Thiosulfate as an Oxidation Inhibitor in Flue Gas Desulfurization Processes: A Review of R&D Results

Sodium thiosulfate (Na₂S₂O₃) has been tested in a pilot plant as an oxidation inhibitor in flue gas desulfurization by lime and limestone slurry scrubbing with and without MgO and adiplc acid additives. The effectiveness of thiosulfate is proportional to the inhibitor product, defined as the product of thiosulfate concentration (M), calcium concentration (M), and the moles of SO₂ absorbed per hour per liter of hold tank volume. Gypsum saturation was less than 100 percent and scaling was eliminated when the inhibitor product exceeded 0.3 × 10^?6(gmol/L)³/h. Thiosulfate was relatively more effective in systems with chlorides and less effective in systems promoted by MgO. An inhibitor product greater than 10^?6(gmol/L)³/h significantly enhanced dewatering of solids from limestone scrubbing. SO₂ removal and/or limestone utilization were increased in systems that started with less than 10 mM dissolved calcium.     

Microbial aspects of the interaction between soil depth and biodegradation of the herbicide isoproturon

Factors controlling change in biodegradation rate of the pesticide isoproturon with soil depth were investigated in a field with sandy-loam soil. Soil was sampled at five depths between 0-10 and 70-80 cm. Degradation rate declined progressively down the soil profile, with degradation slower, and relative differences in degradation rate between soil depths greater, in intact cores relative to sieved soil. Neither the maximum rate of degradation, or sorption, changed with soil depth, indicating that there was no variation in bioavailability. Differences in degradation rate between soil depths were not associated with the starting population size of catabolic organisms or the number of catabolic organisms proliferating following 100% degradation. Decreasing degradation rates with soil depth were associated with an increase in the length of the lag phase prior to exponential degradation, suggesting the time required for adaptation within communities controlled degradation rates. 16S rRNA PCR denaturing gradient gel electrophoresis showed that degradation in sub-soil between 40-50 and 70-80 cm depths was associated with proliferation of the same strains of Sphingomonas spp.     

A review of in vitro testing systems applicable to diesel health effects research

In vitro mutagenicity and carcinogenicity testing techniques are currently being used to assess the potential risk to man of exposure to diesel exhaust emissions. This paper examines general considerations of such systems, the types of in vitro tests currently available, the advantages and disadvantages of each cell line and type of test, the limitations of in vitro techniques, the alternative human cell lines that could be utilized for diesel health effects studies, and recommendations for future research employing in vitro methods.     

COUNTY COMMISSIONERS' WATER KNOWLEDGE1

ABSTRACT: This study examines the social construction of county commissioners' knowledge about water. Factors that influence what commissioners know about water include each commissioner's personal characteristics, education, experience in natural resources management, involvement in policy making, and use and evaluation of various sources of information. This study focused on county commissioners representing rural, mixed, and urban counties in Arizona, Nevada, and Utah and collected data through mail surveys and interviews. County commissioners in the survey were well educated; however, few had taken college courses directly addressing technical, management, or legal aspects of water issues. Approximately one-third had direct experience in farming and ranching; nearly two-thirds indicated that farming and ranching played a major role in their communities. Respondents had experience with a broad range of water policy issues. In evaluating thirteen information sources in terms of their frequency of use, relevancy, and reliability, respondents assessed fellow commissioners and local government staff and managers most positively and nonprofit organizations most negatively. The media was also broadly rated as less relevant and reliable than other sources of information. The commissioners in the study expressed a high level of general concern about water issues and a strung preference for local sources of information.     

Treatment of contaminated soil with phosphorus and manganese oxide reduces lead absorption by Sprague-Dawley rats

