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1.
Enzyme Microb Technol ; 174: 110369, 2024 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-38101243

RESUMO

The entrance of some toxic and hazardous chemical agents such as antibiotics, pesticides, and herbicides into the environment can cause various problems to human health and the environment. In recent years, researchers have considered the use of electrostimulation in the processes of microbial metabolism and biological systems for the treatment of pollutants in the environment. Although several electrostimulation reports have been presented for pollutant removal, little attention has been paid to alternative current (AC) biostimulation. This study presents a systematic review of microbial electrostimulation using bioelectrochemical systems supplied with AC. The utilization of alternating current bioelectrochemical systems (ACBESs) has some advantages such as the provide of appropriate active biofilms in the electrodes due to the cyclical nature of the current and energy transfer in an appropriate manner on the electrode surfaces. Moreover, the ACBESs can reduce hydraulic time (HRT) under optimal conditions and reduce the cost of converting electricity using AC. In microbial electrostimulation, amplitude (AMPL), waveform, C/N, and current have a significant effect on increasing the removal efficiency of the pollutants. The obtained results of the meta-analysis illustrated that various pollutants such as phenol, antibiotics, and nitrate have been removed in an acceptable range of 96% using the ACBESs. Therefore, microbial electrostimulation using AC is a promising technology for the decomposition and removal of various pollutants. Moreover, the ACBESs could provide new opportunities for promoting various bioelectrochemical systems (BESs) for the production of hydrogen or methane.


Assuntos
Fontes de Energia Bioelétrica , Recuperação e Remediação Ambiental , Humanos , Eletricidade , Eletrodos , Poluentes Ambientais , Poluição Ambiental
2.
Chemosphere ; 317: 137890, 2023 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-36693482

RESUMO

In this study, the catalytic activity of the modified microbial cellulose/Fe3O4 (MMC/ Fe3O4) composite was studied for tetracycline (TC) degradation and mineralization in a three-dimensional electro-Fenton system (3D-EF). The MC/Fe3O4 was modified at 400 °C for 60 min. The MMC/ Fe3O4 was fully analyzed (morphological, structural, chemical properties). Complete degradation and 65% mineralization of TC was achieved in the 3D-EF process (0.5 g L-1 MMC/ Fe3O4, 10 mM NaCl electrolyte, and neutral pH) within 20 min and electrical energy consumption (EEC) 0.86 kwh g-1 TC under the 6.66 mA cm-2. High degradation efficiency TC, in 3D-EF system was attributed to significant single oxygen (1O2), superoxide(O2•-) participation and less to Hydroxyl radical (OH•). Reusability of the MMC/ Fe3O4 was successfully carried out for five consecutive runs. Accordingly, greencompositeof MMC/ Fe3O4 can be considered as an efficient and durable particle electrode (PE) to degrade and mineralize emerging pollutants in an aquatic environment.


Assuntos
Compostos Heterocíclicos , Nanocompostos , Poluentes Químicos da Água , Peróxido de Hidrogênio/química , Tetraciclina/química , Antibacterianos , Eletrodos , Poluentes Químicos da Água/análise , Oxirredução
3.
Front Psychol ; 13: 1060424, 2022.
Artigo em Inglês | MEDLINE | ID: mdl-36438319

RESUMO

Despite the growing body of research on boredom and its causes in face-to-face classes, little is known about how pedagogical interventions can mitigate this negative emotion. The purpose of this study was to examine boredom experienced by EAP students in online classes and investigate the effects of an autonomy-oriented intervention program on students' boredom. The boredom scale was administered to 84 students before and after the autonomy-oriented intervention. By designing and implementing autonomy-oriented intervention based on the autonomy enhancement model, positive results were obtained with reduced levels of boredom. The results revealed that the intervention was effective and boredom was reduced to a noticeable extent. In addition, the qualitative results contributed to our understanding of the learners' experiences throughout the intervention. We conclude the study with implications for EAP instructors to employ different pedagogical interventions to mitigate negative emotions in online EAP classes.

