Tadao Mizuno

Toxicity of seven phthalate esters to embryonic development of the abalone Haliotis diversicolor supertexta

The toxicity of seven phthalate esters (PAEs), dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP), butylbenzyl phthalate (BBP), di-n-hexyl phthalate (DnHP), di-(2-ethylhexyl) phthalate (DEHP) and di-n-octyl phthalate (DOP) to embryogenesis and larval development of the marine univalve Haliotisdiversicolorsupertexta was examined by means of two-stage embryo toxicity test. At the blastula stage, the normal embryonic development of H. diversicolorsupertexta showed a good dose-response decrease when exposed to DMP, DEP, DBP, BBP, and DnHP. 9-h EC50 values of DMP, DEP, DBP, BBP, and DnHP were 55.71, 39.13, 8.37, 2.65, and 3.32xa0mg/l, respectively. 9-h EC50 values of DEHP and DOP were not available due to their low solubility. The toxicity order of seven tested PAEs was BBP>DnHP>DBP>DEP>DMP>DOP>DEHP. With the completion of metamorphosis as an experimental endpoint, the 96-h no-observed effect concentration values of DBP, DEHP and the other five tested PAEs were 0.022, 0.021, and 0.020xa0mg/l, respectively. Due to simple obtainment, convenient stimulation to spawn in the lab, greater sensitivity than mature species, and short culture time, the embryos of H. diversicolor supertexta have the potential to be utilized in acute toxicity test for at least PAEs.

Development of Ozone Self-Decomposition Model for Engineering Design

Recently, due to the advancement of O3/H2O2 treatment processes, it has been necessary to further develop the ozone self-decomposition radical model, which includes a variety of radical reactions, because the hydroxyl radical concentration as well as the ozone concentration must be taken into consideration. In this study, an ozone self-decomposition model that is meaningful for environmental engineering design under the practically encountered pH condition in the time scale of water treatment is proposed. First, an overall description model of ozone self-decomposition is developed based on the experimental results. The evaluation clarifies that the ozone self-decomposition can be formulated by a second-order reaction and the rate constant is enhanced 5 times and 2.2 times with increase of one pH unit and 5°C increase of temperature, respectively. Then a radical reaction model was developed. All of the reaction rate constants included in the model are obtained from the literature review except for the reaction rate constant of ozone with hydroxyl radical, which is obtained as 9.0u2009×u2009105 M−1s−1 based on experimental data. Good agreements of calculated results by the model with experimental results under the pH range from 2.7 to 7.8 over 10 minutes are obtained. This radical model of ozone self-decomposition will be applicable in analyzing other reactions, such as the effect of bicarbonate/carbonate ion on ozone self-decomposition, reaction with organic matter, the fate of micropollutants and by-products with ozone as well as hydroxyl radical.

O3/H2O2 Process for Both Removal of Odorous Algal-Derived Compounds and Control of Bromate Ion Formation

The limitation of ozonation and the applicability of ozone/hydrogen peroxide process with a source water for a water supply using a flow-through type contactor were discussed. The water sample was pre-treated in a lab and spiked with bromide ion in the concentration range from 39 to 515 μg/L, and both 2-MIB and geosmin, odorous algal-derived compounds, from 58 to 609 ng/L under the hydrogen peroxide dose of 0 to 3.7 mg/L. When the initial concentration of Br− was around 50 μg/L, the formation of BrO3 − was controlled at less than 10 μg/L at the ozone dose of 2 mg/L, however the concentration of 2-MIB was over 10 ng/L in some cases with its initial concentration of around 100 ng/L during ozonation. When the initial concentration of Br− exceeds 100 μg/L, it seems very difficult to meet the standard for drinking water quality even with the initial 2-MIB concentration of 100 ng/L. The dose of H2O2 from 0.5 to 2.3 mg/L attained the standard for drinking water quality with the initial concentrations of Br− of approximately 50 μg/L and of 2-MIB of up to 500 ng/L at the ozone dose of 2 mg/L. When the initial concentration of 2-MIB was around 100 ng/L with the initial Br− concentration of up to 200 μg/L, the H2O2 dose of 1.7 mg/L also attained the standard for drinking water quality. When the initial concentration of Br− was around 500 μg/L, although the higher dose of H2O2 was required for the control of BrO3 − formation and the increase of the initial concentration of 2-MIB requires more H2O2 dose, the higher dose of H2O2 could attain the standard for drinking water quality of BrO3 − and 2-MIB (geosmin) simultaneously.

