Accepted Manuscript Effects of sludge retention times on reactivity of effluent dissolved organic matter for trihalomethanes formation in hybrid powdered activated carbon membrane bioreactors Defang Ma, Baoyu Gao, Chufan Xia, Yan Wang, Qinyan Yue, Qian Li PII: DOI: Reference:
S0960-8524(14)00748-2 http://dx.doi.org/10.1016/j.biortech.2014.05.082 BITE 13490
To appear in:
Bioresource Technology
Received Date: Revised Date: Accepted Date:
1 April 2014 19 May 2014 21 May 2014
Please cite this article as: Ma, D., Gao, B., Xia, C., Wang, Y., Yue, Q., Li, Q., Effects of sludge retention times on reactivity of effluent dissolved organic matter for trihalomethanes formation in hybrid powdered activated carbon membrane bioreactors, Bioresource Technology (2014), doi: http://dx.doi.org/10.1016/j.biortech.2014.05.082
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Effects of sludge retention times on reactivity of effluent dissolved organic matter for trihalomethanes formation in hybrid powdered activated carbon membrane bioreactors Defang Ma, Baoyu Gao*, Chufan Xia, Yan Wang, Qinyan Yue, Qian Li a
Shandong Key Laboratory of Water Pollution Control and Resource Reuse, School of
Environmental Science and Engineering, Shandong University, Ji’ nan 250100, China
Abstract: In this study, real municipal wastewater intended for reuse was treated by two identical hybrid PAC/MBRs (membrane bioreactors with powdered activated carbon addition), which were operated at sludge retention times (SRTs) of 30 and 180 days, respectively. In order to investigate the effects of SRT on trihalomethanes (THMs) formation in chlorinated PAC/MBR effluents, characteristics and THMs formation reactivity of effluent dissolved organic matter (EfOM) at different SRTs were examined. PAC/MBR-180 had higher level of EfOM, which contained less simple aromatic proteins and exhibited lower specific UV absorbance (SUVA). EfOM with molecular weight k2 ; t ( h ) is the reaction time. 2.5 Analytical methods BOD5, COD, NH3–N, NO2–N, NO3–N, MLSS and MLVSS were measured according to the APHA standard methods (APHA, 1998). Turbidity was examined by a portable microprocessor turbidity meter (Hanna, Italy). DO and pH were measured by a portable DO meter (Precision & Scientific Instrument, China) and a pH meter (Luo Qi Te, China), respectively. DOC was quantified with a TOC-VCPH Total Organic Carbon Analyzer (SHIMADZU, Japan). UV254 was measured with TU-1810 UV/VIS spectrophotometer (PGENERAL, China). SUVA was calculated as the ratio of UV254 to DOC. Concentrations of Br− and Cl− were determined by ion chromatogram (Model: DX-100, Dionex, USA). Residual chlorine was measured with a Free & Total chlorine measuring meter (HANNA, Italy) according to the DPD powder pillow photometric method (APHA, 1998). THMs including bromodichloromethane (CHBrCl2), dibromochloromethane (CHBr2Cl), trichloromethane (CHCl3) and tribromomethane (CHBr3) were extracted by the headspace method (Gary L. Emmert, 2004) and determined with a gas chromatography with ECD detector (SHIMADZU, Japan) according to the standard analyzing methods of EPA 551.1
7
(USEPA, 1995). 3. Results and Discussion 3.1 Water quality of PAC/MBR effluents at different SRTs Water quality characteristics of effluents from PAC/MBRs at SRT of 30 and 180 days are shown in Table 1. The water quality of effluents at both SRTs was excellent and stable, proving the capacities of hybrid PAC/MBRs in municipal wastewater treatment and reclamation. The PAC/MBR effluent at SRT of 180 days exhibited better quality in terms of COD, BOD5, NH3–N, NO2–N, NO3–N, Br− and Cl−, but had higher levels of DOC and UV254 than PAC/MBR-30 effluent. Higher sludge concentration in PAC/MBR at SRT 180 days (MLSS, 6.23 g/L) improved the biodegradation of organic substances and nutrients in wastewater. However higher microorganism amount at long SRT led to more production of EPS and SMP, resulting in high DOC level in effluent. Although the PAC/MBR effluent at SRT of 30 days had lower DOC and UV254, its higher SUVA indicated a relative high content of aromatic components. This can be explained by that acclimated succession microorganisms on/in BAC formed in PAC/MBR at longer SRT (180 days) could degrade refractory DOM especially aromatic compounds, while these bacteria were absent at SRT 30 days. 3.2 Apparent MW distributions of EfOM at different SRTs Apparent MW distributions of DOM in effluents from PAC/MBRs operated at SRT of 30 and 180 days are shown in Fig. 1A. The EfOM had a broad spectrum of MW. Over 45% of the EfOM had MW of larger than 30 kDa. Compared with the >100 and 30–100 kDa fractions, a smaller amount of EfOM was represented in each of the 10–30, 5–10, 1–5 and NHoS > HoN. The PAC/MBR-30 EfOM exhibited higher SUVA than that of PAC/MBR-180 for each XAD-8 fraction except NHoS. For PAC/MBR-30, HoA exhibited rather high SUVA even higher than that of the source water, which was consistent with previous studies (Kitis et al., 2002; Zhang et al., 2009).
