Continuous Stirred Tank Bioreactor Research Articles

Biodegradation of whey waste in a continuous stirred-tank bioreactor

Biodegradation of whey waste in a continuous stirred-tank bioreactor

Continuous Bioleaching of Chalcopyritic Concentrate at High Pulp Density

The main objective of the present study was to investigate the continuous bioleaching of chalcopyrite concentrate at a high pulp density by moderate thermophilic microorganisms. Using a flotation concentrate containing 46% chalcopyrite and 23% pyrite, bioleaching tests were carried out at a high pulp density (15%) and temperature of 47°C using a setup consisting of three continuous stirred tank bioreactors in series. A two-level full factorial design of experiments was used to assess the effects of residence time, particle size and acidity of the leaching solution on the copper recovery. From the results of these tests, we concluded that under the best process conditions (d80 = 30 μm, T = 47°C, and acidity of 130 kg/ton) more than 54% of copper was extracted from the concentrate after 7 days. Also, the concentration of copper in the final solution was higher than 20 g/L.

Direct and indirect effects of oxygen limitation on nitrification process applied to reject water treatment

The direct and indirect influence of temporary oxygen limitation on the nitrification of reject water was investigated using a continuous stirred tank bioreactor operated for 330 d at laboratory temperature (23 ± 1°C). A decrease in dissolved oxygen (DO) concentration from 3 to 0.7 mg L−1 lasted for 38 d and led to effective nitrite accumulation—more than 95% of total oxidized nitrogen was present as nitrite. The drop of DO concentration, at the same time, caused a decrease in the nitrogen oxidation rate from 1.36 to 0.73 kg N m−3 d−1. After a subsequent DO concentration increase to 3 mg L−1, the nitrite accumulation remained stable for another 90 d. This development was caused mainly by the indirect effects of DO limitation, consisting especially in the change of nitrogen species represented. A significant increase in free nitrous acid concentration induced by temporary DO limitation seems to be the key factor in this respect. The results of Fluorescence in situ hybridization analysis confirmed a washout of nitrite-oxidizing bacteria (NOB) during the period with high nitrite accumulation. The representation of NOB in total biomass decreased from 6.4% to less than 1% as a consequence of temporary DO limitation.

Influence of solid polymers on the response of multi-phase bioreactors treating α-pinene-polluted air

The use of biological techniques for the removal of hydrophobic and recalcitrant volatile compounds at industrial scale has recently significantly increased. In the present work, studies were undertaken aimed at comparing the performance of a continuous stirred tank bioreactor (CSTB) with either a single liquid phase or in the presence of a solid non-aqueous phase (NAP), for the biodegradation of α-pinene. Specifically, 3.5mm diameter beads of Hytrel G3548L were selected as solid NAP based on their affinity for α-pinene. Performance was evaluated over a period of 322 days. However, the experimental results showed no significant enhancement of α-pinene biodegradation in presence of the NAP compared to the reactor with a single liquid phase. Under steady-state conditions, when Hytrel G3548L (5%) was added to the CSTB, the maximum elimination capacity (ECmax) achieved was ∼60 g m(-3)h(-1), which was similar as in the absence of the NAP. Under transient shock-load conditions similar results were obtained with or without NAP, although attenuation was observed in the decrease of the removal efficiency (RE) during overload when polymer beads were present.

Biohydrometallurgical iron oxidation and precipitation: Part II — Jarosite precipitate characterisation and acid recovery by conversion to hematite

This study reports the characterisation of precipitates formed in a two-stage continuous stirred tank bioreactor (CSTR) system operated for continuous iron oxidation and removal from high strength iron liquor. The system was operated at ambient temperature without biomass carrier or neutralising agent addition. The elemental composition of the precipitates, for each of the influent pH solutions (pH1.1–2.2), contained varying amounts (%w/w) of Fe (29.2–34.0%), S (11.8–13.2%), K (0.92–5.67%), N (0.10–0.77%), Na (0.055–0.74%), Cu (0.044–0.15%) and Ni (0.002–0.016%). Importantly, the process resulted in efficient precipitation of ferric iron and sulphate with only minor co-precipitation losses of Cu and Ni, making it suitable for use in base metal process flow sheets. The precipitates were predominantly (75–99%) jarosite, with potassium jarosite formation occurring preferentially over that of hydronium, ammonium and sodium jarosite. The jarosite precipitate showed good filterability and settling characteristics which are important for larger scale industrial processes. The jarosite precipitates could be readily converted to hematite and acid by autoclaving at 225°C. The physical and chemical characterisation of jarosite, determined in this study, is relevant in the design and deployment of iron oxidation, precipitation and residue treatment processes in hydrometallurgical flow sheets.

