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Flocculation and coagulation treatment chemicals are used in effluent water treatment processes for solids removal, water clarification, lime softening, sludge thickening, and solids dewatering.
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 both 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. ChemTreat has both NSF-approved and GRAS-applicable coagulation products. Examples of ChemTreat 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 ChemTreat flocculants include low, medium, and high molecular weight polymers.
Discover More | ChemTreat’s coagulant and flocculant programs achieve optimal effluent results.
- Polyamine and PolyDADMAC
These are the most widely used class of organic coagulants. This type of coagulant functions by charge neutralization alone so there is no advantage of the “sweep-floc” mechanism. Polyamines will generally treat higher turbidity raw water (>~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 Formaldehydes 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 as well. This sweep-floc precipitate readily adsorbs organic materials such as oil and grease. The precipitate generally dewaters to low moisture concentration, making this choice of 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 significantly more expensive to use than inorganic coagulants, but it can be economical when sludge removal and disposal costs are factored in.
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” type of mechanism. The sweep-floc mechanism can be compared to snowfall on dirty air. As the snow falls, it adsorbs particulates in the air, which coprecipitate. In this manner the snowfall acts to clean the air. In water treatment, the metal hydroxide sweep-floc acts on water the way a snowfall acts on air. Many difficult-to-treat colloidal suspensions can thus be effectively treated using inorganic coagulants.
Although the metal hydroxide precipitate sweep-floc is advantageous in cleaning the water, these precipitates add to the overall sludge volume that must be treated and removed. These precipitates 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 as diluted sulfuric acid. Alum 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. ChemTreat 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 source of supply. Ferric sulfate is the more commonly used, but ferrous sulfate is typically used in applications where a reducing agent or excess soluble iron ions are required.
- 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.
- 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.