Dynamics and function of intracellular carbohydrate in activated sludge performing enhanced biological phosphorus removal

Various forms of polymers are involved and play different roles in enhanced biological phosphorus removal (EBPR), among which, total carbohydrate has been often measured to represent glycogen (intracellular carbohydrate) in previous EBPR studies. In this study, intracellular carbohydrate was tested after extracellular carbohydrate extraction, and its dynamics and function in activated sludge performing EBPR at 20 °C were examined: (i) during a reactor phase, (ii) when excess organic carbon was available under anaerobic conditions, and (iii) during anaerobic and aerobic starvation conditions. The proportion of intracellular carbohydrate to the total carbohydrate was only 62% in activated sludge taken at the end of the aerobic phase. Intracellular carbohydrate alone, or combined with polyphosphate, was used as an energy source for organic carbon uptake under the anaerobic condition. Intracellular carbohydrates were degraded for maintenance during starvation, with the first-order degradation coefficient of 0.41 1/d under anaerobic starvation and 0.19 1/d under aerobic starvation. Intracellular carbohydrate rather than total carbohydrate should be tested in EBPR studies so as to better understand, operate, control and model the EBPR process.