Mathematical modelling of ideal and non-ideal continuous stirred tank bioreactor using simulated solution

BACKGROUND Chemostats are characterized by an increase in viscosity of the reaction broth and are prone to non-ideality. The present study is mainly focused on the identification of non-idealities, namely dead zone and bypassing of a real chemostat or continuous stirred tank bioreactor. RESULTS Experimental studies were conducted in non-reactive mode to study the hydrodynamic characteristics of a real chemostat involving Lactobacillus sp. isolated from Indian curd. The influence of change of relative viscosity on non-ideality parameters was studied. A simulated solution of PVA having the same viscosity range as the growth medium of Lactobacillus sp. were used to understand the hydrodynamic behavior of the reactor by conducting residence time distribution (RTD) experiments in non-reacting mode. Both steady and unsteady state analyses have been carried out with variation of the two main process parameters, namely dilution rate and substrate concentration. CONCLUSION A clear portrait of the comparison between non-ideal and ideal systems has been cited here, and it was observed that the real or non-ideal system lags behind the ideal one in many aspects. The present study adds to the knowledge of biochemically reacting systems. © 2014 Society of Chemical Industry

Fermentative Hydrogen Production from Carob Pod: A Typical Mediterranean Forest Fruit

The carob-tree (Ceratonica siliqua L.) grows in arid to semi-arid Mediterranean areas and adapts well to poor soils. Carob pod, the fruit of carob tree is a sugar-rich biomass which may theoretically be ideal for biofuel production. During this study, the potential of hydrogen production from carob pod was evaluated in an anaerobic continuous stirred tank bioreactor using mixed microflora. A carob pod extract consisting of soluble carbohydrates at a concentration of 42.6 g/L was obtained from a standard extraction process. The reactor was operated at a hydraulic retention time (HRT) of 36 and 18 h and an organic loading rate of 155.8 and 311.6 mmol glucose/L/days respectively. The results showed a maximum hydrogen production yield of 8.4 L H2 per kg of carob pod biomass or 0.43 mmol H2 per mmol glucose consumed at the HRT of 18 h. Butyric acid was found to be the dominant metabolic product at both examined HRTs while propionic acid production decreased as HRT decreased. The present work suggests that carob tree, an alternative dryland forest crop, can be utilized for the efficient production of biohydrogen.

Steady- and transient-state performance of a thermophilic suspended-growth bioreactor for α-pinene removal from polluted air

The removal of α-pinene from polluted air was examined under thermophilic conditions (50°C) in one- and two-liquid phase continuous stirred tank bioreactors (CSTBs). Steady-state experiments were performed at different gas residence times, and α-pinene concentrations, corresponding to inlet loading rates between 0.5 and 38gm−3h−1 in the one-liquid phase CSTB, and between 2.9 and 176gm−3h−1 in the two-liquid phase CSTB. The presence of a second liquid-phase (5% v/v silicone oil) increased the maximum elimination capacity (85.7gm−3h−1) by ∼6-fold compared to the one-liquid phase CSTB. During transient-state experiments, the CSTB with silicone oil could withstand a higher α-pinene shock load (110gm−3h−1) than the CSTB operated without silicone oil (70gm−3h−1). Besides, the thermophilic specific substrate utilization rates were estimated from batch assays, reaching 89 and 340μgα-pinenemgbiomass-1d-1, in the absence of or presence of silicone oil, respectively.

Stabilization of unstable steady states of a continuous stirred tank bioreactor with predator–prey kinetics

Nonlinear properties of a bioreactor with a developed microbiological predator–prey food chain are discussed. The presence of the predator microorganism completely changes the position and stability of the stationary states. A wide range of unstable steady states appears, associated with high amplitude oscillations of the state variables. Without automatic control such a system can only operate in transient states, with the yield undergoing periodic changes following the dynamics of the stable limit cycle. Technologically, this is undesirable. It has been shown that the oscillations can be removed by employing continuous P or PI controllers. Moreover, with a PI-controller, the predator can be eliminated from the system.

