13 risk issues to explore individual variability in risk perception and to validate the psychometric paradigm. Results indicate that the way individuals rate risk characteristics varies, and observed correlations between risk characteristics at the aggregate level do not hold true for individuals. Despite this observation, they conclude that the paradigm remains an effective tool for predicting the relationship between most risk characteristics and risk perceptions at the level of individuals. {Risk Anal. 1997, 17, 303-12)
whether toxicity declined following the change to chlorine dioxide. Samples were collected before and after chlorine gas replacement, fractionated, and assayed chemically for PAHs and biologically for dioxinlike responses. Assays based on induction of 7-ethoxyresorufin-O-deethylase showed a decrease in dioxinlike compounds after chlorine replacement. Sediment and particulate fractions containing PAHs were more potent than the fraction thought to contain dioxins, although the concentrations of PAHs were too small to explain all of the measured toxicity. {Environ. Toxicol. Chem. 1997, 16, 1187-94)
TOXICITY Pulp mill effluent Pulp bleaching mills are replacing chlorine gas with chlorine dioxide, pardy because of concerns about dioxins and other chlorinated organic compounds in wastewater effluents. M. Engwall and colleagues tested sediment around a Swedish pulp mill that stopped using chlorine gas in 1991 to determine
WASTEWATER Treatment plant VOCs Municipal wastewater treatment facilities have been identified as emissions sources for VOCs and are receiving regulatory scrutiny. R. G. Zytner and co-workers did studies to identify the important physical
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parameters that influence oxygen and VOC transfer at sewer drop structures and to determine whether oxygen transfer measurements are a suitable surrogate for VOC mass transfer. They studied the effects of drop height, liquid flow rate, and water depth on oxygen transfer and stripping a cocktail of 10 volatile tracers. Both oxygen and VOC mass transfer depended on drop chamber height. This suggests that oxygen appears to be a suitable surrogate for studying VOC in drop structures. This work may have application in the measurement of VOC behavior in municipal wastewater treatment systems. {Water Environ. Res. 1997, 69, 286-94)
Phosphorus removal Effluent standards for phosphorus in certain areas of the world require that most new or expanded municipal wastewater treatment facilities be designed for phosphorus removal. Traditionally, physicochemical treatment methods have been used, but enhanced biological phosphorus removal (EBPR) has become popular for retrofitting existing plants. Although effective, EBPR often has the disadvantage of producing additional inorganic dry solids waste compared with a conventional system. N. Jardin and H. J. Popel evaluated a conventional and an EBPR plant over a two-year period in Germany to characterize phosphorus storage mechanisms and compare inorganic and organic sludge production. The increase in dry inorganic solids production in the EBPR plant was quantified. No significant difference in organic sludge production between the two plants was observed. {Water Environ. Res. 1997, 69, 375-81)
Contributors: Michael Brauer, University of British Columbia, Vancouver; Brian Eitzer, Connecticut Agricultural Experiment Station, New Haven; Stephen Geiger, Remediation Technologies, Inc., King of Prussia, Pa.; Vincent Hand, Miami University, Institute of Environmental Sciences, Oxford, Ohio; Louis Kovach, Ecolife Associates, Wilmington, Del.; Geoffrey Nobes, McGill University, Montreal; Raewyn Town, Queen's University of Belfast, Northern Ireland; and Margaret Whittaker, NSF International, Ann Arbor, Mich.
