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关键词： Caproic acid   Megasphaera hexanoica   Clostridium tyrobutyricum   Coculture system   Submerged hollow-fiber membrane reactor  

摘要： In this study, a coculture bioprocess was developed with Clostridium strains producing butyric acid and Megasphaera hexanoica producing caproic acid from the butyric acid. The two bacterial strains were each cultivated in two submerged hollow-fiber membrane bioreactors (s-HF/MBRs), separately. Each fermentation broth was filtered through the membrane modules, and the filtered broth was either interchanged on another reactor or obtained sequentially through. Using s-HF/MBRs, the caproic acid concentration increased to 10.08 g L-1, with the fastest productivity of 0.69 g L-1 h(-1), which higher than that previously reported.

关键词： Signal molecule   Microbial ecology   Biofouling   Membrane process   Fouling control  

摘要： Membrane biofouling, due to biofilm growth after planktonic bacteria attachment to a membrane, is a major bottleneck limiting the energy-efficient operation and maintenance of membrane bioreactors (MBRs). Microbial communications, known as quorum sensing (QS), are responsible for this biofouling behavior. Novel strategies for stopping this communication, known as quorum quenching (QQ), appear to be successful for biofouling control in MBRs used for wastewater treatment. This review describes recent information regarding the signal molecules and mechanisms responsible for QS behaviors, promising approaches for QQ (enzymatic, bacterial, fungal, photocatalytic, mimicking, and biostimulating methods), and efficient fabrication and use of QQ media for MBR applications. We discuss the opportunities and challenges of QQ techniques for their further improvement and practical use in MBRs.

关键词： Mesophilic   AnMBR   Phenol   Temperature susceptibility   Salinity   Microbial community  

摘要： This study examined the temperature susceptibility of a continuous-flow lab-scale anaerobic membrane bioreactor (AnMBR) to temperature shifts from 35 degrees C to 55 degrees C and its bioconversion robustness treating synthetic phenolic wastewater at 16 gNa(+)L(-1). During the experiment, the mesophilic reactor was subjected to stepwise temperature increases by 5 degrees C. The phenol conversion rates of the AnMBR decreased from 3.16 at 35 degrees C to 2.10 ***(-1).d(-1) at 45 degrees C, and further decreased to 1.63 mgPIrgVSS(-1).d(-1) at 50 degrees C. At 55 degrees C, phenol conversion rate stabilized at 1.53 ***(-1)center dot d(-1) whereas COD removal efficiency was 38% compared to 95.5% at 45 degrees C and 99.8% at 35 degrees C. Interestingly, it was found that the phenol degradation process was less susceptible for the upward temperature shifts than the methanogenic process. The temperature increase implied twenty-one operational taxonomic units from the reactor's microbial community with significant differential abundance between mesophilic and thermophilic operation, and eleven of them are known to be involved in aromatic compounds degradation. Reaching the upper-temperature limits for mesophilic operation was associated with the decrease in microbial abundance of the phyla Firmicutes and Proteobacteria, which are linked to syntrophic phenol degradation. It was also found that the particle size decreased from 89.4 gm at 35 degrees C to 21.0 sm at 55 degrees C. The accumulation of small particles and higher content of soluble microbial protein-like substances led to increased transmembrane pressure which negatively affected the filtration performance. Our findings indicated that at high salinity a mesophilic AnMBR can tolerate a temperature up to 45 degrees C without being limited in the phenol conversion capacity. (C) 2018 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.o

摘要： Methanogenic bioreactors have been applied to treat purified terephthalic acid (PTA) wastewater containing complex aromatic compounds, such as terephthalic acid, para-toluic acid and benzoic acid. This study characterized the interaction of microbial populations in 42 samples obtained from 10 PTA-degrading methanogenic bioreactors. Approximately, 54 dominant populations (11 methanogens, 8 syntrophs and 35 functionally unknown clades) that represented 73.9% of total 16S rRNA gene iTag sequence reads were identified. Co-occurrence analysis based on the abundance of dominant OTUs showed two non-overlapping networks centred around aromatic compound- (group AR: Syntrophorhabdaceae, Syntrophus and Pelotomaculum) and fatty acid- (group FA: Smithella and Syntrophobacter) degrading syntrophs. Group AR syntrophs have no direct correlation with hydrogenotrophic methanogens, while those from group FA do. As degradation of aromatic compounds has a wider thermodynamic window than fatty acids, Group AR syntrophs may be less influenced by fluctuations in hydrogenotrophic methanogen abundance or may non-specifically interact with diverse methanogens. In both groups, network analysis reveals full-scale- and lab-scale-specific uncultivated taxa that may mediate interactions between syntrophs and methanogens, suggesting that those uncultivated taxa may support the degradation of aromatic compounds through uncharted ecophysiological traits. These observations suggest that organisms from multiple niches orchestrate their metabolic capacity in multiple interaction networks to effectively degrade PTA wastewater.

