When discussing wastewater system organisms, we clump organisms into functional groups based on their ecological impact(s) in wastewater treatment. After working with Microbial Community Analysis (MCA) testing for over 8 years, Aster Bio now reports % of reads in the top 11 functional groups most important to aerobic system operations. We also have additional archaea reports with methanogens for anaerobic systems. The standard MCA report Functional Group Table is below:
| Ammonia Oxidizers | Nitrite Oxidizers | Nitrate Reducers | Sulfur Oxidizers | Sulfur Reducers | PO4 Accum. | Glyc. Accum. |
| 1.69 | 10.46 | 10.45 | 4.39 | 0 | 10.88 | 8.87 |
| Bulking | Foaming | Filaments | Methylotrophs |
| 0 | 3.37 | 7.64 | 1.5 |
What these functional groups do in wastewater treatment
Ammonia Oxidizing Bacteria (AOB)
Oxidize ammonia to nitrite – the first critical step in chemoautotrophic nitrification. AOB are obligate aerobes and have a slower growth rate than many heterotrophic wastewater bacteria. They are also subject to upset from sulfides, phenols, and surfactants/solvents.
Nitrite Oxidizing Bacteria (NOB)
The second step in nitrification – conversion of nitrite to nitrate – is done by NOB. Obligate aerobes, NOB also have slower growth rates than many heterotrophic bacteria. Nitrospira, one of the most common genera of NOB, has some species with the ability to completely oxidize ammonia to nitrate by a single organism – this is called COMAMMOX bacteria.
Nitrate Reducers
A common feature of many wastewater bacteria is the ability to use nitrate as an alternative electron acceptor under anoxic conditions. Nitrate reduction metabolism produces nitrogen gas bubbles that can float solids in secondary clarifiers. Healthy nitrate reducing populations are also necessary for BNR system operation.
Sulfur Oxidizers
Organisms that can obtain energy from oxidation of reduced sulfur compounds are known as sulfur oxidizers. Healthy sulfur oxidizer populations help prevent H2 formation and help promote AOB/NOB growth. While removal of sulfides is beneficial, sulfur oxidizers can also lower pH as the final sulfate oxidation step produces sulfuric acid. Thiobacillus, one of the most common sulfur oxidizers, thrives at pH < 4 which is created from metabolic oxidation of sulfides/sulfur.
Sulfur Reducers
SRB, or sulfur reducers, are bacteria that can use SO4 as an electron acceptor under anaerobic conditions. Their metabolism produces S= and H2S which is responsible for odors and corrosion. Most commonly found in low redox collection systems, you can also find SRB in EQ tanks and anaerobic digesters.
PO4 Accumulators
Phosphate Accumulating Organisms (PAO) are vital for biological phosphorus removal. Using intercellular polyphosphate for energy storage, PAO effectively remove soluble phosphate while growing in aerobic basins. PAO growth is favored by systems with anaerobic conditions with high organic acid concentrations followed by aerobic zones where phosphorus uptake occurs.
Glycogen Accumulators
Glycogen accumulatios (GAO) occupy the same ecological niche as PAO – anaerobic zone uptake of soluble organic acids followed by aerobic zone growth. Unlike PAO, the GAO do not store energy as polyphosphate and do not remove soluble P in wastewater treatment.
Bulking
Bulking refers to high EPS producing organisms that can trigger what is called Zoogleal or non-filamentous bulking. When at normal levels, these organisms are beneficial providing EPS needed for dense floc formation. Under select conditions, the EPS becomes loosely bound and holds water. This form of bulking can lead to problems with MBR and secondary clarifier operations. It also increases polymer demand in waste sludge handling.
Foaming
Foaming organisms create the stable biological foams on aeration basins. Usually triggered by high grease loadings, these microbes have hydrophobic properties that lead to excess foam. Most common are Nocardia type organisms and M. parvicella.
Filaments
Filaments are common wastewater organisms that provide the macro structure needed for large floc formation. If conditions promote overgrowth of filaments, the system experiences bulking events that make operations difficult. MCA testing compliments traditional microscopic identification.
Methylotrophs
These organisms grow on C1 compounds and organics with no C-C bonds. This includes methane, methanol, and some important industrial amines (methylamine and dimethylamine).