Soluble microbial products (SMPs) are an important group of components in wastewater effluents. In this study, the formation of disinfection by-products (DBPs), including trihalomethanes (THMs), haloacetic acids (HAAs), chlorinated solvents (CSs), haloketones (HKs), haloacetonitriles (HANs) and trichloronitromethane (TCNM) (chloropicrin), from SMPs during chlorination, chloramination and ozonation was investigated. More carbonaceous DBPs (C-DBPs: THMs, HAAs, CSs and HKs) and nitrogenous DBPs (N-DBPs: HANs and TCNM) were formed in chlorination than chloramination. More dichloroacetic and N-DBPs, and higher DBP formation potential were generated by SMPs than by natural organic matter. The results also show that disinfection factors, including temperature, pH, disinfectant dose, reaction time and bromide level significantly affected the formation of DBPs from SMPs. Additionally, the bromine incorporation factor indicates that chloramination may be a good alternative to chlorination in reducing the formation of Br-DBPs from SMPs. Bromide level and pH were the key factors affecting the formation of DBPs in both chlorination and chloramination.
ABBREVIATIONS
- TCM
Trichloromethane
- BDCM
Bromodichloromethane
- DBCM
Dibromochloromethane
- TBM
Tribromomethane
- MCAA
Monochloroacetic acid
- MBAA
Monobromoacetic acid
- BCAA
Bromochloroacetic acid
- BDCAA
Bromodichloroacetic acid
- CDBAA
Chlorodibromoacetic acid
- DBAA
Dibromoacetic acid
- DCAA
Dichloroacetic acid
- TBAA
Tribromoacetic acid
- TCAA
Trichloroacetic acid
- 1,1,1-TCE
1,1,1-Trichloroethane
- CTC
Carbon tetrachloride
- DBE
1,2-Dibromoethane
- PCE
Tetrachloroethylene
- DBC
1,2-Dibromo-3-chloropropane
- 1,1-DCP
1,1-Dichloro-2-propanone
- 1,1,1-TCP
1,1,1-Trichloro-2-propanone
- DCAN
Dichloroacetonitrile
- TCAN
Trichloroacetonitrile
- BCAN
Bromochloroacetonitrile
- DBAN
Dibromoacetonitrile
INTRODUCTION
Due to the worldwide shortage of freshwater resources, wastewater reuse has become a promising way to conserve the limited freshwater resources. To inactivate the pathogenic microorganisms, disinfection must be conducted for wastewater effluents before their reuse. Chlorine has been widely used for disinfection in water treatment owing to its low cost and high efficiency. However, chlorine can also react with organic matter and some inorganic ions to form disinfection by-products (DBPs), such as trihalomethanes (THMs), haloacetic acids (HAAs), halonitromethanes (HNMs), etc. (Hu et al. 2010). For the effluents of biological wastewater treatment plants, soluble microbial products (SMPs), which consist of macromolecules and cellular debris including proteins, polysaccharides, humic acids, and DNA, are usually the major components of soluble organic matter (Ni et al. 2010). According to previous studies, SMPs were the organic precursors of some DBPs, such as THMs, HAAs and dichloroacetonitrile (DCAN), and could increase the DBPs formation in both wastewater effluent and surface water supply after chlorination (Liu et al. 2014).
Previous studies have shown that DBPs were associated with the teratogenic, carcinogenic and mutagenic risks (Plewa et al. 2008). In order to lower the ecotoxicity of reuse water, there has been increasing interest in using chloramine or ozone as the alternative disinfectant. However, new problems may occur with these alternative disinfectants. For example, the use of chloramine may lead to a decrease in regulated DBPs, but more nitrogenous DBPs (N-DBPs), such as HNMs and nitrosamines, may be formed (Luo et al. 2012; Yang et al. 2012). Ozone can significantly reduce or eliminate the formation of THMs and HAAs, however, it can result in the formation of bromate and nitrosamines (von Gunten et al. 2010).
