Which factor will cause problems for chlorination?

Which factor will cause problems for chlorination?

• A. pH of 6.8
• B. long contact time
• C. foreign substances
• D. high concentration

Answer: (C)

Foreign substances in the water cause problems for chlorination because chlorine must remain as free chlorine to sanitize effectively. When water contains dissolved or suspended contaminants—such as natural organic matter, ammonia, iron, or other substances—the chlorine reacts with them. This uses up the chlorine in a process called chlorine demand, leaving less free chlorine available to kill microbes. If the residual free chlorine drops too low, disinfection is incomplete and pathogens can survive, and disinfection byproducts can form if organic matter reacts with chlorine. In contrast, a pH around 6.8 is within a favorable range for chlorine to act as a disinfectant, long enough contact time generally improves disinfection, and a higher chlorine concentration is something that can be adjusted as needed rather than inherently causing a problem.

Foreign substances in the water cause problems for chlorination because chlorine must remain as free chlorine to sanitize effectively. When water contains dissolved or suspended contaminants—such as natural organic matter, ammonia, iron, or other substances—the chlorine reacts with them. This uses up the chlorine in a process called chlorine demand, leaving less free chlorine available to kill microbes. If the residual free chlorine drops too low, disinfection is incomplete and pathogens can survive, and disinfection byproducts can form if organic matter reacts with chlorine.

In contrast, a pH around 6.8 is within a favorable range for chlorine to act as a disinfectant, long enough contact time generally improves disinfection, and a higher chlorine concentration is something that can be adjusted as needed rather than inherently causing a problem.