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Chapter 11

Evaluation of Biohydrogen Production Potential from Marine Macro Algae I˙lknur S¸entu¨rk and Hanife Buÿu¨kgu¨ngo¨r

Abstract Biomass can also be used as a substrate for energy production, particularly for hydrogen production. By use of microorganisms, hydrogen can effectively be obtained from wood and marine biomass according to purposes. Biomass (i.e., organic matter) such as marine macro algae can be degraded biologically. The use of seaweeds as energy crops have certain advantages: the need for large land areas (which may not be available) is avoided; marine crop yields are expected to be considerably higher than land crop yields although experience from large-scale cultivation is lacking; seaweeds do not contain lignin, which is almost nondegradable under anaerobic conditions; and many valuable extracts, such as alginate, can be extracted from the waste, which is important to environmental protection. Recent research has shown that the red algae Gelidium amansii and the brown algae Laminaria japonica are both potential biomass sources for biohydrogen production through anaerobic fermentation. The objective of this review article is to give an overview of marine algae as a prospective source for biohydrogen production. Keywords Biohydrogen • Marina macro algae • Anaerobic fermentation

11.1

Introduction

Over the past 50 years, the world’s population has more than doubled, coupled with an expectation of a higher standard of living and an ever-increasing economic output this has resulted in a large increase in primary energy consumption, particularly the

˙I. S¸entu¨rk (*) • H. Buÿu¨kgu¨ngo¨r Department of Environmental Engineering, Faculty of Engineering, Ondokuz Mayıs University, Atakum, Samsun 55139, Turkey e-mail: [email protected]; [email protected] A. Vezirog˘lu and M. Tsitskishvili (eds.), Black Sea Energy Resource Development and Hydrogen Energy Problems, NATO Science for Peace and Security Series C: Environmental Security, DOI 10.1007/978-94-007-6152-0_11, # Springer Science+Business Media Dordrecht 2013

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use of fossil fuel-derived energy. In 2010, world primary energy consumption grew by 5.6 %, the largest percentage growth in almost 40 years. This growth included an increase in the consumption of all major fossil fuels including oil, natural gas and coal. This trend in increasing energy consumption is expected to continue as the world’s population is projected to increase by an additional 1.4 billion people by 2030, and have an increase of 100 % of the world’s real income. These increases will put enormous pressure on the finite supply of fossil fuel-based energy, exacerbating global concerns over energy security, fossil fuel-based environmental impacts such as climate change, and the rising cost of energy and food. The utilization of current energy sources has been generating environmental pollution of air, water and soil through the years. These negative effects have increased interest in the development of new technologies to obtain clean energy, mainly through the utilization of renewable energy sources [1]. Currently, the world consumes about 15 TW of energy per year and only 7.8 % of this is derived from renewable energy sources [2]. Hydrogen is seen as a future energy carrier. The recent rise in oil and natural gas prices and global awareness of increasing CO2 levels in the atmosphere has drawn attention to renewable energy including hydrogen produced from renewable sources [3]. Hydrogen is a clean and renewable energy source that does not produce carbon dioxide as a by-product, when used in fuel cells for electricity generation [4]. Biomass can also be used as a substrate for energy production, particularly for hydrogen production. By use of microorganisms, hydrogen can effectively be obtained from wood and marine biomass according to purposes [5]. Biological hydrogen production from biomass is considered one of the most promising alternatives for sustainable green energy production and important solution to a sustainable power supply and is nowadays being seen as the versatile fuel of the future, with potential to replace fossil fuels [6]. With the development and commercialization of fuel cells, hydrogen production from biomass is being considered as an alternative energy source for decentralized power generation [4]. Hydrogen fermentation of conventional waste, such as food waste and high-strength wastewater, is an environmentally friendly treatment with the additional benefit of hydrogen production. However, the amount of hydrogen production using the leftover biomass is not sufficient for a H2-based economy [7]. Although hydrogen biogas can be efficiently produced at the laboratory level, there is no known commercially operating hydrogen from biomass production facility in the world today [4]. The feasibility of hydrogen fermentation as a mainstream technology in the near future depends on the utilization of carbohydrate-rich, economical, and sustainable biomass [7]. Till early 2000s, the production of the 1st and 2nd generation biofuels that use edible agricultural crops (sugarcane, sugar beet, wheat, etc.) and lignocellulosic waste biomass (hardwood, softwood, grasses, agricultural residues) as a feedstock, respectively, have been considered an environmentally friendly way [8]. It was estimated that this growth of terrestrial biomass and the replacement of fossil fuels by renewable energy would significantly reduce the greenhouse gases emissions. Global warming has become one of the most serious environmental problems.

