Modelling the stable effluent qualities of the A2O process with activated sludge model 2d under different return supernatant

Abstract

A modified mathematical model based on the Activated Sludge Model No. 2d (ASM2d) was established to describe the effluent qualities of the enhanced biological phosphate removal (EBPR) system ‐ A2O. There were three modifications to the model in this study: (1) the biosorption effect of the soluble COD, (2) the hydrolysis of the organic nitrogen in influent wastewater, and (3) the growth of heterotrophic organisms in the anaerobic tank. The A2O process is composed of an anaerobic/anoxic/oxide process which removes biological phosphorus with simultaneous nitrification‐denitrification. The influent wastewater quality and quantity were fixed, the ratios of return sludge and sludge retention time were 0.25 and 12 days, and the model plant was operated at three different mixed liquid recycling ratios (MLRR, 0.5, 1.25, 2). When a steady state was reached, comparisons between the measured values and predicted values were made for each test. A good consistency between the test values and simulation values was shown. According to our results, the biosorption effect of the soluble COD and the hydrolysis of the organic nitrogen in influent wastewater are the important qualities in activated sludge systems. Additionally, heterotrophic organisms might grow in the anaerobic tank. Furthermore, it was indirectly proved that the denitrifying PAOs existed in the EBPR system.