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peroxymonosulfate-upflow biological aerated filter
Journal Pre-proofs Advanced treatment of bio-treated Chinese patent medicine wastewater using ozone/peroxymonosulfate-upflow biological aerated filter Guomin Tang, Yongbing Zhang, Yujiang Wei, Shuang Wang, Pei Liu, Zhehua Jia, Xuemin Yu, Fang Ma PII: DOI: Reference:
S1385-8947(20)30518-0 https://doi.org/10.1016/j.cej.2020.124527 CEJ 124527
To appear in:
Chemical Engineering Journal
Received Date: Revised Date: Accepted Date:
25 November 2019 19 February 2020 20 February 2020
Please cite this article as: G. Tang, Y. Zhang, Y. Wei, S. Wang, P. Liu, Z. Jia, X. Yu, F. Ma, Advanced treatment of bio-treated Chinese patent medicine wastewater using ozone/peroxymonosulfate-upflow biological aerated filter, Chemical Engineering Journal (2020), doi: https://doi.org/10.1016/j.cej.2020.124527
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© 2020 Published by Elsevier B.V.
Advanced
treatment
of
bio-treated
Chinese
patent
medicine
wastewater
using
ozone/peroxymonosulfate-upflow biological aerated filter
Guomin Tanga,b,c,d*, Yongbing Zhanga, Yujiang Weia, Shuang Wanga, Pei Liua, Zhehua Jiac, Xuemin Yud, Fang Mab
a
Taizhou Institute of Science and Technology, Nanjing University of Science and Technology,
Taizhou 225300, Jiangsu Province, China; b
State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of
Technology, Harbin 150090, Heilongjiang province, China; c
Province Key Laboratory of Environmental Material and Environmental Engineering,
Yangzhou University, Yangzhou 225000, Jiangsu Province, China; d
Province Key Laboratory of Environmental Engineering, Jiangsu Environmental Science
Research Institute, Nanjing 225000, Jiangsu Province, China;
Corresponding author: *Guomin Tang, Tel. /fax: +86 523 86150222; E-mail: [email protected]
1
Abstract The advanced treatment of biotreated Chinese patent medicine wastewater (BCPMW) was urgently necessitated to meet the strictest wastewater discharge standard. In the present study, combined ozone/peroxymonosulfate oxidation and upflow biological aerated filter process (O3/PMS-UBAF) significantly integrated advantages of O3/PMS oxidation and UBAF, and has been demonstrated to be very effective in the advanced treatment of BCPMW. For dissolved organic matter (DOM) in BCPMW, O3/PMS oxidation efficiently degraded higher molecular weight (MW) fractions and non-biodegradable fractions. In addition, O3/PMS oxidation not only increased the overall removal of DOM but also enhanced the biodegradation rate of DOM. Therefore, the beneficial effect of O3/PMS oxidation may mainly be due to the special effect of increased biodegradability and the generalized effect on DOM. Finally, the results also indicated that compared with UBAF alone, O3/PMS-UBAF not only promoted the removal of low MW fractions (＜3kDa) but also inhibited the formation of higher MW fractions (3-10 kDa) that was generated by UBAF alone. Key words: Biotreated Chinese patent medicine wastewater; Upflow biological aerated filter; Ozone/peroxymonosulfate; Advanced treatment; Dissolved organic matter
2
1. Introduction Chinese patent medicine wastewater was a refractory biodegradable industry wastewater, and included more refractory organic pollutants (e.g. cellulose, lignin, and etc.) [1-5]. Biological process was always regarded as a proper approach for Chinese patent medicine wastewater treatment. However, the chemical oxygen demand (COD) and color in BCPMW greatly exceeds the discharge limit in China. Thus, aiming at the strictest discharge standards, it was very necessary for Chinese patent medicine factories to develop an appropriate (namely more cost-competitive) process that could be used for the advanced treatment of BCPMW. Abbreviations BCPMW O3/PMS UBAF DOM MW TOC DOC BDOC NBDOC TE RILR
Biotreated Chinese patent medicine wastewater Ozone/peroxymonosulfate Upflow biological aerated filter Dissolved organic matter Molecular weight Total organic carbon Dissolved organic carbon Biodegradable DOC Non-biodegradable DOC Toxic equivalent Relative Inhibition Light Ratio
In comparison of other advanced treatment technologies, combined advanced oxidation-advanced aerobic treatment process has received considerable attention recently [6-8]. Upflow biological aerated filter (UBAF), as a typical of advanced aerobic process, showed an excellent performance in advanced treatment of biotreated industry wastewater contained low concentration SS and COD [9-12]. Among numerous oxidation processes,
3
ozone alone or persulfate alone did not have a significant effect in the degradation of DOM · [13, 14], however, the oxidation based on sulfate radical (SO4 , a more advantageous
oxidizing specie, E0=2.5–3.1V, relatively better selectivity, and relatively longer duration time) has recently raised a more and more attention because of the high efficiency for the non-biodegradable, hazardous, and refractory organic matter removal [15-17]. Usually, SO4· could be generated from activating PMS (HSO5−) or peroxydisulfate (S2O82−) with UV, catalysts, and etc.. However, PMS has a similar peroxo bond with H2O2, which means that PMS may be easily activated to initiate the formation of sulfate radical during ozonation [18]. In this sense, O3/PMS oxidation, as novel advanced oxidation processes, could more efficiently remove refractory matter in wastewater. Based on the degradation of pure individual compounds in model wastewater, this point was proved in the previous studies [19-22]. Unfortunately, up to now, rare study has ever been published regarding O3/PMS as an advanced oxidation processes used for treating real industry wastewater, especially it was still unclear that how organic matter in real industry wastewater was removed by O3/PMS-UBAF. Thus, a new combined process (O3/PMS-UBAF) was designed in the advanced treatment of BCPMW. The main objectives of the present study were: (1) to investigate the treatment performance of the combined process and O3/PMS oxidation; (2) to explore the relevant mechanism of the removal of organic matter in BCPWM. 2. Materials and methods 2.1. Experimental influent BCPMW was collected from a real Chinese patent medicine factory that was located in
4
Jiangsu province, China. The relevant quality of the BCPMW was summarized in Table S1. 2.2. Experimental method and installation 2.2.1. O3/PMS-UBAF treatment experiment The experimental setup (Fig. S1), which was used to investigate relevant performance of combined O3/PMS-UBAF process, and mainly included the UBAF and the oxidation reactor. Its design treatment capacity was approximately 0.24 m3/d, and all equipment was tabulated in Table S2. In the experiment, hydraulic retention time at UBAF was 4 h, gas/water ratio at UBAF was 4, and backwash period at UBAF was 7 days. O3/PMS-UBAF treatment experiment was executed at 16-28℃, and the UBAF effluent sample was withdrawn at 16-21℃. 2.2.2. O3/PMS oxidation experiment The O3/PMS oxidation was executed at a continuous mode in the oxidation reactor of the above setup (Fig. S1). The ozone–oxygen gas stream from an ozone generator (Qingdao Guolin, model CF-G-2-10g) was fed to the reaction medium through a microporous aerator with a constant flow rate at 1 atm, and the ozone concentration in input gas was adjusted by working electricity. The PMS (available as Oxone, industrial grade, 45% effective ingredient) was purchased from Wuhan Galaxy Chemical Co. Ltd and diluted into liquor with 10% mass concentrations to facilitate dosing. All oxidation experiments were conducted according to the following conditions determined by the previously preliminary test (i.e. an initial pH, 20 min oxidation, 20 mg/L O3 dosage and 50 mg/L Oxone (approximately 22.5 mg/L PMS) dosage). To rapidly terminate oxidation reaction, the 2.0 mL Na2SO3 solution (8.50 mM) was immediately added into the wastewater sample (100 mL) after oxidation. Subsequently the
5
wastewater sample was used for the relevant indicator analysis and the other experiment (i.e. batch biodegradation experiment and filtration experiment). It was to note that O3/PMS oxidation experiment was carried out at 16-28℃, but the oxidation effluent sample was withdrawn at temperature range of 16-21℃. 2.2.3. Batch biodegradation experiment Batch biodegradation experiments were conducted according to the incubation method as reported by other research groups [23, 24]. In the experiment, the aeration of 1000 ml BCPMW sample at 20℃ was used to examine biodegradable dissolved organic carbon (BDOC) or non-biodegradable dissolved organic carbon (NBDOC). During aeration, magnetic stirrer was used to provide sufficient mixing, and the water loss was compensated by adding distilled water. The dissolved organic carbon (DOC) before aeration was measured as an initial DOC. The DOC was measured after each 24 hour of aeration time (for 28 days), the constant value was examined as a NBDOC, and the difference between initial DOC and NBDOC was determined as the BDOC. 2.2.4. Filtration experiment The filtration experiment in a batch mode was used to examine the change of MW. MW distribution was characterized by the membrane with nominal cutoff values of 3, 10, 100 kDa, and 0.45 µm [25], and each fraction was collected for relevant indicator analysis. These experiments were conducted with an ultra-filtration cup (model SCM 300, Shanghai Institute of Atomic Nuclear Research, China) (Fig. S2), and the characteristics of the filtration membrane used was listed in Table S3. 2.2.5. Kinetic experiment
