Abstract:
The rapid depletion of fossil fuels and their associated environmental consequences has
sparked interest in the production of biofuel (bioethanol) from lignocellulosic biomass, such
as water hyacinth (WH). However, the lignocellulose's refractory nature renders it difficult to
convert to bioethanol, thus necessitating its pretreatment to increase enzymatic hydrolysis.
Unlike yeast that utilizes only (C6) sugar, thermophilic bacteria can efficiently convert
lignocellulosic hydrolysate (C5 and C6) sugars to bioethanol. The main objective of this
study was to optimize bioethanol production from WH pretreated with NaClO2 in boiling
water using thermophilic consortium. The specific objectives were; to isolate and characterize
thermophilic bacteria using morphological and biochemical approaches, to develop microbial
consortium, to pretreat and characterize WH , and to optimize the production of bioethanol
with microbial consortium. The bacteria were isolated using serial dilution and plating
technique on nutrient agar. Microbial consortium development was based on the degradation
of filter paper and untreated WH. WH was treated in boiling water for 4hr with and without
NaClO2 addition. Fourier transform infrared (FTIR) analyses were studied on NaClO2 with
boiling water-treated and raw WH. The main factors that affect ethanol production such as
temperature (40-60oC), time(48-96hr), and inoculum dosage(8-12%v/v) were chosen to be
optimized by central composite design (CCD). The results of this research showed that nine
thermophilic bacteria were identified and designated BO1, BO2, BOY, BOW, SO, OL, NW,
YF, and CF. The bacteria isolates were bacillus, cocci, gram-positive, and gram-negative.
Physiological characterizations indicate that all isolates could grow at temperatures 50-55oC,
NaCl concentration of 2% (w/v), and a pH of 5.5-8.5. The biochemical features of the isolates
showed that all of the isolates were positive in glucose fermentation, starch hydrolysis, and
EMB agar fermentation, but the results of the other biochemical tests were different.
Microbial consortium, developed from three isolates (BO1, BO2 & OL), were efficient at
degrading filter paper and untreated WH as substrates. The time yielding maximum total
reducing sugar (TRS) was 2nd hr resulting in 155 mg/g WH and 113 mg/g WH from, with and
without NaClO2 addition pretreated samples respectively. FTIR characterizations of the
pretreated sample revealed both breakdown and an increase in cellulose and hemicellulose
content. The CCD indicated that the optimum conditions for fermentation were inoculum
dose 8.1 %( v/v), temperature 48.8oC, and time 52.3hrs, which resulted in 7.2g/L predicted
ethanol concentration. Meanwhile, 7.7g/L ethanol was produced during experimentation
which is in close agreement to predicted value. Conclusively, utilizing NaClO2 and boiling
water as pretreatment method and thermophic consortium as fermentation microbes is a good
alternative for TRS and bioethanol production. This study suggests that more variables be
tested in the pretreatment of WH to optimize TRS and reduce inhibitory byproducts.