The concentrations and speciation of DBPs were significantly affected by water quality parameters and operating conditions. During chlorination/chloramination, the disinfectant dose, natural organic matter (NOM) level and reaction time had positive influence on the formation of THMs and HAAs (Hua & Reckhow 2012; Roccaro et al. 2014; Hong et al. 2015). High bromide concentration can enhance the formation of bromine-containing DBPs (Br-DBPs) (Chang et al. 2001; Hong et al. 2013). Increasing pH increased THMs and HNMs yields in chlorination, but decreased THMs and HAAs formation in chloramination (Doederer et al. 2014). For ozonation, bromide ions can promote the formation of Br-DBPs and nitrosamines (von Gunten et al. 2010). An increase in the formation of bromate was observed with increasing ozone doses (Zimmermann et al. 2011). However, in most of these previous studies, drinking water and wastewater effluent disinfection were studied, and thus NOM was the organic precursor which generated the studied DBPs. Up to now, few studies have been carried out to investigate the formation of DBPs formed by SMPs during disinfection (Liu et al. 2014), especially by chloramination and ozonation. Studies regarding the influence factors on the formation of DBPs in chlorination and chloramination of SMPs are even fewer. Since wastewater reuse has become a growing portion of water supplies, and chloramine and ozone have gained more and more popularity in water disinfection, it is quite necessary to compare the formation of DBPs from SMPs under chlorination, chloramination and ozonation with various conditions, and thus provide more information for the disinfection of reuse water.
In this study, the DBPs produced from SMPs under chlorination, chloramination and ozonation were studied and compared. The effects of several factors, including temperature, pH, disinfectant dosage, reaction time and bromide level, on the formation of carbonaceous DBPs (C-DBPs; including four THMs, nine HAAs, five chlorinated solvents (CSs) and two haloketones (HKs)) and N-DBPs (including four haloacetonitriles (HANs) and trichloronitromethane (TCNM)) were investigated. The bromine incorporation factor (BIF) and the main factors affecting the formation of DBPs from SMPs were also evaluated.
MATERIAL AND METHODS
Chemicals and reagents
Sodium hypochlorite solution (NaClO, 5%) was obtained from Sigma. Standard solutions of THMs (trichloromethane (TCM), bromodichloromethane (BDCM), dibromochloromethane (DBCM), tribromomethane (TBM)), CSs (1,1,1-trichloroethane (1,1,1-TCE), carbon tetrachloride (CTC), 1,2-dibromoethane (DBE), tetrachloroethylene (PCE), 1,2-dibromo-3-chloropropane (DBC)), HKs (1,1-dichloro-2-propanone (1,1-DCP); 1,1,1-trichloro-2-propanone (1,1,1-TCP)), HANs (DCAN, trichloroacetonitrile (TCAN), bromochloroacetonitrile (BCAN), dibromoacetonitrile (DBAN)), TCNM, HAAs (monochloroacetic acid (MCAA), monobromoacetic acid (MBAA), bromochloroacetic acid (BCAA), bromodichloroacetic (BDCAA), chlorodibromoacetic acid (CDBAA), dibromoacetic acid (DBAA), dichloroacetic acid (DCAA), tribromoacetic acid (TBAA), trichloroacetic acid (TCAA)) and the internal standards, 2-bromofluorobenzene and 1,2,3-trichloropropane, were obtained from Sigma-Aldrich. All other reagents were reagent grade.
Preparation and characterization of SMPs
Activated sludge was collected from an aeration tank in a municipal wastewater treatment plant, and cultivated in a laboratory-scale reactor. Initial biomass concentration was kept at about 2,000 mg/L. Glucose (800 mg/L) was utilized as the sole carbon source, as it could be biodegraded completely leaving only SMPs as the remaining organics in the solution (Liu et al. 2014). The other synthetic influents were as follows according to our previous study (in mg per L): (NH4)2SO4 (189), KH2PO4 (35) (chemical oxygen demand (CODcr):N:P ratio of 100:5:1), CaCl2 (0.37), MgSO4 (5.07), MnCl2 (0.27), ZnSO4 (0.44), FeCl3 (1.45), CuSO4 (0.39), CoCl2 (0.42), Na2MoO4 (1.26) (Zhang et al. 2015). The reactor was operated for 6 h at 25 °C with a precipitation time of 30 min. Supernatant was then collected and filtered through a 0.45 μm filter paper. The filtrate was defined as SMPs.
