Process intensification in micro-fluidized bed systems: A review

Micro-fluidized bed (MFB) is a novel technology for engineering processing and screening application due to its good mixing, high mass/heat transfer, reduced reaction time and cost, but issues that remain unresolved are the low fluidization quality and scalability. In this review paper, fundamental and characteristic studies are reviewed to gain an understanding of the miniaturized fluidized bed system for rapid processing and screening. Subsequently, recent progress of the MFB applications is evaluated and compared with other types of reactors from the perspective of process intensification (PI). Finally, the challenges and prospects for this technology for PI are also discussed

Miniaturized bioreactor for bioprocessing: design and optimisation of a three-phase fluidized bed

Ph. D. Thesis.The fluidized bed reactor (FBR) is a processing platform relying on the fluidization of solids by liquid/gas flows, thus achieving the excellent multi-phases contact, minimum diffusional resistance, good heat and mass transfer. Recently, the miniaturization of fluidized bed has received much attention due to its fast screening and process intensification. However, the application of miniaturized fluidized bed in bioprocessing and bioproduction is still not explored, although FBR enables higher mass transfer, lower shear force and less energy consumption compared with flask, stirred-tank reactor and photobioreactor, respectively. To broaden the applicability of fluidized bed reactor in bioprocessing, this thesis combined the miniaturized fluidized bed reactor with Nidula niveo-tomentosa fungi to investigate the performance of FBR on fungal fermentation and raspberry ketone bioproduction. Thus, four main research themes were subsequently formulated and explored: (I). Design and fabrication of the micro-fluidized bed through 3D-printing technique; (II). Development of deeper understanding of the micro-fluidized bed based on liquid-gas and liquid-solid-gas hydrodynamic characteristics; (III). Investigation the cultivation parameters and different bioreactors for fungal fermentation and production; (IV). Development and investigation of a bench-scale fluidized bed reactor for fungal fermentation and raspberry ketone production. The preliminary study of pellet fluidization provided an experimental basis for the fungal fermentation using fluidized bed reactor, as fungal pellets in the micro-fluidized bed could be well fluidized by both liquid and gas flows, while the gas flow can not only improve the mixing but also decrease pellet agglomeration. Then, the following study demonstrated that the optimal cultivation conditions including 75g/l glucose concentration, 2.5 g/l of phenylalanine, 3-weekold of 40% seed culture can largely improve raspberry ketone (RK) production in flask culture. Besides, the homogenization which breaks the pellets into free mycelia can further promote ii RK production. Finally, the combination of these optimal parameters with the bench-scale fluidized bed bioreactor yielded raspberry ketone (up to 5 times compared to the control study by flask culture) and raspberry compounds (up to 3 times compared to the control study by flask culture), improving the overall bioproduction of Nidula niveo-tomentosa fungi. Therefore, this thesis successfully proved the novel use of fluidized bed bioreactor for fungal fermentation, as the gas/liquid flows can fluidize the pellets which provide sufficient mass transfer and gas supply. Besides, the gas flow can decrease the pellet agglomeration thus mitigating the dead zone. Such a combination of fluidized bed bioreactor with fungal pellets opens up opportunities to develop a suitable and efficient bioprocessing technique in fungal fermentation.Newcastle University, Agency for Science, Technology and Research (A*STAR), Singapor

The Protagonism of Biocatalysis in Green Chemistry and Its Environmental Benefits

The establishment of a bioeconomy era requires not only a change of production pattern, but also a deep modernization of the production processes through the implementation of novel methodologies in current industrial units, where waste materials and byproducts can be utilized as starting materials in the production of commodities such as biofuels and other high added value chemicals. The utilization of renewable raw resources and residues from the agro-industries, and their exploitation through various uses and applications through technologies, particularly solid-state fermentation (SSF), are the main focus of this review. The advocacy for biocatalysis in green chemistry and the environmental benefits of bioproduction are very clear, although this kind of industrial process is still an exception and not the rule. Potential and industrial products, such as biocatalysts, animal feed, fermentation medium, biofuels (biodiesel, lignocelulose ethanol, CH4, and H2), pharmaceuticals and chemicals are dealt with in this paper. The focus is the utilization of renewable resources and the important role of enzymatic process to support a sustainable green chemical industry.The authors are grateful to FAPERJ, CNPq, PETROBRAS, FINEP, PRH-ANP (all Brazilian), and MINECO (Spain) for financial support. We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI)

