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 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 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 - 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.