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The rapidly depleting fossil fuel reserves with rising greenhouse gas levels (GHGs) in the atmosphere necessitate exploring alternate sustainable energy options. Biofuels from microalgae are emerging as a viable renewable energy resource owing to their inherent characteristics of higher biomass and lipid yield per hectare compared to other terrestrial bioenergy feedstocks. In this context, the present communication highlights the prospects of microalgal biofuel and other value-added products produced in a decentralized microalgal biorefinery in the flood plains (gazani lands) of the west coast of India. The spatial extent of potential sites for diatom cultivation estimated in three districts along the Indian west coast was 1940 ha. The opportunities for establishing biorefineries using diatoms as renewable bioenergy feedstocks were investigated through species prioritization, seasonal availability, tolerance, and biochemical composition analyses. Nitzschia and Amphora sp. were prioritized for lab-scale productivity studies based on their tolerance and macromolecular composition. When cultivated in a prototype biofilms-based bioreactor designed using gravel stones as substrates, Amphora sp. Yielded 16 times more productivity (0.56 g L−1) than conventional shake flask cultures. Design of a diatom biorefinery and its mass budgeting considering 100 kg dry biomass yielded ∼15–24 kg of biodiesel. Techno-economic assessment of biodiesel with value-added products of glycerol, biogas, and biofertilizer demonstrated a biodiesel production cost of 30.08–59.52 INR/kg of biodiesel. Harvesting cost in a hybrid mode using mechanized scrubbers and manual labour was estimated as 20 INR/kg of biomass. [Display omitted] • Evaluate the potential of diatoms as a source of biofuel with value-added products. • Biochemical composition and feedstock availability assessment across seasons. • Design and implementation of prototype algal reactor. • Economic feasibility assessment and mass budgeting of the diatom biorefinery. • Promising scope for a diatom biorefinery along the Indian central west coast. [ABSTRACT FROM AUTHOR]

Abstract: Rapidly depleting stocks of fossil fuels and increasing greenhouse gas (GHG) emissions have necessitated the exploration of cost effective sustainable energy sources focussing on biofuels through algae. Abundant wastewaters generated in urban localities every day provide the nourishment to nurture algae for biofuel generation. The present communication focuses on the lipid prospects of algae grown in wastewater systems. Euglena sp., Spirogyra sp. and Phormidium sp. were collected from selected locations of sewage fed urban lakes and sewage treatment plants of Bangalore and Mysore. The total lipid content of Euglena sp. was higher (24.6%) compared to Spirogyra sp. (18.4%) followed by Phormidium sp. (8.8%) and their annual lipid yield potential was 6.52, 1.94 and 2.856t/ha/year, respectively. These species showed higher content of fatty acids (palmitate, stearate followed by oleic and linoleic acids) with the desirable biofuel properties. [Copyright &y& Elsevier]

Burgeoning dependence on fossil fuels for transport and industrial sectors has been posing challenges such as depletion of fossil fuel reserves, enhanced greenhouse gas (GHG) footprint, with the imminent changes in the climate, etc. This has necessitated an exploration of sustainable, eco-friendly and carbon neutral energy alternatives. Recent studies on biofuels indicate that algal biomass, particularly from marine macroalgae (seaweeds) have the potential to supplement oil fuel. Marine macroalgae are fast growing and carbohydrate rich biomass having advantage over other biofuel feedstock in terms of land dependence, freshwater requirements, not competing with food crops, which were the inherent drawback of the first- and second-generation feedstock. The present communication reviews the macroalgal feedstock availability, screening and selection of viable feedstock based on the biochemical composition, process involved, scope and opportunities in bioethanol production as well as technology interventions. The prospect of bioethanol production from algal feedstock of Central West Coast of India has been evaluated taking into account challenges (feedstock sustenance, technical feasibility, economic viability) in order to achieve energy sustainability. The green algae exhibited growth during all seasons and highest total carbohydrate was recorded from green seaweed Ulva lactuca (62.15 ± 12.8%). Elemental (CHN) analyses of seaweed samples indicate 25.31–37.95% of carbon, 4.52–6.48% hydrogen and 1.88–4.36% Nitrogen. Highest carbon, hydrogen and nitrogen content were recorded respectively from G.pusillum (C: 37.95%), G.pusillum (H: 6.48%) and E.intestinalis (N: 4.36%). Green seaweeds are rich in cellulose content (>10%) compared to other seaweeds (2–10%). Higher cellulose content was estimated in U.lactuca (14.03 ± 0.14%), followed by E.intestinalis (12.10 ± 0.53%) and C.media (10.53 ± 0.17%). Cellulose is a glucan present in green seaweeds, which can easily be hydrolysed through enzyme and subsequently fermented to produce bioethanol. Lower sugar removal in acid hydrolysate neutralization process (Na 2 CO 3) was recorded in U.lactuca (39.8%) and E.intestinalis (14.7%). Highest ethanol yield of 1.63 g and 0.49 g achieving 25.8% and 77.4% efficiency in SHF (Separate Hydrolysis and Fermentation) and SSF (Simultaneous Saccharification and Fermentation) process respectively was recorded for green alga E. intestinalis. Image 1 • Reviews the macroalgal feedstock availability, screening of viable feedstock based on the biochemical composition and process. • Scope and opportunities in bioethanol production as well as technology interventions. • Evaluated algal bioethanol prospects considering feedstock sustenance, technical feasibility, economic viability with energy sustainability. • Prioritization of potential macroalgal feedstock for bioethanol production based on biochemical composition. • The green algae exhibited growth in all the season and highest total carbohydrate in Ulva lactuca (62.15 ± 12.8%). • Highest ethanol yield of 1.63 g and 0.49 g achieving 25.8% and 77.4% efficiency in SHF and SSF process respectively was recorded for green alga E. intestinalis. • Potential sites identified in estuary for large scale algal cultivation. [ABSTRACT FROM AUTHOR]