Enhancement of turbulent scalar mixing and its application by a multihole nozzle in selective catalytic reduction of NOx

The mixing characteristics of a passive scalar in the turbulent flow of a selective catalytic reduction process were numerically and experimentally investigated, focusing especially on an injection nozzle with multiple holes for the reducing agent. The multihole injection nozzle studied has six holes that are perpendicular to the ambient flue gas flow and are located near the tip of the nozzle. Large eddy simulation was applied to the turbulent flow and mixing fields to elucidate the mixing mechanism of the proposed nozzle compared with the single-hole nozzle that is commonly used in the conventional selective catalytic reduction process. From the results, there exist broader regions of higher turbulent intensities for the multihole nozzle than for the conventional single-hole nozzle. These regions are well matched with the positions of high vorticity in the near upstream region of the jet flow issuing from the multiple holes of the nozzle. Consequently, the high turbulent intensities and vorticity magnitudes lead to intensified mixing between the flue gas and the reducing agent. Hence, the most suitable molar ratio between NOx and the reducing agent for the catalytic reaction can be easily obtained within a shorter physical mixing length as a result of the enhanced scalar mixing. Finally, the numerical results were applied to a trial design version of a multihole nozzle, and this nozzle was experimentally tested to confirm its mixing performance.     

Leaching behavior of heavy metals from municipal solid waste incineration bottom ash and its geochemical modeling

With the increase in the number of municipal solid waste incineration (MSWI) plants constructed in China recently, great attention has been paid to the heavy metal leaching toxicity of MSWI residues. In this study, the effects of various parameters, including extractant, leaching time, liquid-to-solid ratio, leachate pH, and heavy metal content, on the release properties of Cd, Cr, Cu, Ni, Pb, and Zn from MSWI bottom ash were investigated. Partial least-squares analysis was employed to highlight the interrelationships between the factors and response variables. Both experimental research and geochemical modeling using Visual MINTEQ software were conducted to study the pH-dependent leaching behavior of these metals in fresh and weathered bottom ash, considering precipitation/dissolution and surface complexation reactions (adsorption by hydrous ferric oxide and amorphous aluminum oxide/hydroxide). The results showed that leachate pH was the predominant factor influencing heavy metal leachability. The leaching of Cu, Pb, and Zn was mainly controlled by precipitation/dissolution reactions, whereas surface complexation had some effect on the leaching of Cr, Cd, and Ni for certain pH ranges. The modeling results aggreed well with the experimental results. Part of this work was presented at the Fourth International Conference on Combustion, Incineration/Pyrolysis and Emission Control (i-CIPEC)     

Influence of Technological Process on Biodegradation of PVA/Waxy Starch Blends in an Aerobic and Anaerobic Environment

Improving biodegradability of PVA/starch blends is a reality already documented by a number of works. Admittedly, mechanical properties of products (for example, tensile strength) are somewhat worse, but suitable composition optimizing or chemical modifying of starch may eliminate the problem to a large degree. This work is an attempt to find another potential effect influencing biodegradability, that of technological procedure for producing films from these blends on an extruder. The procedure with a so-called pre-extrusion step (two-stage) and dry-blend (single-stage) produced blends of slightest differences in achieved biodegradability (virtually within limits of experimental error) in aerobic (76 vs. 79%) as well as anaerobic breakdown (48 vs. 52%). Conversely, morphological analysis exhibited superior homogeneity of films prepared by the two-stage process; their tensile strength was also higher.     

Initial Changes in Refilled Lysimeters Built with Metal Polluted Topsoil and Acidic or Calcareous Subsoils as Indicated by Changes in Drainage Water Composition

Soil translocation for recultivation of soil removed from construction sites and for the preparation of refilled lysimeters inevitably involves disturbance of soil structure, and, if intermediate storage is included, also drying and rewetting of the soil. We report on an experiment with model forest ecosystems, where uncontaminated forest subsoils were covered with non-contaminated or freshly heavy metal (mainly Zn and Cu) contaminated topsoil in large lysimeters. Monitoring of the chemical composition of the drainage water revealed two distinct soil conditioning phases. During an initial phase of about a year strongly elevated nitrate and sulfate concentrations occurred that were attributed to a mineralisation flush caused by the increased accessability of mineralisable nitrogen and sulfur in destroyed aggregates. These effects were significantly larger in lysimeters with calcareous subsoil than in those with acidic subsoil. The second phase was characterised by a gradual decrease in dissolved organic carbon and sulfate concentrations, in particular in the acidic subsoil. This decrease may be attributed to the depletion of pools made accessible during aggregate destruction or the formation of new aggregates. These chemical changes had only little effects on the concentrations of copper and zinc in the drainage water. Based on our results, it can be concluded that large refilled lysimeters can be used for many purposes without risk of compromised results, if a conditioning phase of about 1 year with sufficiently moist soil conditions is respected. Nevertheless, gradual changes in soil chemical characteristics still occur after this initial phase. Implications for the recultivation of sites using relocated soils are discussed.     

