A recent study at a wastewater treatment plant showed that real-time monitoring and control of aeration reduced nutrients returned to the main treatment process by 90% and lowered energy consumption by 95%. Learn how the Xylem solution works.

Operators and engineers at wastewater treatment plants are faced with rising operating costs due to increasing energy and chemical prices, as well as stricter effluent permit limits. Many plants are turning to sensors and automation to reduce operating costs, limit capital expenses and enhance treatment performance.

To overcome these challenges, an advanced process control study was conducted in an aerobic digester in Green Lake, Wisconsin. By controlling the process in a smarter way, the solution significantly reduced phosphorus and nitrogen in the returns to the main treatment process and reduced energy consumption and wear on the blower.

Background to the aerobic digestion study


The Green Lake wastewater treatment plant uses a continuous feed ICEAS advanced SBR system (average flow = 0.2 MGD) with aerobic digestion. The digester includes fine bubble diffusers, positive displacement blowers, and a manual telescoping valve for decanting. Digester solids are sent to a belt filter press for dewatering and ultimately land application.

The digester has four zones operating in series, two in the east digester and two in the west digester. Waste activated sludge is automatically pumped from the ICEAS system into the east digester approximately every two hours. The supernatant from the digester is returned to the SBR through the telescoping valve and is manually initiated four days per week. A sludge pump is used to remove sludge from the west digester once per week.

Xylem’s YSI sensors, OSCAR system and DINO controller

During the study, YSI sensors measuring NH4, NO3, K, DO and ORP were installed in the east and west digesters. Additionally, a YSI orthophosphate (PO4) analyzer (P700 model) was installed in the east digester.

The aerobic digester was upgraded with Xylem’s OSCAR process performance optimizer control system with DINO controller, which automatically adjusts the required aeration time in the digester based on potassium readings. The DINO controller alternates aerobic, anoxic and anaerobic conditions in the digester to optimize total nitrogen and phosphorus treatment while minimizing energy consumption.

Result: improved nutrient removal and energy savings

The OSCAR system with DINO controller enabled biological phosphorus removal in the digester, reducing PO4 returned to the ICEAS process via decant or solids dewatering by more than 90% on average. This reduction helped the plant reduce chemical consumption in the main treatment process by more than 50%, while still meeting the effluent phosphorus permit.

The DINO controller also achieved 100% reduction in NO3 returned to the main treatment process when compared to the previous operation, which was continuously aerated. The Green Lake plant’s digester blower energy consumption was reduced by 95% compared to previous operation. Blower energy was shifted from 36% on-peak to 0% on-peak, reducing demand charges and the unit cost of energy.

Overall the aerobic digester, equipped with the OSCAR system with DINO controller, reduced nitrogen and phosphorous returned to the main treatment process by more than 90% and lowering energy consumption by more than 95%.