Mixing and its impact on faecal coliform removal in a stabilisation pond

Abstract

Faecal coliform removal in stabilisation ponds is highly dependent on shortest water retention times. Tracer tests have been performed in a 3,300 m2 and 1.0 m deep pond, located in Southern France, to measure the retention times and bring light on the main influencing factors and mechanisms. Tracer concentrations were monitored at the outlet and 60 locations within the pond--at the surface, mid depth and the bottom of the water column. Pond water temperatures were measured at different depths and locations, together with pH, DO and redox potential. Wind velocity and rainfall were recorded. Water quality was monitored at the inlet, outlet and within the pond. Water retention times were shown to be strongly affected by weather conditions. Windy periods appeared to favour mixing regardless of the season. In sunny periods of spring and summer, a clear stratification was observed during daytime and vanished gradually during the night, suggesting alternation of mixed and stratified hydrodynamic patterns. This alternation was shown to influence microorganism contents within and at the outlet of the pond. Accurate prediction of shortest water retention times and disinfection performance requires 3D unsteady state fluid dynamic models that are able to take the influence of wind and water temperature distribution into account.

Significance of buoyancy in turbulence closure for computational fluid dynamics modelling of ultraviolet disinfection in maturation ponds

“…Consistent cycles of thermal stratification and night-time natural convection in maturation ponds have been reported (e.g. Gu and Stefan, 1995;Brissaud et al, 2003;Dahl et al, 2017a,b). Modelling and experimental evidence reported that the combination of thermal stratification and vertically attenuated sunlight in the water column is the cause for greater die-off in the near surface region of the water column during the day (Brissaud et al, 2003;Dahl et al, 2017a,b).…”

“…Gu and Stefan, 1995;Brissaud et al, 2003;Dahl et al, 2017a,b). Modelling and experimental evidence reported that the combination of thermal stratification and vertically attenuated sunlight in the water column is the cause for greater die-off in the near surface region of the water column during the day (Brissaud et al, 2003;Dahl et al, 2017a,b). This has also generated interest in developing sunlight disinfection models that resolve disinfection in a spatially dependent manner (e.g.…”

Removal of phosphorus from secondary effluents using infiltration–percolation process

“…During the operation phases, the daily hydraulic loads were 0.27 and 0.40 m 3 m −2 of sand basin. Alternation of operational and drying periods has always been considered essential to infiltration-percolation and soil aquifer treatment; it is the only practical way to manage clogging at the surface and in the core of filtrating beds (Brissaud et al 2003).…”

Hydro-epidemiology: the emergence of a research agenda

“…The hydraulic community has led developments in modelling bacterial concentrations in environmental waters [33] and sewage treatment systems [15,24,37,52,61,63,64,69]. In some notable contributions, the links to defined health outcomes have also been addressed in modelling investigations [31,41,42].…”