Akhilesh K. Singh

Progress and Challenges in Microalgal Biodiesel Production.

The last decade has witnessed a tremendous impetus on biofuel research due to the irreversible diminution of fossil fuel reserves for enormous demands of transportation vis-a-vis escalating emissions of green house gasses (GHGs) into the atmosphere. With an imperative need of CO2 reduction and considering the declining status of crude oil, governments in various countries have not only diverted substantial funds for biofuel projects but also have introduced incentives to vendors that produce biofuels. Currently, biodiesel production from microalgal biomass has drawn an immense importance with the potential to exclude high-quality agricultural land use and food safe-keeping issues. Moreover, microalgae can grow in seawater or wastewater and microalgal oil can exceed 50–60% (dry cell weight) as compared with some best agricultural oil crops of only 5–10% oil content. Globally, microalgae are the highest biomass producers and neutral lipid accumulators contending any other terrestrial oil crops. However, there remain many hurdles in each and every step, starting from strain selection and lipid accumulation/yield, algae mass cultivation followed by the downstream processes such as harvesting, drying, oil extraction, and biodiesel conversion (transesterification), and overall, the cost of production. Isolation and screening of oleaginous microalgae is one pivotal important upstream factor which should be addressed according to the need of freshwater or marine algae with a consideration that wild-type indigenous isolate can be the best suited for the laboratory to large scale exploitation. Nowadays, a large number of literature on microalgal biodiesel production are available, but none of those illustrate a detailed step-wise description with the pros and cons of the upstream and downstream processes of biodiesel production from microalgae. Specifically, harvesting and drying constitute more than 50% of the total production costs; however, there are quite a less number of detailed study reports available. In this review, a pragmatic and critical analysis was tried to put forward with the on-going researches on isolation and screening of oleaginous microalgae, microalgal large scale cultivation, biomass harvesting, drying, lipid extraction and finally biodiesel production.

Advances in cyanobacterial polyhydroxyalkanoates production

Polyhydroxyalkanoates (PHAs) have received much attention in the current scenario due to their attractive material properties, namely biodegradability, biocompatibility, thermoplasticity, hydrophobicity, piezoelectricity and stereospecificity. All these properties make them highly competitive for various industrial applications similar to non-degradable conventional plastics. In PHA biosynthesis, PHA synthase acts as a natural catalyst for PHA polymerization process using the (R)-hydroxyacyl-CoA as substrate. Cyanobacteria can accumulate PHAs under photoautotrophic and/or mixotrophic growth conditions with organic substrates such as acetate, glucose, propionate, valerate, and so on. The natural incidence of PHA accumulation by the cyanobacteria is known since 1966. Nevertheless, PHA accumulation in cyanobacteria based on the cell biomass and volumetric productivity is critically lower than the heterotrophic bacteria. Consequently, cyanobacteria are nowadays not considered for commercial production of PHAs. Thus, strain improvements by genetic modification, new cultivation and harvesting techniques, advanced photobioreactor development, efficient and sustainable downstream processes, alternate economical carbon sources and usage of various metabolic inhibitors are suggested for enhancing cyanobacterial PHA accumulation. In addition, identification of transcriptional regulators like RNA polymerase sigma factor (SigE) and a response regulator (Rre37) together with the recent major scientific breakthrough on the existence of complete Krebs cycle in cyanobacteria would be helpful in taking PHA production from cyanobacteria to a new-fangled height in near future.

The path forward for lignocellulose biorefineries: Bottlenecks, solutions, and perspective on commercialization

Lignocellulose biorefinery encompasses process engineering and biotechnology tools for the processing of lignocellulosic biomass for the manufacturing of bio-based products (such as biofuels, bio-chemicals, biomaterials). While, lignocellulose biorefinery offers clear value proposition, success at industrial level has not been vibrant for the commercial production of renewable chemicals and fuels. This is because of high capital and operating expenditures, irregularities in biomass supply chain, technical process immaturity, and scale up challenges. As a result, commercial production of biochemicals and biofuels with right economics is still lagging behind. To hit the market place, efforts are underway by bulk and specialty chemicals producing companies like DSM (Succinic acid, Cellulosic ethanol), Dow-DuPont (1,3-Propanediol, 1,4-Butanediol), Clariant-Global bioenergies-INEOS (bio-isobutene), Braskem (Ethylene, polypropylene), Raizen, Gran-bio and POET-DSM (Cellulosic ethanol), Amyris (Farnesene), and several other potential players. This paper entails the concept of lignocellulose biorefinery, technical challenges for industrialization of renewable fuels and bulk chemicals and future directions.

