the effective simultaneous nitrification and denitrification mechanism is viable. Moreover, material mass change measurements revealed a slight mass reduction of aged MSW (by approximately 4.0%) after 4.5years of aeration. Additionally, experiments revealed that intensive aeration during the final stage of the experiment did not further stimulate the degradation of the aged MSW. Therefore, elimination of the labile fraction of aged MSW should be considered the objective of in situ aeration.

Site specific diel methane emission mechanisms in landfills: A field validated process based on vegetation and climate factors.

Diel methane emission fluxes from a landfill that was covered by vegetation were investigated to reveal the methane emission mechanisms based on the interaction of vegetation characteristics and climate factors. The methane emissions showed large variation between daytime and nighttime, and the trend of methane emissions exhibited clear bimodal patterns from both Setaria viridis- and Neyraudia reynaudiana-covered areas. Plants play an important role in methane transportation as well as methane oxidation. The notable decrease in methane emissions after plants were cut suggests that methane transportation via plants is the primary way of methane emissions in the vegetated areas of landfill. Within plants, the methane emission fluxes were enhanced due to a convection mechanism. Given that the methane emission flux is highly correlated with the solar radiation during daytime, the convection mechanism could be attributed to the increase in solar radiation. Whereas the methane emission flux is affected by a combined impact of the wind speed and pedosphere characteristics during nighttime. An improved understanding of the methane emission mechanisms in vegetated landfills is expected to develop a reliable model for landfill methane emissions and to attenuate greenhouse gas emissions from landfills.

Modeling the formation of the quench product in municipal solid waste incineration (MSWI) bottom ash.

This study investigated changes in bottom ash morphology and mineralogy under lab-scale quenching conditions. The main purpose was to clarify the mechanisms behind the formation of the quench product/layer around bottom ash particles. In the experiments, the unquenched bottom ashes were heated to 300°C for 1h, and were quenched by warm water (65°C) with different simulated conditions. After having filtered and dried, the ashes were analyzed by a combination of methodologies namely, particle size distribution analysis, intact particle and thin-section observation, X-ray diffractometry, and scanning electron microscope with energy dispersive X-ray spectroscopy. The results indicated that after quenching, the morphology and mineralogy of the bottom ash changed significantly. The freshly quenched bottom ash was dominated by a quench product that was characterized by amorphous and microcrystalline calcium-silicate-hydrate (CSH) phases. This product also enclosed tiny minerals, glasses, ceramics, metals, and organic materials. The dominant mineral phases produced by quenching process and detected by XRD were calcite, Friedel's salt, hydrocalumite and portlandite. The formation of quench product was controlled by the fine fraction of the bottom ash (particle size <0.425mm). From the observations, a conceptual model of the ash-water reactions and formation of the quench product in the bottom ash was proposed.

Nitrous oxide production during nitrification from organic solid waste under temperature and oxygen conditions.

Landfill aeration can accelerate the biological degradation of organic waste and reduce methane production; however, it induces nitrous oxide (N2O), a potent greenhouse gas. Nitrification is one of the pathways of N2O generation as a by-product during aerobic condition. This study was initiated to demonstrate the features of N2O production rate from organic solid waste during nitrification under three different temperatures (20°C, 30°C, and 40°C) and three oxygen concentrations (5%, 10%, and 20%) with high moisture content and high substrates' concentration. The experiment was carried out by batch experiment using Erlenmeyer flasks incubated in a shaking water bath for 72 h. A duplicate experiment was carried out in parallel, with addition of 100 Pa of acetylene as a nitrification inhibitor, to investigate nitrifiers' contribution to N2O production. The production rate of N2O ranged between 0.40 × 10(-3) and 1.14 × 10(-3) mg N/g-DM/h under the experimental conditions of this study. The rate of N2O production at 40°C was higher than at 20°C and 30°C. Nitrification was found to be the dominant pathway of N2O production. It was evaluated that optimization of O2 content is one of the crucial parameters in N2O production that may help to minimize greenhouse gas emissions and N turnover during aeration.

The impact of thermal treatment and cooling methods on municipal solid waste incineration bottom ash with an emphasis on Cl.

Municipal solid waste incineration (MSWI) bottom-ash products possess qualifications to be utilized in cement production. However, the instant use of bottom ash is inhibited by a number of factors, among which the chlorine (Cl) content is always strictly restricted. In this paper, the unquenched MSWI bottom ash was used as the experimental substance, and the influences of thermal treatment and cooling methods on the content and existence of Cl in the ash residues were investigated. The characterization of the MSWI bottom-ash samples examined by utilizing X-ray diffraction, optical microscopy, scanning electron microscopy/energy dispersive X-ray spectroscopy. The experimental results show that as a function of thermal treatment, the reduction rate of Cl is slight below 15.0%, which is relatively low compared with water washing process. Different cooling methods had impacts on the existing forms of Cl. It was understood that most of Cl existed in the glass phase if the bottom ash was air cooled. Contrarily in case of water-quenched bottom ash, Cl could also be accumulated in the newly-formed quench products as chloride salts or hydrate substances such as Friedel's salt.

Impact of intermittent aerations on leachate quality and greenhouse gas reduction in the aerobic-anaerobic landfill method.

The aerobic-anaerobic landfill method (AALM) is a novel approach in solid waste management that could shorten the landfill post-closure period and minimize the environmental loads. In this study, the aerobic-anaerobic landfill method was evaluated by using intermittent aeration. In addition, the nitrification-denitrification process was assessed as a means of reducing the emission of greenhouse gases (GHGs) and improving the leachate quality during the degradation of the organic solid waste. The leachate quality and the gas composition in each of the reactors were measured during the experimental period (408days). The aeration process entailed the injection of air into plexiglass cylinders (200cm height×10 cm diameter), filled with fresh organic solid waste collected from a composting plant. Different aeration routines were applied, namely, continuous aeration (aerobic reactor A), aeration for three days/week (aerobic-anaerobic reactor B), aeration for 6h/day (aerobic-anaerobic reactor C), and no aeration (non-aerated reactor D). It was found that aerobic reactor A produced the best results in terms of reduction of GHGs and improvement of the leachate quality. The aerobic-anaerobic reactor C was found to be more effective than reactor B in respect of both the emission of GHGs and the leachate quality; moreover, compared with aerobic reactor A, energy costs were reduced by operating this reactor. The transition period phenomenon was investigated during an intensive seven-day experiment conducted on the discharged leachate obtained from aerobic-anaerobic reactors B and C. The experiment concerned the differences in the composition of the gas during the aeration and the non-aeration periods. It was found that the transition period between the aeration and non-aeration cycles, which followed the simultaneous nitrification-denitrification had a considerable effect on the leachate quality of both the reactors. The results indicated that AALM has the potential to reduce leachate pollutants and the emission of GHGs. Furthermore, the occurrence of simultaneous nitrification-denitrification presents the prospect that intermittent aeration could reduce landfill aftercare and energy costs.