The effects of surfactants (sodium dodecyl sulfate, triton X-100 and cetyl trimethyl ammonium bromide) on the dewaterability of microalgae biomass using pressure filtration

Surfactant-Mediated Microalgal Flocculation: Process Efficiency and Kinetic Modelling

Microalgae are a valuable source of lipids, proteins, and pigments, but there are challenges in large-scale production, especially in harvesting. Existing methods lack proven efficacy and cost-effectiveness. However, flocculation, an energy-efficient technique, is emerging as a promising solution. Integrating surfactants enhances microalgal harvesting and disruption simultaneously, reducing processing costs. This study investigated cetyltrimethylammonium bromide (CTAB), dodecyltrimethylammonium bromide (DTAB), and sodium dodecyl sulphate (SDS) for harvesting Tetraselmis sp. strains (75LG and 46NLG). CTAB exhibits superior results, with 88% harvesting efficiency at 1500 and 2000 mg L-1 for 75LG and 46NLG, respectively, for 60 min of sedimentation-thus being able to reduce the operating time. Beyond evaluating harvesting efficiency, our study explored the kinetics of the process; the modified Gompertz model led to the best fit. Furthermore, the largest kinetic constants were observed with CTAB, thus highlighting its efficacy in optimising the microalgal harvesting process. With the incorporation of the suggested enhancements, which should be addressed in future work, CTAB could hold the potential to optimise microalgal harvesting for cost-effective and sustainable large-scale production, eventually unlocking the commercial potential of microalgae for biodiesel production.

Surfactant-assisted ethylenediamine for the deconstruction and conversion of corn stover biomass

Lignocellulosic biomass is a promising feedstock to produce sustainable fuels and energy toward a green bioeconomy. A surfactant-assisted ethylenediamine (EDA) was developed for the deconstruction and conversion of corn stover in this study. The effects of surfactants on the whole conversion process of corn stover was also evaluated. The results showed that xylan recovery and lignin removal in solid fraction were significantly enhanced by surfactant-assisted EDA. The glucan and xylan recoveries in solid fraction reached 92.1% and 65.7%, respectively, while the lignin removal was 74.5% by sodium dodecyl sulfate (SDS)-assisted EDA. SDS-assisted EDA also improved the sugar conversion in 12 h enzymatic hydrolysis at low enzyme loadings. The ethanol production and glucose consumption of washed EDA pretreated corn stover in simultaneous saccharification and co-fermentation were improved with the addition of 0.001 g/mL SDS. Therefore, surfactant-assisted EDA showed the potential to improve the bioconversion performance of biomass.

A rapid, efficient and eco-friendly approach for simultaneous biomass harvesting and bioproducts extraction from microalgae: Dual flocculation between cationic surfactants and bio-polymer

Microalgal biomass harvesting and cell disruption are the main bottlenecks for downstream processing of microalgae such as high-value bioproducts extraction and biofuels production. In this study, we evaluated the performance of dual flocculation between cationic surfactants and bio-polymer of chitosan for simultaneous biomass harvesting and bioproducts extraction from Chlorella sorokiniana microalgae. First, the effects of individual natural flocculants of chitosan and two cationic surfactants: cetyltrimethylammonium bromide (CTAB) and dodecyltrimethylammonium bromide (DTAB) on biomass harvesting were studied. Next, the synergistic effect of dual flocculation between the cationic surfactants and chitosan on harvesting efficiency, time and flocculant dosage was investigated. Finally, we evaluated the potential of high value bioproducts extraction from microalgae after the individual and dual flocculation processes. Zeta potential analysis and microscopic images were employed to achieve mechanistic understanding. Maximum biomass harvesting efficiencies of 85 %, 88 % and 78 % were achieved using individual flocculants of chitosan, CTAB and DTAB, under their optimum dosages of 100, 400 and 4000 mg/L, respectively. A significant synergistic effect of dual flocculation between chitosan (C) and cationic surfactants on biomass harvesting efficiency (CTAB-C: 99 % and DTAB-C: 97 %), settling time (CTAB-C: 2 min and DTAB-C: 5 min) and optimum dosage of surfactants (CTAB-C: 100 mg/L and DTAB-C: 1000 mg/L) was observed. The synergistic effect was associated with multiple flocculation mechanisms of charge neutralization and bridging induced by cationic surfactants and chitosan, respectively. Furthermore, bioproducts recovery efficiencies of 12 %, 25 % and 15 % of cell dry weight were achieved for protein, carbohydrate and lipid, respectively by using dual flocculation of CTAB surfactant and chitosan at much lower dosage of 100 mg/L.

