Non-filamentous bulking or excess extracellular polymeric substances (EPS). How do you know if you have excess EPS?
- Use India Ink with microscopic exam. Excess EPS appears as clear zones.
- Even without India Ink, high EPS colonies can be identified by rounded, fingers with cells suspended in gelatinous matrix.
- Waste solids have increased bound water, higher polymer demand, difficulty in dewatering
- Secondary clarifiers may have increased floating scum, beds that tend to billow and not compact was well as normal.
EPS is very important for floc formation in suspended growth and for biofilms in attached growth wastewater treatment plants. Wastewater plants were designed to operate in decline phase growth where microbial division slows and cells begin to form aggregates. Key to aggregate formation is the production of EPS. Consisting of polysaccharides, proteins, nucleic acids, and a variety of metabolic byproducts; EPS functions to keep cells protected and viable under the stress of low soluble organics (food). Another function of EPS is the accumulation/storage of nutrients including N, P, and metals. Under normal operations, the proper amousnt of EPS is needed for solids removal and helps remove phosphates in biological nutrient removal systems. The problems happen when the biomass generates excess EPS.
Main organisms responsible for non-filamentous bulking
Using Microbial Community Analysis (total MLSS microbial census) technology, we have identified the major contributors to non-filamentous bulking as:
- Thauera – usually the most common organisms in industrial activated sludge and lagoons in decline phase growth
- Zooglea – more common in domestic wastewater
- Azoarucs – a third genera in the Zooglea family. Less common than Thauera or Zooglea
- High influent soluble organics such as organic acids. Excess soluble BOD is stored by cells in EPS. The EPS stores the energy for future use by the cells. If you don’t have sufficiently low F/M or time for metabolism of stored organics, the EPS accumulates and eventually will produce bulking.
- If you have excess soluble organics with insufficient N, P, or some other vital micronutrient. In this case, the cells store carbon in the EPS as they do not have enough of some key nutrient(s) to divide, produce enzymes, and support full cell metabolic activity.
- Turn up nutrients - if nutrients (N or P) were not a problem, adding in excess will not help
- Wasting - removes EPS and stored carbon with WAS. But also increases the F/M ratio which is not needed!
- Usually add bacteria via bioaugmentation or bringing in non-bulking sludge -> this helps reduce F/M. Both increase numbers of viable microorganisms in the MLSS.
New monitoring & control strategies
- Monitor for system specific Zooglea Forms (qPCR)
- Populations often increase into critical zone before bulking develops
- qPCR detects changes much earlier than microscopic exam & India Ink tests
- Look for signs of increased soluble BOD loadings at influent. Evaluate methods to keep F/M in target range and increase cellular metabolism (sufficient D.O., C:N:P ratios, utilize EQ capacity, improve pre-treatment if possible).