Continuous Bioreactor Research Articles

Flash hydrolysis of yeast (Saccharomyces cerevisiae) for protein recovery

Protein-rich spent yeast is a waste by-product of brewing and other fermentation industry. A continuous-flow hydrothermal treatment called ‘flash hydrolysis’ was deployed for protein recovery and yeast disposal. A feed slurry with 1–15 wt% yeast was hydrolyzed at temperatures ranging between 160 and 280 °C for a very short residence time of 10 ± 2 s. Using 10 wt% yeast at 240 °C, 66.5% carbon, 70.4% nitrogen and 61.0% overall yeast biomass was solubilized in liquid hydrolysate. The liquid hydrolysate in which 63.1% of analyzed amino acids in yeast feed were solubilized, was tested as nutrient for cultivation of E. coli in a continuous bioreactor. The steady-state E. coli concentration was 1.18 g L−1 and 0.93 g L−1 using liquid hydrolysate and commercial yeast extract, respectively. Finally, the kinetic parameters for yeast solubilization (reaction order, activation energy and pre-exponential factor) were found to be 0.86, 21.3 kJ mol−1 and 19.36 [L g−1]n−1 s−1, respectively.

Converting waste molasses liquor into biohydrogen via dark fermentation using a continuous bioreactor

This study investigated the effects of substrate concentration, HRT (hydraulic retention time), and pre-treatment of the substrate molasses on biohydrogen production from waste molasses (condensed molasses fermentation solubles, CMS) with a CSTR (continuously-stirred tank reactor). First, the hydrogen production was performed with various CMS concentrations (40–90 g COD/L, total sugar 8.7–22.6 g/L) with 6 h HRT. The results show that the maximal hydrogen production rate (HPR) occurred at 80 g COD/L substrate (19.8 g ToSu/L, ToSu: Total Sugar), obtaining an HPR of 0.417 mol/L/d. However, maximum hydrogen yield (HY) of 1.44 mol H2/mol hexose and overall hydrogen production efficiency (HPE) of 25.6% were achieved with a CMS concentration of 70 g COD/L (17.3 g ToSu/L). The substrate inhibition occurred when CMS concentration was increased to 90 g COD/L (22.6 g ToSu/L). Furthermore, it was observed that the optimal HPR, HY, and HPE all occurred at HRT 6 h. Operating at a lower HRT of 4 h decreased the hydrogen production performance because of lower substrate utilization efficiency. The employment of pre-heating treatment (60 °C for 1 h) of the substrate could markedly enhance the fermentation performance. With 6 h HRT and substrate pre-heating treatment, the HPE raised to 29.9%, which is 18% higher than that obtained without thermal pretreatment.

Stability and Performance Analysis of Bioethanol Production with Delay and Growth Inhibition in a Continuous Bioreactor with Recycle

This paper proposes and analyzes a mathematical model for the production of bioethanol in a continuous bioreactor with recycling. The kinetics correspond to the use of Saccharomyces bayanus for the fermentation of sugars found in wastewater from soft drinks. The proposed model considers product growth latency, which was experimentally found in batch studies of ethanol production. Furthermore, the inhibition effect of ethanol is expressed by a modified version of the classical Andrew’s model for substrate inhibition. The proposed model consists of only three ordinary differential equations containing a minimal number of operating parameters, which include the bioreactor residence time, glucose feed concentration, recycle ratio and the fraction of biomass removed from the reactor by the flow. The positivity and the boundedness of solutions of the model were confirmed under reasonable restrictions of parameters. The stability analysis showed that there is a value of residence time at which an exchange of stability occurs between the trivial washout and non-washout solutions. This critical value depends only on the substrate feed concentration, biomass death rate, recycle ratio and purge fraction. Dynamic simulations of the model were carried out for substrate concentration in the range of 100–250 g/L, commonly used for the production of ethanol. An inverse response due to the inhibition effects of ethanol was observed in the time evolution of substrate and biomass concentrations. Parametric studies showed that ethanol concentration increases with the recycle ratio, with the inverse of residence time and with the inverse of purge fraction. The effect of ethanol latency has, on the other hand, a substantial effect on ethanol concentration. Despite its unstructured nature and the fact that some parameters such as temperature and acidity were not taken into consideration, the proposed model managed to provide useful results on the bioreactor-settler stability and the effect of key parameters on its dynamic behavior, which could pave the way for future optimization studies.

