Disinfection by-products formation and acute toxicity variation of hospital wastewater under different disinfection processes

Journal Pre-proofs Disinfection by-products formation and acute toxicity variation of hospital wastewater under different disinfection processes Yuchen Luo, Li Feng, Yongze Liu, Liqiu Zhang PII: DOI: Reference:

S1383-5866(19)33366-0 https://doi.org/10.1016/j.seppur.2019.116405 SEPPUR 116405

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Separation and Purification Technology

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30 July 2019 27 November 2019 6 December 2019

Please cite this article as: Y. Luo, L. Feng, Y. Liu, L. Zhang, Disinfection by-products formation and acute toxicity variation of hospital wastewater under different disinfection processes, Separation and Purification Technology (2019), doi: https://doi.org/10.1016/j.seppur.2019.116405

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Disinfection by-products formation and acute toxicity variation of hospital wastewater under different disinfection processes Yuchen Luo, Li Feng, Yongze Liu*, Liqiu Zhang* Beijing Key Laboratory for Source Control Technology of Water Pollution, College of Environmental Science and Engineering, Beijing Forestry University, Beijing 100083, PR China Corresponding Authors: Dr. Yongze Liu and Prof. Liqiu Zhang Phone: 86-010-62338629 E-mail: [email protected] (Yongze Liu) ; [email protected] (Liqiu Zhang)

Abstract Hospital wastewater (HWW) contains a large number of pathogenic microorganisms; therefore disinfection is an indispensable unit for its treatment. This study compared the formation and formation potential of disinfection by-products (DBPs) and assessed the variations of acute toxicity for both of first physical treatment effluent (FPTE) and second biological treatment effluent (SBTE) of HWW under five different disinfection processes, including free chlorine (Cl2), chlorine dioxide (ClO2), ozone (O3), ultraviolet (UV) and ultraviolet/chlorine (UV/Cl2). Firstly, the optimal parameters of each disinfection process for FPTE and SBTE were determined respectively based on the required disinfection efficiency (i.e., controlling the concentration of fecal coliforms). The amounts of total DBPs in different disinfection processes under the optimal disinfectants dosage followed the order of Cl2 > UV/Cl2 > ClO2 > UV ≈ O3, which demonstrated that the amount of DBPs formation was closely related to the dosage of chlorine. Meanwhile, the amounts of total disinfection by-products formation potential (DBPFP) under the optimal

disinfectants dosage followed the order of UV/Cl2 > UV ≈ Cl2 > O3 > ClO2. Besides, it was found that with the reduction of chlorine dosage, the formed DBPs in UV/Cl2 disinfection process decreased. However, UV/Cl2 disinfection process might degrade organic compounds into more DBPs precursors, leading to higher DBPFP than that in Cl2 disinfection process. Significantly, some specific DBPFPs such as haloketones-FP (HKFP), chloral hydrate-FP (CHFP) and trichloronitromethane-FP (TCNMFP) in O3 disinfection process were found higher than that in Cl2 disinfection process, which could be attributed to the formation of O3 oxidation by-products, for instance aldehydes, methyl ketones and trivalent nitrogen compounds. Additionally, apart from O3, the growth inhibition rate of Chlorella vulgaris increased in all the other disinfection processes and the order of the acute toxicity in each disinfected effluent was consistent with that of DBPs formation. Keywords: Hospital wastewater, Disinfection, Disinfection by-products, Disinfection by-products formation potential, Acute toxicity.

1. Introduction Hospital wastewater (HWW) contains a large number of pathogenic microorganisms carried by patients gathering in hospital, therefore its disinfection has caused a growing concern among scientific community. More pathogens and drugs in HWW led to the increase of disinfectants dosage [1, 2], then more disinfection byproducts (DBPs) were formed in the disinfected effluent. This has prompted the launch of studies into disinfection and DBPs in HWW. Although chlorine (Cl2) disinfection, favored for its low cost, was the most common and widely used wastewater disinfection process, the residual chlorine and formed DBPs in the disinfected effluent had potential harm to the water ecology and human health [3-7]. To date, more than 600 types of DBPs have been discovered [8, 9]. Trihalomethanes (THMs) were the first detected carbonaceous DBPs (C-DBP) group in chlorinated drinking water [10], and then haloacetic acids (HAAs) were also discovered, both of which were frequently detected in disinfection process [11, 12]. Chloral hydrate (CH), one of the halogen aldehydes (HALs), was the next most prevalent DBP, followed by haloketones (HKs) [13]. Additionally, with the discovery of

