Chemosphere 117 (2014) 338–344
Contents lists available at ScienceDirect
Chemosphere journal homepage: www.elsevier.com/locate/chemosphere
Technical Note
Impacts of powdered activated carbon addition on trihalomethane formation reactivity of dissolved organic matter in membrane bioreactor effluent Defang Ma a, Yue Gao b, Baoyu Gao a,⇑, Yan Wang a, Qinyan Yue a, Qian Li a a b
Shandong Key Laboratory of Water Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Shandong University, Ji’nan 250100, China Department of Environmental Science and Engineering, Tsinghua University, Beijing 100084, China
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
PAC addition increased chlorine
reactivity, but reduced brominecontaining THMs. PAC addition reduced effluent DOM, but increased the content of aromatic DOM. PAC addition enhanced removal of hydrophilic and HoB > HiS > HoN (Fig. 1d). For MBR and PAC/MBR effluents, HoA exhibited the highest SUVA even higher than that of the source water, which was consistent with previous studies (Kitis et al., 2002; Zhang et al., 2009).
2.5. Analytical methods
3.3. EEM spectra of DOM from MBR and PAC/MBR effluents
BOD, COD, NH+4, NO 2 , NO3 , 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 by a TOC-VCPH Analyzer (SHIMADZU, Japan). UV254 was measured by using 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 by 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 determined according to the headspace method by a gas chromatograph, GC-ECD (SHIMADZU, Japan).
Fig. 2 presents the EEM spectra of DOM in effluents from MBR and PAC/MBR. The EEM spectra were divided into five regions which represented specific components of DOM: Region I (Aromatic protein I), Region II (Aromatic protein II), Region III (Fulvic acid-like), Region IV (Soluble microbial by-product-like, SMP-like) and Region V (Humic acid-like) (Chen et al., 2003). DOM in both MBR and PAC/MBR effluents had fluorophores in region III, region IV and region V. But the peak locations in each region of the MBR effluent DOM showed slight difference compared with those of PAC/MBR effluent DOM. In region V, MBR effluent DOM had three EEM centers at shorter excitation wavelengths, whereas PAC/MBR effluent DOM exhibited an EEM center at longer excitation wavelength. In addition, peak of fulvic acid-like in PAC/MBR effluent DOM was red-shifted by 5 nm along the excitation axis. In order to quantitatively analysis the differences between DOM of MBR and PAC/MBR effluents, the fluorescence regional integration (FRI) was also conducted by using the following equations (Chen et al., 2003):
3. Results
Ui;n ¼ MF i
Z ex
3.1. MW distributions of DOM in MBR and PAC/MBR effluents Fig. 1a shows the apparent MW distributions of DOM in effluents from MBR and PAC/MBR. It can be seen that DOM in effluents from the two bioreactors had a broad spectrum of MW. The majority of DOM, accounting for around 50%, had MW of larger than 30 kDa. Compared with the >100 and 30–100 kDa fractions, each of the four fractions with MW in the range between 1 and 30 kDa represented a much smaller amount of DOM. Compared with MBR effluent; PAC/MBR effluent contained more DOM with MW lager than 30 kDa. The proportions of DOM with MW less than 1 kDa in total DOM from MBR and PAC/MBR effluents were 16% and 12%, respectively. Fig. 1b shows the SUVA of MBR and PAC/MBR effluents and their DOM fractions with different MW obtained by UF fractionation. SUVA is a good indicator of the aromatic content of DOM, which correlated with THM formation reactivity during chlorination of DOM. The PAC/MBR effluent had higher SUVA than the MBR effluent. SUVA of UF fractions for both effluents exhibited a narrow distribution. In general, SUVA increased slightly with the increase of MW, indicating a correlation between the molecular size and aromatic character of DOM. The PAC/MBR effluent exhibited higher SUVA value than the MBR effluent for each size fraction except the 5–10 kDa fraction. 3.2. Polarity properties of DOM from MBR and PAC/MBR effluents Fig. 1c presents the hydrophobic/hydrophilic of DOM in effluents from MBR and PAC/MBR. HiS and HoA are the dominant components in effluent DOM from both the reactors, though their proportions varied in different samples. HoB and HoN fractions only represented less than 10% of the total DOM in each effluent sample. The relative amount of HiS in PAC/MBR effluent DOM (45%) was lower than the MBR effluent DOM (53%). Particularly,
