Application examples

Oxygen measurement at biological wastewater treatment plants

Measurement of the dissolved oxygen concentration in water is mainly used for monitoring and controlling the activation and nitrification process. A suitable concentration of oxygen minimizes the energy consumption of aeration devices and at the same time ensures optimal operation of the activation (nitrification) and denitrification stages in constantly changing operating conditions. It enables effective removal of both organic and nitrogen pollution, and minimizing the consumption of electricity, which is one of the largest costs in the operation of the WWTP.

INSA systems for measuring oxygen concentration work reliably at hundreds of treatment plants, both municipal and those connected to food technologies, tanneries, the pharmaceutic industry, at WWTPs of animal products rendering industry, etc. The devices are mostly connected either to frequency converters or to further control systems, to optimize the performance of aeration devices. The on-line analyzers can also control the aeration directly, without additional control systems.

Another part of WWTP technology, where the monitoring of oxygen concentration is important, is at the regeneration tanks of the sludge management. Measuring oxygen is also important in purification tanks and ponds. In these cases, the measurement is carried out at the minimum speed of water movement, where some kinds of oxygen sensors have problems without additional stirring. Sensors CSOT43 have extremely low oxygen consumption, while sensors CSOT53 and CSOT63 have zero consumption, so they work well in these cases, without any additional stirring. The low flow rate also does not allow self-cleaning of the sensors (unlike in the WWTP activation tanks). In these cases, INSA systems with automatic sensor cleaning have proven themselves excellently.

Sensor contamination is a challenge

Measuring the concentration of oxygen at a WWTP is particularly difficult in cases where slime forms on the surface of the oxygen sensor. For maintenance crew, this would mean cleaning the sensor even once a day in extreme cases. In such situations, the ideal solution is automatic cleaning - the probe SPO41MEK. This completely eliminates the unpleasant manual cleaning of the sensors.

Left: Oxygen sensor without automatic cleaning, installed inside an activation tank where water contains slime microorganisms, after 1 week operation without cleaning.

Right: Oxygen sensor in similar conditions after 12 months operation with automatic cleaning, without any manual intervention.

Maintenance of the system then consists only of a simple recalibration in the air once every 6 months. The recalibration is performed by just pulling the probe out of water and starting the calibration procedure by pressing a button. The calibration then proceeds automatically, so the only remaining task is to return the probe back into water.

Automatic cleaning may provide safer operation and more comfort for the operator even in those cases where slime does not form on the sensor, or where the sensor is more or less cleaned just by the movement of the measured water. In many cases, this self-cleaning by water flow is even sufficient for normal operation, so that the automatic cleaning is not needed. Systems with automatic cleaning prove excellent also in the demanding conditions of regeneration tanks of sludge management, and in post-cleaning tanks and ponds. Even in these cases, INSA systems with automatic cleaning work without the slightest problem.

Oxygen measurement at drinking water treatment plants

Oxygen measurement is also important in drinking water treatment plants that process surface water.

Changes in oxygen concentration indicate changes in organic load and can also signal the release of manganese into the raw water.

The oxygen concentration in the raw water also affects the operating mode of the individual technological stages of the treatment plant.

Oxygen measurement in surface water monitoring

Oxygen concentration is an important indicator of surface water pollution. In clean surface waters, the oxygen concentration is usually between 85 % and 95 % of saturation, but may become significantly lower (or higher) in biologically or chemically contaminated waters. During the daily cycle, the concentration changes due to changes in the intensity of photosynthesis. The dynamics of changes are significantly higher in strongly eutrophic waters.

Oxygen concentration measurement is an important part of any monitoring station. For these applications, it is also advantageous to use probes with automatic sensor cleaning (SPR41ME or SPO41ME), which enable long-term unattended operation of the station.

Oxygen measurement in fish farming

Information about the amount of oxygen in the water is vital for fishing technologies - fish farms, fish tanks, ponds. A concentration of 3 to 4 mg/l is usually considered the lower limit, depending also on the sensitivity of the fish. Salmon-like fish require a concentration of around 6 mg/l.

Depending on the nature and scope of individual facilities, the entire range of INSA instruments is used. The MKT44A pocket-size oxygen meters (bottom image) have proven themselves in the past for portable measurement of oxygen concentration in ponds, fish farms, or even for smaller stable setups. Their long tradition continues to the modernized type MFD79, which is also available with a modern optical sensor CSOT53. Just immerse the sensor in water, wait for the value to stabilize and read the concentration on the display...

