Abstract
Methane fermentation suspensions were filtered in cross -flow mode, using four ceramic microfiltration membranes of pore diameters 0.04, 0.2, 0.8 and 1.5 μm. The influence of operating pressure, feed velocity, concentration of MLSS and temperature was studied.
Limiting fluxes were obtained, and it was found that lower feed velocity and higher concentration of MLSS resulted in lower limiting flux.
At low feed velocity, the limiting fluxes were independent of membrane pore diameter. At high velocity, the limiting fluxes depended on pore diameter and larger pores gave lower limiting flux.
The limiting flux increased with rise in temperature, and this increase could be explained by change of viscosity of permeate solution.
The behavior of these limiting fluxes was analyzed by the resistance of the membrane itself, plugging and cake layer. Cake layer formed easily on the membrane surface at low feed velocity. This layer had such a large permeation resistance that the permeate flux decreased remarkably. On the other hand, plugging resistance mainly affected the flux at high feed velocity, and this resistance increased with increasing membrane pore diameter.
Membranes having a pore diameter of 0.04 or 0.2 μm rejected bacteria completely. However, a little leakage of bacteria through pore membranes of larger pore size was observed.
