Removing nitrogen from toxic wastewater. Highly toxic wastewater is produced during the manufacturing of dryspun acrylic fiber. One way to lessen toxicity is to remove the nitrogen from the wastewater. A group of environmental engineers investigated a promising method—called anaerobic ammonium oxidation—for nitrogen removal and reported the results in the Chemical Engineering Journal

(Apr. 2013). A sample of 120 specimens of toxic wastewater were collected and each treated with the nitrogen removal method. The amount of nitrogen removed (measured in milligrams per liter) was determined as well as the amount of ammonium (milligrams per liter) used in the removal process. These data (simulated from information provided in the journal article) are saved in the NITRO file. The data for the first 5 specimens are shown below.

A simple linear regression analysis, where y = amount of nitrogen removed and x = amount of ammonium used, is also shown in the accompanying SAS printout.

a. Assess statistically the adequacy of the fit of the linear model. Do you recommend using the model for predicting nitrogen amount?

b. On the SAS printout, locate a 95% prediction interval for nitrogen amount when amount of ammonium used is 100 milligrams per liter. Practically interpret the result.

c. Will a 95% confidence interval for the mean nitrogen amount when amount of ammonium used is 100 milligrams per liter be wider or narrower than the interval, part b? Explain.

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First 5 observations of 120 Nitrogen Ammonium 18.87 67.40 17.01 12.49 23.88 61.96 10.45 15.63 36.03 83.66