Wastewater treatment plant cuts energy use by 20% with new biological treatment system

Xylem’s solution helps improve water quality of local river

The Alto Seveso urban wastewater treatment plant, located in northern Italy, treats wastewater from local textile manufacturers. With an aim to reduce the risk of pollutants in its discharge and energy consumption, the plant adopted a biological treatment system from Xylem which has then enabled it to reduce energy use by 20% and improved the water quality of the nearby Seveso River.

Xylem was tasked to revamp the biological treatment process of one train of the treatment plant, a bioreactor where each section can work alternatively as an anoxic or aerobic process, depending on treatment needs. This allows flexibility in reaching the target results depending on variable industrial loads, particularly for nitrogen.

As such, Xylem designed a new biological treatment system to enable flexibility and control. One way this was achieved was by adding instrumentation and sensors to control six different areas of the bioreactor.

The aeration system was also upgraded and optimised. In a typical wastewater treatment plant, the blowers in an aeration system are the single highest energy consumer. Previously, the plant had mechanical surface aerators, which could only operate in on or off mode, so the ability to regulate oxygen was limited. The plant could only turn the aerator off for a few minutes, otherwise settling would occur in the tank. Mechanical aeration is also generally less efficient than fine-bubble aeration, Xylem added.

With the new solution, the plant now has a fine-bubble Sanitaire aeration system, combined with five Flygt 4320 adaptive submersible mixers. This solution enables the plant to operate at a reduced airflow for hours or days within sections of the tanks, resulting in energy savings.

The Alto Seveso plant now also uses Sanitaire TurboMAX turbo blowers to feed different quantities of air to six Sanitaire fine-bubble systems. Sanitaire turbo blowers are direct-drive, high-speed, turbo blowers using the latest airfoil bearing technology to deliver results with lower energy consumption. The company claimed that they use up to 40% less energy than traditional blowers.

The plant’s new PLC-based control system was developed by Mariana Depur, owner and operator of the plant, with the help of Xylem. The system receives process data from Xylem WTW sensors, for dissolved oxygen and nitrogen, and enables the plant to know when to add more or less air, or no air at all, in which case the adaptive mixers are started to avoid sedimentation in the tank.

The upgrades at the plant enabled energy savings of 20%, or 640,000kWh a year, Xylem highlighted, compared to the previous system. Much of the energy reduction was achieved by the new ability to dynamically adjust operations according to the pollutant load to be removed. This flexibility is critical since discharge from local textile businesses can lead to highly variable nitrogen peaks loads.

The improvement of the wastewater treatment plant helped Lariana Depur to enhance the water quality of the Severo River, and consequently, meet the stringent discharge directives regulating the Lake Como area. The upgrade helps the plant to reduce the risk of exceeding the limit of nitrogen concentrations in its discharge. At the same time, the integrated solution lowers the plant’s energy footprint to make the community more sustainable.

“This upgrade sets a new standard for wastewater treatment in industrial zones, particularly those where there is textile manufacturing. We are proud to partner with Lariana Depur in helping to preserve local water resources,” Marco Leoncavallo, customer excellence manager, Xylem Water Solutions Italia, concluded.