Electrostatic precipitator emission and opacity performance control through rapper strategy

The opacity and emission performance of two “identical” cold-side precipitators at a power plant utilizing a Western coal source was investigated through an extensive test program. The test program included establishment of outlet emission versus opacity correlations for the two “identical” units, correlation of rapper strategy (frequency and amplitude) with opacity, and correlation of power-off rapping strategy with opacity. Analysis of the test program data demonstrates that the opacity-emission correlations from the two “identical” units can be significantly different. The potential reasons for the differences between the two units are identified and examined in light of the test program data. Strong correlation of opacity with rapping strategy was developed from the test program. Results demonstrate that an automatic power-off rapping technique can significantly enhance precipitator performance on ash from Western coal.     

Effect of cobalt sorption on metal fractionation in anaerobic granular sludge

A sequential extraction procedure was applied to two anaerobic methanogenic sludges (Eerbeek and Nedalco) to examine the speciation of micro- and macronutrients in the sludges after cobalt sorption by exposing the sludge to a 1 mM Co solution for 4 d at pH 7 and 30 degrees C. The effect of different physicochemical conditions on cobalt sorption was studied as well: effect of pH (6-8), effect of competition by a second trace element (Ni or Fe), modification of the granular matrix by glutaraldehyde or heat treatment, and EDTA (ethylenediaminetetraacetic acid) addition. Sorbed Co was found to distribute between the carbonates, organic matter + sulfides, and residual fractions. Cobalt adsorption resulted in an antagonistic interaction with other metals present in the granular matrix, evidenced by the solubilization of other trace elements (e.g., Ni, Cu, and Zn) as well as macronutrients (especially Ca and Fe). Modification of the sludge matrix by glutaraldehyde or heat treatment, or exposure to EDTA, led to serious modifications of the Co sorption capacity and strong interactions with multivalent cations (i.e., Ca(2+) and Fe(2+)).     

Scope insensitivity in contingent valuation of complex environmental amenities

It has been argued that respondents in contingent valuation (CV) surveys, asked to value complex environmental amenities, will state willingness to pay (WTP) independently of the scope of the project. Such insensitivity to scope would be at odds with rational choice, and could therefore imply that CV is not a theoretically valid method for biodiversity valuation. The scope test in the present CV study was applied to endangered species preservation. Respondents were split in four sub-samples facing different scopes of endangered species preservation. The design allowed for both external and internal scope tests. Furthermore, the tests were split according to elicitation format. Of four external tests of insensitivity to scope, one was rejected, two gave mixed results, depending on either the type of test or elicitation format, and for the last one the null hypothesis could not be rejected. Of five internal tests, insensitivity to scope was rejected in three cases, one test gave mixed results, and one could not be rejected. Survey design features of the CV study, especially an unfamiliar sub-group of endangered species, could explain the apparent insensitivity to scope observed.     

Estimation of critical loads for radiocaesium in Fennoscandia and Northwest Russia

The application of the critical loads methodology for radioactive contamination of Arctic and sub-arctic ecosystems, where natural and semi-natural food products are important components of the diet of many people, is proposed and discussed. The critical load is herein defined as the amount of radionuclide deposition necessary to produce radionuclide activity concentrations in food products exceeding intervention limits. The high transfer of radiocaesium to reindeer meat gives this product the lowest critical load, even though the intervention limit is relatively high compared with other products. Ecological half-lives of radiocaesium in natural and semi-natural products are often very long, and it is therefore important to take account of contamination already present in the event of an accident affecting areas where such products are important. In particular, the long ecological half-life for radiocaesium in moose meat means that the critical load is highly sensitive to prior deposition. An example of the potential application of the method for emergency preparedness is given for the Chernobyl accident.     

