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There are three key biological design variables for the activated sludge process: Solids Retention Time (SRT), mixed Liquor Suspended Solids (MLSS) concentration, Food to Mass Ratio (F:M). Either can ...

The target or operating solids retention time (SRT) depends on treatment goals and water temperature.  Nitrifying bacteria are especially sensitive to water temperatures; growth rates slow as temperat...

Solids Retention Time (SRT) is directly related the growth rate of the biology we are relying on for treatment.  Different microorganisms grow at different rates.  Nitrifiers in particular are known t...

Solids Retention Time (SRT) is the average time the biomass stays in the activated sludge system…the time in days a particle moves around in the aeration basin and clarifier before being wasted out of...

The activated sludge system relies on biology to remove pollutants.  Due to biological growth behavior, every pound of pollutant (e.g. BOD or ammonia) we remove will produce a fixed amount of new biom...

Oxygen uptake rate (OUR) is the rate of oxygen transferred from the bulk liquid to microorganisms; it is sometimes referred to as the breathing or “respiration rate”.  This is typically measured as mg...

Oxygen transfer rate (OTR) is the rate oxygen is transferred from the air into the bulk liquid of the aeration basin (atmosphere/gas to liquid water).  This is typically measured as lbO2/hr. The aerat...

We must provide oxygen to the microorganisms to drive BOD and ammonia removal.  Approximately 1 lb of oxygen is needed for every lb of BOD5. Approximately 4.3 lb of oxygen is needed for every lb of am...

Hydraulic retention time (HRT) is an estimate of how long it takes a particle to travel through a specific tank or volume. HRT is calculated by dividing the tank volume by the flow through it, and is ...

Good mixing is critical to performance of the activated sludge system, regardless of how your aeration tank/reactor is configured. Good mixing will ensure that the microorganisms are in contact with t...

The microorganisms we use in the activated sludge system only grow well within a certain temperature range….usually between 10°C and 38°C (50°F and 100°F). For every 10°C rise in temperature, microorg...

Controlling the amount of microorganisms in the activated sludge process is critical to performance.  The best way to do this is to maintain a target Solids Retention Time (SRT).  The target for your ...