Blowing water used for cooling blast furnace slag from the iron-making process is expected to be strongly alkaline because alkaline components of blast furnace slag are dissolved in it. However, actual blowing water in a water supply tank has a neutral pH. On the assumption that bacteria in blowing water cause pH to decrease, we conducted incubation experiments using blowing water controlled at a pH of 10 or higher. The pH of blowing water decreased at 60°C upon the addition of sodium thiosulfate. The concentration of sulfate also increased. DNA sequencing results revealed that the proportion of Thermi in this thiosulfate-stimulated blowing water increased to 83%. Thus sulfur-oxidizing bacteria that exist in high-temperature, high-pH blowing water oxidized thiosulfate into sulfate and hydrogen ion, so that the blowing water was neutralized. This bacterial reaction in a water supply tank is crucial for wastewater treatment of blowing water to decrease its pH and oxidize sulfur compounds.

View full abstract

This study was aimed at accumulating information on bacterial water quality to define a numerical target of a sanitary indicator in river management. Fecal bacteria (total coliform bacteria, fecal coliform bacteria, Escherichia coli, enterococci) in Oita River, Oita, Japan were monitored. Water samples were collected from a total of 17 stations along Oita River between December 2013 and November 2014 (total of 12 sampling events). A high total coliform bacteria count, which was used as a river-water-quality standard, was detected in water samples from most of the sampling stations (mean: 1.1 x 10⁴ MPN·100 mL^-1). The other three types of bacteria were also often detected at high concentrations. All bacterial counts tend to be high in the summer season. In particular, at stations 1 to 6, the bacterial counts greatly varied. From the results of analyzing the correlation coefficients of each bacterial count, it was found that there is little correlation between individual bacterial counts with the exception of the upstream area of Oita River. Furthermore, multiple regression model analysis revealed that there were no water quality parameters that affect the counts of fecal indicator bacteria. The results indicated that bacterial water quality might be difficult to estimate using water quality parameters.

View full abstract

Musty odor occurred in tap water with Oita River as its source in October 2014. Oita city disclosed that the problem was due to plankton in the Serikawa Dam, which is on a tributary of the Oita River. This study was aimed at elucidating the cause of the problem by comparing water quality in 2014 with that in previous years. 2-Methylisoborneol (2-MIB) showed a high concentration in the Serikawa Dam and downstream in 2014. It was found that thermal stratification was absent from November 2014 to January 2015 because no temperature difference between the upper and lower layers was detected. On the other hand, the ammonia nitrogen concentration remained high, 2.3 mg·L^-1, from November 2014 to January 2015. Iron and manganese ions showed the same pattern as ammonia nitrogen in 2014. This suggests that, in 2014, 2-MIB negligibly decomposed as a result of oxygen depletion caused by the high ammonia nitrogen concentration in the Serikawa Dam Reservoir. It is likely that 2-MIB reached farther downstream without being decomposed.

View full abstract