Here are the answers to the Oct. 19, 2021 edition of TPO's Exam Study Guide:

Which classification of anaerobic digester is the most efficient at pathogen reduction, increased volatile solids reduction and decreased detention times?

The answer to this question is C, thermophilic. Anaerobic digestion is done typically with either mesophilic (85 to 100 degrees F range) or thermophilic (122 to 130 degrees F range). The goal of thermophilic digestion is increased pathogen destruction, but also able to achieve increased volatile solids reduction and decreased detention times when compared to mesophilic digestion. One drawback for thermophilic digestion is the increased energy needs and costs. Mesophilic digestion is more common due to this factor. Understanding the different modes or classifications of digesters is necessary for operators and may be found in some certification guidelines

Using the data below, what is the approximate magnesium concentration in mg/L?

The correct answer is B. Total hardness is the sum of divalent metallic cations (calcium and magnesium) in water. It is important to note the total hardness concentration is expressed as calcium carbonate and the calcium concentration is reported as mg/L. 


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