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Principles of Flocculation & Coagulation in the Treatment of Wastewater
The principles of flocculation and coagulation are well-known water treatment processes. Some historical records suggest that these techniques have been used for centuries. Flocculation and Coagulation can be used for treating freshwater which can be further treated for human consumption, or for the treatment of wastewater effluent. They are perhaps the most widely used forms of water treatment across the globe.
Flocculation and coagulation are primarily utilized to separate suspended solids from water. Suspended solids are small particles that do not settle in water due to their size and characteristics. If not removed, suspended solids will cause downstream treatment processes to fail.
Coagulation involves the addition of a chemical substance called a coagulant to the water. Coagulants have charges that oppose and therefore neutralize the negative charges of the suspended solids. This enables the particles to stick together and form ‘flocs’. Coagulation requires rapid mixing of the water to adequately disperse the coagulant.
Coagulation is followed by flocculation which utilises a gentle mixing technique to further encourage the flocs to grow. These larger particles can then settle to the bottom of the vessel enabling removal via sedimentation and/or filtration.
Coagulation and flocculation are particularly important in the treatment of domestic and industrial wastewater due to their high levels of suspended solids. Coagulation and flocculation can also be used in downstream processes such as sludge dewatering and thickening.
Common Coagulants and their Advantages
The choice of coagulant will depend on the characteristics of the suspended solids and other water parameters. The required final effluent quality, effects on downstream processes, sludge handling, and cost, also play a major role in coagulant selection.
Chemical coagulants used to treat wastewater fall into two main categories: organic and inorganic. In general, inorganic coagulants are used to treat raw wastewater, whilst organic coagulants are used during sludge processing.
Alum (aluminium sulfate), lime, and iron salts are the most common inorganic coagulants. These coagulants have highly charged ions, which, when added to water, neutralize the suspended particles. This encourages clustering of particles and microfloc formation. Mineral-based or inorganic coagulants are widely available, cheap, and if properly applied, effective in removing most suspended solids. Inorganic coagulants can also absorb other impurities such as dissolved organic matter. Inorganic coagulants do, however, add to overall volume of sludge produced in the treatment process.
The most widely used inorganic coagulants are PolyAMINEs and PolyDADMACs. Other common organic coagulants are Melamine Formaldehydes and Tannins. Although these organic coagulants utilize different coagulation mechanisms, they are generally best used for solid-liquid separation.
Organic coagulants are also a good option for facilities that wish to reduce sludge generation. They also offer the advantages of requiring less dosage than inorganic coagulants and have no effect on the pH of the water, which can be a crucial factor for some facilities.
More About Flocculation
During coagulation, flocs (or microflocs), are formed in the wastewater. Flocculation occurs when these flocs form larger particles when gentle mixing is applied. Flocculation can occur spontaneously or with the help of a chemical agent, usually a polymer. Polymers will help to bridge, bind, and strengthen the floc, increasing its weight, and therefore its settling rate.
These large solid particles can then be removed from the wastewater stream either through sedimentation whereby the floc settles to the bottom of the tank and is removed, or by filtration.
Tanks with suitable mixers are an important aspect of flocculation. Adequate contact time must be provided to allow macrofloc formation and at the same time, careful consideration must be given to the mixing velocity to prevent the flocs from tearing apart.
Enduramaxx Mixer Vessels and Settling Tanks
Wastewater treatment facilities are under growing pressure to improve performance, operate sustainably and comply with increasingly stringent regulations. The quality of your process, your staff and your equipment will be the driving factors for success.
Enduramaxx offers a range of quality chemical storage, conical dosing, mixing, and settling tanks to help you operate efficiently and safely. Our tanks are designed taking into account the principles of flocculation & coagulation, manufactured in-house using the highest quality PP and PE materials and are designed to last. Whether you require bunded or double-walled tanks, we have what you need in a large variety of sizes and options.
Our unique 3-stage mixer tanks allow for coagulation, flocculation and sedimentation is one cleverly designed tank with double weirs. Our Polymer Make-up and Dosing tanks enable you to accurately develop your coagulant mixture, with a number of mixers available for both liquid and dry chemicals.