4.
Front Psychol ; 13: 922413, 2022.
Artigo em Inglês | MEDLINE | ID: mdl-35832919

RESUMO

Positive psychology focuses on the constructive effects of positive emotions on human behavior. Considering the recent plethoric research on positive emotions and SLA, this study pursues two important aims. The first aim is to find out whether there is any significant disparity between EFL teachers' and learners' views on an inventory of positive psychology in language learning (IPPLL) which was fostered by researchers. The second goal is to find out whether teachers' practices conform to their views on IPPLL and those expressed in the interview which was conducted with them. To this end, a 54-item questionnaire was developed and the revised questionnaire was administered to 385 learners. The results indicated that the teachers, in comparison with the learners, scored higher on all categories of the IPPLL. Moreover, unlike what they had expressed on the questionnaire and in the interview, the teachers did not capitalize on positive emotions as evinced in both teachers' practice and learners' experience with learning English. Implications of the findings for teacher education courses are presented.

5.
Ecotoxicol Environ Saf ; 239: 113654, 2022 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-35643029

RESUMO

Phenanthrene as the hazardous PAHs-component are extensively detected in industrial wastewater. However, the impacts of bioelectrostimulation process on Phenanthrene degradation in aerobic reactors remained unclear. Here, a novel bioelectrostimulation process equipped with carbon cloth as electrodes was developed to investigate the removal efficiency of Phenanthrene and ATPase enzyme activity in the synthetic wastewater. The results obtained from the present study indicated that a complete Phenanthrene degradation (100%) can be achieved using microbial electrostimulation systems steel mesh coated with carbon cloth (MES-CC) as anode under optimal operational conditions (electrical current: 4 mA, HA concentration: 15 mg L-1) within 18 h. The conductive carbon cloth provides a biofilm carrier to easily transfer the electrons between electrodes and microbial communities. In addition, the highest ATPase enzyme activity (5176 U) was observed when the aerobic MES-CC reactors were operated with electrical current 4 mA. Furthermore, the COD removal efficiency in MES-CC increased from 49% to 96% when the C: N ratio decreased from 20 to 5. The highest value of Vmax in MES-CC for suspended and attached growth were determined to be 2.87 and 0.54 g COD g-1 biomass. Overall, the results demonstrated that MES equipped with carbon cloth and continuous electrical current mode has good potential for efficient Phenanthrene wastewater treatment.


Assuntos
Fontes de Energia Bioelétrica , Fenantrenos , Adenosina Trifosfatases , Carbono , Estimulação Elétrica , Eletrodos , Águas Residuárias/análise
6.
Ultrason Sonochem ; 73: 105531, 2021 May.
Artigo em Inglês | MEDLINE | ID: mdl-33799109

RESUMO

Low-frequency ultrasonics is a potential technology to reduce the hydrolysis phase period in anaerobic digestion process. In this study, theinfluence of combined low frequency ultrasonics and micro-aerobic (MA) pretreatment on sewage sludge solubilization, enzyme activity and anaerobic digestion were assessed. Initially, the effect of ultrasonic density (0.012, 0.014, 0.016, 0.018, 0.1, 0.12 and 0.14 W/mL) and irradiation time (1, 3, 5, 8, 9, 10 and 12 min) of 20 kHz frequency waves were investigated. Accordingly, the effect of micro-aerobic pretreatment (Air flow rate (AFR) = 0.1, 0.2, 0.3 and 0.5 VVM) within 20, 30, 40.48 and 60 h were examined. In addition, the effect of combined pretreatment on COD solubilization, lipase enzyme activation, ATP, percentage of live bacteria and methane gas production during the anaerobic process were examined. The results showed that the highest lipase activity (14.9 Umol/mL) was obtained under the effect of ultrasonic density of 0.1 W/ml within 9 min. The highest solubilization (65%) was observed under optimal micro-aerobic conditions: AFR = 0.2 (VVM) and micro-aerobic time: 40 h. Combined ultrasonic and micro-aerobic (US + MA) pretreatment increases the solubilization (70%), microbial activity (2080%) and lipase enzymatic activity (129%) compared to individual pretreatment. The Biogas production during anaerobic digestion pretreated with combined methods increased by 193% compared to the control, while the elevated values of biogas production in reactors pretreated by ultrasonic and micro-aerobic pretreatment alone were observed to be 101% and 165%, respectively. The net energy in reactor with the combined pre-treatment methods was calculated to be 1.26 kWh, while this value for control, pretreated ultrasonic and micro-aerobic reactors were obtained to be 0.56, 0.67 and 1.2 kWh, respectively.