The characteristics of the SMPs were determined. Dissolved organic carbon (DOC) was measured using a total organic carbon (TOC) analyzer (TOC-VCH, Shimadzu, Japan). Based on theoretical conversion, 1 g glucose is equivalent to 1.067 g CODcr. Therefore, the concentration of glucose can be measured as CODcr. The concentrations of glucose (measured as CODcr), total nitrogen (TN), ammonia nitrogen (NH4+-N), nitrite nitrogen (NO2−-N), and nitrate nitrogen (NO3−-N) were determined using a DR2800 analyzer (HACH, USA). UV254 absorption was analyzed with a visible spectrophotometer (UV7595, Shanghai). Bromide was measured with ion chromatography (Dionex DX-600, German). The parameters of the obtained SMPs were as follows: Glucose (measured as CODcr) = none, DOC = 20.4–25.2 mg/L, UV254 = 0.042–0.058 cm−1, TN = 12.4–15.0 mg/L, NH4+-N = 2.9–3.3 mg/L, NO2−-N = 0.117–0.133 mg/L, NO3−-N = 1.9–2.6 mg/L. These parameters of SMPs were generally constant in different batches.
In addition, SMPs were also collected from two real domestic wastewater treatment plants of Nanjing. The parameters of SMPs were as follows: DOC = 21.5–23.2 mg/L, UV254 = 0.137–0.179 cm−1, TN = 10.4–11.6 mg/L, NH4+-N = 3.8–4.3 mg/L, NO2−-N = 0.176–0.246 mg/L, NO3−-N = 2.2–3.1 mg/L, Br− = 108.4–112.6 μg/L, respectively.
Disinfection of SMPs
Chlorination, chloramination and ozonation were conducted as previously described (Zhang et al. 2015). Briefly, SMPs were chlorinated by adding NaClO (5%). Monochloramine was prepared daily at a Cl/N molar ratio of 0.7:1. Both chlorine and monochloramine solutions were standardized using the N, N-diethylphenylene-1,4-diamine (DPD) colorimetric method before disinfection (SEPA of China 2002). Ozone was produced from extra dry grade oxygen (with a minimum purity of 99.99%) using a WH-H-Y10 ozone-generator (WAOHUANG, China), and the concentration was determined using spectrophotometric methods (Padhye et al. 2013).
Chlorination, chloramination and ozonation were conducted in closed glass bottles. During disinfection, the temperature was kept constant by a thermostatic reactor and pH was adjusted with phosphate buffer. After disinfection, the residual chlorine, chloramine and ozone were quenched using Na2S2O3.
In order to compare and understand the formation of DBPs from SMPs under different conditions, DBPs formation potential (DBPFP, except the formation of DBPs under different disinfectant dosage and reaction time conditions) was used. The details of the prepared samples are shown in Table 1. All samples were conducted in duplicate.