Pi;n ¼
Z
Iðkex kem Þdkex dkem
ð1Þ
em
Ui;n 100% UT;n
ð2Þ
where Ui,n is the normalized EEM volume at region i which represents the cumulative fluorescence response of DOM with similar properties at each region; Iðkex kem Þ 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 and is equal to the inverse of the fractional projected excitation–emission area; Pi,n is the percent fluorescence P response; UT;n ¼ i¼V i¼I Ui;n . FRI parameters, U and P values of operationally defined EEM regions for EEM analysis of MBR and PAC/MBR effluents are shown in Table 1. Region IV exhibited the highest U value, accounting for more than 45% of the total cumulative fluorescence intensities for both DOM samples. It indicated that SMP-like was the most abundant components in MBR and PAC/MBR effluents DOM. Fulvic acidlike (Region III) was the second most abundant fluorescent substances in the two effluents, which represented about 20% of the total fluorescent DOM. For MBR and PAC/MBR, the cumulative fluorescence intensities were in the order of: Region IV > Region III > Region V > Region II > Region I. However the FRI values (P and U) of specific regions of the two DOM were different. It could be seen that compared with MBR effluent DOM, PAC/MBR effluent DOM exhibited higher FRI value in Region I, but had lower FRI values in Region III and IV. It was noted that PAC/MBR effluent DOM had much larger amount of aromatic protein I (simple aromatic proteins such as tyrosine), whereas MBR effluent DOM had more fulvic acid-like and SMP-like. 3.4. THM formation and speciation of MBR and PAC/MBR effluents THMFP and THM formation reactivity (specific THMFP) of the two effluents is shown in Fig. 3. MBR and PAC/MBR effluents exhib-
341
D. Ma et al. / Chemosphere 117 (2014) 338–344 30
a
MBR PAC/MBR
25
3.5
b
MBR PAC/MBR
-1
-1
SUVA (L mg m )
DOC percentage (%)
3.0 20
15
10
5
2.5 2.0 1.5 1.0 0.5
0 > 100
30 –100
10 –30
5 –10
1–5
0.0 Source water > 100 30 –100 10 –30
CHBr2Cl > CHBr3. It was noted that the distribution of THM species was similar in each sample but the proportion of individual THMs varied from sample to sample. As shown in Fig. 3a, the proportion of CHCl3 in the chlorinated PAC/MBR effluent was higher than that in MBR effluents. The proportion of each of the three bromine-containing THMs in the chlorinated MBR effluent was the higher than that of PAC/MBR effluent. Bromine incorporation factor (n) which is used to evaluate the ability of bromine incorporation into THMs to form Br-THMs was also used to further illustrate the differences in THM speciation during chlorination of MBR and PAC/MBR effluents. The MBR effluent had a much higher n value (0.40) than PAC/ MBR effluent (0.15), which indicated that DOM in MBR effluent was prone to produce bromine-containing THMs. THM formation kinetics of DOM from MBR and PAC/MBR effluents are shown in Fig. 4. THM formation kinetics parameters are calculated and listed in Table 2. For both effluents, the TTHM data fit the DBP formation model well, indicating that THM formation was fundamentally depended on chlorine consumption in the chlorinated MBR and PAC/MBR effluents (Gang et al., 2003). About 82% of THM precursors present in PAC/MBR effluent DOM were slow reacting agents, whereas DOM in MBR effluent was comprised about 52% of fast reacting agents. PAC/MBR effluent DOM exhibited significantly higher rapid and slow reaction rates than MBR effluent DOM. However PAC/MBR effluent DOM had a lower a value.
