WEFTEC: Using Batch Activated Sludge Treatability Testing in Process Design

Batch and continuous flow treatability tests have been used for years to develop process design criteria for industrial and municipal wastewater treatment plant design. The continuous flow tests are performed to simulate the actual or projected COD and BOD loading rates and sludge ages and determine the expected effluent quality. These tests are typically performed at a minimum of 3 sludge ages after an initial sludge acclimation period or typically a period of 2 to 3 months to obtain performance data at steady state conditions. These tests can be performed in the laboratory at the bench-scale or as a pilot study at the plant. The pilot study has the advantages of developing performance data on day to day influent wastewater variability thereby providing more representation of a full-scale plant. Batch tests which require much less time and cost are done by adding wastewater to an acclimated biological sludge for a period of 1 to 2 days. Batch studies have traditionally been used to characterize the biodegradability of a waste and develop COD and ammonia removal kinetic rate constants. The batch tests are relatively quick and inexpensive tests to perform compared to continuous flow tests in the laboratory and pilot tests in the field.This paper describes a technique that can be used in analyzing the less costly batch study data to develop treatment plant design criteria without the need for additional testing. A methodology is presented to conduct the batch tests and then develop continuous test K rate. The benefit of this approach is that it can save significant time and expense on a design project for an activated sludge treatment process. The K rate developed can be used to design completely mixed activated sludge processes including membrane bioreactors. A real case study is presented to show the difference in design for a pharmaceutical wastewater treatment nitrification system using batch test data versus continuous flow test data.