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关键词： Membrane bioreactor   Dielectrophoresis   Activated sludge   Aeration   Fouling  

摘要： Membrane bioreactors (MBRs) present a unique opportunity in waste water treatment by combining the activated sludge process with membrane filtration. Although MBRs require less area, produce less volume of sludge and have high purification efficiency, they suffer from high membrane fouling. Membrane fouling can be reduced by applying aeration and Dep voltage. However, application of these two anti-fouling mechanisms would make the process expensive. Thus, a new aeration and DEP scheme of 5 min on - 5 min off is being suggested in this study. With this scheme, it was found that through application of DEP at 100 V and 0.3 L/min.m(2) aeration flow rate and reduced lumen size of 6 mm, the membrane permeate flux can be increased by 58% compared to MBR without DEP and aeration. However, through energy analysis the optimum operating parameters were found to be at 0.3 L/min.m(2) aeration flowrate and 50 V DEP using the suggested 5 min on-5 min off scheme. At the optimum operating condition, the permeability flux is 54% higher than MBR without DEP and aeration.

关键词： membrane bio-rectors   fouling   biomass characteristics   EPS   SMP   mixed liquor characterization  

摘要： Biomass characteristics are regarded as particularly influential for fouling in Membrane Bio-Reactors (MBRs). They primarily include the Mixed Liquor Suspended Solids (MLSS), the colloids and the Extracellular Polymeric Substances (EPS). Among them, the soluble part of EPS, which is also known as Soluble Microbial Products (SMP), is the most significant foulant, i.e., it is principally responsible for membrane fouling and affects all fundamental fouling indices, such as the Trans-Membrane Pressure (TMP) and the membrane resistance and permeability. Recent research in the field of MBRs, tends to consider the carbohydrate fraction of SMP (SMPc) the most important characteristic for fouling, mainly due to the hydrophilic and gelling properties, which are exhibited by polysaccharides and allow them to be easily attached on the membrane surface. Other wastewater and biomass characteristics, which affect indirectly membrane fouling, include temperature, viscosity, dissolved oxygen (DO), foaming, hydrophobicity and surface charge. The main methods employed for the characterization and assessment of biomass quality, in terms of filterability and fouling potential, can be divided into direct (such as FDT, SFI, TTF100, MFI, DFCM) or indirect (such as CST, TOC, PSA, RH) methods, and they are shortly presented in this review.

关键词： CHO cells   perfusion culture   process development   scale-down model  

摘要： The development of mammalian cell perfusion cultures is still laborious and complex to perform due to the limited availability of scale-down models and limited knowledge of time- and cost-effective procedures. The maximum achievable viable cell density (VCDmax), minimum cell-specific perfusion rate (CSPRmin), cellular growth characteristics, and resulting bleed rate at steady-state operation are key variables for the effective development of perfusion cultures. In this study, we developed a stepwise procedure to use shake tubes (ST) in combination with benchtop (BR) bioreactors for the design of a mammalian cell perfusion culture at high productivity (23 pg center dot cell(-1)center dot day(-1)) and low product loss in the bleed (around 10%) for a given expression system. In a first experiment, we investigated peak VCDs in STs by the daily discontinuous medium exchange of 1 reactor volume (RV) without additional bleeding. Based on this knowledge, we performed steady-state cultures in the ST system using a working volume of 10ml. The evaluation of the steady-state cultures allowed performing a perfusion bioreactor run at 20x10(6) cells/ml at a perfusion rate of 1 RV/day. Constant cellular environment and metabolism resulted in stable product quality patterns. This study presents a promising strategy for the effective design and development of perfusion cultures for a given expression system and underlines the potential of the ST system as a valuable scale-down tool for perfusion cultures.