10
3.4 EEM spectra of EfOM at different SRTs The EEM spectra are divided into five regions that represent specific components of DOM according to (Chen et al., 2003). They are as follows: Region I (Aromatic proteins I), Region II (Aromatic proteins II), Region III (Fulvic-like acids), Region IV (Soluble microbial-like products) and Region V (Humic-like acids) (Fig. 2). EfOM at both SRTs had fluorophores in regions III and IV. However, the fluorescence maxima of region III in PAC/MBR-30 EfOM were slightly red-shifted along the excitation axis compared with PAC/MBR-180 EfOM. The red shift indicated the transition of EfOM chemical compositions from fulvic-like acids to humic-like acids. In addition, EfOM at SRT of 30 days had an EEM center in region V, whereas EfOM at SRT of 180 days effluent exhibited an EEM shoulder. Fluorescence regional integration (FRI) was conducted for the quantitative analysis of the fluorescence spectra by using the following equations (Chen et al., 2003):
Φi,n = MFi ∫
∫
ex em
Pi , n =
Φ i ,n ΦT , n
I (λexλem )d λex d λem
×100%
(1)
(2)
Where Φ i , n is the normalized EEM volume at region i that represents the cumulative fluorescence response of DOM with similar properties; I (λex λem ) is the fluorescence intensity at each excitation–emission wavelength pair; MFi is a multiplication factor applied to account for the secondary or tertiary responses at longer wavelengths, which is equal to the inverse of the fractional projected excitation–emission area. Pi , n is the percent
11
i =V
fluorescence response, and ΦT , n = ∑ Φ i ,n . As shown in Table 2, of the fluorescence EfOM i= I
at both SRTs, soluble microbial-like products were the most abundant components, accounting for more than 45% of the total cumulative fluorescence intensities. In addition, the cumulative fluorescence intensities of soluble microbial by-product-like in PAC/MBR-180 EfOM were higher than that of PAC/MBR-30 EfOM. Region III (fulvic-like acids) exhibited the second highest Φ values at both SRTs, which represented about 20% of the total fluorescent EfOM. The cumulative fluorescence intensities for PAC/MBR-30 EfOM were in the order of: region V > region II > region I, while the order was region II > region V > region I for PAC/MBR-180 EfOM. Compared with PAC/MBR-180 EfOM, PAC/MBR-30 EfOM contained larger amount of aromatic proteins I (simple aromatic proteins such as tyrosine). 3.5 THMs formation and speciation of PAC/MBR effluents at different SRTs
THMFP and THMs formation reactivity (specific THMFP) of PAC/MBR effluents at both SRTs is shown in Fig. 3. Effluents at SRT of 30 days exhibited much higher THMFP (612.83 µg/L, Fig. 3A) and specific THMFP (149.54 µg/mg-DOC, Fig. 3B) than that at SRT of 180 days. And that the proportion of initial carbons present in EfOM ended up as THMs at SRT 30 days was much higher than that at SRT 180 days (Table 3), which followed the same trend of THMs yields. CHBrCl2, CHBr2Cl, CHCl3 and CHBr3 were detected in both chlorinated samples. CHCl3 was the predominant THMs species in both effluents. And the yield of THMs species in order was CHCl3 > CHBrCl2 > CHBr2Cl > CHBr3. The distributions of THMs species at different SRTs were similar each other, but the proportion of individual THMs
12
varied. The proportion of CHCl3 in the chlorinated effluent at SRT 30 days was higher than that at SRT 180 days, while the proportion of each of the three bromine-containing THMs in the chlorinated PAC/MBR-180 effluent was higher than PAC/MBR-30 effluent. Bromine incorporation factor ( n ) representing the incorporation of Br into THMs and the formation of Br-THMs was used to facilitate understand the THMs speciation at different SRTs. As shown in Table 3, the effluent at SRT 180 had much highr n value than that at SRT 30 days. Long SRT reduced THMs formation reactivity of EfOM, but increased the formation of bromine-containing species during chlorination of PAC/MBR effluents. THMs formation and speciation are depended on the DOM characteristics (Ma et al., 2013b; Zhang et al., 2009). Effects of DOM MW on THMs formation in nature water and wastewater water are different. It is reported that THMs formation reactivity increased as the MW of DOM in river water decreased (Gang et al., 2003; Zhao et al., 2006). However our previous study indicated that HMW DOM in MBR treated municipal wastewater was the primary THMs precursors (Ma et al., 2014). Hydrophobic DOM especially HoA and aromatic proteins have high THMs formation reactivity (Ma et al., 2014; Zhang et al., 2009). As shown in Fig. 4, HMW EfOM and HoA exhibited higher THMs formation reactivity than LMW and hydrophilic fractions for PAC/MBR effluents, whereas LMW and hydrophilic EfOM had high ability to produce bromine-containing THMs. In addition, EfOM at SRT 180 days exhibited lower THMs formation reactivity but higher bromine incorporation factor ( n ) than that at SRT 30 days for each size and XAD-8 fractions. Thus the relative lower contents of HMW and hydrophobic DOM and simple aromatic protein might account for
13
the lower THMs yields of PAC/MBR-180 EfOM. And the higher production of bromine-containing THMs in PAC/MBR-180 effluent was possibly due to the higher level of LMW and hydrophilic DOM. THMs formation kinetics of EfOM at different SRTs is provided in Supplemental information Fig. S2. TTHM formation kinetics parameters are listed in Table 4. For both effluents, the TTHM data fit the DBPs formation model well with correlation coefficients of 0.99, indicating that THMs formation in chlorinated PAC/MBR effluents was fundamentally depended on chlorine consumption (Gang et al., 2003). TTHM yield coefficient and rapid and slow reaction rates of EfOM at SRT 30 days were higher than that at SRT 180 days. Particularly, the rapid reaction rate of PAC/MBR-30 EfOM was about 12 times higher than that of PAC/MBR-180 EfOM. As can be seen from the x values listed in Table 4, most of THMs precursors in PAC/MBR EfOM at both SRTs were slow reacting agents. Since halogenated intermediates derived from PAC/MBR effluent SMP were difficult to decompose, most THMs were formed after 24 h chlorination. 5. Conclusions
The results indicated that prolonging SRT in PAC/MBR increased EfOM level, but reduced the relative content of aromatic components, which are the primary DBPs precursors. Longer SRT improved the removal of HMW EfOM due to the biodegradation by acclimated succession microorganisms. The greater refreshment of PAC at low SRT enhanced the adsorption removal of LMW EfOM (< 5kDa). EfOM at short SRT exhibited higher hydrophobicity. Prolonging SRT reduced THMs formation reactivity of EfOM, but increased the formation of bromine-containing species during chlorination of PAC/MBR effluents.
14
Acknowledgements
The research was financially supported by the Key Scientific Technology Program for Environmental Protection of Shandong, China (16).
References
1. APHA, 1998. Standard Methods for the Examination of Water and Wastewater, 20th ed., Washington, DC. 2. Chellam, S., Krasner, S.W., 2001. Disinfection byproduct relationships and speciation in chlorinated nanofiltered waters. Environ. Sci. Technol. 35, 3988-3999. 3. Chen, W., Westerhoff, P., Leenheer, J.A., Booksh, K., 2003. Fluorescence Excitation−Emission Matrix Regional Integration to Quantify Spectra for Dissolved Organic Matter. Environ. Sci. Technol. 37, 5701-5710. 4. Ebie, K., Li, F., Azuma, Y., Yuasa, A., Hagishita, T., 2001. Pore distribution effect of activated carbon in adsorbing organic micropollutants from natural water. Water Res. 35, 167-179.
5. Gang, D., Clevenger, T.E., Banerji, S.K., 2003. Relationship of chlorine decay and THMs formation to NOM size. J. Hazard. Mater. A96, 1-12. 6. Gary L. Emmert, G.C., Gija Geme, Neena Joshi, and Mostafizur Rahman, 2004. Methods for Real-Time Measurement of THMs and HAAs in Distribution Systems. AwwaRF, Denver. 7. Guo, W., Vigneswaran, S., Ngo, H.H., Xing, W., Goteti, P., 2008. Comparison of the performance of submerged membrane bioreactor (SMBR) and submerged membrane adsorption bioreactor (SMABR). Bioresour. Technol. 99, 1012-1017.