Assuntos
Lipase/metabolismo , Metano/biossíntese , Esgotos , Ultrassom , Aerobiose
7.
Environ Sci Pollut Res Int ; 28(20): 25327-25338, 2021 May.
Artigo em Inglês | MEDLINE | ID: mdl-33453025

RESUMO

This study aims to improve bacterial laccase enzyme activity (LEA) and dehydrogenase activity (DHA) affecting acetylsalicylic acid (ASA) biodegradation using an alternating current (AC). A microbial consortium was inoculated in an electroactive bioreactor supplied with an AC by a function generator under operating conditions of amplitude (AMPL) = 2-10 peak-to-peak voltage (Vpp), optical fiber splice tray (OFST) = 0.1 V, and sine wave frequency = 10 Hz. The obtained results revealed that at an applied voltage of 8 Vpp and an OFST of 0.1 for 12 h, the maximum bacterial LEA and DHA were 30.6 U/mL and 75.5 micro grTF/cm2.gr biomass; respectively. Cell viability and permeability were equal to 95.7% and 0.3%; respectively, at the voltage of 8 Vpp. Moreover, liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS) analyses showed that by-products had lower intensity at 8 Vpp compared with that of 2 Vpp voltage. Finally, the results demonstrated an optimum applied voltage of the AC, which could stimulate and promote bacterial LEA and DHA. Therefore, an electroactive bioreactor supplied with an AC can be a novel system for stimulation of enzyme activities in the process of ASA biodegradation.


Assuntos
Aspirina , Reatores Biológicos , Bactérias , Biodegradação Ambiental , Eletricidade
8.
Chemosphere ; 263: 127858, 2021 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-33297004

RESUMO

The present study was to enhance catalytic ozonation process (COP) using ferric (Fe)- ethylenediaminetetraacetic acid (Fe-EDTA) integrated with an electrocoagulation (EC) process for landfill leachate pretreatment. For this purpose, the effect of operating parameters such as ozone and Fe-EDTA concentrations, current, initial pH, and reaction time were investigated. The findings revealed that the EC process and single ozonation process (SOP) could alone reduce chemical oxygen demand (COD) in landfill leachate by 23% and 39%; respectively. Moreover, integration of both processes at 100 mA current, 400 mg h-1 ozone concentration, and 3 h reaction time could significantly improve COD reduction to 70%. As well, current efficiency and ozone consumption in the proposed system could considerably develop compared with EC process and SOP. The integrated electro-catalytic SOP using Fe-EDTA could be operated at neutral pH value, which the COD removal efficiency was obtained 79.7%. Subsequently, biochemical oxygen demand (BOD5)/COD ratio of effluent increased to 0.64. Examining pseudo-first-order and pseudo-second-order kinetics, it was realized that constant rate in the system had augmented. These results also indicated that the modified process using Fe-EDTA was a promising landfill leachate pretreatment technique that could significantly enhance COD removal efficiency and BOD5/COD ratio, and ultimately decrease time and sludge production.


Assuntos
Ozônio , Eliminação de Resíduos , Poluentes Químicos da Água , Ácido Edético , Ferro , Oxirredução
9.
Chemosphere ; 270: 128618, 2021 May.
Artigo em Inglês | MEDLINE | ID: mdl-33121817

RESUMO

This paper review is aiming to comprehensively identify and appraise the current available knowledge on microbial composition and microbial dynamics in anaerobic digestion with focus on the interconnections between operational parameters and microbial community. We systematically searched Scopus, Web of Science, pubmed and Embase (up to August 2019) with relative keywords to identify English-language studies published in peer-reviewed journals. The data and information on anaerobic reactor configurations, operational parameters such as pretreatment methods, temperature, trace elements, ammonia, organic loading rate, and feedstock composition and their association with the microbial community and microbial dynamics were extracted from eligible articles. Of 306 potential articles, 112 studies met the present review objectives and inclusion criteria. The results indicated that both aceticlastic and hydrogenotrophic methanogenesis are dominant in anaerobic digesters and their relative composition is depending on environmental conditions. However, hydrogenotrophic methanogens are more often observed in extreme conditions due to their higher robustness compared to aceticlastic methangoens. Firmicutes and Bacteroidetes phyla are most common fermentative bacteria of the acidogenic phase. These bacteria secrete lytic enzymes to degrade organic matters and are able to survive in extreme conditions and environments due to their spores. In addition, among archaea Methanosaeta, Methanobacterium, and Methanosarcinaceae are found at high relative abundance in anaerobic digesters operated with different operational parameters. Overall, understanding the shifts in microbial composition and diversity as results of operational parameters variation in anaerobic digestion process would improve the stability and process performance.


