The use of ceramic microfiltration and ultrafiltration membranes for particle removal from anaerobic digester effluents

Abstract

In the present study, the application of ceramic microfiltration and ultrafiltration membranes for particle removal from anaerobic digester effluent was investigated. The main objective was to study the effect of the operating parameters transmembrane pressure, cross-flow velocity and the membrane pore size on the permeate flux. One important result was that the microfiltration membrane showed flux rates that were about 30% lower than the ones achieved with ultrafiltration membranes. By means of the determination of the filtration resistances and the resistances in series model, the observed phenomenon was explained as blocking of the pore entrances of the microfiltration membranes whereas the smaller pores of the ultrafiltration did not get clogged. Operation at lower pressures turned out to be beneficial for the filtration process, as the permeate flux did not further increase once the transmembrane pressure exceeded 0.5 bar. Regarding cross-flow velocity, 3 m/s was found to be convenient. Further rising can still improve the flux rate but at the cost of highly elevated energy consumption. In addition to that, the particle size distribution turned out to have a high influence on the filtration process. Precipitation experiments with the addition of 0.5% ferric chloride (v/v) led to a shift of the particle size distribution to bigger particles and also to 47% higher flux rates. As a result of particle removal using ceramic membranes as well 85% of the COD were eliminated, whereas nitrogen removal was below 20%.