editorial renewable energy and alternative fuel technologies

EditorialRenewable Energy and Alternative Fuel Technologies

Meisam Tabatabaei,1,2 Keikhosro Karimi,3 Rajeev Kumar,4 and Ilona Sárvári Horváth5

1Biofuel Research Team (BRTeam), Karaj 31438-44693, Iran2Microbial Biotechnology and Biosafety Department, Agricultural Biotechnology Research Institute of Iran, Karaj 31359-33151, Iran3Department of Chemical Engineering, Isfahan University of Technology, Isfahan 84156-83111, Iran4Center for Environmental Research and Technology (CE-CERT), Bourns College of Engineering, University of California, Riverside(UCR), Riverside, CA 92507, USA5Swedish Centre for Resource Recovery, University of Boras, 501 90 Boras, Sweden

Correspondence should be addressed to Meisam Tabatabaei; meisam [email protected] and Keikhosro Karimi; [email protected]

Received 4 December 2014; Accepted 4 December 2014

Copyright © 2015 Meisam Tabatabaei et al. This is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properlycited.

In recent years, biofuels have drawn considerable attentionas clean and renewable source of energy. The most attractivetypes of biofuels are biogas, bioethanol, biodiesel, and biobu-tanol. Some of these biofuels are likely to play roles in theproduction of clean energy carriers as promising alternativesto fossil fuels and bring about environmental benefits glob-ally. Biogas that primarily contains biomethane is producedthrough anaerobic digestion of organic wastes. Among thebiofuels production processes, biogas process seems to bethe easiest to conduct as it does not need sterilization, canbe produced in simple reactors at moderate conditions usinga natural consortium of microorganisms available in naturesuch as manure, and does not need a complicated separationand purification process. However, it is more complicatedthan it appears at first glance specially when high biogasyield is targeted. In fact, the microbiology and biochemistryof biogas production are the most complicated systemscompared to those of the other biofuels, as four differentprocesses, that is, hydrolysis, acidogenesis, acetogenesis, andmethanogenesis are performed parallel where different typesof microbes as a consortium work together. Furthermore,the substrates used for biogas production are a mixture ofdifferent components with different degradation properties.Main feedstocks are solid wastes, for example, agricultural,municipal, and food industrial wastes, and wastewater, forexample, industrial and municipal wastewater. Technologiesfor biogas from municipal wastewater sludge are well devel-oped; however, the recently increasing oil prices, unclearfuture of fossil fuels availability, and environmental impactshave led to significant interest in biogas from other resources

especially from industrial and solid wastes. A number ofpotential substrates, for example, municipal solid wasteand manure mixed with bedding materials, have a highpotential; however, they contain lignocelluloses that are noteasily bioconvertible. Therefore, a number of recent researchactivities are focused on the improvement of biogas fromrecalcitrant substrates, for example, lignocelluloses, andhigh-rate systems for biogas production.

Ethanol, the leading liquid biofuel, is widely used fortransportation. Currently, sugarcane in Brazil and starchymaterials, for example, corn in USA and wheat in Europe,are the main feedstocks (referred to as 1st generation), whilelignocellulosic materials in the last decade (2nd generationor lignoethanol) and more recently algal biomass (3rd gener-ation) are suggested as the rawmaterials. Lignoethanol seemsto be the most promising type for the near future as thesefeedstocks are abundant and available at low prices. However,lignocelluloses are recalcitrant in nature and their processingis more complicated; the process needs a pretreatment stepwhich is still challenging and consumption of hydrolyticenzymes should be minimized. Both of these problems arethe subject of a high number of recent investigations. All inall, lignoethanol is more expensive than the 1st generationethanol and process integration and biorefinery concepts areproposed to make the 2nd generation ethanol competitive.

Biodiesel is a promising alternative to diesel fuel, as ithas a number of advantages including high cetane number,flash point, and inherent lubricity, creates less exhaust emis-sions, and contains no polluting chemicals like sulfur, aswell as being renewable, biodegradable, and compatible to

Hindawi Publishing CorporationBioMed Research InternationalVolume 2015, Article ID 245935, 2 pageshttp://dx.doi.org/10.1155/2015/245935

2 BioMed Research International

the existing fuel distribution infrastructure. The process ofbiodiesel production at industrial scale is developed ratherwell and themost important challenging and limiting issue inbiodiesel production is feedstock supply. In fact, the availablefeedstock is limited and accounts for over 70% of the totalbiodiesel production cost. “Crime against humanity” term israised when edible sources started to be used. Therefore, thefuture sustainability of this industry is heavily dependent onnonedible feedstock supply and achieving more innovative,integrated, and efficient processes.

Biobutanol is considered more advanced compared tothe other existing biofuels. Acetone production via acetone-butanol-ethanol (ABE) fermentation is an old process widelyestablished during the First World War for military purposesin the Union of Soviet Socialist Republics, England, Canada,USA, Japan, China, and South Africa. Recently, ABE processattracted a high interest for the production of butanol as arenewable fuel. Main feedstocks used in the old processeswere sugar-based substrates such as molasses and starchymaterials such as wheat. Recently, low cost lignocellulosicwastes are suggested for ABE fermentation (lignobutanol);however, it suffers from the same problems as in lignoethanol.Furthermore,microorganisms used for biobutanol, for exam-ple, Clostridium acetobutylicum and C. beijerinckii, are moresensitive to inhibitors than the microorganisms used forbiogas and ethanol production. Generally, the process ofbiobutanol production is more complicated than those ofethanol and biogas, as the microorganisms are strictly anaer-obic; butanol-producing bacteria are severely inhibited bythe process products especially butanol, and separation ofproducts is more energy demanding and complicated. Com-pared to lignoethanol, lignobutanol is in its preliminary stageof research and a number of problems should be addressedin laboratory and pilot scales before the process becomescompetitive to other biofuels at commercial scale.

Meisam TabatabaeiKeikhosro Karimi

Rajeev KumarIlona Sarvari Horvath

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