Assuntos
Reatores Biológicos , Microbiota , Anaerobiose , Archaea/genética , Metano
10.
Artigo em Inglês | MEDLINE | ID: mdl-32039189

RESUMO

Bioelectrochemical systems have undergone several modifications to promote the enzymes or pathways used to reduce the energy required for microbial metabolism. Changes in dominant bacteria, population, and growth rates occur when an electric current is applied intermittently. Applying electricity to bioelectrical reactor (BER) biofilms can either stimulate cells or lead to cell death; therefore, determining the applied voltage range that leads to viable and stimulated bacteria is crucial. We investigated the progression of apoptosis induced by a low frequency-low voltage alternating electric current (AC) in a BER biofilm and found that biofilms on carbon cloth (CC) and stainless steel (SS) 304 electrodes had pHzpc values of 8.67. The pHzpc of the biofilms increased by two compared to that of the inoculant bacteria mass. Furthermore, the Henderson-Hasselbalch equation reveals that the compositions of cell walls of the biofilms that formed on the CC and SS304 electrodes are very similar. In contrast, the CC and SS304 biofilms differ from the inoculant biomass without the influence of an AC field; this indicates that there are differences in the compositions of the cell walls in the present bacteria. Fourier transform infrared spectroscopy was used to compare spectra of the biofilms with that of the inoculation mass, and there were differences in shape and absorbance intensity, indicating variability in the composition, and quantity of each individual biofilm component. In addition, the dehydrogenase activity (DHA) content varied under different applied voltages; the highest DHA was obtained at 8 Vpp. A flow cytometry analysis showed a relatively low number of apoptotic cells (10.93 ± 5.19%) for the AC amplitudes studied. Thus, a low voltage-low frequency AC likely induces significant changes in bacterial metabolic activity but causes no significant change in their viability.

11.
Bioelectrochemistry ; 132: 107446, 2020 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-31927190

RESUMO

In the present study, minimization of hazardous bio-sludge production was investigated using a bioelectrochemical system supplied by an alternating current electric field and supplemented with phenol as a cabon source. The experiments were conducted in an air-conditioned bioreactor and at neutral pH value. Moreover, steel wool and carbon cloth were utilized as electrodes in the bioelectrochemical system. The experiments were operated in an air-conditioned bioreactor at 25 ℃ and a neutral pH value with carbon to nitrogen (C/N) ratio of 0.5-6. The results obtainedshowed that complete phenol electro-biodegradation occurred at a C/N ratio ofa frequency of 5 Hz, and 0.4 peak-to-peak voltage (Vpp) over 2 h.Besides, sludge production and sludge yield were obtained at the C/N ratio of 0.5-6 by 200-382 mg VSS/g COD and 82-89.4 mg TSS/g COD, respectively. Ultimately, the C/N ratio of 1 seemed to be optimum for microbial growth with the phenol biodegradation efficiency of 99.9% as well as the lowest sludge production. These results demonstrated that the proposed bioelectrochemical system supplied by low-frequency and low-voltage electric current could reduce hazardous sludge production.


Assuntos
Técnicas Eletroquímicas/métodos , Substâncias Perigosas , Esgotos , Análise da Demanda Biológica de Oxigênio , Biomassa , Reatores Biológicos , Eletricidade , Águas Residuárias/química
12.
RSC Adv ; 10(59): 35718-35728, 2020 Sep 28.
Artigo em Inglês | MEDLINE | ID: mdl-35517111

