Naoyuki Kishimoto

Reusability of iron sludge as an iron source for the electrochemical Fenton-type process using Fe2+/HOCl system

This paper reports on the reusability and the optimal reuse of iron-rich sludge for an electrochemical Fenton-type process using sequencing batch mode and separation batch mode reuse models. In the sequencing batch mode, processes of electrochemical treatment, neutralization, sedimentation, and re-dissolution of iron sludge were all performed in the same reactor, whereas the neutralization and sedimentation of iron sludge in the separation batch mode was carried out in an iron recovery tank separated from the electrochemical reactor. The effects of iron speciation at different pH levels were discussed. It was found that ferric ions at a pH ≤2.5 were suitable for this electrochemical Fenton-type process where ferrous ions acted as hydroxyl radical scavengers, generating brownish deposits on the cathode at pH 3. When the sequencing batch mode was applied, the current efficiency in the Fenton-type process after the iron recovery declined due to the formation of insoluble deposits on the electrodes, which decreased at lower pH. The deposits were mainly formed during the neutralization and sedimentation steps after the electrochemical process. Fortunately, iron from the sludge could be reused for the electrochemical process when the separation batch mode was used, with 100% iron recovery and no decline in current efficiency.

Applicability of Ozonation Combined with Electrolysis to 1,4-Dioxane Removal from Wastewater Containing Radical Scavengers

In this paper, applicability of ozonation combined with electrolysis as an advanced oxidation process for the removal of 1,4-dioxane from synthetic wastewater, has been studied. The combined process easily decomposed 1,4-dioxane, and two byproducts were detected in treated water. Although bicarbonate alkalinity was a strong radical scavenger, its influence was abated by air-stripping of carbon dioxide at the anodic compartment of the reactor. Free chlorine produced through anodic oxidation of chloride ion accelerated the COD removal from wastewater, despite the fact that this ion acted as a weak radical scavenger. The combined process was demonstrated to be applicable to the treatment of wastewater containing high concentration of bicarbonate alkalinity and chloride ions.

Advanced treatment of sewage by pre-coagulation and biological filtration process.

A pre-coagulation and bio-filtration process for advanced treatment of sewage was developed and experimentally discussed with a pilot plant. The bio-filtration unit consists of a denitrification filter, a nitrification filter with side stream to the denitrification filter, and a polishing filter with anoxic and aerobic parts. Concentrations of SS, T-COD(Cr), T-carbonaceous BOD, T-N and T-P in the effluent were stably kept at less than 3, 20, 5mg/L, 2mg N/L and 0.2mg P/L, respectively, and transparency at higher than 100 cm, under total hydraulic retention time of 3.2h in the bio-filtration parts (filter-bed). ORP in an anoxic tank before a nitrification tank should be at a low level of less than -120 mV to keep remaining NO(-)(x) - N less than 1mg N/L, but must be maintained at a level higher than -150 mV. The maximum nitrogen-loading rate under a water temperature of 18 degrees C should be less than 0.25 kg N/(m(3)-filter-bed.d). Concentrations of microorganisms kept in the reactors were as high as 4000-5000 mg COD/L-filter-bed. Denitrification activity of 0.4 or 0.7 kg N/(m(3)-filter-bed.d), and nitrification activity of 0.3 kg N/(m(3)-filter-bed.d) were obtained, respectively, under a water temperature of about 18 degrees C. Backwashing in each tank as well as methanol addition and aeration in the polishing filter were operated successfully by the automatic control systems. These results proved that this process is applicable to advanced treatment of sewage with easy maintenance.

Feasibility of an electrochemically assisted Fenton method using Fe2 +/HOCl system as an advanced oxidation process

The feasibility of an electrochemically assisted Fenton treatment using a Fenton-type reaction of ferrous iron (Fe(2 + )) and hypochlorous acid (HOCl) is discussed in this research. The reactor used was composed of an undivided single cell with a ruthenium dioxide-coated titanium anode and a stainless steel cathode, in which Fe(2 + ) and HOCl were catalytically regenerated from ferric iron at the cathode and chloride ion at the anode, respectively. Although the reactor functioned well, the degradation rate of 1,4-dioxane as a hydroxyl radical probe decreased at the current density more than 6.92 mA cm(-2). The decrease in degradation rate was inferred to be caused by the vain consumption of hydroxyl radicals by excess HOCl and the deposition of ferric hydroxide on the cathode at relatively high current density. The current efficiency of 1,4-dioxane removal remained more than 90% at the current density less than 6.92 mA cm(-2) and the iron concentration not less than 1.0 mmol L(-1). Consequently, this technique is thought to be applicable to the treatment of wastewater containing high concentration of chloride ion such as landfill leachate, scrubber wastewater from incineration plants, etc.

