Neutralization of wastewater is required before releasing it into water bodies or reuse in various technology processes. Wastewater containing acids or alkali must be neutralized.
Water with pH of 6.5 – 8.5 are considered neutral. Neutralization is required where pH is below 6.5 and above 8.5. Practically, the highest danger is posed by acidic wastewater containing salts of heavy metals.
Neutralization is a chemical reaction between two substances, of which one has the properties of an acid and the other one of a base. The result of the process is that both substances lose these properties.
There are several methods of neutralization:
- mixing of acidic and basic wastewater;
- using chemical agents;
- filtration of acidic wastewater through neutralizing materials;
- absorption of acidic gases by basic water or absorption of ammonia by acidic water.
The method is selected based on the following factors:
- volume of waste water;
- concentration of wastewater;
- the manner in which wastewater is transported to treatment facilities;
- availability and the cost of chemicals.
Neutralization of Wastewater. Neutralization by mixing is used when two facilities, each generating separately acidic and basic wastewater are located nearby. It is important that water contains no other contaminants. Mixing can be performed in special tanks, both with or without mechanical agitators. In the latter case the process is driven by the air coming from the supply line at 20-40 meters per second.
The neutralization method is used when the facility only has acidic or basic wastewater and there is no way to set up a reaction between the two. This method is used more often when working with acidic wastewater. While selecting neutralization chemical, consider the specific acid, its concentration and solubility of salts formed in the reaction.
Filtration through neutralizing materials (magnesite, dolomite, lime, marble, chalk etc) is performed in special neutralization filters. Continuous filters are used for neutralization of sulfuric, chlorine and nitric acid if the concentration in water is below 1.5 grams per liter.
Basic wastewater can be neutralized by using gas containing CO2, SO2, NO2 etc. This method allows not only to neutralize wastewater, but also to treat the gases.