Enhancing Scenedesmus obliquus biofilm growth and CO2 fixation in a gas-permeable membrane photobioreactor integrated with additional rough surface

Biofilm and suspension-based cultivation of microalgae to treat anaerobic digestate food effluent (ADFE)

Anaerobic digestion of organic waste produces effluent (ADE) that requires further treatment. Biofilm-based microalgal cultivation is a favoured approach to ADE treatment. This study compared Chlorella sp. MUR 268 and Scenedesmus sp. MUR 269 in biofilm and suspension cultures to treat anaerobic digestate food effluent (ADFE). Chlorella sp. MUR 268 biofilm had significantly higher biomass (50.38 g m-2) than Scenedesmus sp. biofilm (9.39 g m-2). Conversely, Scenedesmus sp. yielded 1.5 times more biomass (1.2 g L-1) than Chlorella sp. in suspension. Chlorella sp. biofilm had 49.3 % higher areal productivity than suspension, while Scenedesmus sp. showed 87.3 % higher areal growth in suspension. Chlorella sp. MUR 268 and Scenedesmus sp. MUR 269 significantly removed nutrients in ADFE. In suspension, COD, ammoniacal nitrogen, and phosphate were reduced to 94.9, 5.2, and 5.98 mg L-1 for Chlorella sp. MUR 268, and 245, 2.89, and 3.22 mg L-1 for Scenedesmus sp. MUR 269, respectively. In biofilm, Chlorella sp. MUR 268 achieved reductions to 149.9, 1.16, and 3.57 mg L-1, while Scenedesmus sp. MUR 269 achieved 100.2, 6.9 and 2.07 mg L-1. Most of these values are below the recommended effluent discharge standard, highlighting the efficacy of this system in ADFE treatment. Biofilm cultures fixed 68-81 % of removed nitrogen in biomass, while in suspension, only 55-71 % ended in the biomass. Chlorella sp. MUR 268 biofilm fixed 88 % of removed phosphorus, while Scenedesmus sp. MUR 269 suspension fixed more phosphorus (55 %) than the biofilm counterpart (34 %). This biofilm design offers advantages like simplified, cost-effective operation, easy biomass recovery, and reduced water usage.

CO2-philicity to CO2-phobicity Transition on Smooth and Stochastic Rough Cu-like Substrate Surfaces

CO2 on metal substrates is essential to CO2 liquefaction and transportation of CO2, yet the manipulation of the wettability of the CO2 and the elucidation of its underlying mechanism have not been fully achieved. Here, using molecular dynamics simulations, we report CO2 wetting characteristics on both smooth and stochastic rough Cu-like substrate surfaces. The results indicate that the apparent contact angle (CA) of the CO2 droplet on the smooth surface decreases from 180° to 0° as the CO2-solid characteristic interaction energy increases from 0.002 to 0.016 eV. In addition, the CAs become greater with increasing the density of surface asperities, regardless of the intrinsic surface wettability. This is attributed to the capillary drying-out of liquid CO2 molecules in gaps between surface asperities at the three-phase contact line of the droplet, which is usually overlooked in previous theoretical studies. Notably, the intrinsically CO2-philic surface transforms to the CO2-phobic due to an increase in the density of surface rugosity. Moreover, we verify the range of applicability of the CA prediction models concerning the nanoscale asperities. This work is beneficial for fully understanding the influence of nanoscale surface topography on CO2 wettability and shedding light on the design of functionalized and patterned surfaces to manipulate CO2 wettability.

