Membrane process for biological treatment of contaminated gas streams.

A hollow fiber membrane bioreactor was investigated for control of air emissions of biodegradable volatile organic compounds (VOCs). In the membrane bioreactor, gases containing VOCs pass through the lumen of microporous hydrophobic hollow fiber membranes. Soluble compounds diffuse through the membrane pores and partition into a VOC degrading biofilm. The hollow fiber membranes serve as a support for the microbial population and provide a large surface area for VOC and oxygen mass transfer. Experiments were performed to investigate the effects of toluene loading rate, gas residence time, and liquid phase turbulence on toluene removal in a laboratory-scale membrane bioreactor. Initial acclimation of the microbial culture to toluene occurred over a period of nine days, after which a 70% removal efficiency was achieved at an inlet toluene concentration of 200 ppm and a gas residence time of 1.8 s (elimination capacity of 20 g m-3 min-1). At higher toluene loading rates, a maximum elimination capacity of 42 g m-3 min-1 was observed. In the absence of a biofilm (abiotic operation), mass transfer rates were found to increase with increasing liquid recirculation rates. Abiotic mass transfer coefficients could be estimated using a correlation of dimensionless parameters developed for heat transfer. Liquid phase recirculation rate had no effect on toluene removal when the biofilm was present, however. Three models of the reactor were created: a numeric model, a first-order flat sheet model, and a zero-order flat sheet model. Only the numeric model fit the data well, although removal predicted as a function of gas residence time disagreed slightly with that observed. A modification in the model to account for membrane phase resistance resulted in an underprediction of removal. Sensitivity analysis of the numeric model indicated that removal was a strong function of the liquid phase biomass density and biofilm diffusion coefficient, with diffusion rates below 10(-9) m2 s-1 resulting in decreased removal rates.

Lifetime exposure to interparental physical and verbal aggression and symptom expression in college students.

This study investigated relations between lifetime exposure to interparental aggression and (1) anxiety, depression, and anger; (2) interpersonal problems; and (3) symptoms of trauma, in a sample of young adults. Participants were 326 (219 female, 107 male) undergraduates from an eastern university. Participants reported on their demographic backgrounds, memories of interparental verbal and physical aggression, past experiences of severe stressors (including child physical and sexual abuse and community violence), and recent symptoms. Results demonstrate that exposure to interparental violence is associated with elevations in depression, anxiety, interpersonal problems, and trauma symptoms. Further analyses indicated that interparental verbal aggression predicted all symptom areas and was a stronger predictor than interparental violence. The impact of both forms of aggression was attenuated and in some cases negated by controlling for the effects of other severe stressors.

The structure and coherence of competence from childhood through adolescence.

The structure and coherence of competence from childhood (ages 8-12) to late adolescence (ages 17-23) was examined in a longitudinal study of 191 children. Structural equation modeling was utilized to test a conceptual model and alternative models. Results suggest that competence has at least 3 distinct dimensions in childhood and 5 in adolescence. These dimensions reflect developmental tasks related to academic achievement, social competence, and conduct important at both age levels in U.S. society, and the additional tasks of romantic and job competence in adolescence. As hypothesized, rule-breaking versus rule-abiding conduct showed strong continuity over time, while academic achievement and social competence showed moderate continuity. Results also were consistent with the hypothesis that antisocial behavior undermines academic attainment and job competence.

Children in homeless families: risks to mental health and development.

This study examined the psychological adjustment of 159 homeless children in comparison with a sample of 62 low-income children living at home. In each group, ages ranged from 8 to 17 years. As expected, homeless children were found to have greater recent stress exposure than housed poor children, as well as more disrupted schooling and friendships. Child behavior problems were above normative levels for homeless children, particularly for antisocial behavior. Across the 2 samples, however, behavior problems were more related to parental distress, cumulative risk status, and recent adversity than to housing status or income. Results suggest that homeless children share many of the risks and problems of other American children being reared in poverty.