关键词： Dynamic membrane   Landfill leachate   Nitrogen removal   Ammonia conversion   16 rRNA   Metagenomics  

摘要： The use of dynamic membranes as a low-cost alternative for conventional membrane for the treatment of landfill leachate (LFL) was investigated in this study. For this purpose a lab-scale, submerged pre-anoxic and post-aerobic bioreactor configuration was used with nylon mesh as dynamic membrane support. The study was conducted at ambient temperature and LFL was fed to the bioreactor in gradually increasing concentration mixed with tap water (from 20% to 100%). The results of this study demonstrated that lower mesh pore size of 52 gm achieved better results in terms of solid-liquid separation performance (turbidity <10 NTU) of the formed dynamic membrane layer as compared to 200 and 85 gm meshes while treating LFL. Consistently high NI4+-N conversion efficiency of more than 98% was achieved under all nitrogen loading conditions, showing effectiveness of the formed dynamic membrane in retaining slow growing nitrifying species. Total nitrogen removal reached more than 90% however, the denitrification activity showed a fluctuating profile and found to be inhibited by elevated concentrations of free nitrous acid and NO2--N at low pH values inside the anoxic bioreactor. A detailed metagenomic analysis allowed a taxonomic investigation over time and revealed the potential biochemical pathways involved in NI4+-N conversion. This study led to the identification of a dynamic system in which nitrite concentration is determined by the contribution of NH4- oxidizers (Nitrosomonas), and by a competition between nitrite oxidizers (Nitrospira and Nitrobacter) and reducers (Thauera). (C) 2018 Elsevier Ltd. All rights reserved.

关键词： Membrane bioreactor (MBR)   Sustainability evaluation   Energy use   Sludge treatment   Membrane life span  

摘要： Membrane bioreactor (MBR) technology is receiving increasing attention in wastewater treatment and reuse. This study presents an integral sustainability evaluation of a full scale MBR plant. The plant is capable of achieving prominent technical performance in terms of high compliance rate, low variation in effluent quality and high removal efficiency during long term operation. It is also more responsive to the new local standard with rigorous limits. However, electricity consumption is found to be the dominant process resulting in elevated life cycle environmental impacts and costs, accounting for 51.6% of the costs. As such, it is suggested to optimize energy use in MBR unit and implement sludge treatment and management. The prolonged membrane life span could also contribute largely to reduced life cycle environmental concerns and expenses. This study is of great theoretical significance and applicable value in guaranteeing the performance and sustainability of large scale MBR schemes.

关键词： Up-flow anaerobic/anoxic/oxic (A(2)O) bioreactor   Meat-processing wastewater   COD/TN ratio  

摘要： A high rate up-flow anaerobic, anoxic and oxic (A(2)O) bioreactor was designed and operated for meat processing wastewater (MPW) treatment as a single cost-effective system with the aim of simultaneous CNP removal. The influence of three essential factors, HRT, COD/TN ratio and aerated volume fraction on the reactor performance was assessed using response surface methodology (RSM). The required HRT to reach 98.5% COD removal was achieved at 7.5 h. Simultaneous CNP removal under denitrification rate of 199.4 mg/l.d gave high nitrate to nitrogen gas conversion of 74.6 mg/l. An HRT, COD/TN ratio and aerated volume fraction of 10 h, 100:20 and 60%, respectively, was a favored condition for an efficient nitrogen removal with effluent total Kjeldahl nitrogen (MN) less than 70 mg/l. Under optimum condition, an HRT, COD/TN and aerated volume fraction of 8 h, 100:14 and 65%, respectively, resulted an effluent phosphorus of 43 mg/l, but 93.97 mg/l phosphorus was released in an anaerobic condition at 6 h. An effluent with a low turbidity of about 1.5 NTU and a sludge volume index (SVI) of 75.9 ml/g was achieved using at HRT of 12.5 h, COD/TN ratio of 100: 8 and aerated volume fraction of 50%. Under these conditions, the removal efficiencies for COD, TKN, nitrate-nitrogen (NO3--N), total nitrogen (TN) and phosphorus (PO43--P) were obtained to be 98.33, 92.06, 91.97, 90.48 and 83.48%, respectively. As a result, the application of the up-flow A(2)O bioreactor is a promising configuration to get hygienic water from wastewater. (C) 2018 Elsevier Ltd. All rights reserved.

