Abstract
Natural gas brine pumped up from below the ground surface contains not only natural gas and iodine, but also high concentrations of ammonia. To sustain healthy water environments, it is important to understand the status of NH4–N in waste brine drained into a public water area after the collection of natural gas and iodine from the brine. In this study, the status of ammonia has been evaluated through field surveys, laboratory experiments, and simulation models of the flow and advection/diffusion of nitrogen in the Ichinomiya River, the tidal river into which the waste brine is drained. As a result of field survey and numerical simulation, the waste brine flows downriver along the top of seawater which inflows through the river bottom. It was calculated that the average residence time of the waste brine was about 1–3 days. Using the nitrification rate obtained from laboratory experiments, the concentration of NH4–N nitrified to NOx–N was estimated to range from 0.06 to 0.22 mg-N L-1 during this residence time. The ammonia nitrogen was not nitrified in the field survey and the maximum NOx–N concentration in the sampled water was about 2.5 mg-N L-1. These simulation model and field survey results suggested that the concentration of NOx–N produced by the oxidation of ammonia nitrogen in the Ichinomiya River would not exceed environmental standards.
