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关键词： CFD modelling   Flat sheet MBR   Shear stress  

摘要： The efficiency of slug flow for fouling control of flat sheet (FS) membrane bioreactors (MBRs) is hindered by uneven bubble distribution leading to inhomogeneous shear stress profile on the membrane. In this work, a 3D CFD model was developed enabling prediction of the hydraulic performance of a novel aeration system designed to reduce the uneven bubble distribution in a full-scale FS MBR. Bubbles generated with aeration channel submerged in 8.0 g/L activated sludge were found to be unevenly distributed with up to 12 folds difference in gas mass flow per single nozzle. More than 41% higher gas mass flow was obtained at nozzles located at higher heights compared to lower nozzles at aeration intensities ranging from 12 m(3)/h to 20 m(3)/h. The subsequent uneven bubble distribution in membrane modules contributed to uneven shear stress distribution resulting in uneven fouling performance of the membrane module. Locating the aerator at a mediate distance of 20 cm to the membrane module (in the range of 15 cm to 25 cm) resulted in higher shear stress at locations closer to the permeate collector where higher flux occurred with a maximum 2.4 times increase in average shear stress. The CFD model was validated by comparison of the simulated height of the air column and bubble frequency with experimentally measured data obtained using a high-speed camera.

关键词： Hydraulic retention time   Bioaugmentation   Cometabolism   Antibiotics   Organic loading rate   Nitrification rate  

摘要： Achromobacter denitnficans strain PR1, previously found to harbour specific degradation pathways with high sulfamethoxazole (SMX) degradation rates, was bioaugmented into laboratory-scale membrane bioreactors (MBRs) operated under aerobic conditions to treat SMX-containing real domestic wastewater. Different hydraulic retention times (HRTs), which is related to reaction time and loading rates, were considered and found to affect the SMX removal efficiency. The availability of primary substrates was important in both bioaugmented and non-bioaugmented activated sludge (AS) for cometabolism of SMX. High HRT (24 h) resulted in low food to microorganism ratio (F/M) and low SMX removal, due to substrate limitation. Decrease in HRT from 24 h to 12 h, 6 h and finally 4 h led to gradual increases in primary substrates availability, e.g. organic compounds and ammonia, resulted in increased SMX removal efficiency and degradation rate, and is more favorable for high-rate wastewater treatment processes. After inoculation into the MBRs, the bioaugmentation strain was sustained in the reactor for a maximum of 31 days even though a significant decrease in abundance was observed. The bioaugmented MBRs showed enhanced SMX removal, especially under SMX shock loads compared to the control MBRs. The results of this study indicate that re-inoculation is required regularly after a period of time to maintain the removal efficiency of the target compound. (C) 2018 Elsevier B.V. All rights reserved.

关键词： Mammalian cell culture   Mass-transfer model   Bioreactor scale up  

摘要： A mathematical mass-transfer model was developed based on the mass balance of gas exchange in cell culture bioreactors. The model combines the bioreactor mass transfer properties and mammalian cell metabolic parameters to predict the cell culture process oxygen demands and carbon dioxide accumulation in bioreactors. With the guidance of the mass-transfer model, a CHO cell culture process to produce a therapeutic antibody was successfully scaled up from 2-L to 1500-L bioreactor directly without intermediate steps. The process performances and product quality attributes demonstrate good robustness and consistency between small and large scales. This mass-transfer model provides a more systematic and reliable approach for mammalian cell culture bioreactor scaling up.

关键词： Filling ratio   aMBR   polluted surface water   PVA-gel   bio-carrier  

摘要： Surface water has been facing increasing loads of various types of organic contamination due to human activities. Attached growth membrane bioreactor (aMBR) has been reported as a promising approach in treating polluted surface water. By using bio-carrier to provide biodegradation and utilize organic pollutants as substrates, aMBR was able to integrate biodegradation and physical rejection in one system. The filling ratio of polyvinyl alcohol gel (PVA-gel), which is an important bioprocess contributor in an aMBR system, was analyzed by batch test and lab-scale aMBR in this study. Batch test with various filling ratios (2%, 5%, 10%, 15% and 30%) were carried out. Oxygen uptake rate (OUR) and specific oxygen uptake rate were used for the comparison of bioactivities. Five percent filling ratio had the highest OUR results of 3.6 mg/L h obtained from the batch test. The chosen filling ratios were tested in a lab-scale aMBR system with hydraulic retention time (HRT) of 1, 2, 2.5 and 3 h. Results shown that at HRT 2.5 h, the aMBR system had the lowest membrane fouling. PVA-gel was able to reject more organic matters than a naturally immobilized membrane bioreactor system, and thus mitigated membrane fouling in the aMBR system.

