Oxy-fuel coal combustion—A review of the current state-of-the-art

Carbon dioxide emissions will continue being a major environmental concern due to the fact that coal will remain a major fossil-fuel energy resource for the next few decades. To meet future targets for the reduction of greenhouse gas (GHG) emissions, capture and storage of CO₂ is required. Carbon capture and storage technologies that are currently the focus of research centres and industry include: pre-combustion capture, post-combustion capture, and oxy-fuel combustion. This review deals with the oxy-fuel coal combustion process, primarily focusing on pulverised coal (PC) combustion, and its related research and development topics. In addition, research results related to oxy-fuel combustion in a circulating fluidised bed (CFB) will be briefly dealt with.During oxy-fuel combustion, a combination of oxygen, with a purity of more than 95 vol.%, and recycled flue gas (RFG) referred to as oxidant is used for combusting the fuel producing a gas consisting of mainly CO₂ and water vapour, which after purification and compression, is ready for storage. The high oxygen demand is supplied by a cryogenic air separation process, which is the only commercially available mature technology. The separation of oxygen from air as well as the purification and liquefaction of the CO₂-enriched flue gas consumes significant auxiliary power. Therefore, the overall net efficiency is expected to be decreased by 8–12% points, corresponding to a 21–35% increase in fuel consumption. Alternatively, ion transport membranes (ITMs) are proposed for oxygen separation, which might be more energy efficient. However, since ITMs are far away from becoming a mature technology, it is widely expected that cryogenic air separation will be the selected technology in the near future. Oxygen combustion is associated with higher temperatures compared with conventional air combustion. Both fuel properties as well as limitations of steam and metal temperatures of the various heat exchanger sections of the boiler require a moderation of the temperatures in the combustion zone and in the heat-transfer sections. This moderation in temperature is accomplished by means of recycled flue gas. The interdependencies between the fuel properties, the amount and temperature of the recycled flue gas, and the resulting oxygen concentration in the combustion atmosphere are reviewed.The different gas atmosphere resulting from oxy-fuel combustion gives rise to various questions related to firing, in particular, with respect to the combustion mechanism, pollutant reduction, the risk of corrosion, and the properties of the fly ash or its resulting deposits. In this review, detailed nitrogen and sulphur chemistry was investigated in a laboratory-scale facility under oxy-fuel combustion conditions. Oxidant staging succeeded in reducing NO formation with effectiveness comparable to that typically observed in conventional air combustion. With regard to sulphur, a considerable increase in the SO₂ concentration was measured, as expected. However, the H₂S concentration in the combustion atmosphere in the near-flame zone increased as well. Further results were obtained in a pilot-scale test facility, whereby acid dew points were measured and deposition probes were exposed to the combustion environment. Slagging, fouling and corrosion issues have so far been addressed via short-term exposure and require further investigation.Modelling of PC combustion processes by computational fluid dynamics (CFD) has become state-of-the-art for conventional air combustion. Nevertheless, the application of these models for oxy-fuel combustion conditions needs adaptation since the combustion chemistry and radiative heat transfer is altered due to the different combustion gas atmosphere.CFB technology can be considered mature for conventional air combustion. In addition to its inherent advantages like good environmental performance and fuel flexibility, it offers the possibility of additional heat exchanger arrangements in the solid recirculation system, i.e. the ability to control combustion temperatures despite relatively low flue gas recycle ratios even when combusting in the presence of high oxygen concentrations.     

How effective are current household recycling policies? Results from a national survey of U.S. households

This paper analyzes a unique dataset collected during a 2006 national survey of U.S. households to explore the effectiveness of common household recycling policies for metals, glass, and plastics: curbside recycling, drop-off recycling, deposit–refund systems (bottle bills), and marginal pricing for household waste. After estimating either generalized ordered logit or multinomial logit models, we find that the most important determinants of household recycling are people's attitudes toward recycling. Our results also suggest that omitting internal variables (perceived recycling obstacles and benefits as well as moral considerations) may bias policy coefficients. Socio-economic variables are typically not statistically significant, with the exceptions of young adults and of African Americans who tend to recycle less than others. Policies with the largest odds ratios are curbside recycling (which is further strengthened if recycling is mandatory), followed by the presence of drop-off collection centers nearby. Bottle bills are also statistically significant but their odds ratios are smaller, possibly because refunds are relatively small and typically do not change for years. Finally, marginal pricing appears to have a limited impact on recycling. These results suggest avenues for improving household recycling at a time when recycling rates appear to be plateauing.     

