Biohydrogen production using algae: Potentiality, economics and challenges
Graphical abstract
Introduction
Fuel used in transporting goods and people is accountable for 33% of total worldwide energy consumption. For instance, the combustion of one-litre diesel leads to the emission of 2.9 kg of greenhouse gases (Ağbulut & Sarıdemir, 2019). In the future scenario, this emission’s likeliness is projected to rise substantially due to the increase in economic and social dynamics caused by rapid globalization. Heavy dependency on fossil fuels has severely damaged earth ecosystems causing extreme heatwaves, the meltdown of arctic ice, a rise in sea level, and frequent droughts. Further, fossil fuel is expected to exhaust within a century if it is not substituted by an alternative (Nogueira et al., 2020). So, the search for sustainable, clean, and green energy that could reduce our dependency on fossil fuels is the need of the hour.
Hydrogen is considered the most promising cleaner substitute to fossil fuel. It is the cleanest fuel as its burning results in hydrogen and oxygen combustion, released as water. Hydrogen as fuel emits no carbon into the air, a significant challenge posed by fossil fuel use. Hydrogen fuel potential is quite eminent from its higher specific energy content (142 MJ kg−1), which is much greater than that of methane (56 MJ kg−1), natural gas (54 MJ kg−1), and gasoline (47 MJ kg−1) (Acar & Dincer, 2019). However, most of the current hydrogen production is from fossil fuels and chemical-based processes. So, due to its dependency on non-renewable resources, conventional hydrogen production techniques are not sustainable (Sambusiti et al., 2015).
On the contrary, hydrogen derived from biomasses and photosynthetic microorganisms is considered as a sustainable energy source (Kim et al., 2021). Algae have been used in recent decades for producing hydrogen more sustainably. Algae have several fermentable sugars (Fig. 1) as their constituents which is desirable for hydrogen production. Features such as higher growth rate and absence of lignin (which helps bypass chemical and cost-intensive pre-treatment procedures) strengthen algae’s candidature for biohydrogen production in a sustainable and economically viable manner (Behera et al., 2020). However, certain constraints, such as the higher water requirement and a significant initial investment, pose challenges in their cultivation at a larger scale (Anwar et al., 2019; Nageshwari et al., 2021). Research for lowering the infrastructure and working cost of the algal production processes are peaking pace in the last decade (Krishnamoorthy et al., 2021).
The biohydrogen production from algae follows specific distinct mechanisms based on its dependency on light. Biophotolysis and photofermentation utilize light for hydrogen production; contrastingly, dark fermentation occurs in the absence of light (Liu et al., 2022). Each method has its advantages and disadvantages; photolysis has challenges, such as lower biohydrogen yield, whereas fermentation is energy-intensive (Kumar et al., 2021). Hence, overcoming the challenges associated with the light-dependent/independent processes and producing biohydrogen at economically competitive prices has become the research focus. Fig. 2 shows the developments in hydrogen production from algae for the last 15 years since its emergence.
Previous review articles have discussed either regarding microalgae or macroalgae as feedstocks for biohydrogen production. In most cases, the discussion on macroalgae is overshadowed by microalgae due to their credibility and environmental benefits. Also, the focus on economic perspectives of algal biohydrogen generation is very limited. This manuscript not only aims in addressing the above-mentioned concerns by commensuration of all algal biomasses and presenting monetary aspects but also details the mechanisms undergone by the biomasses to produce biohydrogen. In addition, the article emphasizes on the strategies explored to improve production, impact of influential experimental parameters and the practical challenges associated with scaling up of the technology. Although the authors have discussed hydrogen production, the overall process has been attempted only in a few papers. This review paper is intended to cover the recent progress, challenges and research gaps in biohydrogen production from algae. The enzymes essential for the hydrogen production processes, their working mechanisms have been discussed in detail and have been compared with each other. Biohydrogen production is coordinated by multiple sequences of reactions and different parameters (experimental and environmental) that could affect the overall process. Hence, it becomes crucial to understand the effect of various parameters to optimize production. This manuscript has examined and discussed the impact of such influential parameters. In addition, the biohydrogen process's economic aspects have been reviewed to evaluate the viability of hydrogen production from algae on a larger scale. This review also discusses the challenges associated with various steps of biohydrogen production from algae and suggests future scopes for overcoming the bottlenecks.
