Leaching characteristics of calcium-based compounds in MSWI Residues: From the viewpoint of clogging risk

Acid controlled washing of municipal solid waste incineration fly ash: Extraction of calcium inhibiting heavy metals and reaction kinetics

Washing method has attracted much attention in the research of municipal solid waste incineration (MSWI) fly ash treatment and resource utilization. However, the controlled leaching of heavy metals and the extraction of recyclable calcium in the washing process are still blank. Acid controlled washing was conducted with different acids, concentrations, times and temperatures to extract calcium while inhibiting heavy metals. The mechanism was investigated by reaction kinetics calculation and washed fly ash characterization. The high Ca concentration of 37,420 mg/L while the low heavy metal concentrations of around or <1 mg/L were achieved at 25 °C for 60 min under a liquid-solid ratio (L/S) of 3/1 in 1.5 M HCl. The reaction kinetics of acid controlled washing conformed the layer diffusion control. The results of X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectrum (EDS) analysis indicated that the rate-limiting step was the diffusion of ions through the product layer. Simultaneously, the washing solution enriched in Ca, Na and K and the washed fly ash, which met the standard requirements (HJ 1134-2020) for leach toxicity, both had the potential for further resource utilization.

Full life cycle and sustainability transitions of phthalates in landfill: A review

Phthalates (PAEs) are added to various products as a plasticizer. As these products age and are disposed of, plastic waste containing PAEs enters the landfill. The landfill environment is complicated and can be regarded as a "black box". Also, PAEs do not bind with the polymer matrix. Therefore, when a series of physical chemistry and biological reactions occur during the stabilization of landfills, PAEs leach from waste and migrate to the surrounding environmental media, thereby contaminating the surrounding soil, water ecosystems, and atmosphere. Although research on PAEs has achieved progress over the years, they are mainly concentrated on a particular aspect of PAEs in the landfill; there are fewer inquiries on the life cycle of PAEs. In this study, we review the presence of PAEs in the landfill in the following aspects: (1) the main source of PAEs in landfills; (2) the impact of the landfill environment on PAE migration and conversion; (3) distribution and transmedia migration of PAEs in aquatic ecosystems, soils, and atmosphere; and (4) PAE management and control in the landfill and future research direction. The purpose is to track the life cycle of PAEs in landfills, provide scientific basis for in-depth understanding of the migration and transformation of PAEs and environmental pollution control in landfills, and new ideas for the sustainable utilization of landfills.

Analysis of heavy metal, rare, precious, and metallic element content in bottom ash from municipal solid waste incineration in Tehran based on particle size

Waste incineration is increasingly used worldwide for better municipal solid waste management and energy recovery. However, residues resulting from waste incineration, such as Bottom Ash (BA) and Fly Ash (FA), can pose environmental and human health risks due to their physicochemical properties if not managed appropriately. On the other hand, with proper utilization, these residues can be turned into valuable Municipal metal mines. In this study, BA was granulated in various size ranges (< 0.075 mm, 0.075-0.125 mm, 0.125-0.5 mm, 0.5-1 mm, 1-2 mm, 2-4 mm, 4-16 mm, and > 16 mm). The physicochemical properties, heavy metal elements, environmental hazards, and other rare and precious metal elements in each Granulated Bottom Ash (GBA) group from Tehran's waste incineration were examined using ICP-MASS. Additionally, each GBA group's mineralogical properties and elemental composition were determined using X-ray fluorescence (XRF) and X-ray diffraction (XRD). The results showed that the average concentration of heavy metals in GBA, including Zn (1974 mg/kg), Cu, and Ba (790 mg/kg), Pb (145 mg/kg), Cr (106 mg/kg), Ni (25 mg/kg), Sn (24 mg/kg), V (25 mg/kg), As (11 mg/kg), and Sb (29 mg/kg), was higher in particles smaller than 4 mm. Precious metals such as gold (average 0.3 mg/kg) and silver (average 11 mg/kg) were significantly higher in GBA particles smaller than 0.5 mm, making their extraction economically feasible. Moreover, rare metals such as Ce, Nd, La, and Y were detected in GBA, with average concentrations of 24, 8, 11, and 7 mg/kg, respectively. The results of this study indicated that BA contains environmentally concerning metals, as well as rare and precious metals, with high concentrations, especially in particles smaller than 4 mm. This highlights the need for proper pre-treatment before using these materials in civil and municipal applications or even landfilling.