Static magnetic field action on some markers of inflammation in animal model system—in vivo

Experimentally induced acute inflammation in rats is a good model system which includes the complexity and dynamics of the processes; moreover there are many defined markers for following and estimating changes in an observed system. In this paper, we discuss an in vivo model of acute inflammation induced by carrageenan. Carrageenan-induced paw edema is a model of non-infectious acute inflammatory reaction to assess the contribution of mediators involved in vascular changes associated with acute inflammation and potential treatments. A complex approach into the investigation of possible effects of static magnetic fields (SMF) action on experimentally induced acute inflammation in rats (by measurements of the levels of specific stress markers) is very important in understanding the possible inflammatory mitigation effects, pain relief, and oxidative stress state of an organism. This approach could help for better understanding of the possible mechanisms of interaction of dynamic processes such as inflammation healing and pain relief with external SMF (25 mT at 10, 20 and 30 min exposure time). Results indicate that SMF with B = 25 mT for 30 min diminished the inflammatory process and decreased the levels of inflammatory markers (fibrinogen) and stress markers (ACTH, Cor) into the blood plasma in rats as when compared with sham exposed animals. The exact mechanism by which SMF contributes to the acceleration of inflammatory healing and decrease of inflammation markers in blood plasma in rats still remains unclear. We assume that two possible mechanisms exist. One is the direct interaction of SMF with free active oxygen forms (free radicals) affected by their membrane processes and related with the physiological functions. Another possible mechanism might be related to dynamic regulation of inflammation healing process.     

Equity in neighbourhood walkability? A comparative analysis of three large U.S. cities

This study examines the spatial and statistical relationships between social vulnerability (SV) and neighbourhood walkability across three large U.S. cities with different urban typologies and development patterns: Charlotte, NC (a low-density, fast-growing “Sunbelt” city); Pittsburgh, PA (a moderate density, shrinking “Rust Belt” city); and Portland, OR (a progressive West Coast city known for its sprawl-containment policies). Binary logistic regression, independent-samples t-tests, and mapping techniques are employed to determine whether neighbourhoods with high SV (i.e. older populations, higher poverty rates, more service occupations, lower educational attainment, and a higher proportion of minorities) are as likely as those with low SV to exhibit a high degree of walkability. The publically available Walk Score® metric, based on proximity to amenities, street network connectivity, and density, was used as a proxy for neighbourhood walkability. The results indicate significant variability among cities, with Charlotte exhibiting the greatest potential for inequitable access to walkable urban environments and the most prominent concentration of “walk-vulnerable” block groups (BGs) with high SV and low walkability. Both Portland and Pittsburgh exhibited more equitable access when comparing BGs with high and low SV; however, they each presented unique spatial patterns, visualised using a series of maps.     

Cloning and expression of α-amylase in E. coli: genesis of a superior biocatalyst for substrate-specific MFC

One of the most practical approaches for establishing a successful microbial fuel cell (MFC) is to fasten the oxidation rate of the substrate by the microorganisms to get quick paced electron transfer between microbes and electrode. A genetically modified Escherichiacoli, overexpressing α-amylase, is constructed and applied as biocatalyst in MFC using starch as substrate. The results are compared with nonrecombinant, native E.coli. The results show better performance for the MFC containing the recombinant strain demonstrated by higher power density (PD), lower resistance, and significant electrochemical activity. Maximum PD has been recorded as 279.04 mW m^?2 compared to 120.33 Mw m^?2 for the MFC operated with nonrecombinant E.coli. The impedance results also suggest the effectiveness of the recombinant strain by lowering the internal resistance by more than half order as compared to the nonrecombinant one. These results affirm that the engineered strain can be used as a superior biocatalyst in contrast to the native strain and by using the technique of genetic alteration; gene of interest can be inserted based on the substrate to be treated. So, this work gives a useful insight for accomplishing successful MFC operation with the use of bacterial stains engineered at the molecular level.     

An affordable green energy source—Evolving through current developments of organic,dye sensitized,and perovskite solar cells

Intensive R&D efforts made in solar photovoltaic area has enabled Si, GaAs, CdTe, and CIGS devices exhibiting nearly ideal efficiencies. However, cost incurred per unit energy does not allow them to qualify for alternate energy source besides environmental issues at production floors. Consequently, search is still continuing not only to reduce cost by improved efficiency, reduced materials cost, and simplified processing resulting in a cleaner and greener technology. Current successes in organic, dye-sensitized, and perovskite solar cells with efficiencies in 10–15% range raise concrete hope for evolving a low cost and green technology involving solution processable organic/inorganic compounds extendable to roll-to-roll production. The current status and future prospects of these three promising routes are reviewed here highlighting the possibility of an emerging alternate green energy source to supplement the conventional ones at commercial level.     

