Ethanol production in a membrane bioreactor - Pilot-scale trials in a cornwet mill

Pilot plant trials were conducted in a corn wet mill with a 7000-L membrane recycle bioreactor (MRB) that integrated ceramic microfiltration membranes in a semi-closed loop configuration with a stirred-tank reactor. Residence times of 7.5-10 h with ethanol outputs of 10-11.5% (v/v) were obtained whe n the cell concentration was 60-100 g/L dry wt of yeast, equivalent to abou t 10(9)-10(10) cells/mL. The performance of the membrane was dependent on t he startup mode and pressure management techniques. A steady flux of 70 L/( m(2.)h) could be maintained for several days before cleaning was necessary. The benefits of the MRB include better productivity; a clear product strea m containing no particulates or yeast cells, which should improve subsequen t stripping and distillation operations; and substantially reduced stillage handling. The capital cost of the MRB is $21-$34/(m(3.)pr) ($0.08-$0.13/ [ gal(.)yr]) of ethanol capacity. Operating cost, including depreciation, ene rgy, membrane replacement, maintenance, labor, and cleaning, is $4.5-9/m(3) ($0.017-$0.034/gal) of ethanol.