Abstract
Many countries and regions have set their schedules to achieve the carbon neutrality between 2030 and 2070. Microalgae are capable of efficiently fixing CO2 and simultaneously producing biomass for multiple applications, which is considered one of the most promising pathways for carbon capture and utilization. This work reviews the current research on microalgae CO2 fixation technologies and the challenges faced by the related industries and government agencies. The technoeconomic analysis indicates that cultivation is the major cost factor. Use of waste resources such as wastewater and flue gas can significantly reduce the costs and carbon footprints. The life cycle assessment has identified fossil-based electricity use as the major contributor to the global warming potential of microalgae-based CO2 fixation approach. Substantial efforts and investments are needed to identify and bridge the gaps among the microalgae strain development, cultivation conditions and systems, and use of renewable resources and energy.
| Original language | English (US) |
|---|---|
| Article number | 137987 |
| Journal | Chemosphere |
| Volume | 319 |
| DOIs | |
| State | Published - Apr 2023 |
Bibliographical note
Funding Information:This study was supported by the Key Research and Development Program of Jiangxi Province , China ( 20214BBG74004 ) and the National Natural Science Foundation of China ( 51808278 ).
Funding Information:
Because there are many factors affecting the growth of microalgae, the simultaneous optimization of multiple operation parameters will cost a large amount of labor and time. Therefore, artificial intelligence (AI) has recently been developed to optimize microalgae culture conditions. Through advanced sensing technology, the microalgae cultivation mimics the implement of the Internet of Things (IoT) and machine learning in agriculture to achieve real-time monitoring and control of multiple operating parameters, significantly reducing the costs of labor and time (Lim et al., 2022a). Yew et al. (2020) compared the effects of waste molasses and commercial BG-11 medium on Chlorella vulgaris FSP-E cultivation by the AI algorithm, and evaluated the optimal nitrogen addition and pH. The study proved that AI algorithm could provide constructive guidance in microalgae cultivation. Giannino et al. (2018) developed a predictive Decision Support System (DSS) for microalgae cultivation based on IoT. This AI monitoring and control system increased microalgae productivity by 9%. Hermadi et al. (2021) developed a smart algae pond system to increase the microalgae production. The system automatically optimized pH, CO2 concentration, temperature, water velocity, and gas velocity in the pond system, reducing the energy consumption of microalgae cultivation by 60%. In general, there are many factors affecting microalgae growth and carbon sequestration, including C, N, P, and micronutrient inlets, culture conditions such as temperature, pH, and illumination, and mass transfer efficiency (thoroughly discussed in the next section). These studies suggested that the implementation of AI technologies and the IoT could integrate multiple factors to improve the microalgae productivity. This would definitely be the direction of the culture condition optimization of microalgae cultivation. However, there is still a need for further research and development of sensing systems with lower cost and higher precision applicable on an industrial scale.Adding new materials to the suspension is another effective design idea to enhance the light utilization efficiency and/or mass transfer for microalgae PBR. Murray et al. (2017) distributed some 30 mm diameter polystyrene-encased wireless light emitters in a suspension bioreactor. These internal light sources provide photons for the shielded microalgae inside the reactor, and the light delivery efficiency of this novel reactor is 5-folds higher than that of the conventional bioreactor. Besides, some novel adsorbents, such as Fe2O3 nanoparticle (NP) supported polymer nanofibers (Vaz et al., 2019), SiO2 NPs (Jeon et al., 2017), and calcined metal-organic framework MIL-100(Fe) (Cheng et al., 2020), were added to microalgal photobioreactor to enhance CO2 assimilation. Some of these new materials could even enhance the accumulation of specific products. For example, Li et al. (2020c) used a light-gold NPs (AuNPs) to enhance the general photosynthesis and promote carotenoid accumulation in microalgae.In addition to many studies based on single-cell culture (monoculture), some studies have dedicated to the development of an artificially mixed microalgal consortium composed of bacteria, fungi, yeasts, or other microalgae to form a co-culture system (Das et al., 2022; Jiang et al., 2019). In these systems, microalgae provide sufficient oxygen for other aerobic microorganisms, which in turn supply microalgae with CO2 and a more easily assimilated organic carbon source. Additionally, co-culture of bacteria and fungi induces bioflocculation, which can be utilized to facilitate microalgae harvesting and significantly reduce harvesting costs (Mathur et al., 2021). Wang et al. (2022a) reported that Synechocystis sp. PCC6803 could be fixed on the surface of the fungal mycelium pellets of Aspergillus fumigatus by the electrostatic attraction of extracellular polymeric substance. The NO3−/NH4+ cycling and CO2/O2 cycling promoted the synthesis of amino acids in both microalgae and fungi. Furthermore, the intermediate metabolites of fungi (CO32− and HCO3−) support the metabolic activities of microalgae. Xu et al. (2021) developed a co-culture system containing microalgae, fungi, and bacteria, i.e., Chlorella vulgaris, Ganoderma lucidum, and Endophytic sp., respectively. The photosynthetic efficiency and growth rate of microalgae in this system were higher than those of single culture of Chlorella vulgaris and microalgal-fungi binary co-culture system. Biogas, which contains 50–70% CH4, 30–50% CO2, 0.005–2% H2S, requires upgrade before use (Li et al., 2022; Rodero et al., 2020). The co-culture system of microalgae and oxidizing bacteria can be used to upgrade biogas to biomethane, with the composition of CO2 < 2.4%, CH4 > 95.5%, O2 < 1%, and no H2S (Rodero et al., 2020). For the risks in collection, storage, and transportation by biogas, Li et al. (2022) developed a co-culture system of Methylocystis bryophila (methanotroph) and Scenedesmus obliquus to convert CH4 into biodiesel. In this system, CH4 was converted into organic intermediates by methanotroph, which were used as carbon sources for microalgae growth, and finally biodiesel was extracted from microalgae.This study was supported by the Key Research and Development Program of Jiangxi Province, China (20214BBG74004) and the National Natural Science Foundation of China (51808278).
Publisher Copyright:
© 2023 Elsevier Ltd
Keywords
- CO fixation improvement
- Carbon neutrality
- Life cycle assessment
- Microalgae