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D. Ma et al. / Chemosphere 117 (2014) 338–344
Table 1 FRI parameters for operationally defined EEM regions and volumetric (U) and percentage (P) values for EEM analysis of MBR and PAC/MBR effluents. FRI parameters
EEM analysis 2
EEM region
Projected excitation–emission area (nm )
I II III IV V Summation
MFi
4000 2500 3500 3200 29,925 43,125
MBR
11 17 12 13 1
800
PAC/MBR
Ui,n (105)
Pi,n (%)
Ui,n (105)
Pi,n (%)
3 12 20 47 13 95
3 13 21 49 14 100
5 11 16 41 12 85
6 13 19 48 14 100
700
a
CHBr3
CHClBr2
CHCl2Br
CHCl3 -1
TTHM concentration (µg L )
-1
THMs concentration (µg L )
600 600
400
200
500 400 300 MBR PAC/MBR Model
200 100 0
0
0 MBR effluent
PAC-MBR effluent
20
40
60
80
100
120
140
160
180
Time (h) Fig. 4. THMs formation kinetics of DOM in MBR and PAC/MBR effluents.
b
-1
Specific THMFP (µg mg DOC)
160
120
80
40
0 MBR effluent
PAC-MBR effluent
Fig. 3. THMFP and specific THMFP (THMFP/DOC) of DOM in MBR and PAC/MBR effluents (error bars represent the standard deviations from 5 separate runs with different samples).
4. Discussion BAC formed in PAC/MBR enhanced biodegradation of DOM adsorbed by PAC. However in the PAC/MBR operated at low SRT (30 d), bacteria that could degrade refractory DOM especially aromatic compounds were absent in/on BAC (Ng et al., 2013), which consequently increased the relative content of aromatic DOM in PAC/MBR effluent. PAC addition enhanced removal of low molecular weight (LMW) DOM, especially the 100
30 –100
10 –30
5 –10
1–5
100
30 –100
10 –30
5 –10
1–5
Contents lists available at ScienceDirect
Chemosphere journal homepage: www.elsevier.com/locate/chemosphere
Technical Note
Impacts of powdered activated carbon addition on trihalomethane formation reactivity of dissolved organic matter in membrane bioreactor effluent Defang Ma a, Yue Gao b, Baoyu Gao a,⇑, Yan Wang a, Qinyan Yue a, Qian Li a a b
Shandong Key Laboratory of Water Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Shandong University, Ji’nan 250100, China Department of Environmental Science and Engineering, Tsinghua University, Beijing 100084, China
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
PAC addition increased chlorine
reactivity, but reduced brominecontaining THMs. PAC addition reduced effluent DOM, but increased the content of aromatic DOM. PAC addition enhanced removal of hydrophilic and HoB > HiS > HoN (Fig. 1d). For MBR and PAC/MBR effluents, HoA exhibited the highest SUVA even higher than that of the source water, which was consistent with previous studies (Kitis et al., 2002; Zhang et al., 2009).
2.5. Analytical methods
3.3. EEM spectra of DOM from MBR and PAC/MBR effluents
BOD, COD, NH+4, NO 2 , NO3 , 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 by a TOC-VCPH Analyzer (SHIMADZU, Japan). UV254 was measured by using 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 by 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 determined according to the headspace method by a gas chromatograph, GC-ECD (SHIMADZU, Japan).