Spirulina: growth in continuous and batch bioreactors and response to stress conditions

Spirulina platensis is a cyanobacterium with high biotechnological potential. Optimization of the cultivation conditions of spirulina takes place constantly, to increase the yield of this valuable crop. An important economic indicator of the process is an increase in the yield of biomass and a decrease in the cost of its production. For example, avoiding the need to cultivate spirulina at elevated temperatures with at least equal biomass yield. The purpose of this work was to develop and compare methods for cultivating Spirulina platensis in two bioreactors, continuous and batch ones, and to assess the resistance of spirulina cells to environmental stress caused by the presence of household chemicals. It was shown that, at room temperature, the wet biomass yield was higher in the bioreactor than with batch cultivation in flasks. However, a decrease in temperature leads to a decrease in the number of colony forming units. The presence of compounds such as phosphates and phosphonates from household chemicals in the cultivation environment negatively affects the survival of Spirulina cells, which reflects the general trend of a decrease in the number of microorganisms as a result of environmental pollution with surfactants.

Modeling of copy number variability in Pichia pastoris.

Development of continuous biopharmaceutical manufacturing processes is an area of active research. This study considers the long-term transgene copy number stability of Pichia pastoris in continuous bioreactors. We propose a model of copy number loss that quantifies population heterogeneity. An analytical solution is derived and compared with existing experimental data. The model is then used to provide guidance for stable operating timescales. The model is extended to consider copy number dependent growth such as in the case of Zeocin supplementation. The model is also extended to analyze a continuous seeding strategy. This study is a critical step towards understanding the impact of continuous processing on the stability of Pichia pastoris and the resultant products.

Bioprocessing of corn rind using continuous multiphase-multistage bioreactor for downstream applications

Corn rind is a major agricultural residue which is often problematic for disposal. However, it is a rich lignocellulose source useful for many downstream industrial applications. The technique commonly used in the bioconversion of organic waste is a static two-stage fermentation system; in the first stage, corn rind is converted to simple sugars, and at the second stage, reduced sugars are used to produce commercial products. The stage one is a resource-consuming process as the product removal is not dynamic, and hence, the bioconversion process comes to an equilibrium due to product accumulation. Therefore, a novel concept of continuous multiphase-multistage bioreactor was introduced, in which the sugars formed are continuously removed to enhance the bioconversion efficiency. A lab-scale model with three digestion modules, each with 2000-ml working capacity, is developed for degradation of corn rind to partially optimize the process parameters that eventually improve corn rind degradation. The multiphase in each stage contributes cumulatively in achieving better degradation of corn rind. In the first stage, out of 150-g feed-stock introduced, a total of 2353 mg of free reducing sugar was released on completion of five phases (1st phase; 431 mg, 2nd phase; 690 mg, 3rd phase; 523 mg, 4th phase; 374 mg, 5th phase; 335 mg) which accounts for 44% of the yield potential. The lab-scale prototype showed promising trend of progressive degradation of corn rind that requires further process optimization to achieve maximum productivity. The reducing sugars thus obtained could be used for subsequent bioconversion processes by using suitable microorganisms.

