Release of pollutants in MBT landfills: Laboratory versus field

A 35-year monitoring of an Italian landfill: Effect of recirculation of reverse osmosis concentrate on leachate characteristics

"Fossetto" landfill (Monsummano Terme - Tuscany, Italy) started operation in 1988 as a controlled landfill accepting mixed municipal solid waste collected without any attempt of recycling. Then, progressively, following the evolution of the state-of-the-art, it adopted biogas extraction and valorisation systems and mechanical-biological treatment for incoming waste (both since 2003). Finally, since 2006, in the plant is performed on-site reverse osmosis leachate treatment with the concentrated leachate being recirculated back into the landfill body. Recently a new landfill cell, separate from the others, was put in operation adding a capacity of 200,000 m3 to the already available 1,095,000 m3. This plant can provide long term leachate composition data to study the evolution and impact of changing landfill technology and waste composition on various parameters. The rise in leachate production (+84 % in 2018-2022 respect to the period before recirculation) cannot be totally attributable to recirculation but could be also linked to the increase in the amount of landfilled waste. The concentration of certain parameters (NH4+, Cl- and to a less extent of COD) increased (+60 %, +58 %, +17 % respectively in the last five years with respect to the period before recirculation); however, this increase did not influence the performance of the treatment plant. Nevertheless, the overall leachate management would benefit from an optimized reinjection system.

The importance of particularising the model to estimate landfill GHG emissions

Methane generation in landfills can be estimated using mathematical models. One of the most widespread estimation models is that developed by the Intergovernmental Panel on Climate Change (IPCC). Despite its popularity, the simplicity that characterises this model markedly limits the possibility of representing operation alternatives, which can strongly impact surface emissions and hinder the introduction of local data that are sometimes available. In this study, the IPCC model was applied to a case study from which field data on gas emissions were available. To fit the model to the studied landfill conditions, a series of modifications were made, including changes in Degradable Organic Carbon (DOC) and methane generation rate constant (k) values, and degradation times for some waste fractions, and by considering leachate carbon and the inclusion of gas lateral migration phenomena or changes in the methane oxidation factor. The model's Final Version improved the fit of its Initial Version to the experimentally estimated values in the case study by more than 65%. Some modifications, such as considering the carbon dragged by leachate or the contour migration of gas, have a minor impact on the model's fit. However, changes in the degradation time of some fractions according to their particular pretreatment or the modification of parameter k in accordance with the moisture conditions in each landfill phase, strongly influence the model's results. This highlights the importance of particularising estimation models to achieve more accurate results, which allow better estimates of the efficiency of mitigation measures for landfill gas emissions in each facility.

Shear strength characterization of fresh MBT and MSWI wastes from a Spanish treatment facility

A laboratory shear strength characterization of the landfilled materials of the Municipal Solid Waste integral treatment plant from the Meruelo Environmental Complex in Cantabria (Spain) was performed. The materials tested come from the rejection of the Mechanical and Biological Treatment (MBT-MSW) and the slags produced in the energy recovery plant (MSWI). Laboratory characterization consisted of direct shear and consolidated drained triaxial testing. Mohr-Coulomb failure criterion parameter values were obtained and compared to reported values in the literature. In some tests, failure was not reached due to the reinforcement effect for fibrous particles; thus, the mobilized shear strength parameters for different values of axial strain were obtained. The triaxial test results showed strain-hardening in MSW-MBT but not in MSWI. Failure was reached on both materials in direct shear testing, with MSWI showing peak and ultimate strengths, whereas MBT-MSW exhibited only ultimate strength. Direct shear test obtained strength can be characterized by a cohesion of 20 kPa and a friction angle of 33° for MBT-MSW ultimate strength, while cohesion and friction angle varies from 13.4 to 29 kPa and from 38.5° to 42.3° for MSWI ultimate and peak strength, respectively. The mobilized cohesion and friction angle obtained for MBT-MSW in consolidated drained triaxial tests ranged from 15.1 to 62.7 kPa and 20° to 28.7°, corresponding to a strain level of 5% and 25%, respectively. In triaxial testing of MSWI specimens, failure was reached, and the material showed a cohesion of 51.3 kPa and a friction angle of 32.8°.

