Glycerol was converted to 1,3-propanediol by fermentation with use of Citrobacter freundii bacteria in a membrane bioreactor with a 3-stage sepn. A clean micro filtrate was sepd. by nano filtration. The aq. soln. of 1,3-propanediol was concd. by membrane distn. Both the distillate and the retentate from nano filtration were recycled to the bioreactor to close the H2O cycle and recover the nutrients.