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Introduction
Rio Earth Summit in 1992 witnessed the beginning of the international political responses and adoption of the UN Framework on Climate Change (UNFCCC), which aimed at stabilising atmospheric concentrations of greenhouse gases (GHGs) to avoid dangerous anthropogenic interference with the climate system. Recent conference COP21 (http://www.cop21paris.org) unanimously agreed to restrict the increase in the global average temperature to well below 2°C above pre-industrial levels and also make efforts to limit the temperature increase to 1.5°C by reducing the dependence on fossil fuels and cutting the greenhouse gas emissions. This has given impetus to the exploration of viable renewable energy alternatives to meet the energy demand of the burgeoning population. Alternative sustainable energy sources are wind solar, geothermal, hydroelectric, biomass and biofuel (Ghadiryanfar et.al,2016).
Earlier attempts in this regard were the manufacture of biodiesel and pure plant oil derived from sugarcane, corn, soybean, potato, wheat or sugar beet (first generation biofuel), which proved to be unsustainable due to the competition with human food resources. This conflict, led to new attempts on biofuel derived from lingo-cellulosic biomass (second generation biofuel). This involved direct and indirect land use changes with the energy crop cultivation inducing a significantly high carbon debt and higher water consumption (Dominguez-Faus. et.al, 2009). Conflict with land for cultivation of biofuel feedstock, led to the exploration of viable alternatives focusing on algal biofuels (third generation biofuels).
Biomass
Productivity dry g/(m2·year)]
Lignocellulosic biomass
Switchgrass
560–2,240
Corn stover
180–790
Eucalyptus
1,000–2,000
Poplar
300–612.5
Willow
46–2,700
Seaweeds
Green seaweeds
7,100
Brown seaweeds
3,300–11,300
Red seaweeds
Sources: Yanagisawa, et al 2011; Ramachandra et al, 2009
Algal feedstock being carbon neutral has proved to be a very promising renewable resource for sustainable energy production. Algae fixes the greenhouse gas (CO2) and have higher photosynthetic efficiency (6-8%) compared to any terrestrial biomass (1.8-2.2%) (Ramachandra et al., 2009; Aresta, 2005; FAO,1997). Also, algae feedstock can be grown in fresh as well as marine waters which reduces the need for higher water consumption. Micro algae grown in marine and freshwater ecosystems and macro algae grown in estuaries have proved to be beneficial feedstock for biofuel production. Microalgae grown in marine ecosystem (with higher salinity and silica) accumulate lipid, while macro-algae, which are multicellular with plant like characteristics are rich in carbohydrate and net energy (net energy of 11,000 MJ/t dry algae; Aitken et al.,2014 ) and are aptly suited for bioethanol conversion (Jin et al.,2013).
Macro-algae or seaweeds have higher potential to produce sustainable bioenergy and biomaterials and do not require land or freshwater for their cultivation. (Lobban et.al., 1985). Macro-algae are currently used for hydrocolloids, fertilizers and to some extent as animal feed (Bixler and Prose, 2011; McHugh,2003). Despite all these environmental and economic merits of macroalgae, challenges are experienced during extraction of biofuel as macro-algae have unique carbohydrate architecture, distinctively different from terrestrial biomass (Roseijadi et al., 2010; sze, 1993). Though macro-algae are ideally suited for biofuel such as biogas, bioethanol, etc., attempts towards economically efficient technological solutions of biofuel production are still at infancy (Bastianoni S et al., 2008). Marine macro-algae are broadly classified as (i) brown algae (Phaeophyceae), (ii) red algae (Rhodophyceae), and (ii) green algae (Chlorophyceae). Table 2 lists number of species and characteristics, which are distinctly different with regard to their photosynthetic reserve and cell-wall polysaccharides. Abiotic parameters of habitat (namely light, temperature, salinity, nutrient, pollution, water motion, etc.) play a vital role in algae’s growth, pigment and also other chemical constituents. Macro-algae are vertically distributed from the upper zone (close to the sea surface) to lower sub-littoral zone to optimally use natural light and the pigment absorb selectively light at specific wavelength (Guiry 2012).
Table 2. Characteristics of Green, Red , and Brown seaweed
Chlorophyta
Rhodophyta
Phaeophyta
Number of species recorded
6032a
7105b
2039c
Photosynthetic pigment
chlorophyll a, chlorophyll b, carotin, xanthophyll
Phycoerythrin
Fucoxanthin
Habitat
Freshwater and Marine
Strictly marine
Reproduction
Asexual and sexual
Asexual and Sexual
Photosynthetic reserve*
Chlorophyta accumulates starch as their photosynthetic reserve.