关键词： air entrainment   breaking waves   cell culture   disposable bioreactor   oxygen mass transfer  

摘要： Rocking disposable bioreactors are a newer approach to smaller-scale cell growth that use a cyclic rocking motion to induce mixing and oxygen transfer from the headspace gas into the liquid. Compared with traditional stirred-tank and pneumatic bioreactors, rocking bioreactors operate in a very different physical mode and in this study the oxygen transfer pathways are reassessed to develop a fundamental mass transfer (k(L)a) model that is compared with experimental data. The model combines two mechanisms, namely surface aeration and oxygenation via a breaking wave with air entrainment, borrowing concepts from ocean wave models. Experimental data for kLa across the range of possible operating conditions (rocking speed, angle, and liquid volume) confirms the validity of the modeling approach, with most predictions falling within +/- 20% of the experimental values. At low speeds (upto 20rpm) the surface aeration mechanism is shown to be dominant with a kLa of around 3.5hr(-1), while at high speeds (40rpm) and angles the breaking wave mechanism contributes upto 91% of the overall kLa (65hr(-1)). This model provides an improved fundamental basis for understanding gas-liquid mass transfer for the operation, scale-up, and potential design improvements for rocking bioreactors.

关键词： Electrocoagulation   Electrostimulation   Microbial community composition   Biomass activity   Phosphorus removal  

摘要： The main objective of this study was to investigate the effect of low-density electrical current application on the performance of a laboratory-scale membrane bioreactor (MBR) treating municipal wastewater. The MBR operation was divided in two experimental runs: without (run I) and with electrocoagulation process (run II). The results demonstrated that the use of electrocoagulation process was beneficial for organic matter and nutrient removal, enabling the average removal efficiencies for COD, NH4+-N and PO43--P of 98.5, 99.8 and 99.2%, respectively. Despite the decreasing of MLVSS/MLSS ratio during the period with electrocoagulation, both autotrophic and heterotrophic biomass activities have increased. Data from the 16S RNA genetic sequencing showed that the electric current application affected the nitrifying bacteria population, specially the genre Nitrospira, which exhibited a significant increase in its relative abundance. Such behavior probably occurred due to electrostimulation phenomenon that can improve microbial metabolism and increase cell growth. These results demonstrate that the electric currents application can improve the MBRs performance on wastewater treatment.

关键词： C/N ratio   biofloc technology   biomass concentrations   16S rRNA sequencing   microbial community  

摘要： Application of biofloc technology could effectively treat wastewater. However, the effect of influent carbon to nitrogen ratio (C/N ratio) on water quality and microbial community structure evolution in suspended growth bioreactors (SGBRs) through biofloc technology is still unclear. Here, we show that the total ammonia nitrogen (TAN) and nitrite nitrogen in the effluent of the C/N 10 treatment was significantly higher than that in the C/N 15, C/N 20 and C/N 25 treatments (p < 0.05). Higher TAN removal efficiency was obtained in treatments of C/N 15, C/N 20 and C/N 25, and there was no accumulation of nitrite nitrogen and nitrate nitrogen. Increasing the C/N ratio strengthened the elimination ability of total phosphorus and chemical oxygen demand (COD). The concentrations of TAN and COD first dropped to the lowest level and then increased slightly within one cycle in all treatments. The accumulation of biomass in the reactors increased with the increasing C/N ratio, indicating that a higher C/N ratio was conducive to microbial proliferation. The 16S rRNA sequencing revealed that the microbial community diversity in SGBRs was significantly higher than that in the natural wastewater (P0). The predominant phylum were Proteobacteria, Bacteroidetes and Verrucomicrobia, but Saccharibacteria occupied a dominant position in the late period of the experiment. Pathogens, such as Aeromonas, Acidovorax, Flavobacterium, and Malikia were significantly decreased after high C/N ratio simulative wastewater treating natural wastewater in the reactors. In summary, the water quality and biomass concentrations in SGBRs can be improved under the conditions of influent C/N ratio, equal to or greater than 15.

关键词： Higher bio-hydrogen production   Fixed-bed bioreactor   Bedding materials   Chlorinated polyethylene (CPE)   Long-term operation  

摘要： Three fixed-bed materials including chlorinated polyethylene (CPE), loofah sponge (LS) and porous nylon (PN) were investigated for enhancing bio-hydrogen production in anaerobic digestion. In the batch operation, the bioreactor fixed with CPE achieved the highest hydrogen production of 676.4 mL/L (5 g-glucose/L). The SEM observation revealed that CPE bioreactor immobilized the highest density of microorganisms, facilitating the conversion of hydrogen through favorable butyrate pathway as well as maintaining stable pH value at optimal range. Among the three fixed-bed materials, CPE was obtained the optimum bedding material due to its roughness surface and high porosity. Additionally, the bioreactor fixed with CPE remained high hydrogen production and carbohydrate degradation under high concentration of glucose (35 g/L), whereas the no fixed-bed reactor (Control) showed negligible hydrogen production. The results indicated that CPE bioreactor could be tolerant to environmental perturbation, being more stable in operation, promoting a higher biological activity due to the higher cell density. Furthermore, the CPE bioreactor proved to be high-efficient and stable for hydrogen production with 32 days long-term operation. This is the first work revealing that the CPE bioreactor is promising for improving bio-hydrogen production.

