What is EPS and what is their role in flocculation and settling rates?
Extracellular polymeric substances (EPS) are high-molecular-weight natural polymers released into the environment by microorganisms. These are regarded as the primary components that dictate the physicochemical features of a biofilm because they establish the functional and structural integrity of biofilms.
They are largely polysaccharides (exopolysaccharides) and proteins, but they also contain DNA, lipids and humic compounds. These are the building blocks of bacterial colonies and are either connected to the cell's outer surface or released into its growth medium. These chemicals play a significant role in biofilm development and cell adhesion to surfaces. They account for 50 to 90% of the total organic matter in a biofilm.
Microorganisms produce a diverse range of multifunctional polysaccharides, including internal polysaccharides, structural polysaccharides, and extracellular polysaccharides, often known as exopolysaccharides. These are composed primarily of monosaccharides with some non-carbohydrate substituents (such as acetate, pyruvate, succinate, and phosphate). Exopolysaccharides have a wide range of uses in the food and pharmaceutical sectors due to their variable composition.
EPS is made up of many chemicals, including:
· The nucleic acids
· The humic acid
Each proportion and kind is defined by:
· Organisms found
· Biological and other energy sources
· Concentrations of nutrients
· Environmental factors.
What is the role of EPS in flocculation and settling rates?
Even though floc and biofilms are both microbial aggregates of living and dead microbial cells held together by a matrix of extracellular polymeric substances (EPS), a general guide to EPS would be useful to many people dealing with floc settling issues such as non-filamentous or viscous bulking.
The aggregation (colony) performs four unique purposes to microbes:
· Aids in the retention of moisture, which is required for soil life.
· Nutrient accumulation, which refers to the accumulation of organic substances (food), nitrogen, phosphorus, and trace metals/vitamins.
· Extracellular enzymes, which are preserved by being kept close to the generating cell and converting insoluble organics into those that can be transported across the cell wall.
· The physical barrier, which guards against hazardous compounds, pH fluctuations, and other environmental conditions.
The appropriateness of EPS for "excellent" wastewater unit performance is due to all of the inputs and the microbial ecology inside the system. It is not a consistent material across all WWTPs, and bulking is a sign of a problem with one or more of the inputs.Because the cells and EPS have a net anionic charge, divalent cations (Ca++ and Mg++) are critical for creating dense, stable aggregates. In most wastewater, 14 - 40 mg/L Ca++ and 8 - 24 mg/L Mg++ are adequate. However, it has been discovered that maintaining a divalent to monovalent cation ratio larger than 0.5 is more crucial for optimal floc formation.
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