After particles suspended in water have been coagulated it is often necessary to add a flocculant that will aggregate the coagulated particles (pin floc) into larger particles that will be easier to settle or float. A common mechanism for doing this is through the addition of synthetic polymers, typically formed from acrylamide monomers, that then bridge together coagulated particles into a more dense particle.
Types of Flocculants
Flocculants are high molecular weight polyacrylamides that range in charge, structure, size, and available form. An outline of all the variables and what is available for potential use will follow. To start, Flocculants have three forms that are available:
- Dry Polymer – The most concentrated way to purchase the material as it will come as 100% active powders or beads. Typically will need to be made down to a less than 1% solution prior to being fed.
- Emulsion Polymer – Polymer comes suspended in an oil based carrier and ranges from 30-50% active. Typically will need to be made down to a less than 1% solution prior to being fed.
- Solution Polymer – Polymer that comes pre-made to the necessary solution and can be fed neat. Typically 1-20% active.
All three forms are perfectly acceptable to use and will be effective. Each facility must weigh the pros and cons of each type and balance the cost and ease of use to make a decision on which will be best for their unique circumstance.
The next variable to consider in polymer selection is the charge. Polymers can come as an Anionic, Cationic, or Non-Ionic Charge and for the Anionic and Cationic there is a wide range of percent charges available ranging from less than 5% all the way to greater than 90%. The percent charge is simply referring to the number of active charge sites available on the polymer chain—the percent needed is very facility specific and water chemistry specific.
Another variable to consider when making a flocculant decision is the molecular weight of the polymer which could be low, medium, high, or anywhere in between. The final variable that must be considered is the structure of the polymer. The most basic structure and the most commonly used structure is simply a linear molecule and is available in all three forms listed above.
Structured polymers are only available as emulsions and can be cross linked or branched. Structured polymers are typically better in high sheer environments like dewatering applications. The sheer will expose more of the charge sites to the material to be aggregated allowing for a better floc to be formed.
Custom Blended Solutions
Flocculant choice is highly facility and chemistry dependent. A flocculant that works at one facility may not work at another facility across town that has the exact same process and waste type. Careful analysis of how different polymers perform and what dosage is necessary across the range of wastewater chemistries seen at a facility is critical when selecting the correct flocculant.
FCT Water can perform testing and analysis at various times of the day and days of the week to understand the profile of the water to be treated. From this information we are able to recommend the best product to use and optimize the cost and efficacy for the facility.
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