Reindeer in the Swedish mountains: an assessment of grazing impacts

During the last decade, several well-publicized grazing-related incidents of vegetation degradation have helped to form an official opinion of overutilization of some mountain areas and a concern that Swedish reindeer husbandry may not be ecologically sustainable. We examine these examples in a temporal and management perspective to assess the scale of impact on summer grazing grounds in the Swedish mountains. Long-term data on population dynamics of reindeer show no trend with fluctuations around 225 000 animals for the last century. Data on grazing effects from L?ngfj?llet (Dalarna) and Mitt?kl?ppen (H?rjedalen) are discussed in detail. We compare these data to the situation in Finnmark, Norway, and in northern Finland where reindeer husbandry in recent decades does not seem to have been ecologically sustainable. We conclude that large-scale overexploitation by reindeer in the Swedish mountains is not evident. However, strong grazing and trampling effects may be found around enclosures and fences.     

Photolysis of atrazine and ametryne herbicides in Barbados sugar cane plantation soils and water

The photodegradation kinetics of atrazine (2-chloro-6-(ethylamino)-4-isopropylamino-1,3,5-triazine) and ametryne (2-methylthio-4-ethylamino-6-isopropylamino-s-triazine), in fresh and coastal salt water from Barbados, were measured under irradiation with artificial solar and UV254-radiation. The first-order rate constants were greater for ametryne than for atrazine, and the rates were reduced in seawater relative to fresh water, and in soil slurries relative to fresh water. However, rates were accelerated in the presence of iron(III) at pH 3 due to photo-Fenton type processes. This rate enhancement was reduced at ambient pH values (pH 7-7.5) representative of surface water in Barbados. These results have important implications for the relative persistence of these contaminants in aquatic environments in tropical areas.     

Remediation with cyclodextrin: Recovery of the remedial agent by membrane filtration

Cyclodextrin‐enhanced flushing of contaminants from the subsurface is a promising innovative remediation technology. It will become more economically viable at more sites if methods can be developed to recover and reconcentrate the cyclodextrin solution after it has been flushed through an aquifer. The goal of this study was to determine if membrane technology is capable of meeting that need. Five membranes with different material properties were tested for this purpose in the laboratory. The results of these tests indicate that there are large differences both in the efficiency of these membranes to extract hydroxpropyl‐β‐cyclodextrin (HPCD) and their stability when exposed to trichloroethylene (TCE) at concentrations near aqueous solubility. Not only does the molecular weigh cutoff (MWCO) of a membrane determine if HPCD can be retained, but crucial selection criteria are the membrane's resistance and compatibility with TCE. Of the five membrane materials tested, only two (polymer composite membrane and polysulfone) met both these requirements. The polymer composite membrane (MPF‐44) showed reliable and stable HPCD recoveries (>95 percent) even when exposed to high TCE concentrations. The polysulfone membrane showed high HPCD recoveries, 88.5 ± 0.4 percent to 97 percent ±1 percent for ultrafiltration and nanofiltration membranes, respectively. However, membrane swelling and deterioration became a problem at high TCE concentrations (>1,000 mg/L). These problems diminished when the TCE concentration was less than 1 mg/L. Field tests demonstrated that batch mode treatment by ultrafiltration doubled the cyclodextrin concentration from 5 to 10 percent within three hours at a constant operating pressure of 13 psi. Under continuous single‐pass treatment conditions, cyclodextrin concentration also increased, although the rate of increase was much smaller than in batch mode. Overall, these tests showed that cyclodextrin recovery is possible under field conditions. © 2007 Wiley Periodicals, Inc.     

Sensitivity analysis of the asymptotic behavior of a model for the environmental movement of radionuclides

The asymptotic behavior of a linear compartment model for the environmental movement of radionuclides is investigated. Here, the expression asymptotic behavior is used to designate the behavior of q(t) as t → ∞, where q is the solution of a vector differential equation of the form dq/dt = h + Kq. The asymptotic behavior of such equations is described. For the model and conditions under consideration, each element of q converges monotonically to a steady-state value. A hydrologic system is defined and used to illustrate this behavior. An approach to sensitivity analysis employing Latin hypercube sampling, rank transformations and stepwise regression is presented and then applied to this system. A total of 20 independent variables is introduced and the following dependent variables are investigated for the various components of the system: amount of radionuclide present at steady state. concentration of radionuclide at steady state, and time required to reach 90% of steady state. Finally, an application of asymptotic behavior in the analysis of a hypothetical site for the geologic isolation of high-level radioactive waste is described and a brief discussion of differential sensitivity analysis is given.