Sometimes, dewatering polymer optimization is not only about the choice of polymer or the dosage, but also about having an expert in your corner to...
Sludge dewatering can be one of the costliest steps of wastewater treatment. The amount of sludge produced is often a parameter that plant operators and managers keep a close eye on but is it the only main economic driver of the dewatering process. Can the selection of a dewatering polymer really affect the bottom line for the plant?
Polymer selection can be a very lengthy process because it does need to account for a multitude of factors. The first factor is the polymer itself. Dewatering polymers come in a multitude of charges, charge densities, molecular weights, physical states, and branching types, each of which can be selected to best suit your sludge. But, even the best performing polymer in bench trials might not be the best suited for your entire application. Application factors such as type of sludge, type of dewatering equipment, flow rate, dilution equipment dosing equipment and levels of automation all need to come into the equation when choosing a polymer. All these factors need to be taken into consideration when a dewatering polymer is chosen and optimized.
Sludge dryness is a great parameter to keep track of what is coming out of the wastewater treatment plant and to optimize with the current chemistry in place. But that doesn’t not necessarily mean that the chemistry in place is the right one. A parameter that tells a bit more of the story is the “kg of polymer / dry solids”. This parameter considers the amount of polymer dosed per kilogram of dry solids produced, this allows to truly optimize the chemistry in both sludge dryness and polymer performance.
In some instances, there might not be a lot of performance gains to be done, but application gains can be made such as uptime, ease of dilution, ease of CIP and other secondary factors that can solve a lot of headaches for employees. In other cases, a lot of financial gain can be achieved with relatively small changes. Here are 2 examples:
Aquasan was in charge of the assessment of a wastewater treatment plant chemical performance. One of the targets was to optimize the chemical performance of the centrifugal dewatering system. After a series of bench trials, AQ-8565 was chosen as the best substitute to make a simple change without any change to any equipment. During the bench tests, to produce good sludge, the centrifuge was running on average at a dosing rate of 1320 mg/L with the initial polymer, yielding sludge of 17.5% solids and water with a turbidity of 370 NTU.
|Turbidity : 370 NTU||Turbidity: 27 NTU|
Our bench trial indicated that AQ-8565 would produce dryer solids at a dosage of 360 mg/L and would also yield water with a turbidity of 27 NTU.
During the plant trial, a step that is assisted by your Aquasan representative, it was confirmed that the results were reflected on the centrifuge. Here is a sample of the results achieved for solid dryness.
|Initial results from AQ-8565 on the centrifuge|
|Date||M initial||M final||% solids|
Applied to a full year, the chemical expenditure on polymer went from 650 000$ annually to around 175 000$ annually, while yielding dryer solids and clearer water.
In other words, the polymer that was in place did a good job, produced sludge that was within discharge parameters, the turbid water was sent back to the biological system, and no problems were observed by the operations teams on this end as well. Everything was thought to run smoothly and efficiently, nonetheless, a gain of 475 000$ was made by optimizing the choice of dewatering polymer.
Sometimes, dewatering polymer optimization is not only about the choice of polymer or the dosage, but also about having an expert in your corner to help troubleshoot and optimize the polymer dosage and application to your need.
In this instance, Aquasan was called on-site after a customer needed to increase the dosage of polymer to dewater the sludge after years of continuous and stable operations. Upon arrival on site Aquasan noticed the change in colour of the sludge and asked about possible change in production. A change in production was indeed made over the last 2 weeks, leading to a change in the composition of the sludge. Nonetheless, the in-house wastewater team tested this possibility and found that the sludge reacted the same way during bench trial than it did before the change in production. During the investigation, the Aquasan representative noticed that the sludge for bench testing was not taken directly from the container from which the sludge was pumped to the dewatering press, but from a sampling point that was situated earlier in the process. Upon further testing, it was realized that the sludge reached a pH of 5 in the holding tank for the sludge, therefore reducing considerably the efficacy of the dewatering polymer. After an adjustment in the pH of the sludge by adjusting the pH set-point for the entire water treatment (6.8 to 7.2), the sludge was back to the original condition and dosages, without any change of polymer or equipment. A simple pH adjustment reduced the polymer dosage by 25% and increased the sludge throughput by 35%, a testament that small changes can affect the bottom line of the entire wastewater treatment plant.
At Aquasan, we specialize in polymer determination and optimization. We know that the process can be overwhelming, but with continuous on-site support and a dedicated account specialist, Aquasan will be on your side for the entire process. To help you determine which replacement product to try, Aquasan offers free jar testing.