Biodegradation Kinetic Studies of Phenol and p-Cresol in a Batch and Continuous Stirred-Tank Bioreactor with Pseudomonas putida ATCC 17484 Cells

The biodegradation of phenol, p-cresol, and phenol plus p-cresol mixtures was evaluated using Pseudomonas putida ATCC 17484 in aerobic batch reactors. Shake-flask experiments were performed separately using growth medium with initial nominal concentrations of phenol (50–600 mg L−1) and p-cresol (50–600 mg L−1) as well as phenol (50–600 mg L−1) plus p-cresol (50–600 mg L−1). The complete degradation of phenol and p-cresol was achieved within 48 h and 48–56 h, respectively, for all initial concentrations of phenol and p-cresol. The maximum cell growth rate using phenol (μmax,P = 0.45 h−1) was much faster than that using p-cresol (μmax,C = 0.185−1 h). The larger Ki value for phenol (310.5 mg L−1) revealed that the P. putida cells had a higher resistance to phenol inhibition compared with p-cresol (243.56 mg L−1). A mixture of phenol and p-cresol in batch experiments resulted in the complete removal of phenol within 52–56 h for initial phenol concentrations of 50–500 mg L−1. The time needed to remove p-cresol completely was 48–56 h for initial p-cresol concentrations of 50–500 mg L−1. In the continuous-flow immobilized cells reactor, the degradation efficiency for phenol and p-cresol was 97.6 and 89.1%, respectively, at a stable condition.

Optimal Control of a MIMO Bioreactor System Using Direct Approach

In this paper, the optimal control of a continuous type bioreactor with multi-input-multi-output signals is presented for the two active phases: growth and stationary. The underlying criterion to be minimized generalizes the classic quadratic forms to address some crucial objectives in controlling the bioreactor. In particular, the protection of actuators against fast switching in the controller output is considered by including a weighting term of the control signal derivatives. The direct optimal control approach is used to carry out the optimization in the presence of various limiting constraints. Direct methods are based on transcribing the infinite-dimensional problem to a finite-dimensional one. In this manuscript, direct single shooting and trapezoidal collocation methods are used for transcription, and the successive quadratic programming method is employed to solve the resulting nonlinear programming problem. It is shown that the trapezoidal method is an effective method for controlling the bioreactor in all the active phases, whereas the single shooting fails in dealing with the unstable one (i.e., growth). To analyze solutions in a more accurate manner, an auxiliary criterion is defined, and then the cheap control analysis is studied. The convergence to the lowest value of the auxiliary cost function and the effects on the optimal state and control trajectories are then examined by varying cheap parameters. Several numerical simulations support the presented theoretical formulation.

Three-dimensional CFD simulation of anaerobic reactions in a continuous packed-bed bioreactor

In this study, a lab-scale continuous packed-bed bioreactor with multi-sized distributed particles has been simulated in a structured layout using computational fluid dynamics. The goal was to achieve a well-estimated simple model which can describe the hydrodynamic regime of flow as well as mass transfer of species within the bioreactor. A MATLAB program was coded to create the packed-bed geometry by generating non-overlapping spherical particles. The flow hydrodynamics was assumed to be single-phase creeping flow regime (Stokes flow). The kinetic data of batch experiments at similar operating conditions were used to formulate the rate of anaerobic reactions. The anaerobic methanogenesis reactions were assumed to occur at the particle surfaces (on the biofilm). The bioreactor temperature was fixed at 37°C. The commercial software COMSOL Multiphysics 5.0 was employed to solve the governing equations. Velocity profiles and concentration distribution of volatile fatty acids (VFAs) are shown inside the packed-bed reactor. Simulation results were found to be in good agreement with the experimental data at various influent flow rates (23.8 – 43.5 mL/h) and various influent concentrations of VFAs (0.001 – 0.042 M). In all cases, the relative error was less than 15% which is acceptable. This proposed model is applicable for scale-up and optimization purposes as well as evaluation of other kinetic models.

