Enhancement of Biodegradability of 1,4-Dioxaneinduced by O3/H2O2

Copyright: © 2015 Takahashi N, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. *Corresponding author: Nobuyuki Takahashi, Institute for Environmental Management Technology, National Institute of Advanced Industrial Science and Technology (AIST)16-1 Onogawa, Tsukuba, Ibaraki 305-8569, Japan, Tel: +81-29-861-8727; Fax: +81-29-861-8722; E-mail: takahashi-nobuyuki@aist.go.jp


Introduction
1,4-Dioxane is widely used as a solvent in the manufacture of organic chemicals; a stabilizer for chlorinated solvents, such as 1,1,1-trichloroethane, and a wetting agent in paper and textile processing [1].1,4-Dioxane is also the by-product of several chemical processes involving ethylene glycol or ethylene oxide [2].1,4-Dioxane is classified as Group 2B by the International Agency for Research on Cancer (IARC) because it is possibly carcinogenic to human [1].In Japan, the new environmental standard of 0.05 mg/L was adopted in 2011 and the drainage regulation standard of 0.5 mg/L was also adopted in 2012.In this regard, the development of a new cost-effective treatment system is strongly desired.
Many studies of the degradation and/or removal of 1,4-dioxane have been conducted.Those studies have shown that 1,4-dioxane is not effectively treated by conventional methods, including biological treatment, coagulation, and activated carbon adsorption, and that advanced oxidation process (AOP) using hydroxyl radical (HO • ) shows the effective degradation of 1,4-dioxane.As AOPs, ozonation with UV irradiation (O 3 /UV) [3,4], ozonation with hydrogen peroxide (O ) at pH 6 to 8 [4][5][6], ozonation with electrolysis [7], UV irradiation with hydrogen peroxide [8], and UV irradiation with titanium oxide [9,10] have been mainly reported.Those studies have also shown the superiority of AOPs to ozonation alone.Among those AOPs, O  [5] and Takahashi et al. [4] have also showed that there is a desirable molar ratio of H 2 as a practical AOP was conducted on a laboratory scale.Afterward, the biodegradability of the reaction products derived from 1,4-dioxane was estimated, and the effect of the reaction products on the water environment was investigated by the biodegradation test using surface water and the Microtox test.

Analytical methods
Ozone concentrations in the inlet gas and the exhaust gas were Open Access 2 measured by the KI method, respectively, and the amount of ozone consumed in the reactor was determined from the difference of them.In order to evaluate the further degradation of intermediate products derived from the degradation of dissolved organic carbon (DOC) and BOD 5 were measured.DOC was measured with a TOC analyzer (TOC-500, Shimadzu, Japan).BOD 5 was measured according to JIS K0102.1,4-Dioxane was measured with a high-performance liquid chromatography (HPLC) (LC-10, Shimadzu, Japan) equipped with a RI detector (RID-10, Shimadzu, Japan).The analytical conditions were as follows; mobile phase: water, flow rate: 1 mL/min, oven temperature: 40°C, column: COSMOSIL 5C18-PAQ (Nacalai Tesque, Japan) [7].The effect of 1,4-dioxane and its reaction products on the water environment was investigated by both the 10-day biodegradation test and the Microtox test.In the Microtox test, bio-toxicity (TU=100/EC 50 ) was measured with a thermostatic photometer (Model 500, Microbics Inc., USA) and freezedried P. phosphoreum (Modern Water Inc., USA). Figure 1 shows the procedure for the 10-day biodegradation [11].Surface water from Ohori River as inoculums, the volume of sample solution was 190 mL and no deionized distilled water was added for dilution.

