Total Suspended Solids (TSS)

 

Introduction
                The laboratory exercises you have performed up until this point have been primarily concerned with water treatment.  This lab, and the rest of the labs in this course, are primarily used for testing wastewater and should be carried out in a wastewater treatment plant. 
                The primary purpose of wastewater treatment is to remove solids from water, so this lab will be concerned with testing for one of the types of solids found in water.  There are a variety of terms referring to solids in wastewater, each of which is defined below:

 

This lab focuses on the total suspended solids, which includes both settleable and nonsettleable solids.  Total suspended solids should be tested at least five times per week using 24-hour, flow-proportioned composite samples.  The test should be performed on both raw water (to determine the solids content of water entering the plant) and on finished water (to determine the efficiency of treatment at the plant.)

Equipment                

  • Dessicator
  • Drying oven, for operation at 103 to 105°C
  • Analytical balance, capable of weighing to 0.1 mg
  • Magnetic stirrer with TFE stirring bar
  • Wide-bore pipets
  • Graduated cylinder
  • Low-form beaker
  • Glass-fiber filter disks with organic binder
  • Filtration apparatus, which can be any one of the following:
    • Membrane filter funnel
    • Gooch crucible, 25 mL to 40 mL capacity, with Gooch crucible adapter
    • Filtration apparatus with reservoir and coarse fritted disk (40 to 60 um) as filter support
  • Filter flasks, of sufficient capacity for sample size selected
  • Vacuum pump
  • Tubing
  • Stop watch
  • Aluminum weighing dishes

Reagents




 

Laboratory Procedure




1. Prepare the glass-fiber filter disks (unless they are pre-prepared.)

      Insert the filter disk with wrinkled side up in filtration apparatus.  Apply vacuum and wash the disk with three successive 20 mL portions of reagent-grade water.  Continue suction to remove all traces of water, turn vacuum off, and discard washings. 
      Remove the filter from the filtration apparatus and transfer to an inert aluminum weighing dish.  If a Gooch crucible is used, remove the crucible and filter combination.  Dry in an oven at 103 to 105°C for 1 hour. 
      Cool the filter in a desiccator to balance the temperature.  Then weigh the filter and record the weight. 
      Repeat the above cycle of drying, cooling, desiccating, and weighing until a constant weight is obtained or until weight change is less than 4% of the previous weighing or 0.5 mg, whichever is less. 
      Store the filter in the desiccator until it is needed.  You will need to prepare a filter disk for each sample you plan to test. 

    2. Select the filter and sample sizes.

      Choose a sample volume which will yield between 2.5 and 200 mg of dried residue.  If the volume filtered fails to meet the minimum yield, you will have to increase the sample size up to 1 L.  If the complete filtration takes more than 10 minutes, you will have to increase the filter diameter or decrease the sample volume. 

    3. Analyze the sample.

Filtration setup

Assemble the filtering apparatus, as shown above, and begin suction.  Wet the filter with a small volume of reagent-grade water to seat it. 
      Stir the sample with a magnetic stirrer at a speed to shear larger particles, if practical, to obtain a more uniform particle size. 
      While stirring, pipet a measured volume onto the seated glass-fiber filter.  For homogeneous samples, pipet from the approximate midpoint of the container but not in the vortex.  Choose a point both middepth and midway between the wall and the vortex. 
      Use the stopwatch to measure the amount of time it takes for the sample water to flow through the filter.  Remember that filtration should take no more than 10 minutes.  If filtration takes too long, choose a smaller sample size or a larger filter and repeat the procedure.  Record the filtration time. 
      Wash the filter with three successive 10 mL volumes of reagent-grade water, allowing complete drainage between washings.  (This washes down solids which may have stuck to the glass on the upper filter holder and removes dissolved solids from the suspended solids captured by the filter.  Samples with high dissolved solids may require additional washings.)  Continue suction for about 3 minutes after filtration is complete. 
      Carefully remove the filter from the filtration apparatus and transfer it to an aluminum weighing dish as a support.  Or remove the crucible and filter combination from the crucible adapter if a Gooch crucible is used. 
      Dry the filter for at least 1 hour at 103 to 105°C in an oven, cool in a dessicator to balance the temperature, and weigh.  Repeat the cycle of drying, cooling, desiccating, and weighing until a constant weight is obtained or until the weight change is less than 4% of the previous weight or 0.5 mg, whichever is less. 
      At least 10% of all samples should be analyzed in duplicate.  Duplicate determinations should agree within 5% of their average weight.