Microalgae cell adhesions on hydrophobic membrane substrates using quartz crystal microbalance with dissipation

Microalgal cell adhesion and biofilm formation are affected by interactions between microalgae strains and membrane materials. Variations of surface properties of microalgae and membrane materials are expected to affect cell-membranes and cell-cell interactions and thus initial microalgal cell adhesion and biofilm formation rates. Hence, it should be possible to identify the dominant mechanisms controlling microalgal cell adhesion and biofilm formation. The effects of surface properties of three different microalgal strains and three different types of membrane materials on microalgal cell adhesion and biofilm formation were systematically investigated in real time by monitoring changes in the oscillation frequency and dissipation of the quartz crystal resonator (QCM-D). The results revealed that in general a higher surface free energy, more negative zeta potential, and higher surface roughness of membrane materials positively correlated with a larger quantity of microalgae cell deposition, while a more hydrophilic microalgae with a larger negative zeta potential preferred to attach to a more hydrophobic membrane material. The adhered microalgal layers exhibited viscoelastic properties. The relative importance of these mechanisms in controlling microalgae cell attachment and biofilm formation might vary, depending on the properties of specific microalgae species and hydrophobic membrane materials used.

Surface properties of membrane materials and their role in cell adhesion and biofilm formation of microalgae

In this study, the effects of surface properties of membrane materials on microalgae cell adhesion and biofilm formation were investigated using Chlorella vulgaris and five different types of membrane materials under hydrodynamic conditions. The results suggest that the contact angle (hydrophobicity), surface free energy, and free energy of cohesion of membrane materials alone could not sufficiently elucidate the selectivity of microalgae cell adhesion and biofilm formation on membrane materials surfaces, and membrane surface roughness played a dominant role in controlling biofilm formation rate, under tested hydrodynamic conditions. A lower level of biofilm EPS production was generally associated with a larger amount of biofilm formation. The zeta potential of membrane materials could enhance initial microalgae cell adhesion and biofilm formation through salt bridging or charge neutralization mechanisms.

Unlocking the potential of microalgae bio-factories for carbon dioxide mitigation: A comprehensive exploration of recent advances, key challenges, and energy-economic insights

Microalgae are promising alternatives to mitigate atmospheric CO₂ owing to their fast growth rates, resilience in the face of adversity and ability to produce a wide range of products, including food, feed supplements, chemicals, and biofuels. However, to fully harness the potential of microalgae-based carbon capture technology, further advancements are required to overcome the associated challenges and limitations, particularly with regards to enhancing CO₂ solubility in the culture medium. This review provides an in-depth analysis of the biological carbon concentrating mechanism and highlights the current approaches, including species selection, optimization of hydrodynamics, and abiotic components, aimed at improving the efficacy of CO₂ solubility and biofixation. Moreover, cutting-edge strategies such as gene mutation, bubble dynamics and nanotechnology are systematically outlined to elevate the CO₂ biofixation capacity of microalgal cells. The review also evaluates the energy and economic feasibility of using microalgae for CO₂ bio-mitigation, including challenges and prospects for future development.

Regulatory mechanism of high-concentration CO2 on polysaccharide accumulation in Tetradesmus obliquus cultured in sludge extract

Microalgae such as Tetradesmus obliquus have great potential in immobilizing high-concentration CO₂ and removing highly toxic organic matters, which could be produced from coal chemical industry and coal chemical wastewater biological treatment process. In this study, Tetradesmus obliquus was cultured in sludge extract and high-concentration CO₂ was added. The maximum cell density and dry weight were respectively (111.46 ± 4.87) × 10⁶ cell/mL and 3.365 ± 0.168 g/L under 30% CO₂. Tetradesmus obliquus accumulated the most polysaccharides (629.60 ± 31.48 mg/L) on the 30th day under 30% CO₂. The results of proteomic showed that the upregulation of A0A2Z4THB7 and A0A383VAT1 promoted polysaccharide accumulation. Polysaccharide was mainly formed at the stable phase instead of the log-growth phase due to the abiotic stress caused by high TOC at the log-growth phase. Collectively, this study revealed the regulatory mechanism of high-concentration CO₂ on the toxicity removal and accumulation of polysaccharides in Tetradesmus obliquus.

