Producing other chemicals and useful products from food waste

Although bioenergy, such as methane and hydrogen, may reduce the cost of food wastewater treatment, it cannot satisfy entirely the energy demands of our society. Therefore, the production of high-value chemicals from the organic material in wastewater might be more feasible than bioenergy production. Table 23.6 shows that 19 different useful products have been fermented from whey products with various types of organisms (Yang and Silva, 1994). Organisms listed in the table could most probably be used with some other carbonaceous substrates. Wastes from the food processing industry often become inexpensive raw materials for integrated fermentation processes. High-carbohydrate wastewaters that are unsuitable for feeding to animals or humans are particularly appropriate for conversion to valuable products in pure-culture or co-culture processes. It is the cost-efficiency of the bioconversion process that ultimately determines whether a specific food waste stream is suitable for production of a specific product. Examples of chemicals that are obtained via fermentation of organic materials in food waste streams are shown in Table 23.7. Lactic acid fermentation and ethanol fermentation have been proposed as the main frame of a bioconversion system for the development of biobased chemicals from food and agricultural wastes (Ohara, 2003). The bioconversion technologies for ethanol fermentation are mainly crop-based, utilizing substrates such as sugar cane juice and corn starch. Since the cost of raw materials can be as high as 40%

Table 23.6 Some products from whey fermentations

Product

Organism

Medium

SCP

Kluyveromyces fragilis,

Sweet whey permeate

Rhodopseudomonas

sphaeroides/Bacillus

megaterium

K. marxianus

Acid whey permeate

Candida pseudotropicalis

Whey plus yeast extract

Various yeasts

Whey plus yeast extract

Alcohol

K. fragilis

Concentrated cottage

cheese whey permeate

K. marxianus

Acid whey permeate

Bakers yeast

Saccharomyces thermophilus

Sweet whey permeate

followed by S. cerevisiae

plus corn steep liquor

Lactic acid

Lactobacillus delbrueckii ssp.

Acid whey permeate plus

lactis

yeast extract

Homolactic acid bacteria

Unsupplemented acid whey

L. helveticus

Supplemented whey

permeate

Acetic acid

Streptococcus lactis ssp. lactis

Whey permeate plus

and Clostridium

yeast extract

formicoaceticum

Propionate

Propionibacterium

Whey permeate

acidipropionici

Polysaccharide

Propionibacterium sp.

Supplemented sweet whey

Oil

Apiotrichum curvatum

Whey permeate

Various fungi

Deproteinized cheese whey

Candida curvata

Whey permeate

Enzymes

Aspergillus niger

Lactose

ß-Galactosidase

Candida pseudotropicalis

Whey plus yeast extract

Acetone-butanol

Clostridium acetobutylicum

Whey permeate plus yeast

extract

Lysine

Mutant Escherichia coli

Whey

Vitamin B12

Propionibacterium sp.

Acid whey

P. shermanii

Sweet whey plus yeast

extract

Citric acid

A. niger

Whey permeate

L-Ascorbic acid

Mutant Candida norvegensis

Sweet whey permeate

Glycerol

K. fragilis

Whey permeate

K. marxianus

Supplemented whey

permeate

Anthocyanins

Ajuga reptans

Supplemented whey

permeate

Insecticides

Bacillus thuringiensis

Unsupplemented sweet

whey

Xanthan gum

Xanthomonas campestris

Hydrolyzed whey permeate

plus yeast extract

Adapted strain of X.

Supplemented whey

campestris

medium

SCP, single-cell protein.

SCP, single-cell protein.

Table 23.7 Chemicals production from food industry waste streams by different microorganisms

Chemical

Waste stream

Function

Organism

References

Lactic acid

Food

Bioplastic

Lactobacillus delbrueckii

Kim et al. (2003)

Polyhydroxyalkanoates

Food

Bioplastic

Ralstonia eutropha

Du and Yu (2002)

Poly-3-hydroxybutyrate

Whey

Bioplastic

Recombinant E. coli

Park et al. (2002)

Lipase

Corn steep liquor

Enzyme

Galactomyces geotrichum

Burkert et al. (2005)

Protease

Whey

Enzyme

Mucor spp.

Tubesha and Al-

Delaimy (2003)

Xylitol

Sugar cane bagasse

Sweetner

Geotrichum Guilliermondii

Carvalho et al. (2002)

Biomass protein

Starch processing

Feed

Rhizopus sp.

Jin et al. (1999)

Monascus pigment

Gluten-free effluent

Dye

Monascus purpureus

Dominguez-Espinosa and

Webb (2003)

Acetic acid

Milk permeate

De-icing salt

Clostridium thermolacticum

Collet et al. (2003)

plus Moorella

Citric acid

Orange wastes

Preservative

Aspergillus niger

Aravantinos-Zafris et al. (1994)

Chitin

Shrimp wastes

Functional

Lactobacillus plantarum

Rao et al. (2000)

additive

Nisin, pediocin

Mussel-processing

Antibacterials

Lactococcus lactis

Guerra and

Pediococcus acidilactici

Pastrana (2002)

Ethanol

By-products from

Fuel

Kluyveromyces marxianus

Ballesteros et al. (2001)

O OP

olive oil extraction olive oil extraction ti a a »

O OP

of the ethanol cost, recent efforts have concentrated on utilizing lignocellulose for producing a biomass-derived fuel (Zaldivar et al, 2001). Lactic acid produced through lactic acid fermentation is polymerized to form poly acetate, which is used as a plastic. Lactic acid and ethanol are esterified to produce ethyl acetate, which is used as a biodegradable solvent (Ohara, 2003). Polyhydroxyalkanoates (PHAs) have also attracted extensive research interest for their potential use as a biodegradable alternative to the petroleum-based synthetic plastics such as polypropylene (PP) and polyethylene (PE). Much effort has been put into the production of PHAs by microbial fermentation from organic matters in agricultural and industrial wastes because producing the biodegradable thermoplastics from pollutants can provide multiple benefits to the environment and contribute to sustainable development (Park et al., 2002; Aldor and Keasling, 2003).

Bioconversion for chemical production has been enhanced by process modification, such as culture immobilization or coupling two separate bioreactors (Carvalho et al., 2002). For example, anaerobic hydrogen fermentation and aerobic conversion of volatile fatty acids by Ralsonia eutropha were combined to enhance the efficiency of PHA production from food wastes (Du and Yu, 2002). Another fermentation strategy for increasing waste bioconversion yield was the use of co-cultures of pure microbial organisms in a single process. Within these step-wise fermentation strategies, one species performs most of the complex nutrient hydrolysis, and in turn provides its metabolic by-products to the second species, which forms the desired products. This study achieved high acetic yields during bioconversion of milk permeate by combining cells of Clostridium thermolacticum, Moorella thermoautotrophica and Methanothermobacter thermoautotrophicus in a microbial consortium. Addition of the hydrogentrophic methanogen decreased the hydrogen partial pressure, which increased the acetic acid production (Talabardon et al., 2000; Collet et al., 2003). In bioconversion of agricultural and food wastes to profitable chemicals, separation and purification of the chemical products from the bulk liquid still represents the higher percentage of the manufacturing cost. Therefore, the economic feasibility of reusing wastes will strongly depend on the fermentation processing efficiency in the downstream.

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