A combined computational-fluid-dynamics model and control strategies for perfusion bioreactor systems in tissue engineering

Abstract This work sets the foundations for the design of control algorithms to facilitate manufacturing of a cell growth process using a continuous perfusion bioreactor. The algorithms are designed to work with different types of cell cultures and deal with major disturbances that might appear in the process. Different types of control strategies are designed, implemented and tested. First, a comprehensive mathematical model of convection and diffusion in a perfusion bioreactor, combined with cell growth kinetics, is developed and implemented using Computational Fluid Dynamics. The model describes the spatio-temporal evolution of glucose concentration and cell density within a 3D polymeric scaffold. Since such a model is too complex to be used directly for control studies, a simplified version is used for the design of the controllers. Finally, the performances of the control strategies are validated against the original high-fidelity CFD model, thus closing the loop. The simulations show good performances and satisfactory behavior.

Optimizing conditions of key factors influencing CN− producing ability of Pseudomonas biofilm to leach Ag from waste printed circuit boards

Abstract With the sharp increase in the number of waste printed circuit boards, biocyanidation is adopted to recover the precious metals from waste printed circuit boards for its environmental friendliness. In this study, Pseudomonas biofilm with CN− producing ability was constructed to leach Ag from mixed metal particles of waste printed circuit boards. The optimal culture conditions for Pseudomonas biofilm to produce CN− were pH 7.0, 20 °C, 100 rpm and 1/25 NB medium. Polyethylene particles were more suitable as carriers than ceramsite. 500 ppm of Cu2+ and 2.5 ppm of Ag+ were beneficial for the CN− production while higher concentrations were adverse. With 0.05% of Ag content, the Ag leaching rate was the highest, which was up to 35.53% after 7 d of leaching. The Pseudomonas biofilm remained stable and active during the whole leaching process. This paper contributes to the construction of continuous bioreactor using biofilm and the industrialization of biocyanidation technology for recovering waste printed circuit boards.

Retroviral-Mediated Gene Transfer in Human Bone Marrow Cells Grown in Continuous Perfusion Culture Vessels

Hematopoietic stem cell gene therapy holds the promise of being able to treat a variety of inherited and acquired diseases of the hematopoietic stem cell. However, to date, genetic modification of the human hematopoietic stem cell has been relatively inefficient. Here, we report the results of using a bioreactor system to expand hematopoietic cells after a brief retrovirus infection using a high titer, replication defective virus encoding for murine CD18. The retrovirus transduced culture continued to produce genetically modified hematopoietic progenitors for up to 6 weeks, the duration of the culture period. Up to one-third of the long-term culture initiating cell (LTC-IC) are genetically modified by the culture conditions. Murine CD18 can be expressed on the cell surface of up to 20% of the mature cells generated by the culture system, suggesting that clinically significant levels of gene transfer may be occurring. These results demonstrate the feasibility of using continuous perfusion bioreactors as a method of efficiently modifying human hematopoietic stem cells.

Ammonia oxidation at pH 2.5 by a new gammaproteobacterial ammonia-oxidizing bacterium

Ammonia oxidation was considered impossible under highly acidic conditions, as the protonation of ammonia leads to decreased substrate availability and formation of toxic nitrogenous compounds. Recently, some studies described archaeal and bacterial ammonia oxidizers growing at pH as low as 4, while environmental studies observed nitrification at even lower pH values. In this work, we report on the discovery, cultivation, and physiological, genomic, and transcriptomic characterization of a novel gammaproteobacterial ammonia-oxidizing bacterium enriched via continuous bioreactor cultivation from an acidic air biofilter that was able to grow and oxidize ammonia at pH 2.5. This microorganism has a chemolithoautotrophic lifestyle, using ammonia as energy source. The observed growth rate on ammonia was 0.196 day−1, with a doubling time of 3.5 days. The strain also displayed ureolytic activity and cultivation with urea as ammonia source resulted in a growth rate of 0.104 day−1 and a doubling time of 6.7 days. A high ammonia affinity (Km(app) = 147 ± 14 nM) and high tolerance to toxic nitric oxide could represent an adaptation to acidic environments. Electron microscopic analysis showed coccoid cell morphology with a large amount of intracytoplasmic membrane stacks, typical of gammaproteobacterial ammonia oxidizers. Furthermore, genome and transcriptome analysis showed the presence and expression of diagnostic genes for nitrifiers (amoCAB, hao, nor, ure, cbbLS), but no nirK was identified. Phylogenetic analysis revealed that this strain belonged to a novel bacterial genus, for which we propose the name “Candidatus Nitrosacidococcus tergens” sp. RJ19.

