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Monitoring TSS (Total Suspended Solids) in effluent discharge

  • Writer: Jo Wouters
    Jo Wouters
  • May 20
  • 3 min read

Real-time effluent TSS monitoring is becoming the new gold standard in Wastewater Treatment

Online monitoring is finding its way in wastewater treatment plants since decades: conductivity, dissolved oxyged, activated sludge concentration,…: the majority of operational parameters of a WWTP is monitored online and complemented by sporadic lab sample analysis. However, looking at WWTP effluent, we often see that only turbidity (in NTU) is measured by using optical probes.


Total Suspended Solids (TSS) is still the single most-cited parameter in discharge permits, yet most facilities are actually monitoring with optical turbidity sensors.  These sensors actually measure turbidity (not TSS!), and are prone to fouling and drift.

In 2025, that's no longer acceptable to regulators or customers.


At Olpas it is our mission to make low maintenance drift-resistant water monitoring accessible, even for challenging circumstances. Online, continuous TSS monitoring can be implemented easily and readily in your system in a cost-effective way.


1. Discharge violations can happen in minutes


Permit limits are often written in flow-averaged concentrations ( mg L⁻¹), but discharge violations can happen in minutes. Storm inflow, chemical overfeed, or a clarifier upset can double effluent TSS in less than ten minutes, and damage is done, long before effluent samples are analyzed. Furthermore, drift of optical turbidity sensor can mask the effect of TSS increase, allowing such events to go undetected.

Drift of optical turbidity sensor can mask the effect of TSS increase, allowing such events to go undetected

For example, take a look at the following graph of effluent TSS concentration in a traditional WWTP:

Real-time TSS monitoring in an effluent stream (mg/L)
Real-time TSS monitoring in an effluent stream (mg/L)

TSS concentrations tend to evolve quickly with flowrate and WWTP loading.


2. Real data = Real savings


High-frequency TSS curves reveal patterns hidden between grab samples: short overnight solids surges, diurnal sludge blanket swings, or the exact point where polymer dose stops helping. Plants that add online TSS control routinely report:

  • 5–15 % lower chemical spend (no more “insurance” overdosing).

  • Reduced energy as aeration and RAS flows are tuned to actual solids loading.

  • Fewer sludge-handling headaches because solids peaks are shaved, not swallowed whole by the dewatering step.


Effluent discharge streams often feature a lot of biofouling (alga, moss, …) indicating the need for fouling resistant TSS probes to reduce maintenance efforts
Effluent discharge streams often feature a lot of biofouling (alga, moss, …) indicating the need for fouling resistant TSS probes to reduce maintenance efforts

3. Future-Proofing against tighter limits


European directives and many U.S. states are already discussing single-event or 95th-percentile TSS caps - rules that treat concealed spikes the same as chronic failure.

Plants equipped with sub-hourly monitoring are ready; those relying on single daily samples will need expensive redundancy or risk fines. Online TSS sensors are essentially an insurance policy against the coming regulatory squeeze.

Plants relying on single daily samples will need expensive redundancy or risk fines

It’s easier than you think with Olpas TSS sensors

Olpas TSS sensors for submerged or inline use are highly sensitive to Total Suspended Solids concentration in a wide range of particle sizes (below µm to above millimeter scale!) and concentrations (0-2000 mg/L). Olpas uses ultrasound backscattering to detect particles in suspension. A resolution of 1 mg/L allows to monitor discharged TSS accurately. Olpas sensors measure a new value every second, allowing for precise time-resolution in discharge peaks of effluent TSS. The measurements are flowrate, turbidity and temperature agnostic.


The ultrasound window of the Olpas TSS sensor is fouling-resistant: the ultrasound waves pass through fouling layers up to 2mm.
The ultrasound window of the Olpas TSS sensor is fouling-resistant: the ultrasound waves pass through fouling layers up to 2mm.


Bottom Line

Fouling resistant TSS probes are the new standard for effluent monitoring. Continuous TSS monitoring delivers instant validation of compliance with your local TSS discharge limits. It allows polymer dosing to be active only when really required, minimizing polymer consumption significantly. Futhermore, optical parameters and (biofouling) do no affect the measurement, making sure the memasurement is reliable even with a minimal operational maintenance cost.

Olpas offers submerged and inline TSS sensors specifically suited for effluent discharge monitoring:

  • 0-2000 mg/L range

  • Particle size agnostic

  • Turbidity independent

  • Fouling-resistant

  • 1 mg/L resolution from 0-100mg/L

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