关键词： cell culture intensification   CHO cells   CSTR   linked bioreactors   perfusion  

摘要： A novel, alternative intensified cell culture process comprised of a linked bioreactor system is presented. An N-1 perfusion bioreactor maintained cells in a highly proliferative state and provided a continuous inoculum source to a second bioreactor operating as a continuous-flow stirred-tank reactor (CSTR). An initial study evaluated multiple system steady-states by varying N-1 steady-state viable cell densities, N-1 to CSTR working volume ratios, and CSTR dilution rates. After identifying near optimum system steady-state parameters yielding a relatively high volumetric productivity while efficiently consuming media, a subsequent lab-scale experiment demonstrated the startup and long-term operation of the envisioned manufacturing process for 83 days. Additionally, to compensate for the cell-specific productivity loss over time due to cell line instability, the N-1 culture was also replaced with younger generation cells, without disturbing the steady-state of the system. Using the model cell line, the system demonstrated a two-fold volumetric productivity increase over the commercial-ready, optimized fed-batch process.

关键词： membrane bioreactor   biohydrogen   dark fermentation   anaerobic process   fouling   polymeric membranes   H-2 separation  

摘要： Biohydrogen is a clean and viable energy carrier generated through various green and renewable energy sources such as biomass. This review focused on the application of membrane bioreactors (MBRs), emphasizing the combination of these devices with biological processes, for bio-derived hydrogen production. Direct biophotolysis, indirect biophotolysis, photo-fermentation, dark fermentation, and conventional techniques are discussed as the common methods of biohydrogen production. The anaerobic process membrane bioreactors (AnMBRs) technology is presented and discussed as a preferable choice for producing biohydrogen due to its low cost and the ability of overcoming problems posed by carbon emissions. General features of AnMBRs and operational parameters are comprehensively overviewed. Although MBRs are being used as a well-established and mature technology with many full-scale plants around the world, membrane fouling still remains a serious obstacle and a future challenge. Therefore, this review highlights the main benefits and drawbacks of MBRs application, also discussing the comparison between organic and inorganic membranes utilization to determine which may constitute the best solution for providing pure hydrogen. Nevertheless, research is still needed to overcome remaining barriers to practical applications such as low yields and production rates, and to identify biohydrogen as one of the most appealing renewable energies in the future.

关键词： Cu-nanowires   microbial density   spontaneous electric field  

摘要： In this study, a spontaneous electric field membrane bioreactor (SEF-MBR), equipped with the innovative Cu-nanowires conductive microfiltration membrane, was developed to achieve membrane fouling mitigation and high-quality effluent. The membrane fouling was significantly mitigated due to the presence of spontaneous electric field that the intensity of the spontaneous electric field in the established SEF-MBR was up to 0.073 V/cm. After over 2-month operation, the membrane flux of SEF-MBR was 2.1 times that of the control reactor. The thickness of fouling layer on the Cu-nanowires conductive membrane surface was about 80 mu m, which was far thinner than that on the surface of commercial polyvinylidene fluoride (PVDF) membrane. Meanwhile, it was featured with the lower microbe density and extracellular polymeric substance (EPS) content. The effluent quality of SEF-MBR met the first-class discharge standards, and the removal rates were 94.5% for chemical oxygen demand (COD), 99.8% for NH4+-N, 78.5% for total nitrogen (TN), and 86.6% for total phosphorus (TP). The established system with the innovative Cu-nanowires conductive membrane showed a promising prospect for using the spontaneous electric field to mitigate membrane fouling and achieve high-quality effluent without extra power consumption. (C) 2019 Water Environment Federation