Landfill gas generation after mechanical biological treatment of municipal solid waste. Estimation of gas generation rate constants

Mechanical biological treatment (MBT) of residual municipal solid waste (RMSW) was investigated with respect to landfill gas generation. Mechanically treated RMSW was sampled at a full-scale plant and aerobically stabilized for 8 and 15 weeks. Anaerobic tests were performed on the aerobically treated waste (MBTW) in order to estimate the gas generation rate constants (k,y(-1)), the potential gas generation capacity (L(o), Nl/kg) and the amount of gasifiable organic carbon. Experimental results show how MBT allowed for a reduction of the non-methanogenic phase and of the landfill gas generation potential by, respectively, 67% and 83% (8 weeks treatment), 82% and 91% (15 weeks treatment), compared to the raw waste. The amount of gasified organic carbon after 8 weeks and 15 weeks of treatment was equal to 11.01+/-1.25kgC/t(MBTW) and 4.54+/-0.87kgC/t(MBTW), respectively, that is 81% and 93% less than the amount gasified from the raw waste. The values of gas generation rate constants obtained for MBTW anaerobic degradation (0.0347-0.0803y(-1)) resemble those usually reported for the slowly and moderately degradable fractions of raw MSW. Simulations performed using a prediction model support the hypothesis that due to the low production rate, gas production from MBTW landfills is well-suited to a passive management strategy.     

Reducing acid leaching of manganiferous ore: effect of the iron removal operation on solid waste disposal

The process of reducing acid leaching of manganiferous ore is aimed at the extraction of manganese from low grade manganese ores. This work is focused on the iron removal operation. The following items have been considered in order to investigate the effect of the main operating conditions on solid waste disposal and on the process costs: (i) type and quantity of the base agent used for iron precipitation, (ii) effective need of leaching waste separation prior to the iron removal operation, (iii) presence of a second leaching stage with the roasted ore, which might also act as a preliminary iron removal step, and (iv) effect of tailings washing on the solid waste classification. Different base compounds have been tested, including CaO, CaCO3, NaOH, and Na2CO3. The latter gave the best results concerning both the precipitation process kinetics and the reagent consumption. The filtration of the liquor leach prior to iron removal was not necessary, implying significant savings in capital costs. A reduction of chemical consumption and an increase of manganese concentration in the solution were obtained by introducing secondary leaching tests with the previously roasted ore; this additional step was introduced without a significant decrease of global manganese extraction yield. Finally, toxicity characteristic leaching procedure (TCLP) tests carried out on the leaching solid waste showed: (i) a reduction of arsenic mobility in the presence of iron precipitates, and (ii) the need for a washing step in order to produce a waste that is classifiable as not dangerous, taking into consideration the existing Environmental National Laws.     

Perceptions of industrial risk and emergency management procedures in Hazmat Logistics: A qualitative mental model approach

In the industrial risk field, Hazmat Logistics research is growing as a sector of special relevance. The road transport of these substances is an activity with an elevated risk, involving drivers, logistics systems, industries, infrastructures, urban areas, etc.In the study of risk and safety of the logistics of hazardous materials there is a special relevance for new and complex elements, as human factors and mental models involved in managing critical incidents ‘‘on the road”. Moreover, the ‘‘emergency management training” of human resources in this field is often limited, and this represents another factor of vulnerability.In collaboration with SBG (one of the leading European Hazmat Logistics corporations), we developed a quali-quantitative study on cognitive representations and semantic perceptions of risk and emergency management procedures in tanker drivers. The main innovation of the study, with the direct involvement of the stakeholder and 47 drivers, is represented by the construction and use of ‘‘ad hoc” psychometrical and knowledge-elicitation, allowing a deeper analysis of workers’ mental models.The application of PCP tools of adapted RepGrid and Landfield Laddering Procedures allows to analyze some of the main qualitative structures of mental models held by drivers about Hazmat Logistics. Through the analysis of these mental models, it could become possible to set up efficient preventive actions for this type of industrial risk. We are going to discuss the consequences of these findings and methodological approaches for the industrial risk-and-safety field.     

Decomposition and oxidation of sodium 3,5,6-trichloropyridin-2-ol in sub- and supercritical water

Sodium 3,5,6-trichloropyridin-2-ol (STCP) is a necessary precursor compound for the production of chlorpyrifos and triclopyr, which are extensively used as pesticide and herbicide, respectively. In the process of STCP production, however, large amount of wastewater containing STCP is discharged, which causes increasingly environmental concerns. Therefore, it is of great significance to develop a rapid and effective method for the disposal of containing STCP contaminants. In this work, the thermal decomposition of STCP in sub- and supercritical water was investigated using a continuous tubular reactor. While STCP was stable below 280 °C, it could be effectively decomposed at elevated temperature. FT-IR spectra of the decomposition products indicated that the pyridine ring structure in the STCP molecule was stable even at temperatures up to 400 °C. The decomposition reaction was mainly caused by the substitution of Cl groups in the STCP molecule with OH groups, resulting in polyhydroxylated pyridines as the major decomposition product. Moreover, high pressure favored the substitution reaction. To completely decompose STCP into non-toxic or low toxic compounds, supercritical water oxidation (SCWO) was employed to evaluate the oxidation of STCP using H₂O₂ as an oxidant. It was found that STCP could be completely oxidized to H₂O, CO₂ and corresponding inorganic ammonium salts with an oxidation rate of 99%.     

