258

16 Bioreactors for the Production of Industrial Chemicals and Bioenergy Recovery from Waste

can be classified into three categories on the basis of ventilation configurations. First,

interior ventilation where air is blown through the bed of koji (bottom up), second

one is surface ventilation, where air is blown across the koji surface, and third is

non-ventilated natural convection which cools the koji. Interior ventilation is by far

the most common. Static flat bed-type, multistage conveyor-type, vapor exchange

non-ventilated-type, drum-type, and rotary disk-type fermenters are used for koji

fermentation.

16.10

Recent Research on Biofuel Manufacturing

in Bioreactors Other than Biohydrogen

In the last few decades, numerous research has been done on the second-generation

biofuel such as bioethanol. Current apprehension over climate change and reduc-

tion of fossil fuels are making to search alternatives for nonrenewable fossil fuels.

The SSF has been investigated as an alternative tool for the generation of ethanol

from agro-industrial residues. The Zymomonas mobilis has been measured as a pro-

ficient strain when apple pomace is used as a substrate for ethanol manufactur-

ing in SSF. However, highest yields were achieved from Saccharomyces cerevisiae. It

was reported that the incorporation of cellulase enzyme in the substrate enhanced

ethanol yields [32]. The prospective of using a single fermenter for biomass expan-

sion, starch hydrolysis, and ethanol manufacturing in SSF using Schwanniomyces

castellii was reported. Numerous starchy substrates for ethanol manufacturing using

S. cerevisiae found that rice starch and sweet sorghum gave the highest yields of

ethanol.

Dogaris et al. studied landfill leachate (LL) as a sustainable source of water and

nutrients for algal biofuel and bioproducts using the microalga, Picochlorum ocu-

latum, in a novel scalable HBR. Pilot-scale (150 l) and commercial-scale (2000 l)

HBRs that were operated outdoors in Florida using LL in batch and semi-continuous

modes generated high cell density cultures (1.7 × 10⁹ cells/ml) and reached up to

1.9 g/l of dry biomass which is appropriate for biofuel manufacturing [37].

Li et al. reported n-butanol production from Clostridium tyrobutyricum in the

presence of hydrolysates of lignocellulosic biomass in a fibrous-bed bioreactor.

Acetone–butanol–ethanol fermentation suffers from high substrate cost and

low butanol yield. In this study, engineered C. tyrobutyricum immobilized in a

fibrous-bed bioreactor was used for butanol production from glucose and xylose

present in the acid pretreated and enzymatic hydrolysates of low-cost lignocellulosic

biomass including corn fiber, cotton stalk, soybean hull, and sugarcane bagasse.

A techno-economic analysis showed that n-butanol could be produced from

lignocellulosic biomass using this novel fermentation process at ∼$2.5/gal [38].

Xue et al. studied cellulase production, lignocellulose saccharification, and

bioethanol fermentation in a modified gas lift bioreactor using A. niger mycelia

immobilized within the reactor in wire meshes, and S. cerevisiae cells immobilized

in resin beads. During four repeated batch fermentations, cellulase activities were

more than 6.28 U/ml and bioethanol production was over 45.9 g/l after 48 hours.