Modelling the biochemical oxidation processes in artificial conditions of waste treatment plants

For natural water bodies there are many models of biochemical oxidation of organic pollutants, from simple to complicated ones. For the artificial conditions of waste water treatment plants there are numerous models of oxidation processes too. The authors believe that a better understanding of these processes in nature would be gained if the oxidation processes in more simple artificial conditions were understood.An attempt has been made to explain the variety of types of models of waste treatment in an activated sludge system or a biofilm reactor by the diffusion mechanism of oxidation of single substrates on the one hand, and by superposition of the kinetics of oxidation of single substrates in measurements of the dynamics of oxidation of a complex pollutant on the other hand.The conditions in which zero- and first-order models are valid in the oxidation of single substrates are derived. Respective formulae for rate constants are given. Monod's model is valid in a broader range of substrate concentration variations. An approximate formula for the half-saturation constant is proposed. Satisfactory agreement with experimental data for glucose and ammonia substrates is shown.The formal character of models being used at present is claimed for multicomponent substrates. The accuracy of the calculation is largely governed by the number of model coefficients. Similar results obtained by Monod's and Grau's models, often used in practice, are emphasized.     

Gravity model formulation for an extensive National Parkway Site

The purpose of this study was to collect specific information on the characteristics and intensity of local Blue Ridge Parkway use and to use that information to develop a recreation use model of local Parkway visitation. Data were obtained from a self-administered mail-back questionnaire sent to a random sample of people living in the 29 counties adjacent to the Parkway.We developed two recreation use projection/demand models that employ three variables (distance, alternative recreation sites, and population density) to predict visitation to different Parkway areas from various local origins. The derived model estimates indicated that about one-fourth of all Parkway visits in 1978 were one-day visits made by area residents.