Engineering Study of a Pilot Scale Process Plant for Microalgae-Oil Production Utilizing Municipal Wastewater and Flue Gases: Fukushima Pilot Plant

Integrated energy informatics technology on microalgae-based wastewater treatment to bioenergy production: A review

The production of renewable biofuel through microalgae and green technology can be a promising solution to meet future energy demands whilst reducing greenhouse gases (GHG) emissions and recovering energy for a carbon-neutral bio-economy and environmental sustainability. Recently, the integration of Energy Informatics (EI) technology as an emerging approach has ensured the feasibility and enhancement of microalgal biotechnology and bioenergy applications. Integrating EI technology such as artificial intelligence (AI), predictive modelling systems and life cycle analysis (LCA) in microalgae field applications can improve cost, efficiency, productivity and sustainability. With the approach of EI technology, data-driven insights and decision-making, resource optimization and a better understanding of the environmental impact of microalgae cultivation could be achieved, making it a crucial step in advancing this field and its applications. This review presents the conventional technologies in the microalgae-based system for wastewater treatment and bioenergy production. Furthermore, the recent integration of EI in microalgal technology from the AI application to the modelling and optimization using predictive control systems has been discussed. The LCA and techno-economic assessment (TEA) in the environmental sustainability and economic point of view are also presented. Future challenges and perspectives in the microalgae-based wastewater treatment to bioenergy production integrated with the EI approach, are also discussed in relation to the development of microalgae as the future energy source.

Advances in microalgae-based carbon sequestration: Current status and future perspectives

The advancement in carbon dioxide (CO2) sequestration technology has received significant attention due to the adverse effects of CO2 on climate. The mitigation of the adverse effects of CO2 can be accomplished through its conversion into useful products or renewable fuels. In this regard, microalgae is a promising candidate due to its high photosynthesis efficiency, sustainability, and eco-friendly nature. Microalgae utilizes CO2 in the process of photosynthesis and generates biomass that can be utilized to produce various valuable products such as supplements, chemicals, cosmetics, biofuels, and other value-added products. However, at present microalgae cultivation is still restricted to producing value-added products due to high cultivation costs and lower CO2 sequestration efficiency of algal strains. Therefore, it is very crucial to develop novel techniques that can be cost-effective and enhance microalgal carbon sequestration efficiency. The main aim of the present manuscript is to explain how to optimize microalgal CO2 sequestration, integrate valuable product generation, and explore novel techniques like genetic manipulations, phytohormones, quantum dots, and AI tools to enhance the efficiency of CO2 sequestration. Additionally, this review provides an overview of the mass flow of different microalgae and their biorefinery, life cycle assessment (LCA) for achieving net-zero CO2 emissions, and the advantages, challenges, and future perspectives of current technologies. All of the reviewed approaches efficiently enhance microalgal CO2 sequestration and integrate value-added compound production, creating a green and economically profitable process.

Revisiting the Effect of U-Bends, Flow Parameters, and Feasibility for Scale-Up on Residence Time Distribution Curves for a Continuous Bioprocessing Oscillatory Baffled Flow Reactor

An oscillatory baffled flow reactor (OBR) has been designed with 60 interbaffled cells. The baffled columns of 40 mm internal diameter together result in a reactor length of 5740 mm. The oscillatory amplitude and frequency were in the range of 2–12 mm and 0.3–2 Hz, respectively. The report investigates the impact of U-bends and the number of reactor sections on axial dispersion for scale-up feasibility. A prediction model using operating parameters has been developed to maximize plug flow conditions using the tanks-in-series (TiS) model. The maximum TiS value was 13.38 in a single column compared to 43.68 in the full reactor at a velocity ratio of 2.27 using oscillatory parameters 8 mm and 0.3 Hz. The mixing efficiency along the reactor was found to decrease after each column at amplitudes <6 mm compared to amplitudes up to 12 mm, where a negligible impact was observed. U-bend geometry had a significant role in the decrease of TiS values.

Microalgae-based livestock wastewater treatment (MbWT) as a circular bioeconomy approach: Enhancement of biomass productivity, pollutant removal and high-value compound production

