EPS are the complex high molecular weight compounds that are excreted by bacteria building floc or biofilms. The aggregation and adhesion of cells occurs once cellular division slows and the EPS builds on the cell surface. The mixture consists of polysaccharides, proteins, humic substances, and nucleic acids, with the majority being made up of polysaccharides and proteins. Key point here is you need an appropriate amount of EPS to get floc or biofilm yet too much EPS with entrained water can lead to viscous or zoogleal bulking.
Research has found EPS composition varies with:
The study presented in Nature, evaluated the impact of salinity on cell adhesion and floc/biofilm formation. High Na+ can be a problem. While Na+ under 10 grams per liter has a negative impact on EPS formation, when you move from 10 g/L Na+ to 20 g/L Na+ that amount of EPS drops by 50%.
The study then went into new territory by extracting the EPS from municipal and hypersaline wastewater biomass. What they found was the biomass manufactured more total EPS in the hyper saline environments where the EPS help protect against osmotic pressures caused by high Na+ concentrations. While the hypersaline had more total EPS, it has a different composition than municipal. The diversity of compounds in the EPS was lower in the hypersaline wastewater and the EPS was not as closely associated with cell aggregation/adhesion.
Also both wastewaters had anerobic/anoxic tanks. What is interesting here is the EPS was not associated with aggregation. Apparently, DO is very important to give us the amount of aggregation needed for bioflm/floc formation.
Here is a link to the Nature article if you would like to go deeper into the research.
http://www.nature.com/articles/srep26721
Research has found EPS composition varies with:
- Carbon sources (what chemicals are present in BOD or COD)
- C:N:P ratio (key cause many bulking events)
- D.O. - higher DO makes for better adhesion & capsular EPS
- Temperature
- MCRT & HRT
- Growth stage (F/M ratio)
- Solution chemistry (pH, ionic strength, divalent cation)
- Toxic (biocides, heavy metals, CN, Phenol)
The study presented in Nature, evaluated the impact of salinity on cell adhesion and floc/biofilm formation. High Na+ can be a problem. While Na+ under 10 grams per liter has a negative impact on EPS formation, when you move from 10 g/L Na+ to 20 g/L Na+ that amount of EPS drops by 50%.
The study then went into new territory by extracting the EPS from municipal and hypersaline wastewater biomass. What they found was the biomass manufactured more total EPS in the hyper saline environments where the EPS help protect against osmotic pressures caused by high Na+ concentrations. While the hypersaline had more total EPS, it has a different composition than municipal. The diversity of compounds in the EPS was lower in the hypersaline wastewater and the EPS was not as closely associated with cell aggregation/adhesion.
Also both wastewaters had anerobic/anoxic tanks. What is interesting here is the EPS was not associated with aggregation. Apparently, DO is very important to give us the amount of aggregation needed for bioflm/floc formation.
Here is a link to the Nature article if you would like to go deeper into the research.
http://www.nature.com/articles/srep26721
RSS Feed