Sodium bisulfite(sodium hydrogen sulfite) is a chemical compound with the chemical formula NaHSO3. This salt of bisulfite can be prepared by bubbling sulfur dioxide in a solution of sodium carbonate in water. Sodium bisulfite in contact with chlorine bleach will release harmful fumes.
Sodium bisulfite is a common reducing agent in the chemical industries. As it readily reacts with dissolved oxygen:
2 NaHSO3 + O2 → 2 NaHSO4
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 wastewater treatment, sodium bisufite is often added following disinfection with a chlorine solution to neutralize the residual chlorine before discharging the treated effluent.