[Show abstract][Hide abstract] ABSTRACT: Polychlorinated biphenyls (PCBs) are persistent organic pollutants in insulating oil of a large number of transformers. A rapid and economical analytical method to detect PCB contamination is still required. To address this issue, we propose here the first microfluidic screening method for PCB contamination in insulating oil. The insulating oil was pretreated using a multilayer capillary column and a microfluidic liquid-liquid partitioning. PCBs in the pretreated oil were measured using a microfluidic kinetic exclusion assay. In order to detect PCBs with high sensitivity, conditions of the microfluidic kinetic exclusion assay were optimized. Measurements were rapidly completed (within 43 min). The measurement range was estimated to be 0.26−3.3 mg/kg defined as the relative absorbance from 20−80%. The screening performance (false positive and false negative rates) was tested on fifty real oil samples; results about these tests were discussed in detail, especially suitable cutoff by comparing with the data analyzed using high-resolution-gas-chromatography/high-resolution-mass-spectrometry. Finally, the screening performance was confirmed using our proposed stochastic screening model. A cutoff of 0.3 to judge as positive is suitable considering the risk of the PCB release into the environment.
Analytical Chemistry Research 11/2014; 3. DOI:10.1016/j.ancr.2014.11.002
[Show abstract][Hide abstract] ABSTRACT: A simple new model for estimating the screening performance (false positive and false negative rates) of a given test for a specific sample population is presented. The model is shown to give good results on a test population, and is used to estimate the performance on a sampled population. Using the model developed in conjunction with regulatory requirements and the relative costs of the confirmatory and screening tests allows evaluation of the screening test's utility in terms of cost savings. Testers can use the methods developed to estimate the utility of a screening program using available screening tests with their own sample populations.
[Show abstract][Hide abstract] ABSTRACT: A rapid, ultra-sensitive, and practical label-free impedimetric immunoassay for measuring trace levels of total polychlorinated biphenyls (PCBs) in insulating oil was developed. First, we developed a novel monoclonal antibody (RU6F9) for PCBs by using a designed immunogen and characterized its binding affinity for a commercial mixtures of PCBs, and its main congeners. A micro comb-like gold electrode was fabricated, and the antibody was covalently immobilized on the electrode through a self-assembled monolayer formed by dithiobis-N-succinimidyl propionate. The antigen-binding event on the surface of the functionalized electrode was determined as the change in charge transfer resistance by using electrochemical impedance spectroscopy. The resulting impedimetric immunoassay in aqueous solution achieved a wide determination range (0.01-10 µg/L) and a low detection limit (LOD) of 0.001 µg/L, which was 100-fold more sensitive than a conventional flow-based immunoassay for PCBs. By combining the impedimetric immunoassay with a clean-up procedure for insulating oil utilizing a multilayer clean-up column followed by DMSO partitioning, an LOD of 0.052 mg/kg-oil was achieved, which satisfied the Japanese regulation criterion of 0.5 mg/kg-oil. Finally, the immunoassay was employed to determine total PCB levels in actual used insulating oils (n = 33) sampled from a used transformer containing trace levels of PCBs, and the results agreed well with the Japanese official method (HRGC/HRMS).
[Show abstract][Hide abstract] ABSTRACT: Development and modifications are described that expand the application of an immunoassay from the detection of Kanechlors (Japanese technical PCBs mixtures) to the detection of Aroclors (U. S. technical PCB mixtures, used in Korea) in contaminated Korean transformer oil. The first necessary modification was the development of a new antibody with a reactivity profile favorable for Aroclors. The second modification was the addition of a second column to the solid-phase extraction method to reduce assay interference caused by the Korean oil matrix. The matrix interference is suspected to be caused by the presence of synthetic oils (or similar materials) present as contaminants. The modified assay was validated by comparison to high-resolution gas chromatography/high-resolution mass spectrometry analysis, and was shown to be tolerant of up to 10% of several common synthetic insulating oils. Finally the screening performance of the modified assay was evaluated using 500 used transformer oil samples of Korean origin, and was shown to have good performance in terms of false positive and false negative rates. This report provides evidence for the first establishment of immunoassay screening for Aroclor based PCB contamination in Korean transformer oil.