Release characteristics of polycyclic aromatic hydrocarbons (PAHs) leaching from oil-based drilling cuttings

Drilling cuttings, the primary byproduct from the exploration and mining of shale gas, are potentially hazardous wastes that are associated with the serious depletion of land resources and environmental safety problems. In this work, the distribution of polycyclic aromatic hydrocarbons (PAHs) in oil-based residues of shale gas drilling cuttings was studied. Furthermore, a column leaching test was carried out to investigate the leaching behaviour of PAHs. The results showed that (1) the concentrations of 4-ring PAHs were highest among the PAH concentrations detected from the oil-based residues, and the concentration of PAHs decreased with increasing particle size of the residues. (2) The PAH concentration in leachates from all the tested residues differed during the leaching process, and the cumulative amount of each leached PAH accounted for 1.50-3.20% of the total PAHs. (3) The first-order diffusion model (FRDM) was the most applicable model for describing the leaching characteristics of the PAHs, and the leaching rate was initially controlled by surface wash-off and then by diffusion.

Reliable environmental trace heavy metal analysis with potentiometric ion sensors - reality or a distant dream

Over two decades have passed since polymeric membrane ion-selective electrodes were found to exhibit sufficiently lower detection limits. This in turn brought a great promise to measure trace level concentrations of heavy metals using potentiometric ion sensors at environmental conditions. Despite great efforts, trace analysis of heavy metals using ion-selective electrodes at environmental conditions is still not commercially available. This work will predominantly concentrate on summarizing and evaluating prospects of using potentiometric ion sensors in view of environmental determination of heavy metals in on-site and on-line analysis modes. Challenges associated with development of reliable potentiometric sensors to be operational in environmental conditions will be discussed and reasoning behind unsuccessful efforts to develop potentiometric on-site and on-line environmental ion sensors will be explored. In short, it is now clear that solely lowering the detection limit of the ion-selective electrodes does not guarantee development of successful sensors that would meet the requirement of environmental matrices over long term usage. More pressing challenges of the properties and the performance of the potentiometric sensors must be addressed first before considering extending their sensitivity to low analyte concentrations. These are, in order of importance, selectivity of the ion-selective membrane to main ion followed by the membrane resistance to parallel processes, such as water ingress to the ISM, light sensitivity, change in temperature, presence of gasses in solution and pH and finally resistance of the ion-selective membrane to fouling. In the future, targeted on-site and on-line environmental sensors should be developed, addressing specific environmental conditions. Thus, ion-selective electrodes should be developed with the intention to be suitable to the operational environmental conditions, rather than looking at universal sensor design validated in the idealized and simple sample matrices.

Leaching behavior of polycyclic aromatic hydrocarbons (PAHs) from oil-based residues of shale gas drill cuttings

Cuttings are the main solid residues which are generated from drilling operations. Due to the presence of heavy and radioactive elements, the environment risk posed by cuttings has attracted increasing attention. In this work, a short-term static immersion experiment was carried out to investigate the leaching of polycyclic aromatic hydrocarbons (PAHs) from oil-based residues of shale gas drilling cuttings. Furthermore, the effects of some relevant environmental factors controlling the leaching behavior were evaluated, including the different particle sizes, pH, extraction time, solid-to-liquid (S/L) ratio and dissolved organic matter (DOM) concentration. The results showed that (1) the concentrations of leached PAHs gradually increased with prolonged leaching time, but the cumulative amount of PAHs released during leaching was less than 3% of the total. (2) The Elovich, parabolic diffusion and power function models were found to fit the experimental data better than the first-order kinetic equation, indicating that the leaching of PAHs was controlled by the coupling of diffusion and chemical reactions at the source surface. (3) Different environmental factors had different impacts on the leaching of PAHs: the shaking time and presence of DOM increased leachability, the particle size and S/L ratio decreased leachability, and the pH did not affect the leachability of PAHs. Therefore, PAHs leaching was a complex process, and it is of scientific and environmental interest to conduct the leaching tests under the simulated environmental conditions.