Photosynthetic based algal-bacterial combined treatment of mixtures of organic pollutants and CO2 mitigation in a continuous photobioreactor

An algal-bacterial microcosm was synthetically constructed of Chlorella vulgaris MMl and Pseudomonas MTl. This microcosm was able to treat simulated wastewater supplemented with mixtures of phenol and pyridine up to 4.6 and 4.4mM, respectively, in a continuous stirred tank bioreactor (CSTR) using photosynthetic oxygenation. Complete pollutant removal and detoxification and 82% removal of introduced chemical oxygen demand (COD) were achieved at a hydraulic retention time (HRT) of 2.7days. Increasing the influent load to 5.3 and 6.3mM reduced the removal of phenol, pyridine and COD to 78, 21 and 59%, respectively. Fertilization of the photobioreactor with 24mM NaHCO3 restored the treatment and detoxification efficiencies. The system was able to additionally mitigate up to 72mM NaHCO3 at the same HRT. Although the fertilization increased the system treatment efficiency, the settleability of the algal-bacterial microcosm was significantly reduced. When the photobioreactor was operated at HRT of 2.7days in a 12/12h of dark/light cycle, complete removal of 4.7mM phenol was recorded but only 11% of 5.7mM pyridine was removed. The COD removal efficiency and CO2 mitigation were also reduced to 65 and 86%, respectively, and the effluent retained significant toxicity where 73% inhibition was recorded. Elongation of the illumination time to 48h (HRT of 4days at 12/12h dark/light cycle) restored the treatment and detoxification efficiencies.

On the Suitability of a Bacterial Consortium To Implement a Continuous PAHs Biodegradation Process in a Stirred Tank Bioreactor

A new microbial consortium made up with two bacterial strains phylogenetically identified as Bacillus pumilus and Staphylococcus warneri was obtained from lab soils polluted with polycyclic aromatic hydrocarbons (PAHs) and heavy metals. Its PAH degradation potential has been demonstrated recently by culturing the consortium in the presence of phenanthrene (PHE), pyrene (PYR), and benzoanthracene (BaA). The efficiency of the proposed degradation process was evaluated at flask and bioreactor scale, operating in fed-batch mode, as a prior step to achieve an effective biodegradation process in continuous mode. An acclimation of the consortium to the selected PAHs has been evidenced in fed-batch cultures after 6 batches (90% of degradation in less than one day). The effect of the dilution rate was analyzed in a continuous stirred tank bioreactor operating for 2 months, observing that some of the dilution rates employed allowed achieving degradation rates higher than 90% per day for all the contaminants.

Fuzzy servo controller for CSTB with substrate inhibition kinetics

Continuous stirred tank bioreactors with non-monotonic growth kinetics can exhibit bifurcation and multiple equilibrium points. Maximum productivity for this bioreactor is located at the limit of a bifurcation. Therefore, when the desired operating point is near optimal productivity, even small perturbations may drive the system from stability to an undesired, unstable condition. This work describes a fuzzy servo controller that was designed based on sector nonlinearities to force the bioreactor to stay near its optimal productivity point. The designed controller enables tracking of a reference signal that switches between stable and unstable nodes and finally stabilizes at the optimal operating point. Two reference signals were evaluated for the substrate and the biomass respectively. The performance of the proposed controller was compared to PID and LQ controllers. Linear matrix inequalities were used to prove the closed-loop stability.

Isolation and characterization of phenol degrading bacteria immobilized onto cyclodextrin-hydrogel particles within a draft tube spouted bed bioreactor

A draft-tube spouted bed bioreactor was developed to investigate the microbial degradation of aqueous phenol using a cyclodextrin-based support material. Bacteria from activated sludge were acclimated to phenol in a continuous stirred tank bioreactor, and then immobilized onto the hydrogel particles within the spouted bed bioreactor. Microorganisms obtained under different operating conditions in both bioreactors were isolated and characterized. Batch phenol degradation assays performed on isolated dominant strains showed that Acinetobacter baumannii was the most resistant to phenol. Microbial population distribution in bioreactors was not only affected by phenol concentration, but also by oxygen availability, the system configuration and the presence of intermediates formed during phenol metabolization. A maximum elimination capacity of 2.79kg-phenol/m3d was achieved in the spouted bed bioreactor, with Comamonas acidovorans being the dominant strain during high degradation periods.