Effect of a global warming-induced increase in typhoon intensity on urban productivity in Taiwan

A number of scientists have recently conducted research that shows that tropical cyclone intensity is likely to increase in the future due to the warming effect of greenhouse gases on surface sea temperatures. The aim of this paper is to establish what would be the likely decrease in the productivity of urban workers due to an increase in tropical cyclone-related downtime. The methodology used simulates future tropical cyclones by magnifying the intensity of historical tropical cyclones between the years 1978 and 2008. It then uses a Monte Carlo simulation to obtain the expected number of hours that a certain area can expect to be affected by winds of a given strength. It shows how annual downtime from tropical cyclones could increase from 1.5% nowadays to up to 2.2% by 2085, an increase of almost 50%. This decrease in productivity could result in a loss of up to 0.7% of the annual Taiwanese GDP by 2085.     

Simultaneous measurements of formaldehyde and nitrous acid in dews and gas phase in the atmosphere of Santiago,Chile

The amounts of formaldehyde and nitrous acid (HONO) in gas phase and dews of Santiago de Chile were simultaneously measured. Formaldehyde concentrations values in the liquid phase (dews) correlate fairly well with those in the gaseous phase and are even higher than those expected from gas–dew equilibrium. On the other hand, nitrite concentrations in dews were considerably smaller (ca. 15 times) than those expected from the gas-phase concentrations. This under-saturation is attributed to diffusion limitations due to the relatively large HONO solubility. In agreement with this, under-saturation increases with the rate of dew formation and the pH of the collected waters, factors that should increase the rate of gas to liquid HONO transfer required to reach equilibrium.     

Solid state speciation and potential bioavailability of depleted uranium particles from Kosovo and Kuwait

A combination of synchrotron radiation based X-ray microscopic techniques (μ-XRF, μ-XANES, μ-XRD) applied on single depleted uranium (DU) particles and semi-bulk leaching experiments has been employed to link the potential bioavailability of DU particles to site-specific particle characteristics. The oxidation states and crystallographic forms of U in DU particles have been determined for individual particles isolated from selected samples collected at different sites in Kosovo and Kuwait that were contaminated by DU ammunition during the 1999 Balkan conflict and the 1991 Gulf war. Furthermore, small soil or sand samples heavily contaminated with DU particles were subjected to simulated gastrointestinal fluid (0.16 M HCl) extractions. Characteristics of DU particles in Kosovo soils collected in 2000 and in Kuwait soils collected in 2002 varied significantly depending on the release scenario and to some extent on weathering conditions. Oxidized U (+6) was determined in large, fragile and bright yellow DU particles released during fire at a DU ammunition storage facility and crystalline phases such as schoepite (UO₃·2.25H₂O), dehydrated schoepite (UO₃·0.75H₂O) and metaschoepite (UO₃·2.0H₂O) were identified. As expected, these DU particles were rapidly dissolved in 0.16 M HCl (84 ± 3% extracted after 2 h) indicating a high degree of potential mobility and bioavailability. In contrast, the 2 h extraction of samples contaminated with DU particles originating either from corrosion of unspent DU penetrators or from impacted DU ammunition appeared to be much slower (20–30%) as uranium was less oxidized (+4 to +6). Crystalline phases such as UO₂, UC and metallic U or U–Ti alloy were determined in impacted DU particles from Kosovo and Kuwait, while the UO_2,34 phase, only determined in particles from Kosovo, could reflect a more corrosive environment. Although the results are based on a limited number of DU particles, they indicate that the structure and extractability of DU particles released from similar sources (metallic U penetrators) will depend on the release scenarios (fire, impact) and to some extent environmental conditions. However, most of the DU particles (73–96%) in all investigated samples were dissolved in 0.16 M HCl after one week indicating that a majority of the DU material is bioaccessible.     

Mutagenic properties of PM2.5 urban pollution in the Northern Italy: The nitro-compounds contribution

PM2.5 is the breathable fraction of the particulate matter and some adverse health effects, such as respiratory functionality, cardiological diseases and cancer, can be in some measure attributable to this risk factor exposure. Some of the most carcinogen compounds transported by PM2.5 are nitro-compounds. In this study, a strengthened in vitro bioassay — able to predict the mutagenic/carcinogenic activity of the environmental mixtures — was conducted on PM2.5 organic extracts to define the nitro-compounds burden. PM2.5 air pollution was daily monitored, during 2006, in three cities located in the Northern part of Italy (Torino, Pavia and Verona) and the mutagenic properties of the PM2.5 organic extracts were assessed with the Ames test. The bacterial used in this study were three Salmonella typhimurium strains: TA98, nitroreductase-less mutant TA98NR and YG1021 carrying a nitroreductase-producing plasmid. The annual PM2.5 mean level measured in Torino was 46.5 (± 31.6) μg/m³, in Pavia 34.8 (± 25.1) μg/m³, and in Verona 37.3 (± 27.8) μg/m³, while the mutagenicity expressed as TA98 net reverants/m³ was 28.0 (± 22.1), 28.3 (± 24.9), and 34.2 (± 30.9) respectively. Monthly pool bioassays, conducted with the three different strains, showed a greater mutagenic response of the YG1021 in each city. The relationship among the mutagenic answers for YG1021:TA98:TA98NR was about 6:3:1 (p < 0.001). Over nitroreductase activity enhanced the response of 2.2, 2.0 and 1.7 times for Torino, Pavia, and Verona (ANOVA Torino p < 0.05) respectively. Without nitroreductase activity the genotoxicity was limited. These biological findings are able to describe a relevant role played by the nitro compounds in the mutagenic properties of the urban PM2.5 in the Padana plain; moreover the bacterial nitroreductase plays a predominant role in DNA interaction primarily for Torino PM2.5 extracts.