dechlorinate

Dechlorinate is the process of removing chlorine or chlorine-containing compounds from a substance. In water treatment, it refers to reducing residual chlorine and chloramines to ensure taste, safety, and compatibility with sensitive equipment or aquatic life. In environmental remediation, dechlorination describes the removal of chlorine atoms from chlorinated solvents and pesticides, typically to render contaminants less toxic and more biodegradable.

Dechlorination methods include chemical, physical, catalytic, and biological approaches. Chemical dechlorination uses reducing agents such as sodium bisulfite, sodium sulfite, or sodium thiosulfate to convert chlorine species to chloride ions. Activated carbon can adsorb free chlorine and chloramines. Aeration or degassing removes dissolved chlorine gas from water. In groundwater cleanup, zero-valent iron or iron-based catalysts promote reductive dechlorination of solvents like trichloroethylene and perchloroethylene, often with hydrogen donors.

Biological dechlorination employs organohalide-respiring microorganisms that operate under anaerobic conditions. These microbes sequentially remove chlorine atoms, converting chlorinated ethenes to ethene, a nonchlorinated end product. Such processes can occur in specialized bioreactors or contaminated sediments and are a focus of bioremediation research and practice.

Applications include municipal drinking-water treatment to remove residual chlorine, aquaria and aquatic transport to prevent chlorine-related stress in fish, and remediation of chlorinated solvent plumes in soil and groundwater. Considerations include ensuring complete dechlorination to prevent toxic byproducts such as vinyl chloride, monitoring residuals, and managing byproducts from chemical reducing agents. The term encompasses chemical, physical, and biological methods used to reduce chlorine content in various media.