15
8. Hu, J., Shang, R., Deng, H., Heijman, S.G.J., Rietveld, L.C., 2014. Effect of PAC dosage in a pilot-scale PAC–MBR treating micro-polluted surface water. Bioresour. Technol. 154, 290-296.
9. Kitis, M., Karanfil, T., Wigton, A., Kilduff, J.E., 2002. Probing reactivity of dissolved organic matter for disinfection by-product formation using XAD-8 resin adsorption and ultrafiltration fractionation. Water Res. 36, 3834-3848. 10. Le Clech, P., 2010. Membrane bioreactors and their uses in wastewater treatments. Appl. Microbiol. and Biot. 88, 1253-1260. 11. Lee, W., 2003. Sludge characteristics and their contribution to microfiltration in submerged membrane bioreactors. J. Membrane Sci. 216, 217-227. 12. Leenheer, J.A., 1981. Comprehensive approach to preparative isolation and fractionation of dissolved organic carbon from natural waters and wastewaters. Environ. Sci. Technol. 15, 578-87. 13. Liang, S., Liu, C., Song, L., 2007. Soluble microbial products in membrane bioreactor operation: Behaviors, characteristics, and fouling potential. Water Res. 41, 95-101. 14. Ma, C., Yu, S., Shi, W., Tian, W., Heijman, S.G.J., Rietveld, L.C., 2012. High concentration powdered activated carbon-membrane bioreactor (PAC-MBR) for slightly polluted surface water treatment at low temperature. Bioresour. Technol. 113, 136-142. 15. Ma, D., Gao, B., Hou, D., Wang, Y., Yue, Q., Li, Q., 2013a. Evaluation of a submerged membrane bioreactor (SMBR) coupled with chlorine disinfection for municipal wastewater treatment and reuse. Desalination 313, 134-139. 16. Ma, D., Gao, B., Sun, S., Wang, Y., Yue, Q., Li, Q., 2013b. Effects of dissolved organic
16
matter size fractions on trihalomethanes formation in MBR effluents during chlorine disinfection. Bioresour. Technol. 136, 535-541. 17. Ma, D., Peng, B., Zhang, Y., Gao, B., Wang, Y., Yue, Q., Li, Q., 2014. Influences of dissolved organic matter characteristics on trihalomethanes formation during chlorine disinfection of membrane bioreactor effluents. Bioresour. Technol. DIO: 10.1016/j.biortech.2014.02.126. 18. Ng, C.A., Sun, D., Bashir, M.J.K., Wai, S.H., Wong, L.Y., Nisar, H., Wu, B., Fane, A.G., 2013. Optimization of membrane bioreactors by the addition of powdered activated carbon. Bioresour. Technol. 138, 38-47. 19. Ng, C.A., Sun, D., Zhang, J., Wu, B., Fane, A.G., 2010. Mechanisms of Fouling Control in Membrane Bioreactors by the Addition of Powdered Activated Carbon. Sep. Sci. Technol. 45, 873-889. 20. Satyawali, Y., Balakrishnan, M., 2009a. Effect of PAC addition on sludge properties in an MBR treating high strength wastewater. Water Res. 43, 1577-1588. 21. Satyawali, Y., Balakrishnan, M., 2009b. Performance enhancement with powdered activated carbon (PAC) addition in a membrane bioreactor (MBR) treating distillery effluent. J. Hazard. Mater. 170, 457-465. 22. Shin, H.S., Kang, S.T., 2003. Characteristics and fates of soluble microbial products in ceramic membrane bioreactor at various sludge retention times. Water Res. 37, 121-127. 23. Tian, J., Liang, H., Yang, Y., Tian, S., Li, G., 2008. Membrane adsorption bioreactor (MABR) for treating slightly polluted surface water supplies: As compared to membrane bioreactor (MBR). J. Membrane Sci. 325, 262-270.
17
24. USEPA, 1995. Determination of Chlorination Disinfection By-products, Chlorinated Solvents, and Halogenated Pesticides/Herbicides in Drinking Water by Liquid–Liquid Extraction and Gas Chromatography with Electron-Capture Detection.Method 551.1. Office of Research and Development, Cincinnati, Ohio 45268, USA. 25. USEPA, 2004. Guidelines for water reuse EPA/624/R-04/108. Environmental Protection Agency, Washington DC. . 26. Van den Broeck, R., Van Dierdonck, J., Nijskens, P., Dotremont, C., Krzeminski, P., van der Graaf, J.H.J.M., van Lier, J.B., Van Impe, J.F.M., Smets, I.Y., 2012. The influence of solids retention time on activated sludge bioflocculation and membrane fouling in a membrane bioreactor (MBR). J. Membrane Sci. 401-402, 48-55. 27. Zhang, H., Qu, J., Liu, H., Zhao, X., 2009. Characterization of isolated fractions of dissolved organic matter from sewage treatment plant and the related disinfection by-products formation potential. J. Hazard. Mater. 164, 1433-1438. 28. Zhang, K., Farahbakhsh, K., 2007. Removal of native coliphages and coliform bacteria from municipal wastewater by various wastewater treatment processes: Implications to water reuse. Water Res. 41, 2816-2824. 29. Zhang, W.D., DiGiano, F.A., 2002. Comparison of bacterial regrowth in distribution systems using free chlorine and chloramine: a statistical study of causative factors. Water Res. 36, 1469-1482. 30. Zhao, Z.Y., Gu, J.D., Fan, X.J., Li, H.B., 2006. Molecular size distribution of dissolved organic matter in water of the Pearl River and trihalomethane formation characteristics with chlorine and chlorine dioxide treatments. J. Hazard. Mater. 134,
18
60-66.
19
Table legends
Table 1 Water quality characteristics of PAC/MBR effluents at different SRTs. Table 2 FRI parameters for operationally defined EEM regions and volumetric (Φ) and percentage (P) values for EEM analysis of PAC/MBR EfOM at different SRTs. Table 3 THMs formation and speciation of PAC/MBR effluents at different SRTsa. Table 4 TTHM formation kinetics parameters for PAC/MBR EfOM at different SRTs.