[Show abstract][Hide abstract] ABSTRACT: Bioelectrochemical (-0.8 V, -0.3 V, and +0.6 V vs. Ag/AgCl) and non-bioelectrochemical co-cultures of a hydrogenotrophic methanogen and a cellulolytic bacterium were conducted. Unlike non-bioelectrochemical co-cultures, a cathodic reaction (-0.8 V) increased the growth of the hydrogenotrophic methanogen and the cellulolytic bacterium, by 6.0- and 2.2-fold respectively, and increased cellulose degradation. In contrast, anodic reactions (-0.3 V, +0.6 V) influenced them negatively.
[Show abstract][Hide abstract] ABSTRACT: Polychlorinated biphenyls (PCBs) are persistent organic pollutants that are present in the insulating oil inside a large number of transformers. To aid in eliminating PCB-contaminated transformers, PCBs in oil need to be measured using a rapid and cost-effective analytical method. We previously reported a pretreatment method for the immunoassay of PCBs in oil using a large-scale multilayer column and a microchip with multiple microrecesses, which permitted concentrated solvent extraction. In this paper, we report on a more rapid and facile pretreatment method, without an evaporation process, by improving the column and the microchip. In a miniaturized column, the decomposition and separation of oil were completed in 2 min. PCBs can be eluted from the capillary column at concentrations seven-times higher than those from the previous column. The total volume of the microrecesses was increased by improving the microrecess structure, the enabling extraction of four-times the amount of PCBs achieved with the previous system. By interfacing the capillary column with the improved microchip, PCBs in the eluate from the column were extracted into dimethyl sulfoxide in microrecesses with high enrichment and without the need for evaporation. Pretreatment was completed within 20 min. The pretreated oil was analyzed using a flow-based kinetic exclusion immunoassay. The limit of detection of PCBs in oil was 0.15 mg kg(-1), which satisfies the criterion set in Japan of 0.5 mg kg(-1).
[Show abstract][Hide abstract] ABSTRACT: A cylindrical bioelectrochemical reactor (BER) containing carbon fiber textiles (CFT; BER + CFT) has characteristics of bioelectrochemical and packed-bed systems. In this study, utility of a cylindrical BER + CFT for degradation of a garbage slurry and recovery of biogas was investigated by applying 10% dog food slurry. The working electrode potential was electrochemically regulated at -0.8 V (vs. Ag/AgCl). Stable methane production of 9.37 L-CH4 . L-1 . day-1 and dichromate chemical oxygen demand (CODcr) removal of 62.5% were observed, even at a high organic loading rate (OLR) of 89.3 g-CODcr . L-1 . day-1. Given energy as methane (372.6 kJ . L-1 . day-1) was much higher than input electric energy to the working electrode (0.6 kJ . L-1 . day-1) at this OLR. Methanogens were highly retained in CFT by direct attachment to the cathodic working electrodes (52.3%; ratio of methanogens to prokaryotes), compared with the suspended fraction (31.2%), probably contributing to the acceleration of organic material degradation and removal of organic acids. These results provide insight into the application of cylindrical BER + CFT in efficient methane production from garbage waste including a high percentage of solid fraction.
AMB Express 03/2013; 3(1):17. DOI:10.1186/2191-0855-3-17
[Show abstract][Hide abstract] ABSTRACT: To investigate the precise effect of the redox potential on the methanogenesis of the hydrogenotrophic methanogen Methanothermobacter thermautotrophicus by using an electrochemical redox controlling system without adding oxidizing or reducing agents. A bioelectrochemical system was applied to control the redox conditions in culture and to measure the methane-producing activity of M. thermautotrophicus at a constant potential from +0·2 to −0·8 V (vs Ag/AgCl). Methane production and growth of M. thermautotrophicus were 1·6 and 3·5 times increased at −0·8 V, compared with control experiments without electrolysis, respectively, while methanogenesis was suppressed between +0·2 and −0·2 V. A clear relationship between an electrochemically regulated redox potential and methanogenesis was revealed.
