In terms of odor pollution, discussions about nonolfactory “irritation”, may be generated by the trigeminal nerve exciting, are very important. The final purpose of this study is to make clear mechanisms of generating the nonolfactory irritation and sensory characteristics of the perceived irritation.
In this paper, concentrations for subjectively equivalent irritation (C_E) of 16 odorous compounds were measured by sensory test. And Relationship between C_E and physicochemical properties of the compounds was discussed.
Obtained results were as follows.
1) C_E of the dissociated compounds were very lower than that of the undissociated ones. And among the dissociated compounds, the acid ones were lower than the basic ones. C_E of acrolein, which is an unsaturated (alkyl) aldehyde was the lowest in the every compound as a subject of this experiment.
2) It was found that the time, till sensation of irritation generating after inhalating acrolein gas, was longer than after inhalating the other gas. Accordingly, the mechanism of generating sensory irritation by acrolein gas may be different from that of the others. By analysis on basis of the relation to some physicochemical properties, it was supposed that electrophilic reactivity of acrolein molecule may relate to the generation of sensory irritation.
3) In the dissociated compounds, C_E relate to the dissociation constant of the compounds. Namely, there was a tendency that the larger acidic and basic dissociation constants (K_a and K_b) were, the lower the C_E were.

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Currently, the applications of oxidation ditch process for small scale domestic waste water treatment facilities have been recommended because of several benifits such as easy maintenance, decrease of waste activated sludge and etc. Although the process design manuals have been past published, they have not descrived in detail regarding various types of special aerators respectively each having different characteristics are adapted.
As one of special aerators, one-point oxygen supply type oxidation ditch process using down draft aerator was developed in 1980, and the kinetic analysis of the process on biological nitrification, denitrification and carbonaceous BOD reduction were reported.
This special process and the down draft aerator are explained schematically, and the constructed process model and the kinetic equations are also described. Further, the rational design factors of this process, such as capacity and length of ditch, flow velocity, adding-point of influent and pulling-out-point of effluent in ditch, influence to reaction of DO, temperature and MLSS concentration and etc. are discussed from the results of the kinetic calculations.

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