If you want to read about WWTPs look at the Office of Water Programs page at the California State University Sacramento website. The address is www.owp.csus.edu . They have at least 6 well written manuals, all reasonably priced, covering pretty much everything that you need to know, including the mathematics of wastewater. Pictures are good, glossaries are real good, math is covered thoroughly. These manuals are aimed at WWTP operators and are widely used in the classroom. Jim Allen