1,721,003 research outputs found
Landfill GHG reduction through different microbial methane oxidation biocovers
Full text linkEmissions from daily and final covers of municipal solid waste (MSW) landfills can produce significant impacts on local and global environments. Simplifying, landfills can cause local impacts with odor emissions and global impacts with GHGs. This work focuses on hydrogen sulfide (H2S) and methane (CH4) emissions, with the aim of studying how it is possible to reduce their impacts by means of biofiltration systems. Both field and laboratory investigations have been carried out in Casa Rota Landfill (Tuscany, Italy). In the field trials, four pilot-scale biocovers made of compost from a source-selected organic fraction (SS compost), compost from a mechanical biological treatment plant-the residual fractions of the MSW, a mixed compost (SS-MSW compost) and sand were monitored in the daily cover area of the landfill, where high emissions were detected. Results showed that high CH4 and H2S emissions reductions occurred in the mixed SS-MSW compost plot, given a maximum methane oxidation efficiency of greater than 98% and an average oxidation efficiency of about 75%. To assess the specific oxidation rate, laboratory tests using SS-MSW compost sampled from the biocovers were done
Evaluation of biological processes performances using different stability indices
Full text linkThe EU's Circular Economy Policy Package aims to minimize waste production in accordance with the Circular Economy concept. In this respect, organic waste valorization through composting and anaerobic digestion process represents a proven solution for converting biomass in bio-based products with high fertilizing and amendment properties. In order to optimize process' performances and reuse the bio-products, biological stability index evaluation of the final products plays a key role. Several respiration tests are currently used for the determination of biological stability and the need to define homogenized regulations both at national and European level, in order to outline harmonized rules for biological stability determination, is becoming increasingly indispensable. Among these, some approaches measure respirometric activity by estimating oxygen uptake rate (SOUR and DRI test) and by recording the maximum temperature achieved by the biomass during the degradation process (Self-Heating test). Others assess the decomposition degree of organic waste by determining the residual biogas potential production (BMP test). This work aims at evaluating biological stability of different organic matrices such as compost, digestate and mixture of them in order to compare different respirometric techniques and define possible correlations between them and their suitability depending on the substrates analyzed. The results show that among the different stability tests analyzed in this work, there is a good linear correlation that allows to affirm a direct proportionality both between DRI and Self-heating test and BMP and SOUR test. The results suggest that all the respirometric methods considered in this study could be used as indicators of the biological stability degree of an organic substrate and are therefore interchangeable with each other, providing the same value of biological stability degree. Nevertheless, future studies on stability index determination could be carried out in order to confirm the results obtained from this work
Comparison of single-stage and two-stage anaerobic Co-Digestion of food waste and activated sludge for hydrogen and methane production
Full text linkIn this study, the co-digestion of food waste and activated sludge was evaluated in a two-stage anaerobic system and compared to the traditional single-stage process. The two-stage system was composed by two reactors connected in series able to perform the fermentative and the methanogenic phases separated. Experiments were carried out in semi-continuous mode under mesophilic conditions (37 °C). The two-stage technology achieved an overall improvement of the anaerobic performances. Results highlighted an increase in biogas production and volatile solids degradation of 26% and 9%, respectively. Considering the whole two-stage system, i.e. the sum of the biogas productions of the first and the second digester, these percentages increased up to 35.0%. Concerning gas quality, the two-stage system achieved a hydrogen rich biogas in the first fermentative reactor and an improvement of methane content in the second methanogenic digester. The average methane content shifted from 61.2% to 70.1%. The highest methane production of the two-stage process was due to improved substrate hydrolysis, with increased amounts of volatile fatty acids made readily available in the second stage
Experimental evaluation of two different types of reactors for CO2 removal from gaseous stream by bottom ash accelerated carbonation
No full textLow methane content landfill gas may be enriched by removing carbon dioxide. An innovative process, based on carbon dioxide capture and storage by means of accelerated carbonation of bottom ash is proposed and studied for the above purpose. Within this research framework we devoted a preliminary research activity to investigate the possibility of improving the way the contact between bottom ash and landfill gas takes place: this is the scope of the work reported in this paper. Two different types of reactors – fixed bed and rotating drum – were designed and constructed for this purpose. The process was investigated at laboratory scale. As the aim of this phase was the comparison of the performances of the two different reactors, we used a pure stream of CO2 to preliminarily evaluate the reactor behaviors in the most favorable condition for the process (i.e. maximum CO2 partial pressure at ambient condition). With