Geological storage of CO2 in saline aquifers—A review of the experience from existing storage operations

The experience from CO₂ injection at pilot projects (Frio, Ketzin, Nagaoka, US Regional Partnerships) and existing commercial operations (Sleipner, Snøhvit, In Salah, acid-gas injection) demonstrates that CO₂ geological storage in saline aquifers is technologically feasible. Monitoring and verification technologies have been tested and demonstrated to detect and track the CO₂ plume in different subsurface geological environments. By the end of 2008, approximately 20 Mt of CO₂ had been successfully injected into saline aquifers by existing operations. Currently, the highest injection rate and total storage volume for a single storage operation are approximately 1 Mt CO₂/year and 25 Mt, respectively. If carbon capture and storage (CCS) is to be an effective option for decreasing greenhouse gas emissions, commercial-scale storage operations will require orders of magnitude larger storage capacity than accessed by the existing sites. As a result, new demonstration projects will need to develop and test injection strategies that consider multiple injection wells and the optimisation of the usage of storage space. To accelerate large-scale CCS deployment, demonstration projects should be selected that can be readily employed for commercial use; i.e. projects that fully integrate the capture, transport and storage processes at an industrial emissions source.     

Environmental Security: A Geographic Information System Analysis Approach—The Case of Kenya

Studies into the relationships between environmental factors and violence or conflicts constitute a very debated research field called environmental security. Several authors think that environmental scarcity, which is scarcity of renewable resources, can contribute to generate violence or social unrest, particularly within states scarcely endowed with technical know-how and social structures, such as developing countries. In this work, we referred to the theoretical model developed by the Environmental Change and Acute Conflict Project. Our goal was to use easily available spatial databases to map the various sources of environmental scarcity through geographic information systems, in order to locate the areas apparently most at risk of suffering negative social effects and their consequences in terms of internal security. The analysis was carried out at a subnational level and applied to the case of Kenya. A first phase of the work included a careful selection of databases relative to renewable resources. Spatial operations among these data allowed us to obtain new information on the availability of renewable resources (cropland, forests, water), on the present and foreseen demographic pressure, as well as on the social and technical ingenuity. The results made it possible to identify areas suffering from scarcity of one or more renewable resources, indicating different levels of gravity. Accounts from Kenya seem to confirm our results, reporting clashes between tribal groups over the access to scarce resources in areas that our work showed to be at high risk.     

Treatment of E. coli HB101 and the tetM gene by Fenton’s reagent and ozone in cow manure

The destruction of antibiotic-resistant microorganisms at the source of contamination is necessary due to their adverse effects and to their increasingly widespread occurrence in the environment. To address this problem, Fenton and ozone oxidation processes were applied to synthetically contaminated cow manure to remove the tetM gene and its host, Escherichia coli HB101. The efficiency of the processes was evaluated by enumeration of E. coli HB101 and by PCR amplification of the tetM gene. The results of this study show that 56.60% bacterial inactivation (corresponding to a 0.36 log reduction) was achieved by a Fenton reagent dose of 50 mM H₂O₂ and 5 mM Fe²⁺ without acidifying the manure. Despite the high organic content of cow manure, 98.50% bacterial inactivation (corresponding to a 1.83 log reduction) was obtained by the ozonation process with an applied dose of 3.125 mg ozone/g manure slurry. The PCR study revealed that the band intensity of the tetM gene gradually decreased by increasing the Fenton reagent and the applied ozone dose. However, significantly high doses of oxidants would be required to completely eliminate bacterial pollution in manure.     

Waste of organic and conventional meat and dairy products—A case study from Swedish retail

Many retailers take initiatives to reduce food waste, which can lead to enhanced sustainability, including reduced environmental impacts and cost savings. Another common environmental strategy in retail management is to increase the range of organic products. This study examined if organic food products have a higher level of waste, which thereby risk to counteract the environmental ambitions behind offering these products. The study also examined to what degree differences in waste level could be explained by turnover, shelf-life and wholesale pack size. In the study, six Swedish supermarkets provided data on all articles sold or wasted in the deli, meat, dairy and cheese departments during 2010 and 2011. 24 organic products were compared to their conventional counterparts; 22 of these had higher waste levels (from 1.5 to 29 times higher). Differences in wastage were also compared across departments; in all four departments, organic products as a group had higher waste percentage at all four departments. There was a negative correlation between the total mass sold of a product and the percentage waste. Also, longer shelf-life was associated with decreased waste, but only for products with low turnover. The systematic problem of retail food waste – particularly of organic products and other products with a low turnover – may be mitigated by increasing turnover, by stocking products with longer shelf-life or by decreasing the ordered volume (e.g. through decreased wholesale pack sizes).     