Carbohydrate reserves of red algae are floridean starch (intermediate between true starch and dextrin)
Carbohydrate reserve is called laminarin and mannitol(hexahydride alcohol)
Source: a A. Pascher, 1914; b Algaebase.org; c Kjellman, 1891 *Smith,1938
Acid hydrolysis involves cleaving the polysaccharide’s glyosidic bond to release monosaccharides. But, acid hydrolysis decomposition also releases undesirable compounds, such as Fufural, 5-hydroxymethylfufural(HMF), levulinic acid and caffeic acid, which inhibit subsequent fermentation. These compounds are derived from xylose and galactose in macroalgal biomass, can be detoxified using activated charcoal treatments (Meinita et al., 2012). Metal contents in macroalgal biomass are (0.5-11% wt) higher than terrestrial biomass (1-1.5% wt) (Lee and Lee, 2012; Ross et al., 2008), which inhibits microbial fermentation during pretreatment. In contrast to this, during enzyme hydrolysis there is no undesirable compounds as enzyme activity is specific to type of polysaccharides (Nguyen et al., 2009). Simple sugar resulting from hydrolysis is subjected to fermentation using various organisms particularly yeasts microorganisms, to produce ethanol. In order to produce bioethanol cost-effective manner, efforts are in progress to screen microorganisms (Table 4) that possess the ability to directly convert polysaccharides (including glucans) into ethanol. Table 4 also lists species wise quantum of ethanol production, while Table 5 lists microorganisms (to convert sugar into ethanol) for different macro algae.
Table 3. Seaweed polysaccharides
Polysaccharides/phycocolloids
Monosaccharides
Chlorophyceae (Green)
Amylose, amylopectin Cellulose, complex hemicellulose Glucomannans, Mannans Pectin, sulfated mucilages (glucuronoxylorhamnans) Xylans
Glucose, Mannose, Rhamnose, Xylose, Uronic acid, Glucuronic acid
Rhodophyceae(Red)
Agars, agaroids Carrageenans, cellulose Mannans, Xylans, rhodymenan
Glucose, galactose, Agarose
Phaeophyceae(Brown)
Alginates cellulose complex sulfated heteroglucans Fucose containing glycans Fucoidans Glucuronoxylofucans Laminarans
Glucose ,galactose, fucose, xylose, uronic acid, mannuronic acid, Guluronic acid
Source: Sudhakar,2013 ;Percival et.al, 1967
Figure 1: Schematic representation of bioethanol production from macro algae or seaweed.
Table 4. Yield and concentration of sugar and ethanol produced by hydrolysis of Macro algae
Seaweed group
Seaweed species
Hydrolysis
Fermentation
Ethanol concentration (g/L)
Red algae
Gelidium amansii
Acid +enzyme
Scheffersomyces stipites
20.5g/l of sugar
Palmaria palmata
Acid
S. cerevisiae
17.3 mg/g of sugar
Kappaphycus alvarezii
64.3g/l of sugar
Gracillaria verrucosa
Acid+enzyme
0.43g/g of sugar
Green algae
Ulva pertusa
Enzyme
18.5
27.5
Enetromorpha instestinalis
20.1 g/L Sugar yield
Ulva fasciata
S.cerevisiae MTCC No.180
0.45 g/g
Ulva reticulate
S.cerevisiae WL P099
90 L/t dried biomass
Brown algae
Sargassum sagamianum
Thermal hydrolysis
Pichia Stpitis CBS 7126
0.386g/g reducing sugar
Undaria pinnatifida
Thermal acid hydrolysis
Pichia angophorae KCTC 17574
9.42 g/L
Acid + enzymatic
12.98 g/L
Saccharina japonica
Saccharomyces cerevisiae DK 410362
6.65 g/L
0.169 g/g reducing sugar
Engineered microbial enzyme
Engineered BAL1611
0.41 g/g reducing sugar
Laminaria digitata
Shredding and enzymatic
Pichia angophorae
167 mL/kg algae
Laminaria japonica
Thermal liquefaction
Pichia stipitis KCTC7228
2.9 g/L using 100 g/L algae
Acid +enzymatic
Ethanologenic strain E. coli KO11
Saccharomyces cerevisiae
143 mL/kg floating residues
Pichia stipitis CBS 7126
0.43–0.44 g/g reducing sugar
Saccharina latissima
Saccharomyces cerevisiae Ethanol red yeast
0.45% (v/v)
Dilphus okamurae
Enzymatic
Mixture of B5201 (Lactobacillus),Y5201 (Debaryomyces I) and Y5206 (Candida I)
0.04g 100 m/l 0.03g 100m/l
Sargassum fulvellum
Acid+ enzymatic
0.0596 0.0215
Alaria crassifolia
0.244
Table 5. Macro algal biomass wise polysaccharides, sugars and organisms (to convert sugars into ethanol)