Long-term landfill leachate exposure modulates antioxidant responses and causes cyto-genotoxic effects in Eisenia andrei earthworms

It is estimated that approximately 0.4% of the total leachate produced in a landfill is destined for treatment plants, while the rest can reach the soil and groundwater. In this context, this study aimed to perform leachate toxicity evaluations through immune system cytotoxic assessments, genotoxic (comet assay) appraisals and antioxidant system (superoxide dismutase - SOD; catalase - CAT, glutathione-S-transferase - GST; reduced glutathione - GSH and metallothionein - MT) evaluations in Eisenia andrei earthworms exposed to a Brazilian leachate for 77 days. The leachate sample contained high organic matter (COD - 10,630 mg L^-1) and ammoniacal nitrogen (2398 mg L^-1), as well as several metals, including Ca, Cr, Fe, Mg, Ni and Zn. Leachate exposure resulted in SOD activity alterations and increased CAT activity and MT levels. Decreased GST activity and GSH levels were also observed. Antioxidant system alterations due to leachate exposure led to increased malondialdehyde levels as a result of lipid peroxidation after the 77 day-exposure. An inflammatory process was also observed in exposed earthworms, evidenced by increased amoebocyte density, and DNA damage was also noted. This study demonstrates for the first time that sublethal effect assessments in leachate-exposed earthworms comprise an important tool for solid waste management.

Mass Transfer Principles in Column Percolation Tests: Initial Conditions and Tailing in Heterogeneous Materials

Initial conditions (pre-equilibrium or after the first flooding of the column), mass transfer mechanisms and sample composition (heterogeneity) have a strong impact on leaching of less and strongly sorbing compounds in column percolation tests. Mechanistic models as used in this study provide the necessary insight to understand the complexity of column leaching tests especially when heterogeneous samples are concerned. By means of numerical experiments, we illustrate the initial concentration distribution inside the column after the first flooding and how this impacts leaching concentrations. Steep concentration gradients close to the outlet of the column have to be expected for small distribution coefficients (Kd<1 L kg-1) and longitudinal dispersion leads to smaller initial concentrations than expected under equilibrium conditions. In order to elucidate the impact of different mass transfer mechanisms, film diffusion across an external aqueous boundary layer (first order kinetics, FD) and intraparticle pore diffusion (IPD) are considered. The results show that IPD results in slow desorption kinetics due to retarded transport within the tortuous intragranular pores. Non-linear sorption has not much of an effect if compared to Kd values calculated for the appropriate concentration range (e.g., the initial equilibrium concentration). Sample heterogeneity in terms of grain size and different fractions of sorptive particles in the sample have a strong impact on leaching curves. A small fraction (<1%) of strongly sorbing particles (high Kd) carrying the contaminant may lead to very slow desorption rates (because of less surface area)-especially if mass release is limited by IPD-and thus non-equilibrium. In contrast, mixtures of less sorbing fine material ("labile" contamination with low Kd), with a small fraction of coarse particles carrying the contaminant leads to leaching close to or at equilibrium showing a step-wise concentration decline in the column effluent.

Metal-organic frameworks for pesticidal persistent organic pollutants detection and adsorption - A mini review

The global population growth demands intensification of anthropogenic processes, thus leading to inter alia pollution of both land and aquatic environments with toxic organic compounds. Particularly harmful synthetic compounds are classified as persistent organic pollutants (POPs). Their relatively high chemical resistance resulted in a worldwide ban or strict control on the use of POPs. The majority of POPs were commonly used as pesticides, and unfortunately, some of them are still utilized as an aid in agricultural practices. Therefore, environmental monitoring in terms of reliable detection and quantification of pesticidal POPs is an ever-increasing need. Chemical sensors and adsorption materials crafted for specific pesticide operate on host-guest interactions should provide selectivity and sensitivity, thus leading to the detection of target molecule down to the nanomolar range. This could be achieved with materials exhibiting a very large active surface area, well-defined structure, and high stability. The novel materials studied in that context are metal-organic frameworks (MOFs). The structure of various MOFs can be functionalized to provide desired host-guest interactions. In this mini-review, we critically discuss the application of MOFs for the detection and adsorption of selected pesticides that are classified as POPs according to the Stockholm Convention.

