To microbes, the aggregate (colony) serves four distinct functions:
- Helps retain moisture needed for survival in soils
- Buildup of nutrients - here we are referring to organic compounds (food), nitrogen, phosphorus, and trace metals/vitamins
- Accumulate enzymes - extracellular enzymes are conserved by being held near the producing cell and making insoluble organics suitable for transport across the cell wall
- Physical barrier - this protects against toxic substances, pH swings, and other environmental factors
The EPS is composed of multiple compounds including (from highest to lowest percentage):
- Polysaccharides
- Proteins
- Glycoproteins
- Nucleic acids
- Phospholipids
- Humic acids
- Organisms present
- organic and other sources of energy
- Nutrient concentrations
- Environmental conditions
Due to the cells and the EPS having a net anionic charge, divalent cations (Ca++. Mg++) are very important to forming dense, stable aggregates. In most wastewater having 14 - 40 mg/L Ca++, and 8 - 24 mg/L Mg++ is sufficient. However, recent research has found that keeping a Divalent to Monovalent cation ratio greater than 0.5 is more important for good floc formation.