6
The kinetic experiment was carried out at 25-27 ℃ with a 500 mL-capacity glass in the setup (Fig. S3), and the ozone generator (Guangzhou Baifeng, model BF-YE-2g) provided the ozone. At 10 min interval, the wastewater sample (10 mL) was withdrawn from the setup, and the 0.2 mL Na2SO3 solution (8.50 mM) was immediately added into the wastewater sample. Subsequently, the wastewater sample was filtrated with membrane (0.45 µm), and the processed sample was used to examine the DOC. 2.3. Analytical method Standard methods, as set up by China Ministry of Environmental Protection, were used for determining the relevant indicator value (i.e. Color degrees, BOD, COD, SS, and acute toxicity) [26]. During COD examining, K2Cr2O7 was used. The pH was determined by pH meter
(PHS-25),
and
UV
absorbance
(UVA280)
was
examined
by
UV-Visible
Spectrophotometer (SHI-MADZUT6). Total organic carbon (TOC) analyzer (TOC-VCPH) was used for the measurement of DOC and TOC. 3. Results and Discussion 3.1. O3/PMS oxidation The degradation of pollutant in BCPMW by O3/PMS oxidation was determined. The results were presented in Fig. 1, where the degradation was indicated by the removal of COD, color, TOC, DOC, UVA280, UVA280 /TOC, UVA280 /DOC (namely SUVA280). Fig. 1 By O3/PMS oxidation, the COD and TOC was reduced by 60.28% and 44.06% respectively, and the DOC was decreased from 88.4 to 42.0 mg/L, giving a removal efficiency of 52.49%. These results indicated O3/PMS oxidation was relatively successful at
7
mineralizing the DOC in BCPMW. At the same time, O3/PMS oxidation presented an excellent de-colorization performance as indicated by the high removal of color (75.26%) (Fig.1). The observed effects of O3/PMS oxidation on changes in these indicators (i.e. COD, color, and DOC) were similar with those reported in other oxidation systems [27, 28]. Furthermore, the 79.06% UVA 280 decrease was obtained in the experiment (Fig. 1). It can be concluded from the high removal in color and UVA 280 that the structure of organic matter in BCPMW was significantly decomposed by O3/PMS oxidation. Meanwhile, this was accompanied by a 62.75% decrease of UVA280/TOC, which was lower than the UVA280 decrease (79.06%). These results were basically consistent with those reported in the literature [29]. At the same time, the decrease was 55.80% for SUVA280, which was slightly lower than that in the literature [29]. It was well known that some characteristics of the wastewater (i.e. pH, acute toxicity, and biodegradability) would influence the bio-treatment of the wastewater. Thus, the effect of O3/PMS oxidation on BCPMW characteristics was also investigated. As presented in Fig. 2 (a), at an initial pH (7.4-8.9), the pH of oxidized BCPMW varied from 7.1 to 8.7. This results means that the pH would not influence the subsequent bio-treatment of oxidized BCPMW. Furthermore, the slight decline of pH (approximately 0.2 pH units) was also observed after O3/PMS oxidation. The possible explanation for this was that during O3/PMS oxidation, organic acids (i.e. carboxylic acids) were generated and PMS was decomposed. The phenomenon was also observed in other study [30]. Fig. 2 Meanwhile, as illustrated in Fig. 2 (b), the toxic equivalent (TE) and the relative
8
inhibition light ratio (RILR) of BCPMW by O3/PMS oxidation significantly lowered from 0.08 mg/L (HgCL2) to 0.02 mg/L (HgCL2), and 36% to 9%, respectively. These results were consistent with those in other study on advanced oxidation processes [27]. The results mean that the toxicity of oxidized BCPMW was weak, and the inhibitory effect of the toxicity pollutant in oxidized BCPMW on microbial growth during subsequent biodegradation was slight. Furthermore, the BOD5/COD value of BCPMW was examined before and after O3/PMS oxidation. As Fig. 2 (b) shown, BCPMW presented poor biodegradability (BOD5/COD = 0.143), but the biodegradability of oxidized BCPMW was significantly improved (BOD5/COD=0.497). These results suggested that O3/PMS oxidation has good performance on the enhancement of the wastewater biodegradability. The change trends on wastewater biodegradability during O3/PMS oxidation were also observed in other oxidation systems [27, 28]. It can be seen from the results that O3/PMS oxidation basically presented a positive effect on some characteristics of BCPMW (i.e. pH, acute toxicity, and biodegradability), and the oxidized BCPMW was suitable for the further bio-treatment. 3.2. DOC removal kinetics during O3/PMS oxidation With the assumption of pseudo-first-order, the following Eqs. (1) can be used to express DOC removal rate in the O3/PMS oxidation stage. ln (C/C0)=−Kt
(1)
Where t was the oxidation time, C was DOC value at the different t, C0 were the DOC in influent, and K was the rate constant. Under optimum conditions, the relationship between ln (C/C0) and t was shown in Fig. S4. The linear fitting of ln (C/C0) as a function of t leads to K=0.0177 and R2=0.9072, as 9
shown in Fig. S4. Therefore, during the O3/PMS oxidation, the DOC removal basically followed the first order (Eq. (2)). ln (C/C0) = − 0.0177*t
(2)
3.3. O3/PMS-UBAF treatment 3.3.1. Treatment performance The treatment of BCPMW by UBAF alone and combined O3/PMS-UBAF process was examined. The quantitative comparison of the treatment of BCPMW by above two processes was showed in Fig.3. Fig.3 The UBAF alone decreased COD from 322.6 to 206.8 mg/L (35.90% removal) and reduced DOC from 88.40 to 72.66 mg/L (17.81% removal), which was lower than the reduction observed in O3/PMS oxidation (Fig.3). At the same time, the removal of color and SUVA 280 by UBAF alone was only 20.45% and 6.35%, respectively, which was also lower than those by O3/PMS oxidation (Fig.3). Furthermore, for TOC, UBAF alone obtained a 35.92% removal. Compared with UBAF alone, combined O3/PMS-UBAF process significantly promoted the organic matter removal. Specially, it increased DOC removal from 17.81% to 77.60%, COD removal from 36.9% to 85.68%, color removal from 20.45% to 81.79%, and SUVA280 removal from 6.35% to 59.67% (Fig.3). Furthermore, 80.90% TOC removal was also observed during O3/PMS-UBAF treatment. The quality of the effluent after O3/PMS-UBAF treatment meets the most stringent discharge standard (namely, discharge standard of water pollutants for pharmaceutical industry Chinese traditional medicine category (GB21906-2008), and the value for COD and color in this standard were respectively 50 mg/L and 30 times). 10
Finally, the TE and RILR of the effluent after O3/PMS-UBAF treatment were only 0.01 mg/L (HgCL2) and 3%, respectively. This means that the toxicity impact of the pollutants in O3/PMS-UBAF effluent on receiving water bodies was negligible. 3.3.2. Treatment cost The cost of O3/PMS oxidation was calculated, and the results were listed in Table S4. The calculated cost was 1.0038 $ /Kg COD removed for the O3/PMS oxidation, being 84.15% and 94.0% of that for O3/H2O2 oxidation and O3/persulfate oxidation respectively. These results indicated that O3/PMS oxidation could remove more organic matter (COD) at a relatively lower cost. In other words, compared with other advanced oxidation processes in Table S4, O3/PMS oxidation was more cost-competitive. Generally speaking, for subsequent biotreatment, O3/PMS oxidation was a preferable pretreatment process. The cost of O3/PMS oxidation was 1.0038 $/Kg COD removed for the removal of COD from 322.60 to 128.14 mg/L (Table S4 and Fig. 3). What’s more, the cost was 0.1938 $/Kg COD removed for the subsequent UBAF that further remove the COD from 128.4 to 46.2 mg/L, only being 19.31% of that for O3/PMS oxidation (Table S4 and Fig. 3). Furthermore, among three combined processes in Table S4, O3/PMS-UBAF presented the cheapest cost and the lowest O3 dosage. This result suggested that for O3/PMS-UBAF treatment, with the decrease of the ozone generator power, the stability of the process operation would correspondingly improve, and the investment on the ozone generator would correspondingly decrease. 3.4. Batch biodegradation experiments The results from batch biodegradation experiments were shown in Fig.4. As reported in
11
the previous literature [31, 32], the decrease of the DOC concentration at an initial period was significantly more rapid than that after this period. During batch biodegradation, the residual amount of DOC, corresponding to the NBDOC, basically remained unchanged (Fig.4). Fig.4 With the assumption of pseudo first order, and the DOC concentration during biodegradation can be expressed as Eq. (3) [33]. DOC = NBDOC + BDOC·e-kt
(3)
