[Case Study - February 2010] The City of Eagan in North Minnesota, USA required a pump capable of accurately dosing 15% sodium hypochlorite or 'hypo' for their new wastewater treatment plant.
Hypo has outstanding disinfection properties. It is used in wastewater treatment to kill off bacteria before being discharged back into the environment and in water treatment as one the primary methods of drinking water disinfection. It is also a challenging product to pump. This is because hypo tends to off-gas, causing some types of pump to vapor lock. Diaphragm pumps are particularly prone to this.
Peristaltic pumps are the pump choice for dosing sodium hypochlorite and Verderflex pumps can be found in wastewater treatment plants worldwide.
The fluid being dosed is kept totally enclosed within the rubber hose, which is then compressed by a rotating shoe forcing the liquid inside, along. Upon restitution of the hose the resulting vacuum draws in more liquid. This process is known as peristalsis and is what makes the peristaltic pump the first choice for liquid metering. Variations in hose type allow for low strength and even high strength hypo dosing.
Naturally the wastewater plant needs to run as cost efficiently as possible and the City of Eagan were impressed with the long life given by the Verderflex hose and the ease of maintenance when the hose needed to be changed.
"We were really pleased with the installation at the treatment plant. There were many other pumps considered for this application but in the end easy maintenance, proven reliability and exceptional hose life of the superior Verderflex design won out," explained Tom Eisemon, National Sales Manager of GPM Pumps, the master distributor for Verderflex in the US. "As a result of this installation, a similar project located nearby chose Verderflex for these same reasons and a third customer in the state recently purchased a new Verderflex DURA after hearing all the positive feedback and the new features of this design. These pumps have certainly been a success for us in this industry."
Several other applications in water and wastewater industries are ideal for Verderflex peristaltic pumps. Lime, Kalic® or Kalkmilch are ideally dosed by these products. The chemicals are used to rectify the pH of wastewater discharges and are particularly abrasive, creating continual wear problems for progressing cavity pumps. This leads to high stator replacement costs and frequent maintenance downtime.
Lime is also relatively viscous, indeed generally too viscous for diaphragm pumps, causing them to clog up and become highly maintenance dependent.
Verderflex pumps are abrasion resistant and ensure the smooth passage of the liquid regardless of its viscosity. Their design also presents no opportunity for the product to settle as the peristaltic action keeps the product in suspension. Furthermore the product can be mixed on site as solids in the liquid stream do not present a problem for the pumps. They also have a linear flow-speed characteristic that is ideal for feedback control systems, allowing precise control of the chemicals being dosed, minimizing chemical usage.
'Ferric' and polymer dosing is another common application for Verderflex. These additives are used in clean water plants to remove peat, suspended solids and residual colors from clean water streams. In wastewater treatment, sophisticated polymers maximize plant throughput by increasing the solid separation rate allowing greater primary waste volumes to be treated.
Most polymers are highly shear sensitive but this is not a problem for Verderflex. The gentle pumping action its products employ ensures that shear sensitive solids and liquids are not damaged or altered, a common problem with other designs.
All water treatment plants produce waste, which has to be prepared for disposal. Usually a filter press is used to minimize volumes and constrain the waste processing costs. Such equipment presents a challenge to traditional pumping solutions as the water is abrasive, resulting in reduced flow. To address the problem pump speed is often increased and the pump is operated with the gland seals pressurized. The result is increased leakage exposing the press mechanism to abrasive wastes.
Variable suction performance is the inevitable consequence and as suction pressure increases 'rat holes' appear in the filter press feed as water is pulled from above the top of the sludge blanket. This increases the water content and the volume of the pressed waste, increasing operation costs.
By contrast Verderflex pumps give consistent suction performance and do not incur significant wear. For this reason they have also become an industry standard for treatment plants across the world to optimize filter press operation.
February 2010
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