Chemicals
Focusing specifically on chemicals used to treat water.
Biocide
Biocide is a chemical substance or microorganism intended to destroy, deter, render harmless, or exert a controlling effect on any harmful organism by chemical or biological means.
Oxidizers
Not all oxidizers are created equal
Quick video tutorial on the process
Chlorine dioxide (ClO2) is a field-generated chemical, made from chlorite and acid, and often with bleach as well, which improves the efficiency of the chemical reaction. It is a common baseline oxidizer, and when applied safely and correctly, it is an effective disinfectant. It does require field generation systems to contain its harsh chemistry, and it is a powerful oxidizing gas. This technology has been adopted by numerous operators.
Peracetic acid (PAA) is an alternative to ClO2 that has comparable efficacy as a biocide, and it is heavily used in the food and agricultural industry for disinfection. PAA does not require field generation in a complex field generator, nor the managing of an array of harsh-chemical feedstocks. Instead, it is delivered and applied from simple totes and chemical feed systems. There are numerous providers of PAA application, and this technology’s adoption by operators is growing.
Sodium hypochlorite, or bleach, is a common household disinfectant that is also experiencing a growth cycle. It can be applied from simple totes, and numerous providers are using field-based electrolytic generator systems. The field-generation systems are having growing success and allow simpler chemical logistics, but they do rely on high-amperage field generation systems. There are numerous providers of hypochlorite-based solutions, either from simple totes or from field generators, and this technology appears to continue to grow in adoption.
Ozone is a powerful oxidizing gas with a particularly short life as a chemical, but it is powerful at killing microbes. It is a field-generated system, using air as the only feedstock, but it does require considerable power and notable initial capital expense. However, the system operates at relatively low cost, once the capital is invested. There have been few providers of ozone treatment in the industry, and while ozone does have efficacy as a disinfectant, the technology appears to continue to be one of limited market adoption in the industry.
Hydrogen peroxide (H2O2) is used more as a bulk oxidizer, such as at a recycling plant, to aid in water clarification, more than as a direct disinfectant. As a biocide, it is nominally published to be around 1/100th to 1/1,000th the potency of PAA, and so it is rarely used as a direct biocide.
Non -Oxidizer Biocide
Less common these days but worthy of discussion. These chemicals work by interfering with reproduction, stopping respiration, or lysing cell walls. Kill time of hours to days.
DBNPA (20% active) 2,2 Dibromo-3-nitrilopropionamide, DBNPA for short, has a short holding time as well as a fast kill rate. The product breaks down into harmless bi-products which will contribute to an increase in total organic carbon, TOC levels (glycol based TOC). DBNPA is also pH dependent. A typical dosage of 100 ppm for 60 minutes is sufficient for controlling bacterial contamination DBNPA can be deactivated by H2S coming from sulfate-reducing bacteria, SRBs.
Isothiazolin requires a longer contact time compared to DBNPA. Isothiazolin effectiveness is also pH dependent. Isothiazolin is a very dangerous biocide (from a health perspective) and careful application of the product should be used. Isothiazolin can also be deactivated by H2S coming from SRBs.
Gluteraldehyde requires long holding times (much longer than isothiazolin or DBNPA) as the kill rate is slow. Higher concentrations of product will lower the required contact time but increase treatment cost. Suggested dosage rates are 100 ppm of active gluteraldehyde for 6 hours. Gluteraldehyde can be deactivated by ammonia coming from denitrifying bacteria.
Quaternary Amines are similar to the above non-oxidizing biocides in effectiveness and applications are very system dependent. The key problem with quaternary amines is due to having a cationic (positive) charge. This positive charge will adversely react with anionic dispersant polymers, used for scale and corrosion management, resulting in product precipitation and reduced product effectiveness.
Coagulants
Used to increase the size of particles (floc) to make them large enough to settle or to be removed by filtration.
Video tutorials on the basics of coagulation and flocculation.
Organic Coagulants
Generally used for solid & liquid separation and sludge generation. Organic formulations are based on the following chemistries:
PolyAMINEs and PolyDADMACs – The most widely used organic coagulants, which are cationic in nature and function by charge neutralization alone. Cationic coagulants neutralize the negative charge of colloids and form a spongy mass called micro flocs.
Melamine Formaldehydes and Tannins – These coagulate the colloidal material in the water, and absorb organic materials such as oil and grease.
The main advantages of organic coagulants include; lower dosage, lower volume of sludge produced and no effect on the pH.
Inorganic Coagulants
Inorganic coagulants are both cost-effective and applicable for a broad variety of water and wastewater. Inorganic coagulants are particularly effective on raw water with low turbidity and will often treat this type of water when organic coagulants cannot.
Once added to water, the inorganic coagulants form aluminum or iron precipitates. These absorb impurities in the water as they fall, serving to clean the water. This process is known as the ‘sweep-floc’ mechanism. However, a downside of metal hydroxide precipitate sweep-floc is that they add to the overall sludge volume that must be treated and removed.
Examples of inorganic coagulants are as below:
Aluminum Sulfate (Alum) – One of the most commonly used water treatment chemicals in the world. Alum is manufactured as a liquid, from which the crystalline form is dehydrated.
Aluminum Chloride – A second choice to Alum as it is more expensive, hazardous and corrosive.
Polyaluminum Chloride (PAC) & Aluminum Chlorohydrate (ACH)
Ferric Sulfate & Ferrous Sulfate – 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. Iron coagulants work similarly to aluminum coagulants but the cost may vary based on the local source of supply.
Ferric Chloride – The least expensive inorganic coagulant, as it is generated as a waste material from steel making operations. However, it’s by far the most corrosive and hazardous inorganic coagulant, and its use is limited to facilities equipped to handle it safely.
Softening
A process that uses chemicals, ion exchange, or thermal treatments to remove elements largely made up of calcium and magnesium carbonates, bicarbonates and sulfates.
Chemical Softening
Resin Exchange
Scale Inhibitors
A class of specialty chemicals that are used to slow or prevent scaling in water systems. Oilfield scaling is the precipitation and accumulation of insoluble crystals (salts) from a mixture of incompatible aqueous phases in oil processing systems.
Carbonate scales such as calcium carbonate or calcite [CaCO3] can be readily dissolved with hydrochloric acid [HCl] at temperatures less than 200f
Sulfate scales such as gypsum [CaSO4·2H2O] or anhydrite [CaSO4] can be readily dissolved using ethylenediamine tetra acetic acid (EDTA).
The dissolution of barytine [BaSO4] or strontianite [SrSO4] is much more difficult.
Chloride scales such as sodium chloride [NaCl] are easily dissolved with fresh water or weak acidic solutions, including HCl or acetic acid.
Iron scales such as iron sulfide [FeS] or iron oxide [Fe2O3] can be dissolved using HCl with sequestering or reducing agents to avoid precipitation of by-products, for example iron hydroxides and elemental sulfur.
Silica scales such as crystallized deposits of chalcedony or amorphous opal normally associated with steam flood projects can be dissolved with hydrofluoric acid.
