Here are the answers to the June 1, 2022 edition of TPO's Exam Study Guide:

What operational parameters are able to be controlled by the operator in an activated sludge treatment process?

The answer to the question is C, DO, return rate and wasting rate. The activated sludge process has many variables that an operator must be aware of, but it's only these three they have total control over. The operator may set the DO in the plant to the point necessary to maintain aerobic conditions and needs of the microorganism population. The operator as has the ability to set the return rates to ensure the sludge is able to settle in the clarifier to an acceptable detention time. The operator also makes the decision on how much sludge needs to be wasted from the system as necessary. By understanding these operational parameters, the operator can make the necessary choices to ensure proper treatment in the plant. Many things are out of the operator’s control but should be taken into consideration when making changes in the treatment process. 

What is the maximum residual disinfectant level for chlorine dioxide?

The correct answer is C, 0.8 mg/L as chlorine dioxide. Chlorine dioxide is an effective primary disinfectant if cryptosporidium or the development of trihalomethanes are of concern. However, chlorine dioxide is unstable at elevated concentrations, so on-site generation by reacting sodium chlorite with chlorine is required. Feeding chlorine dioxide creates a scenario where elevated chlorite levels may hinder the quality of the finished water. To ensure the finished water quality is meeting the national primary drinking water regulations, operators sample the water at the distribution entry point and have it analyzed for chlorite. Chlorite has a maximum contaminant level of 1.0 mg/L.