Total organic carbon as a proxy for metal release from biostabilized wastes

In this study, we introduce a simple screening method to predict the metal release from biostabilized wastes as a function of the total organic carbon (TOC) content of the sample. The method relies on a model that simulates the release of dissolved organic carbon (DOC) as a function of the applied liquid to solid (L/S) ratio. The metal release is then estimated using generic empirical DOC to metal correlation coefficients (K_DOC,Me) extrapolated from the literature. Specifically, the results of leaching tests carried out on different types of biowastes and biostabilized wastes were used to calculate the upper and lower K_DOC,Me values that can be expected for common metals of concern (Al, Ba, Cr, Cu, Mo, Ni, Pb, V, and Zn). The statistical analysis of the estimated empirical coefficients highlighted that for most of the investigated metals, the adoption of generic DOC to metal correlation coefficients introduces relatively low uncertainties. The quartiles ratio (QR calculated as the ratio of third and first quartile) of the K_DOC,Me coefficients extrapolated from the literature was indeed below 3 for Cu, Ni, and Zn and below 5 for Al, Ba, Cr, Pb, and V. Only for Mo, the QR was around 10 indicating that for this element, DOC can be a poor indicator of the release expected as a function of the applied L/S. Furthermore, by performing a sensitivity analysis, we found that the experimental conditions only slightly influence the metals release predicted by the model. Based on this evidence, simple nomograms that estimate the cumulative metal release in percolation column tests as a function of the applied L/S are provided. Furthermore, a simple equation that predicts the cumulative metal release expected at L/S of 10 L/kg is presented. The application of the latter to the results of percolation column tests carried out on 8 mechanical biological treatment (MBT) waste samples highlighted that the predicted metals release was close to the measured values with deviations within a factor of 5 for all the investigated metals.

In situ catalytic reforming of plastic pyrolysis vapors using MSW incineration ashes

The valorization of municipal solid waste incineration bottom and fly ashes (IBA and IFA) as catalysts for thermochemical plastic treatment was investigated. As-received, calcined, and Ni-loaded ashes prepared via hydrothermal synthesis were used as low-cost waste-derived catalysts for in-line upgrading of volatile products from plastic pyrolysis. It was found that both IBA and air pollution control IFA (APC) promote selective production of BTEX compounds (i.e., benzene, toluene, ethylbenzene, and xylenes) without significantly affecting the formation of other gaseous and liquid species. There was insignificant change in the product distribution when electrostatic precipitator IFA (ESP) was used, probably due to the lack of active catalytic species. Calcined APC (C-APC) demonstrated further improvement in the BTEX yield that suggested the potential to enhance the catalytic properties of ashes through pre-treatment. By comparing with the leaching limit values stated in the European Council Decision, 2003/33/EC for the acceptance of hazardous waste at landfills, all the ashes applied remained in the same category after the calcination and pyrolysis processes, except the leaching of Cl^- from the ESP, which was around the borderline. Therefore, the use of ashes in catalytic reforming application do not significantly deteriorate their metal leaching behavior. Considering its superior catalytic activity towards BTEX formation, C-APC was loaded with Ni at 15 and 30 wt%. The Ni-loading favored an increase in overall oil yield, while reducing the gas yield when compared to the benchmark Ni loaded ZSM catalyst. However, Ni addition also caused the formation of more heavier hydrocarbons (C20-C35) that would require post-treatment to recover favorable products like BTEX.

The Air and Sewage Pollutants from Biological Waste Treatment

The mechanical-biological waste treatment plants (MBTP), which include the municipal waste biogas plants, have an important role in sustainable urban development. Some plants are equipped with a sewage pre-treatment plant, which is then directed to the sewerage system and the treatment plant. Others, on the other hand, have only a non-drainage tank. The parameters of technological sewage (TS) or processing technology could reduce sewage contamination rates. In addition to the quality of sewage from waste treatment plants, the emission of odours is also an important problem, as evidenced by the results obtained over the sewage pumping station tank. The conducted statistical analysis shows a significant positive correlation between odour concentration (cod) and volatile organic compounds (VOCs). Analysing the individual compounds, a high positive correlation was also found—the strongest being between H2S, NH3 and VOCs. In the case of sewage compounds, the insignificant correlation between P total and other parameters was found. For the rest of the compounds, the highest positive correlation was found between COD and BOD and N-NO2 and N-NH3 as well as COD and N-NO2. The dilution of sewage is only an ad hoc solution to the problem. Further work should be aimed at reducing sewage pollution rates. The obtained results indicate large pollution of technological sewage and a high level of odour and odorants concentration. The novelty and scientific contribution presented in the paper are related to analyses of various factors on technological sewage parameters and odour and odorant emission from TS tank at biogas plant processing municipal waste, which may be an important source of knowledge on the management of TS, its disposal and minimisation of emitted compound emissions.