Biosurfactant assisted degradation of High Molecular Weight Polycyclic Aromatic Hydrocarbons by mixed cultures from a car service oil dump from Pretoria Central Business District (South Africa)

Abstract Biomineralisation of polycyclic aromatic hydrocarbons (PAHs) and other toxic organic pollutants to CO2 and H2O is one of the most environmentally friendly and economically efficient options for treatment of deleterious organic pollutants in water and soil. Although most intermediate and high molecular weight (I-, HMW) PAHs are biodegradable, the degradability of these PAHs is limited by their low solubility. Experiments were conducted in batch reactors, and later, in continuous flow fixed-film bioreactor systems to take advantage of mass-transport resistance to reduce toxicity exposure within the biofilm. The results from this study showed a tenfold performance improvement in cumulative removal of PAHs in the biofilm reactor system. The active microbial agents were predominated by Pseudomonas aeruginosa MS-1 and Acinetobacter species. 98%, 88%, and 63% degradation of fluoranthene, pyrene and chrysene was achieved in the biofilm process, respectively, at steady doses of 45 kg/d fluoranthene, 12 kg/d pyrene and 7.5 kg/d chrysene, respectively. Product purification was further evaluated in a continuous flow fed-batch and plug-flow reactor system in which a high quality oil product was separated from oily sludge.

Insight into functionally active bacteria in nitrification following Na+ and Mg2+ exposure based on 16S rDNA and 16S rRNA sequencing

Despite increasing interests in osmotic membrane bioreactors, the information regarding the bacterial toxicity effects of reversely transported draw solute (RTDS) is limited. In this study, two representative draw solutes (NaCl and MgCl2) were used at different concentrations (0, 2.5, 5.0, 7.5 and 10.0 g/L) to evaluate their toxicity in a continuous nitrifying bioreactor. Notably, Mg2+ selectively inhibited the activity of ammonia-oxidizing bacteria (AOB), which decreased to 11.3% at 7.5 g-Mg2+/L. The rRNA-based analysis was more effective than the rDNA-based analysis to elucidate the relationship between active communities of nitrifying bacteria and the actual nitrifying performance. Nitrosomonas europaea, a representative AOB, was vulnerable to Mg2+ in comparison to Na+. In contrast, the dominant nitrite-oxidizing bacteria (NOB), Nitrobacter winogradskyi and Nitrolancea hollandica, maintained a relevant level of relative abundance for achieving nitrite oxidation after exposure to 10 g/L Na+ and Mg2+. This fundamental inhibition information of the draw solute can be applied to set the operational regime preventing the critical solute concentration in mixed liquor of nitrifying OMBRs.

Fabrication of Bacteria- and Blood-Repellent Superhydrophobic Polyurethane Sponge Materials.

