In a conventional activated sludge process, what is the typical concentration of mixed liquor suspended solids?

In a conventional activated sludge process, the typical concentration of mixed liquor suspended solids (MLSS) falls within the range of 1000 to 4500 mg/l. This concentration is essential for maintaining effective microbial activity, which is crucial for the biological treatment of wastewater.

The concentration of MLSS affects the process's overall efficiency; it needs to be high enough to support the desired level of microbial activity but not so high that it leads to settling problems in the secondary clarifier. When within the 1000 to 4500 mg/l range, the activated sludge process can achieve a good balance between the retention of microorganisms and the removal of organic matter from the wastewater, allowing for effective treatment.

Higher concentrations, such as those presented in the other choices, could lead to complications, such as difficulty in achieving good settling of the activated sludge and potential operational issues. Thus, the range of 1000 to 4500 mg/l represents an optimal balance for most conventional activated sludge systems.