Youngseob Yu

Pohang University of Science and Technology, Andong, North Gyeongsang, South Korea

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Publications (8)27.21 Total impact

  • Jaai Kim, Youngseob Yu, Changsoo Lee
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    ABSTRACT: Low-temperature thermo-alkaline pretreatment of waste activated sludge (WAS) was studied, within the region of 0-0.2M NaOH and 60-90°C, for the effects of NaOH concentration and temperature on sludge degradability in anaerobic digestion (AD). Significant disintegration of sludge solids (up to 75.6%) and an increase in methane production (up to 70.6%) were observed in the pretreatment trials. Two quadratic models were successfully generated by response surface analysis (R(2)>0.9, p<0.05) to approximate how the degree of sludge disintegration (SD) and methane production (MP) respond to changes in the pretreatment conditions. The maximum responses of SD (77.8%) and MP (73.9% increase over the control) were shown at [0.16M NaOH, 90°C] and [0.10M NaOH, 73.7°C], respectively. NaOH addition showed a significant influence on the evolution of methanogen community structure during AD, whereas temperature did not. Aceticlastic Methanosaeta and Methanosarcina speceies were likely the major methanogens.
    Bioresource Technology 07/2013; 144C:194-201. · 5.04 Impact Factor
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    Youngseob Yu, Jaai Kim, Seokhwan Hwang
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    ABSTRACT: The TaqMan quantitative PCR (QPCR) method was used to detect and quantify the 16S rRNA genes of aceticlastic methanogens at different taxonomic levels. Three different sets of primers coupled with a TaqMan probe for QPCR assays to detect the 16S rRNA genes of the order Methanosarcinales, as well as the families Methanosarcinaceae and Methanosaetaceae, were separately used. Using these primer and probe sets, the 16S rRNA genes of aceticlastic methanogens in samples from various anaerobic processes (i.e., nine pure cultures, batch experiment, and three different continuous processes including a full-scale digester), were monitored and quantified by QPCR assays. A batch experiment cultivating a mixture of aceticlastic methanogens, was conducted to monitor their population dynamics. Using this group-specific quantification method, the dynamics of a competition between two aceticlastic populations, as modulated by the acetate concentration, could well be described. The target 16S rRNA genes in environmental samples, collected from three different anaerobic processes treating sludge, cheese whey, and synthetic wastewaters, were additionally quantified. The quantified 16S rRNA gene concentrations for all samples successfully represented the community structures of the target methanogens, which were correlated accurately with the operational parameters of the anaerobic processes. It was also successful to demonstrate probe nesting of aceticlastic methanogens at the levels of order and family.
    Biotechnology and Bioengineering 03/2006; 93(3):424-33. · 4.16 Impact Factor
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    ABSTRACT: Real-time polymerase chain reaction (PCR) is a highly sensitive method that can be used for the detection and quantification of microbial populations without cultivating them in anaerobic processes and environmental samples. This work was conducted to design primer and probe sets for the detection of methanogens using a real-time PCR with the TaqMan system. Six group-specific methanogenic primer and probe sets were designed. These sets separately detect four orders (Methanococcales, Methanobacteriales, Methanomicrobiales, and Methanosarcinales) along with two families (Methanosarcinaceae and Methanosaetaceae) of the order Methanosarcinales. We also designed the universal primer and probe sets that specifically detect the 16S rDNA of prokaryotes and of the domain Bacteria and Archaea, and which are fully compatible with the TaqMan real-time PCR system. Target-group specificity of each primer and probe set was empirically verified by testing DNA isolated from 28 archaeal cultures and by analyzing potential false results. In general, each primer and probe set was very specific to the target group. The primer and probe sets designed in this study can be used to detect and quantify the order-level (family-level in the case of Methanosarcinales) methanogenic groups in anaerobic biological processes and various environments.
    Biotechnology and Bioengineering 04/2005; 89(6):670-9. · 4.16 Impact Factor
  • Youngseob Yu, Seokhwan Hwang
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    ABSTRACT: Thermomechanical pulping (TMP) wastewater was tested for the feasibility of augmenting readily biodegradable organics for enhanced microbial hydrolysis by thermophilic acidogens. A biochemical methane potential test showed approximately 13±1% of the chemical oxygen demand was anaerobically biodegradable. Three glucose concentrations set up in a ratio of 1:3:6, 5, 15, and 30g/l, were tested to induce the production of short-chain organic acids and ethanol. Compared to the control with no glucose addition, more than six times of the fragmentation of lignocellulosics in the wastewater was achieved.
    Biochemical Engineering Journal - BIOCHEM ENG J. 01/2004; 18(3):225-229.
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    ABSTRACT: For partial acidogenesis of cheese-whey wastewater, a set of experiments were carried out to produce short-chain volatile fatty acids (VFA) in laboratory-scale continuously stirred tank reactors (CSTR). The maximum rate of acetic and butyric acid production associated with simultaneous changes in hydraulic retention time (HRT), pH, and temperature was investigated, in which the degree of acidification of the whey to the short-chain VFAs was less than 20% of the influent chemical oxygen demand (COD) concentration. Response surface methodology was successfully applied to determine the optimum physiological conditions where the maximum rates of acetic and butyric acid production occurred. These were 0.40-day HRT, pH 6.0 at 54.1 degrees C and 0.22-day HRT, pH 6.5 at 51.9 degrees C, respectively. The optimum conditions for acetic acid production were selected for partial acidification of cheese-whey wastewater because of a higher rate in combined productions of acetic and butyric acids than that at optimum conditions for butyric acid production. A thermophilic two-phase process with the partial acidification followed by a methanation step was operated. Performance of the two-phase process was compared to the single-phase anaerobic system. The two-phase process clearly showed a better performance in management of cheese-whey wastewater over the single-phase system. Maximum rate of COD removal and the rate of methane production in the two-phase process were, respectively, 116% and 43% higher than those of the single-phase system.
