2.4 Sugar and Starch Waste for the Production of Biodegradable Plastics and Biogas

23

The AD of a mixture of buttermilk and mozzarella cheese whey amended with

5% (w/v) of industrial animal manure pellets with a culture of lactic acid bacteria

(Lactobacillaceae and Streptococcaceae) for about 14 days increased the amount of

hydrogen production (more than 10 ml H2/g VS). During the incubation, a gradual

decrease of lactic acid bacteria was observed with a simultaneous increase of

Clostridia families (Clostridiaceae and Tissierellaceae). In inoculated sample of dairy

waste, several archaeal genera were identified as compared to non-inoculated same

samples of waste mixture. The Methanoculleus (methanogenic archaea) was a domi-

nant genus during the production of methane, and relative abundance was increased

to 99% at the end of the incubation time. This suggested that methane was formed

from dairy wastes primarily by the hydrogenotrophic pathway in the reactors [15].

2.4

Sugar and Starch Waste for the Production

of Biodegradable Plastics and Biogas

2.4.1

Sugar Waste

Sugar waste can be employed by the microbes as energy source which can be

accumulated intracellularly. Sugar-rich wastes can also be used for the production

of ethanol. Cellulosic sugar can be used for bioethanol production. This cellulosic

material can be obtained as waste during extraction and mashing of the juice from

cane sugar, beetroot, etc. [16, 17].

2.4.1.1

Sugar Waste and PHA

Bacterium (Pseudomonas fluorescens A2a5) was used to produce high amounts of

PHB (up to 70% of dry cell weight) in sugarcane liquor medium. Bacterial cells in sin-

gle or clusters were able to accumulate massive amounts of PHB. The doubling time

for the strain A2a5 is around six hours and the sugarcane liquor medium was opti-

mal for growth. The optimum temperature was around 20–25 ^∘C and the strain A2a5

would not able to grow over 30 ^∘C. The optimum growth was ensured at pH 6.5–7.0

with the PHB concentration of 31 g/l. In the 5-l bioreactor, a maximum cell dry

weight (CDW) of 32 g/l with the concentration of PHB of 22 g/l has been obtained

[18]. The M5 strain of Bacillus cereus was used in sugar beet molasses to produce

PHB. This strain produces higher PHB (73.84% of dry cell mass) and higher amount

of dry cell mass (0.44 g/l) in 1% and 4% molasses [19].

A recombinant Escherichia coli strain (HMS174/pTZ18u-PHB) uses glucose

as a sole carbon source and produces PHB. The process of fermentation with

the molasses is cheaper than with the glucose. The final dry cell weight, PHB

productivity, and PHB content of 39.5 g/l, 1 g/l/h, and 80% (w/w), respectively, were

obtained in 5-l stirred tank fermenter just after 31.5 hours in fed-batch fermentation.

Recombinant E. coli cells could efficiently utilize fructose (97%), glucose (99%),

and sucrose hydrolyzate (96%) for the production of PHB. However, utilization

efficiency on sucrose was very low (20%). But, beet molasses generally contain

30–50% of (w/v) sucrose. Therefore, beet molasses must be hydrolyzed before use.

The production of greater PHB obtained when cell density was higher on molasses.

The highest cell mass of 72.6 g/l and PHB content of 42% of a CDW were observed