Refer to the Journal of the Institute of Engineering (Vol. 8, 2011) study of methane gas (milligrams

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Refer to the Journal of the Institute of Engineering (Vol. 8, 2011) study of methane gas (milligrams per liter) emitted from wastewater treatment sludge, Exercises 12.42 and 12.51. Recall that two different types of treated sludge were investigated: (1) sludge without nutrients added and (2) sludge with nutrients (VHA) added. Data for n = 27 sludge specimens were collected on the variables methane gas emitted (y), treatment time (x1), and sludge type (x2 = if VHA added, 0 if not).

a. Write a complete 2nd-order model for E(y) as a function of x1 and x2.

b. Specify the null hypothesis to test in order to determine whether curvature exists in the relationship between methane gas emission and treatment time.

c. Give the equation of the reduced model to be compared to the     complete model, part a, in order to conduct the test, part b.

d. A SAS printout of the analysis is shown on the next page. Locate the p-value of the test for curvature on the printout. Interpret the results.


Data from exercise 12.42

Wastewater treatment systems are designed to maintain the chemical, physical, and biological integrity of water. These systems, however, tend to generate various greenhouse gases, such as methane (CH4). The Journal of the Institute of Engineering (Vol. 8, 2011) published a study of the amount of methane gas (milligrams per liter) emitted from wastewater treatment sludge. Two different types of treated sludge were investigated: (1) sludge without nutrients added and (2) sludge with nutrients added. The specific nutrient studied was volatile fatty acids (VFA). Data for n = 27 sludge specimens are listed in the table. Use regression to determine if the mean amount of methane gas emitted differs for the two types of sludge, and if so, provide a 95% confidence interval for the magnitude of the difference.

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Statistics For Engineering And The Sciences

ISBN: 9781498728850

6th Edition

Authors: William M. Mendenhall, Terry L. Sincich

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