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Mixed Liquor Volatile Suspended Solids (MLVSS) & (MLSS)

Mixed Liquor Suspended Solids MLSS testing measures the total concentration of mixed liquor suspended (non-soluble) solids in the aeration basin of an activated sludge system. The mixed liquor suspended solids (MLSS) data is critical in determining the operational behavior and solids inventory of the system and it is used to determine when to waste and/or recycle sludge.

In order to test the mixed liquor suspended solids (MLSS) a well-mixed sample should be filtered through a weighed standard glass-fiber filter.   The residue left on the filter is dried to a constant weight at a temperature between 103 °C and 105 °C. The increase in weight of the filter represents the total suspended solids of the sample. Large floating particles or submerged agglomerates of nonhomogenous materials from the sample may be excluded in the total suspended solids measurements if it is determined that their inclusion is not representative of the entire sample. The size of sampling should also be limited to a size the yields no more than 200 mg residue.

High mixed liquor suspended solids (MLSS) values in effluents are often related to excessive solids generation due to an increase in BOD (Biochemical Oxygen Demand) loading or can indicate problems with the biomass like nutrient deficiency or bulking sludge. High MLSS values can also be attributed to high flows or insufficient settling times.

After the mixed liquor suspended solids value is determined a mixed liquor volatile suspended solids (MLVSS) test may be performed in order to determine the concentration of volatile suspended solids in the aeration basin of an activated sludge system. Mixed liquor volatile suspended solids data is critical in determining the operational behavior and biological inventory of the system. The filter used for mixed liquor suspended solids (MLSS) testing is ignited at 550 °C for 30 minutes. The weight lost on ignition of the solids represents the volatile solids in the sample.

Please contact Environmental Business Specialists at 985-674-0660 for complete procedures.