Granular mixtures composed of zero valent iron (ZVI) and lapillus at two different weight ratios (i.e. 30:70 and 50:50) were tested through column experiments for the simultaneous removal of Cu2+, ...Ni2+ and Zn2+ present in aqueous solutions at high concentrations. The results were used to evaluate the feasibility of the above-mentioned granular mixtures as reactive media in permeable reactive barriers (PRB) for the remediation of groundwater polluted by metals. Test results showed that the two granular reactive media efficiently removed the three heavy metals under study according to the following removal sequence Cu > Zn > Ni. The granular mixture with the higher iron content showed a proportionally higher removal rate but also a higher reduction of hydraulic conductivity over time. Different removal mechanisms occurred for the three contaminants in question. Considering that for Ni and Zn the main removal mechanism was probably adsorption, we used different mathematical models, in order to predict the breakthrough curves for the adsorption mechanisms. The Adams-Bohart model showed the best fit with the experimental data and it was thus used to predict the zinc removal front within the barrier thickness. Finally, we showed that the mathematical approach may be used for the design of PRBs for the reactive media and contaminants used in this research.
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•ZVI/lapillus granular mixtures efficiently remove Cu, Ni and Zn from pluri-contaminated solutions.•The reactive and hydraulic behaviour is influenced by the ZVI content per unit volume of the reactive medium.•Different mathematical models were used to predict the breakthrough curves.•The Adams-Bohart model was found to accurately predict Zn breakthrough time.•The applicability of different mathematical models was evaluated for PRB design.
Organic fraction of municipal solid waste (OFMSW) and waste activated sludge (WAS) are the most produced organic waste streams in urban centres. Their anaerobic co-digestion (AcoD) allows to generate ...methane (CH4) and digestate employable as renewable energy source and soil amendment, respectively, fully in accordance with circular bioeconomy principles. However, the widespread adoption of such technology is limited by relatively low CH4 yields that fail to bridge the gap between benefits and costs. Among strategies to boost AcoD of OFMSW and WAS, use of conductive materials (CMs) to promote interspecies electron transfer has gained increasing attention. This paper presents one of the few experimental attempts of investigating the effects of four different carbon(C)-based CMs (i.e., granular activated carbon – GAC, graphite – GR, graphene oxide – GO, and carbon nanotubes – CNTs) separately added in semi-continuous AcoD of OFMSW and thickened WAS. The presence of C-based CMs has been observed to improve CH4 yield of the control process. Specifically, after 63 days of operation (concentrations of GAC and GR of 10.0 g/L and of GO and CNTs of 0.2 g/L), 0.186 NL/gVS, 0.191 NL/gVS, 0.203 NL/gVS, and 0.195 NL/gVS of CH4 were produced in reactors supplemented with GAC, GR, GO, and CNTs, respectively, compared to 0.177 NL/gVS produced in the control process. Likewise, at the end of the test (i.e., after 105 days at concentrations of C-based CMs half of the initial ones), CH4 yields were 0.193 NL/gVS, 0.201 NL/gVS, 0.211 NL/gVS, and 0.206 NL/gVS in reactors supplemented with GAC, GR, GO, and CNTs, respectively, compared to 0.186 NL/gVS of the control process. Especially with regard to GR, GO, and CNTs, results obtained in the present study represent a significant advance of the knowledge on the effects of such C-based CMs to realistic and scalable AD process conditions respect to previous literature.
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•Conductive materials (CMs) were tested for co-digestion of organics and sludge.•CH4 yields of all reactors supplemented with C-based CMs were higher than control.•Carbon nanotubes use led to the highest CH4 yield increase in the short term (27.9%).•Graphene oxide addition led to the highest CH4 yield increase overall (13.0%).
