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The object of this work is to research the sulphide formation process in pressure pipes and how the sulphur rich wastewater influences treatment process in Kohtla-Jiirve wastewater treatment plant (WWTP), In this work the ISO 8192 standard test has been used to estimate the inhibition of oxygen demand of activated sludge microorganisms in different sulphide concentrations and pH values, Two wastewaters has been investigated leachate from cokeand ash hills and wastewater from inflow ofKohtla-Jii.rve WWTP, The leachate from cokeand ash hills, rich of sulphates and sulphides, with high pH values from l O+ 12, did not cause significant inhibition of oxygen demand of activated sludge microorganisms, After the leachate has been mixed with other sulphate and sulphide rich wastewaters with lower pH values, the mixed wastewater inhibits the oxygen demand of microorganisms in activated sludge process. One of the reasons is the increased sulphide concentration but the essential factor is also decreasing of pH.

Sulphide formation in sewage pipes and influence of H2S to aerobic activated sludge microorganisms