Effect of Separation of Ozonation and Electrolysis on Effective Use of Ozone in Ozone-Electrolysis Process

For improving the ozone consumption efficiency (OCE) of the ozone-electrolysis process, an ozone-electrolysis system with an independent electrolytic cell from an ozone contactor (indirect ozone injection system) and a three-dimensional electrode were introduced in this study. The reactor successfully enhanced the OCE and the ratio of 1,4-dioxane degradation rate to ozone injection rate (RDO) in comparison with the previous reactor. The three-dimensional electrode also contributed the improvement of the OCE and the RDO due to lowering the current density on the cathode. As the indirect ozone injection system allows higher degree of freedom for the reactor design, it is useful for application of ozone-electrolysis to practical water treatments.

Behavior of Peridinium bipes (Dinophyceae) resting cysts in the Asahi Reservoir

Abstract The role of resting cysts includes short- and long-term survival under extreme conditions, bloom initiation, species dispersal, reproduction, and preservation of genetic variation. Accordingly, it is important to understand their behavior in a water environment, especially in lakes and reservoirs where dinoflagellate blooms are observed. In this study, we estimated the behavior of the Peridinium bipes cysts in the Asahi Reservoir using laboratory experiments and field surveys. It was observed that the amount of light strongly influenced excystment, and few cysts germinated under dark conditions in the laboratory experiment. The minimum temperature on excystment was inferred from the laboratory experiment and field surveys to be about 5°C. Although the frequency of excystment did not depend on the water temperature from 10° to 20°C, the average preparation period for excystment decreased with the increase of water temperature. In the Asahi Reservoir, the excystment was estimated to occur during the months of March and April. If excystment did not occur in spring, the dinoflagellate bloom was not be observed until about July, although the bloom often began to appear in about May in the Asahi Reservoir. Consequently, the blooming season in the Asahi Reservoir is affected by the biomass of the germinated cysts in spring.

Effects of waste glass additions on quality of textile sludge-based bricks

This research investigated the utilization of textile sludge as a substitute for clay in brick production. The addition of textile sludge to a brick specimen enhanced its pores, thus reducing the quality of the product. However, the addition of waste glass to brick production materials improved the quality of the brick in terms of both compressive strength and water absorption. Maximum compressive strength was observed with the following composition of waste materials: 30% textile sludge, 60% clay and 10% waste glass. The melting of waste glass clogged up pores on the brick, which improved water absorption performance and compressive strength. Moreover, a leaching test on a sludge-based brick to which 10% waste glass did not detect significant heavy metal compounds in leachates, with the product being in conformance with standard regulations. The recycling of textile sludge for brick production, when combined with waste glass additions, may thus be promising in terms of both product quality and environmental aspects.

Bromate Formation Characteristics of UV Irradiation, Hydrogen Peroxide Addition, Ozonation, and Their Combination Processes

Bromate formation characteristics of six-physicochemical oxidation processes, UV irradiation, single addition of hydrogen peroxide, ozonation, UV irradiation with hydrogen peroxide addition (UV/H2O2), ozonation with hydrogen peroxide addition (O3/H2O2), and ozonation with UV irradiation (O3/UV) were investigated using 1.88 μM of potassium bromide solution with or without 6.4 μM of 4-chlorobenzoic acid. Bromate was not detected during UV irradiation, single addition of H2O2, and UV/H2O2, whereas ozone-based treatments produced . Hydroxyl radicals played more important role in bromate formation than molecular ozone. Acidification and addition of radical scavengers such as 4-chlorobenzoic acid were effective in inhibiting bromate formation during the ozone-based treatments because of inhibition of hydroxyl radical generation and consumption of hydroxyl radicals, respectively. The H2O2 addition was unable to decompose 4-chlorobenzoic acid, though O3/UV and O3/H2O2 showed the rapid degradation, and UV irradiation and UV/H2O2 showed the slow degradation. Consequently, if the concentration of organic contaminants is low, the UV irradiation and/or UV/H2O2 are applicable to organic contaminants removal without bromate formation. However, if the concentration of organic contaminants is high, O3/H2O2 and O3/UV should be discussed as advanced oxidation processes because of their high organic removal efficiency and low bromate formation potential at the optimum condition.

Effects of Ozone-Gas Bubble Size and pH on Ozone/UV Treatment

A series of ozone/UV treatment under injection of ozone with different ozone-gas bubble sizes was performed at pH 1.7 and 7.4. The increase in the bubble size and the decrease in pH enhanced the ozone utilization efficiency. The enhancement of ozone utilization efficiency was caused by the shift of the production pathway of hydroxyl radical (OH) from the OH production via O3 – to the UV photolysis of H2O2. The lower pH caused this shift through the chemical equilibrium of H2O2 and HO2 –, and the large bubbles caused this shift through the augmentation of H2O2 transport from the bubble surface to the bulk solution.

Ozonation Combined with Electrolysis of Night Soil Treated by Biological Nitrification-Denitrification Process

Ozonation combined with electrolysis with a two- compartment electrolytic flow cell was developed and its applicability to ammonia nitrogen and total organic carbon (TOC) removal in effluent from a night soil treatment facility was discussed. The developed flow cell with an anion exchanged membrane as a separator was effective to remove by electrochemically generated chlorine and TOC by hydroxyl radical generated via cathodic reduction of ozone. Total nitrogen (TN) removal efficiency under the optimal condition reached to 75% and TOC removal efficiency maximally reached to 47%.