Dr Dawit Bekele

© 2016 Published by Elsevier B.V. Recently, emerging contaminants such as micropollutants presence in water poses significant challenge to regulators, engineers and scientific community. Micropollutants are introduced in the aquatic environment primarily from discharge of treated effluent from wastewater treatment plants (WWTP). Advanced treatment processes: reverse osmosis, and membrane bioreactor (MBR) can achieve higher and more consistent micropollutants removal. Despite the used technology, the removal of micropollutants depends on phsyico-chemical properties of micropollutants and the treatment conditions. Several advantages make MBR to be recognized as the next generation for wastewater treatment. However, its efficiency is limited due to the presence of micropollutants, causing peculiar membrane fouling. This review compares MBR and conventional activated sludge (CAS) for wastewater treatment and discusses problems arising from the presence of emerging micropollutants, such as the low removal efficiency for certain types of compounds. Mechanisms of micropollutants removal are summarized and related to MBRs operational conditions based on the vast literature existing in this topic. Adsorption and subsequent biodegradation of the micropollutants have been identified as the dominant removal processes, and they are influenced by operational conditions such as solid retention time, biomass concentration, temperature, redox conditions and pH. The review also provides a detailed overview of the effects of micropollutants on microbial activities, since microorganisms respond to environmental stress by producing different polysaccharides and proteins that have a direct impact on membrane fouling. Finally, pertinent issues that must be addressed in order to increase the market share of MBR in the removal of emerging micropollutants are highlighted.

© 2015 Elsevier B.V. Current practices in health risk assessment from vapor intrusion (VI) using mathematical models are based on assumptions that the subsurface sorption equilibrium is attained. The time required for sorption to reach near-steady-state conditions at sites may take months or years to achieve. This study investigated the vapor phase attenuation of trichloroethylene (TCE) in five soils varying widely in clay and organic matter content using repacked columns. The primary indicators of TCE sorption were vapor retardation rate (R t ), the time required for the TCE vapor to pass through the soil column, and specific volume of retention (V R ), and total volume of TCE retained in soil. Results show TCE vapor retardation is mainly due to the rapid partitioning of the compound to SOM. However, the specific volume of retention of clayey soils with secondary mineral particles was higher. Linear regression analyses of the SOM and clay fraction with V R show that a unit increase in clay fraction results in higher sorption of TCE (V R ) than the SOM. However, partitioning of TCE vapor was not consistent with the samples' surface areas but was mainly a function of the type of secondary minerals present in soils.

© 2015 Elsevier Ltd. Addressing uncertainties in human health risk assessment is a critical issue when evaluating the effects of contaminants on public health. A range of uncertainties exist through the source-to-outcome continuum, including exposure assessment, hazard and risk characterisation. While various strategies have been applied to characterising uncertainty, classical approaches largely rely on how to maximise the available resources. Expert judgement, defaults and tools for characterising quantitative uncertainty attempt to fill the gap between data and regulation requirements. The experiences of researching 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) illustrated uncertainty sources and how to maximise available information to determine uncertainties, and thereby provide an 'adequate' protection to contaminant exposure. As regulatory requirements and recurring issues increase, the assessment of complex scenarios involving a large number of chemicals requires more sophisticated tools. Recent advances in exposure and toxicology science provide a large data set for environmental contaminants and public health. In particular, biomonitoring information, in vitro data streams and computational toxicology are the crucial factors in the NexGen risk assessment, as well as uncertainties minimisation. Although in this review we cannot yet predict how the exposure science and modern toxicology will develop in the long-term, current techniques from emerging science can be integrated to improve decision-making.