nitrogenous

DBPs

(N-DBPs)

including

trichloronitromethane

(TCNM),

haloacetamides (HAcAms) and haloacetonitriles (HANs), scholars paid much attention to them because they were more cytotoxic and genotoxic than common CDBPs [12, 14]. In previous research, disinfection by-product formation potential (DBPFP) was used to evaluate the precursors of DBPs [15]. Although the occurrence and formation of C-DBPs and N-DBPs in drinking water and wastewater in various studies had been reported in different places around the world [13, 16-20], little information was available about the formation of DBPs and DBPFP in HWW. A number of other disinfectants were adopted to reduce the risk of Cl2

disinfection process. Chlorine dioxide (ClO2) is recognized as a highly effective disinfectant among chlorine-containing disinfectants for its high biocidal efficacy at wide pH range, but it still has the problems of difficulty in preparation and risk in storage [21-23]. Ozone (O3) has been widespread used to reduce the formation of DBPs [24], however, it may change the structure and reactivity of organic matters, leading to an increase in some DBPFP [25, 26]. The ultraviolet (UV) disinfection has advantages of fast biocidal rate, simple equipment, and trivial byproducts, but it has the shortcoming of no continuous disinfecting ability [27-29]. Recently, UV/chlorine process (UV/Cl2) has caused increasing concern because it can achieve multiplebarrier disinfection and maintain residual protection [30, 31]. HWW was often discharged directly into the public pipe network and treated together with urban sewage in wastewater treatment plants [32]. However, this would lead to the wide spread of resistant bacteria and highly toxic chemicals [33, 34]. There were two treatment methods for the discharge of HWW: first physical treatment and second biological treatment [35]. The residual concentrations of pollutants in first physical treatment effluent (FPTE) and second biological treatment effluent (SBTE) were different, resulting in different choices and parameters of disinfectants for FPTE and SBTE. In addition, the formation of DBPs and DBPFP in disinfected effluent were also different due to different treatment processes and disinfectants. However, to the best of our knowledge, the study on the disinfection for FPTE and SBTE of HWW was limited and needs to be further explored. parameters

parameters

chlorella vulgaris

2. Materials and methods 2.1 Chemicals and materials

O3

HAAs standard solution and THMs, HANs, TCNM, CH, and HKs HAcAms

Beijing Chemworks

2.2 Sample collection

Φ first physical treatment

effluent (FPTE).

treated wastewater second biological treatment effluent (SBTE) μ 2.3 Disinfection experiment

In Cl2 and ClO2 experiments, 500 mL experimental wastewater was transformed into device and the specific dosage of disinfectants were added into wastewater to initiate the disinfection process, then sampled at the set times. In O3 experiment, the gas flow was controlled to be 200 mL/min, the concentration of gas O3 produced by ozone generator was determined to be 30 mg/L by iodometric method . The gas O3 was introduced into the 500 mL experimental wastewater to initiate the O3 disinfection process. The 10~90 mg/L ozone dosages were obtained based on the running time of 50 s ~ 450 s for ozone generator (i.e., (50 ~ 450) s × 200 mL/min× 30 mg/L ÷ 0.5 L = (10 ~ 90) mg/L. In UV/Cl2 experiments, in order to warm up the UV lamp, the UV lamp was turned on at least 30 min prior to the experiments, and then the wastewater was injected into device, and chlorine was injected into wastewater, immediately

.

−

−

(Table 1)

USEPA 551.1 and USEPA 552.3.

537.44 mg/L and 59.24 mg/L

2.4 Analytical methods The methods of water quality characteristics were shown in supplementary material (Text S1).

determined based on the gas flow and the concentration of gas O3, which was measured by the iodometric method details were given in section 2.3. All DBPs were analyzed by gas chromatograph (Agilent 6890) equipped with electron capture detector (GC-ECD). The column was a DB-5ms fused silica capillary column (30 m×0.25 mm I.D. with a 0.25 μm film thickness, J&W Scientific). The detection of volatile DBPs, such as THMs, TCNM, HAcAms, CH, HANs and HKs was performed using USEPA method 551.1. The

