[in Japanese]

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Odor problem is one of the major reasons that people dislike sewage treatment plants. Sewage treatment plants, due to their functions of collecting and treating wastewater, cannot avoid producing odorous materials.
Odor control processes are necessary for sewage treatment plants in order to preserve surrounding environment and to be accepted by neighborhood inhabitants. An effective odor control system is required to observe the offensive odor control law, to maintain working environment for plant operators, and also to prevent the system/instruments failure caused by corrosion.
Innovations for miniaturization, functional and cost-effective deodorization systems together with progresses in designing and organizing less odor-producing wastewater/sludge treatment processes are very important.

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In downtown of Japanese big cities, lots of buildings with underground floors are in place. In order to carry wastewater from the underground floor to public sewers, pumps are used because underground floors are below the level of cleanout leading to public sewer. In some pits, wastewater remains for many hours because entering wastewater amount is so small that pumps do not operate regularly. This causes anaerobic reaction of wastewater in the pits. When the pumps start operating under such a situation, corroded wastewater discharged to public sewers releases H₂S gas. The odorous gas comes up to the busy streets nearby through gully pots in combined sewer system or through openings of manhole or cleanout covers in separate and combined system. Lots of complaints are being made to sewer operators for this problem.
In this paper, the enforcement of odor control law was proposed by measuring H₂S gas concentration in cleanouts. It was difficult to identify the pit of odor emission source because odorous gas moves freely within the total system which ranges from many underground cesspits to sewer. To solve this problem, installation of barometer, which works together with H₂S gas meter, into the cleanouts was proposed and its effectiveness was proved.

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Several kinds of countermeasures, which have been carried out in Kobe City, for cesspit malodor were presented, and the investigation results of their respective effectiveness were discussed. Kobe City has nine wards and there are three “Sewage Management and Water Environment Control Center”. As one of the major services in these centers, we are making a variety of instructions to the owners or managers on the appropriate maintenance of their drainage facilities. The ward “Chuo-ku” is located in downtown center, and has much industry and a lot of buildings. This area has many cesspits accounting for 50% of those in Kobe City, therefore, many complaints about malodor arise in this ward more than others. It is a sort of symbolic place of Kobe, and reduction of malodor from cesspits are urgently required.

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From the year 2006, the Waterworks & Sewerage Bureau of the City of Nagoya has been implementing a series of preventive malodor abatements, in order to eliminate hydrogen-sulfide odor by sump pits concentrating in downtown areas.
Odor investigations were carried out in focused areas as a part of preventive countermeasures against sump pit malodor. The result showed that about 60 percent of all sump pits were identified as malodor sources and that proper improvements were required to be added. However, it was also recognized that enforcing immediate and fundamental countermeasures against such malodor would difficult for most of the sump pits. In the future, our city’s relevant bureaus will make further persistent efforts to eliminate sump pit odor through continuous enlightening campaigns and through investigations on the possibility of applicable administrative guidance.

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Building pit is a kind of drain tank placed underground as a facility of a building, and the malodor which is caused by it is generally called “building-pit odor”. It has been known that one of the primary factors on the generation of building-pit odor is a long-term retention of sewage and sludge into the pit. Design methods had not yet been established though it has also been understood that immediate drainage was effective for odor control. This report introduces the effectiveness and the design approach of the immediate-drainage system.

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Since Sick House/Building Syndrome was reported during 1990’s in Japan, the building code was modified and large impact was occurred onto building society. The action programs for formaldehyde control, compulsory installation of mechanical ventilation system in buildings and so on seem to be successful to decrease the indoor chemical pollution level. However occupants and residents still often showed their complaint and dissatisfaction for indoor air quality. Although the concentrations of designated chemicals are below at the permissible level, significant adverse effects are sometimes observed in terms of the odor level or perceived air quality. Since the studies on perceived air quality had been started in building service field by Yaglou in the U.S., many research results in this field have been reported mainly in Europe and North America. These researches are still continuing in forms of “Sensory Assessment of Building Materials”, “Influence of Perceived Air Quality on Human Performance in Offices/Schools”, and so forth.

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