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Evaluation of Biohydrogen Production Potential from Marine Macro Algae

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To cope with the problem, it is necessary to substitute renewable energy for nonrenewable fossil fuel. Biomass, which is one of the renewable energies, is considered to be carbon-neutral, meaning that the net CO2 concentration in the atmosphere remains unchanged [9]. Biofuel is a renewable energy source produced from biomass, which can be used as a substitute for petroleum fuels. The benefits of biofuels over traditional fuels include greater energy security, reduced environmental impact, foreign exchange savings, and socioeconomic issues [10]. Owing to its environmentally friendly aspect in producing H2, biological H2 production has recently gathered considerable attention. In particular, fermentative hydrogen production is considered a promising method, since it is technically simpler and its H2 production rate is much faster than other approaches. In addition, organic pollutants could be degraded along with H2 production [8]. This short review study focuses on the research involved in generating hydrogen using algae as a renewable energy resource. Due to the decline in fossil fuel resource, the energy derived from biomass seems to be the only major source of world’s renewable energy. The hydrogen derived from algae is promising due to its sustainability. There are no greenhouse gas emissions during the combustion of hydrogen, and security of its supply even at remote places. The novel approach of generating hydrogen at commercial scale from algae has been a curiosity among many researchers till today. The generation of hydrogen from algae is still at research level. Hence, this review would be an eye opener for researchers who are interested in generating hydrogen from algae. The renewable technology has garnered great importance due to high raise in oil price and global warming. The energy derived from biofuels especially algae in receiving more and more attraction in recent years [11].

11.2

Biohydrogen Production from Marine Macro Algae

Macrophytic marine algae, commonly known as seaweeds, are nonvascular, multicellular, photosynthetic “marine plants” that inhabit the coastal regions of ocean waters, commonly within rocky intertidal or submerged reef-like habitats. Unlike microscopic algae (micro algae), seaweeds generally live attached to rocky substrates on the ocean bottom and can assume considerable anatomical complexity and intricate life histories. The three major divisions of marine macro algae are brown algae, red algae and green algae, which together encompass over 7,000 species. In the rocky intertidal marine environment, competition for light, nutrients, and space is fierce and much marine seaweed have evolved chemical defense mechanisms to ward off predators and enhance survival [12]. The idea of using marine biomass for energy was first conceived by Howard Wilcox in 1968. At that time, the marine biomass energy program was conducted jointly among governmental organizations, universities, and private corporations in the United States until 1990. The program proposed using giant brown kelp (Macrocystis pyrifera) as a cultivation species, which is a kind of brown algae

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Fig. 11.1 Illustration of energy production from marine biomass

that grows rapidly and may reach up to 43 m long. In Japan, research on energy production from marine biomass was conducted from 1981 to 1983. Figure 11.1 shows of energy production from marine biomass. Seaweeds are cultivated at an offshore farm and then harvested and transported by vessels [9]. If the sea area is utilized efficiently, a vast amount of renewable energy could be produced. In addition, native seaweeds often form submarine forests that serve as habitats for fish and shellfish, and so if a marine biomass energy system is realized, it may boost the production of marine food and promote the marine energy industry leading to CO2 mitigation. The use of marine biomass energy was investigated in the United States and Japan as an alternative energy in the 1970s after the oil crises, but the studies were discontinued when oil prices stabilized. However, now that global warming has become one of the most serious problems to be solved, we should reconsider the use of marine biomass energy as a means to mitigate CO2 emissions [9]. Marine biomass has attracted less attention than terrestrial biomass for energy utilization so far, but is now called “the 3rd generation biomass” is paid most attention as the promising alternative renewable sources for biofuel production [8]. Biomass (i.e., organic matter) such as marine macro algae can be degraded biologically. Seaweeds, referred to as marine macro algae, mainly include red, brown, and some green algae. The use of seaweeds as energy crops have certain advantages: the need for large land areas (which may not be available) is avoided; marine crop yields are expected to be considerably higher than land crop yields although experience from large-scale cultivation is lacking [4] seaweed contains almost no non-degradable lignins, which are almost non-degradable under anaerobic

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Table 11.1 Comparison of H2 production using marine seaweed Feedstock Laminaria japonica (do thermal treatment) Gelidium amansii

Inoculum Heat treated anaerobic sludge

The seed sludge from an anaerobic digester Laminaria The seed sludge japonica from an anaerobic digester Laminaria Heat treated japonica (no anaerobic pretreatment) sludge

Culture type Temperature pH 7.5 Batch 35 C

H2 yield 28 ml/g dry algae

References [4]