Experimental design
Factors . | Chlorination . | Chloramination . | Ozonation . |
---|---|---|---|
Temperature (°C) | 25, 30, 40 | 25, 30, 40 | 25, 30, 40 |
pH | 5.0, 7.0, 9.0 | 6.0, 8.0, 10.0 | 5.0, 7.0, 9.0 |
Reaction time | 1, 3,5, 7 (d) | 1, 3, 5, 7 (d) | 0.5, 2, 12 (h) |
Disinfectant dose | 0.2, 0.5, 1.0, 2.0a | 0.2, 0.5, 1.0, 2.0b | 1, 4, 8, 12 (mg/L) |
Bromide (mg/L) | 0, 0.2, 0.5, 1.0 | 0, 0.2, 0.5, 1.0 | 0, 0.2, 0.5, 1.0 |
Baseline conditions | 25 °C, pH = 7, 7d | 25 °C, pH = 8, 7d | 25 °C, pH = 7, 12h |
2.0a, Bromide = none | 2.0b, Bromide = none | 4 mg/L, Bromide = none |
Factors . | Chlorination . | Chloramination . | Ozonation . |
---|---|---|---|
Temperature (°C) | 25, 30, 40 | 25, 30, 40 | 25, 30, 40 |
pH | 5.0, 7.0, 9.0 | 6.0, 8.0, 10.0 | 5.0, 7.0, 9.0 |
Reaction time | 1, 3,5, 7 (d) | 1, 3, 5, 7 (d) | 0.5, 2, 12 (h) |
Disinfectant dose | 0.2, 0.5, 1.0, 2.0a | 0.2, 0.5, 1.0, 2.0b | 1, 4, 8, 12 (mg/L) |
Bromide (mg/L) | 0, 0.2, 0.5, 1.0 | 0, 0.2, 0.5, 1.0 | 0, 0.2, 0.5, 1.0 |
Baseline conditions | 25 °C, pH = 7, 7d | 25 °C, pH = 8, 7d | 25 °C, pH = 7, 12h |
2.0a, Bromide = none | 2.0b, Bromide = none | 4 mg/L, Bromide = none |
aMolar ratio of chlorine/dissolved organic carbon (DOC).
bMolar ratio of chloramine/DOC.
Analysis of DBPs
THMs, CSs, HKs, HANs, and TCNM were determined using EPA method 551.1. HAAs were measured according to EPA Method 552.3. All DBPs were detected using a gas chromatography electron capture detector (GC-ECD) (Agilent 6890, USA). The recoveries of DBPs ranged from 82.9% to 98.8% and the detection limits of DBPs ranged from 0.04 to 0.56 μg/L.
Statistical analysis
The key factors influencing the formation of DBPs in disinfection of SMPs was investigated using a multivariate regression procedure (backward) of SPSS software (Version 17.0) (Hong et al. 2015). The DBPs were designated as the dependent variable, and the influence factors (temperature, pH, disinfectant dosage, reaction time and bromide level) were defined as independent variables. The regression placed independent variables into the equation in the order of their partial correlation coefficients with the dependent variable. Thus, the key factors were identified using this process.
RESULTS AND DISCUSSION
Factors affecting DBPFP
Effect of temperature
DBPFP as a function of temperature after chlorination (a) and chloramination (b). Means with the same letter are not significantly different (p > 0.05) according to one-way analysis of variance (ANOVA) test (Duncan).
DBPFP as a function of temperature after chlorination (a) and chloramination (b). Means with the same letter are not significantly different (p > 0.05) according to one-way analysis of variance (ANOVA) test (Duncan).
Effect of pH
DBPFP as a function of pH after chlorination (a) and chloramination (b). Means with the same letter are not significantly different (p > 0.05) according to one-way ANOVA test (Duncan).
DBPFP as a function of pH after chlorination (a) and chloramination (b). Means with the same letter are not significantly different (p > 0.05) according to one-way ANOVA test (Duncan).