For larger facilities, a better option it to use a permanently installed hanging probe CSOT63. However, continuous measurement of oxygen concentration in these situations may be relatively difficult for two reasons. One reason is the quick contamination of the sensor membrane, often seen in fish farming facilities. The second reason is the low speed of water flow, which not only requires sensors with very low oxygen consumption, but also reduces the self-cleaning of the sensors by the flow - the sensors often have to be cleaned daily under such conditions.

The INSA sensors and probes offer a solution for these cases. Oxygen consumption is very small (CSOT43 sensors), or even zero (CSOT53 and CSOT63), so they work well even without any water movement. Automatic cleaning of the sensor (SPO41ME and SPR41ME probes) enables reliable operation of the system even in the most demanding cases, requiring virtually no maintenance.

Oxygen measurement in the food industry

Oxygen plays an important role in all fermentation processes - e.g. in the production of beer. There must be a sufficient amount of oxygen in the wort for the fermentation process to be optimal. Conversely, after the end of fermentation, the oxygen concentration must be kept as low as possible.

The residual oxygen concentration determines the shelf life of the produced beverage. To achieve a long storage time, the concentration must be a few tenths of mg/l at most.

Measurement of pH in drinking water treatment plants

The pH value is a basic parameter monitored during the entire drinking water production process.

The pH value of the raw water entering the treatment technology is especially important in the case of surface water, the properties of which change significantly depending on a number of factors. If the measurement is to be reliable and without the need for frequent maintenance, it is necessary to use probes with automatic cleaning of the installed sensors.

When removing iron and manganese by alkalization, control of the pH value is absolutely necessary, but continuous measurement is rather difficult, especially where the concentration of manganese is high. For this application, the probes with automatic cleaning (SPO41ME, SPR41ME) should be used. Thanks to automatic cleaning and high-quality pH electrodes, INSA analyzers work for at least one month with the required accuracy (pH ± 0.1), even in the case of extremely high manganese values, and requiring no maintenance. It is also possible to use the built-in PID controller to maintain the pH value without an additional control system, even in more demanding cases (e.g. where a screw dispenser of calcium hydrate is controlled).

Maintaining an optimal pH value is also necessary to control the coagulation and flocculation processes. Considering that the water after the addition of flocculant contains a number of flakes that settle on the surface of the pH electrode, the probes with automatic sensor cleaning are preferred for such applications.

In most water treatment plants, the pH value is adjusted to the required level by adding milk of lime. For effective dose control, continuous pH measurement is essential. However, without effective automatic sensor cleaning, such measurement is often nearly impossible.

It is also important to measure the pH of treated water at the outlet of the treatment plant, as the pH value determines the effect of water on water distribution systems (such as corrosion or limescale deposits).

Measurement of pH at biological wastewater treatment plants

Given that the optimal function of biological processes takes place only in a narrowly defined range of pH values, the measurement of pH value at the entrance of the WWTP is also very important - especially where occurence of extreme pH values cannot be ruled out, possibly disrupting the entire cleaning process.

Measuring the pH at the inlet of the WWTP is quite difficult, because the water often contains a significant amount of fat and, depending on the properties of installed combs, also various fibrous substances. The optimal solution in these cases is the SPO41K probe with rounded cover, which protects the sensor against clogging with fibrous substances, ensures optimal water flow around the sensor, and also protects the sensor from damage.

An alternative solution may be the use of the SHI63 hanging probe with an integrated input block, in combination with the MUT14 clamp. This solution is more efficient in terms of price and space, but may prove to be less comfortable during later maintenance.

Sensor contamination is a challenge

One of the main problems in the application of pH sensors is the contamination of the electrodes, causing changes in their properties, requiring frequent operator intervention (sometimes even within a few hours) and in some cases making the measurement virtually impossible. One typical example is pH measurement with dosing milk of lime, when the reaction of milk of lime with water is not yet completely finished. Similar problems arise with measurements in water with an aggressive iron content, on chemically or biologically heavily loaded surface streams and similar.

