Challenge

The Rochdale wastewater treatment works (WwTW) treats effluent from the local city.

A major testing regime was carried out towards the end of 2015 at Rochdale WwTW by the United Utilities (UU) Innovation Group using various submersible mixers.

The plant operated 10 x 5.85kW conventional submersible screw-type propeller mixers. During the trial, their performance was compared with that of an Aquaturbo MIX-GS unit by Aquasystems International NV, and other standard submersible mixers.

The trial entailed the measurement of the solids concentration at various levels in the anoxic zones of the works, and also in various positions in each zone.

Trials results

By trialling an Aquaturbo MIX-GS unit for a number of months, UU reported a significant power usage reduction with the Aquaturbo mixer.

The Aquaturbo MIX-GS consistently produced an equal, comprehensive mixing in all areas of the tank and water depth. The MIX-GS only used 1.1kW of energy compared with the existing mixers, which used 5.85kW per zone, and the other mixers used in the trial, which used 3.8kW on average energy use.

Outcome

As part of the scheme, Aquasystems International NV was awarded an order to replace all 10 existing 5.85kW spiral mixers with 10 x 1.1kW submersible MIX-GS units.

Among the major reasons for selecting it were that the Aquaturbo does not rag up compared with other mixers, it operates at a much lower speed with significant energy savings, and requires minimal maintenance.

The expected payback on investment is less than 12months.

A spokesman for United Utilities commented that "all parties involved were extremely impressed with the performance of Aquaturbo submersible MIX-GS unit during this extensive trial by the innovation group at The Rochdale works".

Following the trail, UU awarded Aquasystems International NV with a further contract to supply 14 x 1.5kW Aquaturbo MIX-GS anoxic mixers for their Oldham WwTW.