课程文献中心 更多>>

关键词： Microalgae   genetic modification   recombinant protein   metabolic engineering   bioreactor  

摘要： Microalgae are unicellular organisms that act as the crucial primary producers all over the world, typically found in marine and freshwater environments. Most of them can live photo-autotrophically, reproduce rapidly, and accumulate biomass in a short period efficiently. To adapt to the uninterrupted change of the environment, they evolve and differentiate continuously. As a result, some of them evolve special abilities such as toleration of extreme environment, generation of sophisticated structure to adapt to the environment, and avoid predators. Microalgae are believed to be promising bioreactors because of their high lipid and pigment contents. Genetic engineering technologies have given revolutions in the microalgal industry, which decoded the secrets of microalgal genes, express recombinant genes in microalgal genomes, and largely soar the accumulation of interested components in transgenic microalgae. However, owing to several obstructions, the industry of transgenic microalgae is still immature. Here, we provide an overview to emphasize the advantage and imperfection of the existing transgenic microalgal bioreactors.

关键词： Anammox   Metagenomics   Metatranscriptomics   Nitrogen metabolic pathway   Partial-denitrification  

摘要： Combined partial-denitrification and anammox process has received growing interest for treating wastewaters with high nitrate concentrations, but the underlying molecular mechanisms are currently poorly understood due to the complexity in bacterial community composition and functionality of the coupled system. This study applied metagenomic and metatranscriptomic approaches to gain comprehensive and deep insights into the nitrogen metabolic pathways in a lab-scale partial-denitrification/anammox bioreactor showing stable nitrogen removal. Stoichiometric analysis showed that most of nitrogen was removed by the coupled system (similar to 92.1%), but dissimilatory denitrification also contributed to nitrogen gas production. The latter was further evidenced by nosZ gene transcripts in the metatranscriptome. Metagenomic and metatranscriptomic analyses identified Candidatus Jettenia caeni as the most abundant and active anammox bacteria with relative abundance and mRNA expression of over 5% and 27%, respectively, while Thauera appeared as the major denitrifying bacteria in the system (relative abundance and mRNA expression exceeded 8% and 10%, respectively). mRNA levels of hdh/hzo and hzsA/B/C genes in Candidatus Jettenia caeni and Candidatus Brocadia sinica were much higher than those of other functional genes, confirming the major roles of the anammox bacteria in nitrogen metabolism. In addition, nrfA/B/C/D genes were mainly expressed in anammox bacteria, implying their involvement in that dissimilatory nitrite reduction to ammonia (especially for species Candidatus Brocadia sinica). Nitrate reduction process in Thauera was mainly achieved by the activation of the napA/B/C genes instead of narG/H genes. This study extablished the nitrogen metabolic network based on the comprehensive analyses of the abundance and mRNA expression of functional genes, which might improve our understanding of the nitrogen metabolic mechanisms of the combined partial-denitrification and anam

关键词： Reporter-gene assays   Endocrine disrupting chemicals   Sewage   Advanced wastewater treatment   On-site testing   Transformation product  

摘要： Wastewater treatment plants are major point sources of (micro)pollutant emissions and advanced wastewater treatment technologies can improve their removal capacity. While abundant data on individual advanced treatment technologies is available, there is limited knowledge regarding the removal performance of ozonation combined with multiple post-treatments and stand-alone membrane bioreactors. This is especially true for the removal of in vitro and in vivo toxicity. Therefore, we investigated the removal of 40 micropollutants and toxicity by a pilot-scale ozonation with four post-treatments: non-aerated and aerated granular activated carbon and biological filtration. In addition, two stand-alone membrane bioreactors fed with untreated wastewater and one MBR operating with ozonated partial flow recirculation were analysed. Aqueous and extracted samples were analysed in vitro for (anti)estrogenic, (anti)androgenic and mutagenic effects. To assess in vivo effects, the mudsnail Potamopyrgus antipodarum was exposed in an on-site flow-through system. Multiple in vitro effects were detected in conventionally treated wastewater including estrogenic and anti-androgenic activity. Ozonation largely removed these effects, while anti-estrogenic and mutagenic effects increased suggesting the formation of toxic transformation products. These effects were significantly reduced by granular activated carbon being more effective than biological filtration. The membrane bioreactor performed similarly to the conventional treatment while the membrane bioreactor with ozonation had a comparable removal performance like ozonation. Conventionally treated wastewater increased the growth of P. antipodarum. Ozonation reduced the reproduction indicating a potential formation of toxic transformation products. In the post-treatments, these effects were compensated or remained unaffected. The effluents of the membrane bioreactors induced reproductive toxicity. Our results show that ozonation is effe

