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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
Polysaccharide“Slime Layer”
Lipopolysaccharide“Slime Layer”
Cell Membrane
Cell Membrane
Gram (+) Gram (-)
Cell Wall
Cell Wall
Lipoprotein
Phospholipid
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
Lipopolysaccharide“Slime Layer”
Cell Membrane
Gram (-)
Cell Wall
Lipoprotein
Phospholipid
•Nitrogen is required to makeup the lipoprotein layer
•Phosphorus is required to make up the phospholipid layer.
Slime Bulking
Lipopolysaccharide“Slime Layer”
Cell Membrane
Gram (-)
Cell Wall
Lipoprotein
Lipid
•When Phosphorus is deficient, a small amount of extra lipids (fat) is added to the slime layer.
Slime Bulking
Lipopolysaccharide“Slime Layer”
Cell Membrane
Gram (-)
Cell Wall
Lipid
Lipid
•When Nitrogen is deficient a larger amount of “fat” is added to the slime layer..
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 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 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.