Which of the following is a disadvantage of using combined chlorine (chloramines)?

Using combined chlorine, or chloramines, does indeed have a disadvantage related to the requirement for longer contact time and its sensitivity to temperature. Chloramines, which are formed when chlorine reacts with ammonia in water, are generally less effective as a disinfectant compared to free chlorine. This means that they need more time to achieve the same level of disinfection.

In cooler water temperatures, the efficacy of chloramines can further decline, which means that operational adjustments may be necessary in varying temperature conditions. Ensuring that adequate contact time is maintained is crucial to achieving sufficient disinfection. Therefore, understanding this characteristic of chloramines is essential for managing water treatment processes effectively.

In contrast, the other options do not accurately reflect disadvantages. For example, stating that chloramines are more stable is a property that could be considered an advantage in maintaining residual disinfectant levels in distribution systems. The production of trihalomethanes (THMs) is more commonly associated with the use of free chlorine, making this statement misleading in the context of chloramines. Lastly, while monitoring chloramines can be more complex than monitoring free chlorine, it is not accurate to state that chloramines cannot be monitored at all; rather, there are established methods for monitoring their levels in water. This