injection volume was 1 μL with splitless mode. The temperature was programmed as follows: the initial temperature was 35°C for 9 min, followed by 2°C per minute temperature ramp to 40°C for 1 min, then increased to 80°C at 20°C min-1 and a final ramp of 40°C min-1 increased to 160°C for 4 min with the flow rate of N2 (purity >99.999%) gas at 0.8 mL per minute. The injector temperature was 250°C. The HAAs detection was performed using USEPA method 552.3. The injection volume was 1 μL with splitless mode. The temperature was programmed as follows: the initial temperature was 36°C for 18 min, followed by 1°C min-1 temperature ramp to 40°C, and then increased to 205°C with a final ramp of 25°C min-1 with the flow rate of N2 (purity >99.999%) gas at 0.8 mL per minute. The injector temperature was 250°C. Details for the type and concentration of DBPs determination were shown in supplementary material (Text S2). 2.5 Algae growth inhibition test The inhibition rate of Chlorella vulgaris (algae) growth was measured for characterizing the

Chlorella vulgaris

μ𝑛

μ

μ𝑛 = 𝐼𝑛 =

In𝑋𝑛 −In𝑋0 𝑡

μ0 −μ𝑛 μ0

×

3. Results and discussion 3.1 Determination of the optimal disinfectant dosage in each disinfection process The water quality characteristics of HWW, FPTE and SBTE were shown in Table S1. It showed that the concentrations of fecal coliforms in FPTE (4.0×106 MPN/L) and SBTE (2.5×106 MPN/L) were still high and could not meet the Chinese discharge standard of water pollutants for medical organization (i.e., the concentration of fecal coliforms should be ≤ 5000 MPN/L and ≤ 500 MPN/L respectively for FPTE and SBTE), therefore disinfection process was vital. The sterilization efficiencies of five disinfection processes (i.e., Cl2, ClO2, UV, O3, and UV/Cl2) for treating FPTE and SBTE were shown in Fig. 1. It can be seen that the higher dosage of disinfectant resulted in the greater sterilization efficiencies. To obtain the discharge standard (i.e., the concentration of fecal coliforms should be ≤ 5000 MPN/L and ≤ 500 MPN/L for FPTE and SBTE, respectively), the optimal disinfectant dosage to meet this standard was that Cl2 30 mg/L, ClO2 10 mg/L, UV 70 s, O3 30 mg/L and UV (30 s)/Cl2 (10 mg/L) for FPTE and Cl2 10 mg/L, ClO2 5 mg/L, UV 30 s, O3 10 mg/L and UV (15 s)/Cl2 (4 mg/L) for SBTE, respectively (Table 2). The dosage of chlorine-containing disinfectants to meet this standard followed the order of UV/Cl2 < ClO2 < Cl2. This suggested that combination of UV photolysis and Cl2 could significantly reduce the Cl2 requirement, which might prevent from DBP formation (see following section). It should be noted that the optimal parameters of each disinfection process for SBTE were less than that in FPTE (e.g., 30 mg/L of Cl2 in FPTE vs. 15 mg/L in SBTE) which might be due to the less organic matters content and less fecal coliforms in SBTE [45, 46].

(Figure 1) (Table 2) 3.2 DBPs formation and DBPFPs in different disinfection processes 3.2.1 The background values of DBPs and DBPFP in HWW, FPTE and SBTE the background values of DBPs and DBPFP in HWW, FPTE and SBTE were shown in Fig. 2. It could be seen that the concentration of total DBPs (TDBPs) in HWW was only 21.78 μg/L, and the concentration of each DBP was in the range of 0~12 µg/L. The existence of DBPs could be attributed to the use of disinfection water in hospital instruments and operations. However, the concentration of total DBPFP (TDBPFP) was 2634.29 µg/L, and HAAFP, THMFP and CHFP (names and abbreviation of DBPs and DBPFPs were given in Table S2) accounted for 52.26%, 36.77% and 9.08%, respectively, which indicated that HWW enriched in the precursors of HAAs, THMs and CH. Additionally, a new type of DBP (BCAN) was detected, because reactive bromine species produced by the reaction of enough Cl2 and bromide ion could react with organic matters (OM) to yield brominated disinfection by-products (Br-DBPs) [47]. After filtration treatment, the concentration of each DBP in FPTE was in the range of 0~10 µg/L, which was similar to that in HWW. However, the TDBPFP concentration in FPTE decreased 9.68%. These results indicated that the first physical process had little removal on the DBPs, but could slightly remove the precursors of DBPs by the trap and adsorption [48]. Compared with that in FPTE, the concentrations of DBPs such as THMs, HAAs, TCNM and HAcAms in SBTE decreased 87.49%, 88.46%, 73.11% and 39.01%, respectively. Besides that, most of DBPFP in SBTE decreased 28.12%~83.40%, because the activated sludge could effectively degrade and absorb part of OM, resulting in the decrease of DBPFP [18, 49, 50]. However, TCNMFP in SBTE (1.36

