Flocculation

What is flocculation?

Flocculation is the chemical process in which the colloidal particles come out of suspension to sediment down in flake or floc spontaneously or by adding clarifying agents. This process is different from precipitation as in a liquid, the colloidal particles in flocculation are suspended. In the form of a stable dispersion, the colloidal particles are truly not dissolved in the solution. Being held together by the analogous force to the surface tension in the liquid, these flocculation flakes can be easily disrupted. 

Different methods can be used to eliminate and cause the process of flocculation; the flocculation process may be desirable or undesirable in industries. As flocculation flakes are easily disrupted, many industries find it undesirable. Water treatment plants, sewage treatment, purification drinking water, and some of the applications where flocculation is employed.

Coagulation is a chemical process in which the finely divided particles are aggregated and form the flocs that can be separated and settled from water. Coagulation and flocculation are two important processes for water treatment. 

Flocculation aims to sediment the destabilised particles by causing their flocculation into floc. At the same time, the coagulation process aims to destabilise and aggregate the particles through chemical interactions in coagulants and colloids.  

Types of flocculation

There are two types of flocculation : natural flocculation and chemical flocculation. 

• Natural flocculation: Natural flocculation is environmentally friendly, and the natural process of flocculation is used for wastewater treatment. Plant seeds like moringa, or plantago are very efficient for this process. A natural product like starch can also act as a natural flocculant. The use of natural flocculants for flocculation of wastewater treatment can be very cost-effective; another major advantage of these natural flocculants is they are biodegradable hence non-toxic. The purification is affected by the non-toxic flocculants, this is a preferable and safe process, but the flocculants are natural. They have a short lifespan. 

• Chemical flocculation: The chemical flocculants ensure a very effective treatment in the coagulant process. As the name defines, these flocculants are chemically synthesised from different monomers from electrolytes, cationic, anionic as well as nonionic polymers. But these chemical flocculants are highly toxic as they produce sludge with high metal hydroxides that are harmful to living beings if released in water bodies. Techniques like copolymerisation can occur mainly because of these chemical flocculants. 

Flocculation and its usage

Flocculation is applied in several fields; some of these examples are given below:

1. Flocculation is applied for designing the physical properties of pharmaceutical products or mineral dressing. In addition, flocculation helps in the process of emulation, as the droplets come together and form a cluster. 

1. Flocculation maintains the quality of fresh water under the soil. However, the process of flocculation causes eutrophication through the process of absorption of substances from underwater. 

1. Flocculation helps in the coagulation process of clay particles and polymers through mechanical agitation, thus helping construction work. This application of flocculation is very important for civil engineering processes.

1. The process of flocculation and microfiltration work efficiently; the flocculation process is used in many biological and biotechnological processes. 

1. Flocculation helps in brewing beer; the process is commonly used in brewing industries; for example, yeast gets flocculated. The yeast gets sedimented or floats to the base or top after separating. 

1. Flocculation and coagulation processes are used in stormwater, sewage water, and industrial wastewater treatment. Typical water treatment processes required grates, flocculation, coagulation, granular filtration, and disinfection.

Coagulation and flocculation in water treatment.

The process of coagulation and flocculation in water treatment is used to purify drinking water from stormwater and wastewater. Removal of suspended solids is the one requirement for treating wastewater leaving from wastewater plants. The residuals of small solid floc affect the colour of the water; they also carry impurities that can pollute the natural reservoirs of drinking water like rivers and lakes. The discharge of phosphorus content should be limited as the release of phosphorus content in the water bodies generates algae growth. Fishes and other aquatic life can be harmed if uncontrollable phosphorus content is discharged. 

• Flocculation in water treatment is a chemical-based process in which chemical is added to the wastewater in sequence, allowing the tiny particles to collect together and form a large cluster or floc. In wastewater treatment, the whole flocculation process is carried out in steps. 

• Suspended solid particles are negatively charged in wastewater. Therefore, in the first stage, a coagulant is added to the wastewater, and the positively charged coagulant neutralises the negatively charged solid particles in water.

• High energy mixing is important to ensure that the coagulant molecules are completely mixed with the solid particles present in wastewater. 

• Once the floc or flakes start to form, a polymer content is added; the polymer connects the flocculants to micro to macroparticles of flocculants, which results in collecting particles getting bigger. 

• In the last stage, when the flocculation process has created large impurity masses, it is removed from the wastewater.

The coagulation and flocculation process is used in preliminary and intermediary stages between the wastewater treatment like filtration and sedimentation. The coagulant dose to be used can be determined via jar test. The jar test involves volumes of water samples that need to be treated. Different doses of coagulant particles are added simultaneously and mixed at a high energy mixing level.

Coagulation and flocculation in the water treatment process are employed for filtration of drinking water and purification of wastewater. Understandably, coagulation and flocculation are still essential components in water treatment industries. There are many coagulant elements available for wastewater treatment; some of these varieties are :-

Metal-based coagulants: These are the most available products. These products only contain metal salt like aluminium sulfate. 

Biopolymer coagulants: These are derived from natural sources. Mostly plant sources. There are also polysaccharides and other animal-fungal and microbial-based coagulant particles. 

Synthetic coagulants: These may carry high charged densities on relatively high molecules. 

Deflocculation:  Deflocculation is the exact opposite of flocculation and can cause problems in wastewater treatment. The deflocculation commonly causes sludge settling problems and deterioration of quality. The additive that prevents the formation of colloids into flocculants is called deflocculants. 

Conclusion

 Flocculation is the chemical process in which the colloidal particles come out of suspension to sediment down in flake or floc spontaneously or by adding clarifying agents. Coagulation is a chemical process in which the finely divided particles are aggregated and form the flocs that can be separated and settled from water. Flocculation aims to sediment the destabilised particles by causing their flocculation into floc.