Anaerobic membrane bioreactors for biohydrogen production: recent developments, challenges and perspectives

Biohydrogen as one of the most appealing energy vector for the future represents attractive avenue in alternative energy research. Recently, variety of biohydrogen production pathways has been suggested to improve the key features of the process. Nevertheless, researches are still needed to overcome remaining barriers to practical applications such as low yields and production rates. Considering practicality aspects, this review emphasized on anaerobic membrane bioreactors (AnMBRs) for biological hydrogen production. Recent advances and emerging issues associated with biohydrogen generation in AnMBR technology are critically discussed. Several techniques are highlighted that are aimed at overcoming these barriers. Moreover, environmental and economical potentials along with future research perspectives are addressed to drive biohydrogen technology towards practicality and economical-feasibility

Opportunities, recent trends and challenges of integrated biorefinery: Part II

Availability of cost-competitive biomass conversion technologies plays crucial role for successful realization of biorefinery for sustainable production of fuels and organic chemicals from biomass. The present article provides an outline of opportunities and socio-techno-economic challenges of various biomass processing technologies. The biomass processing technologies were classified into three broad categories: thermochemical, chemical and biochemical. This review article presents an overview of two potential thermochemical conversion processes, gasification and fast pyrolysis, for direct conversion of lignocellulosic biomass. The article further provides a brief review of chemical conversion of triglycerides by transesterification with methanol for production of biodiesel. The highly productive microalgae as an abundant source of triglycerides for biodiesel and various other fuels products were also reviewed. The present article also provides an outline of various steps involved in biochemical conversion of carbohydrates to alcoholic bio-fuels, bio-ethanol and bio-butanols and conversion of nature׳s most abundant aromatic polymer, lignin, to value-added fuels and chemicals. Furthermore, an overview of production of hydrocarbon fuels through various biomass processing technologies such as hydrodeoxygenation of triglycerides, biosynthetic pathways and aqueous phase catalysis in hydrocarbon biorefinery were highlighted. The present article additionally provides economic comparisons of various biomass conversion technologies

ECUT (Energy Conversion and Utilization Technologies) program: Biocatalysis project

The Annual Report presents the fiscal year (FY) 1988 research activities and accomplishments, for the Biocatalysis Project of the U.S. Department of Energy, Energy Conversion and Utilization Technologies (ECUT) Division. The ECUT Biocatalysis Project is managed by the Jet Propulsion Laboratory, California Institute of Technology. The Biocatalysis Project is a mission-oriented, applied research and exploratory development activity directed toward resolution of the major generic technical barriers that impede the development of biologically catalyzed commercial chemical production. The approach toward achieving project objectives involves an integrated participation of universities, industrial companies and government research laboratories. The Project's technical activities were organized into three work elements: (1) The Molecular Modeling and Applied Genetics work element includes research on modeling of biological systems, developing rigorous methods for the prediction of three-dimensional (tertiary) protein structure from the amino acid sequence (primary structure) for designing new biocatalysis, defining kinetic models of biocatalyst reactivity, and developing genetically engineered solutions to the generic technical barriers that preclude widespread application of biocatalysis. (2) The Bioprocess Engineering work element supports efforts in novel bioreactor concepts that are likely to lead to substantially higher levels of reactor productivity, product yields and lower separation energetics. Results of work within this work element will be used to establish the technical feasibility of critical bioprocess monitoring and control subsystems. (3) The Bioprocess Design and Assessment work element attempts to develop procedures (via user-friendly computer software) for assessing the energy-economics of biocatalyzed chemical production processes, and initiation of technology transfer for advanced bioprocesses