Biotechnological Advances in Lignocellulosic Ethanol Production

The worldwide increasing environmental issues owing to fossil fuels and their anticipated shortage in near future have fueled the research towards the search and development of alternative fuels from renewable sources. Recently, the biomass-based transport fuels have turn out to be strategic attention for counties with intention to enhance the sustainability in the terms of bioenergy. Interestingly, bioethanol is an oxygenated biofuel with 35% oxygen content, which can decrease the particulate matter and NOx emissions produced from fuel combustion. Therefore, gasoline blended with bioethanol can considerably decrease the petroleum consumption along with greenhouse gases emission. Though nearly all the present biofuel ethanol is produced from edible materials like sugars, starch etc., the lignocellulosic biomass has received considerable interest in recent years. Nevertheless, the transformation efficiency and ethanol yield of the biomass varies significantly mainly owing to the difference in lignocellulosic content. In lignocellulosic biomass, the complex lignocellulosic network of cellulose and hemicellulose with lignin is extremely resistant towards depolymerization. Thus, there still remain some obstacles that are to be addressed to make lignocellulosic biomass-based bioethanol a commercial reality. Further, the unmet need of cost reduction of lignocellulosic biomass-based bioethanol is progressing towards techno-economic improvements of overall transformation process through efficient biomass pretreatment process as well as recombinant genetic engineering for the microbial strain improvement. Overall, this chapter not only focuses on the current exploitation of different biomasses as substrates but also the biotechnological advances in various bioprocesses leading to improved bioethanol production.

Analysis of genetic variability and correlation among traits in exoticgermplasm of pearl millet [Pennisetum glaucum (L.) R. Br.]

The 27 accessions of pearl millet of African origin were studied during kharif 2013 and 2014 in a randomized complete block design in the hot arid climate of Rajasthan. The study was conducted to assess the magnitude of presence of genetic variability and associations among characters namely, grain yield per plant (gm.), number of tillers per plant, plant height (cm), panicle length (cm), panicle diameter (cm), number of leaves per plant, days to 50% flowering and test weight(gm.). The result showed that genetic variability was present among the accessions for all studied characters. The estimated PCV (%) and GCV (%) were high for all characters. The broad sense heritability (%) and genetic advance (% of mean) estimates were also high for all studied characters. The number of tillers per plant, panicle length (cm), panicle diameter (cm) and days to 50% flowering had positive and significant genotypic, phenotypic and environmental correlation coefficients with grain yield per plant. The presence of genetic variability, high heritability and genetic advance and association with grain yield of number of tillers per plant, panicle length (cm), panicle diameter (cm) and days to 50% flowering amenable them for selection and enhancement of grain yield.

Inter-characters associations in pearl millet ( Pennisetum glaucum L.R.Br . ) germplasm in hot-arid climate

The forty six accessions of pearl millet germplasm collected from different places were studied during Kharif 2012 and 2013 in a Randomized Complete Block Design in the hot arid climate of Rajasthan. The study was conducted to assess the magnitude of presence of genetic variability and inter-characters associations of the characters namely, number of tillers per plant, plant height (cm), panicle length (cm), panicle diameter (cm), number of leaves per plant, days to 50 per cent flowering and test weight (cm). The result showed that genetic variability was present among the accessions for all studied characters. The estimated PCV (%) and GCV (%) were moderate to high for all characters. The broad sense heritability (%) and genetic advance (% of mean) estimates were moderate to high for all studied characters. The number of tillers per plant, plant height (cm), panicle length (cm), panicle diameter (cm), number of leaves per plant, days to 50 per cent flowering and test weight (cm) had positive and significant genotypic, phenotypic and environmental correlation co-efficients with grain yield per plant. The presence of genetic variability, high heritability and genetic advance and association with grain yield of all studied characters amenable them for selection and enhancement of grain yield.

Estimation of g x e Interactions in Exotic Germplasm of Pearl Millet ( Pennisetum glaucum L.)

Twenty seven accessions of pearl millet germplasm of African origin along with check HHB 67 were evaluated in eight environments for eight quantitative traits and data were subjected to regression analysis and also analysed to detect the presence of crossover and non-crossover interactions. Seven accessions namely, EC 539227, EC 539241, EC 468904, EC 539254, EC 539259, EC 468900, and EC468896 were identified to be promising based on regression analysis, whereas accessions EC 539299, EC 541536, EC 468904, EC 539227, EC 468898, EC 541540 and EC 539251 were identified as potential ones by using crossover and non-crossover interactions concepts against standard check HHB 67. Of these accessions EC 468904 was identified as high yielding accession having specific adaptability and responsiveness to higher nitrogen regimes both by regression analysis and crossover and non-crossover interactions concept.