Which of the following is NOT a factor that influences chlorine disinfection efficacy?

Chlorine disinfection efficacy is influenced by various factors that can affect the chlorine's ability to effectively disinfect water. The pH of water is crucial, as it alters the form of chlorine present in the water. At lower pH levels, a higher proportion of the more effective hypochlorous acid exists, while at higher pH levels, more of the less effective hypochlorite ion is present, which can reduce disinfection efficacy.

Temperature of the water also plays a significant role; as temperature increases, the reaction rate of chlorine with pathogens generally increases, improving disinfection efficiency. Additionally, the contact period or contact time between chlorine and pathogens is critical, as adequate contact time is required to ensure that the chlorine has enough time to inactivate microorganisms.

In contrast, the volume of water does not directly influence the disinfection efficacy of chlorine in the same way that the other factors do. While a larger volume of water may require a larger quantity of chlorine to achieve the desired concentration throughout, the fundamental efficacy of chlorine in an adequate concentration remains unaffected by the volume itself. Thus, this characteristic is not a deciding factor in how effective chlorine disinfection will be, making it the correct choice for the question posed.