Characterization and evaluation of substratum material selection for microalgal biofilm cultivation

Biofilm cultivation is considered a promising method to achieve higher microalgae biomass productivity with less water consumption and easier harvest compared to conventional suspended cultivation. However, studies focusing on the selection of substratum material and optimization of the growth of certain microalgae species on specific substratum are limited. This study investigated the selection of membranous and fabric fiber substrata for the attachment of unicellular microalgae Scenedesmus dimorphus and filamentous microalgae Tribonema minus in biofilm cultivation. The results indicated that both algal species preferred hydrophilic membranous substrata and nitrate cellulose/cellulose acetate membrane (CN-CA) was selected as a suitable candidate on which the obtained biomass yields were up to 10.24 and 7.81 g m^-2 day^-1 for S. dimorphus and T. minus, respectively. Furthermore, high-thread cotton fiber (HCF) and low-thread polyester fiber (LPEF) were verified as the potential fabric fiber substrata for S. dimorphus (5.42 g m^-2 day^-1) and T. minus (5.49 g m^-2 day^-1) attachment, respectively. The regrowth of microalgae biofilm cultivation strategy was applied to optimize the algae growth on the fabric fiber substrata, with higher biomass density and shear resistibility achieved for both algal species. The present data highlight the importance to establish the standards for selection the suitable substratum materials in ensuring the high efficiency and sustainability of the attached microalgal biomass production. KEY POINTS: • CN-CA was suitable membranous substratum candidate for algal biofilm cultivation. • HCF and LPEF were potential fabric fiber substrata for S. dimorphus and T. minus. • Regrowth biofilm cultivation was effective in improving algal biomass and attachment.

Life-cycle assessment of flue gas CO2 fixation from coal-fired power plant and coal chemical plant by microalgae

The technology of flue gas CO₂ fixation by microalgae is highly attractive in the era of CO₂ neutrality. However, CO₂ emission along the whole process has yet to be sufficiently evaluated. Here, a life-cycle assessment was performed to evaluate the energy conversion characteristics and environmental impacts of flue gas CO₂ fixation from coal-fired power plant (Case 1) and coal chemical plant (Case 2) by microalgae. The results show that total energy consumption and CO₂ gas emissions for Case 1 are 27.5-38.0 MJ/kg microalgae power (MP) and 5.7-7.7 kg CO₂ equiv/kg MP, respectively, which are lower than that for Case 2 (122.5-181.3 MJ/kg MP and 32.7-48.6 kg CO₂ equiv/kg MP). The CO₂ gas aeration rate and microalgae growth rate are the two most sensitive parameters for the energy conversion and net CO₂ emission. Therefore, increasing the CO₂ aeration efficiency and microalgae growth rate are key to advance the technology of flue gas CO₂ fixation by microalgae which will contribute to carbon naturality.

A Two-Stage Culture Strategy for Scenedesmus sp. FSP3 for CO2 Fixation and the Simultaneous Production of Lutein under Light and Salt Stress

In this study, Scenedesmus sp. FSP3 was cultured using a two-stage culture strategy for CO₂ fixation and lutein production. During the first stage, propylene carbonate was added to the medium, with 5% CO₂ introduced to promote the rapid growth and CO₂ fixation of the microalgae. During the second stage of cultivation, a NaCl concentration of 156 mmol L^-1 and a light intensity of 160 μmol m^-2 s^-1 were used to stimulate the accumulation of lutein in the microalgal cells. By using this culture method, high lutein production and CO₂ fixation were simultaneously achieved. The biomass productivity and carbon fixation rate of Scenedesmus sp. FSP3 reached 0.58 g L^-1 d^-1 and 1.09 g L^-1 d^-1, with a lutein content and yield as high as 6.45 mg g^-1 and 2.30 mg L^-1 d^-1, respectively. The results reveal a commercially feasible way to integrate microalgal lutein production with CO₂ fixation processes.

