Optimizing carbon dioxide utilization for microalgae biofilm cultivation

Immobilized microalgae: principles, processes and its applications in wastewater treatment

Microalgae have emerged as potential candidates for biomass production and pollutant removal. However, expensive biomass harvesting, insufficient biomass productivity, and low energy intensity limit the large-scale production of microalgae. To break through these bottlenecks, a novel technology of immobilized microalgae culture coupled with wastewater treatment has received increasing attention in recent years. In this review, the characteristics of two immobilized microalgae culture technologies are first presented and then their mechanisms are discussed in terms of biofilm formation theories, including thermodynamic theory, Derjaguin-Landau-Verwei-Overbeek theory (DLVO) and its extended theory (xDLVO), as well as ionic cross-linking mechanisms in the process of microalgae encapsulated in alginate. The main factors (algal strains, carriers, and culture conditions) affecting the growth of microalgae are also discussed. It is also summarized that immobilized microalgae show considerable potential for nitrogen and phosphorus removal, heavy metal removal, pesticide and antibiotic removal in wastewater treatment. The role of bacteria in the cultivation of microalgae by immobilization techniques and their application in wastewater treatment are clarified. This is economically feasible and technically superior. The problems and challenges faced by immobilized microalgae are finally presented.

Efficient Mycoprotein Production with Low CO2 Emissions through Metabolic Engineering and Fermentation Optimization of Fusarium venenatum

The global protein shortage is intensifying, and promising means to ensure daily protein supply are desperately needed. The mycoprotein produced by Fusarium venenatum is a good alternative to animal/plant-derived protein. To comprehensively improve the mycoprotein synthesis, a stepwise strategy by blocking the byproduct ethanol synthesis and the gluconeogenesis pathway and by optimizing the fermentation medium was herein employed. Ultimately, compared to the wild-type strain, the synthesis rate, carbon conversion ratio, and protein content of mycoprotein produced from the engineered strain were increased by 57% (0.212 vs 0.135 g/L·h), 62% (0.351 vs 0.217 g/g), and 57% (61.9 vs 39.4%), respectively, accompanied by significant reductions in CO2 emissions. These results provide a referential strategy that could be useful for improving mycoprotein synthesis in other fungi; more importantly, the obtained high-mycoprotein-producing strain has the potential to promote the development of the edible protein industry and compensate for the gap in protein resources.

Enhancing CO2 photo-biochemical conversion in a newly-designed attached photobioreactor characterized by stacked horizontal planar waveguide modules

Aiming at alleviating the adverse effects on attached microalgae biofilm growth caused by heterogeneous spatial light distributions within the attached cultivation photobioreactors (PBRs), an innovative PBR integrated with stacked horizontal planar waveguide modules (SHPW-PBR) was proposed in this work. Different from the conventional PBR, the emergent light from the external LED light bars were guided and evenly redistributed within the SHPW-PBR by the planar waveguides and hence provided light energy for microalgae cells photoautotrophic growth. In comparison with the control PBR, the average light intensity illuminating the attached Chlorella vulgaris biofilm in the SHPW-PBR was elevated by 204.11% and contributed to a 145.20% improvement on areal C. vulgaris biofilm production. Thereafter, responses of attached C. vulgaris biofilm growth in the SHPW-PBR to various light intensities were evaluated and the maximum areal C. vulgaris biofilm density reached 90.43 g m^-2 under the light intensity of 136 μmol m^-2 s^-1 after 9 days cultivation. Furthermore, the SHPW-PBR can be easily scaled-up by increasing the quantity of the stacked planar waveguide modules and thus shows great potential in biofilm-based biomass production.