The intensive livestock activities that are carried out worldwide to feed the growing human population have led to significant environmental problems, such as soil degradation, surface and groundwater pollution. Livestock wastewater (LW) contains high loads of organic matter, nitrogen (N) and phosphorus (P). These compounds can promote cultural eutrophication of water bodies and pose environmental and human hazards. Therefore, humanity faces an enormous challenge to adequately treat LW and avoid the overexploitation of natural resources. This can be accomplished through circular bioeconomy approaches, which aim to achieve sustainable production using biological resources, such as LW, as feedstock. Circular bioeconomy uses innovative processes to produce biomaterials and bioenergy, while lowering the consumption of virgin resources. Microalgae-based wastewater treatment (MbWT) has recently received special attention due to its low energy demand, the robust capacity of microalgae to grow under different environmental conditions and the possibility to recover and transform wastewater nutrients into highly valuable bioactive compounds. Some of the high-value products that may be obtained through MbWT are biomass and pigments for human food and animal feed, nutraceuticals, biofuels, polyunsaturated fatty acids, carotenoids, phycobiliproteins and fertilizers. This article reviews recent advances in MbWT of LW (including swine, cattle and poultry wastewater). Additionally, the most significant factors affecting nutrient removal and biomass productivity in MbWT are addressed, including: (1) microbiological aspects, such as the microalgae strain used for MbWT and the interactions between microbial populations; (2) physical parameters, such as temperature, light intensity and photoperiods; and (3) chemical parameters, such as the C/N ratio, pH and the presence of inhibitory compounds. Finally, different strategies to enhance nutrient removal and biomass productivity, such as acclimation, UV mutagenesis and multiple microalgae culture stages (including monocultures and multicultures) are discussed.

Challenges in microalgal biofuel production: A perspective on techno economic feasibility under biorefinery stratagem

Rapidly exhausting fossil fuels combined with the ever-increasing demand for energy led to an ongoing search for alternative energy sources to meet the transportation, manufacturing, domestic and other energy demands of the grown population. Microalgae are at the forefront of alternative energy research due to their significant potential as a renewable feedstock for biofuels. However, microalgae platforms have not found a way into industrial-scale bioenergy production due to various technical and economic constraints. The present review provides a detailed overview of the challenges in microalgae production processes for bioenergy purposes with supporting techno-economic assessments related to microalgae cultivation, harvesting and downstream processes required for crude oil or biofuel production. In addition, biorefinery approaches that can valorize the by-products or co-products in microalgae production and enhance the techno-economics of the production process are discussed.

A Review on Synchronous Microalgal Lipid Enhancement and Wastewater Treatment

Microalgae are unicellular photosynthetic eukaryotes that can treat wastewater and provide us with biofuel. Microalgae cultivation utilizing wastewater is a promising approach for synchronous wastewater treatment and biofuel production. However, previous studies suggest that high microalgae biomass production reduces lipid production and vice versa. For cost-effective biofuel production from microalgae, synchronous lipid and biomass enhancement utilizing wastewater is necessary. Therefore, this study brings forth a comprehensive review of synchronous microalgal lipid and biomass enhancement strategies for biofuel production and wastewater treatment. The review emphasizes the appropriate synergy of the microalgae species, culture media, and synchronous lipid and biomass enhancement conditions as a sustainable, efficient solution.

Biocrude Oil Production by Integrating Microalgae Polyculture and Wastewater Treatment: Novel Proposal on the Use of Deep Water-Depth Polyculture of Mixotrophic Microalgae

Microalgae have attracted significant attention worldwide as one of the most promising feedstock fossil fuel alternatives. However, there are a few challenges for algal fuels to compete with fossil fuels that need to be addressed. Therefore, this study reviews the R&D status of microalgae-based polyculture and biocrude oil production, along with wastewater treatment. Mixotrophic algae are free to some extent from light restrictions using organic matter and have the ability to grow well even in deep water-depth cultivation. It is proposed that integrating the mixotrophic microalgae polyculture and wastewater treatment process is the most promising and harmonizing means to simultaneously increase capacities of microalgae biomass production and wastewater treatment with a low land footprint and high robustness to perturbations. A large amount of mixotrophic algae biomass is harvested, concentrated, and dewatered by combining highly efficient sedimentation through flocculation and energy efficient filtration, which reduce the carbon footprint for algae fuel production and coincide with the subsequent hydrothermal liquefaction (HTL) conversion. HTL products are obtained with a relatively low carbon footprint and separated into biocrude oil, solid, aqueous, and gas fractions. Algae biomass feedstock-based HTL conversion has a high biocrude oil yield and quality available for existing oil refineries; it also has a bioavailability of the recycled nitrogen and phosphorus from the aqueous phase of algae community HTL. The HTL biocrude oil represents higher sustainability than conventional liquid fuels and other biofuels for the combination of greenhouse gas (GHG) and energy return on investment (EROI). Deep water-depth polyculture of mixotrophic microalgae using sewage has a high potential to produce sustainable biocrude oil within the land area of existing sewage treatment plants in Japan to fulfill imported crude oil.