    4. Calculate the concentration of total suspended solids in the sample using the following formula:

        Where:

A = Sample and filter weight, mg          

B = Filter weight, mg

    5. If two samples were measured, then the average total suspended solids can be calculated as follows:

Equation used to calculate average total suspended solids

Where:

C = Total suspended solids of sample 1, mg/L         D = Total suspended solids of sample 2, mg/L

    6. Calculate the total suspended solids in kilograms per day (KGD) at the plant, as follows:

TSS (KGD) = (Average total suspended solids, mg/L) ×(Flow, MGD) × 3.785

Data                 

Filter  and sample preparation

Weight - Trial 1 Weight - Trial 2 Weight - Trial 3 Final Weight
Filter
Sample 1
Sample 2

Total suspended solids

Sample Sample Source Filter weight (mg) Sample volume (mL) Filtration time (min) Sample and filter weight (mg) Total suspended solids (mg/L)
1
2
Average ---- ---- ---- ---- ----

 

Total suspended solids (KGD) = _____________________________________________




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

Mixed Liquor Volatile Suspended Solids

 

Introduction
               Mixed liquor is a combination of sludge and water removed from the clarifier in the wastewater treatment process and reintroduced into an earlier phase of the treatment process.  The mixed liquor contains microorganisms which digest the wastes in the raw water.  This lab will show you how to test for MLSS and MLVSS in the mixed liquor. 
Mixed Liquor Suspended Solids (MLSS) is a test for the total suspended solids in a sample of mixed liquor.  This test is essentially the same as the test you performed for TSS in the last lab, except for the use of mixed liquor as the water sample.  In addition, the concentration of suspended solids found in the mixed liquor is typically much greater than that found in the raw or treated water.  MLSS concentrations are often greater than 1,000 mg/L, but should not exceed 4,000 mg/L.
MLVSS, or Mixed Liquor Volatile Suspended Solids, is a test for the amount of volatile suspended solids found in a sample of mixed liquor.  Volatile solids are those solids which are burnt up when a sample is heated to 550°C.  Most of the volatile solids in a sample of mixed liquor will consist of microorganisms and organic matter.  As a result, the volatile solids concentration of mixed liquor is approximately equal to the amount of microorganisms in the water and can be used to determine whether there are enough microorganisms present to digest the sludge.
               In a wastewater treatment plant, operators should test for MLSS three times per week and for MLVSS once per week.  Both tests should use grab samples taken from the same location in the treatment plant.   

Equipment

Reagents




 

Laboratory Procedure




1. Collect a grab sample of mixed liquor. 
     2. Measure the total suspended solids in your sample using the procedure outlined in Lab 11.  You will probably need to use a smaller sample volume, such as 5 mL.  Record the sample volume and the combined sample and filter weight in the Data section.  At least 10% of all samples should be analyzed in duplicate. 
     3. Ignite the filter and the total suspended solids residue from step 1 in a muffle furnace at 550°C.  An ignition time of 15 to 20 minutes is usually sufficient for 200 mg residue.  However, when igniting more than one sample or when igniting heavier samples, the ignition time may need to be increased. 
     4. Let the filter cool partially in the air until most of the heat has dissipated.  Then transfer the filter to a dessicator to cool the rest of the way to air temperature. 
     5. Weigh the filter and record the weight in the Data section. 
     6. Repeat the cycle of igniting, cooling, desiccating, and weighing until a constant weight is obtained or until the weight change is less than 4% or 0.5 mg, whichever is less. 
     7. Calculate the volatile solids in the sample, as follows:

Formula for calculating volatile solids

Where:

A = Sample and filter weight from TSS test, mg            B = Sample and filter weight after ignition in muffle furnace, mg

8. If you have tested two samples, you can calculate the average volatile solids as follows:
                  

Formula for calculating average volatile solids  

Where:

                     C = Volatile solids of sample 1, mg/L                      D = Volatile solids of sample 2, mg/L


                Data

Sample Sample volume (mL) Sample and filter weight from TSS test (mg) Sample and filter weight after ignition in muffle furnace (mg) Volatile Solids (mg/L)
1
2
Average --- ---

---




For the volatile solids analysis, see EPA Method