Coagulant

What is the Purpose of Coagulants?

With advancing technology and a changing world order, countries and local governments are establishing regulations to create a more livable and sustainable world. The aim here is to prevent chemical-containing waste, generated from chemical substances used in any facility, from harming nature by ensuring its controlled release into the environment. To achieve this, it is necessary to use a coagulant.

What is a Coagulant?

Coagulant is the general name for chemical substances briefly described as coagulating or flocculating agents.

A coagulant is used to destabilize suspended solid materials (a heterogeneous mixture formed by remaining undissolved in a liquid phase) in a colloidal solution.

Thanks to coagulants, suspended solid materials will gather together and flocculate. The primary liquid in waste processes is water. Colloidal and suspended particles in wastewater exist in a stable, negatively charged state. These particles have no tendency to move or settle from one place to another on their own.

There are some well-known coagulants. These coagulants include FeCl₃ (Iron(III) Chloride), PAC (Polyaluminum Chloride), and some low molecular weight polymers. Their general name is coagulants. These chemical substances generally provide a coagulation function, meaning they have flocculating properties.

Density, Melting Point, Boiling Point, Solubility: Varies depending on the type.

How is a Coagulant Selected in Wastewater Treatment Systems?

By adding coagulants to the colloidal solution, the distance between suspended particles will decrease, and coagulation will occur. This is the main purpose. The goal is to gather the suspended particles within the solution, allowing them to reach a sufficient size for separation methods, thereby achieving separation.

One of the most important processes here is the selection of the coagulant. Coagulants affect each heterogeneous mixture differently. For this reason, before selecting a coagulant, a sample of the wastewater is taken and analyzed in a laboratory setting.

A micro-scale coagulant application is performed based on the colloidal particles in the water and the water's characteristic properties. By establishing the appropriate proportion for the wastewater system, the correct coagulant is selected for the water treatment method.

Coagulants will exhibit their effects better with the help of mixing. The mixing process following the addition of coagulants will destabilize the suspended particles more quickly. This allows the suspended particles to gather together. The mechanism of action of coagulants also depends on the mixing speed of the heterogeneous mixture.

What are the Main Types of Coagulants?

• Iron(III) Chloride
• PAC (Polyaluminum Chloride)
• Low molecular weight polymers
• Polyamides
• Polyanilines
• Iron Chloride Sulfate

Effect of Polyaluminum Chloride (PAC) on Coagulation

Polyaluminum Chloride-based coagulants, used as a tool for water rehabilitation, show different effects depending on the amount of phosphorus in water with low alkalinity.

During the coagulation process, the dosage of the coagulant chemical, the pH of the medium, and the amount of organic matter in the medium are crucial for achieving optimal phosphorus removal.

The lowest phosphorus removal occurs in water environments rich in humic compounds. When performing coagulation in such water types, as the water's alkalinity increases, the amount of aluminum in the water decreases, while the coagulant's ability to adsorb phosphorus increases.

According to the coagulation reaction, phosphate binds to the poorly soluble aluminum phosphate in water, which results in precipitation. Positively charged aluminum hydroxide polymers bind phosphate ions. This coagulation process results in the formation of insoluble phosphorus-containing suspended organic and mineral matter through regulation and flocculation.

Increasing the dosage of the coagulant does not affect coagulation beyond a certain dose.

Coagulants in Wastewater Treatment at Stone and Marble Quarries

In stone and marble quarries, massive blocks are cut with large metal saws. This way, they are divided into smaller or desired pieces and brought to the market for use in the stone and marble industry.

The cutting machines in stone and marble quarries are exposed to high heat due to their operating systems and the materials they cut. At the same time, cooling water must be used during the cutting process to ensure the stone is cut with high quality and smoothness to produce a block.

The main reasons for using water during stone cutting are: to prevent heat generated by friction-related contamination, to suppress dust generated during cutting and abrasion, and its preferential use based on physical appearance.

Water consumption in stone and marble quarries is approximately 0.5 million tons annually worldwide. This amount represents a very high capacity. Therefore, to avoid high costs, wastewater in stone and marble quarries must be treated.

During the wastewater treatment in stone and marble quarries, the wastewater used in the stone cutting process is transferred to holding ponds. In these ponds, the suspended particles in the wastewater are allowed to settle by the force of gravity. The settling time of suspended particles by gravity causes many problems.

In the wastewater treatment system, some coagulants such as polyaluminum chloride, Ferric Chloride, and lime require a jar test study to determine the total suspended solids, water clarity, and total solid content.

It has been determined that the use of lime at a level of 100 ppm provides optimal clarity for removing water turbidity. For the removal of total solid content, 100 ppm of Polyaluminum Chloride gave the best result.

Thus, the use of coagulants has helped to increase the quality of the used water and allowed it to be returned to use more quickly.

What are the Application Areas of Coagulants?

• Generally, coagulation and flocculation processes are applied together. The application areas of coagulants, i.e., the sectors where they are used, include: the Textile Sector, Food Sector, slaughterhouses, and workplaces where metal surface treatments are performed. Coagulants are used intensively in these areas.

What Factors Affect Coagulant Prices?

The price of a coagulant generally varies depending on the type of coagulant used. Alternatively, since the choice of coagulant changes according to the structure of the water to be treated, the price of the coagulant also changes accordingly.

For example, if Iron(III) Chloride (FeCl₃) is used as a coagulant, the coagulant prices will be lower compared to Polyaluminum Chloride (PAC). The point to consider here is to make the correct choice of coagulant. If not done correctly, the money paid for the coagulant will increase even more.

The most important factors affecting coagulant prices are the increase in the number of domestic companies producing in this field. If the number of companies producing coagulants increases, the price of coagulants will decrease inversely. Of course, the developing industry and the increasing application areas of coagulants directly increase the price of coagulants.

Especially in the industrially developed regions of Turkey, coagulant prices have shown a great increase in recent years.