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Wastewater & effluent · Wastewater / effluent (grab or composite sample)

Total Suspended Solids (TSS) Dried at 103–105 °C

A well-mixed sample is filtered through a weighed glass fibre filter. The filter and the solids retained on it are dried at 103–105 °C and weighed again. The increase in mass per litre of sample is the total suspended solids.

  • Environmental & water
  • Filtration through a glass fibre filter and gravimetry
  • Filtration unit
  • Hot air oven
  • Analytical balance

Reference: Typical method based on APHA Standard Methods 2540 D, IS 3025 (Part 17) and ISO 11923.

PRINCIPLE

Why this method works

Solids that cannot pass through a glass fibre filter with a nominal pore size of about 1.5 µm are, by definition, suspended solids. Drying at 103–105 °C removes water but leaves the solids (and some bound water). The mass gain is divided by the volume filtered.

Instruments used

MATERIALS

Reagents & standards

ReagentGrade / specification
Glass fibre filtersWithout organic binder, 47 mm or 55 mm diameter, nominal retention about 1.5 µm
Purified waterFor washing the filter and the filtered residue
SAMPLE PREPARATION

Preparing the sample

  1. 01

    Prepare filter

    Wash, dry at 103–105 °C, cool in a desiccator and weigh (B).

  2. 02

    Mix sample

    Stir the sample so solids are evenly suspended.

  3. 03

    Filter

    Filter a measured volume under vacuum.

  4. 04

    Wash

    Rinse with three portions of purified water.

  5. 05

    Dry

    Dry the filter at 103–105 °C for at least 1 hour.

  6. 06

    Weigh

    Cool in a desiccator and weigh (A); repeat to constant mass.

Procedure

  1. 1Place a filter in the filtration apparatus, apply vacuum and wash it with three 20 mL portions of purified water. Dry at 103–105 °C for 1 hour, cool in a desiccator and weigh. Repeat until the mass is constant; record it as B.
  2. 2Choose a sample volume that gives about 2.5 to 200 mg of dried residue. For example, 100 mL for a typical treated effluent or 25 mL for raw sewage.
  3. 3Mix the sample well with a magnetic stirrer and, while stirring, withdraw the volume with a wide-bore pipette or measuring cylinder.
  4. 4Filter under vacuum. Rinse the measuring vessel and the filter funnel walls with purified water, then wash the residue with three 10 mL portions, letting each drain fully.
  5. 5Continue suction for about 3 minutes after filtration ends.
  6. 6Transfer the filter to a support dish and dry at 103–105 °C for at least 1 hour.
  7. 7Cool in a desiccator to room temperature and weigh. Repeat drying, cooling and weighing until the change is less than 4% of the previous mass or 0.5 mg, whichever is less. Record the final mass as A.

Standard preparation

  1. 1No calibration standard is used. Run a filter blank (purified water through a weighed filter) with each batch to check for filter mass loss.
  2. 2Laboratories may use a suspension of a known material (for example microcrystalline cellulose) as a check sample.

Notes for analysts

  • Exclude large floating particles or lumps that are not part of the representative sample, and note this in the report.
  • If the filter clogs, filtration takes too long and dissolved solids can be retained; use a smaller volume.
  • Igniting the dried residue at 550 °C gives volatile suspended solids (VSS), often reported for aeration tanks.
TEST CONDITIONS

Method parameters (typical)

FilterGlass fibre, nominal 1.5 µm, no binder
Drying temperature103–105 °C
Drying timeAt least 1 hour, then to constant mass
Target residueAbout 2.5–200 mg
BalanceAnalytical balance, readability 0.1 mg
BEFORE YOU REPORT

System suitability & sequence

ParameterLimit
Filter blankMass change typically within ±0.5 mg
Duplicate agreementAs defined in your SOP (for example RPD not more than 10–20% depending on level)
Constant massChange between weighings less than 4% or 0.5 mg, whichever is less

Typical sequence

  1. 1Filter blank
  2. 2Samples
  3. 3Duplicate of one sample per batch
CALCULATION

Calculation with a worked example

Formula
TSS (mg/L) = (A − B) × 1000 ÷ V

Where

A
Mass of filter + dried residue (mg)
B
Mass of prepared filter (mg)
V
Volume of sample filtered (mL)
1000
Converts mL to L

Given

A
118.76 mg
B
105.32 mg
V
100 mL

Working

  1. 1

    Residue = 118.76 − 105.32 = 13.44 mg (within the 2.5–200 mg target)

  2. 2
    TSS = 13.44 × 1000 ÷ 100 = 134.4 mg/L

TSS = 134 mg/L

ACCEPTANCE CRITERIA

What result passes

  • Compare with your consent limit. For example, the general standards for discharge into inland surface water in India typically set TSS at 100 mg/L; check the current notification.
  • Results based on residues below about 2.5 mg have high uncertainty; filter a larger volume where possible.
METHOD VALIDATION

Validation parameters (ICH Q2(R2))

ParameterTypical requirement
PrecisionDuplicate samples and control-charted check samples
RangePractical lower limit set by residue mass and volume filtered
InterferencesLarge floating particles, oil and grease, very saline samples (wash well), and filter clogging
In LimsPulse · Sample Management

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