Jong Moon Park

Continuous-flow metal biosorption in a regenerable Sargassum column

Metal biosorption behavior of raw seaweed S. filipendula in ten consecutive sorption-desorption cycles has been investigated in a packed-bed flow-through column during a continuous removal of copper from a 35mg/L aqueous solution at pH 5. The elutant used was a 1% (w/v) CaCl2/HCl-solution at pH 3. The sorption and desorption was carried out for an average of 85 and 15h, respectively, representing more than 41 days of continuous use of the biosorbent. The weight loss of biomass after this time was 21.6%. The Cu-biosorption capacity of the biomass, based on the initial dry weight, remained relatively constant at approximately 38 mg Cu/g. Loss of sorption performance was indicated by a shortening breakthrough time and a broadening mass-transfer zone. The column service time, considered up to 1 mg Cu/L in the effluent, decreased continuously from 25.4 h for the first to 12.7 h for the last cycle. The critical bed length, representing the mass-transfer zone, increased almost linearly from 28 to 34cm. Life-factors for S. filipendula were found to be 0.0008h(-1) for the breakthrough time and 0.008cm/h for the critical bed length, using an exponential decay and linear fitting functions, respectively. Regeneration with CaCl2/HCl at pH 3 provided elution efficiencies up to 100%. Maximum concentration factors were determined to be in the range 16-44, a decreasing tendency was observed with an increasing exposure time.

Biological nitrogen removal with enhanced phosphate uptake in a sequencing batch reactor using single sludge system.

Simultaneous biological phosphorus and nitrogen removal with enhanced anoxic phosphate uptake was investigated in an anaerobic-aerobic-anoxic-aerobic sequencing batch reactor ((AO)2 SBR). Significant amounts of phosphorus-accumulation organisms (PAOs) capable of denitrification could be accumulated in a single sludge system coexisting with nitrifiers. The ratio of the anoxic phosphate uptake to the aerobic phosphate uptake capacity was increased from 11% to 64% by introducing an anoxic phase in an anaerobic aerobic SBR. The (AO)2 SBR system showed stable phosphorus and nitrogen removal performance. Average removal efficiencies of TOC, total nitrogen, and phosphorus were 92%, 88%, and 100%, respectively. It was found that nitrite (up to 10 mg NO2(-)-N/l) was not detrimental to the anoxic phosphate uptake and could serve as an electron acceptor like nitrate. In fact, the phosphate uptake rate was even faster in the presence of nitrite as an electron acceptor compared to the presence of nitrate. It was found that on-line sensor values of pH, ORP, and DO were somehow related with the dynamic behaviours of nutrient concentrations (NH4+, NO3-, and PO4(3-)) in the SBR. These on-line sensor values were used as real-time control parameters to adjust the duration of each operational phase in the (AO)2 SBR. The real-time controlled SBR exhibited better performance in the removal of phosphorus and nitrogen than the SBR with fixed-time operation.

Neural network modeling for on-line estimation of nutrient dynamics in a sequentially-operated batch reactor.

In monitoring and controlling wastewater treatment processes, on-line information of nutrient dynamics is very important. However, these variables are determined with a significant time delay. Although the final effluent quality can be analyzed after this delay, it is often too late to make proper adjustments. In this paper, a neural network approach, a software sensor, was proposed to overcome this problem. Software sensor refers to a modeling approach inferring hard-to-measure process variables from other on-line measurable process variables. A bench-scale sequentially-operated batch reactor (SBR) used for advanced wastewater treatment (BOD plus nutrient removal) was employed to develop the neural network model. In order to improve the network performance, the structure of neural network was arranged in such a way of reflecting the change of operational conditions within a cycle. Real-time estimation of PO3-(4), NO-3, and NH+4 concentrations was successfully carried out with the on-line information of the SBR system only.

Microbial communities in activated sludge performing enhanced biological phosphorus removal in a sequencing batch reactor

Microbial communities of activated sludge in an anaerobic/aerobic sequencing batch reactor (SBR) supplied with acetate as sole carbon source were analyzed to identify the microorganisms responsible for enhanced biological phosphorus removal. Various analytical methods were used such as electron microscopy, quinone, slot hybridization, and 16S rRNA gene sequencing analyses. Electron photomicrographs showed that coccus-shaped microorganisms of about 1 microm diameter dominated the microbial communities of the activated sludge in the SBR, which had been operated for more than 18 months. These microorganisms contained polyphosphate granules and glycogen inclusions, which suggests that they are a type of phosphorus-accumulating organism. Quinones, slot hybridization, and 16S rRNA sequencing analyses showed that the members of the Proteobacteria beta subclass were the most abundant species and were affiliated with the Rhodocyclus-like group. Phylogenetic analysis revealed that the two dominating clones of the beta subclass were closely related to the Rhodocyclus-like group. It was concluded that the coccus-shaped organisms related to the Rhodocyclus-like group within the Proteobacteria beta subclass were the most dominant species believed responsible for biological phosphorus removal in SBR operation with acetate.