Problems of this kind are particularly typical for neutralization and precipitation processes. If the neutralization is carried out with milk of lime, then as a rule, the sensor quickly becomes clogged with lime incrustations, causing a deviation of the measured value. The pH value can deviate from the actual value by as much as one pH unit over the course of just a few hours. In order to ensure a correct measurement, the sensor needs careful cleaning several times a day.

For such cases, INSA offers automatic mechanical cleaning of sensors (SPO41ME and SPR41ME probes). This method of cleaning proved to be very effective and easy to operate, superior to other methods of cleaning. The system, well proven in dozens of different applications, works reliably even at low temperatures, with both chemical and biological water pollution. It is simple and reliable, without the need for additional chemicals.

In the picture: Measurement of the pH value during water alkalization with milk of lime, the condition of the sensor after four months of operation without manual cleaning.

Control of fermentation processes

For the optimal course of the fermentation process and the achievement of maximum yield, it is necessary to ensure the optimal pH value. The PID controller built into the pH analyzer can reliably control the dosing pumps even without additional control systems, so that the pH value is always optimal.

Multi-channel configurations are particularly suitable for these applications. One analyzer equipped with multiple PID controllers can simultaneously control up to four fermenters.

Thanks to the implemented external calibration mode, the calibration procedure in this kind of application is really simple.

Measurement of the pH value in fish farming

The pH value is also an important factor in fish farming. Above all, salmon-like fish are very sensitive to pH, which means the risk of fish death and thus large economic losses.

A fundamental problem of pH measurement, especially where there is a high density of fish (fish beds), is contamination of the pH sensor. In these cases, the best results are achieved with automatic cleaning (SPO41ME and SPR41ME probes).

Where this is not possible, for example for reasons of economy or space, a suitable alternative for less demanding cases is the SHI63 hanging probe equipped with a compatible pH sensor.

pH and ORP measurement in swimming pools

pH meters in these applications automatically maintain the optimal pH value by base or acid dosing. Usually the chlorine concentration is also measured and regulated at the same time. The requirement to monitor the ORP value is also common.

For these applications, the MFD88 analyzer offers a cost-effective multi-channel configuration. A single device then measures chlorine and pH (or chlorine, pH and ORP), even from several measurement points at the same time. It can also directly control the dosage without the use of other control systems.

pH measurement in surface water monitoring

The pH value is one of the basic parameters in surface water monitoring.

Considering that surface waters are more or less biologically active, contamination of sensors is often a problem in these cases. Biological growths on the pH electrode often cause a change in the pH value of up to 0.5 units. If daily manual cleaning is undesirable, automatic sensor cleaning is the right solution. Maintenance of the pH measurement is thereby reduced to a single-point calibration, usually at an interval of 4 to 6 weeks.

ORP measurement at biological wastewater treatment plants

Oxidation-reduction potential (ORP) is a quantity indicating whether the measured environment is in the aerobic or anaerobic region. In the case of biological WWTPs, the operation of the denitrification stages can be monitored and optimized by measuring the ORP.

A basic prerequisite for reliable ORP measurement is maintaining a clean surface of the electrode. In many cases, this can only be achieved by mechanical cleaning of the sensor, provided by the SPR41ME nad SPO41ME probes.

ORP measurement in drinking water treatment plants

ORP measurement is mainly used to control the preparation of sand filters with permanganate. For this application it is necessary to use probes with automatic cleaning (SPR41ME, SPO41ME).

ORP measurements can also be used to monitor low concentrations (up to approx. 0.15 mg/l) of chlorine, chlorine dioxide or ozone in clean water.

Conductivity measurement in swimming pools

A modern way of disinfecting water for swimming pools uses a salt solution instead of chlorine dosing. Water treated in this way has properties similar to sea water and is especially suitable for people sensitive to chlorine.

Conductivity measurement is used in the preparation of a salt solution with suitable concentration, which is then dosed into the clean water entering the pool. Two-electrode sensors from our offer are suitable for this measurement.

Measurement of conductivity in drinking water treatment plants

Conductivity measurement is used in the preparation of milk of lime for subsequent alkalization. The analyzers control the dosing elements and automatically ensure the optimal concentration of milk of lime.

The conductivity values here are in the tens of mS/cm. Thanks to the advanced technology of INSA analyzers, two-electrode sensors from our offer work well in this case, and may also be easily combined with automatic cleaning where necessary (SPR41ME and SPO41ME probes).

