The potential seaweed resources assessment: Its cultivation prospect and future biofuel feedstock

Lipid or oil-based seaweed for biodiesel production

Kalscheuer et al., reported that biodiesel is biodegradable, with less CO₂ and NOx emissions. It is produced from the transesterification process where the triacylglycerols will be converted into monoalkyl esters of long-chain fatty acids with short-chain alcohols such as fatty acid methyl esters (FAMEs) (biodiesel).^[20] Transesterification is a chemical process that involves reversible reactions between triglycerides from vegetable oil and alcohol with the presence of a catalyst such as acid and alkali or biological catalysts with an alcohol to produce esters and by-products.^[21] Examples of alcohols that can be used include methanol, ethanol, propanol, and butanol, but the most used is methanol. Methanol is cheap and has a favorable physical and chemical nature (shortest-chain alcohol). In addition, transesterification is a simple and cost-effective process that produces biodiesel with low viscosity. It also produces glycerol that has commercial value as a by-product.^[21] For instance, the production and consumption of biodiesel resulted in a 78.5% reduction in carbon dioxide emissions.^[19]

Seaweeds are a potential alternative and renewable source for conventional feedstocks for biodiesel production.^[22] Lipid or oil-based seaweeds are suitable for esterification/transesterification reaction of biodiesel production which could meet the global demand for transport fuels. Biodiesel can be produced from seaweed due to its lipid content [Figure 2]. Fish oil for nutraceutical use has been the major source of docosahexaenoic acid (DHA), it might be produced using marine micro- and macro-algae species. Marine microorganism species might contain large quantities of DHA and be considered a potential source of this important fatty acid. Properly harvested oil can be converted into biofuels.^[23]

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Figure 2:

Seaweed for biodiesel production using the lipid content in its biomass.

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Algae were first explored as a fuel alternative in 1978 under President Jimmy Carter. Gas prices skyrocketed, lines at the pump were endless, and the government was looking to help ease the crisis. The increasing energy demand is expected to provide the much-needed financial incentive to work on improving production and redoubling the efforts to use renewable sources for energy effectively. The incremental barrel of hydrocarbon is getting heavier, and many also believe that the incremental conventional cubic foot of natural gas is getting sourer. This will place an ever-increasing burden on processing equipment. This represents an excellent opportunity to virtually transform the current paradigm of production and refining. This game-changing technology can be applied to deriving usable end products from a biodegradable source of energy. The successful application of the technology could blur the distinction between upstream and downstream operations.^[24] Algae-based feedstock (seaweeds) can be grown on non-arable land (without competition with food crops) using only sunlight and water for growth. This category of aquatic organism has long been considered to have the potential for producing transportation fuels, particularly biodiesel, which is produced by the chemical transesterification of fatty acids.

Algae or seaweed are also the fastest growing of all plant species on earth. These two characteristics give seaweed an exceptional biomass output and fuel conversion potential compared with land crops in per unit area comparisons. Properly supported, large-scale seaweed cultivation presents an achievable opportunity to significantly replace fossil fuel usage. According to Aitken et al., a life cycle assessment study has been initiated for the evaluation of the potential of macroalgae for fuel production.^[25] This study reveals that macroalgae need nutrients (N, P, microelements) associated with nutrient and cultivation energy. Variance analysis has shown that if the energy of nutrients is taken into consideration, the energetic balance may be negative. Therefore, to avoid such a huge amount of energy input, either effluent water from aquaculture plants should be used, or some selected municipal waters.

Seaweed works as a purifying agent and treated water can be either re-circulated to the fishpond or immitted into natural basins without paying any penalties. Such use of effluent water, by the way, generates a credit to the process that may be ultimately considered. The focus on the use of biomass as an alternative feedstock to fossil fuels is intensifying due to its role in reducing CO₂ emissions. At present, many technologies are under investigation for the utilization of biomass both for power generation and to produce biooil for transportation and chemical commodities. Two of the main issues of biomass utilization are the security of supply and the development of an infrastructure capable of maintaining the supply of biomass of sufficient quality.^[26] The upstream and downstream sides of the energy sector, like most other industries, face a challenge in the areas of exploration, production, and refining. These also pose unique opportunities to re-evaluate the processes and develop game-changing technologies to improve overall efficiency. The game-changing technologies should improve the economics of the process and help to improve the safety and reliability of the activity. For example, if hazardous materials, such as CO₂ and H₂S, are treated downhole and not brought to the surface; then, this not only improves the health and safety but also reduces the operating cost by eliminating the need to treat and dispose of these materials. The process should be optimized so that the incremental savings are greater than the incremental cost.^[24,27]

