How do you measure from low NTU all the way up to 8% solids? By using the SoliSense® from Pi. Using patented optical technology the self-cleaning, simple to use, low drift suspended solids sensor from Pi is a cost-effective way of measuring the solids in a range of applications including all those associated with municipal wastewater plants and municipal water plants such as mixed liquor suspended solids (MLSS), return activated sludge (RAS), plant inlet and plant outlet, centrate, filter backwash and other monitoring requirements. Because of its patented technology that allows it to measure such a large range in a single sensor, the SoliSense® has integrated self-cleaning for a long maintenance intervals with calibration checking as little as once per year. Installation can be dipping into a tank or inserting into a pipe.
The SoliSense® has been designed to be suitable for all suspended solids monitoring applications in both water treatment works and wastewater works including:
Each sensor has an LED light source that emits in the infra-red and has a working lifetime of 15 years. Each suspended solids sensor has two detectors.
The light emitted is detected by the emitter detector. That light then goes through the sapphire optical windows and into the sample. With refraction and reflection, some light comes back into the sensor to the detector, which is at 120 degrees to the emitted light, and the ratio of the emitted light to the received light is proportional to the suspended solids in the sample. By varying the amount of light that is outputting the sensor can correct for effects introduced by, for example, the optical properties of the windows or aging optics or drifting electronics (all electronics drift). It is this technique that has been patented and provides for the stability and range of the SoliSense®.
The electronics provide a fully scalable output allowing the SoliSense® to measure any part, or the whole, of the scale. The sensor probe comes equipped with the capability of having a water jet regularly sweep over the optical lenses keeping them clean. If you have an application that ranges from low NTU all the way to %age solids then the SoliSense® is certainly the suspended solids monitor for you! With up to 5 calibration points you can accurately monitor your process across a wide range of sample concentrations.
The probes are constructed of 316 stainless steel with sapphire optical windows, so can withstand demanding operating environments.
By using two detectors in a single probe it is possible to:
Suspended solids are particles suspended in water. They occur naturally and can be seen for example in rivers after a rainfall event when the river appears ‘muddy’.
Treating water and wastewater has two main focuses: the removal of organics and particles, and then disinfection. Having information about the level of suspended solids can be invaluable in informing treatment processes (such as tracking changes in suspended solids in raw water entering a drinking water plant or monitoring the efficacy wastewater at the outlet), and so these kinds of sensors are very common in many industries and applications.
Suspended solids are generally measured in mg/l. Sometimes, if they are present in large amounts, a percentage is used or g/l.
Suspended solids and turbidity are measured differently, but they are related. Suspended solids measurements are based on the mass of solids present in a certain volume of water (mg/l), whereas turbidity is measuring how ‘cloudy’ it is in NTU. A common conversion used is 1mg/l = 2 NTU, but different suspended materials can have a different relationship.
The qualities of the process water and the solids to be measured will affect the effective maximum level that can be measured. For a ‘clean’ application (such as silica in clean water), we could expect to be able to measure up to 50% solids (500,000 mg/l) reliably. On the opposite side of the spectrum, black sludge in a wastewater plant may have a reliable limit as low as 5% (50,000 mg/l). Experience shows that in most wastewater works the upper limit is around 8% solids (80,000 mg/l).
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