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金沢大学理工研究域機械工学系, We have studied an efficient biological process to treat alkaline wastewater containing sulphide by sulphur bacteria, which was acclimated from activated sludge by thiosulfate and active at neutral pH. The sulphide removal rate of the sulphur bacteria was 135-140 mgS2-·g-1 MLVSS·h-1 at 20°C and fifty times as large as that of activated sludge. The sulphur bacteria finally oxidized sulphide to sulphate. Low water temperature and large sulphide-sludge loading tended to restrain the oxidation of sulphide to sulphate, which brought the accumulation of sulphur except sulphate in the reactor. The biological process by the sulphur bacteria could treat the alkaline wastewater containing sulphide of 300 to 600 mg·l-1 with HRT 8 hours and the water temperature of 20°C. H2S emission from the reactor was never observed. The sulphur bacteria could maintain good settleability under FeCl3 addition and the gross yield coefficient was about 0.14 KgVSS·kgS2-.

金沢大学理工研究域機械工学系, Wastewaters from oil refinery factories often contain high concentrations of sulphide and the pH is over 12. Sulphide in wastewater causes the problems of the odor, toxicity and oxygen demand. We have studied an efficient biological process to oxidize sulphide to sulphate at neutral pH. A method to acclimate sulphur bacteria from activated sludge of sewage treatment plant at neutral pH by synthetic wastewater containing thiosulphate and the thiosulphate removal rate by the sulphur bacteria were examined.Sulphur bacteria could be acclimated from activated sludge of sewage treatment plant for about 10 days. The thiosulphate removal rate by the sulphur bacteria was from 350 to 600 mg S2O32-·g VSS-1·h-1 under the neutral pH when the water temperature was from 20°C to 35°C. And the thiosulphate removal rate was 150 mg S2O32-·g VSS-1·h-1 at 5°C. The sulphur bacteria are thought to be bacillus and maintained good settleability even at 5°C. The biological process using the sulphur bacteria acclimated from activated sludge could remove both sulphide of 200 mg·l-1 and thiosulphate of 600 mg·l-1under the HRT of 3 hours and the water temperature of 5°C.