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2 Integrated Approaches for the Production of Biodegradable Plastics and Bioenergy from Waste

2.3

Dairy and Milk Waste for the Production

of Biodegradable Plastics and Biogas

Milk waste comprise of casein protein and lactose sugar. Two wild-type microor-

ganisms, Lava DSM1034 and methyl bacterium sp. ZP24, are extremely efficient in

acquiring PHAs from the lactose [13]. Various biopolymers can also be attained from

dairy industrial effluents. Numerous microorganisms such as Bacillus licheniformis

and B. megaterium can be used for the production of polyhydroxybutyrate (PHB).

The PHB is a common member of PHAs family with monomers consisting of about

four or five carbon atoms [14].

2.3.1

Biodegradable Plastics and Dairy Waste

The gram-positive bacterial strain, SRKP-3, which is similar to B. megaterium could

potentially accumulate PHAs and it was isolated from brackish water. This organism

could use dairy waste containing production medium for the accumulation of PHA

granules. The strain, SRKP-3, produced maximum amount of PHB after 36 hours of

inoculation into the medium containing dairy waste (350 ml/l), rice bran (40 g/l),

and sea water (350 ml/l) at pH 9.0 [14]. B. megaterium is the first organism in which

the synthesis of PHB was reported.

2.3.2

PHB Production in Fermenter

For the production of PHB in fermenter, excess carbon level was maintained by feed-

ing dairy waste as the carbon source at 12th and 24th hours. Initially, the PHB yield

was low and as the dairy feed was given the accumulation of PHB was increased.

The pH was maintained at 9.0 consistently, during the accumulation of PHB. The

maximum production of PHB obtained was 11.32 g/l at 36th hour and the synthesis

of PHB decreased afterward [14].

2.3.3

Bioenergy from Dairy and Milk Waste

The hydrogen and methane can be mainly produced from dairy waste by aerobic

and anaerobic bacteria (lactic acid bacteria) which are commonly available in dairy

waste in high concentration and produce lactic acid by fermentation process (hetero-

lactic or homolactic). The microorganisms of Lactobacillaceae and Streptococcaceae

are most relevant for increasing the production of hydrogen gas, so increase in the

population of lactic acid bacteria will increase the production of H2. When the pro-

duction of hydrogen was increased, the concentration of lactic acid will decrease.

When Clostridium spp. (C. clariflavum, C. thermopalmarium, and C. tyrobutyricum)

and Sporanaerobacteracetigenes join with members of Tissierellaceae, the production

of CH4 and H2 detected. The Clostridium clariflavum fermentation results in the pro-

duction of lactate, ethanol, acetate, CO2, H2, and also a small amount of formate.

Fermentation of sugar by Clostridium thermopalmarium will yield acetate, ethanol,

lactate, H2, and CO2 [15].