Contact Tank Design Impact on Process Performance

In this study three-dimensional numerical models were refined to predict reactive processes in disinfection contact tanks (CTs). The methodology departs from the traditional performance assessment of contact tanks via hydraulic efficiency indicators, as it simulates directly transport and decay of the disinfectant, inactivation of pathogens and accumulation of by-products. The method is applied to study the effects of inlet and compartment design on contact tank performance, with special emphasis on turbulent mixing and minimisation of internal recirculation and short-circuiting. In contrast to the conventional approach of maximising the length-to-width ratio, the proposed design changes are aimed at addressing and mitigating adverse hydrodynamic structures, which have historically led to poor hydraulic efficiency in many existing contact tanks. The results suggest that water treatment facilities can benefit from in-depth analyses of the flow and kinetic processes through computational fluid dynamics, resulting in up to 38 % more efficient pathogen inactivation and 14 % less disinfection by-product formation.     

Field and experimental studies on cadmium in the edible crab Cancer pagurus

The distribution of cadmium within captive crabs (Cancer pagurus) exposed experimentally to cadmium-contaminated food and water is described and illustrated by triangular diagrams. Crabs from the Orkney Islands (Scotland) are known to contain relatively high levels of cadmium (up to 62 g g^-1 wet wt) in the hepatopancreas. The distribution of cadmium between the hepatopancreas, gonad, gill, carapace, claw muscle, heart, and haemolymph, is described in crabs collected during 1978, and compared with similar data from crabs exposed to cadmium for ca. 300 d (September 1978 – June 1979) experimentally. It is concluded that the dominant uptake route of cadmium to Orkney crabs is through their diet.