Performance of intermittent aeration reactor on NH4-N removal from groundwater resources.

To study the effect of intermittent aeration period on ammonium-nitrogen (NH4-N) removal from groundwater resources, synthetic groundwater was prepared and three reactors were operated under different conditions--"reactor A" under continuous aeration, "reactor B" under 6 h intermittent aeration, and "reactor C" under 2 h intermittent aeration. To facilitate denitrification simultaneously with nitrification, "acetate" was added as an external carbon source with step-wise increase from 0.5 to 1.5 C/N ratio, where C stands for total carbon content in the system, and N for NH4-N concentration in the synthetic groundwater. Results show that complete NH4-N removal was obtained in "reactor B" and "reactor C" at 1.3 and 1.5 C/N ratio respectively; and partial NH4-N removal in "reactor A". These results suggest that intermittent aeration at longer interval could enhance the reactor performance on NH4-N removal in terms of efficiency and low external carbon requirement. Because of consumption of internal carbon by the process, less amount of external carbon is required. Further increase in carbon in a form of acetate (1.5 to 2.5 C/N ratios) increases removal rate (represented by reaction rate coefficient (k) of kinetic equation) as well as occurrence of free cells. It suggests that the operating condition at reactor B with 1.3 C/N ratio is more appropriate for long-term operation at a pilot-scale.

Microbial community of anammox bacteria immobilized in polyethylene glycol gel carrier.

Anaerobic ammonium oxidation (anammox) is a recently discovered microbial pathway in the biological nitrogen cycle and a new cost-effective way to remove ammonium from wastewater. We have so far developed new immobilization technique that anammox bacteria entrapped in polyethylene glycol (PEG) gel carrier. However, fate and behavior of anammox bacteria in a gel carrier is not well understood. In the present study, we focused on the population changes of anammox bacteria in a gel carrier. Three specific primer sets were designed for real-time PCR. For quantification of anammox bacteria in a gel carrier, real-time PCR was performed. The anammox bacteria related to HPT-WU-N03 clone were increased the rate in anammox population, and found to be a major population of anammox bacteria in a gel carrier. Furthermore, from the results of nitrogen removal performance and quantification of anammox bacteria, the correlation coefficient between copy numbers of anammox bacteria and nitrogen conversion rate was calculated as 0.947 in total anammox population. This is the first report that population changes of anammox bacteria immobilized in a gel carrier were evaluated.

Preliminary study of continuous glucose monitoring with a microdialysis technique and a null method--a numerical analysis.

Monitoring of the subcutaneous tissue glucose concentration is an attractive method for continuous monitoring of the glucose concentration in diabetic patients. Several researchers have studied this, but no satisfactory method has been developed. We have proposed a new method, which can measure the glucose concentration of subcutaneous tissue continuously, even as the efficiency of membrane perfusion and sensor performance decline. Two reference solutions were prepared with concentrations higher and lower than the objective solution. They were perfused alternately for different ratios of perfusion times. The glucose concentration, after perfusing microdialysis, was detected and the trend of changes in the concentration was used to control the ratio of the two perfusion solutions. When the trend was a unity, the glucose concentration was calculated from the ratio of the two perfusion solutions. The numerical study was performed with a compartment model and a basic control theory. In simulation, the 90% response time to step change was approximately 7 min, which is fast enough when compared with the fluctuation of glucose in the electrolyte. This result suggested that this new system might be useful for continuous monitoring of the glucose concentration in subcutaneous tissue.

Cytotoxicity of 1-amino-4-phenyl-1,2,3,6-tetrahydropyridine and 1-amino-4-phenylpyridinium ion, 1-amino analogues of MPTP and MPP+, to clonal pheochromocytoma PC12 cells.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induces parkinsonism in humans after its oxidation into 1-methyl-4-phenylpyridinium ion (MPP+) by type B monoamine oxidase. The 1-amino analogues of MPTP and MPP+, 1-amino-4-phenyl-1,2,3, 6-tetrahydropyridine (APTP) and 1-amino-4-phenylpyridinium ion (APP+), were synthesized, and their cytotoxicity to clonal pheochromocytoma PC12 cells was examined using a tetrazolium formazan assay. After incubation for 48 and 72 h, both APP+ and APTP were found to be cytotoxic to PC12 cells, whereas with the N-methyl analogues, only MPP+, but not MPTP, was cytotoxic. The cytotoxicity of APTP increased with incubation time and equaled that of MPP+ after 72 h. It was found that APTP was oxidized to APP+ by type A monoamine oxidase in PC12 cells, suggesting that APP+ itself may damage the cells. In addition to APTP and APP+, N-amino analogues of N-methylisoquinolines and related derivatives were also synthesized and examined for their cytotoxicity to PC12 cells.