Spatial-temporal clogging development in leachate collection systems of landfills: Insight into chemical and biological clogging characteristics

The clogging of leachate collection systems (LCSs) is a typical challenge for landfills operation. Although clogging occurs in different LCS components, its spatial-temporal distributions remain unclear. This study aimed to systematically investigate the dynamic clogging development in simulated LCSs by monitoring changes in clogging characteristics over time. Results revealed that clogging accumulated in all components of the simulated LCS during a 215-day period, including chemical clogging and bio-clogging. Distinct spatial variations in clogging components were observed along the leachate flow of the simulated LCS, with the geotextile being severely clogged due to bio-clogging (70.1 ± 3.0%-80.0 ± 0.5%). Additionally, chemical clogging mainly occurred at the top (85.4 ± 0.8%-95.0 ± 0.9%) and middle (91.2 ± 0.8%-94.9 ± 1.1%) gravel layers. Nevertheless, the percentage of chemical clogging decreased from 72.0 ± 2.1% (day 42) to 42.5 ± 2.7% (day 215) at the bottom gravel layer. Chemical clogging was the main type in the pipe, accounting for 69.6 ± 0.5% (day 215). In addition, the ratios of bio-clogging to chemical clogging changed over time in all LCS components. The spatial-temporal characteristics of clogging across LCS components can enhance the understanding of clogging mechanisms, facilitate the design optimization of LCSs, and promote the formulation of effective control strategies.

Experimental study on the influence of curing conditions on the mechanical performance of municipal solid waste incinerated-bottom ash (MSWI-BA)

In this study, three groups of municipal solid waste incinerated-bottom ash (MSWI-BA) with different particle sizes (1.18-2.36 mm; 2.36-4.75 mm; 4.75-9.5 mm) were separately treated under natural dry, half-wet, and wet condition, to investigate the possibility of their mechanical performance. The strength of MSWI-BA was periodicity tested by crushing value test. The changes of microstructure and mineral components over curing time were separately analyzed via scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) and X-ray diffraction (XRD). The results show that the MSWI-BA requires long curing time to develop a certain strength, and the highest strength of MSWI-BA is obtained under half-wet curing condition. The strength development of MSWI-BA is attributed to the formation of hydration products of calcium silicate hydrate (C-S-H) and the increase in well-crystallized minerals of CaCO3. In addition, the results of the indoor long-term immersion test show that the heavy metal leached concentrations of MSWI-BA are far below the limited values in China standard GB 5085. In addition, the curing can solidify heavy metals to a certain extent, ensuring the safety of MSWI-BA as a road construction material.

Coupled effect of microbiologically induced calcium carbonate and biofilms in leachate

Fouling and clogging are persistent challenges to the collection and treatment of leachate. The main components of fouling and clogging are calcium carbonate (CaCO₃) and biofilms. However, the relationships between CaCO₃ and biofilms remain to be clarified. In this study, the interaction between microbially induced CaCO₃ precipitation (MICP) and biofilms was investigated using Luria-Bertani (LB) or urea media. Results showed that the bacteria promoted the precipitation of CaCO₃ and the formation of a complex mixture of biofilms. The amount of formed CaCO₃ in the urea medium was 12.9 times of that in the LB medium. The high MICP potential in the urea medium was associated with increased pH and alkalinity. In addition, the clogging materials exhibited a layered structure and uneven distribution over the clogging width and depth profile. These results indicated the presence of nucleation sites of CaCO₃ on the surface of and inside the bacteria. This research provides insights into the regulation of MICP and biofilms through dynamic control of clogging and fouling.

