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Tokyo, Japan

Kawamoto K.,Okayama University | Miyata H.,Sanki Engineering
Environmental science and pollution research international | Year: 2015

We investigated dioxin formation and removal in a commercial thermal waste treatment plant employing a gasification and melting process that has become widespread in the last decade in Japan. The aim was to clarify the possibility of dioxin formation in a process operation at high temperatures and the applicability of catalytic decomposition of dioxins. Also, the possible use of dioxin surrogate compounds for plant monitoring was further evaluated. The main test parameter was the influence of changes in the amount and type of municipal solid waste (MSW) supplied to the thermal waste treatment plant which from day to day operation is a relevant parameter also from commercial perspective. Here especially, the plastic content on dioxin release was assessed. The following conclusions were reached: (1) disturbance of combustion by adding plastic waste above the capability of the system resulted in a considerable increase in dioxin content of the flue gas at the inlet of the bag house and (2) bag filter equipment incorporating a catalytic filter effectively reduced the gaseous dioxin content below the standard of 0.1 ng toxic equivalency (TEQ)/m(3) N, by decomposition and partly adsorption, as was revealed by total dioxin mass balance and an increased levels in the fly ash. Also, the possible use of organohalogen compounds as dioxin surrogate compounds for plant monitoring was further evaluated. The levels of these surrogates did not exceed values corresponding to 0.1 ng TEQ/m(3) N dioxins established from former tests. This further substantiated that surrogate measurement therefore can well reflect dioxin levels. Source

Shibata K.,Keio University | Terasaka K.,Keio University | Fujioka S.,Keio University | Kato K.,Sanki Engineering
Journal of Chemical Engineering of Japan | Year: 2016

A method for estimation of the volumetric mass transfer coefficient of an entire aeration tank for optimization of tank design was investigated. The gas holdup, bubble diameter, and volumetric mass transfer coefficient of an aeration tank were measured by experiments and the experimental results were compared with two estimation method. One method used empirical equations, while the other used CFD simulation. The rate of oxygen transfer into the aeration tank was assumed to be the sum of the rates at the bubble-liquid interface and free surface. The empirical equation method showed good agreement with the measured gas holdup by assuming that the aeration tank was divided two zones. On the other hand, the CFD simulation method provided a good estimation of the gas holdup and bubble diameter. The sum of the estimated volumetric mass transfer at the bubble-liquid interface and free surface showed good agreement with the measured volumetric mass transfer coefficient of the entire aeration tank. © 2016 The Society of Chemical Engineers, Japan. Source

Takahashi M.,Nagaoka University of Technology | Takahashi M.,Tohoku University | Yamaguchi T.,Nagaoka University of Technology | Kuramoto Y.,Hiroshima Institute of Technology | And 6 more authors.
Bioresource Technology | Year: 2011

Performance of a wastewater treatment system utilizing a sulfur-redox reaction of microbes was investigated using a pilot-scale reactor that was fed with actual sewage. The system consisted of an up-flow anaerobic sludge blanket (UASB) reactor and a down-flow hanging sponge (DHS) reactor with a recirculation line. Consequently, the total CODCr (465±147mgL-1; total BOD of 207±68mgL-1) at the influent was reduced (70±14mgL-1; total BOD of 9±2mgL-1) at the DHS effluent under the conditions of an overall hydraulic retention time of 12h, a recirculation ratio of 2, and a low-sewage temperature of 7.0±2.8°C. A microbial analysis revealed that sulfate-reducing bacteria contributed to the degradation of organic matter in the UASB reactor even in low temperatures. The utilized sulfur-redox reaction is applicable for low-strength wastewater treatment under low-temperature conditions. © 2010 Elsevier Ltd. Source

Yoshioka M.,Sanki Engineering | Yokoyama S.,Hokkaido University
Journal of Environmental Engineering | Year: 2010

Recently, the problem of indoor air pollution by microbes has attracted attention in hospital and other medical facilities. For example, control measures against such as methicillin resistant staphylococcus aureus and legionnaire pneumophila has been needed. The other hands, reducing of carbon dioxide emission has been a matter of great urgency on environmental problem. In buildings field, saving energy of using or operating building equipment important problem. But, air conditioning equipment occupies the large ratio of energy use for arranging indoor air environment satisfying various demands as medical facilities, for example, cleanliness air for patient, prevention from infection. The object of this study is that establishing of methodology on equipment design and schemes of its operating in hospitals .considering preservation of suitable environment for medical facility and energy saving. So, we have made a database on hospital facility design in Hokkaido, and analyzed it for the purpose of understanding the present about hospital equipment systems and its operations. Source

Shibata K.,Keio University | Terasaka K.,Keio University | Fujioka S.,Keio University | Kato K.,Sanki Engineering
Journal of Chemical Engineering of Japan | Year: 2016

Conventionally, both aeration tanks and bubble columns are supplied oxygen from dispersed bubbles. However, the geometry of the aeration tanks is greatly different from that of bubble columns. Although almost all oxygen is absorbed from dispersed bubbles in the water for bubble columns, the aeration tank has such a large free surface area that the oxygen transfer from atmosphere cannot be neglected. Therefore, it is very important to investigate oxygen transfer from not only the free surface, but also bubbles. In this study, the volumetric oxygen transfer coefficient, gas holdup and its two dimensional profile were measured in a large scaled aeration tank of typical size for industrial sewage treatment. Moreover, the effect of the aeration method on gas holdup and water circulation such as spiral flow aeration and whole floor aeration were also investigated. By analyzing the experimental results, a simultaneous oxygen transfer model which consists of the sum of oxygen transfer coefficients not only between bubbles and water, but also between the atmosphere and the free surface, is proposed. The model was evaluated by comparing with two alternative models for the experimental overall oxygen transfer coefficients. The proposed model estimated the experimental results better than the other models. © 2016 The Society of Chemical Engineers, Japan. Source

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