Raw Water Treatment

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. 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.

Organic Coagulants

For certain water sources, organic coagulants are more appropriate for solid-liquid separation. Organic coagulants are generally used when a reduction in 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 reduction characteristics of the organic coagulants. ChemTreat’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. 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 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. ChemTreat’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.

Our solid liquid separation technical support team averages over 25 years of field applications expertise with the following industrial effluent treatment technologies:

Simulation and Testing Capabilities

• Biological treatment for BOD and COD removal
• Chemical softening to remove calcium and magnesium hardness
• Dissolved air flotation
• Membrane filtration
• Multimedia filtration
• Paint detackification
• Physical/chemical treatment of metals and phosphates
• Oily waste demulsification
• Separators: centrifuges, cyclones, strainers, cartridge filters, cross-flow sieves, and electro-osmosis
• Sedimentation and clarification
• Sludge thickening and dewatering

Suspended Solids

Although there is no hard and fast definition, suspended solids tend to be greater than 1–2 microns in size. Contaminants visible to the naked eye, they can generally be filtered out of the water using common filter paper. If the water is left to stand without being disturbed, the suspended solids will settle to the bottom of the container over time.

Dissolved Solids

Dissolved solids are not visible to the naked eye and cannot be removed from the water by filtration. The standard definition of dissolved solids is material generally smaller than 0.45 microns in size. There are two types of dissolved solids:

• Normally soluble substances: These are materials that become more soluble with increasing temperature, such as table salt or sugar. The hotter the water, the more of these materials will dissolve.
• Inversely soluble substances: Normally referred to as hardness ions and generally limited to salts of calcium, magnesium, strontium, and barium in water treatment, these materials become less soluble as temperatures increase, hence their tendency to form scale on the hot surfaces of boiler or heat exchanger tubes. Water treatment would be a simple matter were it not for the inversely soluble hardness salts.

Colloidal Solids

These are solids not quite small enough to be considered dissolved but not quite large enough to be considered suspended. Generally, colloidal materials will appear as a “haze” in the water, and it will not be possible to see distinct particles with the naked eye. Colloidal materials are typically within the size range of approximately 0.45 to 2.0 microns. Colloidal solids will not settle out from the water because they are so small they are greatly affected by their ionic surface charges. Thus, a colloidal suspension in water is said to be a stable suspension.

Color is a type of colloidal suspension. Organic molecules that contribute color to raw surface water are simply macromolecules that fall into the smaller colloidal size range. In water, these macromolecules take on an ionic surface charge that stabilizes them so they cannot settle out.

Contact ChemTreat For Raw Water Treatment

ChemTreat is a trusted water treatment company with over 50 years of service
and expertise. Our experienced field team and laboratory services allow us to provide
custom treatment chemicals and water treatment solutions for your unique raw water treatment needs. We’re here to help you improve the efficiency of your facility and decrease your operational costs. Contact us online to get in touch with our experts and schedule a consultation!

Contact ChemTreat