Where k was the biodegradation rate constant, and t was the biodegradation time. The Eq. (3) was used to fit experiment data from batch biodegradation (ExpDecay1), and the results were presented in Fig.4. After O3/PMS oxidation, the biodegradation rate constant of DOM in BCPMW increased from 0.1861 d-1 to 0.2750 d-1 (approximately 47.77% enhancement) (Fig.4). Yavich et al. [31] reported that the biodegradation rate increased with the increase of the ozone dose. On the contrary, it was reported that the overall kinetics was basically unchanged after the ozonation [32, 34]. Our results indicated that O3/PMS oxidation has a significant effect on the biodegradation rate of DOM in BCPMW. This means that the wastewater quality would still influence biodegradation rate, even though UBAF reached steady state. The difference may mainly be due to the variations in wastewater characteristics and oxidation conditions. Fig.5 At the same time, the ratio of BDOC to DOC in BCPMW increased from 0.3428 to 0.6595 after O3/PMS oxidation (Fig.5). The result indicated that O3/PMS oxidation significantly enhanced the biodegradability of DOM, which contradicts results reported by
12
Black and Be´rube´ [32]. In their works, the ratio of BDOC to DOC in wastewater before and after oxidation remained unchanged at approximately 0.5. However, this result was basically consistent with that reported in the literature [24]. In the literature, after persulfate/H2O2 oxidation, the ratio of biodegradable COD to COD in stabilized landfill leachate significantly increased from approximately 0.3659 to approximately 0.6667 [24]. Fig.5 also showed that by O3/PMS oxidation, the concentration of NBDOC was significantly decreased (75.34% reduction), but the removal of BDOC was slight (only 8.88%). These results suggested that for DOM in BCPMW, O3/PMS oxidation degraded non-biodegradable fractions more efficiently than biodegradable fractions, which were basically consistent with those previously reported by others. In their works, Hilles et al. [24] reported that the removal of non-biodegradable COD (86.0%) was much more than that of biodegradable COD (54.5%) during the O3/persulfate oxidation of the landfill leachate. Black and Be´rube´ [32] observed that after UV/H2O2 oxidation at suitable conditions, the removal of NBDOC (approximately 50%) was more than that of BDOC (approximately 30%). Furthermore, our results also indicated that O3/PMS oxidation did not present a significantly effect on the BDOC formation, which was not consistent with results reported in the previous literature [34, 35]. Digiano et al. [34] reported that the concentration of BDOC was increased with the ozone dose increase. It was also reported that BDOC concentration instead increased after UV/H2O2 oxidation [35]. 3.5. Degradation of different MW fractions during O3/PMS oxidation The MW distributions were divided into five fractions: F1 (＜3kDa), F2 (3-10kDa), F3 (10-100kDa), F4 (100kDa-0.45 µm), and F5 (＞0.45 µm). The removal of organic matter with
13
different MW was investigated during O3/PMS oxidation. 3.5.1. Particulate organic carbon removal The particulate organic carbon was calculated according to the difference between TOC and DOC, and used to indicate the removal of the particulate organic matter (namely organic matter in F5). The particulate organic carbon included the non-biodegradable particulate organic carbon and the biodegradable particulate organic carbon. In BCPMW, the ratio of non-biodegradable particulate organic carbon (35.86 mg/L) to particulate organic carbon (37.1 mg/L) was up to 96.66%, and the biodegradable particulate organic carbon (only 1.24 mg/L) was negligible. The removal of particulate organic carbon and non-biodegradable particulate organic carbon in BCPMW was respectively 24.0% and 24.21% during O3/PMS oxidation. This may be one of reasons that the removal efficiency of TOC in BCPMW was low (44.06%) (Fig.1). Abu Amr et al. [36] observed that for particulate organic matter, advanced oxidation processes did not obtain more degradation. In their works, particulate COD was used for indicating the decrease of particulate organic matter in the stabilized leachate, and removed by only 40% during the O3/Fenton oxidation [36]. 3.5.2. DOC removal Fig.6 showed the removal of DOC in different MW fractions. Fig.6 As presented in Fig.6, after O3/PMS oxidation, the removal of 79.68%, 66.13%, 57.31%, and -28.37% was respectively observed for F4, F3, F2, and F1. These results indicated that O3/PMS oxidation removed the DOC in high MW fractions more efficiently than that in low MW fractions, which was basically consistent with those reported by Zhang et al. [25]. In
14
their works, after ozonation, an 88% or more removal of DOC in higher MW fractions (F4 and F3) was observed, but the removal of DOC in lower MW fractions (F2) was lower (approximately 69.2%) [25]. Furthermore, the increase in concentration of DOC in F1 indicated that larger organic matter was oxidized to smaller organic matter, which was consistent with results in other studies on advanced oxidation processes [32, 37]. In these studies, ozonation increased the concentration of DOC in low MW fractions [32, 37]. However, this result also contradicts that reported by Zhang et al. [25]. In their works, neither S2O82- oxidation nor ozonation achieved the increase of the concentration of DOC in low MW fractions [25]. Fig.6 also exhibited that the total removal of DOC was 52.49% after O3/PMS oxidation. During ozonation at a 50 mg/L O3 dose, an extremely low removal of DOC (only 6%) was observed by Wang et al. [29]. However, an approximately 60% DOC was removed by UV/H2O2 treatment at a suitable condition [32]. These variations were likely due to the difference in experimental conditions and wastewater characteristics. Generally, O3/PMS oxidation resulted into the decomposition and partial oxidation of DOM. As shown in Fig.6, the NBDOC in higher MW fractions (F3 and F4) was approximately 80.86% of total NBDOC, and removed by 78.22% by O3/PMS oxidation. The removal of NBDOC was 83.33% and 47.23% for F2 and F1, respectively (Fig.6). These results suggested that for non-biodegradable dissolved organic matter in BCPMW, the removal of high MW fractions overtook that of low MW fractions, which were basically consistent with some results from other research [32]. Fig.6 also illustrated the removal of BDOC in different MW fractions. For higher MW fractions (namely F4 and F3), the BDOC removal followed similar trends to that of NBDOC,
15
and was up to 59.69% (Fig.6). These results were consistent with those from other research [32]. But for low MW fractions (namely F1), the BDOC instead significantly increased (approximately 72.28%), which were also consistent with results reported in the literature [32]. In the literature, the BDOC in low MW (300-500Da) fractions significantly increased (approximately 66.67% increase as indicated by area count) after UV/H2O2 treatment at a dose of 4000 mJ/cm2 and 10 mg/L H2O2 [32]. Furthermore, in the present study, the ratio of BDOC to DOC in BCPMW increased from 0.3428 to 0.6595 after O3/PMS oxidation (Fig.5). The above results suggested that O3/PMS oxidation increased the biodegradability of DOM by oxidation larger organic matter to smaller organic matter. Generally, O3/PMS oxidation degraded higher MW fractions more efficiently than low MW fractions in DOM, and had a significant effect on the concentrations and characteristics of DOC. In previous studies, some research groups thought that advanced oxidation (e.g., ozonation, and etc.) always equally reacts with organic matter. However, Black and Be´rube´ [32] observed that after UV/H2O2 oxidation at suitable conditions, the removal of NBDOC (approximately 50%) was more than that of BDOC (approximately 30%). Wang et al. [29] reported that for DOM in BDFW, ozonation can more efficiently degrade chromophore fractions than non- chromophore fractions. It was reported that BDOC concentration instead increased after UV/H2O2 oxidation [34, 35]. Hilles et al. [24] reported that the removal of non-biodegradable COD (86.0%) was much more than that of biodegradable COD removal (54.5%) during the O3/persulfate oxidation of the landfill leachate. Furthermore, Black and Be´rube´[32] also observed that ozonation predominantly affected the absorbance of
16
chromophoric natural organic matter with an MW less than 3kDa, UV/H2O2 oxidation at suitable conditions preferentially removed the NBDOC and BDOC in larger MW fraction, and UV/H2O2 oxidation at suitable conditions preferentially reacted with chromophoric natural organic matter with higher MW. These differences in reaction may mainly be attributed to the variations in experimental conditions and characteristics of the wastewater studied. 3.6. Degradation of different MW fractions during UBAF treatment 3.6.1. Particulate organic carbon removal Alone UBAF decreased the particulate organic carbon in BCPMW from 37.1 mg/L to 8.16 mg/L (removal 78.01%), which was significantly more than the removal observed in response to O3/PMS oxidation (24.0%). Furthermore, UBAF alone significantly removed the particulate organic carbon in oxidized BCPMW (removal 85.43%). For UBAF, as the bio-adsorption has been excluded after long time operation, the filtration was mainly responsible for the removal of particulate organic carbon. 3.6.2. DOC removal Fig.7 As presented in Fig.7, the removal of DOC in BCPMW was low after UBAF alone treatment (only 12.60%). For BCPMW, UBAF alone decreased the DOC in low MW fractions more efficiently than that in high MW fraction, with removals of 55.66%, -7.68%, 10.51%, and 2.62% being observed for F1, F2, F3, and F4, respectively (Fig.7). These variations on the removals of DOC in different MW fractions indicated that UBAF alone not only can degrade DOM with low MW (F1) but also form some DOM with higher MW (F2).
