Mr. Kunduru et Al. Pometto, EVALUATION OF PLASTIC COMPOSITE-SUPPORTS FOR ENHANCED ETHANOL-PRODUCTION IN BIOFILM REACTORS, Journal of industrial microbiology, 16(4), 1996, pp. 241-248
Biofilms are a natural form of cell immobilization that result from mi
crobial attachment to solid supports, Biofilm reactors with polypropyl
ene composite-supports containing up to 25% (w/w) of various agricultu
ral materials (corn hulls, cellulose, oat hulls, soybean hulls or star
ch) and nutrients (soybean flour or zein) were used for ethanol produc
tion. Pure cultures of Zymomonas mobilis, ATCC 31821 or Saccharomyces
cerevisiae ATCC 24859 and mixed cultures with either of these ethanol-
producing microorganisms and the biofilm-forming Streptomyces viridosp
orus T7A ATCC 39115 were evaluated, An ethanol productivity of 374 g L
(-1) h(-1) (44% yield) was obtained on polypropylene composite-support
s of soybean hull-zein-polypropylene by using Z. mobilis, whereas mixe
d-culture fermentations with S. viridosporus resulted in ethanol produ
ctivity of 147.5 g L(-1) h(-1) when polypropylene composite-supports o
f corn starch-soybean flour were used, With S. cerevisiae, maximum pro
ductivity of 40 g L(-1) h(-1) (47% yield) was obtained on polypropylen
e composite-supports of soybean hull-soybean flour, whereas mixed-cult
ure fermentation with S. viridosporus resulted in ethanol productivity
of 190 g L(-1) h(-1) (35% yield) when polypropylene composite-support
s of oat hull-polypropylene were used, The maximum productivities obta
ined without supports (suspension culture) were 124 g L(-1) h(-1) and
5 g L(-1) h(-1) with Z. mobilis and S. cerevisiae, respectively. There
fore, for Z. mobilis and S. cerevisiae, ethanol productivities in biof
ilm fermentations were three- and eight-fold higher than suspension cu
lture fermentations, respectively, Biofilm formation on the chips was
detected by weight change and Gram staining of the support material at
the end of the fermentation. The ethanol production rate and concentr
ations were consistently greater in biofilm reactors than in suspensio
n cultures.