A computer simulation of the oxygen balance in a cold climate winter storage WSP during the critical spring warm-up period
Banks, C.J.; Koloskov, G.B.; Lock, A.C.; Heaven, S.
Water Science and Technology a Journal of the International Association on Water Pollution Research 48(2): 189-196
2003
ISSN/ISBN: 0273-1223 PMID: 14510210 Document Number: 563921
The paper considers factors that determine the oxygen balance in extreme climate waste stabilization ponds (WSP) during the critical spring warm-up period. At this time, biochemical oxygen demand load on the pond is a maximum, due to accumulation of waste water under the ice during the winter. The paper describes the operation of a typical cold climate WSP and the events leading to a balanced steady state system as spring develops into summer. A mathematical model to simulate conditions within a batch fed experimental pond over the transient period is described. To model temperature changes in the water body experimental data were fitted to a generalized equation based on diurnal fluctuations in air temperature. The results were plotted in a normalized form and showed the diurnal fluctuation and time lapse as the depth of the pond increases. Maximum daily water temperature lagged behind maximum light intensity. Bacterial growth was simulated by a Monod kinetic model in which growth rate depends on initial substrate concentration; temperature compensation was applied using a temperature activity coefficient. Oxygen utilization was calculated from substrate removal. Algal growth rate was more complicated as it was affected by temperature and light availability. Algal oxygen production potential was considered in terms of its primary metabolite yield, which was then used in a Monod equation to estimate the growth rate. The model uses a mass balance approach to determine dissolved oxygen concentration in the pond. The model is still in a simple form but shows reasonable agreement, in terms of events and time lapses, to measured parameters in experimental ponds recovering from ice cover.