The reactive pump control method uses an ABB low voltage AC drive combined with a specially written software algorithm to measure viscosity and achieve the flow control demanded by the sludge pumps.The drive starts pumping on an internally set time delay and stops pumping when sludge viscosity drops to a pre-determined value. The pump maintains a constant speed using the viscosity measurement to ensure only the correct percentage of solids is pumped. This method can typically achieve savings of over £42,000 for a sewage treatment plant, through reduced energy use, reduced sludge transport vehicles and lower maintenance of the sludge pumps.This in turn can lead to reductions in operating costs, cuts in transport of sludge and savings in capital equipment for new projects. Settling tanks do not need de-canting prior to tanker arrival, while the number of tankers needed is halved as the water content in the sludge in the holding tank is much reduced.In current wastewater treatment practice, sludge is pumped from settling tanks to either holding tanks or decanting tanks using progressive cavity (PC) pumps, from where it is pumped into road tankers for transfer to digesters. Before the sludge can be pumped from the settling tanks, it needs to be of a certain viscosity. Measuring this viscosity is achieved using PLCs and sensors inserted within the sludge to determine the percentage of dry solids. Yet, whatever the level of solids present in the sludge, the pumps need to be run frequently to prevent clogging. As well as wasting energy, this also leads to a requirement for monthly maintenance of the pumps.The reactive pump control method was developed by Inverter Drive Systems (IDS), a variable speed drive (VSD) specialist and one of the members of ABB’s Drives Alliance, a group of 12 partners which help distribute the company’s drives.