What is the main purpose of pre-chlorination in wastewater treatment?

Pre-chlorination serves multiple purposes in the wastewater treatment process, one key function being the control of odor, reduction of biochemical oxygen demand (BOD), and assistance in sedimentation. By adding chlorine early in the treatment process, the formation of offensive odors can be mitigated, which is particularly important in facilities located near populated areas. Additionally, chlorination helps to oxidize organic matter, lowering BOD levels and improving the overall efficiency of the treatment process. This oxidation process can also aid in improving sedimentation by assisting in the coagulation of particles, helping them to settle out more effectively.

While disinfection before secondary treatment is indeed a function of chlorination, this typically occurs in the later stages of treatment, making it less relevant to the primary goal of pre-chlorination. Enhancing nutrient removal and removing heavy metals are specific objectives that may be addressed through other methods or processes in wastewater treatment but are not the central aims of pre-chlorination. Therefore, the correct answer reflects the immediate goals of applying chlorine at the onset of the treatment process, focusing on odor control, BOD reduction, and sedimentation aid.