Aquatic Nuisance Species in the Great Lakes and Mississippi River Basin—A Risk Assessment in Support of GLMRIS

Environmental Management - The U.S. Army Corps of Engineers is conducting the Great Lakes and Mississippi River Interbasin Study to identify the highest risk aquatic nuisance species currently...     

A review on the production of fermentable sugars from lignocellulosic biomass through conventional and enzymatic route—a comparison

The scarcity of fossil fuels has urged the economically developed countries to find the resources for an alternative energy sources. In apprehension to this, biofuels, like bioethanol and biobutanol, produced from lignocellulosic biomass were considered as potential alternative. There are several methods for the pretreatment of biomass before it is being used as a feedstock for the production of fermentable sugars. However, one of the crucial concerns here is to enumerate an economic pretreatment scheme that can be implemented in large scale for the production of mostly exposed cellulosic part from biomass. This will ensure an effective hydrolysis of cellulose for the production of fermentable sugars and the production of biobutanol from these derived sugars. Moreover, the keynote understanding of an effective fermentation is the production of less inhibitory compounds like furfural, hydroxymethyl furfural during the hydrolysis of cellulose. Enzymatic hydrolysis of cellulose was reported as the most efficient method is this aspect. Trichoderma sp. was found the mostly used resources for the enzyme called cellulase and Aspergillus sp. for hemicellulase enzymes. The most crucial part here is the isolation of proper enzyme that will increase the rate of hydrolysis. Moreover, selection of proper pretreatment process will be a key benefit to the production of fermentable sugars through enzymatic hydrolysis. Based on the biomass nature, the evaluated hot water pretreatment followed by enzymatic hydrolysis with a provision of enzyme reusability (like encapsulated or enzyme separation with membrane) seems to be promising for enhanced biofuel-production.     

A multi-criteria decision analysis of solid waste treatment options in Pakistan: Lahore City—a case in point

Population of the world is increasing day by day, resulting in enormous amount of waste production. In the modern age of great technological advancements, there needs to be a systematic method to keep the environment clean. The waste management activities, i.e., collection, transport and disposal, pose a great challenge to the waste managers as they have to factor in various eclectic factors such as land availability, facilities available, budget, time required and the impact it would have on the environment, while tackling this problem. Lahore, despite being the most developed city of Pakistan, does not have a suitable solid waste management system. An increasing population leads to more waste generation, and in Lahore the situation is no different. Several waste management companies are working in the city, but as of yet they have not been able to make significant inroads to completely eradicate the problem. The aim of this paper is to suggest a suitable way for dealing with the waste. To accomplish this aim, a hierarchy-based model is used, considering six criteria and five alternatives. We used multi-criteria decision analysis to decide among different waste management alternatives. Forecasting has been used to find the population and waste produced over the years. Analytical hierarchy process (AHP) and Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) are used to rank the feasible alternative. The results show that the population and waste were increasing drastically. Aerobic digestion was ranked as the best alternative for waste management according to AHP and TOPSIS, but there is great variation among the rank of other alternatives.     

Optimizing the treatment and disposal of municipal solid wastes using mathematical programming—A case study in a Greek region

Goal of the work is to present a simplified methodology to optimize an integrated solid waste management system. The methodology performs two optimizations, namely: (i) minimization of the total cost of the MSW system and (ii) minimization of the equivalent carbon dioxide emissions (CO_2e) generated by the whole system. The methodology is modeled via non-linear mathematical equations, uses 32 decision variables and does not require complex LCA databases. The proposed model optimally allocates eight MSW components (paper, cardboard, plastics, metals, glass, food wastes, yard wastes and other wastes) to four MSW management technologies (incineration, composting, anaerobic digestion, and landfilling) after source separation of recyclables has taken place. The Region of East-Macedonia and Thrace in Greece was selected as a case study. Results showed that there is a trade off between cost and CO_2e emissions. Incineration and composting were favored as the principal treatment technologies, while landfilling was always the least desirable management technology under both objective functions. The recycling participation rate significantly affected all optimum scenarios.