17
Unfortunately, up till now, the report on quantitative information of converting and mineralization was rare for lack of the effective analysis method. The previous studies also reported the formation of some DOM with relatively higher MW during bio-treatment [29, 37]. This may be because some conjugated protein-like substance was generated during bio-treatment. Furthermore, the removal of DOC in oxidized BCPMW was determined, and used to appraise the effect of O3/PMS oxidation on following UBAF performance. As shown in Fig.7, UBAF removed the 52.83% DOC in oxidized BCPMW, and the removal of DOC in oxidized BCPMW was more than four times as much as that in BCPMW. This may be because that during O3/PMS oxidation, more rapidly BDOC (BDOCr) was formed in wastewater. These results indicated that O3/PMS oxidation was helpful for the improvement of the performance of subsequent UBAF. For oxidized BCPMW, the removal of DOC was 74.69%, 66.51%, 19.51%, and 8.04% for F1, F2, F3, and F4, respectively (Fig.7). As the bio-adsorption in the UABF has been excluded at steady state, the removal of low MW DOC in oxidized BCPMW may mainly be due to the biodegradation. Furthermore, comparison of the removals of DOC in BCPMW and oxidized BCPMW suggested that for DOM, O3/PMS-UBAF can inhibit the formation of higher MW fractions (F2) and increase the removal of low MW fractions (F1). The likely reason could be that O3/PMS oxidation produces some small DOM that they were easily to mineralization by following UBAF rather than converting to larger DOM. The same phenomenon was reported in the previous studies [29, 38]. The results in the present study suggested that O3/PMS-UBAF significantly integrated advantages of O3/PMS oxidation and UBAF, enabling it to remove more particulate organic
18
matters, destruct non-biodegradable organic matters, and then mineralize more biodegradable organic matters. Generally, combination O3/PMS-UBAF process was a preferable technology for treating BCPMW. Furthermore, as previously discussed, O3/PMS oxidation influenced not only the amount of DOC but also the biodegradation rate of DOC. Therefore, the beneficial effect of O3/PMS oxidation prior to UBAF may mainly be due to the special effect of increased biodegradability and the generalized effect on DOM. 4. Conclusions It was proved that under experimental conditions (i.e. an initial pH, 20 min oxidation, 20 mg/L O3 dosage, 50 mg/L Oxone dosage, gas to liquid ratio at UBAF (4), hydraulic retention time at UBAF (4 h), backwash period at UBAF (7 days), temperature (16–28 ℃ )), O3/PMS-UBAF can efficiently degrade the pollutants in BCPMW, with removal of 77.60%, 85.68%, 81.79% for DOC, COD, color, respectively. The COD and color in the tread BCPMW by O3/PMS-UBAF were less than 48 mg/L and 25, which fully meets the most stringent discharge standard (GB21906-2008). Specially, the following important conclusion can be drawn from the present study for BCPMW. (1) O3/PMS-UBAF significantly integrated advantages of O3/PMS oxidation and UBAF, and was a preferable technology for treating BCPMW. (2) The removal of particulate organic matter was depended on UBAF, and the degradation of DOM was mainly attributed to O3/PMS oxidation and UBAF. (3) Under O3/PMS oxidation, for DOM, the removal of higher MW fractions was more than that of low MW fractions, and more non-biodegradable fractions were degraded in comparison with biodegradable fractions.
19
(4) O3/PMS oxidation not only increased the overall removal of DOM but also enhanced the biodegradation rate of DOM. (5) O3/PMS-UBAF not only promoted removal of low MW fraction (＜3kDa) but also inhibited formation of higher MW fractions (3-10 kDa) that was generated by UBAF alone. Some results in the present study were not consistent with those reported by others. However, numerous previous studies indicated that the effect of oxidation on organic matter was mainly depended on experimental conditions and characteristics of wastewater studied. Further work was to deeply explore the relevant mechanism (i.e. relatively accurately examining concentration of individual oxidant in the oxidation system contained many oxidation species, relatively accurately identifying reactive oxygen species, relatively accurately distinguishing individual effect of each of reactive oxygen species on subsequent bioprocessing, relatively accurately identifying category or structure of organic matter in non-biodegradable fractions or biodegradable fractions, and etc.).
20
Acknowledgements This work was supported by an open project of the State Key Laboratory of Urban Water Resource and Environment (grant No. QA201525); an open project of Jiangsu Province Key Laboratory of Environmental Material and Environmental Engineering (grant No.K13070); and an open project of Jiangsu Province Key Laboratory of Environmental Engineering (grant No. KF2014009). References [1] C.Y. Su, Q.J. Deng, Y.X. Lu, R.H. Qin, S.L. Chen, J.W. Wei, M.L. Chen, Z. Huang, Effects of hydraulic retention time on the performance and microbial community of an anaerobic baffled reactor-bioelectricity Fenton coupling reactor for treatment of traditional Chinese medicine wastewater, Bioresour Technol 288 (2019) 1-9. [2] C.Y. Su, Y.X. Lu, Q.J. Deng, S.L. Chen, G.E. Pang, W.Y. Chen, M.L. Chen, Z. Huang, Performance of a novel ABR-bioelectricity-Fenton coupling reactor for treating traditional Chinese medicine wastewater containing catechol, Ecotox Environ Ssfe 177 (2019) 39-46. [3] L.Y. Lv, W.G. Y, Y. Li, L.Q. Meng, W. Qin, C.D. Wu, Predicting acute toxicity of traditional Chinese medicine wastewater using UV absorption and volatile fatty acids as surrogates, Chemosphere 194 (2017) 211-219. [4] W.G. Li, L.Y. Lv, X.J. Gong, W. Qin, C.D. Wu, L.Q. Meng, Performance evaluation and hydraulic characteristics of an innovative controlled double circle anaerobic reactor for treating traditional Chinese medicine wastewater, Biochem Eng J 128 (2017) 186-194. [5] L.Y. Lv, W.G. Li, C.D. Wu, L.Q. Meng, W. Qin, Microbial community composition and function in a pilot-scale anaerobic-anoxic-aerobic combined process for the treatment of
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Figure captions Fig. 1. The degradation of pollutants in BCPMW by O3/PMS oxidation, indicated by COD, color, TOC, DOC, UVA280, UVA280/TOC, SUVA280. Fig. 2. The relevant characteristics of BCPMW before and after O3/PMS oxidation ((a). pH; (b). The ratio or the relevant value (mg/L HgCL2)). Fig. 3. The degradation of pollutants in BCPMW by different treatments: (a) COD, (b) color, (c)DOC, (d) SUVA280. Fig. 4. The results for batch biodegradation experiments. Fig. 5. The relevant characteristics of BCPMW before and after O3/PMS oxidation: (a) the BDOC/DOC ratio, (b) the DOC value. Fig. 6. The effect of O3/PMS oxidation on DOM with different MW fractions. Fig. 7. The reduction of DOM with different MW fractions in BCPMW and oxidized BCPMW during UBAF treatment.