关键词： Fermentation process   Optimal PHAs production   Fed-batch vs. continuous cultures   Sequence of continuous bioreactors   Dynamic optimization policies  

摘要： The microbial production of polyhydroxyalkanoates (PHAs) has attracted huge scientific and industrial interest. However, prerequisite to the economically feasible transition from the research scale towards industrial and highly competitive processes is the optimal production of PHAs in a consistent and systematic manner. The use of rigorous, experimentally verified mathematical models enabling the optimal dynamic operation of the fermentative production of PHAs is a promising alternative route against any low-yield empirical handling implemented so far. The present study investigates the model-based dynamic optimization of poly-3-hydroxybutyrate (PHB) production in Azohydromonas lata cultures through discontinuous and continuous bioreactor configurations. A detailed and validated macroscopic, kinetic and oxygen mass transfer mathematical model that relates state variables with operating strategies is used as a tool for the design of various dynamic optimization scenarios under fed-batch and continuous bioreactor policies. A notable improvement on the performance of fedbatch optimal operating bioreactors against heuristically designed operating strategies is proved concerning final polymer concentration, productivity, intracellular content and substrate to polymer yield, under four different strategies resulting in the following maximum values respectively, 27 g/l, 1.40 g/(1 h), 95 % wt. and 0.7. In a continuously operating PHB production process of two stirred tank bioreactors in series, a dynamic optimization problem is formulated and solved for the first time in the literature to ameliorate substantially the polymer productivity and provide the means for a truly sustainable PHB production. A comparison of the fed-batch and continuous operating strategies is finally effected to support studies for process economic feasibility evaluation.

关键词： Oyster shell and lignite modified zeolite (OLMZ)   Ammonium-rich anaerobic digestion   Light stimulation   Ammonia adsorption affinity   Electrical communication between methanogens  

摘要： A novel oyster shell and lignite modified zeolite (OLMZ) fixed bioreactor incorporated with intermittent light illumination process was developed for alleviating ammonia inhibition to improve efficiency of ammonium-rich anaerobic digestion (AD). The SEM morphology of the newly synthesized OLMZ showed porous structure and rough surface, with increased BET surface area compared to unmodified zeolite (UMZ). After modification with oyster shell and lignite, the metal cations content in OLMZ increased significantly and the ammonia adsorption capability of OLMZ improved by 1.3 folds compared to UMZ. Thus, the results suggested that OLMZ is a better adsorbent than UMZ for ammonia uptake. Furthermore, the pseudo-second-order kinetics and the isotherm results verified the adsorption of ammonia on OLMZ was dominated by ion exchange with high affinity for ammonia uptake. As for the anaerobic digestion, the light illuminated OLMZ fixed bioreactor process (OLMZ-I) resulted in the highest methane yield of 372 +/- 30 mL/g-DOCremoved, which showed 300% increase compared to the control (124 +/- 12 mL/g-DOCremoved). In addition, OLMZ-I showed higher ammonia removal capacity and stable pH which indicated that the ammonia inhibition was effectively mitigated. Correspondingly, metal cations supplementation and light stimulation in OLMZ-I showed increased ATP and coenzyme F420 implying high activation of methanogens leading to improved CH4 production. The large biomass quantity and SEM observation of microbes immobilized on the fixed OLMZ system aided by light further supported the enhanced performance of the reactor. Furthermore, the conductance of sludge in OLMZ-I bioreactor increased 3 folds compared to the control, reflecting a potential direct interspecies electron transfer (DIET) between the anaerobes was strengthened. The synergetic effects of ammonia removal, microbes immobilization, metal cations supplementation and accelerated electrical communication between methanogenic syste

关键词： Anaerobic membrane bioreactor (AnMBR)   Thermal hydrolysis (TH)   Methane productivity   Membrane fouling   Energy balance  