Figure Captions
Fig.1 DOC percent and SUVA of UF and XAD-8 fractions from PAC/MBR effluents at different SRTs. (Error bars represent the standard deviations from 5 separate runs with different samples.) (NHoS, non-hydrophobic substances; HoA, hydrophobic acids; HoB, hydrophobic bases; HoN, hydrophobic neutrals) Fig.2 Three-dimensional excitation and emission matrix fluorescence spectroscopy of PAC/MBR EfOM at different SRTs. (Normalized to 1 mg/L DOC. The maximum fluorescence intensity of each EEM was divided into 20 equal-value contour intervals.) Fig.3 THMFP and specific THMFP (THMFP/DOC) of PAC/MBR EfOM at different SRTs. (Error bars represent the standard deviations from 5 separate runs with different samples.) Fig. 4 Specific THMFP (THMFP/DOC) and bromine incorporation factor n of UF and XAD-8 fractions. (Error bars represent the standard deviations from 5 separate runs with different samples.) (NHoS, non-hydrophobic substances; HoA, hydrophobic acids; HoB, hydrophobic bases; HoN, hydrophobic neutrals)
20
30
3.5
A
SRT=30 days SRT=180 days
SRT=30 days SRT=180 days
3.0
25
2.5 20
SUVA (L/mg m)
15
10
5
2.0
1.5
1.0
0.5
SRT=30 days SRT=180 days
kD a 1 00
DOC percentage (%)
B
D
SRT=30 days SRT=180 days
4.0
50
40
3.0
SUVA (L/mg m)
DOC percentage (%)
3.5
30
20
2.5 2.0 1.5 1.0
10 0.5 0
0.0 NHoS
HoA
HoB
HoN
Source water
NHoS
HoA
HoB
HoN
Fig.1 DOC percent and SUVA of UF and XAD-8 fractions from PAC/MBR effluents at different SRTs. (Error bars represent the standard deviations from 5 separate runs with different samples.) (NHoS, non-hydrophobic substances; HoA, hydrophobic acids; HoB, hydrophobic bases; HoN, hydrophobic neutrals)
21
400 95 90 85 80 75 70 65 60 55 50 45 40 35 30 25 20 15 10 5 0 -5
SRT=30 days 350
300
V IV 250
200 250
270
290
III
II
I 310
330
350
370
390
410
430
450
470
490
510
530
550
EX (nm)
EM (nm)
Fig.2 Three-dimensional excitation and emission matrix fluorescence spectroscopy of PAC/MBR EfOM at different SRTs. (Normalized to 1 mg/L DOC. The maximum fluorescence intensity of each EEM was divided into 20 equal-value contour intervals.)
22
800
A
CHBr3
THMs concentration (µg/L)
CHBr2Cl CHBrCl2
600
CHCl3
400
200
0 SRT=30 days
SRT=180 days
SRT=30 days
SRT=180 days
B Specific THMFP (µg/mg-DOC)
160
120
80
40
0
Fig.3 THMFP and specific THMFP (THMFP/DOC) of PAC/MBR EfOM at different SRTs. (Error bars represent the standard deviations from 5 separate runs with different samples.)
23
140
140
A
100
80
60
40
80
60
40
0
kD a
HoA
HoB
HoN
1 00
kD a
0
kD a
20
C
SRT=30 days SRT=180 days
0.7
0.35
D
SRT=30 days SRT=180 days
Bromine incorporation factor n
0.6
0.30 0.25 0.20 0.15 0.10
0.5
0.4
0.3
0.2
0.00
0.0
kD a
HoA
HoB
HoN
1 00
kD a
0.1
kD a
0.05
kD a
Bromine incorporation factor n
100
20
0.40
SRT=30 days SRT=180 days
120
Specific THMFP (µg/mg-C)
120
Specific THMFP (µg/mg-C)
B
SRT=30 days SRT=180 days
Fig. 4 Specific THMFP (THMFP/DOC) and bromine incorporation factor n of UF and XAD-8 fractions. (Error bars represent the standard deviations from 5 separate runs with different samples.) (NHoS, non-hydrophobic substances; HoA, hydrophobic acids; HoB, hydrophobic bases; HoN, hydrophobic neutrals)
24
Table 1 Water quality characteristics of PAC/MBR effluents at different SRTs.
DOC (mg/L) UV254 (Abs/cm) SUVA (L/mg m) COD (mg/L) BOD5 (mg/L) NH3–N (mg/L) NO2–N (mg/L) NO3–N (mg/L) Br− (mg/L) Cl− (mg/L) Turbidity (NTU) pH
SRT = 30 days 4.098±0.301 0.124±0.015 3.042±0.266 11.16±2.12 1.35±0.16 0.45±0.08 0.13±0.01 42.70±2.73 0.34±0.04 161.58±7.35 0 7.43±0.16
SRT = 180 days 4.869±0.170 0.140±0.006 2.875±0.083 6.77±1.03 0.57±0.12 0.34±0.04 0.04±0.01 39.81±3.07 0.29±0.02 137.23±9.22 0 7.74±0.11
Table 2 FRI parameters for operationally defined EEM regions and volumetric (Φ) and percentage (P) values for EEM analysis of PAC/MBR EfOM at different SRTs. EEM analysis FRI parameters
EEM region I
projected excitation-emission area (nm2)
MFi
4000
10.78
SRT=30 days Φi,n Pi,n (×105) (%) 5.22
25
6.12
SRT=180 days Φi,n Pi,n (×105) (%) 3.16
3.35
II III IV V Summation
2500 3500 3200 29925 43125
17.25 12.32 13.48 1.44
11.18 16.42 40.71 11.65 85.18
13.12 19.28 47.79 13.68 100
14.27 20.39 43.49 13.08 94.39
15.12 21.60 46.08 13.85 100
Table 3 THMs formation and speciation of PAC/MBR effluents at different SRTsa. SRT=30 days SRT=180 days CHCl3 (%) 79.05 71.19 CHBrCl2 (%) 15.57 19.42 CHBr2Cl (%) 5.08 8.78 CHBr3 (µ%) 0.30 0.61 n 0.19 0.28 TTHM/total_initial _carbon molar ratio 1.40 0.89 (%) a: Chlorination conditions: chlorine dose was 20 mg/L, contact time was 120 h; n : bromine incorporation factor.
26
Table 4 TTHM formation kinetics parameters for PAC/MBR EfOM at different SRTs.
SRT = 30 days SRT = 180 days
α
k1 (h-1)
k2 (h-1)
x
5.618 0.444
0.016 0.015
0.181 0.284
27
(µg/L-TTHM/mg-Cl2 consumed) 33.227 31.163
R2
0.994 0.993
Highlights
Long SRT reduced chlorine reactivity, but increased bromine-containing THMs yield. High molecular weight EfOM and hydrophobic acid had high THMs formation
reactivity. Prolonging SRT increased EfOM, but reduced the content of aromatic moieties. Long SRT enhanced removal of hydrophobic and high molecular weight EfOM. Low SRT enhanced adsorption removal of low molecular weight EfOM.
