EVALUATION OF PLASTIC COMPOSITE-SUPPORTS FOR ENHANCED ETHANOL-PRODUCTION IN BIOFILM REACTORS

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.