RESUMO

Micro-aeration as a pretreatment method improves the efficiency of anaerobic digestion of municipal sewage sludge and consequently promotes the methane production. In this study, adenosine triphosphate (ATP) and flow cytometry (FCM) were employed to monitor the performance of the micro-aerobic process and investigate the survival of bacterial cells within the process. At first, the effect of air flow rate (AFR) (0.1, 0.2, 0.3 and 0.5 vvm) on hydrolysis of mixed sludge in 5 aeration cycles (20, 30, 40, 48 and 60 hours) was examined. Then, the effects of the micro aerobic process on methane (CH4) production in anaerobic digestion were surveyed. The highest VSS reduction was 30.6% and 10.4% for 40 hours in the reactor and control, respectively. Soluble COD also fluctuated between 40.87 and 65.14% in micro-aerobic conditions; the highest SCOD was achieved at the time of 40 h. Microbial activities were increased by 597%, 170% and 79.4% for 20, 30 and 40 h pretreatment with the micro-aerobic process, respectively. Apoptosis assay showed that micro-aerobic pre-treatment at 20, 30 and 40 h increased the percentage of living cells by 57.4, 62.8 and 67.9%, respectively. On the other hand, FCM results showed that the highest percentage of viable bacteria (i.e., 67.9%) was observed at 40 h pretreating which was approximately 40% higher the ones for the control. Variation in cumulative methane production shows that methane production was increased by 221% compared to anaerobic digestion (control group). Therefore, ATP and FCM can be employed as two appropriate, accurate, relatively specific indicators for monitoring the process and bacteria viability.

13.
J Environ Manage ; 254: 109811, 2020 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-31707195

RESUMO

Landfill leachate contains complex, resistant, and diverse compounds that are considered as an environmental health problem. This study aims to investigate the efficacy of integrated homogeneous catalytic ozonation and electrochemical process for improving the biodegradability of landfill. This experimental study was conducted on real landfill leachate on the laboratory scale. The variables were current density (O3/H2O2-42.1 mA/cm2), ozone concentrations (100-400 mg/h), the initial pH (3-9), and the reaction times (1-6 h). The optimum operating condition was obtained at 1.42 mA/m2, 400 mg/h of ozone concentration, initial pH of 3, during 3 h. In the proposed integrated catalytic ozonation-electrochemical process, the chemical oxygen demand (COD) and biochemical oxygen demand (BOD) concentrations were removed to 3381.9 and 1521.8 mg/L, respectively. Under the optimum condition, the biodegradability index increased from 0.27 to 0.45. The results showed that the electro-catalytic ozonation process has a significant effect on the biodegradability index and could improve the removal efficiency of landfill leachate treatments.


Assuntos
Ozônio , Eliminação de Resíduos , Poluentes Químicos da Água , Catálise , Peróxido de Hidrogênio , Oxirredução
14.
Bioelectrochemistry ; 130: 107200, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31382227

RESUMO

In this study, a microbial electrochemical system (MES) was employed to investigate the effect of isoelectric point (IEP) on cheese whey wastewater treatment. The experiments were carried out in a bioreactor equipped with a semicircular carbon cloth and stainless steel electrodes as anode and cathode, respectively. The effects of IEP, whey protein concentration, electrical current, and time were studied. The IEP of the whey protein was determined at pH 5.9. The optimum electrical current was obtained at 6 mA for synthetic cheese whey wastewater. The results of rotary exponential doping showed that the third structure of proteins chenges to the second structure at the IEP. The highest protein removal (98%) was obtained at pH 6. The results showed that 76%, 83%, and 98% protein removal were achieved at 2, 4, and 8 h, respectively.


Assuntos
Reatores Biológicos/microbiologia , Águas Residuárias/análise , Poluentes Químicos da Água/isolamento & purificação , Purificação da Água/instrumentação , Proteínas do Soro do Leite/isolamento & purificação , Análise da Demanda Biológica de Oxigênio , Queijo/análise , Desenho de Equipamento , Tecnologia de Alimentos , Ponto Isoelétrico
15.
Bioelectrochemistry ; 130: 107230, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31326774

RESUMO

The present study was conducted to investigate the effect of alternating current (AC) on phenol removal in a microbial electrochemical system (MES) and determine its by-products. The bioreactor used for this purpose operates in the batch mode supplied with an AC power supply. The factors stimulating this process including frequency, applied voltage, duty cycle, carbon to nitrogen ratio, and the initial phenol concentration were investigated. The optimum operating conditions of the bioreactor were obtained at 5 Hz frequency, 0.4 peak-to-peak voltage (Vpp), C0 = 100 mg.L-1 phenol, pH = 7, C/N = 1, and the sine wave. Phenol was completely degraded under the optimum operating conditions for 2 h. The GC-MS analysis showed the presence of carboxylic acid, oxalic acid, and propionic acid. It was observed that the generated by-products are non-toxic and phenol is completely removed to nontoxic compounds. The results show that under optimum conditions, using an alternating current, the proposed system generated low-hazard byproducts with a low energy consumption.