28
S0960-8524(14)00748-2 http://dx.doi.org/10.1016/j.biortech.2014.05.082 BITE 13490
To appear in:
Bioresource Technology
Received Date: Revised Date: Accepted Date:
1 April 2014 19 May 2014 21 May 2014
Please cite this article as: Ma, D., Gao, B., Xia, C., Wang, Y., Yue, Q., Li, Q., Effects of sludge retention times on reactivity of effluent dissolved organic matter for trihalomethanes formation in hybrid powdered activated carbon membrane bioreactors, Bioresource Technology (2014), doi: http://dx.doi.org/10.1016/j.biortech.2014.05.082
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Effects of sludge retention times on reactivity of effluent dissolved organic matter for trihalomethanes formation in hybrid powdered activated carbon membrane bioreactors Defang Ma, Baoyu Gao*, Chufan Xia, Yan Wang, Qinyan Yue, Qian Li a
Shandong Key Laboratory of Water Pollution Control and Resource Reuse, School of
Environmental Science and Engineering, Shandong University, Ji’ nan 250100, China
Abstract: In this study, real municipal wastewater intended for reuse was treated by two identical hybrid PAC/MBRs (membrane bioreactors with powdered activated carbon addition), which were operated at sludge retention times (SRTs) of 30 and 180 days, respectively. In order to investigate the effects of SRT on trihalomethanes (THMs) formation in chlorinated PAC/MBR effluents, characteristics and THMs formation reactivity of effluent dissolved organic matter (EfOM) at different SRTs were examined. PAC/MBR-180 had higher level of EfOM, which contained less simple aromatic proteins and exhibited lower specific UV absorbance (SUVA). EfOM with molecular weight k2 ; t ( h ) is the reaction time. 2.5 Analytical methods BOD5, COD, NH3–N, NO2–N, NO3–N, MLSS and MLVSS were measured according to the APHA standard methods (APHA, 1998). Turbidity was examined by a portable microprocessor turbidity meter (Hanna, Italy). DO and pH were measured by a portable DO meter (Precision & Scientific Instrument, China) and a pH meter (Luo Qi Te, China), respectively. DOC was quantified with a TOC-VCPH Total Organic Carbon Analyzer (SHIMADZU, Japan). UV254 was measured with TU-1810 UV/VIS spectrophotometer (PGENERAL, China). SUVA was calculated as the ratio of UV254 to DOC. Concentrations of Br− and Cl− were determined by ion chromatogram (Model: DX-100, Dionex, USA). Residual chlorine was measured with a Free & Total chlorine measuring meter (HANNA, Italy) according to the DPD powder pillow photometric method (APHA, 1998). THMs including bromodichloromethane (CHBrCl2), dibromochloromethane (CHBr2Cl), trichloromethane (CHCl3) and tribromomethane (CHBr3) were extracted by the headspace method (Gary L. Emmert, 2004) and determined with a gas chromatography with ECD detector (SHIMADZU, Japan) according to the standard analyzing methods of EPA 551.1
7
(USEPA, 1995). 3. Results and Discussion 3.1 Water quality of PAC/MBR effluents at different SRTs Water quality characteristics of effluents from PAC/MBRs at SRT of 30 and 180 days are shown in Table 1. The water quality of effluents at both SRTs was excellent and stable, proving the capacities of hybrid PAC/MBRs in municipal wastewater treatment and reclamation. The PAC/MBR effluent at SRT of 180 days exhibited better quality in terms of COD, BOD5, NH3–N, NO2–N, NO3–N, Br− and Cl−, but had higher levels of DOC and UV254 than PAC/MBR-30 effluent. Higher sludge concentration in PAC/MBR at SRT 180 days (MLSS, 6.23 g/L) improved the biodegradation of organic substances and nutrients in wastewater. However higher microorganism amount at long SRT led to more production of EPS and SMP, resulting in high DOC level in effluent. Although the PAC/MBR effluent at SRT of 30 days had lower DOC and UV254, its higher SUVA indicated a relative high content of aromatic components. This can be explained by that acclimated succession microorganisms on/in BAC formed in PAC/MBR at longer SRT (180 days) could degrade refractory DOM especially aromatic compounds, while these bacteria were absent at SRT 30 days. 3.2 Apparent MW distributions of EfOM at different SRTs Apparent MW distributions of DOM in effluents from PAC/MBRs operated at SRT of 30 and 180 days are shown in Fig. 1A. The EfOM had a broad spectrum of MW. Over 45% of the EfOM had MW of larger than 30 kDa. Compared with the >100 and 30–100 kDa fractions, a smaller amount of EfOM was represented in each of the 10–30, 5–10, 1–5 and NHoS > HoN. The PAC/MBR-30 EfOM exhibited higher SUVA than that of PAC/MBR-180 for each XAD-8 fraction except NHoS. For PAC/MBR-30, HoA exhibited rather high SUVA even higher than that of the source water, which was consistent with previous studies (Kitis et al., 2002; Zhang et al., 2009).
