A model and design equations for the intermittent sand filter

Design parameters based upon influent suspended (SS) and volatile suspended solids (VSS) concentrations and hydraulic loading rates were evaluated. Functional relationships and coefficients describing the efficiency of the ISF process were developed based upon laboratory data from filter units containing 0.17 mm effective sand size (ε′) media. Adequate SS and VSS removals were observed for the 0.17 mm ε′ sand filters. Field data from other studies using filter units containing 0.17, 0.40, and 0.68 mm ε′ sand were also evaluated using the model. Sand sizes larger than 0.17 mm ε′ did not produce effluents satisfying a federal secondary standard of 30 mg/1 of SS when the filter influent suspended solids were predominantly algae.     

Wind speed affects prey-catching behaviour in an orb web spider

Wind has previously been shown to influence the location and orientation of spider web sites and also the geometry and material composition of constructed orb webs. We now show that wind also influences components of prey-catching behaviour within the web. A small wind tunnel was used to generate different wind speeds. Araneus diadematus ran more slowly towards entangled Drosophila melanogaster in windy conditions, which took less time to escape the web. This indicates a lower capture probability and a diminished overall predation efficiency for spiders at higher wind speeds. We conclude that spiders’ behaviour of taking down their webs as wind speed increases may therefore not be a response only to possible web damage.     

Degradation of polycyclic aromatic hydrocarbons (PAHs) in an aged coal tar contaminated soil under in-vessel composting conditions

In-vessel composting of polycyclic aromatic hydrocarbons (PAHs) present in contaminated soil from a manufactured gas plant site was investigated over 98 days using laboratory-scale in-vessel composting reactors. The composting reactors were operated at 18 different operational conditions using a 3-factor factorial design with three temperatures (T, 38 degrees C, 55 degrees C and 70 degrees C), four soil to green waste ratios (S:GW, 0.6:1, 0.7:1, 0.8:1 and 0.9:1 on a dry weight basis) and three moisture contents (MC, 40%, 60% and 80%). PAH losses followed first order kinetics reaching 0.015 day(-1) at optimal operational conditions. A factor analysis of the 18 different operational conditions under investigation indicated that the optimal operational conditions for degradation of PAHs occurred at MC 60%, S:GW 0.8:1 and T 38 degrees C. Thus, it is recommended to maintain operational conditions during in-vessel composting of PAH-solid waste close to these values.