Fig. 2 presents the EEM spectra of DOM in effluents from MBR and PAC/MBR. The EEM spectra were divided into five regions which represented specific components of DOM: Region I (Aromatic protein I), Region II (Aromatic protein II), Region III (Fulvic acid-like), Region IV (Soluble microbial by-product-like, SMP-like) and Region V (Humic acid-like) (Chen et al., 2003). DOM in both MBR and PAC/MBR effluents had fluorophores in region III, region IV and region V. But the peak locations in each region of the MBR effluent DOM showed slight difference compared with those of PAC/MBR effluent DOM. In region V, MBR effluent DOM had three EEM centers at shorter excitation wavelengths, whereas PAC/MBR effluent DOM exhibited an EEM center at longer excitation wavelength. In addition, peak of fulvic acid-like in PAC/MBR effluent DOM was red-shifted by 5 nm along the excitation axis. In order to quantitatively analysis the differences between DOM of MBR and PAC/MBR effluents, the fluorescence regional integration (FRI) was also conducted by using the following equations (Chen et al., 2003):
3. Results
Ui;n ¼ MF i
Z ex
3.1. MW distributions of DOM in MBR and PAC/MBR effluents Fig. 1a shows the apparent MW distributions of DOM in effluents from MBR and PAC/MBR. It can be seen that DOM in effluents from the two bioreactors had a broad spectrum of MW. The majority of DOM, accounting for around 50%, had MW of larger than 30 kDa. Compared with the >100 and 30–100 kDa fractions, each of the four fractions with MW in the range between 1 and 30 kDa represented a much smaller amount of DOM. Compared with MBR effluent; PAC/MBR effluent contained more DOM with MW lager than 30 kDa. The proportions of DOM with MW less than 1 kDa in total DOM from MBR and PAC/MBR effluents were 16% and 12%, respectively. Fig. 1b shows the SUVA of MBR and PAC/MBR effluents and their DOM fractions with different MW obtained by UF fractionation. SUVA is a good indicator of the aromatic content of DOM, which correlated with THM formation reactivity during chlorination of DOM. The PAC/MBR effluent had higher SUVA than the MBR effluent. SUVA of UF fractions for both effluents exhibited a narrow distribution. In general, SUVA increased slightly with the increase of MW, indicating a correlation between the molecular size and aromatic character of DOM. The PAC/MBR effluent exhibited higher SUVA value than the MBR effluent for each size fraction except the 5–10 kDa fraction. 3.2. Polarity properties of DOM from MBR and PAC/MBR effluents Fig. 1c presents the hydrophobic/hydrophilic of DOM in effluents from MBR and PAC/MBR. HiS and HoA are the dominant components in effluent DOM from both the reactors, though their proportions varied in different samples. HoB and HoN fractions only represented less than 10% of the total DOM in each effluent sample. The relative amount of HiS in PAC/MBR effluent DOM (45%) was lower than the MBR effluent DOM (53%). Particularly,
Pi;n ¼
Z
Iðkex kem Þdkex dkem
ð1Þ
em
Ui;n 100% UT;n
ð2Þ
where Ui,n is the normalized EEM volume at region i which represents the cumulative fluorescence response of DOM with similar properties at each region; Iðkex kem Þ 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 and is equal to the inverse of the fractional projected excitation–emission area; Pi,n is the percent fluorescence P response; UT;n ¼ i¼V i¼I Ui;n . FRI parameters, U and P values of operationally defined EEM regions for EEM analysis of MBR and PAC/MBR effluents are shown in Table 1. Region IV exhibited the highest U value, accounting for more than 45% of the total cumulative fluorescence intensities for both DOM samples. It indicated that SMP-like was the most abundant components in MBR and PAC/MBR effluents DOM. Fulvic acidlike (Region III) was the second most abundant fluorescent substances in the two effluents, which represented about 20% of the total fluorescent DOM. For MBR and PAC/MBR, the cumulative fluorescence intensities