A Simple Model to Predict Formation of Bromate Ion and Hypobromous Acid/Hypobromite Ion through Hydroxyl Radical Pathway during Ozonation

A simple model is developed to predict the formation of bromate ion as well as hypobromous acid/hypobromite ion through the hydroxyl radical pathway. For simplicity of the model, hydroxyl radical concentrations are represented by the concentration ratio of hydroxyl radical to dissolved ozone under the different pH conditions. A kinetic analysis is conducted to evaluate the ratio under the different pH conditions based on the experimental data. The different extent of the ratio by one pH unit is found to be 3–4 times. This model can favorably simulate the formations of bromate ion as well as hypobromous acid/hypobromite ion in spite of the simplicity of the model. So it is likely that this model will be applicable to the prediction of bromate ion formation in water purification process such as drinking water treatment by introducing the concentration ratio of hydroxyl radical to dissolved ozone.

Evaluation of Solubility and the Gas-Liquid Equilibrium Coefficient of High Concentration Gaseous Ozone to Water

Solubility and the gas-liquid equilibrium coefficient of gaseous ozone to water were examined under higher concentrations of supplied gaseous ozone up to 100 mg/L. The experimental and modeling approach was employed to evaluate the gas-liquid equilibrium coefficients and mass transfer of ozone. The gas-liquid equilibrium coefficients were evaluated as 0.35, 0.31 and 0.25 (mg/L-liquid)/(mg/L-gas) at 15, 20 and 30 °C, respectively. These gas-liquid equilibrium coefficients are applicable for the wide concentration range of supplied ozone gas up to 100 mg/L. The calculation result by a model which has terms of the mass transfer of ozone, the gas-liquid equilibrium coefficient and the rate of ozone self-decomposition, was examined and had a good agreement with the experimental data over the wide range of temperatures, pHs, inorganic carbon concentrations and supplied ozone gas concentrations. The rate of ozone self-decomposition evaluated separately from this study was employed for the calculation. We can conclude that absorption of gaseous ozone to water is expressed by the three terms mentioned above when the rate of ozone self-decomposition is evaluated properly. In sensitive analysis, we elucidated that the rate of ozone self-decomposition affected strongly on the concentration of dissolved ozone at steady-state under higher concentration of supplied gaseous ozone.

Formation of Bromate Ion Through a Radical Pathway in a Continuous Flow Reactor

ABSTRACT The contribution of ozone and hydroxyl radical to the formation of bromate ion was investigated in a continuous flow reactor. Experiments were conducted under a wide range of ozone dose (0.7 ∼ 3.8 mgL), pH (6.5 ∼ 8.5), and t-butanol concentration (0 ∼ 0.5 mM). The formation of bromate ion was found to depend on radical reaction pathway, because the amount of bromate ion formed increased with pH and decreased with t-butanol, a radical scavenger, even when dissolved ozone concentrations were almost the same. In fact, the amount of bromate ion formed was reduced by 90% in the presence of t-butanol. Furthermore, the formation of bromate ion occurred even when dissolved ozone was not significantly detected in the presence of organic matter (TOC of 1 mgCL). The second-order reaction rate constant of hydroxyl radical with bromide ion, k HO,Br− of 1.7 × 109 (M−1s−1), was obtained on the assumption that the reactions of bromide ion and t-butanol with hydroxyl radical were competitive with each other in the presence of t-butanol and that the formation of bromate ion depended on the reaction of bromide ion with hydroxyl radical. Therefore, it is concluded that the reaction of bromide ion with hydroxyl radical dominated in the overall reaction from bromide ion to bromate ion in the continuous flow reactor.

Removal Characteristics of Organic Pollutants in Sewage Treatment by a Pre-Coagulation, Ozonation and Ozone/Hydrogen Peroxide Process