A novel bioelectrochemical method can activate the methanogenesis of M. thermautotrophicus by controlling the redox potential in culture conditions at −0·8 V, which is a difficult potential to achieve by conventional methods (e.g. by adding reducing agents). This study provides useful insights for the application of a bioelectrochemical system in industrial processes involving methanogens, such as in anaerobic digesters.
[Show abstract][Hide abstract] ABSTRACT: Mercury is considered the most important heavy metal pollutant because of the likelihood of bioaccumulation and toxicity. Monitoring widespread ionic mercury (Hg2+) contamination requires high-throughput and cost-effective methods to screen large numbers of environmental samples. In this study, we developed a simple and sensitive analysis for Hg2+ in environmental aqueous samples by combining a microfluidic immunoassay and solid-phase extraction (SPE). By using a microfluidic platform, an ultrasensitive Hg2+ immunoassay, which yields results in only 10 min and with a lower detection limit (LOD) of 0.13 µg/L, was developed. To allow application of the developed immunoassay to actual environmental aqueous samples, we developed an ion exchange resin (IER) based SPE for selective Hg2+ extraction from among an ion mixture. When using optimized SPE conditions, followed by the microfluidic immunoassay, the LOD of the assay was 0.83 μg/L, which satisfied the guideline values for drinking water suggested by the US EPA (2 µg/L; total mercury), and the WHO (6 µg/L; inorganic mercury). Actual water samples, including tap water, mineral water, and river water, which had been spiked with trace levels of Hg2+, were well analyzed by SPE followed by microfluidic Hg2+ immunoassay, and the results were agreed with reduction vaporizing-atomic adsorption spectroscopy.
[Show abstract][Hide abstract] ABSTRACT: A bioelectrochemical reactor (BER) containing carbon fiber fabric (CFF) (BER+CFF) enabled efficient methane fermentation from thickened sewage sludge. A cylindrical BER+CFF was proposed and scaled-up to a volume of 4.0-L. Thickened sewage sludge was treated using three types of methanogenic reactors. The working electrode potential in the BER+CFF was regulated at -0.8V (vs. Ag/AgCl). BER+CFF showed gas production of 3.57LL(-1)day(-1) at a hydraulic retention time (HRT) of 4.0days; however, non-BER+CFF showed a lower gas production rate (0.83LL(-1)day(-1)) at this HRT, suggesting positive effects of electrochemical regulation. A stirred tank reactor (without CFF) deteriorated at an HRT of 10days, suggesting positive effects of CFF. 16S rRNA gene analysis showed that the BER+CFF included 3 kinds of hydrogenotrophic methanogens and 1 aceticlastic methanogen. These results demonstrate the effectiveness of the BER+CFF for scale-up and flexibility of this technology.
