Nitrification Potential in Isumi River Receiving High-Strength Ammonium Brine Waste from a Natural Gas and Iodine Production Plant

Abstract

After the recovery of natural gas and iodine from the brine pumped up from a gas reservoir layer 500–2,000 m below the ground surface, waste brine containing a high concentration of ammonium (about 200 mg L^-1 NH₄-N) is drained into the Isumi River in the Kujukuri district in Chiba Prefecture. In this study, the fate of NH₄ in the Isumi River was investigated. The nitrification rates in the investigated river section from the discharge point to Shiodome Weir ranged from 0.000 to 0.360 mg L^-1 d^-1, and the transformation efficiency of NH₄-N to NO₂-N and NO₃-N was 6.9％ on average. These extant nitrification rates positively correlated with those obtained in a laboratory test using river water samples. The estimated nitrification rates based on the number of ammonia oxidizing bacteria (AOB) present in the river bottom sediment and their biokinetic parameter values available from references were in the range from 0.044 to 0.104 mg L^-1 d^-1, which are of the same order of magnitude as the extant nitrification rates. Furthermore, the nitrification rates determined by a ¹⁵N dilution technique ranged from 0.00 to 0.19 mg L^-1 d^-1, supporting the extant nitrification rates in the investigated river section.