Biofuel Production Technologies: Critical Analysis for Sustainability

The term biofuels refer mainly to fuels derived from biomass, which can be considered as plants and organic residues. In this chapter attention will be focused on liquid biofuels that can be used mainly for transportation. As reported in the IEA Technology Road Map for biofuels, presented in 2011, they can be divided in two main categories, based on the type of technologies used: conventional biofuels (sugar- and starch-based ethanol, conventional biodiesel, biogas) and advanced biofuels (cellulosic ethanol, hydrotreated vegetable oil, biomass-to-liquids, biosynthetic syngas, etc.). The production of these biofuels is object of big research efforts directed through process intensification and increase of the efficiency of biomass conversion into an energy vector. For this reason this chapter takes into account the production of first-generation biodiesel, first-generation bioethanol, second-generation biodiesel, second-generation bioethanol, and hydrotreated vegetable oils focusing on their market and the most importantly production techniques.

There is a wide variety of biomass types, implicating in biofuels and conversion process differences. Lignocellulosic biomass, for instance, can be converted into biofuels by biotechnology route. There are first-, second-, third-, and fourth-generation biofuels coming from different kinds of biomass and process. Besides biofuels, the carbohydrate and lignin of these biomasses can be used to generate other products of aggregated value. The biomasses have properties that resist the conversion processes, such as crystallinity and lignin contents. These difficulties are fought with genetic engineering and pretreatments to alter the material structure, decreasing the heterogeneity and recalcitrance, improving enzymatic hydrolysis and consequently the conversion into biofuels.

Energy is a much crucial necessity for daily errands, either household or industrial. We use it as fuel (transportation or industrial commodity), to provide power, heat, electricity, etc., and we can’t imagine life without it. Several kinds of fuels are available in the market, mainly non-renewables – fossil based (coal, crude oil, etc.). However, due to awareness about long-term issues related to use of fossil fuels, several other types of renewable fuels are gaining much attention. Biogas, biofuels (bioethanol, biodiesel), and biohydrogen are some of the examples for such renewables with very high future potential. However, even with those recent developments, rural areas in some of the developing countries are still using agricultural remains, cow dung, etc., for cooking and heating purposes. This kind of crude practice significantly raises environmental, economic, and public health-related worries. To achieve a worldwide sustainable progress in both developed and developing countries, clean and affordable energy could be offered by using the existing biomass resources (crop residues, agro-industrial, animal, and other type of wastes) to produce a cleaner, more efficient, and reliable energy, such as biogas. Unlike other types of renewable biofuels, biogas production is a natural non-energy intensive process, and the raw materials are mostly renewable resource and wastes – thus serving both purposes, bioremediation and energy generation. Biogas is a blend of gases, mainly methane and carbon dioxide. Over the years, several biogas plant designs are available, which are compiled in present chapter along with its advantages and disadvantages. At present several countries are already utilizing biogas for various household and industrial applications. The main applications are generating electricity, cooking, heating, and using as a fuel for transportation. The ease of operation, maintenance, and easy availability of substrate – waste materials – are some of the key selling points for biogas to be an effective and common energy tool in the near future.

Combustion of nonrenewable energy sources brings about emission of greenhouse gases which lead to global warming. A large number of renewable energy sources are available as an alternative for mitigation of climate change, among which biogas seems to be more popular and attractive option. Biogas is presently still typically used for heating and electricity generation, but in the future, it may find its way as vehicle fuel. Biogas production technology has potential to utilize a large number and variety of lignocellulosic biomass such as vegetable wastes, crop residues, food waste, cattle dung, and other organic fractions. Anaerobic degradation of waste to yield biogas is a widely adopted cost-effective strategy for generation of renewable energy. In addition to energy generation, biogas technology provides additional benefits, such as reduction of odor, improved sanitation, and removal of organic waste, thereby solving a majority of modern-day problems. The slurry left after biogas production can be utilized as manure and thereby aids in nutrient recycling to the soil. Besides a large number of applications, full potential of biogas technology cannot be harnessed due to various limitations associated with it. A large number of technological improvements are done during recent years to increase conversion rates of biomass to biogas. The present article provides an insight regarding recent research for sustainable biogas production.

Biogas is one of the best future alternatives against depleting fossil fuel. Current Indian production of biogas is very low. There are many challenges for BioCNG production which is suitable for vehicle use but needs to adapt various technologies to enhance the content of biomethane. 

Therefore, in current article, technological improvement in Biogas production intended for high production has been discussed in detail.

For use in vehicle, enhanced methane is required. Current article had focused on concise presentation of accumulated knowledge in current past. Bio-CNG can be produced from various biomass biowaste, kitchen waste, algae, and other biowastes which may be a very good option for Bio-CNG production. We have discussed socioeconomic challenges, suitable sources, barrier in production of biogas, and biochemical steps in production of biogas in normal verses reactor conditions, and also application of nanotechnology for green energy applications have been discussed.

A stoichiometric analysis of biogas production by anaerobic digestion from cassava wastewater, wheat bran, and sewage sludge is proposed. A wide range of methods are available to study stoichiometry of biochemical reactions. This work reported elemental balances method to solve stoichiometric coefficients in biogas production from cassava wastewater, wheat bran, and sewage sludge. The method could be employed for various substrates for biogas production and for other biochemical reactions.