The Fossetto landfill has operated in the municipality of Monsummano Terme (Tuscany, Italy) since 1988, being considered a state-of-the-art landfill for 35 years. Initially, Fossetto acted as a ...conventional sanitary landfill for mixed municipal solid waste. With changes in regulations and technology, the Fossetto landfill was gradually equipped with a biogas recovery and valorisation system, a mechanical-biological treatment (MBT) plant in 2003 and a reverse osmosis leachate treatment plant, so the concentrated leachate has been recirculated back into the landfill body since 2006. Long-term biogas monitoring, enables the calculation of the efficiency of biogas recovery using a rather simplified methodology, which was assessed as being approximately 40% over the prior ten-years period. This value was lower than expected, confirming the results of previous studies and indicating the need of attributes. Applying the USEPA LandGEM model showed that the adoption of MBT substantially reduced biogas generation yields and rates by up to approximately 90% which was facilitated by the adoption of landfill leachate recirculation transforming the conventional landfill into a bioreactor. Detailed fugitive emission monitoring has allowed the evaluation of the impact of the cover type (final or temporary) and the emissions hotspots. From these results, possible remedial actions have been suggested including the more frequent monitoring of the fugitive emissions using simple and cost-effective methods (e.g., UAVs). Approximately 50% of fugitive emissions can be attributed to emissions hotspots, which reduce biogas recovery and the efficiency of temporary covers.
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•“Il Fossetto” landfill has followed the evolution of this technology for 35 years.•Mechanical Biological Treatment was effective in reducing methane potential.•The efficiency of biogas recovery was lower that expected and equal to 38 ± 14%.•The efficiency of temporary cover is hindered by methane emissions hotspots.•Hotspots account for about 50% of fugitive emissions.
Bioplastics are currently and increasingly used as substitutes of conventional plastics; furthermore, they are mainly utilised in order to cope with problems related to plastic-based pollution. ...Certified international standard methods identify the criteria a bioplastic must comply with in order to be labelled as compostable and/or biodegradable. In addition, this is particularly the case when operating under the conditions that are expected in full-scale waste facilities. However, biodegradation in natural environments occurs under a manifold of different conditions, such that the aim of research studies is to estimate the extent to which a bioplastic can biodegrade under simulated natural conditions. For this reason, specific indexes are used to quantitatively estimate the degree of degradation. In the present paper, a description of the standard methods, research methods, and the indexes used to assess the biodegradability of bioplastics under different environmental conditions is provided. By summarising the results obtained by this study, it can be concluded that: (i) biopolymers claimed as biodegradable bioplastics may not degrade in full-scale plants due to the fact that the process conditions present in industrial waste treatment plants cannot completely reproduced at lab-scale; (ii) the static conditions set by the standard methods are not representative of the dynamic processes that occur in natural or industrial environments; and (iii) experimental tests are difficult to compare to one other due to the differences in the multitude of matrixes that can be used (i.e., inocula, soils, and biopolymers).
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•Different standards (STDs) are used for testing bioplastics (BPs) biodegradability.•STDs should reflect more natural and industrial environments conditions.•The effects of microBPs on environment and human health need to be studied.•Results are not comparable due to the difference of procedures and materials used.•Research methods need to be more standardised to deliver comparable results.
The management of mature landfill leachate (MLL) represents an increasingly crucial issue to tackle. In this study, the feasibility of an integrated treatment was investigated at the laboratory scale ...using synthetic leachate with the objective of maximizing the recovery of potentially useful compounds present in leachate (especially ammonia nitrogen). First, in order to remove heavy metals, active filtration of the MLL was carried out using zero-valent iron (ZVI) mixed with either lapillus or granular activated carbon (GAC). The average removal rates for the ZVI/lapillus and the ZVI/GAC filter were 33%, 85%, 66%, and 58% and 56%, 91%, 67%, and 75% for COD, Cu, Ni, and Zn, respectively. Then, pre-treated MLL was added during the anaerobic digestion (AD) of cellulose with the aim of providing bacteria with macro (i.e., ammonia nitrogen) and micro (e.g., residual heavy metals) nutrients. After 38 days, the best performance in terms of cumulative methane production (5.3 NL) and methane yield (0.26 NL/gVSadded on average) was recorded in the reactor fed with the lowest dosage (17.9 mL/d) of MLL pre-treated by the ZVI/lapillus filter. The main issue that emerged during AD was the possible inhibition of the process linked to an excessive presence of humic substances; however, in future experiments, this problem can be solved through an optimization of the management of the whole process. The residual digestate from AD, rich in nitrogen and humic substances, may be safely used for agriculture purposes, closing the cycle of MLL management.