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> O3/PMS-UBAF efficiently treated BCPMW. > DOM was mainly removed by O3/PMS and UBAF. > Biodegradation rate of DOM was increased after O3/PMS oxidation. > O3/PMS presented reactivity selectivity.
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S1385-8947(20)30518-0 https://doi.org/10.1016/j.cej.2020.124527 CEJ 124527
To appear in:
Chemical Engineering Journal
Received Date: Revised Date: Accepted Date:
25 November 2019 19 February 2020 20 February 2020
Please cite this article as: G. Tang, Y. Zhang, Y. Wei, S. Wang, P. Liu, Z. Jia, X. Yu, F. Ma, Advanced treatment of bio-treated Chinese patent medicine wastewater using ozone/peroxymonosulfate-upflow biological aerated filter, Chemical Engineering Journal (2020), doi: https://doi.org/10.1016/j.cej.2020.124527
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© 2020 Published by Elsevier B.V.
Advanced
treatment
of
bio-treated
Chinese
patent
medicine
wastewater
using
ozone/peroxymonosulfate-upflow biological aerated filter
Guomin Tanga,b,c,d*, Yongbing Zhanga, Yujiang Weia, Shuang Wanga, Pei Liua, Zhehua Jiac, Xuemin Yud, Fang Mab
a
Taizhou Institute of Science and Technology, Nanjing University of Science and Technology,
Taizhou 225300, Jiangsu Province, China; b
State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of
Technology, Harbin 150090, Heilongjiang province, China; c
Province Key Laboratory of Environmental Material and Environmental Engineering,
Yangzhou University, Yangzhou 225000, Jiangsu Province, China; d
Province Key Laboratory of Environmental Engineering, Jiangsu Environmental Science
Research Institute, Nanjing 225000, Jiangsu Province, China;
Corresponding author: *Guomin Tang, Tel. /fax: +86 523 86150222; E-mail: [email protected]
1
Abstract The advanced treatment of biotreated Chinese patent medicine wastewater (BCPMW) was urgently necessitated to meet the strictest wastewater discharge standard. In the present study, combined ozone/peroxymonosulfate oxidation and upflow biological aerated filter process (O3/PMS-UBAF) significantly integrated advantages of O3/PMS oxidation and UBAF, and has been demonstrated to be very effective in the advanced treatment of BCPMW. For dissolved organic matter (DOM) in BCPMW, O3/PMS oxidation efficiently degraded higher molecular weight (MW) fractions and non-biodegradable fractions. In addition, O3/PMS oxidation not only increased the overall removal of DOM but also enhanced the biodegradation rate of DOM. Therefore, the beneficial effect of O3/PMS oxidation may mainly be due to the special effect of increased biodegradability and the generalized effect on DOM. Finally, the results also indicated that compared with UBAF alone, O3/PMS-UBAF not only promoted the removal of low MW fractions (＜3kDa) but also inhibited the formation of higher MW fractions (3-10 kDa) that was generated by UBAF alone. Key words: Biotreated Chinese patent medicine wastewater; Upflow biological aerated filter; Ozone/peroxymonosulfate; Advanced treatment; Dissolved organic matter
2
1. Introduction Chinese patent medicine wastewater was a refractory biodegradable industry wastewater, and included more refractory organic pollutants (e.g. cellulose, lignin, and etc.) [1-5]. Biological process was always regarded as a proper approach for Chinese patent medicine wastewater treatment. However, the chemical oxygen demand (COD) and color in BCPMW greatly exceeds the discharge limit in China. Thus, aiming at the strictest discharge standards, it was very necessary for Chinese patent medicine factories to develop an appropriate (namely more cost-competitive) process that could be used for the advanced treatment of BCPMW. Abbreviations BCPMW O3/PMS UBAF DOM MW TOC DOC BDOC NBDOC TE RILR
Biotreated Chinese patent medicine wastewater Ozone/peroxymonosulfate Upflow biological aerated filter Dissolved organic matter Molecular weight Total organic carbon Dissolved organic carbon Biodegradable DOC Non-biodegradable DOC Toxic equivalent Relative Inhibition Light Ratio
In comparison of other advanced treatment technologies, combined advanced oxidation-advanced aerobic treatment process has received considerable attention recently [6-8]. Upflow biological aerated filter (UBAF), as a typical of advanced aerobic process, showed an excellent performance in advanced treatment of biotreated industry wastewater contained low concentration SS and COD [9-12]. Among numerous oxidation processes,
3
ozone alone or persulfate alone did not have a significant effect in the degradation of DOM · [13, 14], however, the oxidation based on sulfate radical (SO4 , a more advantageous
oxidizing specie, E0=2.5–3.1V, relatively better selectivity, and relatively longer duration time) has recently raised a more and more attention because of the high efficiency for the non-biodegradable, hazardous, and refractory organic matter removal [15-17]. Usually, SO4· could be generated from activating PMS (HSO5−) or peroxydisulfate (S2O82−) with UV, catalysts, and etc.. However, PMS has a similar peroxo bond with H2O2, which means that PMS may be easily activated to initiate the formation of sulfate radical during ozonation [18]. In this sense, O3/PMS oxidation, as novel advanced oxidation processes, could more efficiently remove refractory matter in wastewater. Based on the degradation of pure individual compounds in model wastewater, this point was proved in the previous studies [19-22]. Unfortunately, up to now, rare study has ever been published regarding O3/PMS as an advanced oxidation processes used for treating real industry wastewater, especially it was still unclear that how organic matter in real industry wastewater was removed by O3/PMS-UBAF. Thus, a new combined process (O3/PMS-UBAF) was designed in the advanced treatment of BCPMW. The main objectives of the present study were: (1) to investigate the treatment performance of the combined process and O3/PMS oxidation; (2) to explore the relevant mechanism of the removal of organic matter in BCPWM. 2. Materials and methods 2.1. Experimental influent BCPMW was collected from a real Chinese patent medicine factory that was located in
4
Jiangsu province, China. The relevant quality of the BCPMW was summarized in Table S1. 2.2. Experimental method and installation 2.2.1. O3/PMS-UBAF treatment experiment The experimental setup (Fig. S1), which was used to investigate relevant performance of combined O3/PMS-UBAF process, and mainly included the UBAF and the oxidation reactor. Its design treatment capacity was approximately 0.24 m3/d, and all equipment was tabulated in Table S2. In the experiment, hydraulic retention time at UBAF was 4 h, gas/water ratio at UBAF was 4, and backwash period at UBAF was 7 days. O3/PMS-UBAF treatment experiment was executed at 16-28℃, and the UBAF effluent sample was withdrawn at 16-21℃. 2.2.2. O3/PMS oxidation experiment The O3/PMS oxidation was executed at a continuous mode in the oxidation reactor of the above setup (Fig. S1). The ozone–oxygen gas stream from an ozone generator (Qingdao Guolin, model CF-G-2-10g) was fed to the reaction medium through a microporous aerator with a constant flow rate at 1 atm, and the ozone concentration in input gas was adjusted by working electricity. The PMS (available as Oxone, industrial grade, 45% effective ingredient) was purchased from Wuhan Galaxy Chemical Co. Ltd and diluted into liquor with 10% mass concentrations to facilitate dosing. All oxidation experiments were conducted according to the following conditions determined by the previously preliminary test (i.e. an initial pH, 20 min oxidation, 20 mg/L O3 dosage and 50 mg/L Oxone (approximately 22.5 mg/L PMS) dosage). To rapidly terminate oxidation reaction, the 2.0 mL Na2SO3 solution (8.50 mM) was immediately added into the wastewater sample (100 mL) after oxidation. Subsequently the
5
wastewater sample was used for the relevant indicator analysis and the other experiment (i.e. batch biodegradation experiment and filtration experiment). It was to note that O3/PMS oxidation experiment was carried out at 16-28℃, but the oxidation effluent sample was withdrawn at temperature range of 16-21℃. 2.2.3. Batch biodegradation experiment Batch biodegradation experiments were conducted according to the incubation method as reported by other research groups [23, 24]. In the experiment, the aeration of 1000 ml BCPMW sample at 20℃ was used to examine biodegradable dissolved organic carbon (BDOC) or non-biodegradable dissolved organic carbon (NBDOC). During aeration, magnetic stirrer was used to provide sufficient mixing, and the water loss was compensated by adding distilled water. The dissolved organic carbon (DOC) before aeration was measured as an initial DOC. The DOC was measured after each 24 hour of aeration time (for 28 days), the constant value was examined as a NBDOC, and the difference between initial DOC and NBDOC was determined as the BDOC. 2.2.4. Filtration experiment The filtration experiment in a batch mode was used to examine the change of MW. MW distribution was characterized by the membrane with nominal cutoff values of 3, 10, 100 kDa, and 0.45 µm [25], and each fraction was collected for relevant indicator analysis. These experiments were conducted with an ultra-filtration cup (model SCM 300, Shanghai Institute of Atomic Nuclear Research, China) (Fig. S2), and the characteristics of the filtration membrane used was listed in Table S3. 2.2.5. Kinetic experiment