A Two-Stage Culture Strategy for Scenedesmus sp. FSP3 for CO2 Fixation and the Simultaneous Production of Lutein under Light and Salt Stress

In this study, Scenedesmus sp. FSP3 was cultured using a two-stage culture strategy for CO2 fixation and lutein production. During the first stage, propylene carbonate was added to the medium, with 5% CO2 introduced to promote the rapid growth and CO2 fixation of the microalgae. During the second stage of cultivation, a NaCl concentration of 156 mmol L-1 and a light intensity of 160 μmol m-2 s-1 were used to stimulate the accumulation of lutein in the microalgal cells. By using this culture method, high lutein production and CO2 fixation were simultaneously achieved. The biomass productivity and carbon fixation rate of Scenedesmus sp. FSP3 reached 0.58 g L-1 d-1 and 1.09 g L-1 d-1, with a lutein content and yield as high as 6.45 mg g-1 and 2.30 mg L-1 d-1, respectively. The results reveal a commercially feasible way to integrate microalgal lutein production with CO2 fixation processes.

A review of recent advances in engineering bacteria for enhanced CO2 capture and utilization

Carbon dioxide (CO₂) is emitted into the atmosphere due to some anthropogenic activities, such as the combustion of fossil fuels and industrial output. As a result, fears about catastrophic global warming and climate change have intensified. In the face of these challenges, conventional CO₂ capture technologies are typically ineffective, dangerous, and contribute to secondary pollution in the environment. Biological systems for CO₂ conversion, on the other hand, provide a potential path forward owing to its high application selectivity and adaptability. Moreover, many bacteria can use CO₂ as their only source of carbon and turn it into value-added products. The purpose of this review is to discuss recent significant breakthroughs in engineering bacteria to utilize CO₂ and other one-carbon compounds as substrate. In the same token, the paper also summarizes and presents aspects such as microbial CO₂ fixation pathways, engineered bacteria involved in CO₂ fixation, up-to-date genetic and metabolic engineering approaches for CO₂ fixation, and promising research directions for the production of value-added products from CO₂. This review's findings imply that using biological systems like modified bacteria to manage CO₂ has the added benefit of generating useful industrial byproducts like biofuels, pharmaceutical compounds, and bioplastics. The major downside, from an economic standpoint, thus far has been related to methods of cultivation. However, thanks to genetic engineering approaches, this can be addressed by large production yields. As a result, this review aids in the knowledge of various biological systems that can be used to construct a long-term CO₂ mitigation technology at an industrial scale, in this instance bacteria-based CO₂capture/utilization technology.

CO2 biocapture by Scenedesmus sp. grown in industrial wastewater

Greenhouse gases (GHG) emissions are widely related to climate change, triggering several environmental problems of global concern and producing environmental, social, and economic negative impacts. Therefore, global research seeks to mitigate greenhouse gas emissions. On the other hand, the use of wastes under a circular economy scheme generates subproducts from the range of high to medium-value, representing a way to help sustainable development. Therefore, the use of wastewater as a culture medium to grow microalgae strains that biocapture environmental CO₂, is a proposal with high potential to reduce the GHG presence in the environment. In this work, Scenedesmus sp. was cultivated using BG-11 medium and industrial wastewater (IWW) as a culture medium with three different CO₂ concentrations, 0.03%, 10%, and 20% to determine their CO₂ biocapture potential. Furthermore, the concomitant removal of COD, nitrates, and total phosphorus in wastewater was evaluated. Scenedesmus sp. achieves a biomass concentration of 1.9 g L^-1 when is grown in BG-11 medium, 0.69 g L^-1 when is grown in a combination of BG-11 medium and 25% of industrial wastewater; both cases with 20% CO₂ supplied. The maximum CO₂ removal efficiency (8.4%, 446 ± 150 mg CO₂ L^-1 day^-1) was obtained with 10% CO₂ supplied and using a combination of BG-11 medium and 50% IWW (T2). Also, the highest removal of COD was reached with a combination of BG-11 medium and T2 with a supply of 20% CO₂ (82% of COD removal). Besides, the highest nitrates removal was achieved with a combination of BG-11 medium and 75% IWW (T3) with a supply of 10% CO₂ (42% of nitrates removal) and the maximum TP removal was performed with the combination of BG-11 medium and 25% IWW (T1) with a supply of 10% CO₂ (67% of TP removal). These results indicate that industrial wastewater can be used as a culture media for microalgae growth and CO₂ biocapture can be performed as concomitant processes.

