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Park, Younghyun,Nguyen, Van Khanh,Park, Seonghwan,Yu, Jaecheul,Lee, Taeho Elsevier 2018 Bioresource technology Vol.258 No.-
<P><B>Abstract</B></P> <P>A flat-panel air-cathode microbial fuel cell (FA-MFC) is known to overcome the low conductivity and biodegradability of domestic wastewater. This study evaluated the normalized energy recovery (NER) based on the volume of wastewater treated (NER<SUB>V</SUB>) and chemical oxygen demand (COD) removal (NER<SUB>COD</SUB>) using FA-MFCs with three anode spacing conditions and different flow rates (within a hydraulic retention time of 30 min). Generation of current was similar (11.7 ± 0.5 mA) at different spacings; however, COD removal was affected by the flow rates. The NER<SUB>V</SUB> for both acetate and domestic wastewater showed good agreements with the flow rates in all anode spacing conditions. The NER<SUB>COD</SUB> results were negatively correlated with the COD removal rates, independent of the anode spacing. The FA-MFCs yielded an NER<SUB>COD</SUB> of 0.22 kWh/kg-COD from extremely low-strength domestic wastewater (150 mg-COD/L). The FA-MFC has a significant potential as an energy-sustainable wastewater treatment technology.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The FA-MFC with shortest anode spacing produced the highest electrical energy. </LI> <LI> NER<SUB>V</SUB> showed a negative correlation with flow rate in all anode spacings. </LI> <LI> NER<SUB>COD</SUB> was correlated with COD removal rate, independent of anode spacing. </LI> <LI> The FA-MFC has a great potential to recover energy from low-strength wastewater. </LI> </UL> </P>
Park, Younghyun,Park, Seonghwan,Nguyen, Van Khanh,Kim, Jung Rae,Kim, Hong Suck,Kim, Byung Goon,Yu, Jaecheul,Lee, Taeho Elsevier 2017 Bioresource technology Vol.226 No.-
<P><B>Abstract</B></P> <P>In order to confirm the effects of the low conductivity and biodegradability of wastewater, flat-panel air-cathode microbial fuel cells (FA-MFCs) were operated by supplying substrates with different volume ratios of domestic wastewater mixed with an artificial medium: the artificial medium only, 25% wastewater, 50% wastewater, 75% wastewater, 100% of wastewater with 500mg-COD/L by adding acetate, and raw domestic wastewater (230mg-COD/L). With the increase of wastewater ratio, the maximum power density and organic removal efficiency decreased from 187 to 60W/m<SUP>3</SUP> and 51.5 to 37.4%, respectively, but the Coulombic efficiency was maintained in the range of 18.0–18.9%. The FA-MFCs could maintain their low internal resistances and overcome the decreasing conductivity. The acetate concentration was more important than the total organics for power production. This study suggests that the FA-MFC configuration has great applicability for practical applications when supplied by domestic wastewater with low conductivity and biodegradability.</P> <P><B>Highlights</B></P> <P> <UL> <LI> FA-MFCs were operated by substrate transition from acetate to domestic wastewater. </LI> <LI> Coulombic efficiency in acetate was similar to that in domestic wastewater. </LI> <LI> Maximum power density had higher correlation with acetate than with COD. </LI> <LI> FA-MFCs could maintain low internal resistance and overcome decreasing conductivity. </LI> </UL> </P>
Park, Younghyun,Park, Seonghwan,Nguyen, Van Khanh,Yu, Jaecheul,Torres, Cé,sar I.,Rittmann, Bruce E.,Lee, Taeho Elsevier 2017 Chemical engineering journal Vol.316 No.-
<P><B>Abstract</B></P> <P>Microbial fuel cells (MFCs) can treat organic compounds from domestic wastewater without aeration, but an additional procedure is required to remove nitrogen. This study developed a flat-panel air-cathode MFC (FA-MFC) that was comprised of five MFC units connected in series and operated to remove organic and nitrogen compounds from domestic wastewater with a short hydraulic retention time (HRT) of 2.5h. During eight months of operation, the removal efficiencies of chemical oxygen demand (COD) and total nitrogen (TN) increased, reaching 85% and 94%, respectively, and the effluent COD and TN concentrations were 20.7±2.5mg/L and 1.7±0.1mg/L, respectively. The greatest removals of COD and TN were in the first and second unit (0.62kg-N/m<SUP>3</SUP>/d of TN removal rate). The FA-MFC system allowed simultaneous removals of COD and TN from domestic wastewater, although it led to minimal power output (6.3W/m<SUP>3</SUP> in the first unit). Because any abiotic ammonia loss was not found under the supplied potential of∼1.1V at a short HRT of 30min, the biological nitrogen removal was thought as a dominant mechanism for TN removal in the FA-MFCs. Microbial community analysis revealed that, near the cathode, <I>Nitrosomonas</I>-like strains contributed to nitrification and <I>Nitratireductor</I>-like strains led to denitrification. <I>Acidovorax</I>-like strains, known for their metabolic diversity, were ubiquitous and appeared to contribute to organics and nitrogen removal in anode and cathode biofilms. This study provides proof of concept that the FA-MFC system has a promise for energy sustainable wastewater treatment.</P> <P><B>Highlights</B></P> <P> <UL> <LI> FA-MFC system for domestic wastewater treatment was operated during 8months. </LI> <LI> FA-MFCs could successfully satisfy COD and TN discharge limits at an HRT of∼2.5h. </LI> <LI> FA-MFC system showed a significantly high TN removal rate up to 0.62kg-N/m<SUP>3</SUP>/d. </LI> <LI> <I>Nitrosomonas</I>, <I>Nitratireductor</I> and <I>Acidovorax</I> spp. contributed to nitrogen removal. </LI> <LI> FA-MFC system has a promise for energy-sustainable domestic wastewater treatment. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Constructing a Competing Risks Model for the Combined Structure with Dependent Relations
Seonghwan Park(박성환),Jihyun Park(박지현),Kiho Bae(배기호),Suneung Ahn(안선응) 한국산업경영시스템학회 2017 한국산업경영시스템학회지 Vol.40 No.3
The rapid growth of engineering technology and the emergence of systemized and large-scale engineering systems have resulted in complexity and uncertainty throughout the lifecycle activities of engineering systems. This complex and large-scale engineering system consists of numerous components, but system failure can be caused by failure of any one of a number of components. There is a real difficulty in managing such a complex and large-scale system as a part. In order to efficiently manage the system and have high reliability, it is necessary to structure a system with a complex structure as a sub-system. Also, in the case of a system in which cause of failures exist at the same time, it is required to identify the correlation of the components lifetime and utilize it for the design policy or maintenance activities of the system. Competitive risk theory has been used as a theory based on this concept. In this study, we apply the competitive risk theory to the models with combined structure of series and parallel which is the basic structure of most complex engineering systems. We construct a competing risks model and propose a mathematical model of net lifetime and crude lifetime for each cause of failure, assuming that the components consisting a parallel system are mutually dependent. In addition, based on the constructed model, the correlation of cause of failure is mathematically analyzed and the hazard function is derived by dividing into net lifetime and crude lifetime.