6
The kinetic experiment was carried out at 25-27 ℃ with a 500 mL-capacity glass in the setup (Fig. S3), and the ozone generator (Guangzhou Baifeng, model BF-YE-2g) provided the ozone. At 10 min interval, the wastewater sample (10 mL) was withdrawn from the setup, and the 0.2 mL Na2SO3 solution (8.50 mM) was immediately added into the wastewater sample. Subsequently, the wastewater sample was filtrated with membrane (0.45 µm), and the processed sample was used to examine the DOC. 2.3. Analytical method Standard methods, as set up by China Ministry of Environmental Protection, were used for determining the relevant indicator value (i.e. Color degrees, BOD, COD, SS, and acute toxicity) [26]. During COD examining, K2Cr2O7 was used. The pH was determined by pH meter
(PHS-25),
and
UV
absorbance
(UVA280)
was
examined
by
UV-Visible
Spectrophotometer (SHI-MADZUT6). Total organic carbon (TOC) analyzer (TOC-VCPH) was used for the measurement of DOC and TOC. 3. Results and Discussion 3.1. O3/PMS oxidation The degradation of pollutant in BCPMW by O3/PMS oxidation was determined. The results were presented in Fig. 1, where the degradation was indicated by the removal of COD, color, TOC, DOC, UVA280, UVA280 /TOC, UVA280 /DOC (namely SUVA280). Fig. 1 By O3/PMS oxidation, the COD and TOC was reduced by 60.28% and 44.06% respectively, and the DOC was decreased from 88.4 to 42.0 mg/L, giving a removal efficiency of 52.49%. These results indicated O3/PMS oxidation was relatively successful at
7
mineralizing the DOC in BCPMW. At the same time, O3/PMS oxidation presented an excellent de-colorization performance as indicated by the high removal of color (75.26%) (Fig.1). The observed effects of O3/PMS oxidation on changes in these indicators (i.e. COD, color, and DOC) were similar with those reported in other oxidation systems [27, 28]. Furthermore, the 79.06% UVA 280 decrease was obtained in the experiment (Fig. 1). It can be concluded from the high removal in color and UVA 280 that the structure of organic matter in BCPMW was significantly decomposed by O3/PMS oxidation. Meanwhile, this was accompanied by a 62.75% decrease of UVA280/TOC, which was lower than the UVA280 decrease (79.06%). These results were basically consistent with those reported in the literature [29]. At the same time, the decrease was 55.80% for SUVA280, which was slightly lower than that in the literature [29]. It was well known that some characteristics of the wastewater (i.e. pH, acute toxicity, and biodegradability) would influence the bio-treatment of the wastewater. Thus, the effect of O3/PMS oxidation on BCPMW characteristics was also investigated. As presented in Fig. 2 (a), at an initial pH (7.4-8.9), the pH of oxidized BCPMW varied from 7.1 to 8.7. This results means that the pH would not influence the subsequent bio-treatment of oxidized BCPMW. Furthermore, the slight decline of pH (approximately 0.2 pH units) was also observed after O3/PMS oxidation. The possible explanation for this was that during O3/PMS oxidation, organic acids (i.e. carboxylic acids) were generated and PMS was decomposed. The phenomenon was also observed in other study [30]. Fig. 2 Meanwhile, as illustrated in Fig. 2 (b), the toxic equivalent (TE) and the relative
8
inhibition light ratio (RILR) of BCPMW by O3/PMS oxidation significantly lowered from 0.08 mg/L (HgCL2) to 0.02 mg/L (HgCL2), and 36% to 9%, respectively. These results were consistent with those in other study on advanced oxidation processes [27]. The results mean that the toxicity of oxidized BCPMW was weak, and the inhibitory effect of the toxicity pollutant in oxidized BCPMW on microbial growth during subsequent biodegradation was slight. Furthermore, the BOD5/COD value of BCPMW was examined before and after O3/PMS oxidation. As Fig. 2 (b) shown, BCPMW presented poor biodegradability (BOD5/COD = 0.143), but the biodegradability of oxidized BCPMW was significantly improved (BOD5/COD=0.497). These results suggested that O3/PMS oxidation has good performance on the enhancement of the wastewater biodegradability. The change trends on wastewater biodegradability during O3/PMS oxidation were also observed in other oxidation systems [27, 28]. It can be seen from the results that O3/PMS oxidation basically presented a positive effect on some characteristics of BCPMW (i.e. pH, acute toxicity, and biodegradability), and the oxidized BCPMW was suitable for the further bio-treatment. 3.2. DOC removal kinetics during O3/PMS oxidation With the assumption of pseudo-first-order, the following Eqs. (1) can be used to express DOC removal rate in the O3/PMS oxidation stage. ln (C/C0)=−Kt
(1)
Where t was the oxidation time, C was DOC value at the different t, C0 were the DOC in influent, and K was the rate constant. Under optimum conditions, the relationship between ln (C/C0) and t was shown in Fig. S4. The linear fitting of ln (C/C0) as a function of t leads to K=0.0177 and R2=0.9072, as 9
shown in Fig. S4. Therefore, during the O3/PMS oxidation, the DOC removal basically followed the first order (Eq. (2)). ln (C/C0) = − 0.0177*t
(2)
3.3. O3/PMS-UBAF treatment 3.3.1. Treatment performance The treatment of BCPMW by UBAF alone and combined O3/PMS-UBAF process was examined. The quantitative comparison of the treatment of BCPMW by above two processes was showed in Fig.3. Fig.3 The UBAF alone decreased COD from 322.6 to 206.8 mg/L (35.90% removal) and reduced DOC from 88.40 to 72.66 mg/L (17.81% removal), which was lower than the reduction observed in O3/PMS oxidation (Fig.3). At the same time, the removal of color and SUVA 280 by UBAF alone was only 20.45% and 6.35%, respectively, which was also lower than those by O3/PMS oxidation (Fig.3). Furthermore, for TOC, UBAF alone obtained a 35.92% removal. Compared with UBAF alone, combined O3/PMS-UBAF process significantly promoted the organic matter removal. Specially, it increased DOC removal from 17.81% to 77.60%, COD removal from 36.9% to 85.68%, color removal from 20.45% to 81.79%, and SUVA280 removal from 6.35% to 59.67% (Fig.3). Furthermore, 80.90% TOC removal was also observed during O3/PMS-UBAF treatment. The quality of the effluent after O3/PMS-UBAF treatment meets the most stringent discharge standard (namely, discharge standard of water pollutants for pharmaceutical industry Chinese traditional medicine category (GB21906-2008), and the value for COD and color in this standard were respectively 50 mg/L and 30 times). 10
Finally, the TE and RILR of the effluent after O3/PMS-UBAF treatment were only 0.01 mg/L (HgCL2) and 3%, respectively. This means that the toxicity impact of the pollutants in O3/PMS-UBAF effluent on receiving water bodies was negligible. 3.3.2. Treatment cost The cost of O3/PMS oxidation was calculated, and the results were listed in Table S4. The calculated cost was 1.0038 $ /Kg COD removed for the O3/PMS oxidation, being 84.15% and 94.0% of that for O3/H2O2 oxidation and O3/persulfate oxidation respectively. These results indicated that O3/PMS oxidation could remove more organic matter (COD) at a relatively lower cost. In other words, compared with other advanced oxidation processes in Table S4, O3/PMS oxidation was more cost-competitive. Generally speaking, for subsequent biotreatment, O3/PMS oxidation was a preferable pretreatment process. The cost of O3/PMS oxidation was 1.0038 $/Kg COD removed for the removal of COD from 322.60 to 128.14 mg/L (Table S4 and Fig. 3). What’s more, the cost was 0.1938 $/Kg COD removed for the subsequent UBAF that further remove the COD from 128.4 to 46.2 mg/L, only being 19.31% of that for O3/PMS oxidation (Table S4 and Fig. 3). Furthermore, among three combined processes in Table S4, O3/PMS-UBAF presented the cheapest cost and the lowest O3 dosage. This result suggested that for O3/PMS-UBAF treatment, with the decrease of the ozone generator power, the stability of the process operation would correspondingly improve, and the investment on the ozone generator would correspondingly decrease. 3.4. Batch biodegradation experiments The results from batch biodegradation experiments were shown in Fig.4. As reported in
11
the previous literature [31, 32], the decrease of the DOC concentration at an initial period was significantly more rapid than that after this period. During batch biodegradation, the residual amount of DOC, corresponding to the NBDOC, basically remained unchanged (Fig.4). Fig.4 With the assumption of pseudo first order, and the DOC concentration during biodegradation can be expressed as Eq. (3) [33]. DOC = NBDOC + BDOC·e-kt
(3)
Where k was the biodegradation rate constant, and t was the biodegradation time. The Eq. (3) was used to fit experiment data from batch biodegradation (ExpDecay1), and the results were presented in Fig.4. After O3/PMS oxidation, the biodegradation rate constant of DOM in BCPMW increased from 0.1861 d-1 to 0.2750 d-1 (approximately 47.77% enhancement) (Fig.4). Yavich et al. [31] reported that the biodegradation rate increased with the increase of the ozone dose. On the contrary, it was reported that the overall kinetics was basically unchanged after the ozonation [32, 34]. Our results indicated that O3/PMS oxidation has a significant effect on the biodegradation rate of DOM in BCPMW. This means that the wastewater quality would still influence biodegradation rate, even though UBAF reached steady state. The difference may mainly be due to the variations in wastewater characteristics and oxidation conditions. Fig.5 At the same time, the ratio of BDOC to DOC in BCPMW increased from 0.3428 to 0.6595 after O3/PMS oxidation (Fig.5). The result indicated that O3/PMS oxidation significantly enhanced the biodegradability of DOM, which contradicts results reported by