摘要： Thermal hydrolysis (TH) was integrated into an anaerobic membrane bioreactor (AnMBR) to stimulate sludge bioconversion and methane production. Sludge solubilization degree and methane productivity increased with TH temperature. The optimal performance was observed at 125 degrees C, with a 2.56-time increase in soluble chemical oxygen demand (1116.2 +/- 62 mg/L). Methane production rate approached 73.2 +/- 7.5 mL/L-reactor/d, rising by 2.96 times. Integration of TH effectively mediated membrane fouling, inducing a stable membrane flux of 10.8 +/- 0.5 L/m(2)/h and low transmembrane pressure (TMP, <= 4.7 kPa). Cake layer deposited on the membrane surface accounted for 66.1 +/- 1.0% of total resistance, with proteins and polysaccharides as the main contributors to membrane fouling (or increased TMP) (protein: R-p = 0.89, p(0.05) = 0.04;polysaccharide: R-p = 0.99, p(0.05) = 0.01). 16s rRNA gene analysis demonstrated that utilization of TH could regulate microbial diversity and enhance the proliferation of organics-degrading bacteria (i.e. Bacteroidetes, Firmicutes, etc.) and methane-producing methanogens (i.e. Methanosaeta, Methanobacterium, etc.), which accelerated the biodegradation of organics while alleviating membrane fouling and upgrading methane production. This study demonstrated the great potential of the combined TH-AnMBR system as a new strategy in promoting sludge solubilization, methane bioconversion and membrane fouling mitigation.

关键词： Specific affinity   HRT   Anaerobic wastewater treatment   AnMBR   Microbial community structure   Methanosaeta  

摘要： Maximum specific growth rate (mu(max)) and substrate saturation constant (K-s) are widely used in determining the growth of microorganisms. The ratio (mu(max)/K-s), also referred to as specific affinity, a(A)(0) is a better parameter to assess the advantage in competition for substrates by bridging microbial growth and the kinetics of enzymatic substrate uptake, but is not well studied. This study investigated the effect of hydraulic retention time (HRT) on the a(A)(0) of anaerobic sludge from an anaerobic membrane bioreactor (AnMBR), associated microbial communities and the overall wastewater treatment performance. The AnMBR was fed with acetate wastewater (similar to 500 mg COD/L) and operated at fixed solids retention time (45 d) while HRT continued to decrease. There was no significant difference in K-s (ranging from 170 to 243 mg COD/L) at different HRTs. However, a(A)(0) increased from (4.0 +/- 02) x 10(-4) to (4.9 +/- 0.2) x 10(-4) and to (6.5 +/- 0.1) x 10(-4) L/mg COD/d as HRT decreased from 24 h to 12 h and further to 6 h, respectively. This was accompanied by the increase in acetoclastic methanogens (mainly Methanosaeta) from 3.85 x 10(10), 8.82 x 10(10 )to 1.05 x 10(11 )cells/L, respectively. The fraction of Methanosaeta in the anaerobic biomass increased from 33.67% to 61.08% as HRT decreased from 24 h to 6 h. Correspondingly, effluent quality was improved, as evidenced from the COD concentrations of 32 +/- 6, 21 +/- 4. and 13 +/- 5 mg/L at the HRTs of 24 h, 12 h. and 6 h, respectively. The results confirm that microorganisms are able to adapt to growth conditions by adjusting their kinetic properties and suggest that short HRTs in the AnMBR favor the growth and accumulation of Methanosaeta with high specific affinity likely because they can compete for acetate at low concentrations by increasing substrate uptake rate and thus specific microbial growth rate. (C) 2020 Elsevier B.V. All rights reserved.