In chloramination, the formation of all the DBPs decreased with increasing pH (Figure 2(b)). The trends of DBPFP were the same as that with NOM as DBPs precursor (Hong et al. 2013). This may be because the main factor which affected the formation of DBPs was not the precursor, but the speciation profile of the disinfectant. The pH affected the speciation of chloramines and the hydrolysis of monochloramine to form free chlorine, which has been suggested to play a significant role in DBPs formation. Under alkaline conditions, monochloramine was the dominant (pH = 8) or the only (pH = 10) species and its hydrolysis to free chlorine was reduced with increasing pH (Morris & Isaac 1983; Yang et al. 2007). This led to the decreasing formation of THMs and CSs with increasing pH. In addition, pH affects the stability of non-THMs DBPs. Their net formation (production minus decomposition) was reduced at a higher pH due to the base-catalyzed decomposition (Reckhow et al. 2001). At pH 6, monochloramine and dichloramine coexisted but dichloramine became the dominant species. Although dichloramine was proved to produce less DBPs than monochloramine, there was a fast formation rate and slow decomposition rate of DBPs at this pH (Yang et al. 2007). Moreover, some DBPs underwent base-catalyzed decomposition at alkaline pH but remained stable at acidic pH.
Effect of disinfectant dose
DBPs concentration as a function of disinfectant dosage after chlorination (a) and chloramination (b). Means with the same letter are not significantly different (p > 0.05) according to one-way ANOVA test (Duncan).
DBPs concentration as a function of disinfectant dosage after chlorination (a) and chloramination (b). Means with the same letter are not significantly different (p > 0.05) according to one-way ANOVA test (Duncan).
Effect of reaction time
DBPs concentration as a function of reaction time from chlorination (a) and chloramination (b). Means with the same letter are not significantly different (p > 0.05) according to one-way ANOVA test (Duncan).
DBPs concentration as a function of reaction time from chlorination (a) and chloramination (b). Means with the same letter are not significantly different (p > 0.05) according to one-way ANOVA test (Duncan).
Effect of bromide level
DBPFP as a function of bromide level after chlorination (a), (b), chloramination (c), (d) and ozonation (e). Means with the same letter are not significantly different (p > 0.05) according to one-way ANOVA test (Duncan).
DBPFP as a function of bromide level after chlorination (a), (b), chloramination (c), (d) and ozonation (e). Means with the same letter are not significantly different (p > 0.05) according to one-way ANOVA test (Duncan).
Ozonation did not produce halogenated DBPs in the above experiments. However, Br-THMs and Br-HAAs were produced in the presence of bromide, and their formation potential increased significantly (p < 0.05) as the bromide level increased (Figure 5(e)). This is because bromide ions can be oxidized by ozone or hydroxyl radicals to form HOBr, a more effective halogen-substituting agent, thus resulting in increased concentrations of Br-DBPs (von Gunten et al. 2010; Zimmermann et al. 2011).
To better assess the extent of bromine substitution of DBPs, BIF was calculated (Table 2). In agreement with previous studies on NOM (Hu et al. 2010; Hong et al. 2013), the BIF values all presented a similar increasing pattern with increasing bromide level in chlorination, chloramination and ozonation (except TBM), implying that dibromo-DBPs and tribromo-DBPs were more easily formed with higher bromide levels. Also, BIF values were generally higher in chlorination than in chloramination. The main reason for this may be that compared with chloramine, free chlorine was a stronger oxidant and reacted with bromide faster, thus resulting in greater HOBr formation (Chang et al. 2001; Hong et al. 2013). Therefore, for wastewater disinfection, chloramination may be a better choice to control the formation of Br-DBPs.