Polysaccharides
Sugar
Organisms
Glucan
Glucose
S.cerevisiae
Ulvan
Xylose
Xylose-fermenting yeast
Xylose-utilizing S.cerevisiae
Ethanologenic E.coli
Clostridium beijerinckii, Clostridium Saccharoperbutylacetonicum
Glucuronic acid
P.tannophilus Ethanologenic E.coli
Ethanologenic E.coli KO11
Ethanologenic E.coli BAL 1611
Mannitol
Zymobacter palmae
Ethanologenic E.coli KO11 developed by integrating zymomonas mobilis ethanol production genes into the pflB gene
Ethanologenic E. coli BAL1611
Alginate
Uronic acid
Ethanologenic sphingomonas sp. A1
Ethanologenic E coli BAL BAL 1611
Agar, Carrageenan
Galactose
S.cerevisiae, Brettanomyces custersii KCTC 18154P
3,6-anhyrdogalactose
NR
Engineered strain
Red seaweed
Agar ,carrageenan
Galactose, or simultaneous co-fermentation of galactose and cellobiase
Saccharomyces cerevisiae (engineered for improved galactose fermentation)
Brown seaweed
Glucose, mannitol
Escherichia coli (engineered for alginate metabolism)
Glucose, mannitol and alginate
Escherichia coli KO11
Source:Yanagisawa,2013; Kim N.J. et al.,2011
Scope for value added products: In India, seaweeds grow abundantly in south coast of Tamil Nadu, Gujarat coast, Lakshadweep and Andaman-Nicobar Islands. Luxuriant growth of seaweeds is also found at Mumbai, Ratnagiri, Goa, Karwar, Varkala, Vizhinjam, Vishakapatnam, Pulicat lake and Chilka Lake. Kaliaperumal, et al., 1992; 1996, recorded about 271 genera and 1053 species of marine algae belonging to four groups of algae namely Chlorophyacea, Phaeophyceae, Rhodophyceae and Cyanophycease from Indian waters. Seaweeds as a food source is used seldom in India, but freshly collected and cast ashore seaweeds are used as manure for coconut plantation either directly or in the form of compost in coastal areas of Tamil Nadu and Kerala. Seaweed manure has been found superior to farm yard manure. It is seen that plants absorb, high amount of water soluble potash, other minerals and trace elements present in seaweeds which aids in controlling mineral deficiency diseases. Also the nature of soil and moisture retaining capacity is improved due to carbohydrates and other organic matter present in the marine algae. Macroalgae in India are used as raw material for manufacture of agar, alginates and liquid seaweed fertilizer. (Chennubhotla et.al. 1978)
2. Seaweed resources in West Coast of Karnataka
Karnataka has a coastline of about 320 km starting from Talapadi in the south to Karwar in the north. Ecology of tidal pond in Mavinahole estuarine creek, Karwar was studied in 1979 by Bopaiah and Neelakantan (1982). Table 6 lists taluk-wise distribution of seaweed species in Uttara Kannada district, which are mostly confined to rocky shores. 43 species of marine algae in the littoral zone of the entire Karnataka coast was reported earlier (Agadi, 1985). NAAS (2003) reported 39 species of seaweeds from Karnataka coast, 39 species of seaweeds from Karnataka coast (Venkataraman and Wafar, 2005; Kaladharan, 2011) and Untawale et al. (1989) reported 65 species belonging to 42 genera from the northern Karnataka coast alone.
SEAWEED SPECIES
KARWAR
ANKOLA
KUMTA
HONAWAR
BHAT*KAL
Amphiroa fragillissima (Linnaeus) Lamouroux
+
Bangia autopurpurea var.fuscopurpurea (Dillwyn) C.Agardh
Caulerpa peltata J.V. Lamouroux
Caulerpa racemosa (Forsskal) J. Agardh
Caulerpa scalpelliformis (R.Brown ex Turner) C. Agardh
Caulerpa sertularioides (S.G.Gmelin) M.A. Howe
Caulerpa taxifolia (Vahl) C.Agardh
Caulerpa verticillata J. Agardh
Chaetomorpha linum (Muller) Kutzing
Chaetomorpha media (C. Agardh) Kutzing
Dictyopteris australis (Sonder) Askenasy
Dictyota bartayresiana Lamouroux
Dictyota dichotoma (Hudson) Lamouroux
Enteromorpha clathrata (Roth) J.Ag
Enteromorpha flexuosa (Wulf) J.Ag.
Enteromorpha intestinalis (Linnaeus) Nees
Gelidium micropterum Kutzing
Gelidium pusillum (Stackhouse) Le Jollis
Grateloupia filicina (Wulf.) Ag.
Grateloupia indica Borgesen
Grateloupia lithophila Borgesen.
