Can Your Secondary Clarifiers Handle More Flow? - A Stress Test Can Tell

Secondary clarifiers are a critical element in a wastewater treatment process. They provide an important gravity thickening function for the mixed liquor (ML) to produce thickened return biological solids to aeration basins and to prevent solids loss to the final effluent. For many wastewater treatment facilities, secondary clarifiers are often the bottle neck of the treatment system. The peak capacity of the clarifiers is impacted by many factors, such as system biomass inventory, ML settling characteristics, and clarifier physical geometry. In this paper, a sludge state point analysis was used for planning a clarifier stress test. Based on the results of the state point analysis, a series of hydraulic stress tests were successfully conducted which demonstrated the testing clarifiers had a capacity to handle two times the design peak flow without elevated secondary effluent total suspended solids if the system solids inventory was controlled at the desired level. The test results rationally matched the state point analysis prediction. The important conclusions from the stress tests can provide critical information for developing facility expansion plan and de-bottlenecking plant peak capacity, as well as for optimizing performance during peak wet weather operation.