Biofilm and thrombus formation on surfaces results in significant morbidity and mortality worldwide, which highlights the importance of the development of efficacious fouling-prevention approaches. In this work, novel highly robust and superhydrophobic coatings with outstanding multiliquid repellency, bactericidal performance, and extremely low bacterial and blood adhesion are fabricated by a simple two-step dip-coating method. The coatings are prepared combining 1H,1H,2H,2H-perfluorooctyltriethoxysilane (FAS-17)-coated hydrophobic zinc oxide and copper nanoparticles to construct hierarchical micro/nanostructures on commercial polyurethane (PU) sponges followed by polydimethylsiloxane (PDMS) treatment that is used to improve the binding degree between the nanoparticles and the sponge surface. The micro/nanotextured samples can repel various liquids including water, milk, coffee, juice, and blood. Relative to the original PU, the superhydrophobic characteristics of the fabricated sponge cause a significant reduction in the adhesion of bacteria (Staphylococcus aureus) by up to 99.9% over a 4-day period in a continuous drip-flow bioreactor. The sponge is also highly resistant to the adhesion of fibrinogen and activated platelets with ∼76 and 64% reduction, respectively, hence reducing the risk of blood coagulation and thrombus formation. More importantly, the sponge can sustain its superhydrophobicity even after being subjected to different types of harsh mechanical damage such as finger-wiping, knife-scratching, tape-peeling, hand-kneading, hand-rubbing, bending, compress-release (1000 cycles) tests, and 1000 cm sandpaper abrasion under 250 g of loading. Hence, this novel hybrid surface with robustness and the ability to resist blood adhesion and bacterial contamination makes it an attractive candidate for use in diverse application areas.

Implementation of Modeling Tools for Teaching Biorefinery (Focused on Bioethanol Production) in Biochemical Engineering Courses: Dynamic Modeling of Batch, Semi-Batch, and Continuous Well-Stirred Bioreactors

Due to the ever-growing pressure on our planet’s natural resources to supply energy, the production of bioethanol by fermentation of lignocellulosic biomass is increasingly important in courses related to engineering and energy. Moreover, recent changes in the teaching–learning paradigm make necessary the introduction of novel teaching tools where students are the protagonist of their education. In this context, the purpose of this study is to compare the results obtained after traditional lessons with those obtained after the implementation of various computer activities based on modeling and simulation of bioreactors to teach biorefinery concepts focused on bioethanol production. Berkeley Madonna was chosen as the digital simulation software package because it is user-friendly, fast, and easy to program. This software allowed students to gain experience writing models that let optimize fermentations in well-stirred bioreactors and others bioprocess of industrial interest. The students (those who participated in the modeling-simulation classes and those who participated in traditional ones) completed a questionnaire and a cognitive test at the end of the course. Students that participated in modeling-simulation classes got a better score than students that participated in traditional classes. Therefore, the study showed the improvement in the understanding of the biorefinery concepts and the students improved their grades. Finally, students’ perception about the proposed modeling-simulation learning was also analyzed and they rated the efficiency of this new learning methodology as satisfactory. There are very few studies providing information about educational experiences regarding the development of skills for the formulation, interpretation, simplification, and use of mathematical models based on mass balances and simple microbial kinetics in biochemical engineering courses. The experience described in this work can be used by professors to plan and conduct courses based on the modeling of biochemical engineering problems.

Anaerobic co-digestion of industrial waste landfill leachate and glycerin in a continuous anaerobic bioreactor with a fixed-structured bed (ABFSB): Effects of volumetric organic loading rate and alkaline supplementation