关键词： Osmotic stress   Saline RAS   Biofilter salt acclimatization   Marine MBBR   Biofilie microbial community composition   Nitrotoga  

摘要： Nitrifying biofilms developed in brackish water are reported to be more robust to salinity changes than freshwater biofilms. This makes them a promising strategy for water treatment systems with variable salinity, such as recirculating aquaculture systems for Atlantic salmon. However, little is known about the time required for nitrification start-up in brackish water or the microbial community dynamics. To investigate the development of nitrifying biofilms at intermediate salinity, we compared the startup of moving bed biolilm reactors with virgin carriers in brackish- (12 parts per thousand salinity) and freshwater. After 60 days, the brackish water biofilm had half the nitrification capacity of the freshwater biolilm, with a less diverse microbial community, lower proportion of nitrifiers, and a significantly different nitrifying community composition. Nitrosomonas and Nitrosospira-like bacteria were the main ammonia oxidizers in the brackish water biofilms, whereas Nitrosomonas was dominant in freshwater biofilms. Nitrotoga was the dominant nitrite oxidizer in both treatments. Despite the lower nitrification capacity in the brackish water treatment, the low ammonia and nitrite concentration with rapidly increasing nitrate concentration indicated that complete nitrification was established in both reactors within 60 days. The results suggest that biofilms develop nitrification in brackish water in comparable time as in freshwater, and brackish startup can be a strategy for bioreactors with varying salinity. (C) 2020 The Authors. Published by Elsevier B.V.

关键词： Human mesenchymal stromal cells   Cell-microcarrier-aggregates   Oxygen transfer   Shear stress   Taylor vortex flow bioreactor  

摘要： It is expected that a high cell volumetric concentration of human mesenchymal stromal cells (hMSCs) for cell therapy can be achieved by using scalable cell culture platforms as bioreactors. In this paper, the Taylor vortex flow bioreactor (TVFB) was evaluated for hMSCs expansion due to its potential to produce low and homogeneous hydrodynamic forces, which is important for the expansion of these cells. Thus, parameters such as volumetric coefficient of oxygen transfer and shear stress were estimated for the TVFB. Additionally, hMSCs cell expansion on microcarriers was evaluated in TVFB and compared with the traditional spinner flasks. Maximum shear stress and k(L)a were in the range of 0.027 - 0.065 Pa and 0.9-11.53 h(-1,) respectively, at rotation speed between 60 -120 rpm. Similar cell concentrations were obtained in both bioreactors, similar to 1.7 x 10(5) cells/mL, representing a fold increase of similar to 10 times. However, cell-microcarrier aggregates formed in the TVFB were smaller, with diameter of 0.36 +/- 0.01 mm compared to 0.75 +/- 0.31 mm obtained in the spinner flask, at the end of the culture. The results obtained in this study demonstrate the potential of TVFB to support manufacturing of anchorage dependent cell cultures for clinical applications.

关键词： Anaerobic self-forming dynamic membrane bioreactor   Dynamic layer   Polysaccharides   Specific surface area   Extracellular polymeric substances  

摘要： The optimum operation strategy for a side-stream external anaerobic self-forming dynamic membrane bioreactor (AnSFDMBR) was investigated by coupling such a system with an up-flow anaerobic sludge blanket reactor. Time-based backwashing with different intervals and transmembrane pressure (TMP)based backwashing were compared as the operation strategies of the AnSFDMBR. The system performance, extracellular polymeric substance (EPS) accumulation in the dynamic layer and on the membrane mesh of the AnSFDMBR, and the physical properties of the dynamic layer were closely monitored. Both operation strategies achieved stable operation with effluent turbidity less than 5 nephelometric turbidity units with a slowly increasing TMP. However, with the time-based backwashing strategy, the EPS accumulation rate in the dynamic layer was more than 20 times higher than that on the mesh, indicating that frequent backwashing might have a negative impact on the AnSFDMBR. The impacts of EPS accumulation on the membrane mesh were negligible considering the small amount of EPS residual and the large pore size of the mesh. On the contrary, the EPS accumulation in the dynamic layer changed the layer's physical properties and further impacted on the performance of the AnSFDMBR. The accumulation of polysaccharides in the dynamic layer was the main reason for the layer's compactness, which was negatively correlated with the specific surface area and further led to the TMP increase. The polysaccharides in the dynamic layer-to-sludge ratio increased to around 1.6 with only 5 days of time-base operation. With TMP-based operation, it took more than 10 days for polysaccharides in the dynamic layer-to-sludge ratio reaching 1.6. The low TMP increase rate, high effluent quality, and slow EPS accumulation with TMPbased backwashing indicated TMP-based operation is applicable in the studied AnSFDMBR. Nevertheless, the correlation between TMP and the accumulation of polysaccharides should be further invest