Production of biodiesel from seaweeds generally involves several steps [Figure 2] which make it less attractive when starting from cell drying to disruptions of cells, lipid or oil extraction, transesterification process, and purification of biodiesel produced.^[28] Nevertheless, the current technology of in situ (lipid extraction and transesterification in a single step) transesterification process makes this biodiesel production more feasible on an industrial scale.^[29] The key raw materials for biodiesel production are oils or lipids. Tripathi et al., reported that the fatty acid composition of seaweed (stearic acid, palmitic acid, and oleic acid) is like the biodiesel standard.^[30] Normally, the yield of lipids produced from this algae-based biomass, especially microalgae is in the range of 2.4–62% of dry biomass, [Table 1].^[30-33] Methyl ester (biodiesel) produced after the transesterification process is high in unsaturated fatty acids, which is one of the prerequisites for being used as biofuel.^[30] Mata et al., in 2010, stated that, from 1 kg of oil extracted from algae-based biomass, 1 kg of biodiesel can be produced.^[32]

Carbohydrate-based seaweed for sugar-based biofuels production

Sustainable biofuel alternatives have been deeply investigated by many researchers to find a potential resource to replace fossil fuels. The potential of algae-based biomass as a third-generation feedstock for biofuel production continues to be investigated. Green algae contain large amounts of sugars in the form of complex carbohydrates. Agwa et al., reported that Chlorella vulgaris consists of approximately, 37–55% of cell dry weight of carbohydrates.^[34]

This high content of carbohydrates shows that algae-based biomass can be one of the potential resources to produce other types of biofuels, especially sugar-based biofuels such as bioethanol and biobutanol. However, this algae-based biomass or seaweed needs to go through pretreatment and hydrolysis to turn this complex carbohydrate into a simple form of sugars for bioethanol or biobutanol production [Figure 3]. The study by Yanagisawa et al., reveals that seaweeds of Ulva pertusa, Alaria crassifolia, and Gelidium elegans have no lignin composition of polysaccharide.^[35] This shows that seaweed did not require any pretreatment process before their hydrolysis. Several hydrolysis methods have been successfully applied for bioethanol production using seaweed as the sole carbon source. Table 2 shows the yield and different types of seaweed or macroalgae used for bioethanol production using several types of hydrolysis methods.^[5,36-40] Fermentation of seaweed biomass will be based on polysaccharide composition since the composition of seaweed will vary from species to species even though the polysaccharide in the cell walls of seaweeds is generally composed of cellulose and hemicellulose.

Seaweed biomass can be considered a new promising feedstock to produce biofuels, especially bioethanol production [Figure 3]. Many of the third-generation biofuels can be grown on non-arable land that are subject to harsh conditions and different environments, such as using unused water space and wastewater as the main medium for the source of nutrients. Their fastest growth compared to any oilseed plants can reach more than 59% lipid per dry weight for certain types of species for biodiesel production and their biomass with high polysaccharide content can be used to produce a wide variety of bioproducts especially other types of biofuels such as bioethanol and biobutanol which can promise us for higher net energy returned (NER) compare to other biofuels and viable feedstock for large-scale production of biofuels without competing with land-based food crops. Thus, there has been a great deal of development of systematic algae-based biofuels production systems for the sustainability of future renewable biofuels.

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Figure 3:

Seaweed for bioethanol and biobutanol production.

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State of the art of cultivation of seaweed biofuel species

Continuous use of petroleum-sourced fuels is now widely recognized as unsustainable due to depleting supplies and the contribution of these fuels to the accumulation of carbon dioxide in the environment. Renewable, carbon-neutral, and transport fuels are necessary for environmental and economic sustainability. Algae have emerged as one of the most promising sources for biodiesel production. It can be inferred that alga grown in CO₂-enriched air can be converted to oily substances. Such an approach can contribute to solving major problems of air pollution resulting from CO₂ evolution and future crisis due to a shortage of energy sources. The government’s use of upstream R&D investments and downstream incentives for renewable energy is intended to achieve commercial breakthroughs in biofuels, batteries, fuel cells, hydrogen, solar, and wind energy. The private sector has reacted to these policy instruments with a significant increase in renewable energy R&D and commercial investment. As the private sector’s exposure to renewable energy markets increases, the public sector will increasingly be pulled by special interests in the direction of insuring against the downside risks of clean energy investments.^[41,42]

