In present study, repeated-batch fermentation in biofilm reactor was evaluated for ethanol production by
using carob extract. Response surface method (RSM) was used to determine optimum initial sugar concentration,
pH, and agitation in the constructed biofilm reactor. The optimum conditions for ethanol production
in biofilm reactor were determined as initial sugar content of 7.71Bx, pH of 5.18 and agitation of
120 rpm. The ethanol production (P), the yield (YP/S) and production rate (QP) were found as 24.51 g/L
48.59% and 2.14 g/L/h at the optimized conditions, respectively. The fermentation time for maximum
ethanol production in carob extract was reduced to 12 h by using a biofilm reactor compared the published
data in the literature, which was 30 and 24 h by using suspended and immobilized yeasts in a stirred
tank reactor, respectively. Furthermore, the effect of various nitrogen sources and enrichment were
also evaluated and YP/S, QS and QP were significantly decreased compared to the results obtained from
optimum conditions in biofilm reactor. Overall, results showed that a biofilm reactor for ethanol production
from carob extract can be successfully implemented in point of reducing fermentation time, eliminate
re-inoculation of the typical batch fermentation as well as increasing production yield.