Anaerobic co-digestion from industrial waste landfill (IWL) leachate and glycerin was evaluated in a continuous anaerobic bioreactor with fixed-structured bed (ABFSB) under mesophilic conditions (30 ± 1 °C). The ABFSB reactor had a useful volume of 4.77 L. The support medium consisted of polyurethane (PU) foam arranged in an orderly manner. The substrate used corresponded to a mixture of 95% IWL leachate and 5% glycerin (v/v) and the inoculum consisted of flocculent anaerobic sludge. The ABFSB reactor was operated in two phases – the 1st phase (between the 49th and the 439th days of operation): started after the inoculum adaptation and the effect of the increase in the organic loading rate (OLR) was evaluated (2; 3.5; 7.1 and 11.6 gCOD L−1 d−1); the 2nd phase (between the 440th and 471st days of operation): the effect of the reduction in alkalinity supplementation via sodium bicarbonate (NaHCO3) was evaluated (0.56; 0.42; 0.28; 0.14 gNaHCO3 gCODinfluent−1 and non-supplementation). The OLR of 7.1 gCOD L−1 d−1 was the condition that presented the best results in the 1st phase for the parameters: maximum methane flow rate (MFR) (7.61 LNCH4 d−1), methane yield (MY) (0.30 LNCH4 gCODremoved−1), volumetric methane production rate (VMPR) (2.79 LNCH4 L−1 d−1), COD removal efficiencies (ERTCOD) and soluble COD (ERSCOD) higher than 90%. In the 2nd phase, the reactor was operated with an OLR of 7.1 gCOD L−1 d−1 and a hydraulic retention time (HRT) of 35.22 h and CODinfluent of 10.68 g L−1. The minimum alkalinity supplementation required was 0.28 gNaHCO3gCODinfluent−1, a condition in which the reactor showed stability and satisfactory performance for the parameters: MFR (9.48 LNCH4 d−1), MY (0.33 LNCH4 gCODremoved−1) and VMPR (3.18 LNCH4 L−1 d−1). It was concluded that the ABFSB reactor proved to be stable in the IWL leachate co-digestion and glycerin, when the alkalinity supplementation, effectively necessary, was met.

Towards an innovative combined process coupling biodegradation and photo‐oxidation for the removal of pharmaceutical residues

AbstractBACKGROUNDThe occurrence of pharmaceutical compounds in wastewater has become a major concern for human health and the environment. Therefore, it is an important challenge to improve conventional wastewater treatment to remove these compounds. Coupling biological treatment with advanced oxidation technology has been widely studied in the literature, but only sequential associations of the two processes have been used. This study proposes an innovative concept based on a real integration of the photocatalytic oxidation process in a continuous recycling loop on a membrane bioreactor. The role of the oxidation here is not to completely degrade pharmaceuticals, but instead to oxidize them moderately to increase their biodegradability so that they can be eliminated by the biological process.RESULTSPreliminary experiments on the oxidation process indicated that a flux density of 5 W m−2 was sufficient to increase biodegradability and decrease the toxicity of a cocktail of three pharmaceuticals. Then the performance of a 20‐L continuous membrane bioreactor treating wastewater with seven pharmaceuticals, without and with pre‐oxidation at 5 W m−2, were compared. Pre‐oxidation increased the global removal for some recalcitrant pharmaceuticals (from 3% to 47% for diclofenac and from 1% to 44% for furosemide) without affecting either the removal of carbon, nitrogen or phosphorous by activated sludge, or of already highly removed pharmaceuticals.CONCLUSIONThis work proves the feasibility of an innovative concept of a continuous hybrid process coupling a photocatalytic oxidation process and a membrane bioreactor for the treatment of pharmaceuticals in wastewater, with low cost and size. © 2020 Society of Chemical Industry (SCI)

A continuous flow membrane bio-reactor releases the feedback inhibition of self-generated free organic carbon on cbb gene transcription of a typical chemoautotrophic bacterium to improve its CO2 fixation efficiency

Since the free organic carbon (FOC) generated by chemoautotrophic bacterium self has a feedback inhibition effect on its growth and carbon fixation, a continuous flow membrane bio-reactor was designed to remove extracellular FOC (EFOC) and release its inhibition effect. The promotion effect of membrane reactor on growth and carbon fixation of typical chemoautotrophic bacterium and its mechanism were studied. The accumulated apparent carbon fixation yield in membrane reactor was 3.24 times that in the control reactor. The EFOC per unit bacteria and cbb gene transcription level in membrane reactor were about 0.41 times and 11.18 times that in control reactor in late stage, respectively. Membrane reactor separated out EFOC, especially the small molecules, which facilitated the release of intracellular FOC, thereby releasing the inhibition of FOC on cbb gene transcription, thus promoting growth and carbon fixation of the typical chemoautotrophic bacterium. This study lays a foundation for enhancing carbon fixation by chemoautotrophic bacteria and expands the application field of membrane reactor.