Comparative Study of Balancing SRT by Using Modified ASM2d in Control and Operation Strategy at Full-Scale WWTP

Detailed knowledge on the composition of the influent going into the wastewater treatment system is essential for the development of a reliable computer model. In the context of WWTPs (wastewater treatment plants), the wastewater characteristics are not only important for activated sludge system modelling, but also have an impact on the appropriate control of single unit operations. The aim of this study was to evaluate the concepts of COD (chemical oxygen demand) fractionation measurement in municipal wastewater with a respirometric method in control, and modelling the biological treatment processes at WWTP using the modified Activated Sludge Model no. 2d (ASM2d) developed by Drewnowski and Makinia. The batch OUR (oxygen uptake rate) test results and COD measurements obtained at BNR plant (96,000 m(3)/d) in Gdansk (Poland), were compared and evaluated with the main BNR (biological nutrient removal) WWTP (144,000 m(3)/d) located in Malaga (Spain). Respirometric tests and COD fractionation provided the experimental database for the comparison of the wastewater characteristics and model predictions at both large WWTPs. Some parameters, such as the heterotrophic growth yield (Y-H) coefficient, required calibration/validation of the range (Y-H = 0.64 and 0.74 gCOD/gCOD for Gdask and Malaga WWTP, respectively) to fit the modified ASM2d. The crucial issue when dealing with the newly developed model and proposed wastewater characterization for both study plants were extremely low and high values of the X-S/X-I ratio, which can be used to control full-scale WWTP and balance the solid retention time (SRT) in activated sludge systems.