Elsevier

Applied Energy

Volume 88, Issue 10, October 2011, Pages 3307-3312
Applied Energy

Microalgae Chlorella as a potential bio-energy feedstock

https://doi.org/10.1016/j.apenergy.2010.11.026Get rights and content

Abstract

Microalgae are promising biomass species owing to their fast growth rate and high CO2 fixation ability as compared to terrestrial plants. Microalgae have long been recognized as potentially good source for biofuel production because of their high oil content and rapid biomass production. In this study Chlorella sp. MP-1 biomass was examined for its physical and chemical characteristics using Bomb calorimeter, TGDTA, CHN and FTIR. The proximate composition was calculated using standard ASTM methodology. Chlorella sp. MP-1 biomass shows low ash (5.93%), whereas high energy (18.59 MJ/kg), carbohydrate (19.46%), and lipid (28.82%) content. The algal de-oiled cake was characterized by FTIR spectroscopy and thermogravimetric study at 10 °C/min and 30 °C/min to investigate its feasibility for thermo-chemical conversion. The present investigation suggests that within the realm of biomass energy technologies the algal biomass can be used as feedstock for bio and thermo-chemical whereas the de-oiled cake for thermo-chemical conversion thereby serving the demand of second generation biofuels.

Introduction

As conventional energy sources across the globe are fast depleting, unless the renewable and non-conventional energy sources are tapped, coupled with prudent use and management of energy, humanity is bound to engender a horrific specter of a global energy vacuum. The quest for renewable energy has geared up and one of the facets with great potential for satisfying mankind’s primary energy demand is energy derived from biomass. The present century has witnessed major emphasis on the use of biomass as an alternative to fossil fuels due to its renewable nature and reduced CO2 emissions. Biomass energy sources are amongst the most promising, most hyped and most heavily subsidized renewable energy sources. Biomass can be sustainable, environmentally benign and economically sound. It can provide heat, power and transportation fuels in an environmentally friendly manner, by reducing green house gas emissions and thus can aid in achieving renewable energy targets.

A major insight into the search operation for new sources of biomass energy can be offered by microalgae. The generic term microalgae refer to a large group of very diverse photosynthetic micro-organisms of microscopic dimensions. They are sunlight driven oil factories which convert carbon dioxide into potential biofuels, feeds, foods and high value bioactives [1], [2], [3], [4], [5], [6], [7], [8], [9]. Algae are the most efficient biological producer of oil on the planet and a versatile biomass source and may soon be one of the Earths most important renewable fuel crops [10]. Microalgae are a major natural source for an enormous array of valuable compounds, including a diversity of pigments, for which these photosynthetic micro-organisms represent an almost exclusive biological resource [11]. The potential of microalgae as the most efficient primary producer of biomass still requires comprehensive understanding, but there is little doubt that they will eventually become one of the most important renewable energy sources. The use of microalgae as bio-energy feedstock seems to be promising because:

  • (1)

    Biomass doubling times in microalgae during exponential growth are commonly as short as 3.5 h [13].

  • (2)

    Due to their simple cellular structure, algae have higher rates of biomass and oil production than conventional crops [12]. Oil content in microalgae can exceed 80% by weight of dry biomass [13].

  • (3)

    Their lipid content could be adjusted through altering growth media composition [14].

  • (4)

    Salty or waste water can be used for the culture of microalgae [15].

  • (5)

    Can be harvested batch-wise nearly all-year-around providing a reliable and continuous supply of oil [15].

  • (6)

    Atmospheric carbon dioxide is the source of carbon for the growth of microalgae [15].

  • (7)

    Depending on species microalgae produce many kinds of lipids, hydrocarbons and other complex oils [5], [16], [17].

  • (8)

    Algae can produce 30–100 times more energy per hectare as compared to terrestrial crops [18].

  • (9)

    The production of biofuels from algae can be coupled with flue gas CO2 mitigation, waste water treatment and production of high value chemicals [18].

The potential value of any biomass depends on the chemical and physical properties of molecules from which it is made. This work is an endeavor to study the biomass properties of Chlorella spp. as several characteristics affect the performance of biomass fuel including the calorific value, moisture content and physico-chemical properties and to evaluate the potential of the above as feedstock for the production of biofuel basing on their chemical and physical characteristics. The study also investigates the feasibility of algal de-oiled cake for thermo-chemical conversion.

Section snippets

Description of the species

Chlorella Beijerinck (Gr. Chloros, green; ella, diminutive). The taxonomic position of Chlorella is depicted in Table 1. Chlorella is a single celled, spherical non-motile green alga 2.0–10.0 μm in diameter. Chlorella occurs in both fresh and marine water. Some call Chlorella ubiquitous since it occurs in various different habitats. They are generally found in fresh water of ponds and ditches, in moist soil or other damp situations such as the surface of tree trunks, water pots and damp walls.

Micro-organism and growth medium

Chlorella sp. MP-1 isolated from water samples collected from Lake Joysagar, one of the largest manmade lake, Sibsagar, Assam, India (26°57′12″N and 94°37′34″E) was used in this study. Stock cultures of Chlorella sp. MP-1 were maintained routinely on both liquid and agar slants of BG-11 media [24] by regular sub-culturing at 15 days interval. The species under investigation was also cultured in BBM [25], modified Chu-13 and [26] and Basal [24] media to estimate the biomass yield in the

Results and discussions

The successful implementation of algal biomass as a potential bio-energy feedstock is largely governed by the quantum of producible biomass. Therefore enhancement of the growth rate of algae in terms of biomass productivity is one of the most important parameters. The growth of Chlorella sp. MP-1 was tested in four different culture media namely, BG-11, Basal, BBM and modified Chu-13 media. Among all the tested media the highest biomass yield of 824 mg/l was obtained in BG-11 media. The study

Conclusion

Microalgae Chlorella sp. MP-1 exhibits several important attributes for futuristic research on renewable energy. With simple and inexpensive nutrient regime to culture, faster growth rate as compared to terrestrial energy crops, high biomass productivity, attractive biochemical profile and good energy content (18.59 MJ/kg) Chlorella sp. MP-1 offers strong candidature as a bioenergy source. The robust nature of pyrolysis technology can be efficiently applied to algal de-oiled cakes for the

Acknowledgements

The first author would like to offer his sincere thanks to the ONGC, Jorhat, India for providing fund in the form of a fellowship project. The authors are also thankful to Dr. J.R. Chetia and S. Banerjee for TGA analysis.

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