What are the common chemical inhibitors used for water treatment?

                     What are the common chemical inhibitors used for water treatment?

The common chemical inhibitors compounds are:

1.     Chromates: These are generally used with zinc and poly-phosphates. When chromates are used alone, the level should be maintained otherwise it would promote corrosion. Few countries/states do not permit the use of chromates because of its toxic nature.

2.     Poly-Phosphates: These basically extend the solubility limit of Calcium. The main limitation of these are that in case pH increases beyond 7.3, these will be converted into ortho-compound, which will react with calcium and form the sludge.

3.     Zinc: These provide film of zinc hydroxide. If pH = 6.5, maintenance is must. If pH > 6.5, zinc will go to the solution. If pH < 6.5, it will precipitate. It will tend to absorb the suspended particulates, which shall lead to higher turbidity.

4.     Nitrates:  These are anodic inhibitors. High level of sulphates and chlorides will affect its performance that leads to high turbidity.

5.     Silicates: This cannot be used if pH is high (> 7) and hardness is over 250 ppm.

6.     Sodium Meta Phosphate (SHMP): This is effective in a sense that it delays the solubility limit of calcium salts and therefore the scale formation is delayed. The disadvantage however is that it degenerates into ortho-compound and require pH to be controlled with in 6.5 to 7.4. It also acts as food for bio fouling. The latest developments are employing Amino Trimithylene Phosphonate Acid (ATMP) and Hydroxyl Ethylkedene di-Phosphonate Acid (HEDP) that does not have the limitations of SHMP.