Uses of flocculation and coagulation in wastewater treatment
Flocculation and coagulation in water treatment are used to remove suspended solids through a process that destabilizes suspended particles in aqueous solutions. The difference between the two is that, coagulation is the aggregation or agglomeration of particles and agglomeration is the sedimentation of coagulated particles. Its purpose is to remove and neutralize the charge density of the particles through use of coagulant. Thereafter, a flocculant is used to promote particle bonding through flocculation. This allows the larger agglomerated particles to easily separate from the water and settle in the bottle.
- Sludge pond Management
- Wastewater Solids Dewatering
- Wastewater Treatment
- Recycled Plastic Wash Water Treatment
- Mine Wastewater Treatment
Why Use Flocculants and Coagulants?
Coagulation: The combined use of agents and coagulants can efficiently and cost-effectively remove suspended particles in aqueous solutions or slurries. Given enough time, some particles will spontaneously settle out of the water. Other particles, however, do not settle out for days or months due to their small particle size and interparticle charge. Coagulants are primarily used to remove very small suspended particles in solutions that do not settle quickly.
Flocculation: The main function of flocculants is to bind and flocculate suspended particles in water to form larger particles, facilitating sedimentation and removal by the separation process of particles and water.
The main purpose of the coagulation/agglomeration process is to remove turbidity from the water. Turbidity is the cloudy appearance of water caused by small particles suspended in the water. Water with little or no turbidity is clear.
Turbidity isn’t just a cosmetic issue in water. Highly turbid water can be very difficult or impossible to disinfect properly. Therefore, the maximum permissible turbidity level in water is 0.5 NTU and the recommended value is around 0.1 NTU. (NTU or TU stands for Nephelometric Turbidity Units, a measure of water turbidity.)
In addition to removing turbidity from water, coagulation and flocculation are beneficial in other ways. This process removes many bacteria floating in the water and can be used to remove colour from water.
Turbidity and color are much more common in surface water than in groundwater. As surface water flows over the surface into streams, through various separate streams, and into rivers, it picks up a large amount of particles. Groundwater needs to be aerated more frequently, while treatment by coagulation and flocculation is common for surface water.
What is aggregation?
Agglomeration is the process that occurs when the interaction of particles in water becomes destabilized in the presence of another molecule and they join together to form large agglomerated particles that readily settle. Polymer molecules are often used to facilitate this process because they can be tuned to increase or decrease their destabilization potential via the surface charge of the molecule. Higher charge densities can lead to instability. Lower charge densities have less effect on particles in suspension. As a result, technologists are using different combinations of charge, molecular structure, and even elemental composition of flocculants to tailor water treatment protocols for each unique application.
How does flocculant work?
Used in a wide variety of industries and applications, flocculant works by binding contaminants into flocs or “flakes” that float or sink to the bottom of the water. They help remove suspended solids from wastewater. It can also be used for lime softening, sludge thickening, and solids dewatering. Natural or mineral flocculants include activated silica and polysaccharides, while synthetic flocculants are most commonly based on polyacrylamide
Coagulants can be used alone or in combination with flocculants, depending on the load and chemical composition of the wastewater. Coagulants differ from flocculants in that coagulants are usually salts whereas flocculants are often polymers. They can vary in molecular size (weight) and charge density (% of molecules with either anionic or cationic charge). It is used to “balance” the charge of particles in water, collecting and dehydrating them. Generally, anionic coagulants are used to trap mineral particles, while cationic coagulants can trap organic particles.
Top Flocculant Chemicals
Our ACCO 090 series of flocculants is a range of flocculants to improve wastewater treatment and reduce overall costs in a wide range of mineral processing applications. We offer a wide range of cationic & anionic, flocculants to meet all your chemical processing needs.
What is coagulation?
Coagulation is the process of bringing insoluble materials together by manipulating the charge of the particles by adding iron or aluminium salts such as aluminium sulfate or ferrous sulfate to the wastewater stream. is a fairly simple chemical process involving the main purpose of using a coagulant, in addition to removing various particulates from the suspension, is that the process makes the water less turbid.
Negatively charged particles in water are neutralized by the positive charge of the coagulant. This causes suspended matter in the water to combine to form larger flakes. These large flocs begin to sink to the bottom of the water supply. The larger the particle size, the faster the flakes settle
Coagulation helps remove various contaminants that make the water dirty or toxic. There are things like:
- Suspended inorganic precipitates such as iron and some metals
- Certain viruses and bacteria
Agglomeration converts industrial waters to their full chemical state, facilitating mechanical filtration. Once the flocs settle to the bottom of the clarifier, equipment such as filter presses can pick up and remove large clumps of these agglomerated particles, returning clean water to the system. The coagulant, clarifier, and filter press combine to deliver maximum water recovery of over 95%. Very little water is actually carried away with the solids, creating a nearly closed-loop process.
Types of Coagulants
Organic Coagulants are ideal for solid-liquid separation. It is also suitable if you want to reduce sludge buildup. These coagulants are organic in nature, act at low doses and offer the added benefit of not affecting the pH of the water.
Organic coagulants are typically based on the following formulations:
Polyamine and Poly DADMAC (Diallyl dimethyl ammonium chloride) – These cationic coagulants work only by neutralizing charges and are the most commonly used organic coagulants. PolyAMINE and PolyDADMAC neutralize the negative charges of colloids in water, forming spongy clumps called “micro-flocs”. They coagulate only by charge neutralization and therefore have no advantage with respect to the sweep flock mechanism (inorganic coagulants are discussed later).
Melamine Formaldehyde and Tannins – These natural coagulants are somewhat similar to inorganic coagulants in that they coagulate colloidal matter in water and contribute to their own settling flocs. This sweeping floc sedimentation can absorb organic matter such as oil and grease while coagulating unwanted particles in water. Since the sedimentation dehydrates everything to low moisture concentrations, these coagulants It is ideal for operations that produce harmful sludges such as those found in oil refineries. Key benefits of organic flocculants include low dosage, low sludge formation and no pH impact.
Inorganic Coagulants are typically less expensive than organic coagulants, making them a cost-effective solution for a wide range of water treatment applications. It is especially effective when used with low turbidity raw water.
Inorganic coagulants form aluminium or iron precipitates when added to water. They help purify the water by picking up impurities in the water as they fall. This process is known as the “sweep floc” mechanism. However, this may increase the overall amount of sludge that needs to be treated and removed, so it is not the right choice in all scenarios. The major types of
inorganic coagulants are:
Aluminium Sulfate (Alum) – One of the most commonly used water treatment chemicals in industrial processes, alum is the coagulant of choice for many. It is prepared as a liquid and the crystalline form of alum is formed when the liquid is dehydrated. Be aware that alum is a mild hazard and has similar health effects/corrosive properties to dilute sulfuric acid.
Aluminium Chloride – This coagulant works similarly to alum, but is more expensive. , dangerous and corrosive. Therefore, in processes where alum cannot be used, it is usually chosen only as a second choice.
Poly Aluminium Chloride (PAC) and Aluminium Chloride (ACH) – These inorganic coagulants are ideal for simple water supplies.
Ferrous Sulfate and Ferrous Sulfate – Both iron coagulants work similarly to aluminium coagulants, although ferrous sulfate is more commonly used. Ferrous sulfate is generally preferred when a reducing agent is required or when excess soluble iron ions are required.
Ferrous Chloride – As a waste product from steel production, ferric chloride is the most cost-effective inorganic coagulant. However, it is only used in facilities that live up to its reputation as the most corrosive and dangerous inorganic coagulant.
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