Choosing right cleaning agents

Treating water chemically

For the chemical treatment of water, a great variety of chemicals can be applied.

Algaecides

Algaecides are chemicals that kill algae and blue or green algae, when they are added to water. Examples are CuSO4, FeSO4 Salts. Algaecides are effective against algae.

Coagulants

Generally salts of Iron, Aliminium are used for this, aluminium as Al2 (SO4)3- (aluin) and iron as either FeCl3 or Fe2(SO4)3-. FeSO4 which is cheaper is also utilised, on condition that it will be oxidised to Fe3+ during aeration.

Coagulation is very dependent on the doses of coagulants, the pH and Suspended matter content. To adjust pH levels Ca(OH)2 is applied as co-flocculent. Doses usually vary between 10 and 90mg Fe3+/ L

Corrosion inhibitors

Corrosion is a general term that indicates the conversion of a metal into a soluble compound.

Corrosion can harm tubes of boiler systems, deposition of corrosion products in critical heat exchange areas, and overall efficiency loss.

That is why corrosion inhibitors are often used. Inhibitors are chemicals that react with a metallic surface, giving the surface a certain degree of protection. Inhibitors often work by attaching themselves on the metallic surface, protecting the metallic surface by covering like a film.

Disinfectants

Disinfectants kill present unwanted microrganisms in water. There are various different types of disinfectants in use most common of them are as follows:

• (Chlorine (dose 2-10 mg/L)
• Chlorine dioxide
• Ozone
• Hypochlorite

Chlorine

Chlorine is the most widely used biocide today. It has been used for disinfection of domestic water supplies and for the removal of tastes and odours from water for a long time. The amount of chlorine that needs to be added in a water system is determined by several factors, namely chlorine demand, contact time, pH and temperature of the water, the volume of water.

When chlorine gas enters a water supply it will hydrolyse to form hypochlorous and hydrochlorous acid. The latter determines the biocidal activity.

This process takes place according to the following reaction:

Cl2 + H2O -> HOCl + HCl

Hydrochlorous acid is responsible for the oxidation reactions with the cytoplasm of microrganisms, after diffusion through the cell walls.

Chlorine than disturbs the production of ATP (adenosine triphosphate), an essential compound for the respiration of microrganisms.

The bacteria that are present in the water will die as a consequence of experienced breathing problems, caused by the activity of the chlorine.

The amount of chlorine that needs to be added for the control of bacterial growth is determined by the pH. The higher the pH, the more chlorine is needed to kill the unwanted bacteria in a water system. When the pH values are within a range of 8 to 9, 0.4 ppm of chlorine must be added. When the pH values are within a range of 9 to 10, 0.8 ppm of chlorine must be added.

Chlorine dioxide disinfection

ClO2 is used principally as a primary disinfectant for surface waters with odour and taste problems. It is an effective biocide at concentrations as low as 0.1 ppm and over a wide pH range. ClO2 penetrates the bacterial cell wall and reacts with vital amino acids in the cytoplasm of the cell to kill the organisms. The by-product of this reaction is chlorite.

Chlorine dioxide disinfects according to the same principle as chlorine, however, as opposed to chlorine, chlorine dioxide has no harmful effects on human health.

Hypochlorite disinfection

Hypochlorite is applied in the same way as chlorine dioxide and chlorine. Hypo chlorination is a disinfection method that is not used widely anymore, since an environmental agency proved that the Hypochlorite for disinfection in water was the cause of bromate consistence in water.

Ozone disinfection

Ozone is a very strong oxidation medium, with a remarkably short life span. It consists of oxygen molecules with an extra O-atom, to form O3. When ozone comes in contact with odour, bacteria or viruses the extra O-atom breaks them down directly, by means of oxidation. The third O-atom of the ozone molecules is than lost and only oxygen will remain.

Disinfectants can be used in various industries. Ozone is used in the pharmaceutical industry, for drinking water preparation, for treatment of process water, for preparation of ultra-pure water and for surface disinfection.

Chlorine dioxide is used primarily for drinking water preparation and disinfection of piping.

Every disinfection technique has its specific advantages and its own application area.

Flocculants

Flocculants are dosed in water to bring together suspended and colloidal matter and form a bond between them to allow them to settle quickly. These polymers have a very specific effect, dependent upon their charges, their molar weight and their molecular degree of ramification. The polymers are water-soluble.

There can be several charges on one flocculent. There are cationic polymers, based on nitrogen, anionic polymers, based on carboxylate ions and polyampholytes, which carry both positive and negative charges.

Neutralizing agents (alkalinity control)

In order to neutralize acids and basics, we use either solution of Sodium Hydroxide (NaOH), CaCO3 (Calcium Carbonate), or lime suspension (Ca(OH)2) to increase pH levels. We use diluted sulphuric acid (H2SO4) or diluted hydrochloric acid (HCl) to decline pH levels. The dose of neutralizing agents depends upon the pH of the water in a reaction basin. Neutralization reactions cause a rise in temperature.

Oxidants

In Chemical oxidation processes chemicals are used to reduce COD/BOD levels, and to remove both organic and oxidisable inorganic components. The processes can completely oxidise organic materials to CO2 (Carbon Disoxide) and water, although it is often not necessary to operate the processes to this level of treatment.

A wide variety of oxidation chemicals are available. Examples are H2O2 (Hydrogen Peroxide), Ozone, Combined ozone & peroxide and Oxygen.

Oxygen scavengers

Oxygen scavenging means preventing oxygen from introducing oxidation reactions.

Most of the naturally occurring organics have a slightly negative charge. Due to that they can absorb oxygen molecules, because these carry a slightly positive charge, to prevent oxidation reactions from taking place in water and other liquids.

Oxygen scavengers include products, such as hydrazine (N2H4) or other organic products like carbohydrazine, hydroquinone, sodium sulphite (Na2SO3) and other inorganic compounds.

pH conditioners

Municipal water is often pH-adjusted, in order to prevent corrosion from pipes and to prevent dissolution of lead into water supplies. During water treatment pH adjustments may also be required. The pH is brought up or down through addition of basics or acids. An example of lowering the pH is the addition of HCl (hydrochloric acid), in case of a basic liquid. An example of bringing up the pH is the addition of sodium hydroxide.