Sodium bisulfite is a common reducing agent in the chemical industry, as it readily reacts with dissolved oxygen:
It is usually added to large piping systems to prevent oxidative corrosion. In biochemical engineering applications, it is helpful to maintain anaerobic conditions within a reactor. Sodium bisulfite should not be confused with sodium bisulfate which is used as a pH lowering chemical for swimming pools.
In drinking water treatment, sodium bisulfite is often added after super chlorination, to reduce the residual chlorine before discharging to the service reservoir.
In wastewater treatment, sodium bisulfite is often added following disinfection with chlorine prior to discharging the effluent to the receiving water. Residual chlorine can have a negative impact on aquatic life.