Quantificação dos processos que afetam o pH em lagoas de polimento.

Abstract

Waste stabilization ponds are know to be efficient in the removal of organic material and pathogens, but nutrient removal is much less efficient. However in pratice nutrient removal can be important for exemple when the effluent from a pond system is to be discharged in a dam. In that case nutrient removal may be necessary to avoid eutrophication. The removal mechanism of the macronutrients nitrogen and phosphorus is different: nitrogen is released as ammonium gas to the atmosphere, whereas phosphorus precipitates as orto phosphate. Both ammonium release and phosphate precipitation can only occur at high pH, when the ammonium equlibrium shifts towards the unionized gas form, NH3, and the phosphorus equilibrium towards the orto phosphate ion PCm3 . In theis study it is attempted to identify the processes that take place in ponds and affect pH. and to determine quantitatively the effect of these processes on p l l and linked parameters: alkalinity and acidity. It was established that the variation of pH alkalinity and acidity in ponds is affected mainly by the removal of CO2 and N H 3 from the liquid phase. CO2 removal takes place to both physical (desorption) and biological processes (photosynthesis). NH3 removal is due to desorption results in increase of acudity and decrease of alkalinity. When both the variation of alkalinity and acidity are known the affect on pH can be calculated with the aid of concepts of water chemistry. Through an experimental investigation it was established that it is possible to predict variations of alkalinity and acidity and hence of p l l when the extent of C O 2 and NH3 removal is known. On the other hand, i f there is a possibility to estimate the rate of the processes of C02 and MH3 desorption and of photosynthesis, it is possible to estimate the required time for a particular desired pi I increase.