were in the order of: Region IV > Region III > Region V > Region II > Region I. However the FRI values (P and U) of specific regions of the two DOM were different. It could be seen that compared with MBR effluent DOM, PAC/MBR effluent DOM exhibited higher FRI value in Region I, but had lower FRI values in Region III and IV. It was noted that PAC/MBR effluent DOM had much larger amount of aromatic protein I (simple aromatic proteins such as tyrosine), whereas MBR effluent DOM had more fulvic acid-like and SMP-like. 3.4. THM formation and speciation of MBR and PAC/MBR effluents THMFP and THM formation reactivity (specific THMFP) of the two effluents is shown in Fig. 3. MBR and PAC/MBR effluents exhib-
341
D. Ma et al. / Chemosphere 117 (2014) 338–344 30
a
MBR PAC/MBR
25
3.5
b
MBR PAC/MBR
-1
-1
SUVA (L mg m )
DOC percentage (%)
3.0 20
15
10
5
2.5 2.0 1.5 1.0 0.5
0 > 100
30 –100
10 –30
5 –10
1–5
0.0 Source water > 100 30 –100 10 –30
CHBr2Cl > CHBr3. It was noted that the distribution of THM species was similar in each sample but the proportion of individual THMs varied from sample to sample. As shown in Fig. 3a, the proportion of CHCl3 in the chlorinated PAC/MBR effluent was higher than that in MBR effluents. The proportion of each of the three bromine-containing THMs in the chlorinated MBR effluent was the higher than that of PAC/MBR effluent. Bromine incorporation factor (n) which is used to evaluate the ability of bromine incorporation into THMs to form Br-THMs was also used to further illustrate the differences in THM speciation during chlorination of MBR and PAC/MBR effluents. The MBR effluent had a much higher n value (0.40) than PAC/ MBR effluent (0.15), which indicated that DOM in MBR effluent was prone to produce bromine-containing THMs. THM formation kinetics of DOM from MBR and PAC/MBR effluents are shown in Fig. 4. THM formation kinetics parameters are calculated and listed in Table 2. For both effluents, the TTHM data fit the DBP formation model well, indicating that THM formation was fundamentally depended on chlorine consumption in the chlorinated MBR and PAC/MBR effluents (Gang et al., 2003). About 82% of THM precursors present in PAC/MBR effluent DOM were slow reacting agents, whereas DOM in MBR effluent was comprised about 52% of fast reacting agents. PAC/MBR effluent DOM exhibited significantly higher rapid and slow reaction rates than MBR effluent DOM. However PAC/MBR effluent DOM had a lower a value.
342
D. Ma et al. / Chemosphere 117 (2014) 338–344
Table 1 FRI parameters for operationally defined EEM regions and volumetric (U) and percentage (P) values for EEM analysis of MBR and PAC/MBR effluents. FRI parameters
EEM analysis 2
EEM region
Projected excitation–emission area (nm )
I II III IV V Summation
MFi
4000 2500 3500 3200 29,925 43,125
MBR
11 17 12 13 1
800
PAC/MBR
Ui,n (105)
Pi,n (%)
Ui,n (105)
Pi,n (%)
3 12 20 47 13 95
3 13 21 49 14 100
5 11 16 41 12 85
6 13 19 48 14 100
700
a
CHBr3
CHClBr2
CHCl2Br
CHCl3 -1
TTHM concentration (µg L )
-1
THMs concentration (µg L )
600 600
400
200
500 400 300 MBR PAC/MBR Model
200 100 0
0
0 MBR effluent
PAC-MBR effluent
20
40
60
80
100
120
140
160
180
Time (h) Fig. 4. THMs formation kinetics of DOM in MBR and PAC/MBR effluents.
b
-1
Specific THMFP (µg mg DOC)
160
120
80
40
0 MBR effluent
PAC-MBR effluent
Fig. 3. THMFP and specific THMFP (THMFP/DOC) of DOM in MBR and PAC/MBR effluents (error bars represent the standard deviations from 5 separate runs with different samples).
4. Discussion BAC formed in PAC/MBR enhanced biodegradation of DOM adsorbed by PAC. However in the PAC/MBR operated at low SRT (30 d), bacteria that could degrade refractory DOM especially aromatic compounds were absent in/on BAC (Ng et al., 2013), which consequently increased the relative content of aromatic DOM in PAC/MBR effluent. PAC addition enhanced removal of low molecular weight (LMW) DOM, especially the 100
30 –100
10 –30
5 –10
1–5
100
30 –100
10 –30
5 –10
1–5