BIF for DBPs as a function of bromide level in chlorination, chloramination and ozonation
. | Chlorination . | Chloramination . | Ozonation . | |||||
---|---|---|---|---|---|---|---|---|
Br−(mg/L) . | THMs . | HAAs . | HANs . | THMs . | HAAs . | HANs . | THMs . | HAAs . |
0.2 | 0.69 | 0.45 | 0.35 | 0.24 | 0.32 | 0.29 | 3.00 | 1.42 |
0.5 | 1.05 | 0.66 | 0.63 | 0.56 | 0.54 | 0.61 | 3.00 | 1.57 |
1.0 | 1.29 | 0.88 | 1.06 | 0.96 | 0.83 | 1.00 | 3.00 | 1.68 |
. | Chlorination . | Chloramination . | Ozonation . | |||||
---|---|---|---|---|---|---|---|---|
Br−(mg/L) . | THMs . | HAAs . | HANs . | THMs . | HAAs . | HANs . | THMs . | HAAs . |
0.2 | 0.69 | 0.45 | 0.35 | 0.24 | 0.32 | 0.29 | 3.00 | 1.42 |
0.5 | 1.05 | 0.66 | 0.63 | 0.56 | 0.54 | 0.61 | 3.00 | 1.57 |
1.0 | 1.29 | 0.88 | 1.06 | 0.96 | 0.83 | 1.00 | 3.00 | 1.68 |
BIF was defined as the ratio of the molar concentration of bromine incorporated into a given class of DBPs to the molar concentration of DBPs in that class. Take THMs as an example, BIFTHMs is the molar amount of bromine in the THMs (CHBrCl2 + 2CHClBr2 + 3CHBr3) divided by total molar THMs concentration: BIF = (CHBrCl2 + 2CHClBr2 + 3CHBr3)/ΣTHMs.
Key factors affecting DBPs formation
The results of key factors affecting DBPs formation from SMPs in chlorination and chloramination are shown in Table 3. Generally, the higher the partial correlation coefficients, the more important the factor is. For THMs, HAAs and CSs formation, bromide level was the most important factor during both chlorination and chloramination. As for HKs, HANs and TCNM formation, effects of pH and then bromide level were generally more significant than those of other factors during chlorination. During chloramination, bromide level showed the most important influence on HKs formation, but less influence on HANs and TCNM formation. Therefore, it is concluded that reducing bromide level will be an effective strategy to control C-DBPs formation from SMPs, whether for chlorination or chloramination. Besides the bromide level, controlling the pH was also very important to control N-DBPs formation.
Results of regression procedure for DBPs
DBPs . | Disinfectant . | Temperature . | pH . | Dosage . | Reaction time . | Bromide level . | Regression coefficients . | p values . |
---|---|---|---|---|---|---|---|---|
THMs | Chlorine | 0.627 | 0.622 | 0.887 | 0.885 | 0.965 | 0.951 | <0.05 |
Chloramine | 0.857 | −0.912 | 0.856 | 0.974 | 0.995 | 0.991 | <0.01 | |
HAAs | Chlorine | 0.923 | −0.659 | 0.871 | 0.935 | 0.956 | 0.959 | <0.05 |
Chloramine | −0.731 | 0.770 | 0.811 | 0.960 | 0.943 | <0.01 | ||
CSs | Chlorine | 0.977 | 0.940 | 0.936 | 0.962 | −0.958 | 0.977 | <0.01 |
Chloramine | 0.795 | −0.527 | 0.741 | −0.946 | 0.898 | <0.05 | ||
HKs | Chlorine | −0.717 | −0.937 | 0.606 | −0.866 | 0.877 | <0.05 | |
Chloramine | −0.848 | −0.706 | 0.836 | −0.944 | 0.877 | <0.05 | ||
HANs | Chlorine | −0.805 | 0.563 | −0.666 | 0.667 | <0.05 | ||
Chloramine | 0.517 | −0.434 | 0.566 | 0.573 | −0.219 | 0.828 | <0.05 | |
TCNM | Chlorine | 0.858 | 0.730 | 0.739 | −0.779 | 0.771 | <0.05 | |
Chloramine | 0.777 | −0.872 | 0.856 | 0.796 | −0.840 | 0.876 | <0.01 |
DBPs . | Disinfectant . | Temperature . | pH . | Dosage . | Reaction time . | Bromide level . | Regression coefficients . | p values . |
---|---|---|---|---|---|---|---|---|
THMs | Chlorine | 0.627 | 0.622 | 0.887 | 0.885 | 0.965 | 0.951 | <0.05 |
Chloramine | 0.857 | −0.912 | 0.856 | 0.974 | 0.995 | 0.991 | <0.01 | |
HAAs | Chlorine | 0.923 | −0.659 | 0.871 | 0.935 | 0.956 | 0.959 | <0.05 |
