Simulation of Water Quality in Tarawera River

The Tarawera River, New Zealand, receives effluent from two paper and pulp mills and exhibits a very high rate of deoxygenation. Attempts have been made to predict water quality in the river using the Streeter-Phelps and various other first order models but none of these can successfully predict the observed concentrations of dissolved oxygen. Investigations of the biological activity in the river have indicated that biomass accumulates in the river sediments and that aerobic metabolism of these organisms on the organic matter in the overlying waters causes the high rate of deoxygenation. A stratified mathematical model is described which uses the Monod equations to predict the rates of growth of bacteria and protozoa in the river sediments. Chemical analyses of the mill effluent are used to formulate a theoretical multisubstrate system that predicts concentrations of dissolved oxygen successfully at varying rates of flow.