Suspended Solids Monitor – SoliSense^®

Water and waste water treatment is largely about removing particles and organics, and then disinfecting water. Being able to measure suspended solids or turbidity can help in determining the best treatment, for example by measuring the suspended solids in the raw water coming in to a plant. Typically, suspended solids in waste water treatment has specific names such as MLSS (Mixed Liquor Suspended Solids) or RAS (Return Activated Sludge) etc. Measuring the suspended solids using an online suspended solids monitor around a waste water treatment plant can provide vital information on the efficiency and efficacy of the treatment process.

Typically, suspended solids are measured in mass per volume units such as mg/l or mgl^-1. Sometimes when the solids are quite high they will be measured in g/l or %.

Suspended solids is a ‘unit per volume measurement’ e.g. 1 mg of suspended solids in 1 litre of water. Turbidity is a measurement of ‘cloudiness’. Although each suspended material will have a different relationship (which will change over the range) a useful ‘rule of thumb’ is that 1 mg/L = 2 NTU although this can range from 1 mg/L = 0.5 NTU to 1 mg/L = 2 NTU.

This depends entirely on how ‘optically clean’ the medium is. So for example if we are measuring sand (silica) in a clean water suspension we can measure up to 50% solids or 500,000 mg/l. If, however, we are measuring black sludge in a waste water plant it may be as low as 5% or 50,000 mg/l. Typically, in most waste water works it is 8% or 80,000 mg/l.

Each SoliSense^® has temperature compensation built in so the effect of temperature on the online total suspended solids meter measurement is negligible. It should be noted though that the SoliSense^® is a large mass that can take time to reach thermal equilibrium so any process where the temperature is changing rapidly >2°C per 10 min could see some temperature effect on the reading.

Many different sites ranging across the whole water industry have a daily struggle to keep instrumentation functioning correctly due to fouling. However, did you know that…

… self cleaning and self flushing systems are now available from Process Instruments for most types of sensors?
… these fouling removal systems can extend the life of sensors and drastically reduce maintenance regimes?
… Pi’s self cleaning/flushing systems are affordable, simple and trouble free by design?

Sensor Fouling

Whatever the process being monitored is, there is often something in the sample water capable of fouling a sensor, and therefore causing erroneous results. The obvious solution to this problem is to clean the sensor, but how regular should inspection and cleaning programs be for each piece of instrumentation? Too regular and the inspection and cleaning regime is time consuming and unnecessarily costly. Not often enough and the instrumentation will give false results and probably fail prematurely.

What is the solution?

Process Instruments’ Autoclean and Autoflush Systems

Simple, reliable and easy to maintain, Process Instruments’ Autoclean/Autoflush systems are an alternative to mechanical cleaning mechanisms which can clog and break. By regularly spraying the sensor/probe with clean water or air, the sensor remains clean and free from fouling for extended periods of time. The sensor cleaning cycle is activated by Pi’s controller for a user selectable length of time and frequency so that no matter how dirty the application, the probe remains clean. With no moving parts in the sensor body or in the cleaning attachment there is nothing to replace or check other than a simple valve positioned in an easy to reach location.

Pi’s Autoclean and Autoflush systems can give trouble free and fouling free functioning of sensors for weeks, if not months, at a time.

A solution for each application

Autoclean

This option can be added to our pH, ORP, Turbidity, Suspended Solids and Dissolved Oxygen (DO) sensors. Consisting of an end cap to direct the flow of clean water (or air for a DO sensor) across the face of the sensor blasting any dirt away. The cleaning is controlled by a single valve positioned in an easily accessible location.

Autoverify

If using air to clean a DO sensor the system can also automatically verify that the sensor is still responding correctly, removing any need to remove the sensor from the sample for months at a time.

Autoflush

For sensors that require flow cell mounting like Chlorine, Ozone and Chlorine Dioxide, an Autoflush system has inbuilt valves which automatically start/stop the sample flow and control the flow of clean water past the probe. The user can set the flushing interval and duration to keep the flow cell and sensor clear from fouling. For particularly dirty or stubborn contaminants, warm water can be used as the flush water to aid cleaning.

With the above options, whatever the application or parameter being measured, Process Instruments will be able to provide a monitoring system that will not only be accurate, precise and long lasting but that will also remain free from fouling and save the operator both time and money.