This study was conducted to determine the extent of Pb absorption into young rats (Rattus norvegicus var. Sprague-Dawley) fed untreated Pb-contaminated soil or Pb-contaminated soil treated with two different sources of P and P + Mn oxide. Data were compared from an in vitro, physiologically based extraction test (PBET) with the animal data to support the validity of the in vitro test to assess bioavailable Pb from a treated Pb-contaminated soil. Soil with a total Pb concentration of 2290 mg kg(-1) was used. Rats were fed 19 different test diets for 21 consecutive days. The test diets represented 95 g AIN93G rat meal kg(-1) diet with varying proportions of silica sand or soil to provide low, medium, or high doses of Pb from either Pb acetate, treated, or untreated soil. Blood, liver, kidney, and bone Pb concentrations were examined. For all four tissues, Pb concentrations for the Pb acetate groups were significantly higher than concentrations for all the soil groups. In general, either triple superphosphate (TSP) or phosphate rock (PR) treatments resulted in significant reductions in tissue Pb concentrations compared with untreated soil. Blood and kidney Pb concentrations for the PR + Mn oxide group were significantly lower than those of the PR group at the low and high doses. Relative bioavailability of Pb, as measured in all tissues, was significantly reduced when comparing untreated with amended soil. Correlation between the in vitro and in vivo tests, based on bone and liver tissue, showed that the in vitro test is successful at predicting Pb bioavailability.     

Indicators of perceived naturalness as drivers of landscape preference

The concept of naturalness is one of the more studied concepts in landscape preference research and describes how close a landscape is to a perceived natural state. In this study we explored the relationship between landscape preference and three landscape indicators of naturalness (level of succession, number of woodland patches and shape index of edges). We used computer-generated visualisations of a hypothetical landscape containing pasture and broadleaved woodland. In the landscape simulations we altered the values of the naturalness indicators between the levels of low, medium and high, creating 27 different visualisations. The survey was distributed as an on-line survey in seven different languages and obtained 703 respondents. The study showed a strong relationship with preference for both the level of succession and number of woodland patches, and a weaker relationship with shape index of edges. The two demographic factors which were shown to contribute most to the formation of preference were gender and having a landscape related profession. The results suggest that the selected indicators are more important drivers of preference than demographic factors.     

Assemblage stability in stream fishes: A review

We quantified the stability of nine stream fish assemblages by calculating coefficients of variation of population size for assemblage members. Coefficients of variation were high and averaged over 96%; indicating that most assemblages were quite variable. Coefficient of variation (CV) estimates were not significantly affected by: (1) years of study, (2) mean abundance, (3) familial classification, or (4) mean interval between collections. We also detected minor regional differences in CVs. The high variability exhibited by many stream fish assemblages suggests that it may be difficult to detect the effects of anthropogenic disturbances using population data alone. Consequently, we urge managers to exercise caution in the evaluation of the effects of these disturbances. More long-term studies of the ecological characteristics of undisturbed stream fish assemblages are needed to provide a benchmark against which disturbed systems can be compared. We suggest that CVs are a better estimator of population/assemblage stability, than either Kendall's W or the standard deviation of the logarithms of numerical censuses. This conclusion is based on the following reasons. First, CVs scale population variation by the mean and, hence, more accurately measure population variability. Second, this scaling permits the comparison of populations with different mean abundances. Finally, the interpretation of CV values is less ambiguous than either of the aforementioned metrics.     

Compartmentalization of metals within the diverse colloidal matrices comprising activated sludge microbial flocs

Activated sludge floc from a wastewater treatment system was characterized, with regard to principal structural, chemical, and microbiological components and properties, in relation to contaminant-colloid associations and settling. Multiscale analytical microscopies, in conjunction with multimethod sample preparations, were used correlatively to characterize diverse colloidal matrices within microbial floc. Transmission electron microscopy, in conjunction with energy dispersive spectroscopy (EDS), revealed specific associations of contaminant heavy metals with individual bacterial cells and with extracellular polymeric substances (EPS). Floc structure was mapped from the level of gross morphology down to the nano-scale, and flocs were described with respect to settling properties, size, shape, density, porosity, bound water content, and EPS chemical composition; gross surface properties were also measured for correlation with principal floc features. Compartmentalization results based on 171 EDS analyses and representative high-resolution images showed that nano-scale agglomerations of (i) silver (100%) and (ii) zinc (91%) were confined almost entirely to EPS matrices while (iii) Pb (100%) was confined to intracellular granules and (iv) aluminum was partitioned between EPS matrices (41%) and intracellular matrices (59%). The results suggest that engineered changes in microbial physiology and/or in macromolecular EPS composition may influence metal removal efficiencies.