Measuring water quality Biochemical oxygen demand BOD measur

Measuring water quality. Biochemical oxygen demand (BOD) measures organic pollutants in water by measuring the amount of oxygen consumed by microorganism that break down these compounds. BOD is hard to measure accurately. Total organic carbon (TOC) is easy to measure, so it is common to measure TOC and use regression to predict BOD. A typical regression equation for water entering a municipal treatment plant is BOD = -55.43 + 1.507 TOC

Both BOD and TOC are measured in milligrams per liter of water.

(a)   What does the slope of this line say about the relationship between BOD and TOC?

(b)   What is the predicted BOD when TOC=0? Values of BOD less than 0 are impossible. Why do you think the prediction gives an impossible value?

Solution

A. The positive slope of this line says that the two variables BOD and TOC are positively related to one another. As TOC goes up, so does BOD.

B. Plugging in 0 for TOC and solving:

BOD = -55.43 + 1.507(0)

BOD=-55.43

This prediction gives an impossible value because having a total organic carbon level of 0 is unlikely. In order for the equation to give a believeable value for BOD, TOC would have to be at least 36.78.

Hope this helps! :) Let me know if you have any other questions.