Degradation by O 3 /H 2 O 2 compared with respective methods
As the reference treatments, the degradation and/or removal of 1,4-dioxane by ozonation at pH 6 to 8, aeration of oxygen gas, and addition of H 2 O 2 solution were first conducted to compare with the treatability of O 3 /H 2 O 2 .Figure 2 shows the change of water quality parameters during the degradation of 1,4-dioxane by O 3 at pH 6 to 8. Slight degradation of 1,4-dioxane was observed, and the decrease in DOC was only 7~8 mg/L.The degradation of 1,4-dioxane by ozonation at pH 6 to 8 was expected to proceed with the production of HO • [12] although the extent of degradation was slight.The removal of 1,4-dioxane by aeration was reported to increase with increasing aeration intensity [13].However, no decrease was observed in this study because of the low aeration intensity of 30 L-ozonized oxygen gas/h to 1.6 L solution.Moreover, 1,4-dioxane was not degraded by addition of H 2 O 2 solution.These results indicate that the extents of degradation and/or removal of 1,4-dioxane by ozonation at pH 6 to 8, aeration, and addition of H 2 O 2 solution were very limited.

Change of biodegradability during degradation of 1,4-dioxane by O 3 /H 2 O 2
In order to estimate the change of biodegradability during the degradation of 1,4-dioxane, the ratio of BOD 5 to DOC (BOD 5 /DOC) were calculated using BOD 5 and DOC obtained from the degradation of 1,4-dioxane [11].Figure 4 shows the change of BOD 5 /DOC with and without H 2 O 2 addition.As shown in Figure 4, BOD 5 /DOC showed a steady increase and/or a maximum, because DOC steadily decreased and BOD 5 showed a maximum with increasing reaction time.The increase in BOD 5 /DOC indicates the accumulation of biodegradable intermediates, and the maximum suggests the further degradation of the intermediates with increasing reaction time.

Presumption of proposed reaction pathway of 1,4-dioxane degradation by AOP
AOP, using HO + as main reaction species, shows the effective degradation of 1,4-dioxane.Several researchers have investigated the reaction pathway of 1,4-dioxane [14,[7][8][9][10].Table 1 summarizes the reaction products derived from the degradation of 1,4-dioxane.Figure 5 shows the initial degradation mechanism for 1,4-dioxane proposed by Beckett et al. [14].1,4-Dioxane was first degraded to initial intermediates, such as ethylene glycol diformate and ethylene glycol monoformate, by HO + .These initial intermediates are further degraded to some low molecular weight organic compounds, and then, those compounds were finally degraded to CO 2 and H 2 O.As a reaction pathway after the  Open Access 3 production of ethlene diformate, Figure 6 shows the degradation pathway of 1,4-dioxane proposed by Maurio et al. [7].The production of CO 2 indicates the decrease of DOC concentration, as shown in Figure 3.In addition, the BOD 5 /DOC values of some low molecular weight organic compounds of glycolaldehyde, formic acid and oxalic acid in Figure 6 are 1.06, 0.50 and 0.32, [15], those are higher than that of 1,4-dioxane of less than 0.05.The result indicates the enhancement of biodegradability induced by O 3 /H 2 O 2 , leading to a decrease in the load on the water environment accepting the discharged effluents.

Estimation of decrease in DOC concentration of 1,4-dioxane and its reaction products by biodegradation test
In order to clarify the enhancement of the biodegradability suggested in the former section, 1,4-dioxane was treated with O 3 /H 2 O 2 and then, the biodegradation test using surface water was conducted on both the original 1,4-dioxane and the treated water.Figure 7 shows the change of the concentration of DOC during the biodegradation test.Figure 8 shows the decrease in DOC concentration (ΔDOC) calculated from Figure 7. 0 on the left of the plots in Figure 7 corresponds to DOC-1 in Figure 1, and 0 on the right to DOC-2 in Figure 1, respectively.As shown in Figure 7, DOC concentration in the treated water was decreased with incubation days, and this tendency was not found in the original 1,4-dioxane solution.Moreover, the extent of the decrease was increased with increasing ozonation time, as shown in Figure 8.These results actually show the enhancement of biodegradability suggested in Figure 4, and indicate the effectiveness of O 3 /H 2 O 2 .
On the other hand, the initial peak areas of 1,4-dioxane in HPLC at 0, 30, 60 120 min were 16569, 5601, 827 and 0, respectively, and those were not changed during incubation, indicating that the concentration of 1,4-dioxane was almost constant in both the original 1,4-dioxane and the treated water, regardless of ozonation time.Therefore, the degradation of 1,4-dioxane is generally impossible on the water environment, and that the discharge less than the criteria is necessary.