Tyler and McGlathery reported that Macroalgae or seaweed, often the dominant primary producers in shallow estuaries, can be important regulators of N cycling.^[43] Like phytoplankton, actively growing macroalgae release N to the water column, and the quantity or nature of this release remains unknown. Using 15N labeling in laboratory and field experiments, we estimated the quantity of N released relative to assimilation and gross uptake by Gracilaria vermiculophylla (Ohmi) Papenfuss (Rhodophyta, Gracilariales), non-native macroalgae. Field experiments were carried out in Hog Island Bay, a shallow back-barrier lagoon on the Virginia coast where G. vermiculophylla makes up 85–90% of the biomass. There was good agreement between laboratory and field measurements of N uptake and release. Daily N assimilation in field experiments was correlated with seasonal and local N availability. The average rate of N release across all sites and dates was 67% of gross daily uptake and varied among sites and seasons (range 33–99%). The release was highest when growth rates and nutrient availability were low, possibly due to senescence during these periods. During summer biomass peaks, the estimated N release from macroalgae mats was as high.

The design and model testing of offshore aquaculture floating structures for seaweed oceanic plantations has been reported by Sulaiman Olanrewaju et al.^[44] Indeed, seaweed farming has become one of the economically important natural resources. The existing cultivation system for seaweed is not suitable for deployment in most deep and open-water areas. Moreover, the current cultivation system is not environmentally sustainable and economically unstable. The design of the offshore floating structures is scientifically based on the improvement of the Long Line System for commercializing scale seaweed farming. Some key factors in the design, prototype, and testing of floating offshore structures considered in the development of ocean farming technology systems are discussed. Sulaiman Olanrewaju reported the mooring analysis for a very large offshore aquaculture ocean plantation floating structure.^[45] Aquaculture activities are inherently undertaken in proximity to the coastline and near the shore. Mounting constraints and environmental impact concerns necessitate the development of offshore aquaculture. Challenges include achieving a reliable structural integrity and mooring system design for ultimate state limit, fatigue state limit, and accidental and progressive state limit against environmental loading and accidental loading. To avoid mooring system failure, selecting an appropriate breaking strength and limit state for mooring system components is essential. The system design accounts for forces and environmental loadings. An evaluation of optimum mooring performance in a wave, wind, and current loadings on mooring components anchor, buoy, and riser elements that are involved in the dynamic system sought to establish suitable safety factors for large offshore aquaculture floating structures and address the risks associated with seaweeds, biofuel renewable and alternative technologies.^[46-48]

Collection of seaweed in natural stock

Bidong Island is an island in Kuala Nerus District, Terengganu, Malaysia in the South China Sea. A scientific expedition was carried out in December 2016 mainly focused on coastal areas of Melaka in Malacca Strait and Johor in Tebrau Strait. The locations of sampling are shown in Figure 4. Five selected localities were surveyed for their natural seaweed populations. Sampling was done during the low tide period. Samples were collected by hand. Further, cleaning, sorting, and storage in cold conditions before being transferred back to the laboratory for analysis. Fresh and healthy plants were kept alive in clean seawater as seaweed stock for cultivation purposes.^[49]

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Figure 4:

Sampling localities of seaweed during a scientific expedition in 2016.

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Species identification

Complete plants were selected and preserved as dried herbarium specimens. Identification was done according to available taxonomic references. Later, these specimens were cataloged and kept in marine algal reference collection in the Herbaria of University Malaysia Terengganu, Central Laboratory as voucher materials.

Seaweed trial cultivation

Freshly collected samples were acclimatized for 6 weeks and healthy thalli were chosen for trial cultivation. The cultivation was focused on Ulva and Gracilaria species using a designed offshore farming system deployed in Bidong Island, Terengganu.^[50]

Species of Ulva and 2 Gracilaria were measured for their fresh weight (as initial weight) and kept in a planting basket with dimensions (26 [L] × 19 [W] × 9 [H] cm) and volume (4.45 L) and covered with fishing net (1.5 cm mesh size). Stocking density for Ulva is 2.5 g/L and 5.0 g/L for both Gracilaria species and triplicates of samples were studied. Three baskets were tied on the same line and parallel with another two lines also with three baskets each. After 2 weeks, measurement of growth was conducted biweekly in situ.

