Ozone Injection into an Activated Carbon Bed to Remove Hydrogen Sulfide in the Presence of Concurrent Substances

ABSTRACT

Adsorption using activated carbon is one of the most reliable techniques for preventing odor by substances such as H₂S. Concurrent substances in effluent gas often reduce the removal capacity of activated carbon for H₂S. As a means of restoring capacity under such conditions, ozone injection into an activated carbon column was examined. When activated carbon was saturated with substances such as toluene, ethanol, n-butanol, or iso-butanol, its capacity to remove H₂S decreased in proportion to the amount of the saturating substance. Under such conditions, ozone injection greatly increased capacity. Toluene, which is not easily decomposed by ozone, was displaced by ozone and by oxidized products of H₂S. Ethanol, which is adsorbed in small amounts by activated carbon and easily decomposed by ozone, was removed by ozone injection. Butanols, which are also decomposed by ozone and adsorbed in large quantities by activated carbon, showed intermediate behavior between that of toluene and ethanol.     

Ozone injection into an activated carbon bed to remove hydrogen sulfide in the presence of concurrent substances

Adsorption using activated carbon is one of the most reliable techniques for preventing odor by substances such as H2S. Concurrent substances in effluent gas often reduce the removal capacity of activated carbon for H2S. As a means of restoring capacity under such conditions, ozone injection into an activated carbon column was examined. When activated carbon was saturated with substances such as toluene, ethanol, n-butanol, or iso-butanol, its capacity to remove H2S decreased in proportion to the amount of the saturating substance. Under such conditions, ozone injection greatly increased capacity. Toluene, which is not easily decomposed by ozone, was displaced by ozone and by oxidized products of H2S. Ethanol, which is adsorbed in small amounts by activated carbon and easily decomposed by ozone, was removed by ozone injection. Butanols, which are also decomposed by ozone and adsorbed in large quantities by activated carbon, showed intermediate behavior between that of toluene and ethanol.     

Development of odorous gas sampler and investigation of its practicality

The existing gas sampler is deficient in regard to its efficiency, handling and ability. In order to solve these problems, a new gas sampler was developed and its function was investigated. The sampler is a vessel made of aluminium and contains a polyester bag inside the vessel. The vacuum method is employed for taking the gas. The maximum capacity of the gas volume that can be taken is about 15 liters and sampling time can be from 15 sec to 10 min per sample. In addition, many odor surveys were carried out and the practicality of the new sampler was investigated. It was concluded that the new sampler was easy to handle and was more efficient than the existing gas sampler.     

A nationwide survey of outdoor radon concentration in Japan

Nationwide outdoor radon (222Rn) concentrations in Japan were measured to survey the environmental outdoor 222Rn level and to estimate the effective dose to the general public from 222Rn and its progeny. The 222Rn concentration was measured with a passive-type radon monitor. The 222Rn monitors were installed at about 700 points throughout Japan from 1997 to 1999. The annual mean 222Rn concentration in Japan was estimated from four quarters measurements of 47 prefectures in Japan. Nationwide outdoor mean 222Rn concentration was 6.1 Bq m(-3). This was about 40% of the indoor 222Rn concentration in Japan. The 222Rn concentration in Japan ranged from 3.3 Bq m(-3) in the Okinawa region to 9.8 Bq m(-3) in the Chugoku region, reflecting geological characteristics. Seasonal variation of outdoor 222Rn concentration was also found to be lowest in July to September, and highest in October to December. From the results of this 222Rn survey and previous indoor 222Rn survey program, the effective dose to the general public from 222Rn and its progeny was estimated to be 0.45 mSv y(-1).     

Composting of food refuse from a student restaurant in Hokkaido University

Over a period of 21 months, we composted food refuse from a student restaurant in Hokkaido University using a commercially available composting machine. The machine had two reactors, each with a working volume of 250 l. The refuse was mixed with sawdust in a ratio of 5 l sawdust to 10 kg refuse, and this mixture was fed into the machine daily. We studied the characteristics of the refuse, the composting mixture, and the finished compost in an effort to optimize the operating parameters. We also evaluated the effectiveness of the composting process by determining the decomposition rates of the composting materials. The optimum moisture content of the composting mixture was between 30% wet basis (wb) and 40% wb in this machine. The composting machine worked well when the first reactor was filled with composting mixture and 0.5 kg lime was added once per week. The mass of the materials supplied was reduced by 84% over the study period. The decomposition rate of the volatile matter in all composting materials was 66%. The mass of the food refuse supplied was 14.8 kg/day on average, and the moisture content of the refuse was 77% wb on average. Received: October 4, 1999 / Accepted: April 4, 2000     

N2O Emissions at Solid Waste Disposal Sites in Osaka City

Nitrous oxide (N₂O) is a trace gas contributing to stratospheric ozone depletion and global warming. Although a large quantity of information exists about N₂O emissions from various ecosystems, this study was initiated to demonstrate the features of N₂O emissions from sea-based waste disposal sites in Osaka City in relation to CH₄ emissions.

