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How to tackle the challenges of TSS measurement in sewer overflows

Sewer overflows (or Combined Storm Overflows, CSO) pose significant challenges to both public health and the environment. When sewer systems become overwhelmed, untreated wastewater can be discharged into water bodies, leading to pollution and potential health hazards.


The measurement of Total Suspended Solids (TSS) plays a crucial role in understanding and managing sewer overflows. More than 30% of the waste discharge load from sewage is due to suspended solids and, subsequently, impacts water quality directly. However, accurately measuring TSS in sewage-water presents numerous challenges. At Olpas we have worked very hard on attacking these challenges in both our measurement technology (which is completely different than the technology for measuring TSS you already know) and in the design of our sensor.


An active combined sewer overflow, temporarily discharging untreated water in a river
An active combined sewer overflow, temporarily discharging untreated water in a river


The importance of TSS measurement in sewer overflows


Sewer overflows occur when the capacity of sewage systems is exceeded, leading to the release of untreated or partially treated wastewater into the environment. These overflows contain various contaminants, including suspended solids, pathogens, nutrients, and pollutants. Among these, TSS is a key parameter used to assess the level of pollution and its impact on water quality. TSS (Total Suspended Solids) refers to the solid particles suspended in water, including organic matter, sediment, and debris.


Monitoring TSS levels in sewer overflows is vital for several reasons.


First of all, TSS serves as an important indicator of overall water quality. High TSS levels can indicate the presence of pollutants and organic matter, which can degrade water quality and harm aquatic ecosystems. Discharge of sewage-water with elevated TSS concentrations can have adverse effects on aquatic life and habitats. Excessive TSS can smother aquatic organisms, reduce sunlight penetration, and disrupt the natural balance of ecosystems.


For that reason many regulatory agencies set limits on TSS concentrations in wastewater discharges to protect water quality and public health.


Sewage overflow events can have an enormous negative impact on nature.  Reliable and economic TSS measurements are key to understanding the impact of those events and to strategically manage the impact.
Sewage overflow events can have an enormous negative impact on nature.

Challenges of a reliable and economical TSS measurement in sewage-water

Despite the importance of TSS measurement, accurately assessing TSS concentrations in sewage-water presents significant challenges due to the complex nature of (urban) wastewater and the presence of interfering substances.

Most state-of-the-art 'TSS'-sensors, actually measure turbidity, an optical parameter of the water which is impacted by changes in water colour and particle size. Two changes that are prevalent during storm-overflow events.

Sewage-water often exhibits high turbidity and changes in fluid colour, caused by suspended particles such as silt, clay, and organic matter. Both high turbidity and changes in optical parameters often interfere with traditional optical TSS measurements, which are often actually optical turbidity measurements.


Also the composition and size distribution of suspended solids in sewage-water can vary widely, depending on factors such as the source of wastewater and weather patterns.


Sampling of sewage-water (both manual or automated) is also challenging due to the heterogeneous nature of wastewater flows, variations in suspended solids concentrations over time, and especially accessibility issues in sewer systems.


An overflow releasing a huge amount of water
Heavy rainfall last winter caused some overflows to discharge huge amounts of untreated water into natural rivers.

Sewage overflow events can have an enormous negative impact on nature. Reliable and economic TSS measurements are key to understanding the impact of those events and to strategically manage the impact.

How do Olpas sensors tackle these challenges?

First of all: Olpas sensors use a proprietary innovative ultrasound measurement technology (the "OLPAS Technology"). This technology is not susceptible to optical changes, thus not impacted by changes in water colour or particle sizes. So no reliability is lost when a heavy rain event colours the water differently or clay and silt have an impact on water colour.

The OLPAS ultrasound pulse is not negatively impacted by fouling on the sensor head. This results in maintenance intervals that are much longer compared to optical sensors. With no need for wipers.

Ultrasound measurements are also much less impacted by (bio)fouling: the ultrasound pulse actually goes 'through' it. This results in maintenance windows that are much longer compared to optical sensors. And Olpas sensors do not need wipers, pressured air or other mechanical cleaning tricks that are often used on sensors in sewers, influent or even in open waters.


So to summarise:

  1. The ultrasound OLPAS Technology provides a robust measurement that is not prone to changing water colour or other optical changes that are not relevant for the actual TSS

  2. Olpas sensors measure through fouling, requiring much less maintenance and no need for automated mechanical cleaning (no wipers, no pressured air)

  3. Due to the longer maintenance window, Olpas sensors can be installed on hard to reach locations (eg. in sewers), while still providing an economical measurement


At Olpas we believe our unique measurement technology and the Olpas sensors using it, can greatly helpt improving the ability to measure TSS in sewage-water to better understand and mitigate the risks associated with sewer overflows, protect water quality, and safeguard public health and the environment.


 

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