We developed an analysis method for total nitrogen using a copper-zinc reduction coil without cadmium by continuous flow analysis. In this study, we attempted to realize a total nitrogen analysis method without using harmful substances by combining the previously reported nitric acid analysis method using a copper-zinc reduction coil and by decomposition using potassium peroxodisulfate. The coefficient of determination was 0.9996, and the instrument limit of detection and the method limit of quantification were lower than the limit of quantification required for the measurement of environmental water and wastewater. In the analysis of environmental water and wastewater samples by this method, we were able to obtain results equivalent to those obtained by the conventional method. In addition, we conducted measurements at three facilities. Repeatability relative standard deviation was lower than 10%, suggesting the validity of this method.

In this study, the effect of medium-layer inflow on the sewage treatment performance of a multistage-constructed wetland with a hybrid filtration bed was determined. Although the BOD and NH₄⁺-N removal performance was less than that of surface-layer inflow, the efficiencies of BOD and NH₄⁺-N removal were more than 98% despite the material of the filtration medium. The enhancement of the T-N removal performance with medium-layer inflow was significant, resulting in a more than 75% removal efficiency despite the material of the filtration medium, whereas the effect for T-P was minimal. Comparison of the microbial communities in the filtration bed indicated a decrease in the ratio of the number of ammonia-oxidizing and nitrite-oxidizing bacteria to that of eubacteria in the case of using medium-layer inflow, whereas the ratio of the number of anammox bacteria increased. These results suggest that the medium-layer inflow enhanced not only the denitrification by heterotrophic bacteria, but also the autotrophic anammox reaction, resulting in a significant improvement in the nitrogen removal performance.

The carbon and nitrogen contents in suspended particles in a euphotic layer shallower than 10 m and the carbon and nitrogen fluxes in settling particles in depths below the euphotic layer were measured in Lake Sagami from May to December 2016. Mass fluxes were more than 10 times higher than those previously reported in eutrophic lakes. The carbon and nitrogen fluxes were higher than those in the primary production in the euphotic layer and likely came from sources in addition to the euphotic layer. The factors that led to increased carbon and nitrogen fluxes were not necessarily related to rainfall. The carbon and nitrogen contents were lower in the settling particles than in the suspended particles and showed no clear seasonal variation. Furthermore, the C/N ratio in the settling particles was approximately 1.3 times higher than that in the suspended particles.