The specific growth rate (SGR) for seaweed was determined as the following formula:

SGR (%/day) = ([LN W2–LN W1]/T2–T1) * 100% (1)

Where, W2 = final weight, W1 = initial weight, T2 = final time, T1 = initial time

The doubling time for seaweed biomass increased 2 times was calculated as the followed formula:

Doubling time (day) = 50/SGR

Hydrological parameters

Salinity was checked using a handheld refractometer and dissolved inorganic nutrients (ammonium, nitrite, nitrate, and phosphate) were analyzed following the standard chemical methods for seawater analysis.^[45]

Biofuel seaweed species in Malaysia

The survey was done in December 2016 in five selected coastal areas in Melaka and Johor. The green seaweed Ulva sp. was found in two localities in Johor and can be a source of bioethanol and biobutanol. Gracilaria sp. (red seaweed) with the potential for bioethanol is found abundantly in Melaka and Johor.^[25] Giant tropical brown seaweed, Sargassum sp. was a perennial species found in Melaka and Johor with potential for bioethanol, biomethane, and bio-oil production.^[51] Table 3 summarized the seaweed species with biofuel potential found in different localities of Peninsular Malaysia.

Figure 5 shows the species pictures collected during the expedition as potential biofuel species. Ulva sp. known as sea lettuce is an edible green alga in the family of Ulvaceae. It is a thin flat green alga that can have a length of 18–30 cm. While Gracilaria sp. is a red type of seaweed that is commonly found in warm waters and traditionally cultivated as a source of agar. Sargassum sp., in contrast, is a brown type of seaweed and generally appears brown or dark green. It will spend its life on the ocean’s surface and float in large masses. This finding reveals that Gracilaria sp. and Sargassum sp. are the common types of seaweed growth in Malaysia’s oceans.

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Figure 5:

(a) Ulva species from Pulau Merambong; (b) Ulva reticulata from Pengerang; (c) Gracilaria sp.1 from Melaka; (d) Gracilaria sp.2 from Pulau Merambong and Teluk C, Johor; (e) Gracilaria sp.3 from Pengerang, Johor; (f) Sargassum sp. from Melaka; (g) Sargassum sp. from Pulau Merambong; (h) Sargassum sp. from Tanjung Balau.; and (i) Sargassum sp. from Teluk C.

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Species identification

The flat sheet of Ulva collected in Pulau Merambong and Pengerang was two different species. The samples from Pulau Merambong have reported a new record as Ulva species. The samples from Pengerang were identified as Ulva reticulata and matched with taxonomic references. Three Gracilaria species were identified as Gracilaria sp. 1 from Pantai Puteri, Melaka, Gracilaria sp. 2 from Pulau Merambong and Teluk C, and Gracilaria sp. 3 from Pengerang. The large Sargassum was identified as four different species in Pantai Puteri, Melaka, Pulau Merambong, Teluk C, and Tanjung Balau, Johor. This species was further grown in the offshore farming system to determine its SGR.

Growth of seaweed in offshore farming system

Table 4 shows the SGR of cultivated species for 14 and 28 days with different stocking densities. The growth rate for Ulva was not available since all samples were lost in the planting baskets. A possible reason is samples of Ulva were not adapted to a new environment. The growth rate for both Gracilaria sp.1 and Gracilaria sp.2 with 3.84%/day and 4.97%/day, respectively [Figures 6 and 7]. Gracilaria spp. was archived doubling time in 10–13 days showing the environment very suitable for its growth. Abundant new branching tips were observed on seaweed thalli and branches became thicker.

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Figure 6:

Gracilaria sp.1.

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Figure 7:

Gracilaria sp.2.

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All Gracilaria samples were covered with an epiphytic organism such as other macroalgae and invertebrates. Besides, the net covering and planting basket are also attached with tiny brownish fouling invertebrates or microalgae. After planting baskets were cleaned with seawater, the seaweed samples were placed back in the same planting units. Since three baskets for Ulva were empty, Gracilaria sp.2 with a stocking density of 2.5 g/L was replaced in each basket [Figures 6 and 7]. The planting of seaweed baskets is now largely done using twist ties instead of the main culture lines raffia.

