*Davis, Mackenzie Leo, and David A. Cornwell. Introduction to Environmental Engineering. Dubuque, IA: McGraw-Hill Companies, 2008. Print.
*Gray, N. F. Biology of Wastewater Treatment. London: Imperial College, 2004. Print.
*Davis, Mackenzie Leo, and David A. Cornwell. Introduction to Environmental Engineering. Boston, MA: WCB McGraw-Hill, 1998. Print.
*http://www.cee.mtu.edu/~nurban/classes/CE3502/spring12/modelreports/MLSSreport.pdf
*http://ragsdaleassociates.com/WastewaterSystemOperatorsManual/Chapter%208%20-%20Activated%20Sludge.pdf