This reference illustrates the application of fundamental concepts in microbiology to provide a sound basis for the design and operation of various biological systems used in solving numerous environmental challenges in the air, water, and soil—opening with an examination of overall metabolism and the resulting growth of bacteria, fungi, algae, protozoa, rotifers, and other microorganisms and progressing to mixed microbial systems where various groups of microorganisms compete, as well as, compliment each other in the processing of a myriad of biodegradable pollutants in our environment.