Different Features of Various Biofuels, Enzyme Hydrolysis, Acid Hydrolysis, Hexose Fermentation, Pentose Fermentation

Different Features of Various Biofuels -

Biofuel	Substrate	Microorganism	Status of production	Limiting Factors
Ethanol	1. Starch, sugar crops	1. Bacillus lichenformis¹ 2. S. cerevisiae, Zymomonas ²	Billions of litres/yr (mostly in Brazil and USA)	1. Low productivity (Brazil) 2. High substrate cost (USA)
	2 . Cellulosic wastes (a) Enzyme hydrolysis	1. Trichoderma reesei (celllulase) 2. S. cerevisiae² 3. Recombinant E.coli³ 4. Clostridium, Fusarium⁴	Likely to enter commercial scale production; suited for energy crops	1. Low yields 2. Slow rate of production 3. Pretreatment needed
	(b) Acid hydrolysis	S. cerevisiae,Zymomonas	Likely to enter commercial production; for waste materials	1. Low yields 2. High acid recycling costs
	(c) From synthesis gas	Clostridium ljungdalii	Preliminary development	Mass Transfer limitations in bioreactor
Methane	Farm and human wastes municipal solid wastes, etc	A group of anaerobic microorganisms	Widely used	1. Slow rates 2. Economically unattractive as transport fuel
Butanol	Soluble carbohydrates	Clostridium acetobutylicum C.beijernickii	Commercial production possible	1. Low product tolerance 2. High product cost
Hydrogen	Sunlight and water	Chlamydomonas	Long term research and development needed	Efficiency declines with high light intensities.
	Sugars and fatty acids	Anaerobic bacteria like Clostridium	---	---
Biodiesel	Sunlight and CO₂	Euphorbian plants, Copaifera tree etc	Long term research and development required	Lack of a genetic transformation system