A variety of treatment products containing forms of nitrate have become available for use in optimizing microbial activities in a manner that results in improved system performance. While many of the traditional approaches to microbiological control have involved the use of biocides to achieve overall reduction in bacteria levels, the nitrate approach involves promoting growth of "beneficial" organisms which can negate the effects of, or out-compete the offending organisms. Suppliers of products, as well as systems operators in the natural gas industry, have reported the approach successful in a wide variety of applications including mitigation of downhole and above-ground produced water sulfide-souring, enhanced recovery of hydrocarbons in production reservoirs, and expediting cleanup of wastewater. In a study sponsored by the Gas Research Institute (GRI), Chicago Illinois, nitrate-based treatment strategies were assessed in field tests for efficacy in wastewater cleanup and mitigation of sulfide-souring in a produced water containment facility. In addition, laboratory tests were done to assess nitrate treatment for its potential for mitigation of downhole sulfide-souring using a test loop containing formation core material which was colonized by microbes producing sour water. Details on the test results, discussion of potential advantages/disadvantages of nitrate treatment, and criteria for determining if nitrate treatment is appropriate are provided herein.