关键词： Stirred bioreactor   CFD   Compartments models   Hydrodynamics   Mixing  

摘要： The ability to understand and predict mixing behaviour in stirred bioreactors through the use of mathematical models is an effective strategy to improve or ensure the performance of a process. Historically, compartment models have been developed to facilitate the prediction of hydrodynamics and in the last decade, computational fluid dynamics (CFD) has become the standard tool to assess this in detail. Despite the continuous increase in computational capacity, performing CFD simulations of bioreactors remains a challenge in industry, where the need for simplified models is apparent due to the complex phenomena occurring at the industrial scale. The combination of CFD and compartment models has been investigated in this work using a pilot scale stirred bioreactor equipped with three Rushton disc turbines and multiple pH sensors as a case study. A hypothesis-driven compartmentalization strategy, comprised of five steps, has been developed and applied to the pilot scale stirred bioreactor. The compartmentalization resulted in 56 compartments with unidirectional flow between adjacent compartments. The performance of the methodology was evaluated against a data-driven compartment approach and the full CFD simulation, in terms of its ability to recreate transient tracer profiles following top and bottom feeding of the tracer. The data-driven compartment model proved to be the most accurate of the three investigated methods, whereas the hypothesis-driven compartment method had a 10-12% higher error on prediction. Nevertheless, the developed methodology should be considered a viable alternative to conventional CFD methods, especially when models of complex phenomena - for example multi-dimensional population balance models - are to be incorporated in the final model as well.

关键词： Hybrid membrane bioreactor   Extracellular polymeric substances   Soluble microbial products   Biocarrier   Membrane fouling   Greywater  

摘要： In this research, the influence of biocarriers on the mixed liquor characteristics, extracellular polymeric substances (EPS), and fouling rates of a hybrid membrane bioreactor (HMBR) were examined during greywater reclamation. The addition of the biocarriers increased the relative abundance of filamentous bacteria within the HMBR, which decreased the settleability of the sludge, but did not affect its dewaterability or filterability. Settleability was found to be strongly correlated to the biocarrier filling ratio (R-2 = 9.0). The biocarriers appeared to have no effect on the total concentration or protein-to-polysaccharide (PN/PS) ratio of the mixed liquor EPS. However, an analysis of the fouled membranes revealed that the PN/PS ratio of the cake layer EPS was significantly reduced in the presence of the biocarriers. It was also found that the biocarriers reduced the fouling rate of the HMBR and extended its operating time by up to 40% (or 11 days). This rate reduction could not be attributed to any mechanical scouring mechanism, since the biocarriers were prevented from contacting the membrane module during operation.

关键词： Membranes   Biomass   Electrical energy   Carbon nanotubes   Sludges  

摘要： A novel anaerobic treatment system that combines the impact of applied voltage with membrane filtration over carbon nanotubes hollow fiber membranes (CNTs-HFMs) was developed at low temperature (15-20 degrees C) to mitigate membrane fouling, treat wastewater, and recover energy (CH4). Herein, electro-assisted CNTs-HFMs served a dual function as the cathode and membrane filtration. In contrast with other two anaerobic membrane bioreactors (AnMBRs;polyvinylidene fluoride hollow fiber membranes and CNTs-HFMs without electro-assistance), the CNTs-HFMs with electro-assistance (-1.2 V applied voltage) had slower transmembrane pressure (TMP) increasing rates and better TMP recovery with a more than 95% effluent chemical oxygen demand (COD) removal rate during an almost 100-day operation period. This result can be attributed to the presence of an electrostatic repulsion force pushing pollutants (mainly extracellular polymeric substances, EPS) away from the membrane surface, thereby hindering the formation of a gel layer and mitigating membrane pore blocking in the anaerobic electro-assisted membrane bioreactor (AnEMBR). Due to the almost two-times higher Methanomicrobia content and more H-2-utilizing methanogens than the other two AnMBRs, approximately more than 111.12 mL/gVSS d of CH4 was obtained in the AnEMBR with electro-assistance. This work provides an efficient strategy for mitigating membrane fouling, improving water quality, and enhancing CH4 yield.