Towards value from waste: Bioreactor selection for the reduction of nutrient load and production of Poly-y-glutamic acid

Humanity is reaching a critical point in history where the re-use of resources previously classified as waste is becoming a necessary strategy to long term sustainability, through concepts such as circular economies. The re-use and reimagination of wastewater through the concept of a wastewater biorefinery (WWBR) is one such potential opportunity. It is the merging of integrated wastewater processing with bioproduction of valuable products from a waste stream, whilst still achieving clean water as an equally important and valuable product. These value-add products need to have sufficient value, and fulfil a market need to ensure that the WWBR is economically viable. South Africa's wastewater treatment plants, whilst faced with the challenges of rapidly growing populations, limited financial investment in infrastructure, maintenance and skilled operators, have the potential to achieve the goals of the bioeconomy and wastewater treatment through the implementation of the wastewater biorefinery concept. One of the main challenges facing the implementation of WWBR is the dilute and non-sterile nature of the wastewater. In traditional bioprocessing, this does not favour product formation due to the high flowrate and dilute streams. However, through optimisation of bioreactor design and careful selection against a set of design and operational criteria, a suitable reactor technology can be chosen that will facilitate bioproduction from these dilute streams and overcome the tensions. This project investigated the current wastewater treatment technologies used in a South African context and selected a reactor technology that meets the bioreactor selection criteria to address the challenges of bioproduction. To test its concept, the study focuses on an example product and microorganism from wastewater. One such product that has high potential for application in a WWBR is poly-ɣ-glutamic acid (ɣ-PGA.) It is a naturally occurring biopolymer with potential for application in medical, food, agricultural, wastewater treatment and cosmetic industries. A known ɣ-PGA-producing Bacillus subtilis strain was isolated (referred to as Isolate 1) from a wastewater treatment facility in Mitchells Plain, South Africa by Madonsela (2013). The kinetics of Isolate 1 were studied in stirred tank reactors (STRs) with a dilute minimal media under ideal temperature conditions (37°C) as well as uncontrolled room temperature to mimic environmental fluctuations that could be seen in a WWBR. The biomass productivity and maximum specific growth rates were estimated. Fed-batch room temperature cultivation was used to investigate if the biomass and PGA productivities could be maintained over extended time by feeding at the maximum glucoseutilisation rate seen during the batch cultivations. The maximum specific growth rates determined were used to inform the critical dilution rate expected in the continuous experiments. A detailed review of the existing reactor technologies used in South Africa's wastewater treatment plants was contrasted against the criteria for WWBR reactor selection, and through further literature review and refinement of the criteria, a SWOT analysis was done. The Moving Bed Biofilm Reactor or MBBR fulfilled the key criteria of a WWBR. With its reputation as a simple, yet robust technology with the ability to be retrofitted into existing wastewater treatment plant infrastructure (Odegaard, 2006; Wang et al., 2006; van Haandel & van der Lubbe, 2012), it was identified as the most promising reactor technology to investigate the aims of this research. A lab-scale MBBR was designed and constructed to demonstrate the continuous production of ɣ-PGA and the impact of biomass retention on productivities and nutrient removal, under continuous and nonsterile conditions. The dilution rate was increased beyond the calculated critical dilution rate to confirm that biomass retention would allow operation at higher dilution rates, whilst still maintaining or improving biomass and ɣ-PGA yields. The results from the STR batch cultivations compared the growth and productivity of Isolate 1 (Bacillus subtillis) at room temperature (RT) and 37 °C. The overall and maximum biomass productivities in the room temperature batch cultivations were an average of 0.071 ± 0.007 g/L/h and 0.425 ± 0.108 g/L/h respectively. These increased to 0.174 g/L/h and 1.246 g/L/h at 37 °C. The maximum specific growth rates under the RT conditions achieved average