연속생물반응기에서 perchlorate 환원 세균에 의한 perchlorate의 제거

In this study, the treatment ability of the wastewater containing perchlorate by non-salt tolerant perchlorate reducing bacterial consortium (N-PRBC) was evaluated in a continuous stirred tank bioreactor (CSTR). To obtain the optimal operating condition the bioreactor was operated with the different wastewater empty bed retention time (EBRT). The treatment performance in the bioreactor could be maintained at 100 <TEX>$mg-ClO_4{^-}L^{-1}$</TEX> up to a EBRT of 3 h, and the removal capacity in the CSTR was about 3.3 times higher than that in a batch operation. With a decrease from 9 h to 2 h in a EBRT, the volumetric perchlorate reduction rate was increased from 11.1 <TEX>$mg-ClO_4{^-}L^{-1}h^{-1}$</TEX> to 50.0 <TEX>$mg-ClO_4{^-}L^{-1}h^{-1}$</TEX>, and the specific perchlorate reduction rates were increased from 3.01 <TEX>$mg-ClO_4{^-}g-DCW^{-1}h^{-1}$</TEX>. In conclusion, the treatment capacities in a CSTR were much better than those obtained in a batch operation.

Sustainable ethanol fermentation from synthesis gas by Clostridium ljungdahlii in a continuous stirred tank bioreactor

AbstractBACKGROUND: Ethanol production from synthesis gas (syngas) by Clostridium ljungdahlii was autotrophically carried out in a continuous flow stirred tank bioreactor (CSTR). A 2 L bioreactor was operated at 37 °C and constant agitation rate of 500 rpm. The experiments were conducted at various media flow rates and uncontrolled culture pH condition while the gas flow rate was kept constant at 14 mL min−1.RESULTS: Continuous fermentation of the syngas containing 55% CO, 20% H2, 10% CO2 and 15% argon as internal standard resulted in cell dry weight of 2.34 g L−1 and CO conversion of 93%. Maximum concentration of ethanol and acetate was 6.50 g EthOH L−1 and 5.43 g Ac L−1.CONCLUSION: High ethanol concentration was achieved in continuous fermentation using C. ljungdahlii. The ethanol producing ability of this acetogene and succesful switch of the metabolic pathway from acetogenesis to solventogenesis during the fermentation process was confirmed. Copyright © 2012 Society of Chemical Industry

Adaptive Control of a Fermentation Bioprocess for Lactic Acid Production

This paper presents the design and the analysis of an indirect adaptive control strategy for a lactic acid production, which is carried out in continuous stirred tank bioreactors. Firstly, an indirect adaptive control structure based on the nonlinear process model is derived by combining a linearizing control law with a new parameter estimator. This estimator is used for on‐line estimation of the bioprocess unknown kinetics, avoiding the introduction of a state observer. Secondly, a tuning procedure of estimator design parameters is achieved by stability analysis of the control scheme. The effectiveness and performance of estimation and control algorithms are illustrated by numerical simulations applied in the case of a lactic fermentation bioprocess for which kinetic dynamics are strongly nonlinear, time varying, and completely unknown, and not all the state variables are measurable.

Reduction of petroleum hydrocarbons content from an engine oil refinery wastewater using a continuous stirred tank reactor monitored by spectrometry tools

AbstractBACKROUND: Hydrocarbon contamination of groundwater resources has become a major environmental and human health concern in many parts of the world. Microbial degradation of hydrocarbons, through either naturally occurring processes or engineered systems, has been successfully used to reduce concentrations of these pollutants. In order to develop an aerobic bioreactor tailored for this purpose, the present study aims to investigate petroleum contaminated wastewater remediation and toxicity reduction by acclimated microbial consortium enriched in a continuous stirred tank bioreactor (CSTR). Characterization and quantification of refinery wastewater components were performed by gas chromatography mass spectrometry (GC/MS) and Fourier transform infrared (FTIR) spectroscopy.RESULTS: The petroleum hydrocarbons were significantly degraded (97%) by the microbial consortium. After continuous aerobic treatment in the CSTR, the CODeffluent and BOD5effluent average removals were high reaching 97% and 78%, respectively. Also, strong degradation of C10C35 n‐alkanes was observed. The concomitant use of GC/MS and FTIR proved to be a useful complementary tool to assess the impact of treatment strategies on hydrocarbon‐contaminated wastewater. In addition, the toxicity of the contaminated wastewater decreased drastically after bioremediation.CONCLUSION: This work shows the ability of this consortium to degrade hydrocarbons and reduce toxicity, which makes them useful candidates for environmental restoration applications at other hydrocarbon‐contaminated environments. Copyright © 2011 Society of Chemical Industry

