Exploring Local Algae Based Biofuels as One of the Plausible Options for Biodiversity Conservation and Climate Change Mitigation

Kalyani Kulkarni1, Mukul Mahabaleshwarkar2 and Nitant Mate3

1Department of Biodiversity, Abasaheb Garware College, Karve Road, Pune–411004, India

2Environmental Scientist, Kirloskar Integrated Technologies Limited, 13/ A, Karve Road, Kothrud, Pune–411038, India

3Head, Technology & Execution, Bioenergy Business, Kirloskar Integrated Technologies Limited, 13/ A, Karve Road, Kothrud, Pune–411038, India

E-mail: 2mukul.mahabaleshwarkar@kirloskar.com/ mmukul@gmail.com

ABSTRACT

Global economy runs on energy. The need for energy is continuously on the rise, because of the increase in industrialization as well as the growing human population. At present the primary sources for energy are fossil fuels, coal, natural gas, hydro and nuclear. Since fossil fuels are no more sustainable and emit more greenhouse gases, there is search for the alternate and reliable sources of energy that are carbon-neutral. For renewable energy sources, particularly biofuels, carbon dioxide emitted through their burning is less than or equal to the atmospheric carbon dioxide consumed during their production and usage.

Marine and freshwater Algae are being explored as source of third generation biofuels. The present study is an example of how local freshwater algae can be used as a potential option for generating Biofuel and can contribute to reducing greenhouse gas emissions. Biogas generation potential of Spirogyra, a green filamentous alga, was evaluated using anaerobic digesters was estimated as 420 l/kg-TS after 17 days of digestion, with about 58% methane content. This is better than that of cattle waste and other unprocessed leafy biomass based substrates. Spirogyra thus can be a source for alternate and sustainable energy. Additional benefits include generation of excellent quality organic fertilizers from the micronutrients rich byproduct, considerable reduction in emissions of SOx, Nox and other greenhouse gases as compared to the fossil fuels, Biodiversity conservation through effective utilization of local algal species and employment generation opportunities.

Keywords: Algae, Biofuel, Climate Change, Replacing Fossil Fuel, Biodiversity Conservation

INTRODUCTION

Global economy runs on energy. The need for energy is continuously on the rise, because of the increase in industrialization as well as the growing human population1. At present the basic sources for energy are fossil fuel, coal, natural gas, hydro and nuclear2. Exhaustive use of fossil fuels is now widely recognized to be unsustainable as the resources are finite and their combustion leads to emission of greenhouse gasses (GHGs)1,2,3. It is estimated that world’s oil and other fossil fuel resources will deplete to a level of it becoming economically unviable by year 20401,4. Thus, alternate and renewable sources of energy that are carbon-neutral (the carbon emitted through the burning of the biofuels/

62 Green India: Strategic Knowledge for Combating Climate Change: Prospects & Challenges

renewable sources is less than or equal to the atmospheric carbon consumed during their production and usage) need to be explored. Biofuels such as, biogas, biodiesel, bio-ethanol, pyrolysis oil, producer gas, etc. are the fuels, that are derived from biomass and provide one such non-exhaustible, recyclable, renewable energy option5. Presently, the biomass sources contribute 14% of global energy and expected to provide 38% of fossil fuel based energy in developing countries6,7 used mainly for cooking (wood, biogas) and power generation (biogas and biodiesel). Biogas can meet the basic need for fuel in rural areas and can be generated using local resources, like organic wastes such as agricultural produce, residue/waste, sugar industry waste, waste from food and pulp industries, dairy waste, poultry waste, animal dung, etc. and different types of biomass such as edible or non-edible oilcakes of different oil seeds, elephant grass, paddy straw etc.

The rise in greenhouse gases (GHGs) in the atmosphere is already affecting the global climate. Under current projections, concentrations of GHGs will continue to increase into the process of global warming8. Many studies have been conducted world-wide to examine environmental impact of biofuels for their emission and observed biofuels can significantly reduce carbon emission as compared to fossil fuels. Since the Sulfur and nitrate contents are very less, the emissions of SOx, NOx and other greenhouse gases is less.

Biodiversity on the earth exists in the form of millions of species of flora and fauna. Global biodiversity is threatened due to rampant urbanization, unsustainable industrialization and overharvesting/overexploitation of natural resources. Biodiversity needs to be conserved for maintaining balance of various ecosystems existing on the Earth and to balance out the adverse impacts of climate change and global warming. Efforts in the form of applying in-situ conservation techniques e.g., National parks, Sanctuaries, Gene pools, etc. and ex-situ conservation techniques e.g. Seed banks, germplasm, herbaria etc. are being made for biodiversity conservation all over the globe. Along with these direct methods of conservation, it is important to promote indirect ways of conservation, sustainable use and equitable sharing of benefits emerging out of biodiversity resources, as nowadays there are frequent interactions taking place between human being and biodiversity9,10. This will promote decentralised democratic systems of governance and institutions of co-management of natural resources leading towards biodiversity conservation.

