• Energy Research

The biorefinery approach for the production of fuels and chemicals is gaining more and more attraction in recent years. The major advantages of biorefineries are the generation of multiple products with complete utilization of biomass with zero waste generation. Moreover the process will be economically viable when it targets low volume high value products in addition to high volume low value products like bioethanol. The present review discuss about the potential of rice straw based biorefinery. Since rice is a major staple food for many Asian countries, the utilization of the rice straw residue for fuel and chemicals would be very economical. The review focuses the availability and the potential of this residue for the production of fuel and other high value chemicals.

A novel ultrasound-assisted alkali pretreatment strategy was developed which could effectively remove lignin and hemicelluloses and improve the sugar yield from chili post harvest residue. Operational parameters that affect the pretreatment efficiency were studied and optimized. Inhibitor analysis of the hydrolyzate revealed that major fermentation inhibitors like furfural, 5-hydroxymethyl furfural as well as organic acids like citric acid, succinic acid and propionic acid were absent. Hence fermentation can be carried out without detoxification of the hydrolyzate. Changes in structural properties of the biomass were studied in relation to the pretreatment process using Scanning Electron Microscopy (SEM) and the changes in chemical composition were also monitored. The biomass pretreated with the optimized novel method could yield 0.428g/g of reducing sugars upon enzymatic hydrolysis. The hydrolyzate obtained by this novel pretreatment strategy was found to be suitable for bioethanol and xylanase production.

The objective of the research was to investigate the effect of biomass loading, acid concentration and pre-treatment time on the yield of sugars obtained after acid pre-treatment and enzymatic hydrolysis of oilseed rape (OSR) straw. The highest concentration of glucose (313.4 ± 7.53 mg g−1 biomass) extracted after hydrolysis was achieved when OSR straw was pre-treated for 90 min; a glucan conversion efficiency of 81%. The highest concentration of sugars extracted immediately after pre-treatment was achieved with a pre-treatment time of 60 min. Pre-treatment energy efficiency in terms of total yield of sugars per MJ of energy consumed was higher when OSR straw was pre-treated for 60 min compared to 90 min even though the conversion of sugar extracted was lower at 60 min.

Abstract Cell immobilisation provides the opportunity to reduce the cost of producing bioethanol from lignocellulosic biomass such as oilseed rape (OSR) straw, in addition to enhancing operational stability. Bioethanol fermentation of OSR straw hydrolysate by free and immobilised Saccharomyces cerevisiae was studied. Cells were either entrapped in alginate beads or Lentikat ® discs or immobilised as a biofilm on spent grains, Leca, or reticulated foam. The overall aims of the research were to compare bioethanol yields produced from free and immobilised systems, and to identify the most suitable immobilisation technique in terms of bioethanol yield and longevity of the immobilised cell system. Cell entrapment in alginate beads and Lentikat ® discs resulted in significantly higher bioethanol yields compared to when cells were free in suspension or immobilised as a biofilm on a support material. The maximum amount of bioethanol produced by cells immobilised in alginate beads and Lentikat ® discs were 169.26 ± 0.24 and 165.13 ± 0.67 g bioethanol kg −1 OSR straw after 3 h and 7 h of fermentation, respectively. Due to the high mechanical stability and bioethanol yield, immobilisation of S. cerevisiae in Lentikat ® discs was considered the most appropriate immobilisation technique for bioethanol production.

Biogas is a combination of methane, CO2, nitrogen, H2S and traces of few other gases. Almost any organic waste can be biologically transformed into biogas and other energy-rich organic compounds through the process of anaerobic digestion (AD) and thus helping in sustainable waste management. Although microbes are involved in each step of AD, knowledge about those microbial consortia is limited due to the lack of phylogenetic and metabolic data of predominantly unculturable microorganisms. However, culture-independent methods like PCR-based ribotyping has been successfully employed to get information about the microbial consortia involved in AD. Microbes identified have been found to belong mainly to the bacterial phyla of Proteobacteria, Chloroflexi, Firmicutes and Bacteroidetes. Among the archaeal population, the majority have been found to be methanogens (mainly unculturable), the remaining being thermophilic microbes. Thus, the AD process as a whole could be controlled by regulating the microbial consortia involved in it. Optimization in the feedstock, pH, temperature and other physical parameters would be beneficial for the microbial growth and viability and thus helpful for biogas production in AD. Besides, the biogas production is also dependent upon the activity of several key genes, ion-specific transporters and enzymes, like genes coding for methyl-CoM reductase, formylmethanofuran transferase, formate dehydrogenase present in the microbes. Fishing for these high-efficiency genes will ultimately increase the biogas production and sustain the production plant.

The objective of the research was to investigate the effect of biomass loading, alkali (NaOH) concentration and pre-treatment time on the yield of glucose obtained following alkaline pre-treatment and enzymatic hydrolysis of oilseed rape (OSR) straw. A maximum glucose yield of (440.6 ± 14.9)g glucose kg(-1) biomass was obtained when OSR straw was pre-treated at a biomass loading of 50 g kg(-1) and an alkali concentration of 0.63 mol dm(-3) NaOH for 30 min. The energy efficiency of glucose extraction (0.39 kg glucose MJ(-1) consumed) was highest when OSR straw was pre-treated at a biomass loading of 50 g kg(-1) and an alkali concentration of 0.63 or 0.75 mol dm(-3) for 30 min. The study demonstrated alkaline pre-treatment of OSR straw is superior to acid pre-treatment in terms of glucose yield and energy efficiency.

Cotton post-harvest residue/cotton stalk (CS) - a major agro-residue in south asian countries was evaluated as a feed stock for bioethanol production. The common thermochemical pretreatment strategies based on dilute acid and alkali and different combinations of biomass hydrolyzing enzymes were evaluated for saccharification of CS biomass. A hydrolytic efficiency of 80% was achieved for alkali treated biomass using cellulase supplemented with beta glucosidase. Recycling of undigested/residual biomass and/or enzyme supported same final sugar concentration as for fresh hydrolytic experiments. Fermentation was carried out using a novel, inhibitor-resistant strain of Saccharomyces cerevisiae where 76% of theoretical maximum efficiency was attained. Material balances were derived for the entire process from biomass pre-processing to hydrolysis.

The aim of the study was to evaluate continuous bioethanol production from oilseed rape (OSR) straw hydrolysate using Saccharomyces cerevisiae cells immobilised in Lentikat® discs. The study evaluated the effect of dilution rate (0.25, 0.50, 0.75 and 1.00 h(-1)), substrate concentration (15, 22, 40 and 60 g L(-1)) and cell loading (0.03, 0.16 and 0.24 g d.c.w.mL(-1) Lentikat®) on bioethanol production. Volumetric productivity was found to increase with increasing substrate concentration from 15 g L(-1) to 60 g L(-1). A maximum volumetric productivity of 12.88 g L(-1)h(-1) was achieved at a substrate concentration of 60 g L(-1) and at a dilution rate of 0.5h(-1). An overall mass balance for bioethanol production was created to determine the energy recovery from bioethanol and concluded that a biorefinery approach might be the most appropriate option for maximising the energy recovery from OSR straw.

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