Modelling and optimization of the ion exchange membrane bioreactor for removal of anionic pollutants from drinking water streams

Dissertação para obtenção do Grau de Doutor em Engenharia Química, especialidade de Engenharia BioquímicaThe present work aimed at studying the treatment of drinking water supplies contaminated with perchlorate and nitrate, using the Ion Exchange Membrane Bioreactor (IEMB) concept. This system combines the transport of these two anions from contaminated water, through an anion exchange membrane, with their biological reduction in a separate compartment. In the IEMB, the mass transport is dependent not only from membrane properties but also from the biocompartment conditions. Multivariate statistical techniques allowed determining the most important process parameters related mainly to the compositions of the polluted water stream and biomedium and to the fluid dynamics operating conditions. The combination of statistical techniques with mechanistic modelling was a major achievement since the counterion transport across the membrane was successfully simulated and predicted under biological reactions ratelimiting conditions. Since nitrate is present in the contaminated water in much higher concentration than that of perchlorate, the IEMB process rate was mainly limited by the perchlorate bioreduction kinetics. This difference influenced organisation of microbial communities in the biofilm. This organization allows sequentially reduction of nitrate and perchlorate thus minimizing perchlorate inhibition by nitrate. Considering a possible large-scale application, it is essential to determine the effect of the key process variables. In this work, the performance of a plate and-frame module configuration, consisting of a series of anion-exchange membranes was investigated. It was found that contaminated water streams are effectively treated and that secondary contamination of treated water by the carbon source used was avoided by a start-up procedure involving a gradual increase of ethanol feeding to the IEMB biocompartment.Fundação para a Ciência e Tecnologia - SFRH/BD/25275/200