Smart microalgae farming with internet-of-things for sustainable agriculture

Agriculture farms such as crop, aquaculture and livestock have begun the implementation of Internet of Things (IoT) and artificial intelligence (AI) technology in improving their productivity and product quality. However, microalgae farming which requires precise monitoring, controlling and predicting the growth of microalgae biomass has yet to incorporate with IoT and AI technology, as it is still in its infancy phase. Particularly, the cultivation stage of microalgae involves many essential parameters (i.e. biomass concentration, pH, light intensity, temperature and tank level) which require precise monitoring as these parameters are important to ensure an effective biomass productivity in the microalgae farming. Besides, the conventional practices in the current process equipment are still powered by electricity, thus further development by integrating IoT into these processes can ease the production process. Further to that, many researchers has studied the machine learning approach for the identification and classification of microalgae. However, there are still limited studies reported on applying machine learning for the application of microalgae industry such as optimising microalgae cultivation for higher biomass productivity. Therefore, the implementation of IoT and AI in microalgae farming can contribute to the development of the global microalgae industry. The purpose of this current review paper focuses on the overview microalgae biomass production process along with the implementation of IoT toward the future of smart farming. To bridge the gap between the conventional and microalgae smart farming, this paper also highlights the insights on the implementation phases of microalgae smart farming starting from the infant stage that involves the installation and programming of IoT hardware. Then, it is followed by the application of machine learning to predict and auto-optimise the microalgae smart farming process. Furthermore, the process setup and detailed overview of microalgae farming with the integration of IoT have been discussed critically. This review paper would provide a new vision of microalgae farming for microalgae researchers and bio-processing industries into the digitalisation industrial era.

Development a novel hexagonal airlift flat plate photobioreactor for the improvement of microalgae growth that simultaneously enhance CO2 bio-fixation and wastewater treatment

A novel hexagonal airlift flat plate (HAFP) photobioreactor was designed to improve microalgae growth rate and compared with traditional flat plate (TFP) photobioreactor. The computational fluid dynamics (CFD) simulation was used to determine hydrodynamic parameters and optimal aeration rate in the photobioreactors. Additionally, the capability of the HAFP photobioreactor to enhance microalgae based CO₂ bio-fixation and wastewater treatment were investigated. The results of CFD simulation indicated that the HAFP photobioreactor could improve hydrodynamic parameters of turbulence kinetic energy (TKE), average fluid velocity, dead zone (DZ), and water shear stress (WSS) up to 78 %, 41 %, 44 % and 40 %, respectively, under optimal aeration rate of 0.6 vvm. The proposed HAFP photobioreactor showed a drastic improvement in microalgae growth (up to 61 %). The maximum CO₂ removal of 53.8 % and bio-fixation of 0.85 g L^-1 d^-1 were achieved in the HAFP photobioreactor which were approximately 70 % more than that in the TFP photobioreactor. The results suggested that the HAFP photobioreactor could accelerate nutrients removal and achieve remarkably higher efficiencies of 91 %, 99 %, 97 % and 93 % of ammonia (NH₃), nitrate (NO₃^-), phosphate (PO₄^3-) and chemical oxygen demand (COD) within seven days of cultivation.

Simultaneous harvesting and extracellular polymeric substances extrusion of microalgae using surfactant: Promoting surfactant-assisted flocculation through pH adjustment

In this research, the use of four different types of surfactants on biomass harvesting and extracellular polymeric substances (EPS) extrusion of Chlorella sorokiniana sp was investigated. The synergy between cationic surfactants and pH was tested to improve flocculation efficiency through the combined mechanism of charge neutralization, bridging and sweeping. Zeta potential and microscopic images were used to gain mechanistic understanding. The harvesting efficacy correlated positively with the biomass zeta potential and the surfactants alkyl-chain length; i.e., CTAB (88%) > DTAB (66%) > triton X-100 (41%) > SDS (11%). When the pH increased from 8 to 12, the harvesting efficiency was improved 12% and 39% for CTAB and DTAB, respectively. More interestingly, pH adjustment dramatically reduced the optimal dosages of CTAB and DTAB from 400 to 50 and 1000 to 300 mg/L, respectively. All selected surfactants could successfully release high value components of EPS such as protein and polysaccharide.

Preparation of genetically engineered murine SINE RNA without endotoxin contamination

RNAs have been elucidated to play the critical role in regulating gene expression and to be expected as effective drugs in the treatment of cancer and age-related diseases. RNAs are extracted by SDS-NaCl centrifugation after transformation of E.coli by expression vectors, which is a method to obtain genetically engineered RNAs. But the prepared RNAs by this method contain endotoxin, which limits their application in vivo and in cell experments. Here we improved SDS-NaCl filtration method based on SDS-NaCl centrifugation method. Endotoxin removal efficiency of SDS-NaCl filtration was nearly 4.2 times more than did SDS-NaCl centrifugation. Triton X-114 phase separation was used to reduce futher the endotoxin content of SDS-NaCI filtration-extracted RNA (from 11.25 EU/µg RNA/ml to 0.08 EU/µg RNA/ml). RNA prepared using the methods established in this paper meets the requirements for in vivo and cell culture experiments. Here we describe the process of preparing endotoxin-free B1as RNA from pET-B1as-DE3 E. coli (DE3 transformed by pET-B1as expression vector which containing a tandem SINE B1 elements) using SDS-NaCl filtration incorporating Triton X-114 phase separation.•

The endotoxin removal efficiency of SDS-NaCl filtration is higher than that of SDS-NaCl centrifugation.