Batch

35 0.1 C >5.5

Batch

35 0.1 C 8 0.1 67.0 mL H2/ [8] g TS

Batch

35 0.1 C 7.5

0.518 L H2/ [7] gVSS/d

71.4 mL H2/ [17] g TS

conditions and thus sugars can be obtained without expensive pretreatment for lignin removal; and many valuable extracts, such as alginate, can be extracted from the waste, which is important to environmental protection [4, 7, 13]. The CO2 capture rate of marine algae is higher than that of terrestrial biomass. For example, Laminaria japonica (4,800 g C/m2/year) has more than a twofold higher CO2 utilization rate of tropical rainforests (2,000 g C/m2/year) [8]. The marine biomass energy system is, therefore, one of the potential countermeasures for global warming mitigation. The use of marine biomass for energy may also have the advantage of providing good fisheries. However, problems still remain to be solved. Example; an economical and energy-saving by-product extraction process should be developed. Cultivation techniques for rapid growth of seaweeds and energysaving drying process are also important [9]. Due to the complex composition of seaweeds, complete degradation of the material necessitates the presence of microorganisms with a broad substrate range. During anaerobic degradation of organic material, energy carriers such as hydrogen and methane may be produced. This is particularly true for the cell wall of brown algae, which contain cellulose, alginates, sulfated fucans, and protein. As a result of this carbohydrate content, brown seaweeds can be a potential source for the production of hydrogen and methane [4]. The results obtained with other species of algae are given in Table 11.1. So far, however, most of studies were focused on producing bioethanol and biodiesel. Scarce researches has been conducted to use 3rd generation biomass for fermentative hydrogen production [8]. Algae can be classified as either micro algae or macro algae based on morphology and size. Micro algae are microscopic organisms while macro algae are typically composed of multicellular plant-like structure, like giant kelp. Although macro algae can look similar to land plants, these organisms in fact do not have the same lignin crosslinking molecules in their cellulose structures because they grow in aquatic environments where buoyancy allows for upright growth in the absence

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Fig. 11.2 Metabolic pathways in green algae related to biofuel and biohydrogen production [15] (see color plates)

of the lignin crosslinking. While having a low lignin content, macro algae contain significant amount of sugars (at least 50 %) [2] that could be used for biofuel and biohydrogen production through anaerobic fermentation. Macro algae or “seaweeds” are multicellular plants growing in salt or fresh water. Macro algae are classified into three broad groups based on their pigmentation: (1) Brown seaweed (Phaeophyceae); (2) red seaweed (Rhodophyceae) and (3) green seaweed (Chlorophyceae) [7, 10, 14]. Some species of red seaweed such as those belonging to the genera Gelidium, Gracilaria, and Euchema are known for high carbohydrate content [7]. This also allows enormous potential as an excellent source for biohydrogen production. Figure 11.2 shows metabolic pathways in green algae related to biofuel and biohydrogen production [15].

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In the past few years, most algae biofuel research has focused on liquid fuels, particularly those that can replace transportation fuels such as biodiesel and bioethanol; however, algae are also a potential source of commercial biohydrogen and biogas (biomethane) used as a gas fuel or for electricity generation [2]. Macro algae are a potential source of biomass for the production of these gases due to their fast growth rates, ability to grow in oceanic environments and their lack of the structural lignin which is typically difficult to digest. Many species of macro algae are known for having high levels of carbohydrate, although in many cases these carbohydrates consist of nonglucose monosaccharides such as galactose [2]. Various seaweeds have been considered to be potential energy crops: Macrocystis pyrifera, Laminaria, Gracilaria, Sargassum, Ulva, etc. These seaweeds have a high productivity which is required for energy production. Recent research has shown that the red algae Gelidium amansii and the brown algae Laminaria japonica are both potential biomass sources for biohydrogen production through anaerobic fermentation, but bioprospecting of macro algae for their fermentative future continues. The marine algae are considered an important biomass source; however, their utilization as energy source is still low around the world. The technical feasibility of marine algae utilization as a source of renewable energy was studied to laboratory scale [4]. It will be also necessary to optimize pretreatment methods for maximum biohydrogen production. Many studies have focused on determining the optimal pretreatment conditions (thermal, ultrasonic, acidification, and alkaline pretreatments) for improving the solubilization of algal biomass and waste activated sludge [4, 16]. Although hydrogen production from algae still seems years away from commercial viability, continued progress in this area shows its ultimate potential [2].

11.3

Conclusions

The marine algae are considered as an important biomass source; however, their utilization as energy source is still low around the world. The technical feasibility of marine algae utilization as a source of renewable energy was studied to laboratory scale. Hydrogen can be produced from various marine macro algae quite simply by batch cultures. Security of abundant, carbohydrate-rich, economical, and sustainable biomass determines the practicability of hydrogen fermentation processes. Seaweeds are regarded as alternative non-food sources for bioenergy production, especially for nations having limited land for energy crop cultivation such as East Asian countries. The renewable technology has also garnered great importance due to high raise in oil price and global warming. The energy derived from biofuels especially algae in receiving more and more attraction in recent years.

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