Hi Kristaps, Generally you ...

Hi Kristaps,

Generally you do not need to choose the bacteria you need, they are naturally there in the wastewater - they are present in our intestines and so are excreted with our faeces.  However as indicated by the contributors, the aim of the wastewater treatment process is to create optimum conditions for selected species to thrive, and to reduce the proliferation of unwanted species.  Hence in a biological nutrient removal wastewater treatment process you will create different conditions in different process units of the plant for the different species.  An anaerobic unit followed by an anoxic unit followed by an aerobic unit - each unit allowing certain species to proliferate and perform the function we want them to do.  This includes the units for stabilisation and digestion of wastewater sludges.

In some applications, suppliers require the addition of proprietary bacterial cultures and/or enzymes from time to time to improve particular process functions for their process configurations.  These may be costly but may result in improved performance, particularly in terms of reducing the process time for breakdown of organics in the wastewater.

Prem has given a good description of particularly the anaerobic bacteria groups, and you should read a good book on the microbiology of wastewater treatment