(606d) Recycling Biobutanol Spent Broth by Ultrafiltration

The
application of a clean technology for alcohol fermentation was developed by
recycling spent broth from the production of biobutanol to reduce
energy, save water, protect the environment and reduce wastewater treatment
cost.  Spent broth was recycled by ultrafiltration and permeate was directly reused
as raw water in the production of biobutanol. Ultrafiltration was used to remove
most high molecular weight fermentation by-products and proteins, and partially
removed some low molecular weight organics. Polysulfone hollow fiber membrane (Romicon
HF0.8-0.75 PM500, Koch Membrane Systems, Inc., Wilmington, MA) did not show any
significant fouling during ultrafiltration of fermentation broth. It was
observed that the increase in temperature and pressure increased rate of
permeation (Figure 1). Performance of fermentation showed that the biobutanol
titer was reduced from ~21 g/L to ~14 g/L and ~12 g/L in the first and second
recycle, respectively (Figure 2). After two consecutive recycle of the broth,
glucose consumption continuously decreased which resulted in lower productivity
of butanol. The fermentation time, on the other hand, was not prolonged but productivity
was reduced from 0.22g butanol/L-hr to approximately 0.17 productivity in the
first recycle and 0.14 in the second recycle.The reduction in yield, however,
was observed to be less significant from 23% to 21%. The decrease in productivity
can be attributed to the accumulation of low molecular weight organics, and
salts in the recycled permeate which inhibit fermentation. Based on the results
ultrafiltration can be considered as a cost effective method of recycling
fermentation broth up to second recycle in this study.

Figure
1.  Effect of operating temperature and pressure on ultrafiltration flux

(a)                                                                    (b)

Figure
2. Fermentation kinetics  (a) first recycle, (b) second recycle