μg/L) was slightly higher than that in FPTE (0.99 μg/L), which might be due to the increase of the dissolved organic nitrogen (DON) after biological treatment. Previous studies showed that numerous metabolic by-products produced by the biological treatment process could raise DON level [51], which had reasonably positive relationship with TCNMFP level [51, 52]. (Figure 2) 3.2.2 Comparison of DBPs formation in different disinfection processes The formation of DBPs at the optimal disinfectant dosage in different disinfection processes was shown in Fig. 3. The concentration of TDBPs in each disinfected effluent for both of FPTE and SBTE followed the order of Cl2 > UV/Cl2 > ClO2 > UV ≈ O3 (Fig 3.a). Previous study confirmed that the formation of TDBPs depended on the chlorine dosage [53]. Due to no free chlorine in UV and O3 disinfection processes, the concentrations of TDBPs in FPTE and SBTE after these two processes were similar to that of the FPTE and SBTE in Fig. 2.a. It was generally known that a small amount of free chlorine was often accompanied in ClO2 preparation process [54, 55], so it was found that the content of Cl2 in ClO2 stock solution in this study was 0.32% by continuous iodometric method [36], and the residual Cl2 resulted in the formation of chlorinated DBPs in the disinfected effluent by ClO2, where the concentrations of TDBPs in FPTE and SBTE were 30.70 µg/L and 12.62 µg/L respectively. Furthermore, Fig. 3 showed that the concentrations of DBPs in SBTE and FPTE after Cl2 disinfection process followed the order of HAAs > THMs > HAcAms > HANs > HKs > CH > TCNM. The concentrations of HAAs and THMs in FPTE and SBTE were 86.33 µg/L and 49.18 µg/L, 36.69 µg/L and 24.11 µg/L respectively after Cl2 disinfection process, and the concentrations of other DBPs were less than 13.32 µg/L in FPTE and 11.09 µg/L in SBTE. These results indicated that HAAs and THMs were easily formed during Cl2 disinfection process. It could be also seen in Fig. 3 that almost all of DBPs in SBTE were less than that in FPTE after Cl2 disinfection process. There were two reasons for this observation: (i) firstly, the organic matter content in SBTE was lower than that in FPTE, resulting in less precursors

of DBPs; (ii) another reason was lower chlorine dosage in SBTE (30 mg/L in FPTE vs. 15 mg/L in SBTE). However, it was found that more HAN (11.09 µg/L) was formed in SBTE than that in FPTE (10.18 µg/L) after Cl2 disinfection, and the sum of N-DBPs in SBTE accounted for 22.10% of the TDBPs, which was higher than that in FPTE (14.79%). The possible reason for these phenomena was that numerous metabolic by-products such as DON, the main precursor of N-DBPs [51], were produced during the biological treatment process. The order of DBPs concentration (HAAs > THMs > HAcAms > HANs > HKs > CH > TCNM) in FPTE and SBTE after UV/Cl2 disinfection process was similar to that in Cl2 disinfection process, but it should be noted that the proportion of HKs in UV/Cl2 disinfection process was 7.20% of the TDBPs, which was higher than that in Cl2 disinfection process (5.57%) (Fig. 3.e). Some scholars got the same result by studying humic acid treated by Cl2 and UV/Cl2 disinfection processes [56], and found the formation of HKs during UV/Cl2 disinfection process was possibly due to the reaction of chlorine atom (·Cl) with lower molecular weight molecules such as aldehydes, ketones, and carboxylic acids.