10
3.4 EEM spectra of EfOM at different SRTs The EEM spectra are divided into five regions that represent specific components of DOM according to (Chen et al., 2003). They are as follows: Region I (Aromatic proteins I), Region II (Aromatic proteins II), Region III (Fulvic-like acids), Region IV (Soluble microbial-like products) and Region V (Humic-like acids) (Fig. 2). EfOM at both SRTs had fluorophores in regions III and IV. However, the fluorescence maxima of region III in PAC/MBR-30 EfOM were slightly red-shifted along the excitation axis compared with PAC/MBR-180 EfOM. The red shift indicated the transition of EfOM chemical compositions from fulvic-like acids to humic-like acids. In addition, EfOM at SRT of 30 days had an EEM center in region V, whereas EfOM at SRT of 180 days effluent exhibited an EEM shoulder. Fluorescence regional integration (FRI) was conducted for the quantitative analysis of the fluorescence spectra by using the following equations (Chen et al., 2003):
Φi,n = MFi ∫
∫
ex em
Pi , n =
Φ i ,n ΦT , n
I (λexλem )d λex d λem
×100%
(1)
(2)
Where Φ i , n is the normalized EEM volume at region i that represents the cumulative fluorescence response of DOM with similar properties; I (λex λem ) is the fluorescence intensity at each excitation–emission wavelength pair; MFi is a multiplication factor applied to account for the secondary or tertiary responses at longer wavelengths, which is equal to the inverse of the fractional projected excitation–emission area. Pi , n is the percent
11
i =V
fluorescence response, and ΦT , n = ∑ Φ i ,n . As shown in Table 2, of the fluorescence EfOM i= I
at both SRTs, soluble microbial-like products were the most abundant components, accounting for more than 45% of the total cumulative fluorescence intensities. In addition, the cumulative fluorescence intensities of soluble microbial by-product-like in PAC/MBR-180 EfOM were higher than that of PAC/MBR-30 EfOM. Region III (fulvic-like acids) exhibited the second highest Φ values at both SRTs, which represented about 20% of the total fluorescent EfOM. The cumulative fluorescence intensities for PAC/MBR-30 EfOM were in the order of: region V > region II > region I, while the order was region II > region V > region I for PAC/MBR-180 EfOM. Compared with PAC/MBR-180 EfOM, PAC/MBR-30 EfOM contained larger amount of aromatic proteins I (simple aromatic proteins such as tyrosine). 3.5 THMs formation and speciation of PAC/MBR effluents at different SRTs
THMFP and THMs formation reactivity (specific THMFP) of PAC/MBR effluents at both SRTs is shown in Fig. 3. Effluents at SRT of 30 days exhibited much higher THMFP (612.83 µg/L, Fig. 3A) and specific THMFP (149.54 µg/mg-DOC, Fig. 3B) than that at SRT of 180 days. And that the proportion of initial carbons present in EfOM ended up as THMs at SRT 30 days was much higher than that at SRT 180 days (Table 3), which followed the same trend of THMs yields. CHBrCl2, CHBr2Cl, CHCl3 and CHBr3 were detected in both chlorinated samples. CHCl3 was the predominant THMs species in both effluents. And the yield of THMs species in order was CHCl3 > CHBrCl2 > CHBr2Cl > CHBr3. The distributions of THMs species at different SRTs were similar each other, but the proportion of individual THMs
12
varied. The proportion of CHCl3 in the chlorinated effluent at SRT 30 days was higher than that at SRT 180 days, while the proportion of each of the three bromine-containing THMs in the chlorinated PAC/MBR-180 effluent was higher than PAC/MBR-30 effluent. Bromine incorporation factor ( n ) representing the incorporation of Br into THMs and the formation of Br-THMs was used to facilitate understand the THMs speciation at different SRTs. As shown in Table 3, the effluent at SRT 180 had much highr n value than that at SRT 30 days. Long SRT reduced THMs formation reactivity of EfOM, but increased the formation of bromine-containing species during chlorination of PAC/MBR effluents. THMs formation and speciation are depended on the DOM characteristics (Ma et al., 2013b; Zhang et al., 2009). Effects of DOM MW on THMs formation in nature water and wastewater water are different. It is reported that THMs formation reactivity increased as the MW of DOM in river water decreased (Gang et al., 2003; Zhao et al., 2006). However our previous study indicated that HMW DOM in MBR treated municipal wastewater was the primary THMs precursors (Ma et al., 2014). Hydrophobic DOM especially HoA and aromatic proteins have high THMs formation reactivity (Ma et al., 2014; Zhang et al., 2009). As shown in Fig. 4, HMW EfOM and HoA exhibited higher THMs formation reactivity than LMW and hydrophilic fractions for PAC/MBR effluents, whereas LMW and hydrophilic EfOM had high ability to produce bromine-containing THMs. In addition, EfOM at SRT 180 days exhibited lower THMs formation reactivity but higher bromine incorporation factor ( n ) than that at SRT 30 days for each size and XAD-8 fractions. Thus the relative lower contents of HMW and hydrophobic DOM and simple aromatic protein might account for
13
the lower THMs yields of PAC/MBR-180 EfOM. And the higher production of bromine-containing THMs in PAC/MBR-180 effluent was possibly due to the higher level of LMW and hydrophilic DOM. THMs formation kinetics of EfOM at different SRTs is provided in Supplemental information Fig. S2. TTHM formation kinetics parameters are listed in Table 4. For both effluents, the TTHM data fit the DBPs formation model well with correlation coefficients of 0.99, indicating that THMs formation in chlorinated PAC/MBR effluents was fundamentally depended on chlorine consumption (Gang et al., 2003). TTHM yield coefficient and rapid and slow reaction rates of EfOM at SRT 30 days were higher than that at SRT 180 days. Particularly, the rapid reaction rate of PAC/MBR-30 EfOM was about 12 times higher than that of PAC/MBR-180 EfOM. As can be seen from the x values listed in Table 4, most of THMs precursors in PAC/MBR EfOM at both SRTs were slow reacting agents. Since halogenated intermediates derived from PAC/MBR effluent SMP were difficult to decompose, most THMs were formed after 24 h chlorination. 5. Conclusions
The results indicated that prolonging SRT in PAC/MBR increased EfOM level, but reduced the relative content of aromatic components, which are the primary DBPs precursors. Longer SRT improved the removal of HMW EfOM due to the biodegradation by acclimated succession microorganisms. The greater refreshment of PAC at low SRT enhanced the adsorption removal of LMW EfOM (< 5kDa). EfOM at short SRT exhibited higher hydrophobicity. Prolonging SRT reduced THMs formation reactivity of EfOM, but increased the formation of bromine-containing species during chlorination of PAC/MBR effluents.
14
Acknowledgements
The research was financially supported by the Key Scientific Technology Program for Environmental Protection of Shandong, China (16).
References
1. APHA, 1998. Standard Methods for the Examination of Water and Wastewater, 20th ed., Washington, DC. 2. Chellam, S., Krasner, S.W., 2001. Disinfection byproduct relationships and speciation in chlorinated nanofiltered waters. Environ. Sci. Technol. 35, 3988-3999. 3. Chen, W., Westerhoff, P., Leenheer, J.A., Booksh, K., 2003. Fluorescence Excitation−Emission Matrix Regional Integration to Quantify Spectra for Dissolved Organic Matter. Environ. Sci. Technol. 37, 5701-5710. 4. Ebie, K., Li, F., Azuma, Y., Yuasa, A., Hagishita, T., 2001. Pore distribution effect of activated carbon in adsorbing organic micropollutants from natural water. Water Res. 35, 167-179.
5. Gang, D., Clevenger, T.E., Banerji, S.K., 2003. Relationship of chlorine decay and THMs formation to NOM size. J. Hazard. Mater. A96, 1-12. 6. Gary L. Emmert, G.C., Gija Geme, Neena Joshi, and Mostafizur Rahman, 2004. Methods for Real-Time Measurement of THMs and HAAs in Distribution Systems. AwwaRF, Denver. 7. Guo, W., Vigneswaran, S., Ngo, H.H., Xing, W., Goteti, P., 2008. Comparison of the performance of submerged membrane bioreactor (SMBR) and submerged membrane adsorption bioreactor (SMABR). Bioresour. Technol. 99, 1012-1017.