关键词： electrocoagulation   electro-membrane bioreactor   extracellular polymeric substances   fouling control   soluble microbial products  

摘要： This study evaluated the effects of electrochemical processes on the mixed liquor characteristics of an electro-membrane bioreactor (e-MBR) applied to municipal wastewater treatment. A laboratory-scale e-MBR was assessed under two experimental runs: without the electric field (run I) and with electric field, controlled by the application of an electric current set in 10.0 A m(-2) under intermittent exposure mode of 6 minutes ON/18 minutes OFF (run II). The electric field caused approximately 55% removal of both soluble microbial products (SMP) and extracellular polymeric substances (EPS), whereas the proteins/carbohydrates ratio in EPS was increased from 1.9 in the run I to 2.9 in run II, leading to an increment of flocs' hydrophobicity. Additionally, the sludge floc size average value was reduced from 42.2 mu m in run I to 24.6 mu m in run II, which led to a significant enhancement in the sludge settleability. As a result, the membrane fouling rate was always less than 3.80 mbar d(-1) in run II, whereas in run I these values reached up to 34.7 mbar d(-1). These results demonstrated that the electrochemical processes enhanced the mixed liquor filterability. Therefore, their implementation represents a great alternative to improve the operational stability of membrane bioreactors.

关键词： bioprocess engineering   mixing  

摘要： The effect of dissolved oxygen fluctuations on suspended plant cells was investigated using a scale-down stirred bioreactor system to simulate the heterogeneous conditions found in large-scale vessels. Transgenic Nicotiana tabacum cells expressing IgG1 antibody and Thalictrum minus cells producing berberine were subjected to gas switching cycles based on a stochastic model of log-normal circulation time distributions. Because pumping severely damaged the cells, the scale-down approach was restricted to a single-vessel system. Dissolved oxygen oscillations of amplitude about +/- 5% air saturation were achieved in the N. tabacum cultures;however, most simulations produced highly damped fluctuations due to oxygen transfer limitations and no significant effect on the cultures was observed. In contrast, berberine production by T. minus cells was reduced when fluctuations of +/- 10-15% air saturation were superimposed on mean dissolved oxygen tensions of 25 and 35% air saturation. This work demonstrates that dissolved oxygen gradients such as those found in large-scale mixing vessels can be detrimental to plant cell cultures even when sufficient average dissolved oxygen levels are provided. (c) 2018 American Institute of Chemical Engineers

关键词： MTC   Quorum sensing   Exopolysaccharides   16S rRNA   Aeromonas diversa  

摘要： Cadmium is one of the toxic heavy metals which tend to accumulate in the biome posing threat to the living system. The present study investigated the cadmium removal efficiency by effective cadmium-resistant isolate in a novel dual-chambered horizontal continuous-flow bioreactor. Cadmium-resistant bacterial isolates were obtained from sewage effluent samples and were tested for their maximum tolerable concentration. The isolate VITKKAJ1 was found to be highly resistant to cadmium and exhibited high degree of biofilm formation. The capability of VITKKAJ1 in producing short-chain quorum-sensing molecules (acyl-homoserine lactone) was significantly correlated with the increased production of exopolysaccharides. Substrates such as gravels and alginate beads were packed in the perforated compartments of the bioreactor with a bed height of 15cm for the adsorption of cadmium. The percentage removal of cadmium with and without biofilm (substrates) was 90.56 and 70.7%, respectively. The phylogenetic analysis based on 16S rRNA sequencing indicated the isolate to be a representative of Aeromonas diversa (Acc. No. KU560509).