Gracilaria corticata J. Agardh
Hypnea valentiae (Turner) Montagne
Jania adherence Lamouroux
Laurencia cartilaginea Yamada
Laurencia obtusa (Hudson) Lamouroux
Laurencia papillosa (C. Agardh) Greville
Padina gymnospora (Kutzing ) Sonder
Padina tetrastromatica Hauck
Porphyra vietnamensis T.tanaka & Dham-Hoang Ho
Sphacelaria furcigera Kuetz
Spatoglossum asperum J. Agardh
Sargassum cinereum J. Agardh
Sargassum ilicifolium (Turner) C. Agardh
Sargassum polycystum C.Aga
Sargassum tenerrimum J. Agar
Sargassum wightii Greville
Stoechospermum marginatum (C. Agardh) Kutzing
Ulva fasciata Delile
Ulva lactuca Linnaeus
Ulva rigida C. Agardh
Source: Agadi, 1985; Untawale et al., 1989; NAAS 2003, Venkataraman and Wafar, 2005; Kaladharan, 2011; * http://www.niobioinformatics.in/seaweed/index.htm
Uttara Kannada district is endowed with four productive estuaries namely Kali estuary in Karwar, Gangawali estuary in Ankola, Aghanashini estuary in Kumta, Sharavathi estuary in Honnavar. Aghanashini estuary situated in Kumta taluk on the rive Aghanashini, this estuarine region extends from the river mouth to about 25 km upstream. The Aghanashini estuary has several mudflats and small islands and network of drainage canals called kodis. Farmers of this region traditionally cultivated a variety of salt tolerant rice- “kagga” in large expanses of the reclaimed backwaters, called gaznis, also known as Kharlands or Khajans. In these gazni land, farmers practice alternate rice cultivation and prawn filtration. There are few abandoned gazni in these estuarine region which could serve as a potential site for seaweed cultivation. (Suryanath ,1985). Table 7 lists the distribution of seaweeds along west Coast of India with the wide scope for biofuel production. There is a potential to develop large scale cultivation of seaweeds in west coast of India with optimization of existing labour intensive cultivation and harvesting technologies to reduce cost and energy demand. Extraction of value added products from macro algal biomass along with bioethanol production, further boosts the livelihood of local people while meeting the energy demand.
SEAWEED
GUJARAT
MAHARASHTRA
GOA
KAR
KER
Amphiroa fragillissima
Acanthophora specifera
Bangia fuscopurpurea
Bryopsis plumosa
Caulerpa peltata
Caulerpa racemosa
Caulerpa scalpelliformis
Caulerpa sertularioides
Caulerpa taxifolia
Caulerpa verticillata
Chaetomorpha linum
Chaetomorpha media
Cheilosporum spectabile
Cladophora fascicularis
Dictyopteris australis
Dictyota bartayresiana
Dictyota dichotoma
Enteromorpha clathrata
Enteromorpha flexuosa
Enteromorpha intestinalis
Gelidium micropterum
Gelidium pusillum
Grateloupia filicina
Grateloupia indica
Grateloupia lithophila
Gracilaria corticata
Gracilaria verrucosa
Hypnea musciformis
Hypnea pannosa
Hypnea valentiae
Jania adherence
Laurencia cartilaginea
Laurencia obtusa
Laurencia papillosa
Padina gymnospora
Padina tetrastromatica
Porphyra vietnamensis
Sphacelaria furcigera
Spatoglossum asperum
Sargassum cinereum
Sargassum ilicifolium
Sargassum polycystum
Sargassum tenerrimum
Sargassum wightii
Stoechospermum marginatum
Ulva lactuca
Ulva reticulata
Ulva rigida
Source: http://www.niobioinformatics.in/seaweed/index.htm
Considerable work has been carried out with respect to commercial production of agar and algin from macro algae in India. Different microorganisms are being employed for effective conversion of seaweed polysaccharides as well as of fermentation processes, in order to commercialize macroalgae based fuels, a priority needs to be put on identifying microorganisms that metabolizes macroalgal carbohydrates. Alginate and Ulvan are macroalgae specific carbohydrate which are not readily metabolized by commercially applied fermenting microorganisms such as saccharomyces cerevisiae (Wegeberg and Felby,2010). To overcome these constraints, macroalgae specific enzymes were developed to hydrolyze macroalgal carbohydrates (Erasmus et al., 1997; Jang et al., 2012). An attempt was made to cultivate red algae Kappaphycus alvarezii alongMandapam coast and demonstrated commercial scale production of bioethanol. Over the past twenty years, large scale cultivation of carrageenophytes (Khambhaty, 2012). In India, edible seaweeds such as Gracillaria edulis, Caulerpa spp., Poryphyra etc. can be cultivated along with biofuel feedstock seaweeds, in estuarine areas and coastal inundated waters. Appropriate technology for large scale seaweed cultivation is imperative to meet the growing energy demand. Implementing seaweed cultivation combined with post harvesting processing units could bring economic returns to seaweed cultivators.