Molecular Analysis of Bacterial Communities in a Three-Compartment Granular Activated Sludge System Indicates Community-Level Control by Incompatible Nitrification Processes.

Bacterial community structure and the predominant nitrifying activities and populations in each compartment of a three-compartment activated sludge system were determined. Each compartment was originally inoculated with the same activated sludge community entrapped in polyethylene glycol gel granules, and ammonium nitrogen was supplied to the system in an inorganic salts solution at a rate of 5.0 g of N liter of granular activated sludge-1 day-1. After 150 days of operation, the system was found to comprise a series of sequential nitrifying reactions (K. Noto, T. Ogasawara, Y. Suwa, and T. Sumino, Water Res. 32:769-773, 1998), presumably mediated by different bacterial populations. Activity data showed that all NH4-N was completely oxidized in compartments one and two (approximately half in each), but no significant nitrite oxidation was observed in these compartments. In contrast, all available nitrite was oxidized to nitrate in compartment three. To study the microbial populations and communities in this system, total bacterial DNA isolated from each compartment was analyzed for community structure based on the G+C contents of the component populations. Compartment one showed dominant populations having 50 and 67% G+C contents. Compartment two was similar in structure to compartment one. The bacterial community in compartment three had dominant populations with 62 and 67% G+C contents and retained the 50% G+C content population only at a greatly diminished level. The 50% G+C content population from compartment one hybridized strongly with amo (ammonia monooxygenase) and hao (hydroxylamine oxidoreductase) gene probes from Nitrosomonas europaea. However, the 50% G+C content population from compartment two hybridized strongly with the hao probe but only weakly with the amo probe, suggesting that the predominant ammonia-oxidizing populations in compartments one and two might be different. Since different activities and populations come to dominate in each compartment from an identical inoculum, it appears that the nitrification processes may be somewhat incompatible, resulting in a series of sequential reactions and different communities in this three-compartment system.

Determination of the target volume of HeLa cells treated with platinum-195 m radiolabeled cis-diammine(1, 1-cyclobutane-dicarboxylato)-platinum(II); comparison with cis- and trans-diamminedichloroplatinums(II).

HeLa S-3 cells were treated with 195mPt-radiolabeled cis-diammine(1, 1-cyclobutane-dicarboxylato)platinum(II) (carboplatin) under various conditions, and the relationship between lethal effect and the number of Pt atoms binding to DNA, RNA and proteins was examined. The mean lethal concentrations for the cells treated with carboplatin at 37 degrees C for 1, 2 and 3 h were 553.4, 194.3 and 68.7 microM, respectively. By using identically treated cells, the numbers of Pt-atoms combined with DNA, RNA and protein molecules were determined after fractionation of the cells. In this way the D0 values (D0, dose that would give an average of one lethal event per member of the population), expressed as the drug concentration, were substituted for the number of Pt atoms combined with each fraction. The target volumes, the efficiency of Pt atom to kill cells expressed as the reciprocals of the D0 values, were then calculated with each fraction. The results suggested that DNA was the primary target for cell killing by carboplatin. The target volumes for DNA were 0.891 x 10(4), 2.01 x 10(4) and 3.96 x 10(4) nucleotides for 1, 2 and 3 h treated cells, respectively. The cell killing effects of carboplatin were lower than those of cis-diamminedichloroplatinum(II) (CDDP) by factors of 6.0, 2.8 and 2.6 for 1, 2 and 3 h treatments at 37 degrees C, respectively, in terms of the target volume, while those in terms of the mean lethal dose (D0) were 59.5, 29.0 and 21.5, respectively.