Valorization of municipal solid waste incineration bottom ash (MSWIBA) into cold-bonded aggregates (CBAs): Feasibility and influence of curing methods

The municipal solid waste incineration bottom ash (MSWIBA) contains amounts of hazardous elements or composition, and its disposal to landfills may pose a serious threat to the ground water and soil. To reduce the environmental impact of MSWIBA, a novelty application into the utilization of MSWIBA for the manufacture of cold-bonded aggregates (CBAs) was investigated in this study. This study explored the impacts of curing systems on the comprehensive properties of CBAs. Furthermore, the hydrating phases of the designed CBAs were studied by X-ray diffractometer, and the micro characteristics of CBAs was analyzed by Scanning Electron Microscopy. The results show that CBAs produced from the MSWIBA had good properties with density of 1.75-1.98 g/cm³, moisture content of 0.78-16.48 %, water absorption of 3.99-14.02 % and compressive behavior of 1.6-4.8 MPa. Moreover, the heating water curing environment can significantly improve the comprehensive properties of CBAs. Specifically, the compressive strength of the CBAs under the 80 °C curing condition was increased by 74 %-113 %, and the water absorption rate was reduced by 3.4 %-8 %, compared with other curing regimes. Additionally, the XRD analysis showed that there are spinel phases in the CBAs compounds, which is beneficial to solidify the hazardous metals. Also, low-carbon CBAs also greatly reduce the amount of Cu and Pb leaching, which meets the limit requirements in the Chinese standards. Overall, application of MSWIBA as admixture in CBAs is an effective approach to recycle waste and replace natural aggregates. Meanwhile, this work can provide an insight for the production of eco-friendly LWAs.

Effect of incineration ash leachates on the hydraulic conductivity of bentonite-polymer composite geosynthetic clay liners

A study was conducted to evaluate the hydraulic conductivity (k) of six bentonite-polymer composite (BPC) geosynthetic clay liners (GCLs) using five synthetic municipal solid waste incineration ash (IA) leachates with ionic strength (I) ranging from 174 to1978 mM. The BPC GCLs contained a dry blend of bentonite and proprietary polymers and had polymer loading ranging from 0.5 to 5.5%. The polymers used in the BPC GCLs were classified as linear polymer (LP) or crosslinked polymer (CP) based on the swelling characteristics of specimens extracted from the GCLs. Comparable hydraulic conductivity tests were also performed on two conventional bentonite (CB) GCLs as controls. The BPC GCLs had k of 2.6 - 6.7 × 10^-11 m/s when permeated with IA leachate with I = 174 mM, whereas the CB GCLs had k > 5.0 × 10^-8 m/s when permeated with the same leachate. However, k of the BPC GCLs ranged from the order of 10^-10 to 10^-7 m/s when permeated with IA leachates with I > 600 mM. BPC GCLs with high polymer loading generally had lower k compared to those with lower polymer loading when permeated with the same IA leachate, regardless of the polymer type. Polymer eluted from the BPC GCLs containing LP during permeation with DI water or IA leachate. Unlike CPs, LPs are water-soluble, therefore, they seem to easily migrate during permeation. There was no correlation between the percentage of polymer retained and the final hydraulic conductivity of the LPB GCLs used in this study.

Fabrication of anti-scaling HDPE/fluorinated acrylate polymer/nano-silica composite for landfill leachate piping system

Clogging generally happens to the leachate piping system, which poses a risk to the environment. A low surface energy nanocomposite is prepared to mitigate the cloggings, by adding the fluorinated acrylate polymer and hydrophobically modified nano-silica into high-density polyethylene (HDPE) substrate. The best addition of the fluorinated acrylate polymer and the nano-silica is given as 15% and 5%, to produce the composite with a low surface energy of 29.4 mJ/m². Through the characterization of contact angle (CA), electrochemical corrosion, scanning electron microscopy (SEM) with energy dispersive X-ray spectrometer (EDS), atomic force microscope (AFM) and thermogravimetry (TG), the composite shows low wettability, good corrosion resistance and thermal stability. The surface hydrophobic property of the composite remains unchanged after being immersed in an acidic (pH = 2) and an alkaline (pH = 12) solution, indicating that the prepared composite has strong adaptability to the extreme environments. In addition, the composite shows better anti-scaling performance than that of the commercial high-density polyethylene (HDPE) and polyvinyl chloride (PVC) pipe materials by application of a dispensing leachate immersion test. The results provide insights into engineering practice for the design and manufacture of pipe materials for leachate collection and transport.

