Submersible mixers adjust speed to suit real-time environmental conditions

As part of one of the largest investments in Europe for wastewater treatment, a plant near Naples, Italy, was equipped with innovative technologies to improve water quality while minimising energy usage. At the core of effective denitrification operations are Sulzer’s XRW 400 submersible mixers with a permanent magnet motor, which could cut energy costs by up to EUR 45,000.

The large-scale project aims at improving the quality of the coastal environment and the waters around Naples by revamping and upgrading key water and wastewater treatment facilities in the region. This program represents the most considerable European investment in water purification and decontamination for the past 20 years, supporting the treatment of wastewater from over 4.5 million inhabitant equivalents (900,000 m3 of water per day) in the region. 

One of the five facilities selected is among the largest in Europe. Established in the 1970s, it gathers wastewater from a large area in the northern part of Naples and has a processing capacity of 240,000 m3 of water per day (1.2 million inhabitant equivalents). To continue supporting the region, key improvements were required to optimise the sewage treatment process and energy consumption while ensuring regulatory compliance.

To meet the objectives set out for the successful re-functionalisation and modernisation of this infrastructure, a leading water and waste service specialist contacted Sulzer. The companies have a longstanding relationship and, through multiple international collaborations, it has been able to learn more about Sulzer’s technologies and services, growing its confidence in the ability of its partner to deliver well-suited solutions. In particular, there was enthusiasm to adopt 28 of Sulzer’s highly energy efficient mixers, such as the XRW 300 range of submersible units, for the 14 denitrification tanks within the wastewater treatment plant.

Used to remove nitrogen from wastewater effluents, the tanks installed in the facility have an unusual geometry, being 22m long but only 7.85m and 4.8m in width and height. Therefore, it was necessary to specify mixers featuring propellers with a limited diameter, which are typically regarded as difficult to adjust in order to minimise energy usage.

In practice, the use of conventional solutions with IE3-equivalent, three-phase, squirrel-cage motors could reduce energy costs by EUR 8,000 at the plant. Conversely, the XRW 400 series could slash such expenditures by more than five times, delivering savings of up to EUR 45,000. Even more, the presence of drives supports self-cleaning functions, enhancing the service life of the mixers in such challenging applications while reducing downtime, maintenance activities and their associated costs.

Following the installation, commissioning and startup of Sulzer’s submersible mixers, the plant and its denitrification tanks have been running smoothly. These have been efficiently processing large volumes of wastewater daily while meeting environmental standards for effluents.