Saturday, April 21, 2018

Biomass conversion is the transformation of feedstock into fuel, electricity, or other consumable forms of energy. First generation technologies for biofuels production included the conversion of corn and sugar to ethanol and vegetable oils to biodiesel. The second generation of technologies will avoid the "fuel vs. food" competition and will include gasification, pyrolysis, and biochemical methods of producing end use energy products and co-products from fiber and lower valued end-products.

Value-added Co-products from Biofuel Residues

Biofuel production processes generate considerable amounts of low-value residues such as stillage (starch-to-biofuel), vinasse (sugar-to-biofuel), algal biomass, crude glycerol and seed cake/meal. These residues streams often pose disposal burden to biofuel plants. Our research group has been working to convert these low-value residues into high-value fungal protein.

  • Stillage/Vinasse: These are liquid streams left after the recovery of biofuel. Biofuel production processes generate considerable amounts of high-strength waste stream such as stillage from corn-ethanol (6 to 7 L/L ethanol) and vinasse from sugar cane-ethanol (8 to 15 L/L ethanol). The high organic matter, and macro- and micro-nutrient contents of stillage, and vinasse coupled with low pH makes these streams an ideal substrate for growing edible fungus Rhizopus oligosporus. Fungal processing could potentially improve the economics of biofuel industries as the protein-rich fungal biomass can be formulated to produce high-value aquaculture and animal feeds, especially for monogastrics, providing a market value close to $500 to 700 per dry ton. The effluent following fungal treatment can be recycled back as process water for in-plant use.

Fungal cultivation on thin stillage (left) and vinasse (right).

  • Crude glycerol:Crude glycerol is a co-product of oil/fat-to-biodiesel production process. On a weight basis, every 100 lbs of biodiesel produced, 10 lbs of crude glycerol is generated, which is equivalent to 0.09 kg glycerol per L biodiesel. Our research group has been successful in converting the crude glycerol to fungal biomass.

Fungal cultivation on biodiesel-derived crude glycerol (left)
and the glycerol sample & fungal protein product (right).
  • Jatropha seedcake/meal: The biodiesel production from Jatropha generates a huge amount of Jatropha seed cake (650-700 kg seed cake/metric ton seed). The cake is non-edible due to the presence of toxic/antinutritional factors such as curcin, phorbol esters among others. However, Jatropha seed cake contains a high protein of excellent quality. Hence, it is indeed desirable to develop the strategies for detoxification and meaningful utilization of Jatropha seed cake. There are many detoxification methods reported wherein chemical, organic solvents and microbial fermentation has been used. However, the reported methods are either economically not viable or result in considerable loss of protein. We are developing biological detoxification method using edible fungus. The Jatropha cake/kernel meal acts as a substrate for solid state fermentation to simultaneously detoxify the Jatropha cake/meal and improve protein content. The detoxified cake/meal could be used in animal feeds.  The generation of high-valued feed from Jatropha cake/meal, which would enhance economic viability and sustainability of Jatropha-based biofuel production systems

Defatted Jatropha seed cake (left) and fungal

cultivation on the seed cake after two days (right).

The fungal biomass had a relatively high protein content of 43% (dry weight) with various essential amino acids, including 1.8% lysine, 1.8% methionine, 1.5% threonine, and 0.3% tryptophan. In another study, our group was also successful in cultivating fungal biomass on sugar-based biofuel residues, vinasse. The fungal biomass was found to contain 40 - 45% crude protein, and 4 to 5% crude lipid with significantly high amino acids, lysine, arginine, and threonine. We also developed complete essential amino acid profiles for fungal biomass, and the essential amino acids in fungal biomass were comparable to commercial animal and aquaculture feeds.

Freeze-dried fungal protein from cultivating fungus on vinasse.

It is also important to mention that nutritious food-grade fungal biomass could also possibly be processed into an inexpensive dietary protein supplement for human consumption in the developing world. This will certainly have significant positive impact on the issue of food and feed versus fuel currently facing the biofuel industries.

Schematics of Jatropha seedcake detoxification step 

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