Environmental impact and limnological response of a deep wastewater treatment pond

Abstract

The annual and seasonal response of water quality variables to the annual hydrometeorological variation is evaluated at the 10 ft. deep wastewater treatment pond no. 3 of Boxelder Sanitation District. Data of six water quality variables are collected, in one foot depth increments from the surface to the bottom of the pond, to investigate their temporal and spatial response to the seasonal variations in maximum-monthly solar radiation, air temperature, and peak wind gusts. Discrete Fourier series of the nine hydrometeorological variables are generated to study the maximum response of the water quality variables to changes in hydrological phenomena at the surface of the pond.The inter-relationships among the variables under investigation are identified by performing multiple linear regression. The results of the Fourier and regression analyses aid in the identification of the variables which significantly affect the performance of the deep wastewater treatment pond, at an elevation of 5000 ft., operating under the widely varying climatic conditions experienced in Northern Colorado.Analysis of the depth profiles of water temperature, dissolved oxygen, conductivity, and salinity reveal that the 10 ft. deep wastewater treatment Pond No. 3 functions as a shallow lake. The limnological behavior of the deep wastewater treatment ponds is signified by the formation of thermoclines, negative heterogrades, positive heterogrades, clinogrades, and chemoclines. The temporal and spatial observations of the dissolved oxygen, oxidation reduction potential, conductivity, and pH point toward the occurrence of photosynthetic activity, algae blooms, summer anoxia, eutrophication, aerobic, anoxic and anaerobic zones at various depths-and-times in the pond. The strongly aerobic and anoxic periods are the respective indicators of nitrification and denitrification-and-phosphorus releases in the pond. Formation of the winter ice cover and the subsequent warmup lead to the episodes of densimetric mixings as witnessed by the corresponding dissolved oxygen depth profiles. The pH depth profiles under the ice cover indicate acidification of the pond waters. The frequency of the process-altering limnological phenomena classify the 10 ft. Pond No. 3 as discontinuous cold polymictic.