Algae are lower aquatic plants that are able to perform photosynthesis. They can be found in different shapes, sizes and colors. Algae, based on their habitat type, can be categorized as “fresh water” and “marine” algae. Fresh water algae are found in habitats such as rivers, lakes, streams, ponds, etc11,12

Spirogyra is a green filamentous alga; its long and thin strands are usually present in vast numbers and form a fresh green slimy blanket in the water bodies. Each filament consists of long chain of identical cells. Each cell contains a helical chloroplast, a nucleus, cytoplasm and a vacuole enclosed in a cellulose

Exploring Local Algae Based Biofuels as One of the Plausible Options for Biodiversity 63

cell wall. They contain chlorophyll and perform photosynthesis. Reproduction in Spirogyra is of two types Sexual and Asexual.

Studies in renewable fuels have taken Algae into account, among different bio-feedstock; oil-rich algae can be the most promising and sustainable source for biogas and biodiesel production2,3. Biofuel produced from algae are called as third generation biofuel, having low input high yielding capacity and have advantages over presently available resources13.

The present algal research on biofuels is restricted to most of the marine species and only a few freshwater algal species14. This study throws more light on the sustainable use of local algal resources. It relates to analysis of the potential of select algal species as source of renewable energy. It is directed towards production of Biofuel in the form of biogas from the locally available fresh water algae Spirogyra.

MATERIALS AND METHOD

The algal samples were collected in transparent pet bottles from inland water bodies in and around Pune city (Fig 1). Local algal species are found abundant in all seasons and are easily accessible when needed. Due to the inbuilt capacity to adjust with the local environment, they are more resistant to infections or contaminations as compared to especially cultured exotic species. Thus they can be reliable source of feedstock for the generation of biofuel. Hence, selecting a local algal variety is definitely logical.

Fig. 1: Collection Sites in and around Pune City

64 Green India: Strategic Knowledge for Combating Climate Change: Prospects & Challenges

Among different algal species, Spirogyra was selected for this study because of following reasons: 1) it is available locally in good quantities, 2) it has high growth rate in presence of shallow water and sunlight, 3) it doesn’t require any special conditions for growth, 4) it has high lipid content ranging between 11–21% on dry matter basis and 5) Due to filamentous form, it is easy to harvest compared to other algal species.

DETERMINATION OF BIOGAS POTENTIAL

Biogas consists mainly of methane and carbon dioxide and is produced by anaerobic digestion of organic matter by microorganisms. To decide whether or not any substrate would make enough biogas, some parameters like Total Solids (TS), Volatile Solids (VS), and true density need to be considered. Experimental batch set–up was arranged with three experimental digesters namely Algae I, Algae II, Algae III and one Control. Required ratio of gram-VS of feed / gram-VS of slurry was decided, as it is crucial for deciding the volume of feed and slurry in the digester. Accordingly feed and slurry was added into the digester and headspace of approximately 40 ml was kept in the 120 ml digester. Quantity of feed and slurry was adjusted such that there should be proper digestion of biomass and no acidic condition occurs in the digester. Anaerobic conditions were maintained in the digesters. The digesters were then kept in the incubator at 37 ˚C. For the TS fed, biogas generation (l/g-TS), cumulative biogas generation (l/g-TS) along with methane percentages in the biogas were measured every day for 17days as generation of biogas was seen to be negligible after that.

DETERMINATION OF TS%, VS% AND DENSITY

TS is the percentage of solids, both dissolved and un-dissolved in the total fresh weight of the sample. VS is the percentage, of volatile solids present per unit TS of sample. TS and VS of feed and slurry were determined to know required weight percentage, as both feed and culture are responsible for generation of biogas. If feed with less TS gives more biogas, then that feed is good for biogas generation. Density can be defined as measure of relative heaviness of object with constant volume and is determined as mass per unit volume.

RESULT AND DISCUSSION Algae biomass contains a large percentage of water, which will not amount to any gas generation. The total solids (TS) present in algae would be responsible for generating all the observed biogas.

