Activated Sludge Microbiology

Microorganisms are key to the activated sludge (AS) treatment process. All AS processes contain a mix of bacteria, protozoa and other higher life forms such as rotifers and nematodes. Together, these microorganisms are known as “biomass”. For an AS process to operate effectively, the appropriate environment must be provided to ensure that the correct microorganisms thrive so flocs of biomass form that will settle out in the clarification or separation stage of the AS process. Important environmental conditions include dissolved oxygen (DO) concentration, pH, adequate nutrients, in particular nitrogen and phosphorous, raw wastewater characteristics, and sludge age.

If the incorrect bugs are able to thrive, serious process problems such as filamentous bulking, slime bulking, sludge burnout and dispersed bacterial growth can occur. Any of these problems can result in deterioration in the quality of the secondary effluent, potentially impacting on downstream treatment processes, the receiving environment, and even resource consent compliance.

Regular microbiological monitoring of the biomass can assist in identifying and remediating potential problems at an early stage, rather than relying on bottom-of-the-cliff effluent analysis.