Case study of aerobic granular sludge and activated sludge-Energy usage, footprint, and nutrient removal

Abstract

This study demonstrates a comparison of energy usage, land footprint, and volumetric requirements of municipal wastewater treatment with aerobic granular sludge (AGS) and conventional activated sludge (CAS) at a full-scale wastewater treatment plant characterized by large fluctuations in nutrient loadings and temperature. The concentration of organic matter in the influent to the AGS was increased by means of hydrolysis and bypassing the pre-settler. Both treatment lines produced effluent concentrations below 5 mg BOD₇ L^-1 , 10 mg TN L^-1 , and 1 mg TP L^-1 , by enhanced biological nitrogen- and phosphorus removal. In this case study, the averages of volumetric energy usage over 1 year were 0.22 ± 0.08 and 0.26 ± 0.07 kWh m^-3 for the AGS and CAS, respectively. A larger difference was observed for the energy usage per reduced population equivalents (P.E.), which was on average 0.19 ± 0.08 kWh P.E.^-1 for the AGS and 0.30 ± 0.08 kWh P.E.^-1 for the CAS. However, both processes had the potential for decreased energy usage. Over 1 year, both processes showed similar fluctuations in energy usage, related to variations in loading, temperature, and DO. The AGS had a lower specific area, 0.3 m² m^-3 d^-1 , compared to 0.6 m² m^-3 d^-1 of the CAS, and also a lower specific volume, 1.3 m³ m^-3 d^-1 compared to 2.0 m³ m^-3 d^-1 . This study confirms that AGS at full-scale can be compact and still have comparable energy usage as CAS. PRACTITIONER POINTS: Full-scale case study comparison of aerobic granular sludge (AGS) and conventional activated sludge (CAS), operated in parallel. AGS had 50 % lower footprint compared to CAS. Energy usage was lower in the AGS, but both processes had potential to improve the energy usage efficiency. Both processes showed low average effluent concentrations.

Keywords: activated sludge; aerobic granular sludge; biological nutrient removal; electricity usage; full-scale wastewater treatment; land footprint; volume requirement.