Phase changes during various treatment processes for incineration bottom ash from municipal solid wastes: A review in the application-environment nexus

Incineration technology has been widely employed, as an effective method to decrease the volume of waste disposal. In this review, relationships between municipal solid waste (MSW) inputs and residues after combustion-specifically, the incineration bottom ashes (IBA) of MSW, were discussed, with an emphasis on the geoenvironmental impacts of IBA associated with the complex crystal and amorphous phase reactions and changes during combustion and from their downstream treatments, whereas, their influences on IBA leaching behaviors are considered as another focus. This review summarizes the IBA leaching behaviors based on literature, showing the leaching variabilities induced by natural weathering and artificial intervention conditions, such as accelerated carbonation, washing treatment, stabilization/solidification, and thermal treatments, all of which can be attributed to changes of mineral phases and microstructure. It helps to understand IBA characteristics and transitions in application-environment nexus, and better reuse it for multiple applications.

Impact of bottom ash co-disposed with municipal solid waste on geotextile clogging in landfills

Co-disposal of bottom ash (BA) with municipal solid waste (MSW) in landfills is commonly used for BA management. However, BA co-disposal may cause clogging of geotextiles in MSW landfills. This study investigated the effect of different BA co-disposal ratios on geotextile clogging, including MSW, low ash co-disposed (BA_L), high ash co-disposed (BA_H) landfills, and BA mono-fill. Results showed that the BA_L group increased the geotextile clogging by 0.1-0.6 times, compared to that in the MSW landfill. In contrast, the geotextile clogging of the BA_H and BA groups was reduced than that in the MSW landfill. The clogging was in a dynamic process during the experimental period in all the conditions, including chemical clogging and bio-clogging. Moreover, bio-clogging was the main contributor to the geotextile clogging, accounting for 64-83% of the total clogging mass. The BA co-disposal affected the leachate characteristics, such as pH, calcium concentration, and alkalinity, resulting in chemical clogging. When pH was above 7.0, calcium concentration and alkalinity were limiting factors for the calcium carbonate formation. In terms of the bio-clogging, the microbial analysis indicated that different BA co-disposal ratios influenced the diversity and structure of microbial community. These findings could help clarify the effect of BA co-disposal on geotextile clogging, thus useful to landfill operation in practice.

Deciphering acyl-homoserine lactones-mediated quorum sensing on geotextile bio-clogging in municipal solid waste and bottom ash co-disposal landfills

Bottom ash co-disposed in landfills accelerates geotextile clogging and decreases landfill stability. As the main contributor to clogging, bio-clogging may be associated with quorum sensing (QS) in microbial communities. This study investigated the potential roles of acyl-homoserine lactones (AHLs)-mediated QS in geotextile bio-clogging under different landfill conditions, including municipal solid waste landfill and bottom ash co-disposal landfill. The unit area of geotextile bio-clogging mass in the municipal solid waste landfill (MSW_G) ranged from 5.2 × 10^-3 to 8.2 × 10^-3 g/cm²_, while it was in the range of 8.4 × 10^-3 to 1.2 × 10^-2 g/cm² in the bottom ash co-disposal landfill (BA_G). Two types of AHLs were detected and the total AHLs content in the MSW_G (1,616.9 ± 103.8 ng/g VSS) was half of that in the BA_G (3,233.0 ± 646.8 ng/g VSS). High contents of the AHLs could increase bio-clogging. The bio-clogging was also attributed to QS genes and extracellular polymeric substances (EPS). EPS aggregation was stimulated due to the higher Ca²⁺ and Mg²⁺ in the BA_G. These results suggested that the co-disposal of bottom ash could increase the AHLs content, resulting in accelerated bio-clogging.

