In situ measurements of oxygen uptake by benthic layer (including sediment surface and over-lying water) in Hiuchi-Nada, the Seto Inland Sea were made with a specially designed system having a bell-jar. Mean values of obserbed oxygen uptake of three periods, Sep.1986 and Jul, and Sep.1987 were 650 and 410 mg·m^-2·d^-1 in the central part and the western part of the Hiuchi-Nada, respectively. Since oxygen supply by photosysthesis in the benthic layer was found in the eastern part of the basin, oxygen uptake in this area was estimated to be 950 mg·m^-2·d^-1 by compensating its effect. The high vale of the oxygen uptake in Hiuchi-Nada was found in the eastern part with high organic carbon content in sediment.

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In order to utilize the denitrifying capability of sulfur denitrifying bacteria for nitrogen removal of wastewater, the preparation method of enrichment culture with high denitrification activity and the acclimation method of this enriched culture to elemental sulfur were investigated.
Isolation of Thiobacillus denitrificans was carried out in order to evaluate the denitrifying capability of T. denitrificans. The enrichment cultures of T. denitrificans were easily established from various inoculating sources, such as activated sludge and the bottom mud of polluted river, in a medium wherein HCO₃^- was used as the inorganic carbon source and S₂O₃^2- and S⁰ were used as the reduced sulfur source. Plating cultures of these enriched microorganisms were conducted and the single yellow colony, in which the deposit of sulfur particles was observed, was obtained. A pure single isolate was obtained through repeated plating cultures, and was identified as T. denitrificans.
The medium which was defined by K. Baalsrud was found to be a suitable medium for the enrichment culture of sulfur denitrifier. The stoichiometric values of autotrophic sulfur denitrification reaction such as Y_s, Y_alk, Y_ob and C_R for enriched microorganisms were in fair agreement with the theoretical values, so that the nitrogen removal capability of the enriched culture was proved to be mainly governed by the denitrification capability of sulfur denitrifier. The sulfur denitrifier which were acclimated to S₂O₃^2- could be successfully acclimated to elemental sulfur by the gradual stepwise replacement of S₂O₃^2- to elemental sulfur. Denitrification reaction by the enriched sulfur denitrifier followed the zero order kinetics. The specific denitrification rates of enriched microorganinsms were 9.4 mg-N·mg^-1TOC·d^-1 in case of S₂O₃^2- and 2.5 mg-N·mg^-1TOC·d^-1 in case of S₀, respectively, which were comparable with that of heterotrophic denitrifiers.

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By elevating the denitrification capability of activated sludge through the addition of elemental sulfur to the anaerobic denitrification tank of modified aerobic-anaerobic activated sludge process with supplement dephosphothickener, the possibility of simultaneous nitrogen and phosphorus removal without massive internal sludge recycle was investigated using bench scale experimental equipment. Granular elemental sulfur was found to be the best substance as the supplement reduced sulfur source in the anaerobic denitrification tank of modified aerobicanaerobic activated sludge process. 96.6% of influent TOC, 80% of influent T-N and 70% of influent T-P were successfully removed under 20 hours of operational retention time by this treatment method.
Important operational parameters of this simultaneous nitrogen and phosphorus removal process were revealed to be the nitrate loading rate and ORP for the anaerobic denitrification tank. The best treatment result was obtained under the operational condition of 0.028 g NO₃-N·g^-1 MLSS·d^-1 and (E_h) ₇ = 200mV for the anaerobic denitrification tank.

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[in Japanese]

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