Motoyuki Suzuki

Activated carbon adsorption of trichloroethylene (TCE) vapor stripped from TCE-contaminated water

Ground water contaminated with trichloroethylene (TCE) used in electronic, electric, dry cleaning and the like industries is often treated by air-stripping. In this treatment process, TCE in its vapor form is stripped from ground water by air stream and sometimes emitted into the atmosphere without any additional treatments. Activated carbon adsorption is one of the practical and useful processes for recovering the TCE vapor from the exhaust air stream. However, adsorption of the TCE vapor from the stripping air stream onto activated carbons is not so simple as that from dry air, since in the exhaust air stream the TCE vapor coexists with water vapor with relatively high concentrations. The understanding of the adsorption characteristics of the TCE vapor to be adsorbed on activated carbon in the water vapor-coexisting system is essential for successfully designing and operating the TCE recovery process. In this work, the adsorption equilibrium relations of the TCE vapor adsorption on activated carbons were elucidated as a function of various relative humidity. Activated carbon fibers (ACFs) were used as model activated carbon. The adsorption equilibrium relations were studied by the column adsorption method. The adsorption isotherms of TCE vapor adsorbed on sample ACFs were successfully correlated by the Dubinin-Radushkevich equation for both cases with and without coexistent water vapor. No effects of coexistent water vapor were found on the limiting adsorption volume. However, the adsorption characteristic energy was significantly reduced by the coexistence of water vapor and its reduction was successfully correlated with the equilibrium amount of water vapor adsorbed under the dynamic condition.

A mathematical model of a shallow and eutrophic lake (The Keszthely basin. Lake Balaton) and simulation of restorative manipulations

Concern about the overall management of lakes has been growing, and a lake ecological model provides the guidelines necessary for such management. In this study, an ecological model describing the ecosystem of the Keszthely Basin, Lake Balaton, Hungary, one of the typical shallow and eutrophic lakes, was proposed. This model includes three types of zooplankton and two types of fish as well as two types of algae and nutrients. Parameters concerning the algae and fish were estimated based on observations in the basin between 1991 and 1995. The other parameters and the structure of the model were determined by our previous study. The parameters of the model were calibrated with the Monte Carlo technique, and its predictability was confirmed. The effects on the basins ecosystem of three restorative manipulations, namely a biomanipulation, reduction of loading phosphorus, and dredging the sediment, were assessed by simulation studies using the proposed model. The simulation results indicated that a biomanipulation that removed 90% of the bream should suppress the growth of algae temporarily through bottom-up regulation; however, this effect seemed to not be perpetuated in this basin. The reduction of loading phosphorus seemed to be the most effective means to suppress algal growth, while dredging of sediment seemed to be the most desirable restoration method from the standpoint of the overall management of the lake, because it was expected to accelerate the growth of fish population as well as to suppress algal growth. Furthermore, the algal growth suppression mechanism of the dredging was discussed on the basis of the model calculations.

Fabrication of carbon coated ceramic membranes by pyrolysis of methane using a modified chemical vapor deposition apparatus

Abstract An 80-cm long tubular carbon coated membrane was fabricated by chemical vapor deposition (CVD) of methane on a multilayered porous ceramic substrate at a temperature of 1000xa0°C. The deposition of pyrocarbon on the membrane generated a carbon film, the nature of which not only reduced the pore size of the membrane but also changed the physical properties of the membrane, including its hydrophobicity, electrical conductivity, and thermal conductivity. To ensure a uniform deposition of carbon on the membrane, a CVD apparatus equipped with process piping was employed to periodically reverse the direction of the gas flow in the reactor. The CVD experiments were then conducted by varying parameters such as the rate of flow of the gas mixture (methane and nitrogen), the percentage concentration of methane, and so on. To analyze the uniformity of the carbon film, we measured the electrical resistance of the membrane and the permeation of six gases through the sectioned membranes. In the range of our study, it was found that the flow rate of the gas mixture and the alternation of the direction of the gas flow were two important factors for determining the uniformity of the carbon deposit in the membranes. Observation by scanning electron microscope (SEM) and measurement of the nitrogen permeation of the membranes revealed that fabrication of uniform carbon coated ceramic membranes with a desired pore size is possible for applications involving microfiltration, ultrafiltration, and nanofiltration. In addition, the utilization of the superior properties of the membranes such as hydrophobicity and electrical conductivity were suggested for enhancing the degree of separation of the membranes.

A modelling approach to global nitrate leaching caused by anthropogenic fertilisation.

Water quality associated with nitrate (NO3-) leaching from agricultural soils is an important environmental issue. This paper describes a new modelling approach to quantitatively evaluate the effect of the use of fertilisers on global nitrate leaching. A global process-based simulation model was previously developed for the nitrogen cycle in terrestrial ecosystems, in which soil inorganic nitrogen in the form of ammonium (NH4+) and NO3- was considered. After introducing data on world fertiliser consumption (FAO, 1995) into the steady-state model, the extent of disturbance to the nitrogen cycle caused by fertilisation was calculated. Although fertilisation resulted in an annual increase in net primary production (NPP, represented as carbon) of 18 Gt year-1, NO3- leaching and gaseous losses of nitrogen oxides and ammonia were also accelerated. Most regions with heavy fertiliser application (over 100 kg ha-1 year-1) showed a high annual leaching load equal to or more than 20 kg ha-1 year-1. About 2.5% of the land area occupied by terrestrial ecosystems suffered a serious leaching load of more than 30 kg ha-1 year-1. Of the total amount of applied fertilisers (138 Tg year-1) 19% was lost to NO3- leaching, 8% to gaseous ammonia, and 3% to gaseous nitrogen oxides. The rest was assumed to be fixed in the ecosystems through vegetation uptake.

Removal of trichloroethylene from air stripping off-gas by adsorption on activated carbon fibre

Abstract Recently commercialized activated carbon fibres (ACFs) have several advantages over conventional granular activated carbons (GACs) such as rapid adsorption kinetics. For removing trichloroethylene (TCE) in the air stripping off-gas from the treatment plant of contaminated ground water, the co-adsorption effect of water and TCE must be determined. Fundamental data of adsorption of TCE on ACF with respect to the coexistent humidity were obtained and the pilot-plant operation was investigated with and without temperature control of the gas influent to the adsorption unit. Heating the influent gas to 318 K results in lowering the relative humidity below 0.3, which is sufficient for utilizing the adsorption capacity of the ACF bed.

Carbon Whisker Membrane

We report a recent developed membrane called carbon whisker membrane (CWM). The CWMs consist of a tubular ceramic membrane covered by a layer of carbon film and carbon whiskers formed on the surface of the carbon film. Hydrocarbons such as methane and a modified chemical vapor deposition apparatus were employed for fabricating uniformed CWMs. Because of the unique feature of the CWMs, the filtration performance of the CWMs was investigated and it was found that the CWMs possess a function of anti-attachment of particles and/or biomaterials on the membranes so that the permeate flux and the cleaning process of the membrane can be improved.