Bioethanol is a major renewable biofuel obtained from different waste biomass. It can potentially substitute the depleting and pollution-causing fossil fuels. It can endow with energy security along with environmental protection over fossil fuels. Biofuels can be classified into four different generations (G), i.e., first generation (1G), second generation (2G), third generation (3G), and fourth generation (4G) based on the groups of feedstocks used. Bioethanol can be produced from all groups of feedstocks; therefore, ethanol obtained from respective group can be named after that generation, i.e., 1G-, 2G-, 3G-, and 4G-based bioethanol. Different microorganisms which can efficiently convert waste biomass into bioethanol are studied, and several biotechnological techniques have been applied for enhancing the production. Similarly, different pretreatment technologies, fermentation processes, and experimental design have been implemented for maximally utilizing the waste and converting it to bioethanol. There are several factors which affect various steps of bioethanol production which affect the final ethanol yield. Therefore, this chapter gives an insight onto current status measurements of 1G, 2G, 3G, and 4G bioethanol production with a focus on using different feedstock and associated technologies, role of microorganisms, factors affecting overall bioethanol production, and current global scenario along with limitations and future prospects.

The present age has seen technological development at a large scale and has imposed tremendous pressure on the natural resources. The usage of fossil fuel has resulted in the release of greenhouse gases, thereby promoting global warming and increased environmental concern among the researchers. Therefore, the quest to find “clean energy” has become the chief concern of the environmentalist. In order to address the issue, third-generation biofuel involving microalgae has been regarded as one of the most effective biological sources as it only requires sunlight, carbon dioxide, and nutrition for its growth. The biofuel derived from the living organism has numerous advantages as it effectively decreases the concentration of emitted greenhouse gases. The microalgae have numerous applications and can be effectively used in biofuels, cosmetics, and pharmaceuticals and as human and animal nutritional sources. Thus, the present chapter would focus on microalgae production processes, advantages and disadvantages of natural and artificial cultivation system, various harvesting techniques followed by its application in various sectors, and lastly the limitations and its future prospects.

Biogas, an ultimate renewable energy, is of enormous demand currently, due to increased fuel price and its fluctuations with expansive pollution emission. Biogas is environmentally feasible and viable. Biomethane production is of high impact, and hence the present chapter is concentrated on various biogas upgradation technologies conjugated with carbon dioxide and hydrogen sulphide removal strategies. The upgrading methods such as absorption, adsorption, membrane separation, biological methods, cryogenic technology, hybrid methods, supersonic separation, industrial lung, in situ methane enrichment and chemical dehydrogenation are discussed. High methane purity with minimized methane loss is the key for an effective upgradation method. A comprehensive study of comparison between various biogas upgradation technologies is analysed, showcasing the advantages and disadvantages too. It is concluded that the recently innovated technologies have wide potential advantages than the conventional biogas upgrading technologies. Although innovated technologies are so far better, detailed analysis, research and development is required for acquiring a technology which is economically, environmentally, technologically, operationally and socially feasible and acceptable.

Many industries including fermentation, pulp and paper industry, brewing sector, fermentation, food and animal feed industry, and detergent and textile use cellulases due to its environment benign and sustainable process. Academic and industrial researches are being done and still ongoing on cellulases due to its enormous industrial application and make these processes green. In this article, extensive review is performed on the use of cellulases in the industrial sector in both crude and pure form. It has been observed that crude cellulases are preferred in the industrial sector due to its low cost and stimulate the process using impurities present in enzymes. Pure cellulases are mainly used in laboratories and are case specific as they are costly to use in industries.

The biotechnological production of enzymes from microorganisms was proved to generate enormous wealth that influences significant sectors of the world’s economy. Among the microbial enzymes, the potentiality of cellulases in different manufactories including food, paper, biofuel, animal feed, drug, brewery, textile, agriculture and recycling of waste materials has been the compelling factor for the intense limelight on cellulases for the past several decades. Extensive studies were carried out on aerobic fungi producing cellulases and are considered as the leading workhorses in industrial processes. The enzyme production usually depends on distinct governing parameters essentially inoculum size, pH value, temperature, growth, time, aeration, inducers and medium supplements. Therefore, choosing optimum pivotal factors that throw impact on biomass of various microorganisms and build-up of the target product becomes the preliminary criteria for any profitable recovery process. Often the optimisation of multifarious criterions is a laborious and tedious chore. Hence, this chapter highlights the diverse physical and chemical parameters that immensely influence fungal cellulase production.

Pyrolysis is used to produce bio-char, bio-oil and syngas from industrial residues through thermochemical processing route. Pyrolysis decomposes biomass at an elevated temperature in an inert atmosphere. The aim of this study is to develop a model and evaluate activation energy for pyrolysis of teak sawdust. Teak sawdust was pyrolysed at four different temperatures from 300 to 600 °C. The mathematical model was developed for pyrolysis of teak sawdust. Kinetic constants were calculated by fitting the data from pyrolysis experiments to the model. Activation energy was determined from Arrhenius equation which related kinetic constant and temperature. The results reveal that pyrolysis of waste biomass, teak sawdust, could be the effective thermochemical route for bioenergy.