Tips for Selecting the Right Polymer for Sludge Thickening

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Tips for Selecting the Right Polymer for Sludge Thickening

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Polymers — the chemicals used in wastewater to thicken sludge and facilitate the removal free water — are critical to the operational efficiency of sludge thickening equipment. Unfortunately, it’s common practice at treatment facilities to order and install sludge thickening equipment before even considering what the ideal polymer might be for the sludge produced at the specific plant. 

Once the equipment is installed, startup becomes a lengthy activity of experimentation with a variety of polymers to find the best fit. This flawed process is time consuming and disruptive to plant operations, and can become very costly in both the short term as well as drive up the long term operational costs of the sludge thickening equipment.

When a trial-and-error approach for polymer selection is undertaken, the operations staff, consultants or contractors must procure a variety of polymer types to run the test. This step in itself is both costly as well as a significant logistical exercise when taking into account delivery and storage requirements. Once all the materials are on site the process of testing for the best fit can mean several days of hit-and-miss attempts. It can also lead to improper information for selecting a final polymer. One common error is choosing a polymer that is cheaper per pound but requires significantly more product to produce the desired result.

Do your homework

To avoid these issues, JWC Environmental recommends performing on-site sludge sampling and analysis prior to dewatering equipment selection. Sludge sampling and analysis tests a variety of diluted polymers against the sludge from a wastewater plant.

The benefits of doing this exercise prior to equipment selection include the opportunity to size and optimize the design of the drum thickener to work in concert with the best polymer. Testing will evaluate such things as how quickly water shears off the sludge and what ratios will be needed for ideal sludge flocculation. With this data the quantity, and therefore the cost, of the polymer required to process the sludge can be estimated.

Armed with the information provided by advance sludge sampling, wastewater plant operators — with help from their consulting engineers — can also more accurately calculate both the capital and long-term operating costs of the sludge thickening operations. In some cases, these details can be critical to gaining stakeholder approval for a project. Finding out after the fact that long-term cost estimates for polymer were incorrect can produce operational budget problems that are difficult to resolve.

Following a few simple guidelines in the sludge sampling process will provide optimal results. 

Polymer test day

Conducting sludge sampling and analysis involves testing a number of diluted polymers against the sludge from a wastewater plant. Analysis should be performed on site as opposed to sending sludge samples out to laboratories. The chemical composition of sludge will begin to break down after just a few hours, which will alter the results from lab samples. Additionally, with on-site analysis, the sampling technician can speak directly with plant operators to gather additional information about the operations that may be useful in their approach to the analysis process as well inform the recommendations they come up with.

The value of on-site analysis was highlighted during a recent technician’s visit to a wastewater operation in Indiana. The sludge sampling technician, in speaking with plant operators, discovered their intent to use effluent water mixed with polymer in a new drum thickener. The technician altered his sampling point to the effluent and used it in the analysis, making it as realistic as possible. In an off-site laboratory setting this local operator knowledge would have been missed. 

Sludge thickening equipment manufacturers that are looking to provide the best possible solution for their customer will typically have a sludge analysis program. JWC Environmental, for example, offes complimentary sludge testing to municipalities. JWC facilitates the testing with a partner organization that is specially trained in polymer selection. This on-site service includes detailed evaluation of how the sludge polymer combination behaves when exposed to shearing effects that are common in drum thickeners. The test, usually performed by putting each sample in the equivalent of a food processor, simulates the shearing and allows the technician to observe the results to determine which polymer produced the best floc, or collection of solids. 

Avoid the pitfalls 

One alternative used by some drum sludge thickener manufacturers is to ship a temporary unit to wastewater plants for pilot testing to determine the proper polymer prior to startup. While this option can be effective, it doesn’t avoid the costs and labor associated with the trial-and-error method. Onsite sludge sampling, by comparison, allows for rapid and efficient testing of a much larger number of polymers and for selection of a polymer feed system so plant operators can avoid a last-minute scramble. 

Additionally, avoid the temptation of skipping polymer selection altogether by using the same polymer in a new drum thickener that’s already being used downstream in a centrifuge. That might seem to make sense at first, because of the ease of logistics and storage. However, the operating parameters of centrifuges, such as rotational speeds, are significantly different than drum thickeners. Using the centrifuge polymer in the drum thickener by default will likely result in poor performance.

Sludge sampling and analysis prior to sizing a drum thickener or selecting a polymer is a relatively simple process that offers a variety of benefits. Most important, it provides valuable data to the consulting engineers and a clearer understanding of costs to the municipality.


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