Lysimeter Experiments to Investigate the Fate of Chemicals in Soils – Comparison of Five Different Lysimeter Systems

Several lysimeter scenarios and approaches exist to study the fate of agro-chemicals or contaminants from deposition in soil columns. In many systems just transport and leaching of the parent compound is followed, in some systems the leaching and transport of the metabolites is investigated as well. In more sophisticated lysimeter systems the volatilization and also the mineralization of the applied chemicals can be additionally monitored. Depending on the lysimeter system used and on the fact whether the applied chemicals are ¹⁴C-labeled or not, different results and various interpretations of the results might be achieved. Different lysimeter systems are described in this paper and a real dataset of a specific lysimeter experiment was transferred and evaluated in a virtual approach in the different lysimeter systems in order to show the advantages and disadvantages of the various systems.     

Anti-sense expression of putrescine N-methyltransferase confirms defensive role of nicotine in Nicotiana sylvestris against Manduca sexta

Summary. Several lines of evidence support the defensive function of nicotine production in the Nicotiana genus against a range of herbivores, but the evidence is largely correlative. To suppress nicotine production in planta and to test its defensive function, we expressed DNA of putrescine N-methyl transferase in an anti-sense orientation (AS-PMT) in N. sylvestris and fed leaf material from two lines of transformed and wild type plants to Manduca sexta larvae. Larvae consumed more leaf area and gained more mass on the foliage of plants with low PMT expression and low nicotine levels as compared to plants with high PMT expression and high nicotine levels and wild type plants. Overall, larval consumption and performance were negatively correlated with constitutive nicotine levels. We conclude that nicotine decreases the palatability of N. sylvestris leaves to the nicotine-resistant M. sexta larvae.     

A survey on the utility of the USEPA CADDIS stressor identification procedure

The Environmental Protection Agency (EPA) has made available on the worldwide web a systematic stream stressor identification procedure, the “Causal Analysis/Diagnosis Decision Information System” or CADDIS. We report here the results of a survey of regulators and scientists in 11 states who use CADDIS or another stressor identification procedure in their work. The 13 survey questions address guidelines as to what impairment scenarios to approach with stressor identification, what information is needed to perform stressor identification, and what the stakeholder role is in performing stressor identification. At the time of this survey (the summer of 2009), the EPA CADDIS website was less commonly used among the state regulators surveyed than the published EPA stressor identification document on which it is based. The respondents generally find the EPA stressor identification procedure useful and capable of being adapted to their individual needs. Survey respondents all use stressor identification in their Total Maximum Daily Load work, but also in a wide variety of other applications. All the “types of evidence” included in the CADDIS stressor identification procedure are used by the practitioners surveyed with the exception of the results of ecological simulation models. While the CADDIS documentation encourages the involvement of stakeholders in stressor identification, most respondents do not assemble stakeholder teams of local officials and citizens to participate in stressor analyses.     

Modeling 4-Chlorophenol Removal from Aqueous Solutions by Granular Activated Carbon

Since phenols and phenolic compounds in many industrial wastewaters are toxic organic contaminants for humans and aquatic life, to remove these compounds via the most efficient way is very important for environmental remediation treatment. In this context, almost all of the isotherm models (Freundlich, Langmuir, Temkin, Redlich–Peterson, Sips, and Khan) for adsorption in the literature were applied to explain the adsorption mechanism of 4-chlorophenol on activated carbon in this study. Also theoretical modeling data were obtained using model equations; interpolation and analysis of variance were made to compare data by using statistics software. In addition, the thermodynamic and kinetic studies for adsorption mechanism were included in the article. The adsorption of 4-chlorophenol on activated carbon fits well to the pseudo-first-order kinetic model than the pseudo-second-order, intraparticular diffusion and Bangham models. It is also indicated that 4-chlorophenol adsorption by granular activated carbon would be attributed to a type of transition between physical and chemical adsorption rather than a pure physical or chemical adsorption process. As a result, an environmental remediation problem and the adsorption mechanism on activated carbon that can be regarded as a solution to this problem are described and explained using the mathematical models and calculations in this study.     

Prioritizing GM crop monitoring sites in the dynamics of cultivation systems and their environment

EU legislation stipulates that GM crops have to be monitored for potential adverse environmental effects. Monitoring preferably should take place in the most exposed areas-the cultivated fields and their neighbouring environment. Current monitoring designs do not give detailed consideration to the different exposure intensities in agricultural practice. At the same time, the selection of specific, more exposed sites is difficult considering the dynamic and diversity of crop cultivation and rotation systems and their environments. We developed an approach for prioritising the monitoring of on-farm and neighbouring sites based on differing exposure levels using a minimum dataset of cultivation and land use information. Applying a Bt-maize cultivation scenario to Brandenburg, Germany, where presently no GM crops are cultivated, we systemised and categorised areas with different spatio-temporal exposure intensities including 50 m, 200 m and 1000 m buffers. These categories correspond to different suitabilities to serve as monitoring sites. Sites are prioritised using a sequential scheme. This yields an improved and objective spatial monitoring design providing detailed exposure information. This methodology is flexible and transferable to any agricultural setting, therefore enabling superior statistical comparisons between locations and regions and thus enhancing monitoring data quality.