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RNA prepared by SDS-NaCl filtration incorporating Triton X-114 meets the requirements for in vivo experiments on animals.

Current and novel approaches to downstream processing of microalgae: A review

Biotechnological application of microalgae cultures at large scale has significant potential in the various fields of biofuels, food and feed, cosmetic, pharmaceutic, environmental remediation and water treatment. Despite this great potential application, industrialisation of microalgae culture and valorisation is still faced with serious remaining challenges in culture scale-up, harvesting and extraction of target molecules. This review presents a general summary of current techniques for harvesting and extraction of biomolecules from microalgae, their relative merits and potential for industrial application. The cell wall composition and its impact on microalgae cell disruption is discussed. Additionally, more recent progress and promising experimental methods and studies are summarised that would allow the reader to further investigate the state of the art. A final survey of energetic assessments of the different techniques is also made. Bead milling and high-pressure homogenisation seem to give clear advantages in terms of target high value compounds extraction from microalgae, with enzyme hydrolysis as a promising emerging technique. Future industrialisation of microalgae for high scale biotechnological processing will require the establishment of universal comparison-standards that would enable easy assessment of one technique against another.

Critical processes and variables in microalgae biomass production coupled with bioremediation of nutrients and CO2 from livestock farms: A review

Development of renewable and clean energy as well as bio-based fine chemicals technologies are the keys to overcome the problems such as fossil depletion, global warming, and environment pollution. To date, cultivation of microalgae using wastewater is regarded as a promising approach for simultaneous nutrients bioremediation and biofuels production due to their high photosynthesis efficiency and environmental benefits. However, the efficiency of nutrients removal and biomass production strongly depends on wastewater properties and microalgae species. Moreover, the high production cost is still the largest limitation to the commercialization of microalgae biofuels. In this review paper, the state-of-the-art algae species employed in livestock farm wastes have been summarized. Further, microalgae cultivation systems and impact factors in livestock wastewater to microalgae growth have been thoroughly discussed. In addition, technologies reported for microalgal biomass harvesting and CO₂ mass transfer enhancement in the coupling process were presented and discussed. Finally, this article discusses the potential benefits and challenges of coupling nutrient bioremediation, CO₂ capture, and microalgal production. Possible engineering measures for cost-effective nutrients removal, carbon fixation, microalgal biofuels and bioproducts production are also proposed.

A new approach for modeling flux variation in membrane filtration and experimental verification

It is important to model flux variation during the membrane filtration process, particularly in the early stage of filtration where severe fouling causes rapid flux decay in a short period of time. The objective of this study was to develop a combined fouling mathematical model based on energy head loss principle for prediction of flux variation in the membrane filtration. The complete-cake model was employed in the model in order to describe the loss of membrane available area due to pore clogging, while, the classical cake model was used for cake filtration. A new dimensionless parameter, namely the filter number (FN) was proposed in this study to account for the unmeasurable properties of the membrane in the model. The application of the proposed model was tested and compared with the existing models using experimental data for the filtration of wastewater sludge, microalgae suspension and sodium alginate solution with different membranes and pressures. The results showed that the flux calculated values of the new model had good agreements with the experimental data under different conditions. According to statistical analyses, the model improved the representing accuracy of flux variation in the early stage of filtration. In addition, the model provides better performance and efficiency in comparison to the existing models for high flux operations which is more conventionally applied in the industry and is expected to be more in the future.

Efficient elimination and re-growth inhibition of harmful bloom-forming cyanobacteria using surface-functionalized microbubbles

The elimination of cyanobacteria is frequently required for treating and controlling the waters with harmful algal blooms. In this study, an improved flotation technology was developed using colloidal gas aphrons (CGAs) surface-modified with the inorganic coagulant of polyaluminum chloride (PACl); the Microcystis aeruginosa (M. aeruginosa) cells were efficiently removed and their re-growth was effectively inhibited. The so-created coagulative CGAs (CCGAs) exhibited the attractive characteristics of both CGAs and PACl for the cell removal. The experimental results clearly showed that 94.2-99.2% of cells were removed within 3 min at the optimum dosage of cetyltrimethyl ammonium bromide (CTAB) and PACl at three different initial cell densities (OD₆₈₀ = 0.05, 0.26 and 0.76); and the re-growth of M. aeruginosa did not occur in 10 days. The flocs derived from the CCGA-flotation were of smaller size and looser configuration in contrast with those obtained from coagulation-flotation. The CCGAs were robust in charge neutralization, cell capture, cell attack and destruction. Even at low CTAB dosages, those bubbles could provide large surface area for capturing the M. aeruginosa cells in both unicellular and colonial form compared with the unmodified CTAB-CGAs. The CCGAs reduced 59.5-87.9% of CTAB dosage with the assistance of PACl and the required flotation retention time was largely shortened in comparison with the sedimentation and flotation-based treatment options. This would lead to low treatment cost and sludge production. The present work provides a novel insight into the development of flotation technologies for treating and controlling dense harmful algal blooms.