Background
The expense and inconvenience of pump failures is unfortunately 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.
The Challenge
Unscreened sludge was being imported into the Flag Fen works which contained large accumulations of rag and surface crust (See Pic 1) and the key to finding an effective solution was essentially reliable mixing. P&M PUMPS the UK distributor of VAUGHAN PUMPS were invited to provide a self-priming chopper pump on a sale or return basis for a 4 week trial. The Vaughan model SP4C pump would be working alongside a new Gorman Rupp T4 trash pump with belt drive and 11Kw motor on a head-to-head evaluation basis.
The Result
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.
As a result, and in addition to the strain press feed pump, P&M Pumps supplied and installed (on a free trial basis) a mixing and conditioning solution to Anglian Water. This consisted of a Vaughan model SE8N chopper pump (See Pic2) 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, (See pic3).
Following a short period of operation and a recirculation flow of 360m³/hr the imported sludge in the tank was effectively mixed (See pic4) and the surface accumulation was removed (apart from a large floating mass that had been static in the centre of the tank). The immediate result following the installation of the mixing system was a period of 5 days without a single strain press feed pump blockage. 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.
In Conclusion
Through their experiences at Anglian Water and numerous other waste water treatment sites across the UK, P&M Pumps have demonstrated that Vaughan Chopper Pumps are an effective solution to the most challenging ‘solids pumping’ situations where 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, with unrivalled payback periods in some cases being a matter of months, thereafter minimising the effect to the budget holders.