Calcium leaching characteristics in landfill leachate collection systems from bottom ash of municipal solid waste incineration

Calcium leaching is a critical factor in the clogging of leachate collection systems (LCS), a phenomenon that affects landfill stability and operation. The bottom ash (BA) of municipal solid waste (MSW) incineration plants contains large quantities of calcium-based compounds. Landfilling is the main disposal method for BA in China that intensifies the consequences of LCS clogging. The factors influencing BA calcium leaching were investigated using simulated leachate. The results showed that fine BA particles, low pH values, high temperature, and ratios of leachate to BA solids were conducive to calcium leaching. Calcium leaching was found to be higher in actual leachate than in simulated leachate. At pH = 5, the cumulative calcium dissolution ratios (CDRs) were 83.36% and 31.49% after 20 days of leaching in the actual and simulated leachate, respectively; at pH = 6, the values were 50.67% and 12.06%, respectively. The introduction of landfill gas could decrease the calcium dissolution and leaching rates. When the ratio of leachate to BA solid was 20:1 mL/g, the accumulative CDR values were 45.98% (pH = 6) and 5.80% (pH = 8) without landfill gases, and 4.59% (pH = 6) and 0.48% (pH = 8) with landfill gases. These results provide the scientific basis for clogging risk prediction with respect to calcium leaching in the LCS of landfills. BA landfilling in old landfill areas with relatively high leachate pH and low chemical oxygen demand, as well as when leachate mixed with an appropriate amount of landfill gases, could be feasible measures to reduce calcium leaching and further prevent clogging in LCS.

Comparison of bio-clogging characteristics of geotextiles in MSW and bottom ash co-disposal landfills

Bio-clogging of geotextile is a big challenge for the leachate collection system in landfills. It is important to understand the characteristics of geotextile bio-clogging to develop control technologies. This study investigated the characteristics of geotextile bio-clogging in municipal solid waste landfill (MSW_G) and bottom ash (BA) co-disposal landfill (BA_G). Results showed that the bio-clogging mass of per area in MSW_G and BA_G was 49 ± 5 g/m² and 57 ± 3 g/m², respectively. Bio-clogging was dominated by live cells in both MSW_G and BA_G. The confocal laser scanning microscopy images revealed that live cells percentage was 46% in MSW_G, while it increased to 77% in BA_G. In contrast, the percentage of the dead cells was 47% and 9% in MSW_G and BA_G, respectively. The biofilm formed in BA _G was thinner and denser than that in MSW_G. Based on the microbial analysis, the biofilms of BA_G had a higher genetic amount and diversity than these of MSW_G. The total amount of extracellular polymeric substances in BA_G was 45.29 ± 4.52 mg/g volatile suspended solids, which was 1.5 times of that in MSW_G. The co-disposal of BA increased the microbial diversity and accelerated bio-clogging due to the high calcium concentration. These findings provide a better understanding of the bio-clogging characteristics, which is helpful to control bio-clogging in co-disposal landfills.

An IVTIFN–TOPSIS Based Computational Approach for Pipe Materials Selection

This paper proposes a multicriteria decision-making (MCDM) approach, coupling intervalued trapezoidal intuitionistic fuzzy number (IVTIFN) with the technique for order preference by similarity to ideal solution (TOPSIS) to facilitate the selection of pipe materials. Their integration can maximize the advantage in better expressing decision maker’s preference on the proposed evaluation criteria by using a bounded limit instead of an exact value, to rank material alternatives based upon their functional, economic and environmental attributes. To reduce possible information overlapping resulted from the criteria, Mahalanobis distance is incorporated into IVTIFN–TOPSIS to improve the selection results. An illustrative example is provided to verify the proposed approach and demonstrate its practical application, in which four common alternative materials, including carbon steel, galvanized steel, polyvinyl chloride (PVC) and high-density polyethylenes (HDPE), are subject to precise selection to determine their adaptability in waste-water piping. The selection result indicates that the plastic materials are superior to the metal materials. In particular, HDPE is the optimal material alternative for waste-water collection and transport.

