What Is an MLSS Meter?
An MLSS Meter is a device that measures the concentration of suspended solids (SS) in a liquid.
It is mainly used in the field of water treatment. In sewage treatment, the activated sludge method, which is a biological treatment using activated sludge, is generally used.
MLSS stands for “Mixed Liquor Suspended Solids” and refers to the suspended solids in the mixture of sewage and return sludge that flows into the treatment system.
Usage of MLSS Meters
MLSS Meter is used in the water treatment field to control the function of the activated sludge process. MLSS concentration is an important maintenance standard for activated sludge treatment facilities.
The activated sludge method uses bacteria that use organic matter as a nutrient source. If there is too much organic matter in relation to the amount of microorganisms, not only will the organic matter not be fully decomposed, but the bacteria will also divide excessively and the settling of flocs will deteriorate. Conversely, if there is not enough organic matter, it is known that the floc will collapse due to self-digestion, thus worsening the settling ability of the floc.
By measuring MLSS concentration, which is an indicator of microbial content, and managing it in accordance with the amount of organic matter, the treatment facility can function at its best.
Principle of MLSS Meters
MLSS Meter is a device to measure MLSS concentration by utilizing the light scattering phenomenon. When light is incident on a liquid containing MLSS, the light is scattered by MLSS. As the MLSS concentration increases, the amount of transmitted light decreases, while the amount of scattered light increases.
For this reason, the MLSS concentration can be determined by knowing the amount of transmitted light, scattered light, or both. Most MLSS meters on the market use either the transmitted light measurement method or the scattered light measurement method.
1. Transmitted Light Measurement Method
In the transmitted light measurement method, light from a light source lamp is incident on the MLSS-containing liquid introduced into the measurement cell, and transmitted light is measured. Since fluctuations in the amount of incident light can cause measurement errors, the system is designed to maintain a constant amount of light from the light source by installing a light receiver.
2. Scattered Light Measurement Method
In the scattered light measurement method, light is incident directly on the liquid to be measured, and the scattered light is measured by the MLSS. As with the transmitted light measurement method, fluctuations in the amount of incident light can cause errors. Therefore, a double scattered light comparison method using two photodetectors is used.
How to Select an MLSS Meters
1. Measurement Principle
There are various measurement principles of MLSS meters, such as the membrane filter method and the solids rotation method. It is important to select the appropriate principle according to the purpose and application. Select the best one considering accuracy, reproducibility, ease of operation, and other factors.
2. Measurement Range
Select an MLSS Meter with a measurement range suitable for the MLSS range of the target water treatment process, which typically ranges from a few mg/L to several g/L. Ensure that the measurement range matches the requirements of your process.
3. Accuracy and Reliability
The accuracy and reliability of MLSS meters are essential for accurate data collection and process evaluation. Selecting an MLSS Meter with high accuracy and reliability will ensure accurate data. In addition, selecting a highly reliable manufacturer and product will ensure stable measurements over a long period of time.
4. Ease of Operation and Maintenance
It is important to select an MLSS Meter that is simple to operate and easy to use. Selecting an MLSS Meter that can be easily calibrated and maintained on a regular basis will help maintain accurate measurements and stable performance.
Other Information on MLSS Meters
1. How to Use the MLSS Meter
General measurement procedure of the MLSS Meter:
1. Turn on the power.
2. Place the probe in the test water and submerge it until the sensor is submerged.
3. Hold the reading steady, and when it stabilizes, read the indicated value. The indicated value varies from MLSS Meter to MLSS Meter, so multiply the indicated value by a constant or value according to your needs.
Some MLSS Meters have a wobble mitigation function for the indicated value.
How to measure the interface:
- Turn on the power.
- Place the probe in the test water and submerge it until the sensor is submerged.
- Read the depth indication at the point where the MLSS measurement value changes significantly.
Interface measurement method using the interface lamp
- Set the concentration at which the interface is to be determined.
- Slowly submerge the probe in the test water.
- Read the indicated value of the depth when the interface lamp lights up.
Calibration of the Mlss Meter
When performing calibration of the MLSS Meter, follow the instructions below:
- When the detector is replaced.
- When the prism assembly is replaced.
- When the measurement error of the MLSS Meter exceeds the permissible value.
- After periodic maintenance.
In addition, there are two methods of calibration as follows.
Actual solution calibration method
This is a calibration method in which the measured liquid is manually analyzed or measured with a reference instrument and adjusted to the obtained value. This calibration method is necessary for accurate MLSS measurements.
There are three calibration procedures for this method:
- Since the MLSS value varies depending on the nature and condition of the liquid being measured, a sample of the liquid to be measured is taken near 100% of the measurement range, and the point at which 100% is reached is matched.
- Dilute the liquid used for calibration of the 100% point and adjust the 50% point.
- Adjust the 0% point using tap water.
Simple Calibration Method
The simple calibration method uses a set of calibration plates. The calibration plate is attached to the detector immediately after the above actual solution calibration method is performed. The MLSS value at that time is written on the calibration plate.
The next calibration is performed to match the value recorded on the calibration plate. This calibration method is employed during routine maintenance. The calibration plate with the values already entered cannot be transferred to another MLSS Meter.