Average N₂O emissions at an active landfill (S-Site) were several times higher than those at a closed landfill (N Site). Average CH₄ emissions were also much greater at the S-Site. Regarding the nature of N₂O emissions, remarkable emissions often were observed with aerobic waste layers at the N-Site, suggesting almost inversely related N₂O emissions with CH₄ production at the N-Site. However, at the S-Site a few exceptionally high N₂O emissions were noted in cases of high CH₄ emissions.     

Improved quartz furnace method for chlorine and sulfur determination in municipal solid waste

 A method of determining the chlorine (Cl) and sulfur (S) in municipal solid waste (MSW) was studied. The quartz furnace method was improved in two ways: recovery from ash by hot extraction with dilute nitric acid, and avoidance of the volatilization of alkali (earth) metal chlorides by setting the sample combustion temperature at 600°C. In a comparison with the bomb method, using nine sets of kitchen garbage and waste plastics, the bomb method yielded a 15%–25% lower value than the improved quartz furnace method. Combustion in the bomb was frequently incomplete, resulting in recovery losses of Cl and S. The average kitchen garbage involved 5.2 mg Cl/g, of which at least 24.1% would be converted to HCl. Plastics contained 23 mg Cl/g generating 88.1% HCl on average. In the same way, kitchen garbage contained 3.0 mg S/g, generating 52.3% SO _x , whereas plastics contained 1.1 mg S/g with 55.1% SO _x formation. Received: March 20, 2002 / Accepted: October 13, 2002     

Malodor emission characteristics in rendering plants

Odor emission characteristics in rendering plant was studied by measuring 14 kinds of odorants in the emission gases from main processes: cooking of raw bone, concentrating of glue, refining of fat, and drying of bone. The odor from cooker had higher concentration of all odorous components compared with the other processes. From any process except the drying one, there were detected sulfur‐containing odorants in very high concentration. Of the odorants, concentrations of hydrogen sulfide and methyl mercaptan were higher. The odor from drying bed had comparatively low concentration of sulfur‐containing odorants, and higher concentration of ammonia and trimethylamine were detected. Lower fatty acids were detected from all processes though the concentrations were low. In the odorous gases taken at both the emission source and borderline side, high correlations were recognized between organoleptic test value and concentrations of measured odorants.     

Ecological risk assessment of TBT in Ise Bay

An ecological risk assessment of tributyltin (TBT) in Ise Bay was conducted using the margin of exposure (MOE) method. The assessment endpoint was defined to protect the survival, growth and reproduction of marine organisms. Sources of TBT in this study were assumed to be commercial vessels in harbors and navigation routes. Concentrations of TBT in Ise Bay were estimated using a three-dimensional hydrodynamic model, an ecosystem model and a chemical fate model. Estimated MOEs for marine organisms for 1990 and 2008 were approximately 0.1-2.0 and over 100 respectively, indicating a declining temporal trend in the probability of adverse effects. The chemical fate model predicts a much longer persistence of TBT in sediments than in the water column. Therefore, it is necessary to monitor the harmful effects of TBT on benthic organisms.     

Testes size and breeding systems in Japanese annrans with special reference to large testes in the treefrog,Rhacophorus arboreus (Amphibia : Rhacophoridae)

Summary Testes size was compared among 19 species of Japanese anurans in relation to their breeding systems. Although the mean body mass of the species examined varied markedly between 1.8 and 116 g, the mean proportion of testes mass to body mass was fairly constant at 0.2 to 0.4% across all species except the rhacophorid species. Foam-nest building rhacophorids had relatively large testes constituting more than 1% of their body mass. Among them, Rhacophorus arboreus had the largest, exceeding 5% of the body mass. Multi-male breeding, where a female is grasped by two or more males during spawning, occurs frequently in these rhacophorids, especially in R. arboreus. This close association between large testes size and multi-male breeding strongly suggests that sperm competition is an important factor affecting the evolution of relative testes size in Japanese anurans. Offprint requests to: T. Kusano