NCEES FE Civil Practice Exam

Chlorine is the most commonly used disinfectant in water treatment due to its effectiveness, longevity, and cost-efficiency. It is a powerful biocide that can eliminate a wide range of pathogens, including bacteria and viruses, thus ensuring the safety of drinking water. One of its key advantages is its ability to form chloramines when it reacts with ammonia in water, which helps maintain residual disinfection throughout the distribution system, providing ongoing protection against microbial regrowth. Chlorine is also readily available and can be applied easily, either in gas form or as liquid compounds such as sodium hypochlorite. Its use has been established for more than a century, allowing for extensive research on its effectiveness and safety, which further solidifies its position as the primary method of disinfection in municipal water systems. While other disinfectants like ozone and UV light provide effective disinfection as well, they often lack the residual effect that chlorine offers, making them less practical for long-term water treatment solutions. Ozone, for instance, is an excellent oxidant that can effectively kill microorganisms, but it does not provide lasting disinfection in the water distribution system. Furthermore, UV light requires careful handling and monitoring, as it does not leave any residual chemical in the water.