Abstract
Produced waters containing high levels of oxidant demanding chemicals such as ammonia, hydrogen sulfide, and iron are often thought to be difficult to disinfect using oxidizing biocides such as hypochlorite. It is the goal of this paper to present evidence that chloramines generated in situ through the reaction of native ammonia present in produced water with hypochlorite added as a disinfectant can effectively control microbial populations in produced water. Testing was accomplished by treating produced waters being held in retention ponds with a hypochlorite-based disinfectant solution produced at the pond location using a mobile on-site generation (OSG) system. OSG in this treatment scenario involves the electrolysis of sodium chloride brines to yield a hypochlorite-based oxidizing biocide solution. This solution is then injected into the produced water at a rate to ensure that the Oxidation-Reduction Potential (ORP) of the treated water is ~450 mV. Samples of both the raw and treated water were analyzed for both chemical composition as well as microbial populations. Raw water in this study was found to consistently have relatively high ammonia content in the range of 58 to 120 mg/L along with an ORP in the range of −228 to 190 mV. Populations of Acid Producing Bacteria (APB) and Sulfate Reducing Bacteria (SRB) were found to be 1010 and 1011 MPN/mL, respectively. On site analysis of the treated water fond that the ORP after oxidant injection was between 464-543 mV, a value consistent with the presence of chloramines and not free chlorine. Populations of APBs and SRBs in the treated water were found to be 1 and 10 MPN/mL, respectively, representing a 10 log reduction in the resident bacteria population of these waters. Overall, this data clearly demonstrates that chloramines generated in situ through the treatment of high ammonia waters with OSG produced hypochlorite can effectively control the populations of key microbes in produced waters. Effectively controlling microbial populations using in situ generated chloramines offers the ability to achieve required disinfection of produced waters with hypochlorite based biocides without meeting the total chlorine demand of the water being treated.