Synergic degradation of phenanthrene by consortia of newly isolated bacterial strains

Three different bacteria capable of degrading phenanthrene were isolated from sludge of a pulp wastewater treatment plant and identified as Acinetobacter baumannii, Klebsiella oxytoca, and Stenotrophomonas maltophilia. Phenanthrene degradation efficiencies by different combinations (consortia) of these bacteria were investigated and their population dynamics during phenanthrene degradation were monitored using capillary electrophoresis-based single-strand conformation polymorphism (CE-SSCP). When a single microorganism was used, phenanthrene degradation efficiency was very low (48.0, 11.0, and 9.0% for A. baumannii, K. oxytoca, and S. maltophilia respectively, after 360 h cultivation). All consortia that included S. maltophilia degraded approximately 80.0% of phenanthrene and reduced lag time to 48 h compared to the 168 h of pure A. baumannii culture. CE-SSCP analysis showed that S. maltophilia was the predominant species during phenanthrene degradation in the mixed culture. The results indicate that mixed cultures of microorganisms may effectively degrade target chemicals, even if the microorganisms show low degradation activity in pure culture.

Engineering the pentose phosphate pathway to improve hydrogen yield in recombinant Escherichia coli.

Among various routes for the biological hydrogen production, the NAD(P)H‐dependent pentose phosphate (PP) pathway is the most efficient for the dark fermentation. Few studies, however, have focused on the glucose‐6‐phosphate 1‐dehydrogenase, encoded by zwf, as a key enzyme activating the PP pathway. Although the gluconeogenic activity is essential for activating the PP pathway, it is difficult to enhance the NADPH production by regulating only this activity because the gluconeogenesis is robust and highly sensitive to concentrations of glucose and AMP inside the cell. In this study, the FBPase II (encoded by glpX), a regulation‐insensitive enzyme in the gluconeogenic pathway, was activated. Physiological studies of several recombinant, ferredoxin‐dependent hydrogenase system‐containing Escherichia coli BL21(DE3) strains showed that overexpression of glpX alone could increase the hydrogen yield by 1.48‐fold compared to a strain with the ferredoxin‐dependent hydrogenase system only; the co‐overexpression of glpX with zwf increased the hydrogen yield further to 2.32‐fold. These results indicate that activation of the PP pathway by glpX overexpression‐enhanced gluconeogenic flux is crucial for the increase of NAD(P)H‐dependent hydrogen production in E. coli BL21(DE3). Biotechnol. Bioeng. 2011;108: 2941–2946.

Phenanthrene Biodegradation in Soil Slurry Systems: Influence of Salicylate and Triton X-100

The effects of a nonionic surfactant (Triton X-100) and a metabolic inducer (salicylate) were investigated in order to enhance the biodegradation rate of phenanthrene in soil slurry systems. The addition of salicylate reduced the time for the complete degradation of phenanthrene up to about 3 times (12.9 mg/L-d) even at highly concentrated soils of 650 mg/kg. The inducer was beneficial not only by increasing metabolic activity of existing cells, but also by increasing cell mass since it was utilized as an additional carbon source. The fraction of fast growing bacteria in total with salicylate addition was much higher compared to that without salicylate. The addition of Triton X-100 ranging from 0 to 10 g/L increased the apparent solubility of phenanthrene in soil slurry, but significantly inhibited the phenanthrene degradation in both slurry and pure liquid systems without any inhibition to cell growth. The phenanthrene degradation was inhibited much more with increasing the surfactant concentration. The inhibition by surfactant addition might be due to the prevention of bacterial adhesion to phenanthrene sorbed to soil and/or decrease of micellar-phase bioavailability

Engineering glyceraldehyde-3-phosphate dehydrogenase for switching control of glycolysis in Escherichia coli.

Glycolysis has evolved to be a highly robust mechanism for maintaining the cellular metabolism of living organisms. However, relevant modifications of glycolytic activity are required to intentionally modulate cellular phenotypes. Here, we designed a platform that allows switching control of glycolysis in Escherichia coli in response to an environmental signal, in this case, temperature. This system functions by regulating the expression of gapA, which encodes glyceraldehyde‐3‐phosphate dehydrogenase (GAPDH), one of the key glycolytic enzymes. Because a very low level of gapA expression is capable of maintaining cellular physiology, we also modified GAPDH through directed evolution to provide sensitive regulation of glycolytic activity. The switching control of glycolysis was successfully demonstrated by regulating the expression of engineered gapA through changes in temperature. This system offers potential control over the cells central carbon‐metabolism switch, providing the ability to perform reprogrammed tasks with desired timing depending on environmental signals. Biotechnol. Bioeng. 2012; 109: 2612–2619.