Chopper pumps provide robust solution for unscreened sludge

The expense and inconvenience of pump failures is a recurring theme at some of the UK’s sewage treatment works (STW) and often the cause of the problem is a lack of reliable mixing of unscreened sludge before it enters pumping systems.

This was the situation at Flag Fen STW, one of Anglian Water’s main sites in Peterborough, where problems were occurring with blocked lobe pumps on a strain press feed application. Unscreened sludge was being imported into the Flag Fen works which contained large accumulations of rag and surface crust. 

Head to head

P&M Pumps was invited to provide a self-priming chopper pump on a sale or return basis for a one month trial. This involved the Vaughan pumps distributor’s model SP4C pump competing for evaluation with a new Gorman Rupp T4 trash pump with belt drive and 11Kw motor.

The Vaughan chopper pump exceeded the performance of the GR pump in effectively handling the unscreened, rag-laden sludge with far fewer blockages. However, it was still susceptible to the large masses of reweaved material entering the pump suction line and it was clear to Anglian Water that there was a need to condition the sludge on a permanent, ongoing basis.

The immediate result was there was not a single strain press feed pump blockage over five days. In addition, the performance of the sludge centrifuge improved

So, in addition to the strain press feed pump, P&M Pumps supplied and installed a free trial mixing and conditioning solution. This consisted of a Vaughan model SE8N chopper pump powered by an 18.5Kw motor which was free standing along with an attached nozzle manifold all of which was secured to an existing submersible mixer gantry after being positioned by crane. 

Following a short period of operation and a recirculation flow of 360m³/hr the imported sludge in the tank was effectively mixed and the surface accumulation was removed apart from a large floating mass that had been static in the centre of the tank.

Results driven

The immediate result was there was not a single strain press feed pump blockage over five days. In addition, the performance of the sludge centrifuge improved, resulting in a uniform performance and increase in throughput due to higher feed solids being achieved.

P&M Pumps stated these and other tests demonstrated that Vaughan Chopper Pumps were an effective solution to challenging solids pumping situations in which other types of chopper, macerating or whole solids passing-pumps have traditionally struggled.

In most cases, retrofitting a Vaughan Chopper Pump into a problematic area improves the whole process and will be self-financing, asserts the distributor. 

Process optimisation is primarily about acquiring the correct data and using it as effectively as possible. This requires experience in the application as well as with the equipment itself to ensure a cost-effective and reliable installation.