Chlorinated hydrocarbons (CHC) have been produced an an industrial scale since the 1920＇s and 1930＇s and are frequently used as solvents, extractants, and disinfectants, Because their low biodegradability they are often enriched in the food chains of animals, resulting in high mortality, It is therefore necessary to prevent the discharge of CHC＇s into water, air, and soil. They are often not biodegraded in municipal or industrial activated sludge plants or in trickling filters, Until harmless substitutes become widely available, CHC＇s will continue to pose a threat and must be eliminated from all effluents before entering wastewater treatment plants. Information about specific: conditions for anaerobic and aerobic: biodegradation of selected CHC＇s is given below, Two topics will be discussed in greater detail: the kinetics of dechlorination and mineralization and some examples of the reaction engineering process in lab and pilot scale.