15
8. Hu, J., Shang, R., Deng, H., Heijman, S.G.J., Rietveld, L.C., 2014. Effect of PAC dosage in a pilot-scale PAC–MBR treating micro-polluted surface water. Bioresour. Technol. 154, 290-296.
9. Kitis, M., Karanfil, T., Wigton, A., Kilduff, J.E., 2002. Probing reactivity of dissolved organic matter for disinfection by-product formation using XAD-8 resin adsorption and ultrafiltration fractionation. Water Res. 36, 3834-3848. 10. Le Clech, P., 2010. Membrane bioreactors and their uses in wastewater treatments. Appl. Microbiol. and Biot. 88, 1253-1260. 11. Lee, W., 2003. Sludge characteristics and their contribution to microfiltration in submerged membrane bioreactors. J. Membrane Sci. 216, 217-227. 12. Leenheer, J.A., 1981. Comprehensive approach to preparative isolation and fractionation of dissolved organic carbon from natural waters and wastewaters. Environ. Sci. Technol. 15, 578-87. 13. Liang, S., Liu, C., Song, L., 2007. Soluble microbial products in membrane bioreactor operation: Behaviors, characteristics, and fouling potential. Water Res. 41, 95-101. 14. Ma, C., Yu, S., Shi, W., Tian, W., Heijman, S.G.J., Rietveld, L.C., 2012. High concentration powdered activated carbon-membrane bioreactor (PAC-MBR) for slightly polluted surface water treatment at low temperature. Bioresour. Technol. 113, 136-142. 15. Ma, D., Gao, B., Hou, D., Wang, Y., Yue, Q., Li, Q., 2013a. Evaluation of a submerged membrane bioreactor (SMBR) coupled with chlorine disinfection for municipal wastewater treatment and reuse. Desalination 313, 134-139. 16. Ma, D., Gao, B., Sun, S., Wang, Y., Yue, Q., Li, Q., 2013b. Effects of dissolved organic
16
matter size fractions on trihalomethanes formation in MBR effluents during chlorine disinfection. Bioresour. Technol. 136, 535-541. 17. Ma, D., Peng, B., Zhang, Y., Gao, B., Wang, Y., Yue, Q., Li, Q., 2014. Influences of dissolved organic matter characteristics on trihalomethanes formation during chlorine disinfection of membrane bioreactor effluents. Bioresour. Technol. DIO: 10.1016/j.biortech.2014.02.126. 18. Ng, C.A., Sun, D., Bashir, M.J.K., Wai, S.H., Wong, L.Y., Nisar, H., Wu, B., Fane, A.G., 2013. Optimization of membrane bioreactors by the addition of powdered activated carbon. Bioresour. Technol. 138, 38-47. 19. Ng, C.A., Sun, D., Zhang, J., Wu, B., Fane, A.G., 2010. Mechanisms of Fouling Control in Membrane Bioreactors by the Addition of Powdered Activated Carbon. Sep. Sci. Technol. 45, 873-889. 20. Satyawali, Y., Balakrishnan, M., 2009a. Effect of PAC addition on sludge properties in an MBR treating high strength wastewater. Water Res. 43, 1577-1588. 21. Satyawali, Y., Balakrishnan, M., 2009b. Performance enhancement with powdered activated carbon (PAC) addition in a membrane bioreactor (MBR) treating distillery effluent. J. Hazard. Mater. 170, 457-465. 22. Shin, H.S., Kang, S.T., 2003. Characteristics and fates of soluble microbial products in ceramic membrane bioreactor at various sludge retention times. Water Res. 37, 121-127. 23. Tian, J., Liang, H., Yang, Y., Tian, S., Li, G., 2008. Membrane adsorption bioreactor (MABR) for treating slightly polluted surface water supplies: As compared to membrane bioreactor (MBR). J. Membrane Sci. 325, 262-270.
17
24. USEPA, 1995. Determination of Chlorination Disinfection By-products, Chlorinated Solvents, and Halogenated Pesticides/Herbicides in Drinking Water by Liquid–Liquid Extraction and Gas Chromatography with Electron-Capture Detection.Method 551.1. Office of Research and Development, Cincinnati, Ohio 45268, USA. 25. USEPA, 2004. Guidelines for water reuse EPA/624/R-04/108. Environmental Protection Agency, Washington DC. . 26. Van den Broeck, R., Van Dierdonck, J., Nijskens, P., Dotremont, C., Krzeminski, P., van der Graaf, J.H.J.M., van Lier, J.B., Van Impe, J.F.M., Smets, I.Y., 2012. The influence of solids retention time on activated sludge bioflocculation and membrane fouling in a membrane bioreactor (MBR). J. Membrane Sci. 401-402, 48-55. 27. Zhang, H., Qu, J., Liu, H., Zhao, X., 2009. Characterization of isolated fractions of dissolved organic matter from sewage treatment plant and the related disinfection by-products formation potential. J. Hazard. Mater. 164, 1433-1438. 28. Zhang, K., Farahbakhsh, K., 2007. Removal of native coliphages and coliform bacteria from municipal wastewater by various wastewater treatment processes: Implications to water reuse. Water Res. 41, 2816-2824. 29. Zhang, W.D., DiGiano, F.A., 2002. Comparison of bacterial regrowth in distribution systems using free chlorine and chloramine: a statistical study of causative factors. Water Res. 36, 1469-1482. 30. Zhao, Z.Y., Gu, J.D., Fan, X.J., Li, H.B., 2006. Molecular size distribution of dissolved organic matter in water of the Pearl River and trihalomethane formation characteristics with chlorine and chlorine dioxide treatments. J. Hazard. Mater. 134,
18
60-66.
19
Table legends
Table 1 Water quality characteristics of PAC/MBR effluents at different SRTs. Table 2 FRI parameters for operationally defined EEM regions and volumetric (Φ) and percentage (P) values for EEM analysis of PAC/MBR EfOM at different SRTs. Table 3 THMs formation and speciation of PAC/MBR effluents at different SRTsa. Table 4 TTHM formation kinetics parameters for PAC/MBR EfOM at different SRTs.
