Download Wastewater Microbiology Process Control

Slime, Slime, Slime!
Toni Glymph
Environmental Toxicologist
Wisconsin DNR
Slime Bulking
• There is a condition in wastewater treatment
often called slime bulking.
• Occurs when bacteria “over-produce” the
lipopolysaccharide normally found outside
the bacteria cell wall.
• Found most often in industrial wastewater
treatment systems, but may also occur in
municipal systems.
Slime Bulking
• What makes the bacteria “over-produce”
lipopolysaccharide?
– Lack of sufficient nutrients (mostly nitrogen)
– Excess organic acids
Slime Bulking
Gram (+)
Polysaccharide
“Slime Layer”
Gram (-)
Lipopolysaccharide
“Slime Layer”
Phospholipid
Lipoprotein
Cell Wall
Cell Wall
Cell Membrane
Cell Membrane
Slime Bulking
• 3 main elements are required in the
development of the cell wall components.
• They make up 18% of the dry weight of the
cell components.
– Nitrogen (15%)
– Phosphorus (2%)
– Sulfur (1%)
Slime Bulking
•Nitrogen is required to
makeup the lipoprotein
layer
•Phosphorus is required
to make up the
phospholipid layer.
Gram (-)
Lipopolysaccharide
“Slime Layer”
Phospholipid
Lipoprotein
Cell Wall
Cell Membrane
Slime Bulking
•When Phosphorus is
deficient, a small amount
of extra lipids (fat) is
added to the slime layer.
Gram (-)
Lipopolysaccharide
“Slime Layer”
Lipid
Lipoprotein
Cell Wall
Cell Membrane
Slime Bulking
•When Nitrogen is
deficient a larger amount
of “fat” is added to the
slime layer..
Gram (-)
Lipopolysaccharide
“Slime Layer”
Lipid
Lipid
Cell Wall
Cell Membrane
Slime Bulking
• When slime bulking occurs, nitrogen and
phosphorus are the nutrients that are usually
deficient.
• Slime bulking is more severe when nitrogen
is deficient.
• Nutrient ratio 100:10:1 (BOD:N:P)
Slime Bulking
• Excess Organic Acids
– A ready food source that does not contain
nitrogen
– Usually added through sludge processing
recycle streams (anaerobic digester supernatant)
• Any other anaerobic process side stream
Slime Bulking
• India Ink stain
– When India ink is added to a drop of mixed
liquor the carbon black particles penetrate the
floc from outside to inside
– The lipopolysaccharide prevents the India ink
from penetrating the floc particle.
Slime Bulking
India Ink Stain
Slime Bulking
India Ink Stain
Slime Bulking
Case Study
• Industry
–
–
–
–
–
2 SBRs
excessive filamentous bacteria
severe nutrient deficiency (nitrogen)
severe bulking problems
discharging 60% of the flow to WWTP
Slime Bulking
Case Study
• WWTP
– very few filamentous bacteria
– severe bulking problems
– having difficulty dewatering sludge
Slime Bulking
(Industry Tank #1)
Slime Bulking
(Industry Tank #2)
Slime Bulking
(WWTP Mixed Liquor)
Slime Bulking
(WWTP Digester Supernatant)
Slime Bulking
Case Study - Conclusions
• Due to poor operations and severe nitrogen
deficiency, excess lipopolysaccharides were
being produced in the SBR tanks.
• This slime was being discharged into the
WWTP and accumulated over time.
• Present in the aeration basin, clarifiers and
digesters.
Slime Bulking
• Operational Considerations
– The solution involves adding the deficient
nutrient
– Ammonia to provide nitrogen
– Phosphoric acid to provide phosphorus
Slime Bulking
• Operational Considerations
– There is no nutrient deficiency if, in a filtered
(.045 um) effluent sample:
• ammonia + nitrate is > 1 mg/L and,
• soluble orthophosphate is > 0.5 mg/L
Slime Bulking
• The excess lipopolysaccharide can only be
wasted out of the system.
• You have to stop the bacteria from
producing the excess amounts.
– Making sure sufficient nutrients are available
– Adding anaerobic recycle streams slowly
and/or add more organisms (increase return)
when excessive amount of organic acids are
present.