Geotextile clogging at different stages of municipal solid waste landfills co-disposed with bottom ash

Co-disposal of bottom ash (BA) with municipal solid waste (MSW) in landfills is a common way for BA management. However, BA co-disposal in MSW landfills may accelerate geotextile clogging and reduce the performance of leachate collection system. This study compared geotextile clogging in a simulated MSW landfill leachate (MSWL) and a BA co-disposed landfill leachate (BAL) at different landfill stages. Geotextile clogging test was conducted using the MSWL and BAL taken from the simulated landfills on the 10th, 80th, 140th and 200th day, respectively. The results demonstrated that geotextile clogging varied with landfill age, due to the change of leachate characteristics. The mass of clogging material in geotextiles with BAL increased from 0.45 g to 2.74 g, which was 43.87%-63.73% greater than those with MSWL. The formation of biofilm was the main contributor for the geotextile clogging. At the same stage, the amount of biofilm formed on geotextile in different leachate was comparable. However, the amounts of CaCO₃ precipitation on geotextile in BAL were 3.85-10.44 times of those in MSW leachate. The pH of leachate played a critical role in CaCO₃ precipitation. The microbial analysis revealed that the co-disposal of the BA greatly influenced the microbial community diversity and structure.

Review of leaching behavior of municipal solid waste incineration (MSWI) ash

Incineration is widely adopted in modern waste management because it provides an effective way to minimize municipal solid waste that needs to be disposed of in landfills. The ash residue is often disposed by landfilling. Alternatively, the incineration ash may be recycled and reused for various applications. The crucial issues, however, are the leaching of harmful elements during the use and the end-of-life phases. This review summarizes extensive studies on leaching behavior of municipal solid waste incineration ash. Specifically, pollutants generated through leaching, factors governing leaching, methodologies to study leaching, leaching mechanisms, and treatments to reduce leaching. Many types of pollutants are generated through leaching from municipal solid waste incineration ash, in which heavy metals and organic contaminants are the most toxic and concerned. Ash properties, pH and liquid to solid ratio are the main factors governing municipal solid waste incineration ash leaching. Leaching behavior of municipal solid waste incineration ash is complicated and existing methods to evaluate leaching may not be able to represent the field conditions. Solubility and sorption are the two major leaching mechanisms. Many treatment methods have been proposed. However, not all methods are effective and some approaches are associated with high energy and high cost, which makes them less economically feasible and attractive.

Impacts of different aged landfill leachate on PVC corrosion

Landfill leachate is generally transferred to in situ facilities for advanced treatment by using a pipe system. Because of its harmful and complex compounds, leachate may react with pipe materials, leading to corrosion and scaling. This experimental study uses typical PVC pipe material and investigates its anti-corrosion performance by placing the material samples into different aged leachates. By evaluating the changes in different experimental parameters, including calcium, magnesium, and chloride ion concentration, oxidation-reduction potential, dissolved oxygen, and pH, combined with a characterization of the material properties, we infer the main causes of pipe scaling-corrosion. Results show that the scaling is more intense in the younger leachate, and the concentration of calcium ions is the dominant influencing factor. The scaling might be resulted from joint actions of chemical precipitation and microbial metabolic activities. It is expected the study to provide useful insights into taking effective actions on anti-clogging, and enhance pipes design by selection of appropriate materials for future modification.

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.

