Polymer is typically the third or fourth most-expensive line item in a treatment plant’s operating budget, making it crucial to choose the right partner when it is time to select your polymer blending and feed system.
So, how do you know where to start when it comes to selecting the right system? Well, for one, the major polymer suppliers are explicit in their operating manuals that the best feed systems use initial high energy mixing (> 1000 rpm) for a short time (< 30 seconds) to achieve good dispersion followed by low energy mixing (< 400 rpm) for a longer period of time (10-30 minutes).
Systems that don’t follow this practice often waste polymer. Consider this: if a municipality is spending $100,000 per year on polymer and a more-efficient system can help reduce that number by 20%, the cost of the system (in most instances) will be covered in the first two years of operation. We’ve seen occasions where switching to a two-stage mixing system can save as much as 50% on polymer usage.
| The relationship between the high energy moment of initial wetting (MOIW) and the more gentle agitation zone (quiescent zone) optimizes polymer activation. The mix chamber configuration must include both of these features as well as provide enough volume for the flow to achieve these objectives – this volume and flow relationship is measured as residence time. Too low a residence time means that there is not enough “processing” volume to activate polymer and too much residence time is wasted space and energy. In summary, the key to proper polymer activation is “the right energy at the right time”. It’s a two-step process and those steps are very different from each other, but equally as important. Without both high energy at the start and low energy at the end, you are going to waste polymer and waste time, which frankly means you’re going to waste money. |
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