[Show abstract][Hide abstract] ABSTRACT: The membraneless bioelectrochemical reactor (Ml-BER) is useful for dark hydrogen fermentation. The effect of the electrochemical reaction on microorganisms in the Ml-BER was investigated using glucose as the substrate and compared with organisms in a membraneless non-bioelectrochemical reactor (Ml-NBER) and bioelectrochemical reactor (BER) with a proton exchange membrane. The potentials on the working electrode of the Ml-BER and BER with membrane were regulated to -0.9 V (versus Ag/AgCl) to avoid water electrolysis with a carbon electrode. The Ml-BER showed suppressed methane production (19.8 ± 9.1 mg-C·L(-1)·day(-1)) and increased hydrogen production (12.6 ± 3.1 mg-H·L(-1)·day(-1)) at pH(out) 6.2 ± 0.1, and the major intermediate was butyrate (24.9 ± 2.4 mM), suggesting efficient hydrogen fermentation. In contrast, the Ml-NBER showed high methane production (239.3 ± 17.9 mg-C·L(-1)·day(-1)) and low hydrogen production (0.2 ± 0.0 mg-H·L(-1)·day(-1)) at pH(out) 6.3 ± 0.1. In the cathodic chamber of the BER with membrane, methane production was high (276.3 ± 20.4 mg-C·L(-1)·day(-1)) (pH(out), 7.2 ± 0.1). In the anodic chamber of the BER with membrane (anode-BER), gas production was low because of high lactate production (43.6 ± 1.7 mM) at pH(out) 5.0 ± 0.1. Methanogenic archaea were not detected in the Ml-BER and anode-BER. However, Methanosarcina sp. and Methanobacterium sp. were found in Ml-NBER. Prokaryotic copy numbers in the Ml-BER and Ml-NBER were similar, as were the bacterial community structures. Thus, the electrochemical reaction in the Ml-BER affected hydrogenotrophic and acetoclastic methanogens, but not the bacterial community.
[Show abstract][Hide abstract] ABSTRACT: Bioelectrochemical systems (BESs) can control electric flow and resultant microbial activity. We designed a single chamber BES to investigate hydrogen production from artificial garbage slurry. A 3-electrode system was applied and the potential of the working electrode was regulated to −1.0 V (vs. Ag/AgCl). Thus, the potential on the counter electrode was 1.38 V (vs. Ag/AgCl). Hydrogen fermentation in the BES was initiated by methanogenic seed sludge. The BES achieved a hydrogen production rate of 2196 mL L−1 day−1 at an organic loading rate of 58.7 g dichromate chemical oxygen demand L−1 day−1. Acetate and butyrate were the main products, indicating that favorable hydrogen fermentation occurred in the system. Combination of high potential on the counter electrode and relatively low pH condition (5.5–6.4) was effective for constructing hydrogen fermentation even in single chamber system by inhibiting methanogenesis. However, it may be necessary to increase the space between the working and counter electrodes so as to decrease the electrical input. The single-chamber BES could be scaled-up for efficient hydrogen fermentation from garbage slurry.
[Show abstract][Hide abstract] ABSTRACT: We previously described our systematic progress that eventually resulted in a commercially available immunoassay based biosensor (PCB biosensor) for detecting PCBs in oil. However, IC50 of the commercialized PCB biosensor was approximately 2 ppb for PCBs, and did not achieve the theoretical detection limit (TDL) which would represent an IC50 of approximately 0.5 ppb. In this study, we characterize the effects of the antibody concentration, flow volume and flow rate on the PCB biosensor's response. Using the optimum operating conditions, the PCB biosensor achieved the TDL and its performance as a screening test was improved. Working at the stringent maximum residue limit specified by Japanese law (0.5 ppm total PCBs), the optimized biosensor exhibited excellent performance (0% false negatives and 7% false positives) in the screening of 110 samples of used Japanese transformer oil. The general approach for optimization described here is expected to benefit immunoassay researchers attempting to achieve optimum performance.
[Show abstract][Hide abstract] ABSTRACT: Although the effects of syntrophic relationships between bacteria and methanogens have been reported in some environments, those on cellulose decomposition using cellulolytic bacteria from methanogenic reactors have not yet been examined. The effects of syntrophic co-culture on the decomposition of a cellulosic material were investigated in a co-culture of Clostridium clariflavum strain CL-1 and the hydrogenotrophic methanogen Methanothermobacter thermautotrophicus strain ΔH and a single-culture of strain CL-1 under thermophilic conditions. In this study, strain CL-1 was newly isolated as a cellulolytic bacterium from a thermophilic methanogenic reactor used for degrading garbage slurry. The degradation efficiency and cell density of strain CL-1 were 2.9- and 2.7-fold higher in the co-culture than in the single-culture after 60 h of incubation, respectively. Acetate, lactate and ethanol were the primary products in both cultures, and the concentration of propionate was low. The content of acetate to total organic acids plus ethanol was 59.3% in the co-culture. However, the ratio decreased to 24.9% in the single-culture, although acetate was the primary product. Therefore, hydrogen scavenging by the hydrogenotrophic methanogen strain ΔH could shift the metabolic pathway to the acetate production pathway in the co-culture. Increases in the cell density and the consequent acceleration of cellulose degradation in the co-culture would be caused by increases in adenosine 5'-triphosphate (ATP) levels, as the acetate production pathway includes ATP generation. Syntrophic cellulose decomposition by the cellulolytic bacteria and hydrogenotrophic methanogens would be the dominant reaction in the thermophilic methanogenic reactor degrading cellulosic materials.