Impact of co-landfill proportion of bottom ash and municipal solid waste composition on the leachate characteristics during the acidogenesis phase

Incineration has become an important municipal solid waste (MSW) treatment strategy, and generates a large amount of bottom ash (BA). Although some BA is reused, much BA and pretreatment residues from BA recycling are disposed in landfill. When BA and MSW are co-landfilled together, acid neutralization capacity and alkaline earth metal dissolution of BA, as well as different components of MSW may change environmental conditions within the landfill, so the degradation of organic matter and the physical and chemical properties of leachate would be affected. In this study, the effect of co-landfilled BA and MSW on the leachate characteristics during the hydrolysis and acidogenesis phase was studied using different BA/MSW ratios and MSW compositions. The results showed that the co-landfill system increased leachate pH, electric conductivity and alkalinity. For MSW with a high content of degradable components, the release and degradation of total organic carbon (TOC) and volatile fatty acids (VFA) from MSW were promoted when the BA ratio by wet weight was less than 50%, and the biodegradability of leachate was improved. When the BA ratio exceeded 50%, the degradation of organic matters was inhibited. For MSW with low content of degradable components, when the proportion of BA was less than 20%, the release and degradation of TOC and VFA from MSW were promoted and alkalinity increased. When the BA ratio exceeded 20%, the degradation of organic matters was inhibited. The 50% BA ratio could improve the bio-treatability of leachate indicated by the leachate pH and C/N ratio. However, BA inhibited the release of nitrogen (TN and NH₄⁺-N) at all BA ratios and MSW compositions. At the same time, the addition of BA increased the risk of leachate collection system clogging due to the dissolution and re-precipitation of alkaline earth metals contained in BA.

Leaching behaviour of municipal solid waste incineration bottom ash: From granular material to monolithic concrete

The aim of this work was to assess the leaching behaviour of the bottom ash derived from municipal solid waste incineration (MSWI) used in concrete production. In particular, the release of pollutants was evaluated by the application of different leaching tests, both on granular materials and monolithic samples (concrete mixtures cast with bottom ash). The results confirmed that, according to Italian regulations, unwashed bottom ashes present critical issues for the use as alternative aggregates in the construction sector due to the excessive release of pollutants; instead, the leachate from washed bottom ashes was similar to natural aggregates. The concentration of pollutants in the leachate from concrete mixtures was lower than regulation limits for reuse. The crushing process significantly influenced the release of pollutants: this behaviour was due both to the increase in surface area and the release of contaminants from cement. Moreover, the increase in contact time (up to 64 days) involved more heavy metals to be released.

Approximation of clogging in a leachate collection system in municipal solid waste landfill in Osecna (Northern Bohemia, Czech Republic)

The research was focused on approximation of clogging in a leachate collection system in municipal solid waste landfill in Osecna, situated near the location Osecna, region Liberec, Northern Bohemia, Czech Republic, by analysis of numerical experiment results. To approximate the clogging of the leachate collection system after fifteen years of landfill operation (1995-2009) were successfully tested modified De Zeeuw-Hellinga transient drainage theory. This procedure allows application of the reduction factors to express clogging of the leachate collection system in Osecna landfill. The results proved that the modified De Zeeuw-Hellinga method with reduction factors can serve as a good tool for clogging approximation in a leachate collection system in Osecna landfill.

Inhibitory effect of high calcium concentration on municipal solid waste leachate treatment by the activated sludge process

This research focused on the inhibitory effects of Ca on the aerobic biological treatment of landfill leachate containing extremely high Ca concentrations. When the Ca concentration in leachate to be treated was more than 4500 mg l^-1, the total organic carbon removal rate was significantly reduced and the processing time to achieve the same removal efficiency was 1.4 times that in the control treatment without added Ca. In contrast, the total nitrogen and ammonia nitrogen (NH₄⁺-N) removal efficiencies were positively related to the Ca concentration, increasing from 65.2% to 81.2% and from 69.2% to 83.7%, respectively, when the dosage of added Ca increased from zero to 8000 mg l^-1. During aerobic treatment, the reductions of solution Ca concentration were in the range of 1003-2274 mg l^-1 and were matched with increases in the Ca content in the residual sludge. The inhibition threshold of Ca in the leachate treated by the activated sludge process appeared to be 4500 mg l^-1, which could be realized by controlling the influent Ca concentration and using an appropriate sludge return ratio in the activated sludge process.