Improving wastewater treatment reliability

Louise Smyth

The Ensdorf sewage treatment plant processes the wastewater generated by the German region’s 50,000 inhabitants, together with effluent generated by several local industries.

Ensuring that water leaving the facility meets strict cleanliness rules and that the remaining solids are also transformed into a condition suitable for safe disposal, is a delicate balancing act. The inflow rate to the plant can vary significantly, from 26,000m3 per day in dry weather to 57,888m3 per day during periods of heavy rain. The volumes of contaminants and solid wastes processed by the facility similarly vary over time. To keep the plant’s processes running properly, staff must adjust the operating speeds of equipment across the facility as demand rises and falls.

Originally, speed control in some of the plant’s important equipment was achieved via mechanical means. As part of the sludge dewatering process, the pumps that supply sludge to the two centrifuges were powered by 7.5kW asynchronous geared motors with belt drive adjustment. Additional pumps used a similar system with 4kW motors to transport the thickened sludge away from the centrifuges and on to the next process.

While the belt drive approach did enable the necessary speed control, the system proved unreliable in operation. Adjusting the belts frequently was inconvenient for operators, and breakages were common, leading to downtime and disruption.

In search of a better approach, the plant’s managers contacted drive technology specialists, Klebs + Hartmann, a Bauer Gear Motor Gear Centre. The solution it devised was based on the introduction of variable speed drive (VSD) controls and high-efficiency permanent magnet gear motors supplied by Bauer Gear Motor.

The new approach solved Ensdorf’s reliability challenges at a stroke. The VSDs eliminated the need for belts and allowed the automation of speed control in the transport systems for the centrifuges. Furthermore, the new motors are IP66 rated, providing increased protection.