Low solids measurement system for wastewater plants

Valmet Low Solids Measurement (Valmet LS) provides great savings in costs to wastewater treatment plants, by optimising their polymer dosage and minimizing the solids content in the reject water.


Valmet LS is the first and only meter which can measure centrate suspended solids reliably and is used specifically with the sludge dewatering machines. Operators can easily select the right type of polymer while continuously following its quality. Valmet LS device can be connected online to the process and it is possible to measure continuous sample flow through the system by utilising an integrated centrifugal pump. The system has two light sources LED and Laser. When the sample passes through the measurement cell, the absorption, scattering, and depolarisation signals from both light sources are measured.

Valmet LS continuously measures both the entrained air index, which indicates overdosing of polymer and the suspended solids content within the range of zero to 5,000 mg/l. If bigger, please contact Valmet personnel. The Valmet LS measurement system deaerates, filters and measures the process solids along with possessing self-cleaning capabilities to keep the measurement optics clean. The measurement cell has extremely strong sapphire glass with high optical properties. The cell and sample lines are automatically cleaned at given intervals.



VALMET LS Royce Water Technologies-MEASUREMENT

With online monitoring:

  • Process changes and errors are noticed quickly.
  • The cause of and the solution to the error is found quickly.
  • The system provides immediate online responses to all chemical and equipment test runs.
  • The system provides more and continuous process information with less laboratory work.

In this example, automatic control has been implemented in the mill’s automation system. In the figure below, the control was set to auto mode at one hour. The control system aims to continuously decrease polymer dosage (black graph) but in a way that keeps the suspended solids (blue graph) at the set level. This results in optimal/minimal polymer dosage. As can be seen from the graph, the control system decreases polymer dosage from the normal manual dosage level to an optimized and automatically controlled amount/ minimum amount. At the 4 hour point, the maximum polymer dosage was lowered. This example and the graphs below show that Valmet LS measurements allow for automatic and accurate polymer control.

Suspended solids measurement and control of polymer

  • Facilitates centrifuge optimization and provides improved performance.
  • Better control over recycling materials: a high solids rate in the reject water causes the excess centrate solids to be needlessly and potentially harmfully treated and centrifuged several times.
  • Facilitates polymer dosage.
  • Decreases costs resulting from polymer dosage and centrifuge usage.

Depending on process capacity, the return of investment can be as short as one year. The resulting savings are based on avoiding polymer overdosing and reducing the solids recycling back into the process. Based on our experience, the savings resulting from decreased polymer costs can be as high as 30 %. Please contact Valmet to discuss savings possibilities in your process.


  • Polymer savings
  • Process optimization
  • Improved throughput
  • Improved centrifuge functionality
  • Dryer output solids from the centrifuge:
  • Lower transit costs when shipping to landfill
    • Facilitates material burning
    • Reduced laboratory/sampling work
  • Faster polymer test runs
  • Polymer type optimisation


  • Local operation unit TCU (Transmitter Central Unit)
  • Valmet FieldCare PC connection for configuration and calibration
  • Analog outputs to DCS (2 pcs.)
  • Binary inputs from DCS (2 pcs.)


  • Reject water suspended solids measurement of the sludge dewatering unit.



  • The sampling pump that provides stable, continuous and representative sampling in all production situations
  • An automatic cleaning feature that cleans the measurement cell and sample line automatically with water at configurable intervals
  • Advanced self-diagnostics that use clean flush water to calibrate the light sources of the measurement cell, which prevents measurement drift
  • An automatic screening system that screens the sample from the debris (plastics, strings, etc. ) and automatically cleans the screens when the device is flushed
  • A deaeration module that stabilizes and deaerates sample before it goes through the measurement cell
  • An automatic chemical cleaning feature that doses diluted cleaning chemical at configurable intervals independent of normal cleaning/flushing. This minimizes the use of the cleaning chemical
  • The system utilizes two light sources. When the sample passes through the measurement cell, the absorption, scattering and depolarization signals from both of the light sources are measured. (This is critical for accurate TSS)
  • The self-diagnostics automatically monitor the optics and alert operators if the measurement cell becomes too dirty for accurate measurement
  • The sapphire lenses used in the measurement cell provide accurate measurements in dirty and high wear conditions and have optimum optical properties
  • Easy calibration and low maintenance
  • Extremely high measurement accuracy
  • Excellent usability


  • Optimisation of the capacity of the wastewater plant
  • Polymer savings
  • Optimisation of the dewatering machine
  • Reduced laboratory/sampling work
  • Faster polymer test runs and selection