The conventional chemical oxygen demand (COD) test requires mercuric sulfate (HgSO₄) for masking chlorides (Cl⁻) in a sample. Since the use of mercury (Hg) will be strictly restricted under the Minamata Convention on Mercury, the feasibility of Hg-free COD test by closed reflux, colorimetric method with excessive addition of silver sulfate (Ag₂SO₄) was discussed in this research. Although Cl⁻ contamination tended to increase the dichromate consumption even in the conventional COD test, the Ag₂SO₄ dose in sulfuric acid reagent not less than 10.3 g/kg-H₂SO₄ successfully masked Cl⁻ not more than 500 mg-Cl/L. As a result of applying to 14 organic compounds with theoretical oxygen demand of 90 mg-O₂/L, the Hg-free COD test tended to output slightly higher COD than the conventional one; the average degradation efficiency of 96% in the Hg-free test and 94% in the conventional test. The average accuracy for the Hg-free COD test was superior to the conventional one. In the economical viewpoint, the Hg-free COD test successfully cut off the chemical cost of Ag₂SO₄ and HgSO₄ from 13,459 to 7,831 JPY/1,000 samples. Consequently, the Hg-free COD test was thought to be feasible for water samples containing Cl⁻ not more than 500 mg-Cl/L.

Various transformations in wastewater quality along sewers, such as that due to self-purification, have been reported. However, little is known about the contributions of the attached (sewer-wall) and suspended biomass originally existing in wastewater due to a lack of experimental fields. In this study, we examined the effects of attached and suspended biomass on the dynamics of the microbial communities in sewers by conducting recirculating batch tests in a pilot-scale sewer system equipped with sponge media and a lab-scale aerating batch test, respectively. The changes in the quantity and quality of organic matter indicated that the contribution of the attached biomass to self-purification was much larger than that of the suspended biomass, because the former was sufficiently acclimated to the wastewater. Moreover, the microbial community analysis by pyrosequencing suggested that there were two candidates responsible for self-purification: 1) Comamonadaceae and Rhodocyclaceae, which could immediately proliferate under attached conditions and become dominant (15% each) in the attached biomass, and 2) Pseudomonadaceae, which could proliferate under suspended conditions after a lag period of several hours and remain a small component (4%) of the attached biomass.

Laboratory and field experiments revealed that indigenous microbes attached to flowing carriers can remove 1,4-dioxane, a recalcitrant substance, from wastewater in landfill facilities. The 1,4-dioxane reduction efficiency of microbes collected from two landfills were different. Landfill Y exhibited higher biodegradation activity than landfill Z. The wastewater of landfill Y contained low biodegradable organic matter as the biochemical oxygen demand (BOD)/chemical oxygen demand (COD) ratio was low, and contained a significantly high proportion of organic carbon in 1,4-dioxane to dissolved organic carbon (> 4.0%). These environmental conditions might have contributed to the high 1,4-dioxane degradation activity of the microbes in landfill Y. Furthermore, the results of the batch experiments suggested that reducing biodegradable organic matter by aeration during pretreatment can accelerate biodegradation. The results also showed that the removal rate constant by stripping and biodegradation for both the batches increased with increasing water temperature. At landfill Y, even at a low temperature of 3°C in the aeration tank that received flowing carriers, over 20% of 1,4-dioxane was removed from wastewater, and a removal rate of 57% was observed at 17°C.

Contamination of groundwater by 1,4-dioxane has been detected in many regions worldwide, especially in illegal industrial waste dumping sites. As 1,4-dioxane is a potential human carcinogen that is highly resistant to most conventional biological and physicochemical treatments, the development of a practical application method for treating 1,4-dioxane-contaminated groundwater is strongly desirable. Therefore, this study aimed to develop an on-site treatment system for 1,4-dioxane-contaminated groundwater using Pseudonocardia sp. D17, and assess the feasibility of the developed system for long-term treatment. This bacterial strain is capable of constitutively degrading 1,4-dioxane and using it as a source of carbon and energy. The on-site treatment of 1,4-dioxane-contaminated groundwater was performed in a 450-L continuous-flow bioreactor using strain D17 with a hydraulic retention time of 12 ‒ 18 h. To maintain a sufficiently high microbial concentration, strain D17 was monitored by qPCR, targeting the thmC gene associated with 1,4-dioxane degradation, and inoculated when needed. 1,4-Dioxane removal to meet the Japanese environmental quality standard for groundwater pollution (0.05 mg/L) was achieved for nearly 3 months by the additional inoculation of strain D17. These results suggest that on-site treatment using strain D17 could provide a practical solution for the treatment of 1,4-dioxane-contaminated groundwater.