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

摘要

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 8 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~(-1),air flow rate range of 1.7-5.1 m~3 h~(-1),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 tau_(MBR)were calculated The relative residence time defined as the ratio of HF MBR tau_(MBR)and CSTR tau_(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.