(Figure 3) 3.2.3 Comparison of DBPFP in different disinfection processes In order to reveal the effect of different disinfection processes on the precursors of DBPs, the DBPFP was investigated and the results were given in Fig 4. As shown in Fig. 4(a), the concentrations of TDBPFP in FPTE and SBTE after different disinfection processes followed the order of UV/Cl2 > UV > Cl2 > O3 > ClO2. 3.2.3.1 DBPFP in Cl2 disinfection process It could be seen from Fig. 4 that the concentrations of each DBPFP in FPTE and SBTE after Cl2 disinfection process were in the range of 1.05~1297.94 μg/L and 1.34~293.72 μg/L, which were similar to each DBPFP concentration in FPTE and SBTE (Fig. 2). As mentioned in 2.3, during DBPFP experiments, the total dosages of chlorine in the FPTE and SBTE after different disinfection processes were consistent. In Cl2 disinfection process, the total dosages of chlorine in DBPFP experiments for

FPTE and SBTE were 537.44 mg/L and 59.24 mg/L, respectively, which included the dosage of chlorine for disinfection experiment (30 mg/L and 15 mg/L) and DBPFP experiment (507.44 mg/L and 44.24 mg/L). In addition, the total contact time of chlorine in FPTE and SBTE after Cl2 disinfection process included 1 h or 0.5 h for Cl2 disinfection and 24 h for DBPFP, and the short contact time of Cl2 disinfection (i.e., 1 h or 0.5 h) had little effect on DBPFP [57, 58]. So the concentrations of each DBPFP in FPTE and SBTE after Cl2 disinfection process were similar to each DBPFP concentration in FPTE and SBTE. It was generally known that more Cl2 dosage and long reaction time in the DBPFP experiment could increase the concentrations of DBPs [18]. However, it should be noted that HANFPs in FPTE and SBTE were similar to the concentrations of HANs in FPTE and SBTE after Cl2 disinfection process. The possible reason for this observation was that the DBPFP experiment had longer reaction time (24h) than that in Cl2 disinfection process (1h), and the formed HANs could be easily hydrolyzed as the time went on [16, 59]. 3.2.3.2 DBPFP in ClO2 disinfection process Compared with Cl2 disinfection process, the concentrations of each DBPFP in FPTE

and

SBTE

after

ClO2

disinfection

decreased

6.63%~42.55%

and

7.08%~57.58%, respectively (as shown in Fig. 4(b-h)). This might be because the aromatic and conjugated structures of organic matter were destroyed by ClO2 into small hydrophilic organics [60], resulting in the decrease of the precursors of DBPs. 3.2.3.3 DBPFP in UV disinfection process HAAFP, THMFP, HKFP, TCNMFP, and CHFP after UV disinfection process were similar to those after Cl2 disinfection process (Fig. 4(b, c, e, f, g)), indicating that UV had little effect on the precursors of these DBPs. It could be seen from Fig. 4(d, h) that HANFP and HAcAmFP increased in FPTE (11.63% and 5.52%) and

SBTE (6.29% and 9.25%) after UV disinfection process compared with Cl2 disinfection process. Similar results were found in the UV based advanced oxidation processes [61], this was likely to be ascribed to that UV could convert the highmolecular-weight OM to low-molecular-weight OM such as nitriles, amines, nitrogenous heterocyclics etc, which contributed more precursors for HANs and HAcAms [62]. 3.2.3.4 DBPFP in UV/Cl2 disinfection process It can be seen from Fig. 4(b-h) that the concentrations of each DBPFP in the FPTE and SBTE after UV/Cl2 disinfection process increased 6.64%~57.69% and 2.87%~24.39%, respectively, compared with UV disinfection process. These results indicated that free radicals (i.e., ·Cl, ·OH and O·-) with strong oxidization ability produced in UV/Cl2 process might react with OM, leading to the increase of DBPs precursors [63, 64] 3.2.3.5 DBPFP in O3 disinfection process HAAFP, THMFP, HANFP, and HAcAmFP after O3 disinfection process reduced comparing with Cl2 disinfection process (Fig. 4(b, c, d, h)), and O3 disinfection process had the highest removal rate of THMFP precursors (i.e., 37.71% in FPTE and 33.57% in SBTE). However, it was worthwhile to note that the content of Br-DBPs increased and the concentrations of HKFP, TCNMFP, and CHFP in FPTE and SBTE after O3 disinfection process increased 14.49% (1.45 μg/L), 215.45% (2.26 μg/L), 88.03% (162.83 μg/L) and 16.16% (0.93 μg/L), 230.31% (3.09 μg/L), 201.47% (65.31 μg/L), respectively (Fig. 4(e, f, g)). There were four reasons for these observations: (i) O3 could degrade macromolecular OM and transform some substances with aromatic double bonds, etc., (the precursors of THMs and HAAs) to aldehydes and methyl ketones which were the precursors of CH and TCP [15, 25, 65, 66]; (ii) O3 could destroy some organic nitrogen compounds (the precursors of HANs)

