Water purification methods come in multiple forms and steps, depending on various factors like budgetary constraints, environmental concerns, and usage. However, every water treatment system has one constant – adding chemicals to treat water.
Coagulants and flocculants, like polyacrylamide pam, are particularly useful to remove debris from wastewater, as they are efficient and cost-effective. The process of flocculation is one of the basic and most significant steps in the water treatment process.
What are Flocculants?
Flocculants are materials that help in promoting the accumulation of fine particles in water that creates a floc, floating to the surface or settling in the bottom. This makes it easier to remove these particles from the water. Flocculants are inorganic or organic and are in multiple forms, molecular weights, charge densities, and charges.
Organic polymeric flocculants are being widely used nowadays because of their ability to promote flocculation with small dosages. Biopolymers are also popular as they are more environmentally friendly, but they require a higher dosage and have a shorter shelf-life.
What is Flocculation Process?
Flocculation is the water purification process to remove contaminants from the water. It is the most common process to treat wastewater management, stormwater, and drinking water, making it clean and disinfected to use.
The process of flocculation is separating the solution from the sediment and debris mixed in it. The word comes from ‘floc,’ meaning flakes of material. When water is flocculated, the sediment has become bigger aggregated flakes, making it easier to spot and remove in the next stage. This process can happen naturally or can be forced using physical processes and/or flocculants.
One of the major requirements to treat water from any resource is to eliminate the suspended solids. Tiny particles can have an impact on the water color and also carry with them multiple impurities in the sources of natural water, like oceans and rivers.
It is also essential to limit the phosphorus content in the wastewater as phosphorus is released in the river; it encourages algae growth. Uncontrolled phosphorus releases have been found to result in drastically altering the health and life of fishes and other aquatic life.
Due to applications of some industries, a high amount of phosphorus is released in the wastewater that requires pretreatment of water before being released to water treatment plants. Therefore, the process of flocculation is integral to remove these impurities.
Uses of Flocculants
Flocculants, like polyacrylamide pam, are utilized in numerous industries, including biotechnology, earth sciences, and civil engineering. However, their primary use is in the water treatment plants for solids dehydration, sludge thickening, lime softening, water clarification, and solids removal.
Water might comprise colloidal solids, like decaying plant materials, plankton, bacteria, clay particles, and other matter. Using the process of flocculation and coagulation to disinfect and purify water has been a centuries-old practice, but the technologies have now been updated.
Flocculation followed by sedimentation are stages used in several water treatment systems, including industrial wastewater, stormwater, sewage water, and drinking water treatments.
Ways Flocculants Work
In the process of coagulation and flocculation, positively charged chemicals are included in the water to help neutralize the negative charges. These negative charges are usually held by the solids, including dissolved organic materials, clay, and dirt.
The coagulants destabilize the particles in a stable solution and aggregate them. Once the charge is neutralized, larger particles are created with the added chemical. After the coagulation process, flocculation occurs. This is a process of gentle mixing that causes micro-flocs to collide and bond with one another to create suspended particles, called flocs.
Flocs continuously increase in size because of additional mixing and ultimately reach the right strength and size to prepare for the next step. These flocs either float to the surface to be removed or fall to the bottom of the container as sediment.
The right combination of inorganic or organic coagulants and flocculants depends on the substances to be removed from the water and the separation methods being used in the water treatment plant.
Stages Involved in Flocculation Process
Flocculation is done through a chemical procedure involving chemicals in the wastewater to enable the small particles and debris to gather and combine to form a large mass known as floc. This process is conducted in different stages to treat water:
First Stage
The goal of the first stage in this process is to negatively charge the suspended solid materials in the water. In order to accomplish this, a coagulant or flocculant like polyacrylamide pam is included in the water. This positive charge element neutralizes the negatively charged particles.
When these particles are neutralized, it paves the way for them to combine and become bigger masses called flocs.
Second Stage
Once the particles have been neutralized, the second stage begins in which the water has to be agitated through mixers. Initially, higher energy mixing is needed to make sure that the coagulant or flocculant is spreading all through the water.
Once the process of flocculation begins, the high energy mixing is reduced to avoid the flocs from separating again.
Third Stage
A polymer substance is included in the water in the third stage, when the floc starts forming. The polymers addition bridges the flocculant to macro from micro flocculant. As a result, the mass of particles starts getting bigger.
The chemical also helps bind the mass tightly together to prevent it from disintegrating even if the water becomes slightly agitated.
Fourth Stage
Once the process of flocculation finishes, the large masses formed can easily be eliminated from the water. This can be done through the process of sedimentation in which the floc settles to the bottom of the tank to get removed or through the process of filtration in which the masses are captured in the filters.
Some water treatment plants use both these steps to effectively remove all the flocs from the water. However, it is essential to take extra precautions when the flocs are being cleaned from the filters to contain and treat the floc that is rich in phosphorus.
Once the flocculation process is successful, the water treatment plant moves to the next stage of water treatment, depending on the purpose of the treated water. Some include additional steps to thoroughly disinfect the water. It is essential to consider various factors when considering your options for flocculant and coagulant to ensure you get the right end result.
