Total Suspended Solids
The volume of sample to be filtered depends upon the amount of suspended matter in the sample. In general, only about 50 – 100 mL of raw influent can be filtered; while filtering 1000 mL of clean effluent is common. High solids content samples like mixed liquor from an activated sludge plant may only allow filtration of 10 – 20 mL. Samples should be carefully measured in clean graduated cylinders or using clean wide-tipped pipettes. Choose sample volumes that yield between 10 and 200 mg dried residue. If more than 10 minutes are required to complete filtration, use less sample volume or use a larger diameter filter. When very low suspended solids wastewater is encountered, less than 10 mg of dried residue is acceptable, but compensate by using a high-sensitivity analytical balance (capable of measuring 0.002 mg) if very high accuracy is required.
To begin sample filtration, assemble the filtration apparatus, place a filter with the wrinkled side up on the apparatus and begin suction. Wet the filter with a small amount of rinse water to seat it. While stirring the sample with a magnetic stirrer or after thoroughly mixing the sample in the sample container, transfer a measured volume to the filter funnel with a pipet or graduated cylinder. After the sample has been drawn through the filter, rinse the pipet or graduated cylinder and the walls of the filter funnel down with three successive volumes of about 10 mLs of rinse water, allowing complete drainage between washings. Some samples require more thorough rinsing. Continue suction until all liquid is removed from the filter. Carefully remove the filter and residue with forceps and transfer to the planchet. Dry filter, residue and dish in an oven at 103 – 105º C for at least one hour. Cool filter, residue and dish in a desiccator and then weigh filter, residue and dish together on an analytical balance. Repeat cycle of drying and desiccating until a constant weight is obtained or until the weight change is less than 4% of the previous weighing or 0.5 mg, which ever is less. Carefully record each drying/ desiccating/ weighing on the TSS benchsheet.
Calculating TSS using the initial and final weigh of the filter, dish and residue, calculate total suspended solids as:
[(Weight of filter, dish and dried residue – Weight of filter and dish) X 1,000,000] / (Sample Volume, mL)
As is the case with all test methods, the TSS analysis’ accuracy can only be relied upon when the methodology has been closely followed. In order to check the analyst’s technique, run duplicate analysis on at least 10% of samples. Duplicate determinations should agree within 5% of their average. Externally supplied standards should be analyzed at least annually to verify the accuracy of the laboratory and analyst.