Waster Water Treatment - United Utilities Case Study

United Utilities are one of the UK’s largest utilities and have an extensive clean water and water treatment business. A significant part of this business is the treatment of waste-water so that water outflows from its sewerage plants to rivers and the sea meet stringent purity standards.

In common with most other waste water treatment plants world-wide, this treatment includes an ‘active sludge’ process. Essentially this process uses microbes to feed on the effluent and thus enable a further process to separate out clean water. In order for these microbes to live they demand large volumes of oxygen which has to be added to the effluent via an aeration process.

Aeration generally consumes large quantities of energy and accounts for around 60% of the operating cost of a treatment plant. The Newton Gravity Aerator was introduced to United Utilities with the projection of significantly reducing energy and maintenance costs.

United Utilities decided to undertake a feasibility test of the aerator at their Ellesmere Port R & D facility. The feasibility trial was awarded a SMART grant by the DTI.

The trial took effluent from their normal feed into a test tank in which a trial aerator was installed. The test tank had a capacity of 2 cu m. A trial aerator was designed to aerate this small tank and had a throughput of around 1 l/s.

United Utilities measured oxygen transfer of this aerator using industry standard methods, calculating KLa and kgO2/kWHr.The result of this test was the Newton Aerator consumed around 50% of the energy of comparable aerators in the test tank. With an inefficient small pump, the aerator’s efficiency was calculated to be 1.6 kgO2/kWHr.

Based on the success of this feasibility test, United Utilities decided to undertake a ‘production scale’ trial. This test will run in one of their standard aeration lanes at their Skelmersdale Waste Water Treatment plant. The aeration lane is one of nine on sites that are all fed by a common source. It has a capacity of 750 cu m and currently surface aerators are used (as shown in the photo).

These trials are also being supported by a DTI R & D grant. They aim to compare directly the energy consumption of the Newton Aerator with surface aerators and compressor/diffuser aerators. Energy efficiency is projected to be in the region of 2.5 kgO2/kWHr. Additionally measurements will be taken of the quality of the microbe population in order to assess its mixing capabilities. 25 year life time cost models of the aerator will be projected and compared to current aeration systems.

Initial projections are that the Newton Aerator will save United Utilities in the region of £50,000 per annum per lane. Reduced maintenance costs need to be added to this figure. The final assessment is expected by Spring 2005.