Sequential Anaerobic-Aerobic Digestion of Secondary Sludge: Aerobic Temperature Effect on the Process Performance

In this paper we investigated the sequential anaerobic-aerobic digestion of secondary sludge in two series of tests performed at different aerobic temperatures: 20°C in the first series (S1) and 37 °C in the second one (S2). In both series, the aerobic phase was operated under intermittent aeration to achieve nitrogen removal. A very positive effect of the increased temperature on the process performance was observed. Achieved additional VS removal in the aerobic phase was 19.6% and 32.8% for S1 and S2 respectively. Specific biogas production was 0.95 Nm3/(kg/VSdestroyed) for both series. Nitrification efficiencies >= 80% were achieved in the entire experimental period, while a significant increase of the denitrification efficiency, up to 97%, was observed for S2. The beneficial effect of the increased aerobic temperature on the dewaterability of the digested sludge was also demonstrated by the CST trend showing a decrease of 26% in S1 and 51% in S2.