Increase of pH in polishing ponds can be predicted quantitatively from variations in alkalinity and acidity. These variables are affected by processes that develop simultaneously in ponds: (1) CO2 desorption, (2) biological CO2 removal by photosynthesis and (3) NH3 desorption. An experimental investigation was carried out to determine the desorption rate of carbon dioxide and ammonium. It is shown that CO2 and NH3 desorption can be described by Fick’s law, which describes desorption of a gaseous compounds from water as a first order process with respect to the degree of oversaturation, which is the driving force of the process. An experimental investigation was carried out to determine the desorption rate constants. The value of the constant proved to be inversely proportional to the depth of the pond (H) and its value for H=1 m and at 26°C was established as KCO2=0.34/H d−1 for carbon dioxide and KNH3=0.33/H d−1 for ammonium.
Keywords: desorption, pH, polishing ponds, volatile compounds