Chloramine | −0.731 | 0.770 | 0.811 | 0.960 | 0.943 | <0.01 | ||
CSs | Chlorine | 0.977 | 0.940 | 0.936 | 0.962 | −0.958 | 0.977 | <0.01 |
Chloramine | 0.795 | −0.527 | 0.741 | −0.946 | 0.898 | <0.05 | ||
HKs | Chlorine | −0.717 | −0.937 | 0.606 | −0.866 | 0.877 | <0.05 | |
Chloramine | −0.848 | −0.706 | 0.836 | −0.944 | 0.877 | <0.05 | ||
HANs | Chlorine | −0.805 | 0.563 | −0.666 | 0.667 | <0.05 | ||
Chloramine | 0.517 | −0.434 | 0.566 | 0.573 | −0.219 | 0.828 | <0.05 | |
TCNM | Chlorine | 0.858 | 0.730 | 0.739 | −0.779 | 0.771 | <0.05 | |
Chloramine | 0.777 | −0.872 | 0.856 | 0.796 | −0.840 | 0.876 | <0.01 |
DBPs speciation and formation from different disinfection methods and real wastewater
DBPs species and concentrations upon different disinfection methods with (b, Br− = 0.5 mg/L) or without (a) bromide under baseline conditions (Table 1).
DBPs species and concentrations upon different disinfection methods with (b, Br− = 0.5 mg/L) or without (a) bromide under baseline conditions (Table 1).
DBPFP of two real domestic wastewater treatment plants (a and b) upon different disinfection methods under baseline conditions (Table 1).
DBPFP of two real domestic wastewater treatment plants (a and b) upon different disinfection methods under baseline conditions (Table 1).
DBPs formation from SMPs and NOM
For both chlorinated and chloraminated SMPs, the amount of DCAA was higher than that of TCAA, which is distinct from the typical speciation profile of HAAs formed by NOM, which yields much more TCAA than DCAA (Hua & Reckhow 2007). The formation potentials of C-DBPs and N-DBPs were much higher (about two times) than those formed from NOM (Hong et al. 2013), this may be because of the higher portion of low molecular weight (MW) hydrophobic acids of SMPs, which was associated with DBPs formation (Chang et al. 2001). Moreover, the N-DBPs fraction of the DBPs formed from SMPs (1.3% for chlorination and 1.9% for chloramination, Figure 6(a)) was also higher than that of the DBPs from NOM and humic substances (both less than 0.5%) (Liu & Li 2010; Hong et al. 2013), probably due to the higher organic nitrogen content of SMPs (Dotson et al. 2009).
Additionally, the main factor which affected N-DBPs formation of SMPs was also distinct from that of NOM reported by Hong et al. (2013), in which bromide showed the most important influence on both C-DBPs and N-DBPs. The reason for this may be that (1) the species of studied N-DBPs was different (HNMs for NOM, HANs and TCNM for SMPs) and (2) the precursors of N-DBPs in NOM and SMPs were different.
CONCLUSIONS
C-DBPs and N-DBPs were investigated during chlorination, chloramination and ozonation of SMPs from synthetic and real wastewater. Chloramine rather than chlorine generally resulted in lower formation of C-DBPs, N-DBPs and Br-DBPs. Ozonation could only generate TBM and Br-HAAs in the presence of bromide. The effects of different factors on the formation of DBPs resulting from SMPs were similar to those from NOM. However, SMPs generated more DCAA and N-DBPs, and higher DBPFP than NOM. Moreover, reducing the bromide level and controlling the pH could effectively reduce the formation of DBPs from SMPs, either for chlorination or chloramination.
ACKNOWLEDGEMENTS
The authors gratefully acknowledge financial support from Natural Science Foundation of Jiangsu Province (Nos. BK2011032, BK20131271), National Natural Science Foundation of China (No. 20777032), and National Hightech R&D Program of China (Grant No. 2013AA06A309).