reagent in fermentation process. Previously, Budhavaram et al.
investigated lactic acid production from paper sludge with Bacillus
coagulan in a SSF process and found high lactic acid yield (>80%)
were achieved without pH control because of the buffering effect
of CaCO3 (Budhavaram and Fan, 2009). However, excessive CaoCO3
inhibited enzymatic hydrolysis. Margues et al. showed paper
sludge needs to be neutralized before enzymatic hydrolysis
(2008). It be noted that calcium carbonate also showed inhibition
on glucose utilization in ethanol production from paper sludge
by Zymomonas mobilis (Zhang and Lynd, 2010), they found calcium
carbonate and high temperature were responsible for the accumulation
of glucose in high solid loading of paper sludge SSF process.
This indicated utilization of paper sludge should not only consider
the benefits of buffering effect of CaCO3 in fermentation, but also
take into account its inhibitory effect on enzymatic hydrolysis
and glucose utilization. In addition, attempts to convert alkalipretreated
switchgrass to butanol in a SSF process have not been
successful, residual lignin or other toxic compounds on the pretreated
substrates potentially inhibit the cell growth and fermentation
activity.