A computer simulation of the oxygen balance in a cold climate winter storage WSP during the critical spring warm-up period

Abstract

The paper considers factors that determine the oxygen balance in extreme climate waste stabilisation ponds during the critical spring warm-up period. At this time BOD load on the pond is a maximum, due to accumulation of wastewater 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 generalised equation based on diurnal fluctuations in air temperature. The results are plotted in a normalised form and show the diurnal fluctuation and time lapse as the depth of the pond increases. Maximum daily water temperature lags behind maximum light intensity. Bacterial growth is simulated by a Monod kinetic model in which growth rate depends on initial substrate concentration; temperature compensation is applied using a temperature activity coefficient. Oxygen utilisation is calculated from substrate removal. Algal growth rate is more complicated as it is affected by temperature and light availability. Algal oxygen production potential is considered in terms of its primary metabolite yield, which is 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.

On the hydrodynamics and treatment efficiency of waste stabilisation ponds: From a literature review to a strategic evaluation framework

“…In fact, regions with distinct seasons (cold winters and warm summers) and extreme climate conditions, such as the continental climate zones, equally appreciate WSPs in wastewater treatment (Heaven and Banks, 2005;Heinke et al, 1991;Price et al, 1995;Ragush et al, 2015;Rockne and Brezonik, 2006;Tilsworth and Smith, 1984;Whalley et al, 2012;Whalley et al, 2007). There have been studies reporting on the performance of WSPs in cold climate regions since 1940s (Banks et al, 2003; Heaven Heaven et al, 2011;Liu et al, 2015;Oleszkiewicz and Sparling, 1987;Prince et al, 1995;Zhang et al, 2013). WSPs in these regions experience an average annual air temperature as low as -12ºC, with extremes of -59 ºC in cold winters to ºC in hot summers (Tilsworth and Smith, 1984).…”

“…intermittent; once a year in late summer or early fall prior to freeze-up (Banks et al, 2003;Price et al, 1995;Ragush et al, 2015) or twice a year, late spring and fall (Heinke et al, 1991); pond layout: baffling -installation of baffles is recommended but can be difficult to implement due to ice cover (Heaven and Banks, 2005); volume -accommodate the change in pond volume during ice formation (Heaven and Banks, 2005); seasonal features of the functional mechanisms:…”

A Closer Look on Spatiotemporal Variations of Dissolved Oxygen in Waste Stabilization Ponds Using Mixed Models

“…Especially noteworthy is that the WSP system as an open natural system should be considered as a complicated assemblage of different processes and inputs, hence, its mechanistic models are nearly always overparameterized [43]. In fact, to simplify the models, some important processes were neglected in Kayombo, Mbwette, Mayo, Katima and Jorgensen [6] and Banks, Koloskov, Lock and Heaven [7], e.g., nutrient uptake of bacteria and algae, nitrification/denitrification, and air/water exchange. More importantly, numerous parameters applied in mechanistic models have been taken from different systems and model assumptions based on external characteristics might have to be applied.…”

“…To the authors' knowledge, there are only two studies, i.e., Kayombo et al [6] and Banks et al [7], which applied mathematical models to investigate the oxygen balance in facultative ponds (FPs). Including only algal photosynthesis, the model of Kayombo et al [6] considered four driving forces of oxygen variation in pond systems, i.e., light intensity, pH, temperature, and CO 2 .…”

“…This model suggested that 99% of oxygen production was from the algal photosynthesis while the inflow from primary FP brought 1% left. Banks et al [7] advanced their model by adding aerobic bacterial assimilation of organic matter whose rate was strongly affected by temperature. Although both studies considered the effect of climatic factors, i.e., light intensity and air temperature, on oxygen balance in pond systems, the interactions between these climatic factors and temporal characteristics were not taken into account.…”