Retarded Transport and Accumulation of Soluble Microbial Products in a Membrane Bioreactor

Abstract

The accumulation of soluble microbial products (SMP) in a membrane bioreactor (MBR) was investigated both experimentally and theoretically. The sieving mechanism of the microfiltration membrane was experimentally demonstrated as inadequate to explain the salient accumulation of SMP in an MBR. The retarded transport of SMP through porous membranes was postulated as a new mechanism for the elevated SMP concentration in the MBR. Owing to the higher affinity of SMP to the membrane matrix, the convection velocity of SMP across the membrane can be much slower than that of water. The ratio of SMP concentration in the effluent to that in the MBR can be determined with a rigorous solution of the convection-dispersion equation developed based on the retarded transport. In addition, a mass balance model considering SMP generation in the MBR and SMP transport through the membrane was developed to describe the SMP concentrations in the MBR and in the effluent. The simulation results were in good agreement with the experimental data, indicating that the accumulation of SMP in the MBR could be attributed to the retarded transport of SMP through the membrane. The proposed model provides a new conceptual framework for evaluating the fate of SMP and the performance of MBR.