WATER QUALITY STRATIFICATION IN SHALLOW WASTEWATER STABILIZATION PONDS¹

Abstract

The physical limnology of three modern wastewater stabilization ponds serving a small community in Minnesota was investigated over a 1‐year period (July 1989 ‐ October 1990). Water temperatures and associated meteorological parameters were recorded continuously; underwater light, dissolved oxygen, pH, and Secchi depth were measured intermittently (about weekly). Measurements of nutrients and planktonic species were made by other investigators. Water quality stratification dynamics were studied by analyzing variations of water temperature, dissolved oxygen, and pH distributions with time and over depth. Intermittent stratification and mixing of the shallow waste stabilization ponds (1–2 m deep) were documented and related to weather. The strong response of the ponds to seasonal and daily weather variations was observed. Three types of pond stratification conditions have been identified: (1) completely mixed during consecutive day and night, (2) stratified during the day and well‐mixed during the night, and (3) continuously stratified during day and night. A diurnal cycle of stratification dynamics was first noticed in late April and persisted through summer and into fall. Differences in light attenuation and hence temperature stratification and DO distribution between pond 1 (primary), pond 2 (second primary) and pond 3 (secondary) in the wastewater treatment system were documented and related to different waste loading conditions. Temperature stratification affects chemical, microbial, and planktonic processes in the ponds. Results presented in this paper can be used to provide guidance for water quality sampling in monitoring of pond performance. Information on true mixing conditions is also needed to gain better understanding of important factors affecting pond operation, and for process simulations and reactor modeling of waste stabilization ponds.

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

“…Stratification occurs within ponds on a seasonal or daily basis (Gu et al, 1996), due to the M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT comparatively warmer temperature in summer and during daylight hours than that of winter and at night. Stratification simply means a noticeable temperature gradient develops within the water body, resulting in a density variation in the pond.…”

Solar-induced Thermal Activity and Stratification in Pond Water

“…This paper presents the high-resolution thermal activity of a pond, whereby the temperature was continuously measured every 50 seconds throughout the water column. Ruochuan Gu, et al, (1996) [1] employed a resolution of 20 minutes in a similar study, whereas other studies by Abis, Karen L., et al, (2006) [3], Escobar, Jaime, et al, (2009) [4] and Moss, Brian (1969) [5] observed much longer times between data collections. There appears to be no literature on long-term year round data collection.…”

Predicting the onset of thermal stratification in shallow inland waterbodies

“…Shallow lakes and ponds can stratify and destratify (with regard to both density and chemistry) on a daily basis, and may even remain persistently stratified over multiple days (MacIntyre, 1993;Gu et al, 1996;Condie and Webster, 2001;Ford et al, 2002). Thus, the entire water column of a shallow lake or pond may behave as a diurnal mixed layer (diurnal stratification/ destratification cycle), the physical dynamics of which are described in detail by Imberger (1985).…”

“…Thus, the entire water column of a shallow lake or pond may behave as a diurnal mixed layer (diurnal stratification/ destratification cycle), the physical dynamics of which are described in detail by Imberger (1985). Strong coupling between the diurnal physical dynamics and the dynamics of phytoplankton (Ganf, 1974), dissolved oxygen (Gu et al, 1996;Ford et al, 2002;Branco, 2007), methane (Ford et al 2002), and other biogeochemical processes has been demonstrated, yet it is still common in the literature to sample shallow lakes and ponds as if they were well-mixed with little or no justification. The well-mixed assumption is likely to be false in many instances and can lead to inappropriate sampling strategies or misleading interpretation of results.…”