A Comparative Study of Improvement of Phycoremediation Using a Consortium of Microalgae in Municipal Wastewater Treatment Pond Systems as an Alternative Solution to Africa’s Sanitation Challenges

The reuse of wastewater has been observed as a viable option to cope with increasing water stress in Africa. The present case studies evaluated the optimization of the process of phycoremediation as an alternative low-cost green treatment technology in two municipality wastewater treatment pond systems that make up the largest number of domestic sewage treatment systems on the African continent. A consortium of specific microalgae (Chlorella vulgaris and Chlorella protothecoides) was used to improve the treatment capacity of domestic wastewater at two operational municipality wastewater pond systems under different environmental conditions in South Africa. Pre- and post-phycoremediation optimization through mass inoculation of a consortium of microalgae, over a period of one year under different environmental conditions, were compared. It was evident that the higher reduction of total phosphates (74.4%) in the effluent, after treatment with a consortium of microalgae at the Motetema pond system, was possibly related to (1) the dominance of the algal taxa C. protothecoides (52%), and to a lesser extent C. vulgaris (36%), (2) more cloudless days, (3) higher air temperature, and (4) a higher domestic wastewater strength. In the case of the Brandwag pond treatment system, the higher reduction of total nitrogen can possibly be related to the dominance of C. vulgaris, different weather conditions, and lower domestic wastewater strength. The nutrient reduction data from the current study clearly presented compelling evidence in terms of the feasibility for use of this technology in developing countries to reduce nutrient loads from domestic wastewater effluent.

The Effects of Total Dissolved Carbon Dioxide on the Growth Rate, Biochemical Composition, and Biomass Productivity of Nonaxenic Microalgal Polyculture

The biosequestration of CO2 using microalgae has emerged as a promising means of recycling CO2 into biomass via photosynthesis, which could be used to produce biofuels as an attractive approach to CO2 mitigation. We investigated the CO2 fixation capability of the native nonaxenic microalgal culture using a 2 L photobioreactor operated in batch mode. The cultivation was carried out at varying concentrations of total dissolved CO2 (Tco2) in the bulk media ranging from 200 to 1000 mg L−1, and the temperature and light intensities were kept constant. A maximum CO2 fixation rate was observed at 400 mg L−1 of Tco2. Characteristic growth parameters such as biomass productivity, specific growth rate, maximum biomass yield, and biochemical parameters such as carbohydrate, protein, and lipids were determined and discussed. We observed that the effect of CO2 concentration on growth and biochemical composition was quite significant. The maximum biomass productivity was 22.10 ± 0.70 mg L−1 day−1, and the rate of CO2 fixation was 28.85 ± 3.00 mg L−1 day−1 at 400 mg L−1 of Tco2. The maximum carbohydrate (8.17 ± 0.49% dry cell weight) and protein (30.41 ± 0.65%) contents were observed at 400 mg L−1, whereas the lipid content (56.00 ± 0.82% dry cell weight) was the maximum at 800 mg L−1 of Tco2 in the bulk medium.

Reduction in Energy Requirement and CO2 Emission for Microalgae Oil Production Using Wastewater

A comparative evaluation of energy requirement and CO2 emission was performed for native polyculture microalgae oil production in a wastewater treatment plant (WWTP). The wastewater provided nutrients for algae growth. Datasets of microalgae oil production and their details were collected from the Minamisoma pilot plant. Environmental impact estimation from direct energy and material balance was analyzed using SimaPro® v8.0.4. in two scenarios: existing and algal scenarios. In the existing scenario, CO2 emission sources were from wastewater treatment, sludge treatment, and import of crude oil. In the algal scenario, CO2 emission with microalgae production was considered using wastewater treatment, CO2 absorption from growing algae, and hydrothermal liquefaction (HTL) for extraction, along with the exclusion of exhausted CO2 emission for growing algae and use of discharged heat for HTL. In these two scenarios, 1 m3 of wastewater was treated, and 2.17 MJ higher heating value (HHV) output was obtained. Consequently, 2.76 kg-CO2 eq/m3-wastewater in the existing scenario and 1.59 kg-CO2 eq/m3-wastewater in the algal scenario were calculated. In the HTL process, 21.5 MJ/m3-wastewater of the discharged heat energy was required in the algal scenario. Hence, the efficiency of the biocrude production system will surpass those of the WWTP and imported crude oil.

Resource recovery from wastewaters using microalgae-based approaches: A circular bioeconomy perspective

The basic concepts of circular bioeconomy are reduce, reuse and recycle. Recovery of recyclable nutrients from secondary sources could play a key role in meeting the increased demands of the growing population. Wastewaters of different origin are rich in energy and nutrients sources that can be recovered and reused in a circular bioeconomy perspective. Microalgae can effectively utilize wastewater nutrients for growth and biomass production. Integration of wastewater treatment and microalgal cultivation improves the environmental impacts of the currently used wastewater treatment methods. This review provides comprehensive information on the potential of using microalgae for the recovery of carbon, nitrogen, phosphorus and other micronutrients from wastewaters. Major factors influencing large scale microalgal wastewater treatment are discussed and future research perspectives are proposed to foster the future development in this area.