respect to the simple fixed bed reactor concept, some modifications were proposed, consisting of separating the ash bed in three layers. With the three layer configuration we would like to reduce the possibility for the gas to follow preferential paths through the ash bed. However, the results showed that the process performances are not significantly influenced by the multiple layer arrangement. As an alternative to the fixed bed reactor, the rotating drum concept was selected in order to provide continuous mixing of the solids. Two operating parameters were considered and varied during the tests: the filling ratio and the rotating speed. Better performances were observed for lower filling ratio while the rotating speed showed minor importance. Finally the performances of the two reactors were compared. The rotating drum reactor is able to provide improved carbon dioxide removal with respect to the fixed bed one, especially when the rotating reactor is operated at low filling ratio values and slow rotating speed values. Comparing the carbon dioxide specific removal obtained by using the rotating reactor (35–37 g/kgBA), in the best operating conditions, with that measured for the fixed bed reactor (21–23 g/kgBA), an increase of about 61–66% is observed
Risk assessment of a methane oxidizing biofilter for reducing landfill gas emissions from a post-closure landfill
Full text linkThis study focuses on the assessment of volatile organic compounds (VOCs) and odor compounds emissions from a post-closure landfill. A human health risk assessment and an air quality evaluation were performed to compare two different landfill gas management scenarios and to assess whether a methane oxidizing biofilter mitigates the risk from inhalation exposure to VOCs and odor emissions. Three specific monitoring campaigns were performed: one sample of raw biogas at the biofilter inlet and three air samples from the biofilter surface were collected and analyzed to determine the concentration levels of VOCs, H2S and odor compounds accordingly to US EPA, 1995 and US EPA TO-15, 1999, NIOSH 6013:1994, and dynamic olfactometry (EN 13725:2003), respectively. Concerning the raw biogas, five odor compounds were selected from the mixture and then the odor activity value (OAV) was evaluated. CALPUFF dispersion model was used to evaluate the VOCs concentration in air at eleven sensitive receptors. In the risk assessment, cyclohexane, n-hexane, 2-methylpentane, 3-methylpentane, benzene, xylenes, toluene, dichlorodifluoromethane, vinyl chloride were selected to evaluate the hazard index (HI) for non-carcinogenic compounds and the cancer risk (R) for carcinogenic compounds (benzene). The results showed that for both LFG management scenarios HI and R resulted negligible (HI≤1 and R<10-6) and the odor concentration resulted always below 1 UO m-3 at each sensitive receptor. Furthermore, emerged that the biofilter reduce HI and R on average by 93% and 17%
Centralization of wastewater treatment in a tourist area: A comparative LCA considering the impact of seasonal changes
No full textNowadays, environmental protection has become a topic of primary importance, and the interest in wastewater treatment plants (WWTPs) has increased due to the need for a paradigm shift from linear to circular economy. The centralization level of wastewater infrastructure is the basis for a successful system. The aim of this study was to investigate the environmental impacts generated from the centralized treatment of wastewater in a tourist area in central Italy. The combined use of BioWin 6.2 simulation software and life cycle assessment (LCA) methodology was implemented to evaluate the potential connection of a small decentralized WWTP to a medium-size centralized facility. Two different scenarios (decentralized system, corresponding to the current situation, and centralized) were evaluated in two separate periods: high season (HS), corresponding to the main tourist season, and low season (LS), which is the period before the main tourist season. Two sensitivity analyses were conducted, assuming different N2O emission factors, and considering the period at the end of tourist season, respectively. Although with modest advantages (up to −6 % in pollutant emissions), WWTP connection was the best management option in 10 out of 11 indicators in HS, and 6 out of 11 categories in LS. The study showed that wastewater centralization was promoted by scale factors in HS, as the most impactful consumptions decreased as the degree of centralization increased; on the other hand, the decentralized system was less penalized in LS, as small WWTP was less stressed and energy consuming in this period. Sensitivity analysis confirmed the results obtained. Site-specific conditions can lead to conflicting circumstances, as key parameters may have different behaviors depending on seasonal variations, and the degree of centralization in tourist areas should be addressed by distinguishing separate periods, based on changes in tourist flows and pollution loads
Methane oxidation of residual landfill gas in a full-scale biofilter: human health risk assessment of volatile and malodours compound emissions