The applicability of a sequential process of ozonation and ozone/hydrogen peroxide process for the removal of soluble organic compounds from a pre-coagulated municipal sewage was examined. 6–25% of initial T-CODCr was removed at the early stage of ozonation before the ratio of consumed ozone to removed T-CODCr dramatically increased. Until dissolved ozone was detected, 0.3 mgO3/mgTOC0 (Initial TOC) of ozone was consumed. When an ozone/hydrogen peroxide process was applied, additional CODCr was removed. And we elucidated that two following findings are important for the better performance of ozone/hydrogen peroxide process; those are to remove readily reactive organic compounds with ozone before the application of ozone/hydrogen peroxide process and to avoid the excess addition of hydrogen peroxide. Based on these two findings, we proposed a sequential process of ozonation and multi-stage ozone/hydrogen peroxide process and the appropriate addition of hydrogen peroxide. T-CODCr, TOC and ATU-BOD5 were reduced to less than 7 mg/L, 6 mgC/L and 5 mg/L, respectively after total treatment time of 79 min. Furthermore, we discussed the transformation of organic compounds and the removal of organic compounds. The removal amount of CODCr and UV254 had good linear relationship until the removal amounts of CODCr and UV254 were 30 mg/L and 0.11 cm−1, respectively. Therefore UV254 would be useful for an indicator for CODCr removal at the beginning of the treatment. The accumulation of carboxylic acids (formic acid, acetic acid and oxalic acid) was observed. The ratio of carbon concentration of carboxylic acids to TOC remaining was getting higher and reached around 0.5 finally. Removal of TOC was observed with the accumulation of carboxylic acids. When unknown organic compounds (organic compounds except for carboxylic acids) were oxidized, 70% was apparently removed as carbon dioxide and 30% was accumulated as carboxylic acids. A portion of biodegradable organic compounds to whole organic compounds was enhanced as shown by the increase ratio of BOD/CODCr.

Effect of inorganic carbon on ozone self-decomposition

The effect of inorganic carbon on ozone self-decomposition was examined in this study. Experiments were carried out under a wide concentration range of inorganic carbon of 0–30 mgC/L. First, the rate constant in the overall description model with nth order reaction on dissolved ozone was evaluated. A clear difference in the rate constants with and without inorganic carbon was observed even when the concentration of inorganic carbon was as low as 3 mgC/L; the difference with and without inorganic carbon was almost one order of magnitude. Reaction rate constant was lower with an increase of inorganic carbon concentration. The reaction rate constants were in the range from 1.4u2009×u200910−5–1.9u2009×u200910−4 (mg/L)−1sec.−1 under pH of 6.8–8.1 and inorganic carbon concentration of 6–30 mgC/L and converged on the order of 1.0u2009×u200910−4 (mg/L)−1sec.−1. The difference of the second-order reaction rate constant under the practical range of pH and inorganic carbon concentration was one order of magnitude at most. Depression of ozone self-decomposition rate by inorganic carbon was also evaluated as a scavenging rate by inorganic carbon species against hydroxyl radical. Although the profile of scavenging rate constant was complex, the order of scavenging rate was 102 sec−1 at most in the practical range of pH and inorganic carbon concentration. Because the overall effect of inorganic carbon species on hydroxyl radical scavenging was evaluated qualitatively, the depression extent on ozone self-decomposition, as well as scavenging extent on hydroxyl radical by inorganic carbon is able to be analyzed qualitatively.

Environmental and economic assessment of municipal sewage sludge management – a case study in Beijing, China

A case study was conducted in Beijing to identify municipal sewage sludge (SS) management systems appropriate for a sound material-cycle society. The environmental and economic impacts of four realistic SS-handling scenarios were investigated: stabilization by thermal drying, increased inclusion of SS in cement manufacture, and using either dried or carbonized SS as substitute fuel for coal-fired power generation plants. The results showed that the current sludge management system had the lowest operating cost but higher greenhouse gas (GHG) emissions and a low recycling rate. The case with the use of carbonized SS reused in coal-fired power plants had higher energy consumption and almost the same GHG emissions as the current system. On the other hand, the case including more SS in cement manufacture had the same level of energy consumption with much lower GHG emissions. The case with the use of dried SS in coal-fired power plants also resulted in lower energy consumption and lower GHG emissions than at present. Furthermore, sensitivity analysis showed that drying SS with surplus heat from cement plants used less energy and emitted less GHG compared to the other two drying methods.

Applicability of Corbicula as a bioindicator for monitoring organochlorine pesticides in fresh and brackish waters

The applicability of Corbicula as a bioindicator for monitoring organochlorine pesticides (OCPs) in fresh and brackish waters is presented here. Differences in isomer compositions and OCP bioaccumulation levels were analyzed in western Japan and the Pearl River Delta (PRD) in China. Isomer compositions of DDTs, chlordanes, and HCHs were significantly different between the two areas because of their different historical uses and property of the chemicals. This is represented by the (DDE + DDD)/DDT ratio in Corbicula, ranging 4.9–39 in western Japan and 1.1–2.4 in the PRD. However, isomer compositions in Corbicula reflected those in water, and the different patterns in Corbicula likely reflected the usage history. Concentrations of dissolved oxygen, suspended solids, and volatile suspended solids in water, and the difference in species did not influence OCP bioaccumulative levels in Corbicula when conducting biomonitoring. These levels are likely similar to those in Mytilus galloprovincialis. Therefore, Corbicula could be an appropriate bioindicator for monitoring OCPs in fresh and brackish waters.