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Black and Be´rube´ [32]. In their works, the ratio of BDOC to DOC in wastewater before and after oxidation remained unchanged at approximately 0.5. However, this result was basically consistent with that reported in the literature [24]. In the literature, after persulfate/H2O2 oxidation, the ratio of biodegradable COD to COD in stabilized landfill leachate significantly increased from approximately 0.3659 to approximately 0.6667 [24]. Fig.5 also showed that by O3/PMS oxidation, the concentration of NBDOC was significantly decreased (75.34% reduction), but the removal of BDOC was slight (only 8.88%). These results suggested that for DOM in BCPMW, O3/PMS oxidation degraded non-biodegradable fractions more efficiently than biodegradable fractions, which were basically consistent with those previously reported by others. In their works, Hilles et al. [24] reported that the removal of non-biodegradable COD (86.0%) was much more than that of biodegradable COD (54.5%) during the O3/persulfate oxidation of the landfill leachate. Black and Be´rube´ [32] observed that after UV/H2O2 oxidation at suitable conditions, the removal of NBDOC (approximately 50%) was more than that of BDOC (approximately 30%). Furthermore, our results also indicated that O3/PMS oxidation did not present a significantly effect on the BDOC formation, which was not consistent with results reported in the previous literature [34, 35]. Digiano et al. [34] reported that the concentration of BDOC was increased with the ozone dose increase. It was also reported that BDOC concentration instead increased after UV/H2O2 oxidation [35]. 3.5. Degradation of different MW fractions during O3/PMS oxidation The MW distributions were divided into five fractions: F1 (＜3kDa), F2 (3-10kDa), F3 (10-100kDa), F4 (100kDa-0.45 µm), and F5 (＞0.45 µm). The removal of organic matter with
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different MW was investigated during O3/PMS oxidation. 3.5.1. Particulate organic carbon removal The particulate organic carbon was calculated according to the difference between TOC and DOC, and used to indicate the removal of the particulate organic matter (namely organic matter in F5). The particulate organic carbon included the non-biodegradable particulate organic carbon and the biodegradable particulate organic carbon. In BCPMW, the ratio of non-biodegradable particulate organic carbon (35.86 mg/L) to particulate organic carbon (37.1 mg/L) was up to 96.66%, and the biodegradable particulate organic carbon (only 1.24 mg/L) was negligible. The removal of particulate organic carbon and non-biodegradable particulate organic carbon in BCPMW was respectively 24.0% and 24.21% during O3/PMS oxidation. This may be one of reasons that the removal efficiency of TOC in BCPMW was low (44.06%) (Fig.1). Abu Amr et al. [36] observed that for particulate organic matter, advanced oxidation processes did not obtain more degradation. In their works, particulate COD was used for indicating the decrease of particulate organic matter in the stabilized leachate, and removed by only 40% during the O3/Fenton oxidation [36]. 3.5.2. DOC removal Fig.6 showed the removal of DOC in different MW fractions. Fig.6 As presented in Fig.6, after O3/PMS oxidation, the removal of 79.68%, 66.13%, 57.31%, and -28.37% was respectively observed for F4, F3, F2, and F1. These results indicated that O3/PMS oxidation removed the DOC in high MW fractions more efficiently than that in low MW fractions, which was basically consistent with those reported by Zhang et al. [25]. In
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their works, after ozonation, an 88% or more removal of DOC in higher MW fractions (F4 and F3) was observed, but the removal of DOC in lower MW fractions (F2) was lower (approximately 69.2%) [25]. Furthermore, the increase in concentration of DOC in F1 indicated that larger organic matter was oxidized to smaller organic matter, which was consistent with results in other studies on advanced oxidation processes [32, 37]. In these studies, ozonation increased the concentration of DOC in low MW fractions [32, 37]. However, this result also contradicts that reported by Zhang et al. [25]. In their works, neither S2O82- oxidation nor ozonation achieved the increase of the concentration of DOC in low MW fractions [25]. Fig.6 also exhibited that the total removal of DOC was 52.49% after O3/PMS oxidation. During ozonation at a 50 mg/L O3 dose, an extremely low removal of DOC (only 6%) was observed by Wang et al. [29]. However, an approximately 60% DOC was removed by UV/H2O2 treatment at a suitable condition [32]. These variations were likely due to the difference in experimental conditions and wastewater characteristics. Generally, O3/PMS oxidation resulted into the decomposition and partial oxidation of DOM. As shown in Fig.6, the NBDOC in higher MW fractions (F3 and F4) was approximately 80.86% of total NBDOC, and removed by 78.22% by O3/PMS oxidation. The removal of NBDOC was 83.33% and 47.23% for F2 and F1, respectively (Fig.6). These results suggested that for non-biodegradable dissolved organic matter in BCPMW, the removal of high MW fractions overtook that of low MW fractions, which were basically consistent with some results from other research [32]. Fig.6 also illustrated the removal of BDOC in different MW fractions. For higher MW fractions (namely F4 and F3), the BDOC removal followed similar trends to that of NBDOC,
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and was up to 59.69% (Fig.6). These results were consistent with those from other research [32]. But for low MW fractions (namely F1), the BDOC instead significantly increased (approximately 72.28%), which were also consistent with results reported in the literature [32]. In the literature, the BDOC in low MW (300-500Da) fractions significantly increased (approximately 66.67% increase as indicated by area count) after UV/H2O2 treatment at a dose of 4000 mJ/cm2 and 10 mg/L H2O2 [32]. Furthermore, in the present study, the ratio of BDOC to DOC in BCPMW increased from 0.3428 to 0.6595 after O3/PMS oxidation (Fig.5). The above results suggested that O3/PMS oxidation increased the biodegradability of DOM by oxidation larger organic matter to smaller organic matter. Generally, O3/PMS oxidation degraded higher MW fractions more efficiently than low MW fractions in DOM, and had a significant effect on the concentrations and characteristics of DOC. In previous studies, some research groups thought that advanced oxidation (e.g., ozonation, and etc.) always equally reacts with organic matter. However, Black and Be´rube´ [32] observed that after UV/H2O2 oxidation at suitable conditions, the removal of NBDOC (approximately 50%) was more than that of BDOC (approximately 30%). Wang et al. [29] reported that for DOM in BDFW, ozonation can more efficiently degrade chromophore fractions than non- chromophore fractions. It was reported that BDOC concentration instead increased after UV/H2O2 oxidation [34, 35]. Hilles et al. [24] reported that the removal of non-biodegradable COD (86.0%) was much more than that of biodegradable COD removal (54.5%) during the O3/persulfate oxidation of the landfill leachate. Furthermore, Black and Be´rube´[32] also observed that ozonation predominantly affected the absorbance of
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chromophoric natural organic matter with an MW less than 3kDa, UV/H2O2 oxidation at suitable conditions preferentially removed the NBDOC and BDOC in larger MW fraction, and UV/H2O2 oxidation at suitable conditions preferentially reacted with chromophoric natural organic matter with higher MW. These differences in reaction may mainly be attributed to the variations in experimental conditions and characteristics of the wastewater studied. 3.6. Degradation of different MW fractions during UBAF treatment 3.6.1. Particulate organic carbon removal Alone UBAF decreased the particulate organic carbon in BCPMW from 37.1 mg/L to 8.16 mg/L (removal 78.01%), which was significantly more than the removal observed in response to O3/PMS oxidation (24.0%). Furthermore, UBAF alone significantly removed the particulate organic carbon in oxidized BCPMW (removal 85.43%). For UBAF, as the bio-adsorption has been excluded after long time operation, the filtration was mainly responsible for the removal of particulate organic carbon. 3.6.2. DOC removal Fig.7 As presented in Fig.7, the removal of DOC in BCPMW was low after UBAF alone treatment (only 12.60%). For BCPMW, UBAF alone decreased the DOC in low MW fractions more efficiently than that in high MW fraction, with removals of 55.66%, -7.68%, 10.51%, and 2.62% being observed for F1, F2, F3, and F4, respectively (Fig.7). These variations on the removals of DOC in different MW fractions indicated that UBAF alone not only can degrade DOM with low MW (F1) but also form some DOM with higher MW (F2).
