MLSS stands for Mixed Liquor Suspended Solids, which refers to the concentration of suspended solids in the aeration tank during the activated sludge process. The “mixed liquor” is a combination of raw or settled wastewater and activated sludge, containing beneficial microorganisms that play a crucial role in breaking down organic pollutants.
The Role of MLSS in the Wastewater Treatment
The aeration tank is where the biological treatment of wastewater primarily occurs. After the primary clarifier, the effluent is introduced into the aeration tank and mixed with return activated sludge (RAS) from the secondary clarifier. RAS is a biomass composed of bacteria and other microorganisms that help convert non-settleable organic matter (such as dissolved and colloidal solids) into settleable solids, carbon dioxide, water, and energy.
The effluent from the primary clarifier, combined with the return sludge (known as mixed liquor), is aerated by introducing air through diffusers at the bottom of the tank. This aeration provides both the necessary oxygen for the microbial activity and the turbulence to mix the biomass with the wastewater, facilitating efficient treatment.
Importance of MLSS Monitoring
Monitoring the concentration of suspended solids in the aeration tank is essential for maintaining the proper balance of biomass. This ensures optimal performance of the treatment process and helps prevent energy inefficiency. If too much biomass is present, excess air will be required, leading to wasted energy. Conversely, insufficient biomass results in inadequate removal of organic pollutants, compromising treatment efficiency.
- Energy Efficiency: By ensuring the right amount of biomass, MLSS monitoring helps optimize oxygen usage, reducing energy costs.
- Process Control: It allows operators to adjust the treatment process in response to varying plant loads, maintaining consistent treatment performance.
- Improve Plant Efficiency: Consistent monitoring ensures stability in the aeration tank, improving overall plant efficiency and treatment reliability.
- Real-time Measurement: Real-time, continuous monitoring reduces the need for time-consuming laboratory tests, providing quicker feedback and more accurate process adjustments.
- Prevent Overloading: Continuous monitoring helps detect changes in the biomass concentration, preventing issues such as sludge accumulation, which could overload the system.
MLSS Sensors Working Principle
MLSS sensors measure the concentration of suspended solids in the mixed liquor by analyzing the interaction between light and the particles in the liquid.
- A light-emitting unit releases light beams into the liquid.
- The suspended solids in the liquid scatter the light beams.
- A photodetector unit receives both the transmitted and scattered light beams.
- The photodetector converts the light beams into an electric signal.
- The analyzer compares the transmitted and scattered light beams to calculate the ratio and determine the MLSS concentration
To maintain accuracy and reliability, the MLSS sensor feature a self-cleaning mechanism, which uses a wiper to prevent the buildup of contaminants and biological growth on the sensor. This reduces the need for manual cleaning and ensures consistent performance.