The growth rate for Gracilaria sp.1 on day 28 decreased from 3.84%/day to 2.15%/day. Gracilaria sp.2 for two stocking densities 7.5 g/L and 2.5 g/L showed different growth rates which were 3.31%/day and 3.42%/day, respectively, on day 14. Gracilaria spp. was archived doubling time in 15–17 days showing the environment still suitable for its growth. New branching tips were observed to be bigger on seaweed thalli, and branches became thicker as well. However, the growth rates for both Gracilaria spp. decreased from day 14 to day 28 with possible reasons: nutrients, light, and space competition between seaweed and fouling organisms; seaweed stock used for cultivation was kept in the hatchery for two months and getting older before cultivation started; and tropical temperature making growth synergy slow due to high metabolism rate.

All Gracilaria samples were covered with epiphytic organisms such as micro-and macro-algae [Figures 8 and 9] and invertebrates [Figure 10]. Besides, the net covering and planting basket was also attached with tiny brownish fouling invertebrates or microalgae and became abundant on day 28 for all baskets. Since the fouling organisms were too abundant and strongly attached to the net covering, after fresh weight measurement all baskets without cleaning planting baskets and tied back to the prototype for following growth observation.^[49,50]

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Figure 8:

Gracilaria sp.2 was replaced by an empty basket used for Ulva.

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Figure 9:

Fouling and epiphytic macroalgae.

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Figure 10:

Some invertebrates and vertebrates.

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Fouling and epiphytic organisms were found such as invertebrates: Share, copepod, roundworm, shrimp; vertebrates: fish (not considered as fouling); microalgae: diatom mainly pennate diatom and macroalgae: Unidentified cyanobacteria; Bryopsis, Chaetomorpha, and Cladophoropsis (green seaweed); and Acanthophora, Herposiphonia, Laurencia, Polysiphonia, and Tolypiocladia (red seaweed).^[49,50]

The offshore farming system was designed, and simulation tests were done. After simulation tests, the system was planned for deployment in front of Pantai Pasir Cina, Pulau Bidong, and Terengganu. The dimension of the system is 2.0 m × 2.0 m with four large buoys at each corner, two small floats for each marginal line, and three small floats on three parallel lines for seaweed planting. The length of each mooring was 5.4 m, and the depth was 1.4 m during low tide.^[49,50]

The deployment of the system was before the Northeast monsoon season in October 2016. After the monsoon, the system remained in its original position, which was considered feasible. Biofuel species such as Ulva and Gracilaria were trial cultivated on the system. However, Ulva was not able to adapt to this new environment. Both Gracilaria species performed a good growth rate and fast doubling time for biomass production as well compared to some commercial farming practices. Inorganic ammonium, nitrate, and phosphate were low in concentration except nitrate was much higher than the safety limit suggested by DOE, Malaysia [Figure 11]. A broad range of salinity 32–35% [Figure 12] was tolerant by seaweed with growth. In the future, the food species Kappaphycus will be cultivated to understand its growth performance in this system.

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Figure 11:

Dissolved inorganic nutrient availability in Bidong waters during pre-monsoon and post-monsoon.

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Figure 12:

Salinity range of Bidong waters during the cultivation period.

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Plant oils or triglycerides are converted through the transesterification reaction with methanol and base catalyst to produce FAME or biodiesel. Production of biodiesel from plant oil is a renewable, sustainable, and alternative to petroleum-based fuel. Algae oil (AO) from macroalgae has the potential to become a sustainable fuel source as biodiesel. The lipid contents or oil in algae, once extracted and purified, represent an excellent sustainable feedstock for biodiesel production. The Ulva species from Sabah was reported as a potential biodiesel source.^[52] The AO was extracted by the chemical extraction method. The transesterification reaction of AO with methanol and base catalyst was used to produce biodiesel. The engine performance test showed a slight increase in specific fuel consumption, but biodiesel blends showed higher brake power. The emission of CO, HC, and NOx reduced as the biodiesel blend percentage increased over the engine speed range.

Seeweed farming and aquaculture development require sustainable surveillance, the review of Xing et al.^[53] is seminal. The multi-sensor remote sensing technology can be a part of the surveillance of coastal ocean for hazard management and engage sustainable farming strategies involving cultivation infrastructure systems to support high productivity, and source of seaweed biofuels supply chain.^[53,54]