No full textA human health risk assessment was performed to evaluate if a biofilter for the biological methane oxidation reduces the risk from exposure to landfill gas emissions and improves the air quality mitigating odour emissions from an aftercare landfill. Accordingly, three different scenarios of landfill gas management were defined, 9 volatile organic compounds (VOCs) (cyclohexane, n-hexane, 2-methylpentane, 3-methylpentane, benzene, xylenes, toluene, dichlorodifluoromethane, vinyl chloride) were identified and using the CALPUFF dispersion model; the pollutant concentration at eleven sensitive receptors was determined. Consequently, the risk (for cancer and non-cancer compounds) was assessed applying the methodology proposed by USEPA 2009. From one hand, to determine concentration and emission rates of VOCs and hydrogen sulphide, a sample of raw landfill gas and three air samples from the biofilter surface were collected with dynamic flux chamber method and analysed in accordance with US EPA, 1986 and USEPA TO-15, 1999. To the other hand, odour emissions were assessed based both on chemical and dynamic olfactometric measurements (EN 13725:2003). The field surveys results showed a reduction of the cancer risk on average by 79% and of the hazard quotient on average by 92%. In contrast, the results of olfactometry measurements showed a lower efficiency on odour reduction than the target value of 70%. Nonetheless, the odour concentration was always far below 300 uoE m−3 at the biofilter surface and odour concentration never exceed 1 uoE m−3 at the sensitive receptors
Methane oxidation efficiency in biofiltration systems with different moisture content treating diluted landfill gas
Full text linkThis study investigates the influence of moisture content on the potential oxidation efficiency of methane (CH4) of biofiltration systems treating landfill gas containing high oxygen concentrations. Column tests filled with compost with different moisture contents (20%, 30%, and 40%) loaded with different methane flows were set up on a laboratory scale. Analyzing the results the following evidences can be summarized: With low methane load (<100 g CH4m-2d-1), a moisture content of 20% was not enough to support bacterial activity, while a moisture content of 40% advantaged the compost respiration assisting it to become the dominating process; with higher methane load (100-300 g CH4 m-2 d-1), a moisture content of 30% resulted in an optimal value to support methanotrophic activity showing the highest CH4 concentration reduction; moving on to a CH4 load above 300 g CH4 m-2 d-1, the inhibition of methanotrophic activity emerged independently to the moisture content of the filter media. The optimal configuration is obtained for a moisture content of 30% and in the case of flows below 200 g CH4 m-2 d-1 for which the oxidation efficiency results higher than 80%
Environmental impacts of dry anaerobic biorefineries in a Life Cycle Assessment (LCA) approach
No full textThe organic fraction of municipal solid waste (OFMSW) represents the 34% of European waste and the overall share is going to increase since separate collection will be implemented across the member states. There is still lack of studies on environmental impacts of dry anaerobic biorefineries applying innovative solvents to produce biopolymers (e.g., polyhydroxyalkanoates – PHA) from the OFMSW. A comparative Life Cycle Assessment (LCA) analysis was applied to assess the environmental impacts of a conventional management strategy to recover biomethane and compost from the OFMSW with a dry anaerobic biorefinery recovering biomethane, fertilizers and PHAs. Four approaches to recover PHAs were included in the study, comprising two innovative and environmentally sustainable extraction methods (i.e., solvent extraction with ethyl acetate (EA) and ionic liquids (ILs)). The inventory data were derived from an Italian case study plant, while the data for modelling the PHA selection/accumulation and PHA extraction processes were retrieved from the literature. The comparison revealed that, at the current technological readiness level (TRL), the conventional management strategy has better environmental performances than the novel approach producing PHAs. For example, biomethane recovery, for which a substitution with natural gas was assumed, showed the highest avoided impacts for abiotic depletion of fossil fuel (65.5%), global warming (57.4%) and ozone layer depletion (65.4%) categories. PHA recovery scenarios showed high environmental impacts in all categories linked to natural resource depletion. PHA extraction with EA proved to be the most environmentally sustainable and promising technique towards an industrial application
Environmental assessment of gasification and green hydrogen potential role in waste management decarbonization
No full textAchieving sustainability involves implementing a circular economy model and decarbonizing the waste management sector. The development of innovative technologies that enable the reduction of emissions and resource recovery is one of the sector's greatest challenges. From this perspective, the waste-to-methanol (WtM) process represents a viable prospect, the potential environmental impacts of which have never been studied from a life-cycle perspective. A cradle-to-grave LCA analysis was conducted, studying WtM technology and its potential implementation of green hydrogen (WtM-GH) in the process, through a comparison with traditional waste-to-energy (WtE). The results showed that WtM-GH performs best for global impacts, with a global warming potential of 3.52·107 kgCO2eq instead of 1,04·108 kgCO2eq proper of the WtE. Positive effects take place also for the fossil resource scarcity. Looking for non-toxic regional/local impacts WtE represents the best scenario, with the best performance on water consumption (7.96·107 m3) and ionising radiation (2.82·107 kBq Co-60eq). Cumulative impact results, obtained through the normalization, found that WtM is the best scenario, thanks to the less toxic impact compared to the other two, especially for freshwater ecotoxicity (5.26·106 kg 1,4-DCB) and marine ecotoxicity (6.73·106 kg 1,4-DCB). WtM-GH allows the production of 1366 kg of methanol per ton of Refuse Derived Fuel, thanks to the conversion of the entire CO2 contained in the waste, enhancing the value of by-products and carbon credits on the market and making the process more economically sustainable
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