Permeable reactive barriers (PRBs) based on the use of zero valent iron (ZVI) represent an efficient technology for the remediation of contaminated groundwater, but the literature evidences ...“failures”, often linked to the difficulty of fully understanding the long-term performance of ZVI-based PRBs in terms of their hydraulic behavior. The aim of this paper is to provide an overview of the long-term hydraulic behavior of PRBs composed of ZVI mixed with other reactive or inert materials. The literature on the hydraulic performance of ZVI-based PRBs in full-scale applications, on long-term laboratory testing and on related mathematical modeling was thoroughly analyzed. The outcomes of this review include an in-depth analysis of factors influencing the long-term behavior of ZVI-based PRBs (i.e., reactive medium, contamination and the geotechnical, geochemical and hydrogeological characteristics of the aquifer) and a critical revision of the laboratory procedures aimed at investigating their hydraulic performance. The analysis clearly shows that admixing ZVI with nonexpansive granular materials is the most suitable choice for obtaining a long-term hydraulically efficient PRB. Finally, the paper summarizes a procedure for the correct hydraulic design of ZVI-based PRBs and outlines that research should aim at developing numerical models able to couple PRBs’ hydraulic and reactive behaviors.
The organic matter and nitrogen contents of swine wastewater (SW) can be reduced and, at the same time, a fertiliser as ammonium salt can be recovered by wastewater treatments. One of the most ...promising technique is air stripping (AS). However, the operational parameters (pH, temperature and air flow rate) of AS must be optimised, in order to maximise the ammonia recovery and reduce the requirement of chemicals and energy.
In this study 27 batch tests at laboratory scale were carried out on real SW, varying (individually or simultaneously) the pH (not adjusted, 8 and 10), temperature (ambient, 40 and 60 °C) and flow rate (0, 1 and 5 Lair LSW−1 min−1) of AS; the changes in soluble COD (sCOD) and total ammonia nitrogen (TAN) concentrations were evaluated in response to the parameters adjustments. For the tests including AS, the ammonium sulphate recovered was also measured.
In general (about 50% of the tests), more than 80% of TAN was removed. Most of these tests were carried out with pH and temperature control and AS at the highest flow rate; the highest efficiency was found for a combination of chemical, thermal and aeration treatments. For a few tests with the same process control, an increase (up to 50%) or a very limited (less than 10%) decrease of sCOD were detected; therefore, these treatments can be adopted prior of anaerobic digestion of SW. A high flow rate, which increases the removal efficiency of both sCOD and TAN, should be adopted, when AS is used as pre-treatment of activated sludge or lagooning plants. Very high amounts (over 80% of the theoretical yield) of ammonium sulphate were recovered by AS at the maximum air flow rate (5 Lair LSW−1 min−1), which would provide a nitrogen fertiliser at a sustainable cost.
•Swine wastewater (SW) treatments are needed to avoid environmental pollution.•The operational parameters (pH, T and air flow rate) of the treatments have been optimised.•TAN removal was over 80% with pH and temperature control, and the highest air stripping flow rate.•Some treatments increasing soluble COD are suggested prior of anaerobic digestion of SW.•High amounts of ammonium sulphate have been recovered by AS at the maximum air flow rate.
