Consideration of Transport of Ammonium Nitrogen in a Tidal River

Abstract

This study was aimed at investigating the influence of a sewage treatment plant's seasonal operation on the water quality and nutrient transport of a tidal river. Cross-sectional observations were carried out in the Honjoe River, which flows into Ariake Bay in Japan. Field surveys and experiments focusing on the transport of ammonium nitrogen (NH₄⁺-N) in the tidal river were performed. As a result, suspended solid (SS) sediment formation close to the river, including in the vegetation areas, was accelerated and exhibited the potential local accumulation of NH₄⁺-N with SS. In addition, some experiments revealed an empirical equation for the removal rate of NH₄⁺-N. According to the equation, the NH₄⁺-N sedimentation rates tended to be low when the salinity and initial SS were high. Furthermore, the removal rate of NH₄⁺-N calculated using the empirical equation agreed qualitatively with the field results.