Section snippets
Enzymes involved in algal biohydrogen production
The biohydrogen production in algae occurred after a series of reactions. During these biological and electrochemical reactions, hydrogen is produced and consumed in different steps. The reaction is facilitated by two key enzymes, namely hydrogenase and nitrogenase. These enzymes are vital in defining the net evolution of hydrogen during the complete process.
The mechanisms involved in algal biohydrogen production
Biological production of hydrogen employing algae involves two main approaches: (1) Light-independent process, where the algal intracellular macromolecules assist as substrate for fermentation and (2) light-dependent process entailing photolysis.
Factors influencing algal biohydrogen production
Besides the type of organism chosen for H2 production, the operational conditions such as light intensity, pH, temperature, substrate availability and conversion efficiency can significantly affect the performance of bio-H2 synthesis. The influence of various parameters on hydrogen yield has been shown in Fig. 4.
Economic assessment of the algal biohydrogen production processes
The predominantly used technologies for commercializing hydrogen production are autothermal reforming (ATR), partial oxidation (POX) and steam reforming of methane (SMR). However, around 90% of total hydrogen generation is through the SMR technique. It could avail hydrogen at the cost of USD 7/GJ (El-Emam and Özcan, 2019). Unfortunately, the intermittent processes result in the emission of CO2, which makes the process carbon positive, thus jeopardizing environmental sustainability. To make the
Challenges associated with biohydrogen production: The research gap
The biologically produced hydrogen from algal biomass is a sustainable source, and in terms of energetic value, the hydrogen is considered superior to that of other conventional and available fuels. However, hydrogen from algae still has to overcome a number of bottlenecks before being accepted on the industrial scale. The overall process consists of several sub-processes (starting from selecting an algal strain to the purification of produced hydrogen) with bottlenecks. Some of the significant
Future scope
By focusing on the following research aspects, the cost of operation and production could be reduced without compromising the process's sustainability.
Availability of cheaper substrate (here algal biomass) is one of the critical needs for hydrogen production. To reduce the cost, wastewater can be utilized for growing algal biomass; moreover, emphasis on fast-growing algal strain could also be the right step in increasing the production efficiency.
For overcoming the challenges of dark
Conclusion
Hydrogen could potentially be a clean and renewable substitute for the currently utilized fossil fuels. Although hydrogen from algae promises a clean energy source, the overall production cost is still expensive compared to other available fuel options. Recent researchers are focused on developing various techniques for improving efficiency and reducing the cost of hydrogen production from algae. However, there are several bottlenecks associated with the overall hydrogen production process
CRediT authorship contribution statement
Abhijeet Pathy: Conceptualization, Data curation, Writing – original draft, Writing – review & editing. Krishnamoorthy Nageshwari: Conceptualization, Data curation, Writing – original draft, Writing – review & editing. Rameshprabu Ramaraj: Conceptualization, Writing – review & editing. Gaanty Pragas Maniam: Conceptualization, Writing – review & editing. Natanamurugaraj Govindan: Conceptualization, Writing – review & editing. Paramasivan Balasubramanian: Conceptualization, Investigation, Funding
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
The authors thank the Department of Biotechnology and Medical Engineering of the National Institute of Technology Rourkela for providing the research facility. The authors greatly acknowledge the ASEAN-India Science, Technology & Innovation Cooperation [File No. IMRC/AISTDF/CRD/2018/000082] for sponsoring the PhD programme of the second author.
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2024, International Journal of Hydrogen EnergyCitation Excerpt :The acidic pretreatment of defatted algal biomass residue resulted in more reducing sugar solubilization compared to the base approach. Several other experimental studies reported the employment of algal biomass for the creation of biohydrogen [10,24–26]. The biohydrogen production process from algal biomass via several routes is highly nonlinear and involves several independent control factors which influence the yield of the biohydrogen.
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Equal Contributions.