Abstract: The ammonia concentration present in waste water is reduced by treating the waste water with a suspended growth microbial system such as an activated sludge containing organisms of the genus Nitrosomonas and organisms of the genus Nitrobacter, but in which the microbial activity of Nitrobacter is effectively inhibited. The process includes a step of treating the microbial system under conditions effecting inhibition of the Nitrobacter but substantially unaffecting the growth and metabolic characteristics of the Nitrosomonas, and subjecting the ammonia containing waste water to the so treated microbial system for a hydraulic retention time which is less than the recovery time of the inhibited Nitrobacter. As a result, the retrograde step of nitrite-nitrate conversion in the overall denitrification process also is reduced or eliminated, with consequent energy and cost savings.

Abstract: A method of treating wastewater containing a contaminant selected from the group consisting of heavy metal cations, tars, oils and phenols or mixtures thereof, comprising mixing said wastewater with an effective amount of desulfurization slag, the composition of said slag including calcium oxide, calcium sulfide and iron oxides, causing deposition of said contaminant from the mixture, and separating the deposit from the supernatant liquid.