Journal of Bioscience and Bioengineering 05/2012; 114(4):435-9. DOI:10.1016/j.jbiosc.2012.05.002 · 1.88 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The aim of this study was to show the effectiveness of the membrane free bioelectrochemical system (BES) using three electrodes on inhibition of methanogenesis and construction of hydrogen fermentation from the artificial garbage slurry. The electrical redox-potential on the working electrode was adjusted to -1.0V (vs. Ag/AgCl) that has positive effect on methanogenesis. The redox-potential on the counter electrode was measured to be 1.6V. The pH in the effluents was 5.5-6.4. Hydrogen production rate at the cathode side was similar to that at the anode side and much higher than that calculated from current, and reached a maximum of 2445±815 (average±standard deviation) mL L(-1) d(-1) at an organic loading rate of 58.7g dichromate chemical oxygen demand per L d(-1). Methane production was negligible throughout the experiment. Acetate and butyrate were the main products of the fermentation using a BES; these offered favorable conditions for hydrogen production. The bacterial community in the bioelectrochemical hydrogen fermentor differed from that in the methanogenic seed sludge and included hitherto unknown species. These results show that high redox-potential on the anodic electrode and acidic pH in the membrane free BES can be utilized for hydrogen fermentation from the artificial garbage slurry by avoiding methanogenesis.
Journal of Bioscience and Bioengineering 05/2012; 114(1):64-9. DOI:10.1016/j.jbiosc.2012.02.028 · 1.88 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A simple and rapid flow-based multioperation immunoassay for heavy metals using a microfluidic device was developed. The antigen-immobilized microparticles in a sub-channel were introduced as the solid phase into a main channel structures through a channel flow mechanism and packed into a detection area enclosed by dam-like structures in the microfluidic device. A mixture of a heavy metal and a gold nanoparticle-labeled antibody was made to flow toward the corresponding metal through the main channel and make brief contact with the solid phase. A small portion of the free antibody was captured and accumulated on the packed solid phase. The measured absorbance of the gold label was proportional to the free antibody portion and, thus, to the metal concentration. Each of the monoclonal antibodies specific for cadmium-EDTA, chromium-EDTA, or lead-DTPA was applied to the single-channel microfluidic device. Under optimized conditions of flow rate, volume, and antibody concentration, the theoretical (antibody K(d)-limited) detection levels of the three heavy metal species were achieved within only 7 min. The dynamic range for cadmium, chromium, and lead was 0.57-60.06 ppb, 0.03-0.97 ppb, and 0.04-5.28 ppb, respectively. An integrated microchannel device for simultaneous multiflow was also successfully developed and evaluated. The multiplex cadmium immunoassay of four samples was completed within 8 min for a dynamic range of 0.42-37.48 ppb. Present microfluidic heavy metal immunoassays satisfied the Japanese environmental standard for cadmium, chromium and, lead, which provided in the soil contamination countermeasures act.
