Toni Glymph

Environmental Toxicologist

Wisconsin DNR

Slime, Slime, Slime!

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 India Ink Stain

Slime BulkingIndia 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.