Flocculation

20^th January, 2024.

In this post, we will see the concept of flocculation process.

In water treatment, there are times when an organic impurity is small in size and it becomes difficult to remove it from water. This is because lighter weight molecules and particles always float at the surface when compared to heavier particles, which come down due to weight and gravity. To solve this, many methods are used in water treatment for eliminating it. One of the most popular methods used is flocculation. In this post, we will see the concept of flocculation and understand how it is of utmost importance in water treatment plants.

Why is flocculation required?

In an impure water, there are some suspended particles which are small in size and difficult to dissolve. They are generally called as colloids. They are dangerous for use, because they even contain pathogens and harm human bodies or environment for further use. Because they float in the water, a cloudy surface forms in the water layer, which looks very uneasy for use. If this water is used further, then it is impromptu for any application. They can either clog filters ahead, cause further growth of microorganisms due to their presence, or simply provide impure water for any process which requires high purity water for use. For all these reasons, flocculation is a great process to help.

What is flocculation?

So, let us understand what is this method. Refer to the below image. Flocculation is a technique in which these colloids combine with each other to form a larger size impurity called flocs. If the size becomes large, then it becomes easy to dissolve these materials at the bottom. This is done by the addition of a chemical called flocculant. They promote clumping and help in easy attachment of colloids with each other. The chemical used is generally a polymer. Polymer is that chemical which best promotes flocculation due to it's atomic properties.

A colloid generally has negative ions present in it. Due to this, the positive ions present in water (hydrogen and oxygen) attract to it and stick around it to form a single piece of impurity. Because both positive and negative ions are present in this outside border, other colloids with the same property will not attract each other or in short, they will repel each other. Due to this, the colloids never combine with each other and instead, just float in the water.

Now, to start flocculation, flocculant chemical is added in this mixture with a gentle mix speed. These chemicals are heavier as compared to colloids. When they meet the colloids, they start to burden themselves on these colloids. Due to their heavy weight, they start to compress the colloids and in a short period of time, the flocculant must have been adhered to the colloid surface. This adherence then starts to bring colloids close to each other, due to it's weight. When they finally bind with each other, it makes a bigger colloid or particle, which indirectly causes it to go beneath and settle down at the bottom. Due to this, apart from the bottom layer, almost all of the water becomes clean for further processing.

Types of flocculants:

1. Inorganic flocculant

They are low molecular salts which are inorganic in nature and are mostly classified as polyaluminium chloride, aluminium sulphate, aluminium chloride, alum, and ferric chloride. As you can see, it is mostly composed of aluminium, sulphate or chlorine. They have a very good performance due to it's chemical structure, but they can also cause further pollution in water, which requires some further secondary treatment to remove. But it is the most effective of all.

2. Organic flocculant 

They are mostly polyacrylamide and polyethylene amine. They are a bit less effective than inorganic ones, but they flocculate quickly. It generally creates some toxication in the water and that requires some further secondary treatment for use.

3. Natural flocculant 

As the name implies, there is no chemical in it and purely natural. The most common types are cellulose, gum, mucilage, tannin, moringa or plantago. This is the safest as compared to organic or inorganic ones. But they are less effective and takes a longer time to flocculate.

Flocculation in water treatment:

Let us see the applications of flocculation in water treatment industry:

1. It is extensively used in sewage treatment plants where it is required to make the sludge more solid to remove it easily from a centrifuge machine or filter press machine. This process will flocculate the sludge, which is more in a semi liquid form, and makes it more solid to be removed easily afterwards.

2. It is also mainly used for irrigation purposes. This is because it helps to retain pure water by forming adhesive layers with impurities and helping them dissolve beneath the soil.

3. It helps a lot in complex biological processes and micro-organisms treatment where some simpler techniques cannot comply to them.

I have covered some general principles related to flocculation technology. I have also not attempted to cover all the methods, as it can vary from case to case and there is no end to it. Once you are familiar with this filter technique, you can easily tackle all types of problems in it.

Thank you for reading the post. I hope you liked it and will find a new way in this type of technology.