Activated Sludge Process Control | Activated Sludge Process | Wastewater Treatment Plant

 Activated Sludge Process Control  

To ensure proper treatment, an activated sludge plant requires influent water quality testing as well as activated sludge process testing. 

Incoming Wastewater Testing 

Monitoring influent wastewater is an essential part of running an activated sludge plant. 

• Influent BOD testing will allow for the monitoring of the F/M ratio as well as plant organic loading.
• Because of their impact on organism health, the water quality parameters of pH and alkalinity, as well as the presence of toxic substances, can have an impact on plant operation.
• The organic loading on the plant is affected by the incoming wastewater flow rate.

Activated Sludge Process Testing 

The performance of the activated sludge process will be influenced by a number of process variables. The number of organisms in the aeration tank or the concentration of activated sludge, the sludge age, the dissolved oxygen concentration, the proper flow distribution to parallel treatment units, and the management of return activated sludge (RAS) and waste activated sludge (WAS) are all factors to consider (WAS). Each parameter is briefly explored below.

1. Activated Sludge Concentration

The mass of microorganisms is a component that must be monitored and adjusted in order for the plant to function properly. 

• The Mixed Liquor Volatile Suspended Solids (MLVSS) concentration is a measure of the organism concentration in the mixed liquor. The Mixed Liquor Suspended Solids (MLSS) concentration must first be determined for the MLVSS test. The MLVSS is calculated as a percentage of the MLSS.
• In conjunction with MLSS testing, conduct 30-minute settleability tests. It is possible to derive a general correlation between the two tests. Due to the short time required to conduct the test, the 30-minute test may be used more frequently to assist in process control of aeration tank solids levels.

2. Mean Cell Resident Time (MCRT) 

The Resident of the Mean Cell Microorganisms stay in touch with the substrate for an average amount of time, which is measured in time (food source). Solids retention time is another name for MCRT (SRT). Managing the MCRT is a critical component of an activated sludge plant's operation. The population dynamics of the organisms in the activated sludge process change when the MCRT is changed. 

• MCRT can have an effect on BOD removal.
• The operation of the clarifier and the solids settleability can be affected by MCRT.
• The oxygen requirements of the activated sludge process can be affected by MCRT.
• MCRT can have an effect on sludge production. Older sludge produces less, and vice versa.
 

MCRT, days = 

SS in aeration system, lbs 

SS lost from the aeration system, lbs/day 

The aeration system's suspended solids (SS) can be computed using simply the solids in the aeration tank, or solids from both the aeration tank and the secondary clarifier. The option you select is determined by the information provided to you in order to perform the MCRT calculation. Either method can be used, but choose one and stick to it.

3. Dissolved Oxygen Levels

To function properly, the organisms in an activated sludge plant require a sufficient level of dissolved oxygen (DO). 

• Aerobe activity will be reduced in the aeration tank if the DO is low.
• Low levels of DO may encourage the growth of filamentous and other undesirable organisms.
• High DO levels in the aeration tank encourage the growth of organisms responsible for pin floc formation, which has a negative impact on sludge settling.

4. Flow Splitting Where Sufficient Loadings Exist

When there are multiple plant units, precise flow splitting is required to ensure consistent operation and effluent quality.

• A hydraulic imbalance can result in an organic overload that exceeds a unit's design capability.
• The operation of aeration tanks and clarifiers can be hampered by unbalanced flows and organic load.
• Unbalanced flows and organic load can affect the activated sludge process by affecting sludge volumes, sludge age, and the F/M ratio.
• Uneven flows can result in overfeeding or starvation, which can disrupt the activated sludge process.

 

5. Solids Handling: Return and Waste Sludge 

The handling of solids is a critical function in the operation of an activated sludge plant. Clarifier sludge is either returned to the aeration tank or disposed of, as previously stated. In response to the incoming wastewater characteristics, the proper balance of WAS and RAS is required to provide the appropriate amount of organisms for the aeration tank.