Energy savings with a new aeration and control system in a mid-size Swedish wastewater treatment plant

Sammanfattning: Within this study it was investigated how much energy and money that could be saved by implementing new aeration equipment and aeration control in Sternö wastewater treatment plant (WWTP). Sternö WWTP is a full-scale plant built in 1997 and dimensioned for 26 000 population equivalents. The plant has two parallel biological treatment lines with pre-denitrification. During the study, one of the treatment lines was used as a test line, where new aeration equipment and control was implemented. The other line was used as a reference line, where the aeration equipment and control was maintained as before. The new aeration equipment that was implemented to support the test line was an AtlasCopco screw blower, fine bubble Sanitaire low pressure diffusers and measurement equipment. Two control strategies were tested: oxygen control and ammonium control. The results show that 35 percentage points of the test line energy consumption was reduced with the new screw blower. The diffusers saved another 21 percentage points and by fine tuning the controllers, the oxygen concentrations and the air pressure a further 9 percentage points could be saved. The ammonium control gave no energy savings, since the lowest allowed DO set-point (0.7 mg L-1) kept effluent ammonium below the ammonium set-point of 1 mg L-1.  The final energy savings of the test line was 65 ± 2 %. Each aeration equipment upgrade increased the energy savings with: •    Blower 35 %. •    Diffusers 32 %. •    Oxygen control with decreased DO concentrations and air pressure 21 %. The final savings correspond to 13 % of the total energy consumption of Sternö WWTP. These savings are equivalent to annual savings of 178 MWh, which decreases the energy costs by 200 000 SEK per year. The payback period of the implemented aeration equipment and control was 3.7 years.