A diagram of a branched polymer chain. Image via Wikimedia.
Is it a good idea to use polymers for water treatment? How does polymer water treatment work and what advantages does it offer to facility managers? Read on to learn about this in more detail and to examine how polymers can be deployed within your own wastewater treatment strategy.
What is a polymer?
When we think of a polymer, we may think of a resin or plastic-like substance, such as the polymer clay often used in primary school art lessons. However, this is just one example of a polymer in action, and the term actually has a very specific scientific definition.
A polymer is a chemical compound formed of molecules that are bound together in chains. These chains are often long and can be repeated to expand the size of the molecular structure. The individual molecules within the chains are known as monomers, and the chain structure can be artificially manipulated or modified to achieve specific properties and attributes.
The creation of a versatile modeling clay is one application of a modified polymer molecule structure. However, in this article, we will be focusing on polymers in industry — in particular, polymer water treatment.
How are polymers used in water treatment?
Polymers are very useful in the treatment of wastewater. In a basic sense, these molecular chains work to separate the solid content of the wastewater from its liquid content. Once the two components of wastewater are separated, it is far easier to complete the treatment process by isolating solids and treating liquids to leave behind clean water, ready for safe disposal or for use in other industrial applications.
In this sense, a polymer is a form of flocculant — a substance that reacts with solids suspended in the water to form clumps, known as flocs. This is very useful in the wastewater treatment process, and so polymers are often used by themselves, achieving flocculation so that solids can be easily removed. To get the best from the process, however, polymer flocculants are often deployed alongside a coagulant.
A coagulant takes the flocculation process to the next level, bringing flocs together to form a thick sludge, which can then be removed or treated further. Polymer flocculation may take place before a coagulant is added, or it may be applied to accelerate the process of electrocoagulation. As there are both advantages and disadvantages to electrocoagulation, optimizing the procedure with a polymer flocculant is a highly attractive proposition for facility managers.
Different kinds of water treatment polymers
Depending on the kind of monomer used to create the polymer chain, polymer water treatment can work in different ways. Polymers are generally grouped into two main kinds. These are cationic and anionic, referring to the relative charge of the molecule chain.
- Anionic polymers in water treatment
An anionic polymer carries a negative charge. This makes them particularly suitable for flocculating inorganic solids from waste solutions, such as clay, silt, or other forms of soil. Wastewater produced by mining projects or heavy industry may be rich in this kind of solid content, and so anionic polymers may be particularly useful in this kind of application.
- Cationic polymers in water treatment
A cationic polymer is basically the opposite of an anionic polymer in terms of its relative charge, as it is charged positively. The positive charge of the cationic polymer makes it well suited to remove organic solids from a wastewater solution or mixture — for instance, human waste, animal matter, or vegetation and plant life. As there tends to be a great deal of organic matter in civil sewage lines, cationic polymers are frequently used in municipal wastewater treatment plants, although agricultural and food processing facilities also use these polymers.
Other types of water treatment polymers
Both anionic and cationic polymers may also be grouped into other categories depending on their form and the method of delivery. For example, you may opt for a dry or a liquid polymer at your facility.
- Liquid polymers in water treatment
Liquid polymers are also known as emulsion polymers because they are added to wastewater in many small drops that do not dissolve into the water mixture. This type of polymer has a lower concentration of active molecules compared to dry polymers, which means the effectiveness of the treatment is diluted by the method of delivery.
If it is sourced locally, liquid polymers may be the more cost-effective option as they can be purchased at a lower price than the dry polymer option. However, the cost of shipping liquid polymers from further afield may be greater, simply because the logistics of transit are more complex. It is also important to note that liquid or emulsion varieties are less effective at polymer flocculation than their dry counterparts.
- Dry polymers in water treatment
Dry polymers contain a greater concentration of active molecules. This makes the dry option a far more effective flocculant than a liquid or emulsion polymer.
Generally, dry polymers will be more expensive, although the shipping and logistics costs may be lower. For larger-scale flocculation projects, dry polymers tend to be the preferred choice. However, it is important to remember that using this form of polymer will take up more space at your facility.
Accelerating water treatment with polymers
The polymer does not treat the wastewater itself. Instead, it assists in the clumping together — or flocculation — of solids that are either dissolved or mixed into your wastewater sample. The idea is not to use polymers on their own, but instead to accelerate the overall treatment process by using these handy additions to your wastewater treatment strategy.
The volume of wastewater you will need to treat, the amount of space available at your facility, and your budget will help you determine whether you will use dry or liquid polymers during treatment. In addition, how much organic or inorganic matter is present in your wastewater is another consideration you will have to make, as this will tell you whether you need to deploy cationic or anionic polymers.