through decarboxylation and aldehyde pathway [16]; (iii) hypobromous acid produced by the reaction between bromide and O3 could react with OM to form more Br-DBPs [67]; (iv) O3 could also convert amine compounds into trivalent nitrogen compounds such as nitromethane and nitrophenol which could increase the production of TCNM in the subsequent chlorination process [52]. (Figure 4) 3.3 Comparison of the acute toxicity in different disinfected effluents The inhibition rate of Chlorella vulgaris growth was measured in this section for characterizing the

Fig. 5a and 5b showed

the comparison of the effects of different disinfected effluents on the growth inhibition rates of Chlorella vulgaris. In each disinfected effluents (e.g., Cl2, UV/Cl2, ClO2, UV), the growth inhibition rate of algae increased, while in O3 disinfected effluents, the growth inhibition rate of algae decreased (as shown in Fig. 5 a and 5b ). Especially, the growth inhibition rate of algae in Cl2 and UV/Cl2 disinfected effluents exceeded 100%. The acute toxicity in each disinfected effluent followed the order of Cl2 > UV/Cl2 > ClO2 > UV > O3. which was in the same order of the TDBPs formation discussed in 3.2.2. This result demonstrated that the higher concentrations of TDBPs, the stronger inhibition on the growth of algae [12, 68-70]. It could be seen in Fig. 3 that only a small amount of DBPs were produced in the effluents after ClO2 disinfection process, so the acute toxicity of these effluents increased slightly. However, as a strong oxidant, O3 could decompose some highly toxic drugs into small molecules to reduce the toxicity of the effluent [71, 72]. (Figure 5)

4. Conclusion To control fecal coliforms under the discharge standard of water pollutants for

medical organization, the optimal parameters of five disinfection processes for FPTE and SBTE were determined. At the optimal disinfectants dosage, the concentrations of total DBPs in FPTE and SBTE followed the order of Cl2 > UV/Cl2 > ClO2 > UV ≈ O3, indicating more chlorine dosage used, more DBPs formed. Moreover, the concentrations of total DBPFP in FPTE and SBTE after disinfection processes followed the order of UV/Cl2 > UV > Cl2 > O3 > ClO2. UV/Cl2 disinfection process could effectively reduce the dosage of chlorine and improve the disinfection efficiency, resulting in the decrease of DBPs formation. However, UV/Cl2 produced free radicals which could react with organic matters to increase the precursors of DBPs. After O3 disinfection process, HAAFP, THMFP, and HANFP decreased, but HKFP, TCNMFP, CHFP increased compared with Cl2 disinfection process, because O3 could react with some matters such as aromatic double bonds and some organic nitrogen compound, leading to the increase of aldehydes, methyl ketones, nitromethane and nitrophenol, etc. Furthermore, the acute toxicity order of the disinfected effluents was Cl2 > UV/Cl2 > ClO2 > UV > O3, which was closely related to the formation of DBPs in each disinfection process. It should be noted that the disinfected effluent by O3 had the lowest inhibition rate against algae.

Acknowledge We gratefully acknowledge funding from the Fundamental Research Funds for the Central Universities (No. 2018ZY16 and No. 2015ZCQ-HJ-02), National Natural Science Foundation of China (No. 51578066 and 51608036), Beijing Natural Science Foundation (No. 8182037), and Major Science and Technology Program for Water Pollution Control and Treatment (2017ZX07102-002).