Impacts of surface wettability and roughness of styrene-acrylic resin films on adhesion behavior of microalgae Chlorella sp

Biofilm attached cultivation is a promising method for efficient production of microalgae. Determining the surface property index to select an appropriate substrate benefiting the algae adhesion and biofilm formation is very important for the cultivation method. This work focused on elucidating and quantifying the influence of surface wettability and roughness of substrate on Chlorella vulgaris adhesion. Firstly, surface modified styrene-acrylic (SA) resin films by adding different dosage of perfluoroalkyl ethyl acrylate (FM) were prepared. Property characterization shows that the surface contact angle in water, formamide and diiodomethane of FM modified SA films is significantly associated with the FM dosage, while the other surface properties including zeta potential, surface potential and surface roughness have insignificant difference. The calculated surface free energy parameters show that the SA films belong to the non-polar substrata. A well quantitative correlation that the adhesion capacity of C. vulgaris linearly declines with the increase of water contact angle was obtained. And a near linear relationship between the adhesion capacity and the surface free energy (γ), or the cohesion free energy (ΔG_coh) was also observed. Secondly, the surface roughness solely changed SA films were prepared by replicating the morphology of stainless steel sieves through the PDMS template method. The patterned SA films have alternately arranged rectangular "valleys" and "ridges". A well linear correlation between the microalgae adhesion capacity and the surface roughness was also obtained.

The Effectiveness of Nafion-Coated Stainless Steel Surfaces for Inhibiting Bacillus Subtilis Biofilm Formation

Stainless steel is one of most commonly used materials in the world; however, biofilms on the surfaces of stainless steel cause many serious problems. In order to find effective methods of reducing bacterial adhesion to stainless steel, and to investigate the role of electrostatic effects during the formation of biofilms, this study used a stainless steel surface that was negatively charged by being coated with Nafion which was terminated by sulfonic groups. The results showed that the roughness of stainless steel discs coated with 1% Nafion was similar to an uncoated surface; however the hydrophobicity increased, and the Nafion-coated surface reduced the adhesion of Bacillus subtilis by 75% compared with uncoated surfaces. Therefore, a facile way to acquire antibacterial stainless steel was found, and it is proved that electrostatic effects have a significant influence on the formation of biofilms.

Enhancing CO2 Hydrogenation to Methane by Ni-Based Catalyst with V Species Using 3D-mesoporous KIT-6 as Support

Using renewable H2 for CO2 hydrogenation to methane not only achieves CO2 utilization, but also mitigates the greenhouse effect. In this work, several Ni-based catalysts with V species using 3D-mesoporous KIT-6 (Korea Advanced Institute of Science and Technology, KIT) as support were prepared at different contents of NiO and V2O5. Small Ni nanoparticles with high dispersibility on 20Ni-0.5V/KIT-6 were identified by X-ray diffraction (XRD), TEM and hydrogen temperature-programmed desorption (H2-TPD) analysis, which promoted the production of more Ni active sites for enhancing catalytic activity for CO2 methanation. Moreover, TEM and hydrogen temperature-programmed reduction (H2-TPR) characterizations confirmed that a proper amount of Ni and V species was favorable to preserve the 3D-mesoporous structure and strengthen the interaction between active Ni and KIT-6. The synergistic effect between Ni and V could strengthen surface basicity to elevate the ability of CO2 activity on the 20Ni-0.5V/KIT-6. In addition, a strong interaction with the 3D-mesoporous structure allowed active Ni to be firmly anchored onto the catalyst surface, which was accountable for improving catalytic activity and stability. These results revealed that 20Ni-0.5V/KIT-6 was a catalyst with superior catalytic activity and stability, which was considered as a promising candidate for CO2 hydrogenation to methane.