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The Price of Polymer Doesn't Matter
Did the title of this article get your attention? It was designed to. Please humor me and try to reserve judgment until the end. You might even agree with me!
Dewatering biosolids is one of the most significant cost centers for a wastewater system, often only eclipsed by personnel costs. The equipment, chemicals, workforce, energy, and disposal fees required to remove biosolids add a massive expense to your operation. Good managers frequently look for ways to reduce this cost, and polymer pricing is often a manager's or purchasing agent's first target. It seems like common sense; if you can buy a cheaper polymer, you will save money, right? It may be hard to believe but switching to an inexpensive polymer will often cost your system much more money in the long run.
Polymer Quality
As with most things in life, when it comes to polymer, you get what you pay for. In recent years there has been tremendous consolidation within the polymer industry. As of this writing, the United States has three major manufacturers of long-chain flocculants, and all of them use similar methods to produce their products. Each manufacturer has different polymer grades; the top-tier products contain the highest active content, quality raw materials, and robust surfactant packages. Then there are the lower-cost, mid-tier, and low-tier categories. These products generally have less active content and use lesser quality raw materials and manufacturing methods to reduce cost. This reduction in price looks good on paper, with low-tier polymers often costing as much as 30% less than their top-tier counterparts. Unfortunately, cheap polymer often costs a wastewater system significant unnecessary expense.
Polymer Dose
A polymer is a long-chain molecule with a charge, and it works to attract the biosolids to this chain to allow for water/solids separation using the law of magnetism. The less activity a flocculant contains, the more polymer it will take to accomplish water/solids separation. Another cost area that is cut in the mid-low tier liquid products is the surfactant package. Surfactants accomplish two goals; they keep the emulsified polymer in a homogenous solution for shipping and storage and break the emulsion when mixed with water. The polymer chains often do not fully unwind when a lessor-quality surfactant is used. Partially developed chains do not expose all the available charge sites and require a higher dose.
Dry Polymer
What about dry polymer? Since there are no surfactants, you might think one dry polymer should be the same as another; unfortunately, this is not the case. Dry polymer manufacturing costs are reduced by adding non-active fillers. The most common is sodium, and salt is cheap. If a manufacturer adds 10%-20% sodium to their dry polymer, they substantially reduce costs and increase margins. We have tested some dry products on the market and have seen over 25% sodium in some instances. Non-active fillers will increase the dose and reduce performance. Also, sodium will immediately break down polymer chains, further decreasing performance. Have you ever wondered why a batch of dry polymer that you made up Friday doesn't want to work on Monday? Chances are good that a sodium filler is in the polymer, which has broken down polymer chains over the weekend.
Cake Solids
A drier cake means more water is removed during the dewatering process. Most modern dewatering methods use some form of external pressure to extract water from the flocculated solids. The more pressure that can be exerted, the more water will be released, creating a drier cake. The drier the cake, the less water you are paying to dispose of, and the less room the solids will take up in the truck, meaning a drier cake=less trucks/less cost. Lower-tier polymers will often not stand up to high pressures resulting in less water being removed which you will need to pay for when disposing.
Disposal Costs
Disposing of dewatered biosolids is expensive, and landfill requirements are increasingly more stringent. Biosolids are required to be at least 20% dry in my home state of New York. Numerous landfills are restricting biosolids altogether or have increased tipping fees. Many of our clients are paying more than $100.00/wet-ton tipping fees. The more water in your dewatered sludge, the more you will pay to dispose of it. If that cheap polymer is causing you even a 1% wetter cake, you will most likely spend much more on disposal costs than the inexpensive polymer saved you.
Operational Costs
Polymer works on a bell curve. Once the optimum dose is reached, the maximum performance of a given polymer is achieved. In theory, we want the top of this bell curve to be flat. A flat bell curve will allow for a wide window of operation, which translates to ease of use and better performance. Dewatering biosolids is like shooting at a moving target. There are variables in sludge consistencies and pumping rates. A high-quality flocculant will provide its best performance over a wide operation window, meaning that less dose adjustment will be required to maintain peak performance during a run. A lessor grade polymer has a sharper bell curve which requires more adjustment to keep it in peak operation. More adjustments mean more time that the equipment is producing substandard results. A sharper bell curve also means a lot more work for operators.
Inside Baseball
Here is a little-known fact: Polymer manufacturers make more money on lessor-grade flocculants. The margins are higher, and you will use more; hence they will sell more. Guess who uses the most low-grade polymer. Large municipalities that purchase on price, not performance. Don't fall into the trap of looking only at the price of the polymer; that's what the manufacturers want you to do.
Evaluate Polymer by Total Cost of Use
Making sure you are getting the lowest total cost of use polymer takes a little work but will pay huge dividends. We developed a spreadsheet that makes it easy to compare two polymers' total cost of use. When you click on the link, you will see data from a test we recently ran for a new client. You will see how a seemingly more expensive polymer will save this system thousands of dollars annually. Plug in your polymer price, tipping fees, and dose, and it will calculate total daily and yearly expenses. I encourage you to play around with it. See how differences in polymer dose and cake dryness affect your bottom line. With this tool, you can quickly evaluate a new polymer to know if it will save you money. Run your own polymer test, and don't just rely on a salesperson to sell you the best product for your plant. The price of the polymer is not that important; its performance is. The best-performing polymer will be the least expensive to use.
A link to the spreadsheet is here: Resources (cleanwaters.us)
Have fun with the spreadsheet and reach out if you have any questions. Thanks for reading.
Steve Wardell
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