Modelling and dynamic simulation of a moving bed bioreactor for the treatment of municipal wastewater

A model for the dynamic simulation of a pilot scale moving bed bioreactor (MBBR) used for the treatment of municipal wastewater is proposed. The proposed MBBR model includes attachment of particulates to the biofilm and detachment of biofilm into the bulk liquid. The biofilm growth kinetics are modelled with the activated sludge model no. 1 (ASM1). Diffusional mass transport limitations are implemented implicitly by ASM1 and manifest by adapted half-saturation coefficients in the Monod expressions of the activated sludge model. The model layout incorporates completely mixed aeration tanks and flow splitters and can be implemented using the respective standard blocks available in wastewater treatment plant simulators. A calibration guideline is proposed. Attachment and detachment rates are adjusted during calibration in order to match the measured biofilm solids in the MBBR and effluent ammonium and nitrate data. The process dynamics of the MBBR were well reproduced using ASM1 with default parameter values. The biofilm age was calculated analogous to the sludge age in an activated sludge plant and it was found to be 2.6 d in the first and 2.1 d in the second compartment of the MBBR, which is small compared to typical sludge ages in nitrifying activated sludge plants.