values of 0.150 ± 0.049 h -1 and 0.376 h -1 at 37 °C. Based on the maximum specific growth rates, a range of critical dilution rates were calculated to guide the process design and operating parameters in the continuous cultivation studies. Duplicate fed-batch experiments were conducted with the feed-rate set to the maximum glucose utilisation rate calculated from the batch experiments to achieve a final glucose loading of 2.86 g/L/h. Overall biomass productivities were increased from batch to fed batch phase from 0.092 ± 0.004 g/L/h to 0.189 ± 0.008 g/L/h. The average overall yield and productivities of ɣ-PGA (YP/S) in the fed-batch cultivations were calculated to be 0.681 ± 0.066 gP/gS and 0.667 ± 0.801 g/L/h. Following the design and construction of the MBBR, optimal operating parameters such as the loading of carrier and aeration rate needed to be found. Mass transfer studies using the static gassing in-out method were conducted to determine the preferred biofilm carrier loading (percentage of carrier volume in the reactor working volume) allowing the highest oxygen mass transfer. It was found that the optimal filling percentage was 40% and aeration rates of 3 to 5 L/min with volumetric mass transfer coefficient range of 17.23 to 35.64 h -1 . Hydrodynamic studies conducted at three different retention times (24h, 12 and 6 hours) and fixed aeration rate of 4 L/min. An increase in the liquid flowrate through the reactor resulted in shortened mixing times. No dead zones were observed. The mixing times of 40.5 ± 5.2 minutes (24 h), 24.5 ± 3.8 minutes (12 h) and 12.5 ± 2.7 minutes (6 h) found to be significantly smaller than the retention times, and thus the system was well-mixed with no visible dead zones or poor mixing. Biofilm attachment of Isolate 1 was demonstrated on the K3 Annox Kaldnes9® carriers. After a 4-week acclimation period, SEM imaging confirmed a thin and robust biofilm layer consisting of rod-shaped Bacillus-looking cells on the carriers. The MBBR continuous studies were commenced at a 24 h retention time (0.042 h-1 dilution rate) to ensure adequate biofilm retention and attachment onto the carriers. SEM imaging of the carriers again confirmed the presence of attached biofilm and dominance of rod-shaped bacteria as expected from Bacillus subitilis. The dilution rate was gradually increased until it reached the critical dilution rates calculated from the RT batch experiments. To test the robustness of the system the dilution rates were doubled twice thereafter until a decrease in substrate utilisation was observed at dilution rate 3-fold higher than the critical dilution rate. The retention times tested were 24, 21, 15, 10, 6.6, 4 and 2 hours (corresponding dilution rates of 0.042, 0.048, 0.037, 0.100, 0.152, 0.250 and 0.500 h-1 ). The steady-state results showed an increase in biomass and ɣ-PGA productivities with an increase in dilution rate. The biomass productivity increased from 0.156 g/L/h at 24 h (0.042 h-1 ) to 0.839 g/L/h at 2 h (0.500 h -1 ). The substrate utilisation (total carbon fed) decreased from 100% at a retention time of 0.042 to 95% at a retention time of 0.500 h-1 , while ɣ-PGA productivity increased from 0.367 g/L/h to 7.519 g/L/h. At dilution rates > 0.152 h-1 , the OD600 of the planktonic cell started to decrease. This is a significant result as, in a suspension culture, it would signify that cell washout was occurring and there would be a decrease in productivity. This is, however, not the case with productivity increasing; this demonstrates that significant biomass retention and biofilm development within in the MBBR and the uncoupling of hydraulic and biomass retention times drive productivity up, with decreasing dilution rates. One of the key objectives of this research was to demonstrate the proof of concept of the MBBR following its selection against key criteria required for the WWBR bioreactor and prove that bioproduction is possible. The MBBR was able to achieve increasing productivities of biomass and ɣPGA and high substrate utilisation at dilution rates higher than the critical dilution rate. This result demonstrates that WWBR using existing wastewater reactor technologies have great potential. Alongside this, the MBBR is easily retrofitted into existing activated sludge infrastructure that is widely used across South Africa. It is recommended that further study at a larger scale and conditions closer mimicking those of a WWTP be investigated to further test the potential of a WWBR in a South African context in fulfilling the sustainable future we all hope to achieve