Innovative strategies in algal biomass pretreatment for biohydrogen production

Valorization of Algal Biomass to Produce Microbial Polyhydroxyalkanoates: Recent Updates, Challenges, and Perspectives

Biopolymers are highly desirable alternatives to petrochemical-based plastics owing to their biodegradable nature. The production of bioplastics, such as polyhydroxyalkanoates (PHAs), has been widely reported using various bacterial cultures with substrates ranging from pure to biowaste-derived sugars. However, large-scale production and economic feasibility are major limiting factors. Now, using algal biomass for PHA production offers a potential solution to these challenges with a significant environmental benefit. Algae, with their unique ability to utilize carbon dioxide as a greenhouse gas (GHG) and wastewater as feed for growth, can produce value-added products in the process and, thereby, play a crucial role in promoting environmental sustainability. The sugar recovery efficiency from algal biomass is highly variable depending on pretreatment procedures due to inherent compositional variability among their cell walls. Additionally, the yields, composition, and properties of synthesized PHA vary significantly among various microbial PHA producers from algal-derived sugars. Therefore, the microalgal biomass pretreatments and synthesis of PHA copolymers still require considerable investigation to develop an efficient commercial-scale process. This review provides an overview of the microbial potential for PHA production from algal biomass and discusses strategies to enhance PHA production and its properties, focusing on managing GHGs and promoting a sustainable future.

Design, construction and application of algae-bacteria synergistic system for treating wastewater

The wastewater treatment technology of algae-bacteria synergistic system (ABSS) is a promising technology which has the advantages of low energy consumption, good treatment effect and recyclable high-value products. In this treatment technology, the construction of an ABSS is a very important factor. At the same time, the emergence of some new technologies (such as microbial fuel cells and bio-carriers, etc.) has further enriched constructing the novel ABSS, which could improve the efficiency of wastewater treatment and the biomass harvesting rate. Thus, this review focuses on the construction of a novel ABSS in wastewater treatment in order to provide useful suggestions for the technology of wastewater treatment.

Epitomizing biohydrogen production from microbes: Critical challenges vs opportunities

Hydrogen is a clean and green biofuel choice for the future because it is carbon-free, non-toxic, and has high energy conversion efficiency. In exploiting hydrogen as the main energy, guidelines for implementing the hydrogen economy and roadmaps for the developments of hydrogen technology have been released by several countries. Besides, this review also unveils various hydrogen storage methods and applications of hydrogen in transportation industry. Biohydrogen productions from microbes, namely, fermentative bacteria, photosynthetic bacteria, cyanobacteria, and green microalgae, via biological metabolisms have received significant interests off late due to its sustainability and environmentally friendly potentials. Accordingly, the review is as well outlining the biohydrogen production processes by various microbes. Furthermore, several factors such as light intensity, pH, temperature and addition of supplementary nutrients to enhance the microbial biohydrogen production are highlighted at their respective optimum conditions. Despite the advantages, the amounts of biohydrogen being produced by microbes are still insufficient to be a competitive energy source in the market. In addition, several major obstacles have also directly hampered the commercialization effors of biohydrogen. Thus, this review uncovers the constraints of biohydrogen production from microbes such as microalgae and offers solutions associated with recent strategies to overcome the setbacks via genetic engineering, pretreatments of biomass, and introduction of nanoparticles as well as oxygen scavengers. The opportunities of exploiting microalgae as a suastainable source of biohydrogen production and the plausibility to produce biohydrogen from biowastes are accentuated. Lastly, this review addresses the future perspectives of biological methods to ensure the sustainability and economy viability of biohydrogen production.

Mathematical modeling of dark fermentative hydrogen and soluble by-products generations from water hyacinth

The production of hydrogen and soluble metabolite products from water hyacinth via dark fermentation was modeled. The model was built on the assumption that the substrate exists in two forms (i.e., soluble and particulate) and undergoes two stages (i.e., hydrolysis and acidogenesis) in the dark fermentation process. The modified Michaelis-Menten and surface-limiting models were applied to describe the hydrolysis of soluble and particulate forms, respectively. Meanwhile, the acidogenesis stage was modeled based on the multi-substrate-single-biomass model. The effects of temperature, pH, and substrate concentration were integrated into the model to increase flexibility. As a result, the model prediction agreed with the experimental and literature data of water hyacinth-fed dark fermentation, with high coefficient of determination values of 0.92 - 0.97 for hydrogen and total soluble metabolite products. These results indicate that the proposed model could be further applied to dark fermentation's downstream and hybrid processes using water hyacinth and other substrates.

Solid-state fermentation-based enzyme-assisted extraction of eicosapentaenoic acid-rich oil from Nannochloropsis sp

Enzymatic treatment of microalgal biomass is a promising approach for extraction of microalgal lipid, but high cost of commercially sourcing enzyme is a major drawback in industrial implementation. Present study involves extraction of eicosapentaenoic acid-rich oil from Nannochloropsis sp. biomass using low cost cellulolytic enzymes produced from Trichoderma reesei in a solid-state fermentation bioreactor. Maximum total fatty acid recovery of 369.4 ± 4.6 mg/g dry weight (total fatty acid yield of 77%) was achieved in 12 h from the enzymatically treated microalgal cells, of which the eicosapentaenoic acid content was 11%. Sugar release of 1.70 ± 0.05 g/L was obtained post enzymatic treatment at 50 °C. The enzyme was reused thrice for cell wall disruption without compromising on total fatty acid yield. Additionally, high protein content of 47% in the defatted biomass could be explored as a potential aquafeed, thus enhancing the overall economics and sustainability of the process.