What is the primary concern when noticing an increase in chlorine demand without a change in chlorine flow rate?

An increase in chlorine demand without an associated change in chlorine flow rate typically indicates that there are additional contaminants present in the effluent that require more chlorine to achieve the desired degree of disinfection. Chlorine demand refers to the amount of chlorine needed to react with substances in the water, such as organic materials, bacteria, or other pollutants. When the chlorine flow rate remains constant but the demand increases, it suggests that the quality of the influent or the presence of new contaminants may have changed, necessitating further evaluation of the wastewater's composition.

This situation highlights the importance of monitoring effluent quality to ensure that chlorination is effective in achieving the required levels of disinfection. Identifying and addressing the sources of these contaminants is essential to maintain treatment performance and protect public health, making the presence of contaminants in the effluent the primary concern in this scenario.