DBP Levels in Chlorinated Drinking Water: Effect of Humic Substances

Chlorination is the most widely used technique for disinfection of drinking water. A consequence of chlorination is the formation of Disinfection By-Products (DBPs). The formation of DBPs in drinking water results from the reaction of chlorine with naturally occurring organic materials, principally humic and fulvic acids. This paper focuses on the effect of humic substances on the formation of twenty-four compounds belonging to different categories of DBPs. This investigation was conducted in two water treatment plants in Greece, Menidi and Galatsi, from July 1999 to April 2000. Humic substances were determined by the diethylaminoethyl (DEAE) method with subsequent UV measurement. The techniques used for the determination of DBPs were liquid-liquid extraction, gas chromatography and mass spectrometry. The concentrations of DBPs were generally low. Total trihalomethanes (TTHMs) ranged from 5.1 to 24.6 microg L(-1), and total haloacetic acids (HAAs) concentration ranged from 8.6 to 28.4 microg L(-1), while haloaketones (HKs) and chloral hydrate (CH) occurred below 1 microg L(-1). The content of humic substances was found to influence the formation of DBPs and especially TTHMs, trichloroacetic acid (TCA), dibromoacetic acid (DBA), CH, 1,1-dichloropropanone (1.1-DCP) and 1,1,1-trichloropropanone (1,1,1-TCP). Seasonal variation of TTHMs and HAAs generally followed that of humic substances content with peaks occurring in autumn and spring. The trends of 1,1-DCP, 1,1,1-TCP and CH formation seemed to be in contrast to TTHMs and HAAs. Trends of formation of individual compounds varied in some cases, probably due to influence of parameters other than humic substances content. Statistical analysis of the results showed that the concentrations of TTHMs, CH, 1,1-DCP, 1,1,1-TCP, TCA and DBA are strongly affected from humic substances content (at 0.01 confidence level). The opposite is true for dichloroacetic acid (DCA) concentration. Humic substances also vary to a statistically significant degree during different months, as well as the concentrations of TTHMs, CH, 1,1-DCP, 1,1,1-TCP, TCA and DCA. The variance of DBA was not statistically significant. Regarding the effect of sampling station, humic substances content showed no statistically significant difference between the two raw water sources studied.     

Computer simulation of shock waves transmission in obstructed terrains

Generation and transmission of blast waves in real terrains is of major importance for risk analysis procedures involving accidental explosion scenarios. The problem arises from the impact of overpressure wave on people and structures that may be lethal or catastrophic under certain conditions. In this paper, a CFD simulation of shock wave propagation in obstructed terrain is attempted. Overpressure histories as well as a series of critical parameters, namely the positive and negative peak overpressure, the arrival time, and the positive and negative phase duration at specific points within the domain were obtained during the simulation. Their comparison with experimental measurements from field-scale high explosive blast tests performed by HSE showed a reasonably good agreement indicating that CFD computer programs provide reliable tools for estimating explosive shocks in complex terrains.     

Tail autotomy affects bipedalism but not sprint performance in a cursorial Mediterranean lizard

Running is essential in all terrestrial animals mainly for finding food and mates and escaping from predators. Lizards employ running in all their everyday functions, among which defense stands out. Besides flight, tail autotomy is another very common antipredatory strategy within most lizard families. The impact of tail loss to sprint performance seems to be species dependent. In some lizard species, tail shedding reduces sprint speed, in other species, increases it, and, in a few species, speed is not affected at all. Here, we aimed to clarify the effect of tail autotomy on the sprint performance of a cursorial lizard with particular adaptations for running, such as bipedalism and spike-like protruding scales (fringes) on the toepads that allow high speed on sandy substrates. We hypothesized that individuals that performed bipedalism, and have more and larger fringes, would achieve higher sprint performance. We also anticipated that tail shedding would affect sprint speed (though we were not able to define in what way because of the unpredictable effects that tail loss has on different species). According to our results, individuals that ran bipedally were faster; limb length and fringe size had limited effects on sprint performance whereas tail autotomy affected quadrupedal running only in females. Nonetheless, tail loss significantly affected bipedalism: the ability for running on hindlimbs was completely lost in all adult individuals and in 72.3% of juveniles.