Abstract: This invention provides an activated sludge process for treating wastewater containing ammonia as a contaminant and further for treating wastewater containing ammonia as a contaminant and other contaminants which may possibly be present including cyanide, thiocyanate, sulfide and/or organics, wherein the process involves treating wastewater in the presence of an appropriate microorganism population acclimated to the wastewater contaminants and their levels in the wastewater, this microorganism population including (1) nitrifying microorganisms capable of converting ammonia to nitrite, (2) optionally, nitrifying microorganisms capable of converting nitrite to nitrate, and (3) facultative microorganisms capable of denitrifying nitrite and/or nitrate by oxidizing organic material and converting nitrite and/or nitrate to free nitrogen, with the process being operated under a series of controlled conditions to ultimately achieve in the activated sludge process a microbial conversion of ammonia to nitrite and/or ni