Coagulants neutralize the negative electrical charge on particles, which destabilizes the forces keeping colloids apart. Water treatment coagulants are comprised of positively charged molecules that, when added to the water and mixed, accomplish this charge neutralization. Inorganic coagulants, organic coagulants, or a combination of the two are typically used to treat water for suspended solids removal.

When an inorganic coagulant is added to water containing a colloidal suspension, the cationic metal ion from the coagulant neutralizes the negatively charged electric double layer of the colloid. Much the same occurs with an organic coagulant, except the positive charge most commonly comes from an amine (NH₄⁺) group attached to the coagulant molecule. ClearWater has both NSF-approved and GRAS-applicable coagulation products. Examples of ClearWater coagulants include aluminum salts, iron salts, and polyelectrolytes.

Flocculants gather the destabilized particles together and cause them to agglomerate and drop out of solution. Examples of ClearWater flocculants include low-, medium,- and high-molecular weight polymers.

Organic Coagulants

For certain water sources, organic coagulants are more appropriate for solid-liquid separation. Organic coagulants are generally used when sludge generation is desired. Furthermore, blended organic and inorganic chemicals are often more effective than either organic or inorganic coagulants alone. The correct blend can often combine the advantages of using the inorganic coagulant sweep-floc mechanism  with the sludge generation characteristics of the organic coagulants. ClearWater’s formulations are based on the following chemistries:

• Polyamine and PolyDADMAC: These are the most widely used classes of organic coagulants. They function by charge neutralization alone, so there is no advantage to the sweep-floc mechanism. Polyamines will generally treat higher-turbidity raw water (approximately >20 NTU) effectively. Polyamines are also effective in treating many types of wastewater. PolyDADMACs are a specific class of polyamines that fit in this category.
• Melamine Formaldehyde and Tannins: These all-organic polymers act similarly to the inorganic coagulants in that they not only coagulate the colloidal material in the water, but also contribute their own precipitated floc. This sweep-floc precipitate readily adsorbs organic materials such as oil and grease. The precipitate generally dewaters to low moisture concentration, making this coagulant particularly well-suited to unit operations that generate hazardous sludge, such as DGF and IGF units in oil refineries. This self-precipitating chemistry is generally more expensive to use than inorganic coagulants, but it can be economical when sludge removal and disposal costs are factored in.

Inorganic Coagulants

Inorganic coagulants are both cost-effective and applicable to a broad range of water and wastewater. Inorganic coagulants are particularly effective on raw water with low turbidity (TSS concentration) and will often treat this type of water when organic coagulants cannot.

Once added to water, the inorganic coagulants react with the alkalinity and hydrate to form metal (aluminum or iron) hydroxide precipitates, which act in a sweep-floc mechanism, which can be compared to snowfall on dirty air. As the snow falls, it adsorbs particulates in the air, which coprecipitate, thus cleaning the air. In water treatment, the metal hydroxide sweep-floc acts on water like a snowfall acts on air. Many difficult-to-treat colloidal suspensions can be effectively treated using inorganic coagulants.

Although the metal hydroxide precipitate sweep-floc is advantageous in cleaning water, these precipitates add to the overall sludge volume that must be treated and removed. They also tend to lower the overall density and dewaterability of sludge versus precipitates created with organic coagulants. For influent water applications where the sludge is generally non-hazardous, the penalty for creating more sludge with higher water content is small. For wastewater applications with hazardous sludge, the economic penalty can be significant.

• Aluminum Sulfate (Alum): Alum is mildly hazardous, with similar health effects and corrosion characteristics to diluted sulfuric acid. It is manufactured as a liquid, and the crystalline form is dehydrated from the liquid. Alum is one of the most commonly used water treatment chemicals in the world.
• Aluminum Chloride: Generally, aluminum chloride works similarly to alum, but is usually more expensive, hazardous, and corrosive. Because of this, it is normally a distant second choice to alum. ClearWater has aluminum chloride available as a liquid.
• Polyaluminum Chloride (PACl) & Aluminum Chlorohydrate (ACH): ChemTreat has a portfolio of varying combinations of PACl/ACH engineered for the basicity of your water.
• Ferric Sulfate and Ferrous Sulfate: Iron coagulants work similarly to aluminum coagulants, but the cost may vary based on the local supply source. Ferric sulfate is more commonly used, but ferrous sulfate is typically used in applications that require a reducing agent or excess soluble iron ions.
• Ferric Chloride: Ferric chloride is generally the least expensive inorganic coagulant because it is generated as a waste material from steel-making operations (waste “pickle liquor”). However, it is by far the most corrosive and hazardous inorganic coagulant, and its use is limited to facilities equipped to handle it safely.

Flocculants

Charge-neutralized solids can be further agglomerated by using flocculants. Flocculants can be thought of as a high-tech rope tying particles together, thereby increasing particle size. Flocculants come in various charges, charge densities, molecular weights, and forms. ClearWater’s portfolio includes:

• Cationic Flocculants: Mostly based on copolymers of AETAC (N,N-Dimethylaminoethyl Acrylate Methyl Chloride Quaternary) or METAC (N,N-Dimethylaminoethyl Methacrylate Methyl Chloride Quaternary) and acrylamide. These products can perform a dual function by both coagulating with their positive ionic charge and flocculating with their high molecular weight.
• Anionic Flocculants: Mostly based on copolymers of acrylamide and acrylic acid, anionic flocculants possess a negative ionic charge and work by binding with residual cationic charges on coagulants adsorbed to coagulated colloids.