Determine the chlorine demand of an effluent if the chlorine dose is 10 mg/L and the chlorine residual is 1.1 mg/L.

To determine the chlorine demand of an effluent, you can use the formula:

Chlorine Demand = Chlorine Dose - Chlorine Residual.

In this case, the chlorine dose is 10 mg/L, and the chlorine residual is 1.1 mg/L. Plugging the values into the formula gives:

Chlorine Demand = 10 mg/L - 1.1 mg/L = 8.9 mg/L.

This calculation indicates that the chlorine demand of the effluent is 8.9 mg/L, making it the correct answer in the context of this question. Chlorine demand represents the amount of chlorine that has been consumed by the substances present in the effluent, thus providing insight into the oxidation potential of the effluent. The higher the chlorine demand, the more chlorine is necessary to treat the water effectively.