In wastewater measurement, accurate readings are essential to ensure proper pump operation. If such a measurement system fails, unhygienic wastewater can overflow and pollute the environment.
The pump systems themselves can also suffer damage if operated incorrectly on the basis of erroneous measurement values. Among other things, wastewater contains organic compounds such as proteins, carbohydrates and fats (grease). The latter in particular have the unpleasant habit of clumping together and forming sediments that are difficult to dislodge.
False measurements due to the formation of sediments
Newport News, Virginia in the USA offers a good example of what can happen in such a situation. Newport News was founded in 1621. It is situated along the James River and its nearly 180,000 residents make it the fifth largest city in Virginia. Here, several restaurants were built in an area serviced by the same municipal wastewater lift station. The high grease content in the wastewater then polluted the existing level measurement equipment, ultimately leading it to break down completely.
Prior to the development of the commercial district, the Newport News Waterworks and the Hampton Roads Sanitation District relied on a combination of mechanical floats and conventional submersible transmitters. Both measurement systems stopped working after the restaurants opened: Both the primary and redundant level measurement equipment failed to properly transmit level data to the pump controller.
The heightened grease content in the wastewater caused by the restaurants led clumps to form on the level transmitter membranes, which ultimately blocked the flow of water to the measuring membrane. On the redundant float switch, whose purpose was to trigger the pump in the event of a failed level transmitter, the accumulation of grease blocked the mechanical operation of the float ball. The failure of the level transmitter and the backup system led to the failure of the entire lift station because the pumps either operated constantly or not at all. If technicians hadn’t acted quickly, the entire sewage system could have come to a complete standstill.
Kynar® membrane offers better resistance
If a lift station is to function properly, grease must not be allowed to block the measuring devices. Various manufacturers offer non-fouling products that often present difficulties in other areas, however. The instruments usually employ a Teflon-coated elastomer membrane, which, while non-fouling, is also relatively weak and prone to puncture. The membrane is therefore equipped with a rather bulky protective shield that is mounted on bolts. Grease tends to accumulate in the gaps that result from this setup, however, which means the problem just moves to another location, as clumps of fibres, grease and sludge form the wastewater continue to impair correct measurements.
In the case of Newport News, city officials contacted KELLER Pressure, whose 36KyX level transmitter, which is known in the USA as the LevelRat, enables a unique approach to wastewater level measurement.
The Kynar® membrane used in the 36KyX is harder and offers superior abrasion and puncture resistance relative to other non-fouling solutions. Bulky shields are therefore no longer needed, which also enables a more compact design for the sensor. The 36KyX can fully exploit the advantages offered by a non-fouling membrane without anyone having to worry about floating particles and small objects. Put simply, the level transmitter is perfect for this application. No incorrect measurements due to grease deposits have been recorded at Newport News Waterworks since the new transmitters went into operation: The LevelRat solved the problem.