Norweco Note:

The term MLVSS is usually limited to mixed liquor sampled and analyzed for total suspended solids and used as a control for treatment plants using a suspended growth process. While the test method for MLVSS is identical to the test method for VSS, particular attention must be paid to Section 2540D.3b.


2540 SOLIDS*

* Approved by Standard Methods Committee, 1997.


2540 E. Fixed and Volatile Solids Ignited at 550C


1. General Discussion


    a. Principle: The residue from Method B, C, or D is ignited to constant weight at 550C. The remaining solids represent the fixed total, dissolved, or suspended solids while the weight lost on ignition is the volatile solids. The determination is useful in control of wastewater treatment plant operation because it offers a rough approximation of the amount of organic matter present in the solid fraction of wastewater, activated sludge, and industrial wastes.

    b. Interferences: Negative errors in the volatile solids may be produced by loss of volatile matter during drying. Determination of low concentrations of volatile solids in the presence of high fixed solids concentrations may be subject to considerable error. In such cases, measure for suspect volatile components by another test, for example, total organic carbon (Section 5310). Highly alkaline residues may react with silica in sample or silica-containing crucibles.


2. Apparatus


    See Sections 2540B.2, 2540C.2, and 2540D.2.


3. Procedure


    Ignite residue produced by Method 2540B, C, or D to constant weight in a muffle furnace at a temperature of 550C. Ignite a blank glass fiber filter along with samples. Have furnace up to temperature before inserting sample. Usually, 15 to 20 min ignition are required for 200 mg residue. However, more than one sample and/or heavier residues may overtax the furnace and necessitate longer ignition times. Let dish or filter disk cool partially in air until most of the heat has been dissipated. Transfer to a desiccator for final cooling in a dry atmosphere. Do not overload desiccator. Weigh dish or disk as soon as it has cooled to balance temperature. Repeat cycle of igniting, cooling, desiccating, and weighing until a constant weight is obtained or until weight change is less than 4% or 0.5 mg, whichever is less. Analyze at least 10% of all samples in duplicate. Duplicate determinations should agree within 5% of their average weight. Weight loss of the blank filter is an indication of unsuitability of a particular brand or type of filter for this analysis.


4. Calculation


                                                    (A B) X 1000

                mg volatile solids/L =                                    

                                                    sample volume, mL



                                                    (B C) X 1000

                mg fixed solids/L =                                      

                                                    sample volume, mL




    A = weight of residue + dish before ignition, mg,

    B = weight of residue + dish or filter after ignition, mg, and

    C = weight of dish or filter, mg.


5. Precision


    The standard deviation was 11 mg/L at 170 mg/L volatile total solids in studies by three laboratories on four samples and 10 replicates. Bias data on actual samples cannot be obtained.





Standard Methods for the Examination of Water and Wastewater. 20th Ed. American Public Health Association, American Water Works Association, Water Environment Federation.