Micro organisms play a vital role in the normal biological cycle

Bacteria are the most important biological converters of organic wastes (animal and plant life ) to water, new cells and gases.

Bacteria generally thrive in a pH range from 6.5 to 8.5 and will not survive at a pH of less than 4.3 or above 10.5

There are both Pathogenic and Non pathogenic, Aerobic ( require oxygen) and Anaerobic ( absence of oxygen ) bacteria.
Since pathogenic ( generally anaerobic ) bacteria cause disease, it is preferable to introduce and promote growth of a larger number of non pathogenic aerobic bacteria.

In the absence of oxygen ( anaerobic bacteria ) produce end products such as organic acids , aldehydes, keytones and alcohol's, and produce odours and dark colours in the water.

Bacteria are single cell organisms ( classified as plants but non photosynthetic) and all their food must be hydrolysed.
To accomplish this the bacteria excretes enzymes which break down particulate matter.
the resulting solution is then absorbed into the cellular membrane and diffused through the inner cell wall as cellular enzymes before they can then convert it to food.
This process produces mainly CO2 , water, and bacterial cells.
Carbohydrates and proteins are readily hydrolysed