Effect of oil concentration and residence time on the biodegradation of α-pinene vapours in two-liquid phase suspended-growth bioreactors

Recently, research on the use of binary aqueous-organic liquid phase systems for the treatment of polluted air has significantly increased. This paper reports the removal of α-pinene from a waste air stream in a continuous stirred tank bioreactor (CSTB), using either a single-liquid aqueous phase or a mixed aqueous-organic liquid phase. The influence of gas flow rate, load and pollutant concentration was evaluated as well as the effect of the organic to aqueous phase ratio. Continuous experiments were carried out at different inlet α-pinene concentrations, ranging between 0.03 and 25.1 g m⁻³ and at four different flow rates, corresponding to residence times (RTs) of 120 s, 60 s, 36 s and 26 s. The maximum elimination capacities (ECs) reached in the CSTB were 382 g m⁻³ h⁻¹ (without silicone oil) and 608 g m⁻³ h⁻¹ (with 5%v/v silicone oil), corresponding to a 1.6-fold improvement using an aqueous-organic liquid phase. During shock-loads experiments, the performance and stability of the CSTB were enhanced with 5% silicone oil, quickly recovering almost 100% removal efficiency (RE), when pre-shock conditions were restored. The addition of silicone oil acted as a buffer for high α-pinene loads, showing a more stable behaviour in the case of two-liquid-phase systems.

Neural network models for biological waste-gas treatment systems

This paper outlines the procedure for developing artificial neural network (ANN) based models for three bioreactor configurations used for waste-gas treatment. The three bioreactor configurations chosen for this modelling work were: biofilter (BF), continuous stirred tank bioreactor (CSTB) and monolith bioreactor (MB). Using styrene as the model pollutant, this paper also serves as a general database of information pertaining to the bioreactor operation and important factors affecting gas-phase styrene removal in these biological systems. Biological waste-gas treatment systems are considered to be both advantageous and economically effective in treating a stream of polluted air containing low to moderate concentrations of the target contaminant, over a rather wide range of gas-flow rates. The bioreactors were inoculated with the fungus Sporothrix variecibatus, and their performances were evaluated at different empty bed residence times (EBRT), and at different inlet styrene concentrations (C(i)). The experimental data from these bioreactors were modelled to predict the bioreactors performance in terms of their removal efficiency (RE, %), by adequate training and testing of a three-layered back propagation neural network (input layer-hidden layer-output layer). Two models (BIOF1 and BIOF2) were developed for the BF with different combinations of easily measurable BF parameters as the inputs, that is concentration (gm(-3)), unit flow (h(-1)) and pressure drop (cm of H(2)O). The model developed for the CSTB used two inputs (concentration and unit flow), while the model for the MB had three inputs (concentration, G/L (gas/liquid) ratio, and pressure drop). Sensitivity analysis in the form of absolute average sensitivity (AAS) was performed for all the developed ANN models to ascertain the importance of the different input parameters, and to assess their direct effect on the bioreactors performance. The performance of the models was estimated by the regression coefficient values (R(2)) for the test data set. The results obtained from this modelling work can be useful for obtaining important relationships between different bioreactor parameters and for estimating their safe operating regimes.

Performance Evaluation and Neural Modeling of Gas-Phase Styrene Removal in One- and Two-Liquid Phase Suspended-Growth Bioreactors

The removal of gas-phase styrene was studied in both one- and two-liquid phase continuous stirred tank bioreactors (CSTBs) inoculated with Sporothrix variecibatus. Experiments were carried out at different gas residence times and inlet styrene concentrations to reach inlet loading rates varying between 10 and 838 g m−3 h−1 in the bioreactors. The addition of 10% (v/v) silicone oil acted as a buffer for high styrene loads and improved the two-liquid phase CSTB performance 3.1-fold in comparison to the one-liquid phase CSTB, with maximum elimination capacities of 426 and 137 g m−3 h−1, respectively. The CSTBs performance was modeled using artificial neural networks (ANNs) with inlet concentration (g m−3) and unit flow (h−1) as the input variables. The best network topology, selected by a trial and error approach and by estimating the determination coefficient (R2) values, was found to be 2−5−1 and 2−6−1, respectively, for the one- and two-liquid phase CSTB.