Assuntos
Bactérias/metabolismo , Reatores Biológicos/microbiologia , Fenol/metabolismo , Poluentes Químicos da Água/metabolismo , Biodegradação Ambiental , Eletricidade , Técnicas Eletroquímicas/instrumentação , Desenho de Equipamento , Redes e Vias Metabólicas , Fenol/isolamento & purificação , Águas Residuárias/análise , Águas Residuárias/microbiologia , Poluentes Químicos da Água/isolamento & purificação , Purificação da Água/instrumentação
16.
Chemosphere ; 232: 35-44, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31152901

RESUMO

The main aim of this study is to investigate the biodegradation of highly concentrated aspirin as an emerging pollutant from aqueous solution using an alternating current microbial electrochemical system. A single-chamber Plexiglas cylindrical reactor equipped with stainless steel mesh electrodes (18 cm height × 16 cm diameter) was applied as the bioreactor in batch mode with an effective volume of 5 L, height of 20 cm, and the diameter about 20 cm by AMPL = 2 Vpp, OFST = 0.1 V, waveform = sinusoidal, frequency = 10 Hz, and pH = 7. The process parameters including initial concentration (100-400 mg L-1), chemical oxygen demand (COD), activity of enzymes, biokinetic and pathway studies at very low voltage and very low frequency alternating current were investigated. The specific biodegradation rate of aspirin was calculated based on Michaelis-Menten model. The complete aspirin removal efficiency and the maximum enzymatic activity were achieved at 250 mg L-1 aspirin, voltage of 2 Vpp and applied current = 3 mA during 6 h. The bioassay of aspirin concentrations in biofilm of the system using flow cytometry analysis resulted in the live and necrotic cells shares of 96.2%, and 0.44%, respectively. Moreover, the LC and GC-MS analysis showed low molecular weight acids such as oxalic and acetic acid at 6 h time under the optimal conditions using very low applied voltage and frequency. Obtaining low reaction time for degradation, high potential in biodegradation, oxidation and mineralization ability were the novelty of treatment system with high concentration aspirin in the study.


Assuntos
Aspirina/metabolismo , Biodegradação Ambiental , Poluentes Químicos da Água/metabolismo , Aspirina/análise , Análise da Demanda Biológica de Oxigênio , Reatores Biológicos , Eletrodos , Oxirredução , Poluentes Químicos da Água/análise
17.
Environ Sci Pollut Res Int ; 25(33): 33591-33598, 2018 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-30269283

RESUMO

The present study considers the impact of the alternating electric current on the viability and biological activity of denitrifying bacteria in a microbial electrochemical system (MES). The bio-stimulation using low-frequency low-voltage alternating current (AC) was studied in terms of the adenosine triphosphate (ATP) level of bacteria, viability, morphological characteristics, cell size, and complexity. Apoptosis assays by flow cytometry revealed that 81-95% of the cells were non-apoptotic, and cell membrane damage occurred < 18%. The applied AC could affect the bacterial metabolic activity and ATP content in the denitrifying bacteria depending on characteristics of the alternating electric current. Scanning electron microscopy (SEM) analysis of cell morphology illustrated low cell deformations under AC stimulation. The obtained results revealed that the applied alternating electrical current could increase the metabolic activity of denitrifying bacteria, leading to a better denitrification. Graphical abstract ᅟ.


Assuntos
Trifosfato de Adenosina/metabolismo , Biofilmes/crescimento & desenvolvimento , Reatores Biológicos/microbiologia , Técnicas Eletroquímicas/métodos , Purificação da Água/métodos , Bactérias/metabolismo , Desnitrificação , Eletricidade , Viabilidade Microbiana
18.
Bioelectrochemistry ; 120: 49-56, 2018 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-29175273

