Effects of Activated Sludge on Hydrodynamic Characteristics of a Hollow Fiber Membrane Bioreactor

Abstract A submerged hollow fiber membrane module is a widely accepted wastewater membrane bioreactor. Membrane bioreactor with submerged membrane (HF MBR) is complex multiphase physico-chemico-biological system with internal interactions between process variables and dynamic changes within gas-liquid-solids phases. A study of hydrodynamics in an operating laboratory bioreactor at realistic working conditions is crucial for design and scale up of a bioreactor for wastewater treatment processes. Accumulation of high concentrations of biomass causes the occurrence of heterogeneous regions in a bioreactor. This paper focuses on the effects of activated sludge on average residence time, which is often quite different from the ideally designed hydraulic residence time (HRT) in a submerged hollow fiber membrane bioreactor. In this work, tracer experiments using Dirac δ impulse of the saturated NaCl solution and monitoring electrical conductivity in the outflow with a flow-through conductivity cell were performed. From experiments at liquid flow rate range of 7.2-16.5 L h , and activated sludge concentrations MLSS 4.5-7.4 g L -1 probability density of residence time distribution (RTD) functions for hollow fiber membrane bioreactor and average residence times τ MBR were calculated The relative residence time defined as the ratio of HF MBR τ MBR and CSTR τ id were evaluated as function of MLSS concentration. Proposed is a linear regression model of the relative residence time with MLSS concentration. The model has negative proportionality coefficient k = -0.0814 g/L of MLSS due to decrease of the relative residence time with increase of active sludge concentration. Statistical evaluation of the model gives the correlation coefficient of R 2 = 0.8374. Decrease of the mean residence time with increase of MLSS is discussed in view of non-uniform membrane fouling