In order to overcome anaerobic digestion (AD) inhibition due to the large nitrogen content of swine wastewater (SW), air stripping (AS) and other chemical and physical pretreatments were applied on ...raw SW before AD. The efficiency of these pretreatments on both ammonia removal—recovering ammonia salts to be used as fertilizers in agriculture—and the increase of methane production were assessed in batch tests. Since the pH, temperature, and air flow rate heavily influence AS efficiency and the composition of treated SW, these parameters were set individually or in combination. In more detail, the pH was increased from the natural value of SW to 8 or 10, temperature was increased from the room value to 40 °C, and the air flow rate was increased from zero to 5 Lair LSW−1 min−1. AS was generally more efficient at removing ammonia (up to 97%) from raw (non-treated) SW compared to the other treatments. However, the tested pretreatments were not as efficient as expected in increasing the biogas production, because the methane yields of all pretreated substrates were lower (by about 10–50%) to compared raw SW. The inhibitory effect on AD could have been due to the lack of nutrients and organic matter in the substrate (due to the excessive removal of the pretreatments), the concentration of toxic compounds (such as metal ions or furfural due to water evaporation), and an excess of alkali ions (used to increase the pH in AS). Overall, AS can be considered a sustainable process for the recovery of ammonium sulphate and the removal of other polluting compounds (e.g., organic matter) from SW. Conversely, the use of AS and other chemical and/or thermal processes tested in this study as pretreatments of SW before AD is not advised because these processes appear to reduce methane yields.
The problems linked to plastic wastes have led to the development of biodegradable plastics. More specifically, biodegradable bioplastics are the polymers that are mineralized into carbon dioxide, ...methane, water, inorganic compounds, or biomass through the enzymatic action of specific microorganisms. They could, therefore, be a suitable and environmentally friendly substitute to conventional petrochemical plastics. The physico-chemical structure of the biopolymers, the environmental conditions, as well as the microbial populations to which the bioplastics are exposed to are the most influential factors to biodegradation. This process can occur in both natural and industrial environments, in aerobic and anaerobic conditions, with the latter being the least researched. The examined aerobic environments include compost, soil, and some aquatic environments, whereas the anaerobic environments include anaerobic digestion plants and a few aquatic habitats. This review investigates both the extent and the biodegradation rates under different environments and explores the state-of-the-art knowledge of the environmental and biological factors involved in biodegradation. Moreover, the review demonstrates the need for more research on the long-term fate of bioplastics under natural and industrial (engineered) environments. However, bioplastics cannot be considered a panacea when dealing with the elimination of plastic pollution.
Despite recent therapeutic advances, there is an unmet need in cardiovascular disease prevention. Clinical trials and meta-analyses have established that LDL-C lowering, particularly by statin ...therapy, reduces the progression of coronary atherosclerosis and the risk of coronary events. Insufficient LDL-C reduction and high residual risk in a significant proportion of statin-treated patients signify that additional therapies are required to deliver more effective coronary care. Pharmacological inhibition of cholesterol absorption (with ezetimibe) and PCSK9 activity (with evolocumab or alirocumab) provides potentially useful approaches for the therapeutic modulation of LDL-C metabolism in statin-treated patients. In recent trials, combination strategies involving a statin and non-statin agent (ezetimibe or evolocumab) have been shown to promote coronary atherosclerosis regression and improve cardiovascular outcomes in patients with moderate-to-high cardiovascular risk. This review summarizes recent evidence on the effects of dual lipid-lowering therapy on coronary atherosclerosis.
•Plasma LDL-C is a central determinant of the progression of the atherosclerotic disease and its complications.•Lowering LDL-C by statins in individuals with CAD produces the stabilization and regression of coronary atherosclerosis.•Dual lipid-lowering therapy is superior in inducing plaque regression compared with statin monotherapy.•Controversies regarding the effect of non-statin agents on plaque composition have to be fully elucidated.•The selection process for patients that may benefit from dual lipid-lowering therapy has to be further implemented.
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