Tuning of activated sludge in winter based on respirogram profiles under standard and site temperatures.

Respirograms of activated sludge OURTx and OUR20x were measured under site (T) and standard (20°C) temperatures, respectively, and the predicted standard temperature respirogram OUR20x,cal was also calculated using the Arrhenius equation. These respirogram profiles reveal more information than effluent quality. A decrease of OUR20x is a critical alarm signal for the loss of pollutant removal capacity, and a sudden increase of the predicted value OUR20x,cal is an alarm signal for the unrecoverable deterioration of biomass. The sign of OUR20x–OUR20x,cal can be used for selection of tuning strategies. For example, a negative value of OUR20x–OUR20x,cal indicates that doubling biomass is difficult, thus strategies such as extending the reaction time with limited available biomass is preferred. The findings in this study elucidated the respiration profile of activated sludge under changes of temperature and can be effectively used for the stable operation of Wastewater Treatment Plants under cold temperatures and seasonal variations.