RESUMO

In this study, a microbial electrochemical system (MES) was designed to evaluate the effects of a low frequency-low voltage alternating electrical current on denitrification efficacy in the presence of ibuprofen as a low biodegradable organic carbon source. Cylindrical carbon cloth and stainless steel mesh electrodes containing a consortium of heterotrophic and autotrophic bacteria were mounted in the wall of the designed laboratory-scale bioreactor. The effects of inlet nitrate concentration (50-800mgL-1), retention time (2.5-24h), waveform magnitude (0.1-9.6Vp-p), adjustable direct current voltage added to offset voltage (0.1-4.9V), alternating current frequency (10-60Hz), and waveforms (sinusoidal, square, and ramp) were studied in this work. The results showed that the proposed system removes 800mgL-1 nitrate up to 95% during 6.5h. Optimum conditions were obtained in the 8Vp-p using a frequency of 10Hz of a sinusoidal waveform. The morphology studies confirmed bacterial morphology change when applying the alternating current. Dehydrogenase activity of biofilms formed on surface of stainless steel electrodes increased to 15.24µgTFmgbiomasscm-2d. The maximum bacterial activity was obtained at a voltage of 8Vp-p. The experimental results revealed that the MES using a low frequency-low voltage alternating electrical current is a promising technique for nitrate removal from pharmaceutical wastewaters in the presence of low biodegradability of carbon sources such as ibuprofen.


Assuntos
Técnicas Eletroquímicas/instrumentação , Ibuprofeno/isolamento & purificação , Nitratos/isolamento & purificação , Águas Residuárias/análise , Águas Residuárias/microbiologia , Poluentes Químicos da Água/isolamento & purificação , Purificação da Água/instrumentação , Reatores Biológicos/microbiologia , Desnitrificação , Desenho de Equipamento
19.
Carbohydr Polym ; 162: 56-61, 2017 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-28224895

RESUMO

In the present study, microbial cellulose (MC) as a carbohydrate polymer was made conductive by oxidative polymerization with aniline. Sulfate-reducing bacteria (SRB) were immobilized on the surface of the conductive biopolymer, and this was used as a biocathode in a bioreduction process to reduce Cr (VI) as a model of heavy metals. The results of Fourier transform infrared analysis confirmed that the polyaniline was distributed on the cellulose surface. The maximum tensile stress of the conductive biopolymer was obtained 23MPa using calculating Young's modulus. A current density of 60mA/m2 was determined as optimal, and an increase in pH from 5 to 7 significantly reduced the required time for reduction of Cr (VI). The system reached >99% removal of Cr (VI) within 1.5h at pH 7. Kinetic experiment studies showed a high constant rate (mean Kobs 0.78, R2 0.95). The results showed that the conductive MC can be used as an appropriate bioelectrode to reduce Cr (VI) in bioelectrochemical processes. It is expected that experimental results could be used as a reference for the utilization of MC in bioelectrochemical systems.


Assuntos
Bactérias/metabolismo , Celulose/química , Cromo/metabolismo , Compostos de Anilina/química , Condutividade Elétrica , Cinética , Oxirredução
20.
Environ Sci Pollut Res Int ; 23(19): 19735-43, 2016 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-27406226

RESUMO

In this study, a titanium plate was impregnated with SnO2 and Sb (Ti/SnO2-Sb2O4) for the electrocatalytic removal of phenol from wastewater, and the chemical degradation pathway was presented. The effects of various parameters such as pH, current density, supporting electrolyte, and initial phenol concentration were studied. At optimum conditions, it was found that phenol was quickly oxidized into benzoquinone because of the formation of various strong radicals during electrolysis by the Ti/SnO2-Sb2O4 anode from 100 to <1 mg/L over 1 h. The results of GC/MS analysis showed the presence of some esters of organic acid such as oxalic acid and formic acid. HPLC analysis showed only trace amounts of benzoquinone remaining in the solution. The efficiency of TOC removal at the Ti/SnO2-Sb2O4 anode surface showed a degradation rate of 49 % over 2 h. Results showed that the molecular oxygen potential at the electrode was 1.7 V. The phenol removal mechanism at the surface of the Ti/SnO2-Sb2O4 anode was influenced by the pH. Under acidic conditions, the mechanism of electron transfer occurred directly, whereas under alkaline conditions, the mechanism can be indirect. This research shows that the proposed electrolyte can significantly influence the efficiency of phenol removal. It can be concluded that the treatment using an appropriate Ti/SnO2-Sb2O4 electrode surface can result in the rapid oxidation of organic pollutants.


Assuntos
Fenol/química , Águas Residuárias/química , Poluentes Químicos da Água/química , Purificação da Água/métodos , Ácidos , Eletroquímica/métodos , Eletrodos , Eletrólise , Cromatografia Gasosa-Espectrometria de Massas , Compostos Orgânicos , Oxirredução , Compostos de Estanho , Titânio/química
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