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Unfortunately, up till now, the report on quantitative information of converting and mineralization was rare for lack of the effective analysis method. The previous studies also reported the formation of some DOM with relatively higher MW during bio-treatment [29, 37]. This may be because some conjugated protein-like substance was generated during bio-treatment. Furthermore, the removal of DOC in oxidized BCPMW was determined, and used to appraise the effect of O3/PMS oxidation on following UBAF performance. As shown in Fig.7, UBAF removed the 52.83% DOC in oxidized BCPMW, and the removal of DOC in oxidized BCPMW was more than four times as much as that in BCPMW. This may be because that during O3/PMS oxidation, more rapidly BDOC (BDOCr) was formed in wastewater. These results indicated that O3/PMS oxidation was helpful for the improvement of the performance of subsequent UBAF. For oxidized BCPMW, the removal of DOC was 74.69%, 66.51%, 19.51%, and 8.04% for F1, F2, F3, and F4, respectively (Fig.7). As the bio-adsorption in the UABF has been excluded at steady state, the removal of low MW DOC in oxidized BCPMW may mainly be due to the biodegradation. Furthermore, comparison of the removals of DOC in BCPMW and oxidized BCPMW suggested that for DOM, O3/PMS-UBAF can inhibit the formation of higher MW fractions (F2) and increase the removal of low MW fractions (F1). The likely reason could be that O3/PMS oxidation produces some small DOM that they were easily to mineralization by following UBAF rather than converting to larger DOM. The same phenomenon was reported in the previous studies [29, 38]. The results in the present study suggested that O3/PMS-UBAF significantly integrated advantages of O3/PMS oxidation and UBAF, enabling it to remove more particulate organic
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matters, destruct non-biodegradable organic matters, and then mineralize more biodegradable organic matters. Generally, combination O3/PMS-UBAF process was a preferable technology for treating BCPMW. Furthermore, as previously discussed, O3/PMS oxidation influenced not only the amount of DOC but also the biodegradation rate of DOC. Therefore, the beneficial effect of O3/PMS oxidation prior to UBAF may mainly be due to the special effect of increased biodegradability and the generalized effect on DOM. 4. Conclusions It was proved that under experimental conditions (i.e. an initial pH, 20 min oxidation, 20 mg/L O3 dosage, 50 mg/L Oxone dosage, gas to liquid ratio at UBAF (4), hydraulic retention time at UBAF (4 h), backwash period at UBAF (7 days), temperature (16–28 ℃ )), O3/PMS-UBAF can efficiently degrade the pollutants in BCPMW, with removal of 77.60%, 85.68%, 81.79% for DOC, COD, color, respectively. The COD and color in the tread BCPMW by O3/PMS-UBAF were less than 48 mg/L and 25, which fully meets the most stringent discharge standard (GB21906-2008). Specially, the following important conclusion can be drawn from the present study for BCPMW. (1) O3/PMS-UBAF significantly integrated advantages of O3/PMS oxidation and UBAF, and was a preferable technology for treating BCPMW. (2) The removal of particulate organic matter was depended on UBAF, and the degradation of DOM was mainly attributed to O3/PMS oxidation and UBAF. (3) Under O3/PMS oxidation, for DOM, the removal of higher MW fractions was more than that of low MW fractions, and more non-biodegradable fractions were degraded in comparison with biodegradable fractions.
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(4) O3/PMS oxidation not only increased the overall removal of DOM but also enhanced the biodegradation rate of DOM. (5) O3/PMS-UBAF not only promoted removal of low MW fraction (＜3kDa) but also inhibited formation of higher MW fractions (3-10 kDa) that was generated by UBAF alone. Some results in the present study were not consistent with those reported by others. However, numerous previous studies indicated that the effect of oxidation on organic matter was mainly depended on experimental conditions and characteristics of wastewater studied. Further work was to deeply explore the relevant mechanism (i.e. relatively accurately examining concentration of individual oxidant in the oxidation system contained many oxidation species, relatively accurately identifying reactive oxygen species, relatively accurately distinguishing individual effect of each of reactive oxygen species on subsequent bioprocessing, relatively accurately identifying category or structure of organic matter in non-biodegradable fractions or biodegradable fractions, and etc.).
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Acknowledgements This work was supported by an open project of the State Key Laboratory of Urban Water Resource and Environment (grant No. QA201525); an open project of Jiangsu Province Key Laboratory of Environmental Material and Environmental Engineering (grant No.K13070); and an open project of Jiangsu Province Key Laboratory of Environmental Engineering (grant No. KF2014009). References [1] C.Y. Su, Q.J. Deng, Y.X. Lu, R.H. Qin, S.L. Chen, J.W. Wei, M.L. Chen, Z. Huang, Effects of hydraulic retention time on the performance and microbial community of an anaerobic baffled reactor-bioelectricity Fenton coupling reactor for treatment of traditional Chinese medicine wastewater, Bioresour Technol 288 (2019) 1-9. [2] C.Y. Su, Y.X. Lu, Q.J. Deng, S.L. Chen, G.E. Pang, W.Y. Chen, M.L. Chen, Z. Huang, Performance of a novel ABR-bioelectricity-Fenton coupling reactor for treating traditional Chinese medicine wastewater containing catechol, Ecotox Environ Ssfe 177 (2019) 39-46. [3] L.Y. Lv, W.G. Y, Y. Li, L.Q. Meng, W. Qin, C.D. Wu, Predicting acute toxicity of traditional Chinese medicine wastewater using UV absorption and volatile fatty acids as surrogates, Chemosphere 194 (2017) 211-219. [4] W.G. Li, L.Y. Lv, X.J. Gong, W. Qin, C.D. Wu, L.Q. Meng, Performance evaluation and hydraulic characteristics of an innovative controlled double circle anaerobic reactor for treating traditional Chinese medicine wastewater, Biochem Eng J 128 (2017) 186-194. [5] L.Y. Lv, W.G. Li, C.D. Wu, L.Q. Meng, W. Qin, Microbial community composition and function in a pilot-scale anaerobic-anoxic-aerobic combined process for the treatment of
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Figure captions Fig. 1. The degradation of pollutants in BCPMW by O3/PMS oxidation, indicated by COD, color, TOC, DOC, UVA280, UVA280/TOC, SUVA280. Fig. 2. The relevant characteristics of BCPMW before and after O3/PMS oxidation ((a). pH; (b). The ratio or the relevant value (mg/L HgCL2)). Fig. 3. The degradation of pollutants in BCPMW by different treatments: (a) COD, (b) color, (c)DOC, (d) SUVA280. Fig. 4. The results for batch biodegradation experiments. Fig. 5. The relevant characteristics of BCPMW before and after O3/PMS oxidation: (a) the BDOC/DOC ratio, (b) the DOC value. Fig. 6. The effect of O3/PMS oxidation on DOM with different MW fractions. Fig. 7. The reduction of DOM with different MW fractions in BCPMW and oxidized BCPMW during UBAF treatment.
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> O3/PMS-UBAF efficiently treated BCPMW. > DOM was mainly removed by O3/PMS and UBAF. > Biodegradation rate of DOM was increased after O3/PMS oxidation. > O3/PMS presented reactivity selectivity.
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