Technical feasibilities of a Fenton-type reaction of cuprous ion (Cu⁺) with hypochlorous acid (HOCl) and an electrochemical Fenton-type process using this reaction were discussed in this research. Since 1,4-dioxane was decomposed by mixing Cu⁺ and HOCl, it was inferred that the reaction of Cu⁺ + HOCl → Cu²⁺ + ·OH + Cl⁻ happened. As a result of electrolyzing 1,4-dioxane solution containing cupric ion (Cu²⁺) and chloride ion (Cl⁻), 1,4-dioxane was decomposed with the current efficiency (η) of 6.1%, which was higher than that for control experiments (1.7 − 1.8%). Therefore, it was confirmed that the electrochemical Fenton-type process with the cathodic reduction of Cu²⁺ to Cu⁺ and the anodic oxidation of Cl⁻ to chlorine was feasible. The effect of current density on the electrochemical Fenton-type process was discussed by a series of experiments. Although 1,4-dioxane removal rate was enhanced with the increase in current density in the range of 2.5 − 10 mA/cm², the η did not depend on current density clearly. Since deposition and precipitation of copper during electrolysis were thought to affect the η, it will be required to develop a technique avoiding the deposition and precipitation of copper in the future.

To assess the potential risk of viral infection through drinking water, a rapid and effective method to quantify pathogenic viruses is necessary. Ethidium monoazide (EMA) combined with reverse transcription qPCR (EMA-RT-qPCR) is a currently widely accepted method to assess the integrity of viruses. However, this technique can be hampered by humic acids which are co-concentrated during virus concentration processes (VCPs). Co-concentration of four commercially available humic acids (Ald, Wa, Na, and IH) during VCPs and their impacts on the subsequent EMA-RT-qPCR over spiked intact Aichi virus 1 and its naked RNA were studied. The recoveries of Ald, Wa, Na, and IH during VCPs were less than 8.9%, 5.4%, 7.2%, and 0.7%, respectively, indicating that IH was much less concentrated than other humic acids. In the concentrates, Ald, Wa, and Na caused severe inhibition of EMA-RT-qPCR, whereas only a slight inhibitory effect on IH was observed. Tests of the influence of actual drinking water concentrates on EMA-RT-qPCR indicated the absence of severe inhibition. Therefore, EMA-RT-qPCR has a high potential for monitoring enteric viruses in drinking water.

The influent of municipal wastewater treatment plants (WWTP) can contain micropollutants such as antibiotics, chlorine, detergents, and biocides. In vitro studies have shown that these micropollutants may induce antibiotic resistance in bacteria. Previous studies have reported increases or decreases of antibiotic-resistant bacteria between the influent and effluent of WWTP in an unpredictable manner. Thus, the triggers of resistance induction in WWTP are largely unknown. To investigate the effects of unit operations in WWTP on antibiotic resistance induction, we incubated sixteen strains of Escherichia coli susceptible to amoxicillin or norfloxacin under simulated conditions of the primary sedimentation tank, aeration tank and final sedimentation tank in sterilized and filtered wastewater from each tank at 25°C for 1, 6 and 2 hours, respectively, which are typical hydraulic retention time of each tank. The minimum inhibition concentration towards amoxicillin or norfloxacin was compared before and after incubation to evaluate the occurrence of induction. We found that resistance to both antibiotics was more likely to increase in the aeration tank than in the primary sedimentation tank or final sedimentation tank. The longer contact time with the wastewater and the aeration are factors that appeared to induce antibiotic resistance in an activated sludge process.

A new one-stage nitritation/anaerobic ammonium oxidation (anammox) process with two-inflow was proposed to provide suitable coexistence conditions for ammonium oxidation bacteria (AOB) and anammox bacteria. Reactor performances were examined using a two-inflow biofilm reactor fed with artificial ammonia-containing wastewater. For start-up, an anammox biofilm was cultivated in a wound filter set in the center of the reactor until the anammox process occurred stoichiometrically. Then, sponge media containing abundant AOB were added to the reactor, and aeration of the reactor began, also nitrite concentrations in the substrate decreased and the ammonium concentration increased gradually. Both anammox and nitritation occurred in the reactor. The maximum nitrogen removal efficiency achieved was 49%, the maximum ammonium conversion efficiency was 60%, and the maximum nitrogen removal rate was 0.228 kg-N/(m³·d) at the nitrogen loading rate of 0.5 kg-N/(m³·d). It was estimated that ammonium oxidation (nitritation) occurred in the sponge; hence, the anammox reaction occurred in the biofilm attached to the filter.

In the aluminum industry, as an alkaline waste, red mud is composed of Fe and Al. It is difficult to safely dispose certain types of some arsenic-containing red mud owing to hazardous arsenic leaching. Hence, the method of arsenic stabilization using Fe (III) or H₂SO₄ to reduce arsenic leaching from red mud was investigated. The results indicated that the addition of 3 − 5% Fe₂(SO₄)₃ or H₂SO₄ (ratio of H⁺ (mM)/red mud (g) ≈ 1.5) into red mud and maintaining the pH at 4 until dryness was achieved at room temperature, decreased arsenic solubility from 360 to 2 − 6 µg/L (< 10 µg/L: Environmental criteria in Japan) and maintained the same for several months. In the mechanism of arsenic stabilization, Fe³⁺ ions added or Fe³⁺ and Al³⁺ ions dissolved from red mud by adding H₂SO₄ reacted with arsenic and formed insoluble Fe–As and Al–As compounds. Through X-ray diffraction analysis, insoluble arsenic compounds including iron arsenate, iron hydrogen arsenate, aluminum arsenate, and aluminum arsenate hydrate were detected and considered as responsible for low arsenic leaching. Additionally, the results suggested that HCl was not appropriate for stabilizing arsenic in red mud because the high amounts of Cl⁻ negatively influence the formation of insoluble arsenic compounds.