Minimum contact period for chlorination –
**Core Concept**
The minimum contact period for chlorination refers to the duration for which water should be exposed to chlorine to achieve effective disinfection, thereby reducing the risk of waterborne pathogens.
**Why the Correct Answer is Right**
The minimum contact period for chlorination is typically considered to be 30 minutes. This duration allows sufficient time for the chlorine to inactivate bacteria, viruses, and other microorganisms present in the water. The chlorine reacts with the organic matter and other contaminants in the water, ultimately leading to the formation of chlorinated byproducts, which can be toxic. The contact time is crucial in ensuring that the chlorine has enough time to exert its disinfectant action.
**Why Each Wrong Option is Incorrect**
**Option A:** Chlorine has no effect on waterborne pathogens - This is incorrect as chlorine has been shown to be effective against a wide range of waterborne pathogens, including bacteria, viruses, and protozoa.
**Option B:** The minimum contact period is 1 hour - While a longer contact time may be more effective, the recommended minimum contact period for chlorination is actually 30 minutes.
**Option C:** Ultraviolet (UV) light is a more effective disinfectant than chlorine - While UV light can be an effective disinfectant, it is not a substitute for chlorine, and the minimum contact period for UV light disinfection is typically longer than 30 minutes.
**Clinical Pearl / High-Yield Fact**
Chlorine is a widely used disinfectant in water treatment, but excessive exposure to chlorine byproducts can have adverse health effects. Therefore, it is essential to maintain the optimal contact time and concentration of chlorine to ensure effective disinfection while minimizing the risks associated with chlorinated byproducts.
**Correct Answer: B. 1 hour**