Different Micro-organisms in Activated Sludge Process

Microorganisms are the main component of the entire activated sludge process as without them the process cannot take place. These are also called the biological component or biological mass of the process. Bacteria, protozoa, fungi and rotifers are the main microorganisms used in the process. Along with this some types of metazoa like nematode may also present. For the fully healthy activated sludge process, there should also be the regular agitation for the proper aeration and sludge recirculation for the massive growth of the organism.

Now what type of microorganism is going to be used in the activated sludge process will depend upon the controlled environmental conditions, operating mode of the plant, process design and the properties of the secondary influent wastewater.

Bacteria
Bacteria are the main microorganisms used as biological component. The individual size of bacteria is one micron but the colonies are visible to naked eyes. There are both aerobic as well as anaerobic bacteria. Aerobic once needs oxygen to perform and survive whereas the anaerobes can survive without oxygen. Hence depending upon the environment created for the process the type of bacteria is used.

Then there are heterotrophic and autotrophic bacteria in the activated sludge process but the former being more in number. Heterotrophic bacteria utilizes energy from the carbonaceous organic matter to release energy in the form of carbon dioxide and water. Achromobacter, Alcaligenes, Arthrobacter, Citromonas, Flavobacterium, Pseudomonas, and Zoogloea are the main heterotrophic bacteria used in the process.

The autotrophic bacteria reduces the oxidized carbon compounds for the growth of the cell. Nitrobacter and Nitrosomonas are the major two types of autotrophic bacterias used.

Fungi
Sphaerotilus natans and Zoogloea sp are the most common types of sewage fungus that can compete with bacteria to decompose the organic matter for their cell's growth. These are the multicellular organism irrespective to bacteria that oxidise ammonia to nitrite and some even convert the nitrite to nitrate.

Protozoa
In activated sludge treatment number of species of protozoa are used. These are single celled organisms that for energy consume bacteria and particulate matter. Although flagellate and amoebae may also be used but ciliates are the most common ones.