[Show abstract][Hide abstract] ABSTRACT: Bioelectrochemical systems can affect microbial metabolism by controlling the redox potential. We constructed bioelectrochemical cultures of the proteolytic bacterium, Coprothermobacter proteolyticus strain CT-1, both as a single-culture and as a co-culture with the hydrogenotrophic methanogen, Methanothermobacter thermautotrophicus strain ∆H, to investigate the influences of bioelectrochemical regulation on facultatively syntrophic proteolysis. The co-culture and single-culture were cultivated at 55°C with an anaerobic medium containing casein as the carbon source. The working electrode potential of the bioelectrochemical system was controlled at -0.8V (vs. Ag/AgCl) for bioelectrochemical cultures and was not controlled for non-bioelectrochemical cultures. The cell densities of hydrogenotrophic methanogen and methane production in the bioelectrochemical co-culture were 3.6 and 1.5 times higher than those in the non-bioelectrochemical co-culture after 7 days of cultivation, respectively. Contrastingly, the cell density of Coprothermobacter sp. in the bioelectrochemical co-culture was only 1.3 times higher than that in the non-bioelectrochemical co-culture. The protein decomposition rates were nearly proportional to the cell density of Coprothermobacter sp. in the all types of cultures. These results indicate that bioelectrochemical regulation, particularly, affected the carbon fixation of the hydrogenotrophic methanogen and that facultatively syntrophic proteolysis was accelerated as a result of hydrogen consumption by the methanogens growing well in bioelectrochemical co-cultures.
Journal of Bioscience and Bioengineering 03/2012; 114(1):59-63. DOI:10.1016/j.jbiosc.2012.02.013 · 1.88 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Polychlorinated biphenyls (PCBs) that are present in transformer oil are a common global problem because of their toxicity and environmental persistence. The development of a rapid, low-cost method for measurement of PCBs in oil has been a matter of priority because of the large number of PCB-contaminated transformers still in service. Although one of the rapid, low-cost methods involves an immunoassay, which uses multilayer column separation, hexane evaporation, dimethyl sulfoxide (DMSO) partitioning, antigen-antibody reaction, and a measurement system, there is a demand for more cost-effective and simpler procedures. In this paper, we report a DMSO partitioning method that utilizes a microfluidic device with microrecesses along the microchannel. In this method, PCBs are extracted and enriched into the DMSO confined in the microrecesses under the oil flow condition. The enrichment factor was estimated to be 2.69, which agreed well with the anticipated value. The half-maximal inhibitory concentration of PCBs in oil was found to be 0.38 mg/kg, which satisfies the much stricter criterion of 0.5 mg/kg in Japan. The developed method can realize the pretreatment of oil without the use of centrifugation for phase separation. Furthermore, the amount of expensive reagents required can be reduced considerably. Therefore, our method can serve as a powerful tool for achieving a simpler, low-cost procedure and an on-site analysis system.
[Show abstract][Hide abstract] ABSTRACT: Protein is a major component of organic solid wastes, and therefore, it is necessary to further elucidate thermophilic protein degradation process. The effects of hydrogenotrophic methanogens on protein degradation were investigated using the proteolytic bacterial strain CT-1 that was isolated from a methanogenic thermophilic (55°C) packed-bed reactor degrading artificial garbage slurry. Strain CT-1 was closely related to Coprothermobacter proteolyticus, which is frequently found in methanogenic reactors degrading organic solid wastes. Strain CT-1 was cultivated in the absence or presence of Methanothermobacter thermautotrophicus by using 3 kinds of proteinaceous substrates. Degradation rates of casein, gelatin, and bovine serum albumin were higher in co-cultures than in monocultures. Strain CT-1 showed faster growth in co-cultures than in monocultures. M. thermautotrophicus comprised 5.5-6.0% of the total cells in co-culture. Increased production of ammonia and acetate was observed in co-cultures than in monocultures, suggesting that addition of M. thermautotrophicus increases the products of protein degradation. Hydrogen produced in the monocultures was converted to methane in co-cultures. These results suggest that thermophilic proteolytic bacteria find it favorable to syntrophically degrade protein in a methanogenic environment, and that it is important to retain hydrogen-scavenging methanogens within the reactor.
Journal of Bioscience and Bioengineering 07/2011; 112(5):469-72. DOI:10.1016/j.jbiosc.2011.07.003 · 1.88 Impact Factor