When selecting methods and processes for treatment of industrial wastewater, several factors must be considered, such as the amount and nature of waste, concentration and type of contaminants, requirements treatment results as well as the possibility of using this water in water supply systems.
In recent years, chemical, ion-exchange and electrochemical methods have come into wide use. Chemical reagent methods are mostly used for treatment of water contaminated with chrome and other heavy metals.
The idea of these methods is the use of special agents to reduce hexavalent chrome to trivalent and precipitate it. Some of the reagents are ferrous sulfate, steel scrap, sodium bisulfite etc.
Evaluating the perspectives of chemical treatment, the following disadvantages become apparent:
- low degree of heavy metal removal;
- high content of salts, which does not allow to use the water in return cycle;
- irrecoverable loss of metals;
- high consumption of reagents;
- large equipment footprint.
Ion-exchange method is a promising approach in industrial wastewater treatment. It facilitates almost complete removal of contaminants from wastewater and allows to reuse the water. However, this method has certain limitations in removal of heavy metal salts.
This approach dominates in design of closed loop water supply systems, and allows to reduce consumption of fresh water in industrial processes. However, one of the effects of this method is the large footprint of treatment facilities.
Among the disadvantages of ion exchange are:
- high reagent consumption for ionite regeneration;
- large amount of salts entering water bodies along with neutralized regeneration products;
- high water consumption on ionite processing and washing.
Electrochemical treatment has come into wider use recently. It allows to remove chrome and heavy metals from wastewater by steel electrodes. The idea is to reduce chrome by bivalent iron ions, which form from electrode dissolution. In general, the specifics of electrochemical method make it quite complex.