In nature, microbiological mechanisms have always been responsible for the break down of biodegradable waste matter which either inadvertently or by design found its way into the aquatic environment. Self-purification of surface waters is a well known phenomenon, but the solubility of oxygen in water is low. Adding too much biodegradable pollution as towns and cities grow and develop rapidly has caused too much microbiological activity that consumes too much oxygen. Overloading tends to cause anaerobiosis; the waters became aesthetically objectionable and unsuitable as sources of drinking water production. Before discussing the relationships between microbes and waste management we have to know the classification of these microorganisms.