    Water Research 06/2003; 37(10):2467-77. · 4.66 Impact Factor
  • Youngseob Yu, Seokhwan Hwang
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    ABSTRACT: Thermomechanical pulping (TMP) wastewater was used for augmenting readily biodegradable organics in order to enhance microbial hydrolysis by mesophilic and thermophilic acidogens. A biochemical methane potential test with the TMP wastewater revealed that approximately 12–14% of the total chemical oxygen demand was anaerobically biodegradable. Mesophilic and thermophilic acidogens at 35 and 55°C in batch mode were tested to investigate the effects of various concentrations of organic acids and ethanol produced from readily biodegradable organics on the hydrolysis of lignocellulosics. The experiment was designed to have initial glucose concentrations of 5, 15 and 30 g/l. The combined effects of the production of organic acids, ethanol, and enriched acidogenic populations by addition of glucose promoted hydrolysis. Compared to the control with no glucose addition, approximately 5.3 and 6.6 times more fragmentation of lignocellulosics in the wastewater occurred in mesophilic and thermophilic acidogenesis, respectively. Higher efficiencies in the thermophilic trials than those in the mesophilic tests were likely due to the elevated temperature.
    Process Biochemistry 01/2003; 38(10):1489-1495. · 2.44 Impact Factor
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    ABSTRACT: A novel approach to utilize cheese whey, cultivating mycelium of an edible mushroom Ganoderma lucidum using cheese whey as a substrate, was introduced. Response surface analysis (RSA) with central composite in cube design was successfully applied to determine the optimal conditions where the maximum mycelial production occurred, which was at pH 4.2 and 28.3°C. The high extract ratio as well as high content of polysaccharide (i.e., 1.2g/l) indicated that the whey could be an alternative substrate for the mycelial production. Soluble chemical oxygen demand (SCOD) removal ranged from 80.7 to 93.1% within the design boundary. Therefore, cultivation of G. lucidum mycelia using cheese whey can provide a unique solution to solve the dual problems of an alternative utilization of the whey and waste management. The substrate inhibition biokinetics at the optimal conditions were also evaluated using a method of fourth-order Runge–Kutta approximation. The nonlinear least-squares (NLLS) method with 95% confidence interval was used. The maximum microbial growth rate, μmax, and half saturation coefficient, Ks, for lactose and SCOD were determined to be 2.28±0.11 and 2.27±0.15 per day, and 95.5±9.1 and 128.0±12.1g/l, respectively. The microbial yield coefficient, Y, and microbial decay rate coefficient, kd, for lactose and SCOD were determined to be 0.49±0.03 and 0.39±0.03gVSS/g of each substrate, and 0.05±0.01 and 0.05±0.01 per day, respectively. Inhibition coefficients were 37.6±2.9 and 49.3±3.3g/l for lactose and SCOD, respectively.
    Biochemical Engineering Journal 01/2003; 15(2):93-99. · 2.58 Impact Factor
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    ABSTRACT: In this paper, we pointed out the problems of using conventional volatile suspended solids (VSS) and chemical oxygen demand (COD) to evaluate biokinetic coefficients, especially for the treatment of highly suspended organic wastewater. We also introduced a novel approach to evaluate biokinetic coefficients by measurement of adenosine 5'-triphosphate (ATP) of microorganisms. The concept of using ATP analysis in biokinetic evaluations with highly suspended wastewater was shown to be effective. This study also showed that the conventional VSS and COD methods were strongly affected by incoming suspended organics in the wastewater and by biokinetics of microorganisms. A cheese-processing wastewater was used in evaluating the biokinetics of mesophilic acidogens. The concentration of COD and total suspended solids in the wastewater was 63.3 g/L and 12.4 g/L, respectively. The TSS was 23.6% of total solids concentration. A high ratio of VSS to total suspended solids of 96.7% indicated that most of the suspended particles were organic materials. Lactose and protein were the major organic components contributing COD in the wastewater, and a total of 94.2% of the COD in the wastewater was due to the presence of lactose and protein. Two different physiological conditions where the maximum rates of acetate and butyrate production occurred were tested. These were pH 7 (condition A for acetate production) and pH 7.3 (condition B for butyrate production) at 36.2C, respectively. Based on the molecular structures of the major organic substances and microbial ATP analysis, the residual substrate and microbial concentrations were stoichiometrically converted to substrate COD (SuCOD) and microbial VSS (MVSS), respectively, using correlation coefficients reported previously. These SuCOD and MVSS were simultaneously used to evaluate the biokinetic coefficients using Monod-based mathematical equations. The nonlinear least squares method with 95% confidence interval was used to evaluate biokinetic coefficients. The maximum microbial growth rate, mu(max) and half saturation coefficient, K(s), for conditions A and B were determined to be 9.9 +/- 0.3 and 9.3 +/- 1.0 day(-1) and 134.0 +/- 58.3 and 482.5 +/- 156.5 mg SuCOD/L, respectively. The microbial yield coefficient, Y, and microbial decay rate coefficient, k(d) for conditions A and B were determined to be 0.29 +/- 0.03 and 0.20 +/- 0.05 mg MVSS/mg SuCOD, and 0.14 +/- 0.05 and 0.25 +/- 0.05 day(-1), respectively. Specific substrate utilization rate at condition B was 43.8 +/- 20.6 mg SuCOD/mg MVSS/day, which was 31% higher than that at condition A.
    Biotechnology and Bioengineering 05/2002; 78(2):147-56. · 4.16 Impact Factor