Forecasting the performance of membrane bioreactor process for groundwater denitrification

Abstract

A mathematical model was developed for performance prediction, simulation, and design of membrane bioreactor (MBR) process for biological denitrification of two groundwaters. The process mass transfer chronologically involved the following aspects: biological reaction in bulk liquid phase, film transfer from liquid phase to biofilm, biofilm diffusion and biological reaction, adsorption at the biofilm–adsorbent interface, and adsorbent particle diffusion. The liquid film and biofilm transport equations constituted a time-varying moving boundary problem. Model biokinetic parameters for denitrification using ethanol as electron donor were estimated from batch reactor studies. Laboratory-scale MBR experiments showed that steady state was reached rapidly and over 99% nitrate removal was consistently achieved for influent concentrations in the 16 to 45 mg/L range. Furthermore, comparison of experimental data and model predictions established the accuracy, reliability, and utility of the model. The MBR experiments also demonstrated that powdered activated carbon (PAC) did not particularly improve nitrate removal or permeate flux. Model sensitivity studies illustrated the dependence of process dynamics on parameters related to influent nitrate concentration, biomass concentration, biodegradation kinetics, and hydraulic residence time. Key words: bioreactor, membrane bioreactor, denitrification, biodegradation, membrane filtration, water treatment, membrane fouling.