Figure 2 shows generation of biogas (l/g-TS). The four lines represent daily biogas generation in three experimental and one control batch digesters which indicates similar pattern of digestion of algal biomass. The peak observed on day 3 is due to hydrolysis of more quantity of high molecular weight polymeric compounds of algae in to its monomers. Due to hydrolysis the complex organic molecules are broken down in to simple sugars, amino acids and fatty acids.

Exploring Local Algae Based Biofuels as One of the Plausible Options for Biodiversity 65

Thus, gradual decrease in gas generation indicates that most of the easily digestible solids have been used up by acidogens and methanogens to produce biogas in the first 8 days. Subsequent biogas generation was probably from slowly digesting cellulosic mass. Till day 8 cumulative 71% of the total gas was generated, after which the daily gas generation kept reducing till the end of the experiment. The negligible daily gas quantity at the end signifies near complete recovery of the biogas potential from the input algal biomass.

Fig. 2: Daily Gas Generation from Algal Biomass

Fig. 3: Cumulative Biogas Generation/ g-TS of Algal Biomass

Figure 3 shows cumulative biogas generation/g-TS of feed. The lines represent three experimental showing similar trend in case for cumulative gas

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66 Green India: Strategic Knowledge for Combating Climate Change: Prospects & Challenges

generation. Since all three experimental digesters have similar feed: culture ratio (0.5:1), and average TS of the biomass is 11%, the biogas generation would be comparable. Average cumulative gas generated from algal feed per g of TS is 0.420 l, which is more than biogas generation potentials of cattle waste (0.360 l/g-TS), paddy straw (0.365 l/g-TS), wheat straw (0.249 l/g-TS), Napier grass (0.260 l/g-TS)15and is about half the biogas generation potential of pure starch and sugar (0.800 l/g-TS)16. Spirogyra has 11–21 % lipids, 33–64 % carbohydrates out of which 19 % is cellulose17. The biogas generated from Spirogyra is mainly from most of the carbohydrates and some of the lipids.

Fig. 4: Daily Generation of Methane (%)

Figure4 shows percent generation of methane (CH4) from algal feed. The lines indicate daily generation of methane (%) in three experimental batch digesters. In 17 days 58% of average methane generation was observed, which matches average methane percentage in biogas.

CONCLUSION

TS percentage of the feed is responsible for generation of biogas. Average of 420 l/kg-TS biogas with an average methane content of 58 % was generated in 17 days. The biogas generation potential of Spirogyra is better than that of all the leafy biomass based biogas substrates. Also the average methane percentage in the biogas generated from Spirogyra was observed to be comparable with that of other substrates. Thus Spirogyra as feed for biogas generation is of better quality as compared to the other leafy biomass based substrates can be used as an alternative to burning fossil fuel for cooking.

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Exploring Local Algae Based Biofuels as One of the Plausible Options for Biodiversity 67

Fig. 5: Biomass Potential Of different Biomass (l/g-TS)

BYPRODUCTS

Biogas generation process from algal feed produces by products, which have good commercial value. The effluent (digestate) coming out of the biogas digester is rich in micronutrients and can be converted to excellent quality organic fertilizers by adding complementary minerals.

COMMERCIAL USE OF BIODIVERSITY AND BIODIVERSITY CONSERVATION

Algal species are used commercially as organic manure, in pharmaceuticals, as cattle feed18 etc. Production of different commercial algal products can help in utilization of algal biodiversity effectively for generation of commercially valuable products. Different algal species can be potential source of renewable energy and can be used commercially for various purposes. Therefore different algal species need to be studied and cultured. Locally available species are easily accessible and can be cultivated on large scale in controlled conditions. This will help in conservation of locally available algal species.

EMPLOYMENT GENERATION

A solution can be called sustainable if it is environmentally friendly, economically viable, technically feasible and socially acceptable. The social acceptance is highly dependent on the economic benefits to the society and social taboo. Employment generation opportunities through such solutions are possible as the human resource, which India has in ample, will be required for conducting the various activities throughout the operating life cycle of the solution. India is facing serious issues related to unemployment and increasing population below the poverty line and decreasing employment opportunities due to technical advancements. Implementation of algae based biofuel generation projects at local levels in decentralized fashion will open the employment opportunities to the native people. This, in a way, will also help in

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68 Green India: Strategic Knowledge for Combating Climate Change: Prospects & Challenges

improving the local economy, the overall lifestyle, standard of living and health which are part of the global millennium development goals19.

ACKNOWLEDGEMENTS

We would like to express our gratitude to authorities of Kirloskar Integrated Technologies Pvt. Ltd. (KITL) for providing infrastructure support required during this research. We also would like to thank Ms. Shailaja Danve and Ms. Maitreyi Pandit for their help in laboratory experiments.

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