Glossary term

Total Suspended Solids

Mass concentration of suspended particulate matter in water or wastewater, used to assess effluent quality, stormwater load, clarifier performance and treatment compliance.

Branch: Environmental Engineering
Glossary type: metric
Content: Glossary term
Updated: Jun 25, 2026
Revision: v1.0.0 · reviewed

Definition

metric

Total suspended solids is the mass concentration of particulate matter retained by a specified filter or separation method from a water or wastewater sample.

Total suspended solids, commonly abbreviated TSS, is used in wastewater treatment, stormwater management, mine-water discharge, industrial effluent and receiving-water assessment. It represents suspended particulate matter on a method basis, not all solids in the water. Engineering interpretation depends on sample location, filtration method, particle size, settling behaviour, turbidity relation, flow, event timing, solids carryover, treatment boundary and compliance objective.

Total suspended solids is the mass concentration of particulate matter retained from a water or wastewater sample by a specified laboratory method. It is commonly abbreviated TSS and usually reported in $\text{mg/L}$ .

TSS matters because suspended particles affect effluent clarity, receiving-water habitat, pollutant transport, sedimentation, stormwater treatment, mine-water discharge and wastewater process stability. In activated-sludge plants, high effluent TSS can also mean biomass loss from secondary clarification.

Measurement Basis

At a reporting level, TSS is a concentration:

TSS=C_{TSS}

with units:

\text{mg/L}

The method basis matters. Filter type, pore size, drying temperature, sample mixing, holding time and particle settling can change the reported result. TSS is not the same as turbidity, total dissolved solids or mixed-liquor suspended solids.

Concentration to Load

For dilute water-quality calculations, TSS load is:

L_{TSS}=QC_{TSS}(0.001)

where $Q$ is flow in $\text{m}^3/\text{day}$ , $C_{TSS}$ is concentration in $\text{mg/L}$ and $L_{TSS}$ is $\text{kg/day}$ .

For:

Q=16000\ \text{m}^3/\text{day},\quad C_{TSS}=28\ \text{mg/L}

the effluent load is:

L_{TSS}=16000(28)(0.001)=448\ \text{kg/day}

This can be more meaningful than concentration alone when wet-weather flow changes the mass discharged.

Overflow Mass Example

For a sanitary-sewer overflow volume:

V=510\ \text{m}^3

with overflow TSS:

C_{TSS}=180\ \text{mg/L}

the released suspended-solids mass is:

M_{TSS}=VC_{TSS}(0.001)=510(180)(0.001)=91.8\ \text{kg}

Event mass is useful for receiving-water impact, cleanup triage and comparison of source-control options.

Stormwater and Mine-Water Use

For a stormwater detention retrofit with runoff volume:

V_{runoff}=14454\ \text{m}^3

and event mean TSS:

C_{TSS}=90\ \text{mg/L}

the event load is:

M_{TSS}=14454(90)(0.001)=1301\ \text{kg}

For mine-water discharge, a stream at $650\ \text{mg/L}$ TSS may need settling, flocculation, staged pumping or filtration before release. The controlling constraint can be treatment capacity rather than pump capacity.

Removal Check

If mine-water TSS is reduced from:

650\ \text{mg/L}

to:

50\ \text{mg/L}

the concentration removal is:

\displaystyle \eta_{TSS}=\frac{650-50}{650}=0.923

or about $92\%$ . This percentage should be checked with flow, solids particle size, rainfall condition, treatment bypasses and discharge hold points.

Relation to Clarifier Metrics

TSS is an output or stream-quality metric. Mixed-liquor suspended solids, solids loading rate, sludge volume index and surface overflow rate are process or unit-operation metrics that help explain why TSS rises or falls.

For example, high effluent TSS during a wet-weather event may reflect high surface overflow rate, high solids loading, poor settleability, rising blanket depth, return-sludge problems or short-circuiting. The TSS result identifies the symptom; clarifier and process metrics explain the mechanism.

Validation Evidence

Useful TSS evidence includes sample location, total or filtered basis, method, filter and drying basis, preservation, holding time, mixing procedure, replicate results, turbidity, flow, rainfall or event timing, bypass state, treatment units online, clarifier blanket depth, MLSS, SVI, chemical dose, mine sump condition, stormwater sediment storage and laboratory QA/QC.

Validation should connect TSS to the decision: effluent compliance, overflow impact, stormwater retrofit performance, mine-water discharge release, clarifier recovery, process washout, sediment-control maintenance or receiving-water assessment.

Limits and Common Mistakes

TSS is not a universal particle-size distribution. A low TSS result can still hide dissolved pollutants, fine colloids or toxic dissolved species. A high turbidity value may correlate with TSS on one site and fail on another because particle size, color and mineralogy differ.

Common mistakes include using turbidity as TSS without a site correlation, calculating concentration compliance without flow, comparing grab samples from different event phases, treating MLSS as effluent TSS, ignoring solids settled before sampling, and accepting clarifier recovery without effluent TSS and blanket-depth evidence. A strong TSS review states method basis, sample location, concentration, flow/load basis, particle or settling context and validation evidence.

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