Figure Captions
Fig.1 DOC percent and SUVA of UF and XAD-8 fractions from PAC/MBR effluents at different SRTs. (Error bars represent the standard deviations from 5 separate runs with different samples.) (NHoS, non-hydrophobic substances; HoA, hydrophobic acids; HoB, hydrophobic bases; HoN, hydrophobic neutrals) Fig.2 Three-dimensional excitation and emission matrix fluorescence spectroscopy of PAC/MBR EfOM at different SRTs. (Normalized to 1 mg/L DOC. The maximum fluorescence intensity of each EEM was divided into 20 equal-value contour intervals.) Fig.3 THMFP and specific THMFP (THMFP/DOC) of PAC/MBR EfOM at different SRTs. (Error bars represent the standard deviations from 5 separate runs with different samples.) Fig. 4 Specific THMFP (THMFP/DOC) and bromine incorporation factor n of UF and XAD-8 fractions. (Error bars represent the standard deviations from 5 separate runs with different samples.) (NHoS, non-hydrophobic substances; HoA, hydrophobic acids; HoB, hydrophobic bases; HoN, hydrophobic neutrals)
20
30
3.5
A
SRT=30 days SRT=180 days
SRT=30 days SRT=180 days
3.0
25
2.5 20
SUVA (L/mg m)
15
10
5
2.0
1.5
1.0
0.5
SRT=30 days SRT=180 days
kD a 1 00
DOC percentage (%)
B
D
SRT=30 days SRT=180 days
4.0
50
40
3.0
SUVA (L/mg m)
DOC percentage (%)
3.5
30
20
2.5 2.0 1.5 1.0
10 0.5 0
0.0 NHoS
HoA
HoB
HoN
Source water
NHoS
HoA
HoB
HoN
Fig.1 DOC percent and SUVA of UF and XAD-8 fractions from PAC/MBR effluents at different SRTs. (Error bars represent the standard deviations from 5 separate runs with different samples.) (NHoS, non-hydrophobic substances; HoA, hydrophobic acids; HoB, hydrophobic bases; HoN, hydrophobic neutrals)
21
400 95 90 85 80 75 70 65 60 55 50 45 40 35 30 25 20 15 10 5 0 -5
SRT=30 days 350
300
V IV 250
200 250
270
290
III
II
I 310
330
350
370
390
410
430
450
470
490
510
530
550
EX (nm)
EM (nm)
Fig.2 Three-dimensional excitation and emission matrix fluorescence spectroscopy of PAC/MBR EfOM at different SRTs. (Normalized to 1 mg/L DOC. The maximum fluorescence intensity of each EEM was divided into 20 equal-value contour intervals.)
22
800
A
CHBr3
THMs concentration (µg/L)
CHBr2Cl CHBrCl2
600
CHCl3
400
200
0 SRT=30 days
SRT=180 days
SRT=30 days
SRT=180 days
B Specific THMFP (µg/mg-DOC)
160
120
80
40
0
Fig.3 THMFP and specific THMFP (THMFP/DOC) of PAC/MBR EfOM at different SRTs. (Error bars represent the standard deviations from 5 separate runs with different samples.)
23
140
140
A
100
80
60
40
80
60
40
0
kD a
HoA
HoB
HoN
1 00
kD a
0
kD a
20
C
SRT=30 days SRT=180 days
0.7
0.35
D
SRT=30 days SRT=180 days
Bromine incorporation factor n
0.6
0.30 0.25 0.20 0.15 0.10
0.5
0.4
0.3
0.2
0.00
0.0
kD a
HoA
HoB
HoN
1 00
kD a
0.1
kD a
0.05
kD a
Bromine incorporation factor n
100
20
0.40
SRT=30 days SRT=180 days
120
Specific THMFP (µg/mg-C)
120
Specific THMFP (µg/mg-C)
B
SRT=30 days SRT=180 days
Fig. 4 Specific THMFP (THMFP/DOC) and bromine incorporation factor n of UF and XAD-8 fractions. (Error bars represent the standard deviations from 5 separate runs with different samples.) (NHoS, non-hydrophobic substances; HoA, hydrophobic acids; HoB, hydrophobic bases; HoN, hydrophobic neutrals)
24
Table 1 Water quality characteristics of PAC/MBR effluents at different SRTs.
DOC (mg/L) UV254 (Abs/cm) SUVA (L/mg m) COD (mg/L) BOD5 (mg/L) NH3–N (mg/L) NO2–N (mg/L) NO3–N (mg/L) Br− (mg/L) Cl− (mg/L) Turbidity (NTU) pH
SRT = 30 days 4.098±0.301 0.124±0.015 3.042±0.266 11.16±2.12 1.35±0.16 0.45±0.08 0.13±0.01 42.70±2.73 0.34±0.04 161.58±7.35 0 7.43±0.16
SRT = 180 days 4.869±0.170 0.140±0.006 2.875±0.083 6.77±1.03 0.57±0.12 0.34±0.04 0.04±0.01 39.81±3.07 0.29±0.02 137.23±9.22 0 7.74±0.11
Table 2 FRI parameters for operationally defined EEM regions and volumetric (Φ) and percentage (P) values for EEM analysis of PAC/MBR EfOM at different SRTs. EEM analysis FRI parameters
EEM region I
projected excitation-emission area (nm2)
MFi
4000
10.78
SRT=30 days Φi,n Pi,n (×105) (%) 5.22
25
6.12
SRT=180 days Φi,n Pi,n (×105) (%) 3.16
3.35
II III IV V Summation
2500 3500 3200 29925 43125
17.25 12.32 13.48 1.44
11.18 16.42 40.71 11.65 85.18
13.12 19.28 47.79 13.68 100
14.27 20.39 43.49 13.08 94.39
15.12 21.60 46.08 13.85 100
Table 3 THMs formation and speciation of PAC/MBR effluents at different SRTsa. SRT=30 days SRT=180 days CHCl3 (%) 79.05 71.19 CHBrCl2 (%) 15.57 19.42 CHBr2Cl (%) 5.08 8.78 CHBr3 (µ%) 0.30 0.61 n 0.19 0.28 TTHM/total_initial _carbon molar ratio 1.40 0.89 (%) a: Chlorination conditions: chlorine dose was 20 mg/L, contact time was 120 h; n : bromine incorporation factor.
26
Table 4 TTHM formation kinetics parameters for PAC/MBR EfOM at different SRTs.
SRT = 30 days SRT = 180 days
α
k1 (h-1)
k2 (h-1)
x
5.618 0.444
0.016 0.015
0.181 0.284
27
(µg/L-TTHM/mg-Cl2 consumed) 33.227 31.163
R2
0.994 0.993
Highlights
Long SRT reduced chlorine reactivity, but increased bromine-containing THMs yield. High molecular weight EfOM and hydrophobic acid had high THMs formation
reactivity. Prolonging SRT increased EfOM, but reduced the content of aromatic moieties. Long SRT enhanced removal of hydrophobic and high molecular weight EfOM. Low SRT enhanced adsorption removal of low molecular weight EfOM.
28