Production of distilled and deionized water

Conductivity is a basic parameter to indicate the quality of distilled, redistilled or deionized water.

The conductivity value in these cases varies from tenths of µS/cm to units of µS/cm. The CE11 two-electrode sensor is suitable for this measurement.

Conductivity measurement in surface water monitoring

Conductivity is one of the standard parameters measured in surface waters. In this case, the value of conductivity indicates primarily the sodium chloride content.

For this application, it is advisable to use sensors with automatic cleaning of the sensors, which eliminate contamination of the electrodes and the resulting effect on the measured value.

Measurement of chlorine concentration in drinking water treatment plants

Chlorine analyzers make it possible to control the dosage for disinfection of drinking water and to ensure the hygienic safety of water distribution systems (pipes and water reservoirs).

The supplied CSCT43 and CSUT43 membrane sensors offer long membrane life and resistance to pollution. In applications of this type, they are usually installed into cost-effective flow through units PB42V or PB43V.

Measurement of chlorine concentration in swimming pools

The analyzers automatically control the disinfection process so that the required concentration of disinfectants in the water is achieved. Without automatic dosing, it is often not possible to maintain the necessary concentrations of disinfectants within the required accuracy. Simultaneous measurement of pH and ORP values is also often required, which can be integrated into the same MFD88 analyzer in a multi-channel configuration.

The supplied CSCT43 and CSUT43 membrane sensors offer long membrane life and resistance to pollution. In applications of this type, they are usually installed into cost-effective flow through units PB42V or PB43V.

Measurement of chlorine dioxide in drinking water treatment plants

Chlorine dioxide analyzers are mainly used to control the dosage for disinfection of drinking water and to ensure the hygienic safety of water distribution systems (pipes and water reservoirs).

The supplied CSDT43 membrane sensors offer long membrane life and resistance to pollution. In applications of this type, they are usually installed into cost-effective flow through units PB42V or PB43V.

Ozone measurement in drinking water treatment plants

Ozone analyzers make it possible to control the dosage for disinfection of drinking water, to check the maximum permissible concentration in the outlet water and to maintain the optimal concentration during pre-ozonation at the input technological stages of water treatment plants.

Unlike chlorine, ozone removes not only bacterial but also viral infection. It is also used to eliminate odors, turbidity and discoloration caused by organic water pollution. Equally important is the use of ozone in the removal of iron, manganese and other metals in the production of drinking water. The application of ozone also has the same importance in the disposal of ecological burdens.

The supplied CSZT43 membrane sensors offer long membrane life and resistance to pollution. In applications of this type, they are usually installed into cost-effective flow through units PB42V or PB43V. However, problems with ozone measurement may occur in the presence of manganese, even in minimal concentrations. In such cases, the deployment of the SPR41ME flow through probe with automatic cleaning has proven successful.

Ozone measurement in swimming pools

The analyzers control the disinfection process so that the required concentrations of ozone in the water entering the pool are achieved. Without automatic dosing, it is nearly impossible to keep the concentrations of disinfectants within the required limits.

Treating pool water using ozone is a very effective and environmentally friendly method. It removes all microorganisms, including viruses, reduces the concentration of a number of other dangerous substances and also reduces water turbidity.

The supplied CSZT43 membrane sensors offer long membrane life and resistance to pollution. In applications of this type, they are usually installed into cost-effective flow through units PB42V or PB43V.

Ion-selective measurements in industrial technologies

Ion-selective electrodes cover a wide range of different measurements, and the range of their applications is no less wide. These are modern analytical sensors for determination of various ionic analytes, used in analytical laboratories, in agriculture, the food industry, biochemistry, pharmacy, medicine, for ecological measurements of surface, ground, drinking and waste water, in tribodiagnostics, in the analysis of explosives and pyrotechnic compositions, for applications in research laboratories, and many other uses.

With advancing development, these sensors are increasingly used for in-technology measurements in industry, although their use in this area still has its limits. These are relatively demanding and sensitive sensors, the use of which in industry must be carefully considered in each individual case. In some applications it may be necessary to use probes with automatic cleaning of the sensors (SPO41ME, SPR41ME). (In the picture: Electrode for ammonia measurement.)