A Novel System for Real-Time, In Situ Monitoring of CO2 Sequestration in Photoautotrophic Biofilms

Climate change brought about by anthropogenic CO₂ emissions has created a critical need for effective CO₂ management solutions. Microalgae are well suited to contribute to efforts aimed at addressing this challenge, given their ability to rapidly sequester CO₂ coupled with the commercial value of their biomass. Recently, microalgal biofilms have garnered significant attention over the more conventional suspended algal growth systems, since they allow for easier and cheaper biomass harvesting, among other key benefits. However, the path to cost-effectiveness and scaling up is hindered by a need for new tools and methodologies which can help evaluate, and in turn optimize, algal biofilm growth. Presented here is a novel system which facilitates the real-time in situ monitoring of algal biofilm CO₂ sequestration. Utilizing a CO₂-permeable membrane and a tube-within-a-tube design, the CO₂ sequestration monitoring system (CSMS) was able to reliably detect slight changes in algal biofilm CO₂ uptake brought about by light–dark cycling, light intensity shifts, and varying amounts of phototrophic biomass. This work presents an approach to advance our understanding of carbon flux in algal biofilms, and a base for potentially useful innovations to optimize, and eventually realize, algae biofilm-based CO₂ sequestration.

Associated bacteria of Botryococcus braunii (Chlorophyta)

Botryococcus braunii (Chlorophyta) is a green microalga known for producing hydrocarbons and exopolysaccharides (EPS). Improving the biomass productivity of B. braunii and hence, the productivity of the hydrocarbons and of the EPS, will make B. braunii more attractive for industries. Microalgae usually cohabit with bacteria which leads to the formation of species-specific communities with environmental and biological advantages. Bacteria have been found and identified with a few B. braunii strains, but little is known about the bacterial community across the different strains. A better knowledge of the bacterial community of B. braunii will help to optimize the biomass productivity, hydrocarbons, and EPS accumulation. To better understand the bacterial community diversity of B. braunii, we screened 12 strains from culture collections. Using 16S rRNA gene analysis by MiSeq we described the bacterial diversity across 12 B. braunii strains and identified possible shared communities. We found three bacterial families common to all strains: Rhizobiaceae, Bradyrhizobiaceae, and Comamonadaceae. Additionally, the results also suggest that each strain has its own specific bacteria that may be the result of long-term isolated culture.

Microalgal biofilms: A further step over current microalgal cultivation techniques

The scientific community has turned its interest to microalgae lately, because of their countless applications such as wastewater treatment and pharmaceutical industry. Nevertheless, so far applied cultivation methods are still prohibitive. Ordinary cultivation techniques in which microalgae are suspended in liquid medium suffer from many bottlenecks, such as low biomass productivities, difficulty in biomass harvesting and recovery, high installation and operating cost, high water requirements etc. Although, microalgal biofilms are known to be a nuisance because of surfaces fouling, they have emerged as an innovative technology with which microalgae are developed attached to a solid surface. This technique seems to be advantageous as compared to conventional cultivation systems. Microalgal biofilm systems could resolve the problematic aspects of ordinary cultivation techniques such as low biomass productivities, water management and biomass recovery. A detailed description of this technique with respect to the parameters affecting them is reviewed in this work.

Cultivation of microalgal biomass using swine manure for biohydrogen production: Impact of dilution ratio and pretreatment

This study assessed the impact of swine manure (SM) dilution ratio on the microalgal biomass cultivation and further tested for biohydrogen production efficiency from the mixed microalgal biomass. At first, various solid/liquid (S/L) ratio of the SM ranged from 2.5 to 10 g/L was prepared as a nutrient medium for the algal biomass cultivation without addition of the external nutrient sources over a period of 18 d. The peak biomass concentration of 2.57 ± 0.03 g/L was obtained under the initial S/L loading rates of 5 g/L. Further, the cultivated biomass was subjected to two-step (ultrasonication + enzymatic) pretreatment and evaluated for biohydrogen production potential. Results showed that the variable amount of hydrogen production was observed with different S/L ratio of the SM. The peak hydrogen yield of 116 ± 6 mL/g TS_added was observed at the 5 g/L grown SM mixed algal biomass.