Refer to the Journal of the Institute of Engineering (Vol. 8, 2011) study of methane gas (milligrams per liter) emitted from wastewater treatment sludge, Exercise 12.42. 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 are reproduced in the table on p. 683. Note that the table includes the variable, length of time (in days) the sludge was processed The researcher estimated the emission rate (i.e., the rate of increase in emitted methane gas for each additional day of treatment) for both untreated and treated sludge. Use regression to determine if the emission rates differ for the two types of sludge, and if so, provide an estimate of each emission rate.

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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SLUDGE Specimen Methane(CH,) Time Nutrients(VHA) 5 20 No 9. 21 No 3 18 24 No 4 35 26 No 61 29 No 65 32 No 105 35 No 8 120 37 No 117 42 No 10 154 44 No 11 200 47 No 12 198 49 No 13 203 51 No 14 21 20 Yes 15 25 21 Yes 16 61 24 Yes 17 75 26 Yes 18 102 29 Yes 19 150 32 Yes 20 183 34 Yes 21 194 36 Yes 22 245 37 Yes 23 308 42 Yes 24 295 44 Yes 25 272 47 Yes 26 280 49 Yes 27 287 51 Yes