Estimation of bio-toxicity of reaction products by the Microtox test
As shown in Figure 7, DOC components will probably remain in the treated water in proportion to ozonation time and incubation day.In order to investigate the bio-safety of the treated water, the Mocrotox test was conducted.The Microtox test measures the extent of light emission in a sample solution using photobacterium, and can yield results within short-term reaction [16].Taking this characteristic into account, the bio-toxicities after 5-and 15-min reactions (TU (5) = 100/EC 50 and TU (15)=100/EC 50 ) were measured.Figure 9 shows the change of bio-toxicity after 5-and 15-min reactions.Bio-toxicity showed a maximum at 30~60min reaction, and decreased thereafter to a value lower than the detection limit.These results show that in the case of short-term reaction, bio-toxic Open Access 4 intermediates will remain in the solution and the intermediates will be further degraded to bio-safe compounds with reaction time.As a result, the establishment of desirable reaction conditions under which bio-toxic intermediates do not remained in the solution is very important.

Conclusions
The degradation of 1,4-dioxane by O 3 /H 2 O 2 was investigated on a laboratory scale.The biodegradability of the reaction products was estimated, and the effect of the reaction products on the water environment was measured by the biodegradation test using surface water and the Microtox test.The following conclusions were obtained: (1) The degradation 1,4-dioxane by O 3 /H 2 O 2 was proceeded rapidly compared with that by ozonation at pH 6 to 8.
(2) The biodegradability represented as the ratio of BOD 5 to DOC of the reaction products was higher than that of original 1,4-dioxane.
(3) The decrease in DOC concentration of the reaction products was observed during the incubation, showing the enhancement of biodegradability.
(4) The bio-toxicity of the reaction products measured by the Microtox test showed an initial increase followed by a decrease with increasing reaction time.Open Access

2 O 2 to O 3 . 3 /H 2 O 2
However, the effect of the reaction products of 1,4-dioxane by O on the water environment has been hardly investigated, and detailed studies of whether or not the organic compounds derived from the degradation of 1,4-dioxane are further decreased on the water environment are necessary.In this study, the degradation of 1,4-dioxane by O n H U B f o r S c i e n t i f i c R e s e a r c h Citation: Takahashi N, Ichikawa H, Kiyono F, Hibino T, Torii H, al. (2015) Enhancement of Biodegradability of 1,4-Dioxane induced by O 3 /H 2 O 2 .Int J Water and Wastewater Treatment 1(1): doi http://dx.doi.org/10.16966/2381-5299.105

Figures
Figures 3A and 3B shows the change of water quality parameters during the degradation of 1,4-dioxane by O 3 /H 2 O 2 .The degradation of 1,4-dioxane by O 3 /H 2 O 2 was accelerated compared with that by ozonation at pH 6 to 8. 1,4-Dioxane at the initial concentration of 150 mg/L was completely degraded by 1~2 h reaction.During the degradation, both the decrease in DOC and the appearance of a maximum value for BOD 5 were observed.The comparison between Figures 3A and 3B showed that the oxidation potential affected the residual concentration of DOC and/or BOD 5 as well as the degradation of 1,4-dioxane.As shown in Figure 3A, large amount of DOC and/or BOD 5 remained in the solution after O 3 / H 2 O 2 with low oxidation potential.On the other hand, as shown in Figure 3B, the increase in the amount of H 2 O 2 added from 0.1 to 0.6 mL caused both the further decrease in the residual concentration of DOC and/or BOD 5 .These results show the effective degradation of 1,4-dioxane by O 3 / H 2 O 2 compared with ozonation at pH 6 to 8.
min at 25℃ and 125rpm Leave the inoculated solution for 15 min Measurement of DOC concentration (DOC-1) Measurement of DOC concentration (DOC-2) Agitation at 25℃ and 125rpm Measurement of DOC concentration at fixed days Sample solution 190 mL Solution containing inorganic salts 4 mL Urea solution (50.2 mg/L) 1 mL