Wastewater treatment in a microbial membrane bioreactor — a model of the process

A model of microbial membrane bioreactor with convective flow through the membrane is presented in the paper. Permeability coefficients hi in reference to microbial cells, substrates and possible reaction products as well as intensification coefficient Ψ which is a hydrodynamic parameter very significant for this bioreactor type, were introduced. The latter coefficient is used to control the bioreactor operation. Advantages of the membrane bioreactor over the classical flow bioreactor are presented. A reduction of residence time, with other parameters kept constant, or an increase of the conversion degree which enables the growth of feed stream, is reached in the range of coefficient 1 < Ψ < 3. A further increase of parameter Ψ does not cause such a significant intensification any longer. Due to high efficiency of the membrane bioreactor operating in a broad range of inlet concentrations and at low outlet concentration, this type of a microbial bioreactor is particularly recommended in industrial wastewater biodegradation.

Analysis of the efficiency of the microbial membrane bioreactor based on the proposed model shows that this bioreactor has a prevalence over the classical agitated bioreactor. Due to the use of a membrane which arrests cells, an increase of biomass concentration in the system causes a reduction of the residence time, i.e. a decrease of the reactor size and/or an increase of the feeding stream, or when the residence time is kept constant the conversion degree can be increased. Such intensification is particularly significant when concentration in the feeding stream is low. This case is typical of the microbiological industrial wastewater treatment and in this process the use of the membrane bioreactor may be extremely efficient which is illustrated by the relation for some operation parameters of the membrane bioreactor (Fig. 5).