关键词： Synthesis gas fermentation   Stirred-tank bioreactor   Gas-lift bioreactor   Myoglobin-protein assay   Clostridium aceticum(T)   Clostridium carboxidivorcrnsP7(T)  

摘要： A retrofit approach enables the non-invasive and reversible modification of a commercially available stirred-tank bioreactor into a gas-lift bioreactor within a few minutes. The gas-lift bioreactor configuration was characterised using a non-coalescent medium at working volume-specific volumetric gas flow rates of up to 20 L L-1 h(-1), showing mean gas bubble diameters of up to 0.57 mm, volumetric power inputs of up to 23 W m(-3), gas-liquid mass transfer coefficients of up to 153 h(-1) (CO) and up to 122 h (H-2), mixing times (theta(90)) of down to 0.5 min and gas hold-ups of up to 1.2%. A comparison of autotrophic batch processes with Clostridium aceticum and Clostridium carboxidivorans in the stirred-tank (2.0 L) and the retrofitted gas-lift bioreactor (2.5 L) at identical operating conditions showed differences in the cell dry weight and product concentrations (acetate, ethanol, butyrate, 1-butanol, hexanoate, 1-hexanol) due to gas-liquid mass transfer limitations caused by the reduced power input in the gas-lift bioreactor. CO limitation was demonstrated by a myoglobin-protein assay for CO measurement in the liquid phase. The simple retrofitting of a stirred-tank bioreactor for gas-lift operation thus provided comparative data on process performances of acetogenic bacteria that convert synthesis gas in gas-lift and stirred-tank bioreactors on a lab-scale.

关键词： Acidophilic sulfidogenic bioreactor   Acid mine drainage   Remediation  

摘要： Mining contributes to water pollution through the generation and uncontrolled release of sulfuric acid and metalliferous drainage (AMD). While sulfate reducing bacteria have been used for the bioremediation of AMD, one of the main limitations to using sulfate-reducing bioreactors is that most species are highly sensitive to acidity;therefore it is necessary to avoid direct contact between acidic mine waters and the bacteria, which is normally achieved by using "off-line" systems. There have been few successful applications using acidophilic, sulfate-reducing bacterial populations, which tolerate low pH and high metal concentrations and allow direct metal sulfide precipitation to occur within a single bioreactor unit. Here, we describe the performance of a low pH sulfidogenic bioreactor inoculated with an indigenous microbial community to treat mine-impacted water. The inoculum was obtained from anaerobic sediments collected from an acidic river located in northern Chile. The sulfidogenic bioreactor system (2.3 L) was operated as a continuous flow mode unit for 99 days at 30 degrees C and fed with synthetic water based on the chemical composition of the acidic river, characterized by extremely low pH (2.1) and, zinc and iron as main transition metals (0.5 and 2 mM, respectively). The bioreactor pH was set to 4.5 initially and was increased in stages to pH 6.0 during the experiment. The results show that zinc concentrations in liquors draining the bioreactor were below the detection level in most of the samples analyzed. In addition, by progressively increasing the glycerol concentration, it was possible to increase the removal of iron (70% of the total present), though more acetic acid (from 1 to 5 mM) was generated. Analysis of the microbial populations showed that they changed with varying operation parameters, and a known acetogenic sulfidogen (Desulfoporosinus acididurans) became more dominant over time. The modular unit used for treating mine-impacted water demo

关键词： Sulfadiazine/tetracycline   antibiotics   membrane bioreactors   removal pathway   bacterial community  

摘要： In this study, the removal pathway of sulfadiazine (SDZ) and tetracycline (TC) and their roles in shaping microbial community were separately explored in two lab-scale membrane bioreactors (MBRs) operating in parallel with one control MBR. Results show that the MBR system eliminated more than 90% of TC in the feed, whereas removal efficiency of SDZ decreased from 100% to 40% with increasing SDZ concentrations (1-1000 mu g/L). Based on batch tests, biodegradation and adsorption was the main removal route for SDZ and TC, following pseudo-first-order kinetic and pseudo-second-order kinetic model with a rate constant of 1.21 L/(g MLSS center dot d) and 1.91 h(-1), respectively, in the acclimated sludge. As expected, the acclimated sludge possessed a higher removal potential for the antibiotics compared with unacclimated sludge. Notably, high-throughput sequencing revealed that the most abundant phylum Proteobacteria was resistant to TC (1-1000 mu g/L), but was suppressed by SDZ (100-1000 mu g/L). Members of the phylum TM7 were likely responsible for SDZ degradation. Overall, TC exhibited a stronger inhibitory effect on bacterial species and significantly reduced the biodiversity compared with SDZ, which could be strongly related to the persistent toxicity of TC to microbes resulting from its high adsorption potential on activated sludge.