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The concentration of Fecal coliform (MPN/L)

50000 49000

The concentration of Fecal coliform (MPN/L)

8250 8000

a)

39000 13000 5000 1000 0

5000

30 40 50 Cl2 (mg/L)

10 20 30 ClO2 (mg/L)

10 30 50 70 UV(s)

30 50 70 90 10 15 20 O3 (mg/L) UV (30s)/Cl2 (mg/L)

b)

2000 500

500 250 0

15 20 25 Cl2 (mg/L)

5 10 15 ClO2 (mg/L)

10 20 30 40 UV(s)

10 20 30 40 4 8 12 O3 (mg/L) UV (15s)/Cl2 (mg/L)

Fig. 1 The concentration of fecal coliforms under different disinfection processes a）FPTE b）SBTE (Blue dashed line in Fig. a, b represented the standard of fecal coliforms concentration for FPTE (≤ 5000 MPN/L) and SBTE (≤ 500 MPN/L))

3000

16

DBPFP

25

2500

20

2000

15

1500 1000

10 5

500

0

0

HAcAms CH TCNM HKs HANs THMs HAAs

1000

8

800

6

600

4

400

2

200 0

14

1600

TBM DBCM BDCM TCM

HANs

HANFP

12

12

10

10

8

8

0.8

1200

0.6

800

0.2

400

2

2

0.0

0

0

0

W FPE SBE WW FPE SBE H

1.6

12

1.4

10

1.2

1.2

1.0

1.0

0.8

0.8

0.6

0.6

0.4

0.4

8

6

6

4

4

2

2

0

0 W FPE

HW

SBE HWW FPE

2.5

CH

1.5

150

1.0

100

0.5

50

0.0

0 W FPE

SBE HWW FPE

SBE

CH

HAcAms ( µg/L)

200

W E SBE WW FPE SBE HW FP H

TCNM

25 h) HAcAms

CHFP ( µg/L)

2.0

HW

0.2 0.0

CHFP 250

1.4

0.0

2.5

300 g)

TCNMFP

0.2

SBE

3.0

CH (µg/L)

TCP DCP

TCNM

TCNMFP ( µg/L)

8

1.6 f)

HAcAmFP

2.0

20

1.5

15

1.0

10

0.5

5

0.0

HAcAmFP ( µg/L)

10

4

14

TCNM ( µg/L)

HKFP

HKFP ( µg/L)

HKs ( µg/L)

12

HKs

6 4

DBAN BCAN DCAN TCAN

W E SBE WW FPE SBE HW FP H

HW

14

6

HANFP ( µg/L)

1.0

HANs ( µg/L)

2000

14

d)

THMFP

1.2

e)

DBAA MBAA MCAA BCAA TCAA DCAA

W FPE SBE WW FPE SBE HW H

THMFP ( µg/L)

THMs ( µg/L)

1400 1200

0

2400 THMs

HAAFP

10

W FPE SBE WW FPE SBE H

c)

HAAs

12

HW

1.4

1600 b)

14 HAAs ( µg/L)

DBPs

TDBPFP ( µg/L)

TDBPs ( µg/L)

a)

HAAFP ( µg/L)

30

TCAcAm DCAcAm

0 W W E E E E HW FP SB HW FP SB

Fig. 2 The background values of DBPs and DBPFP in HWW, FPTE and SBTE (a) TDBPs; (b) HAAs; (c) THMs; (d) HANs; (e) HKs; (f) TCNM; (g) CH; (h) HAcAms

200

100

120 80

60 40 20

0

0

SBTE

FPTE

60

14

THMs ( µg/L)

40 30

TBM DBCM BDCM TCM

20

10 8

SBTE

FPTE

SBTE

1.2

e)

f)

TCP DCP

TCNM (µg/L)

1.0

TCNM

0.8 0.6 0.4 0.2

FPTE

CH

FPTE

18 16 14 12 10 8 6 4 2 0

h)

SBTE TCAcAm DCAcAm

Cl Cl 2 O 2 U V O U 3 V /C l Cl 2 Cl 2 O U 2 V O U 3 V /C l2

HAcAms ( µg/L)

g)

SBTE

Cl Cl 2 O 2 U V O U 3 V /C l Cl 2 Cl 2 O U 2 V O U 3 V /C l2

4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0

Cl Cl 2 O 2 U V O U 3 V /C l Cl 2 2 Cl O U 2 V O U 3 V /C l2

0.0 Cl Cl 2 O 2 U V O U 3 V /C l Cl 2 Cl 2 O U 2 V O U 3 V /C l2

HKs( µg/L)

Cl Cl 2 O 2 U V O U 3 V /C l Cl 2 Cl 2 O U 2 V O U 3 V /C l2

0 Cl Cl 2 O 2 U V O U 3 V /C l Cl 2 Cl 2 O U 2 V O U 3 V /C l2

0

FPTE

CH (µg/L)

DBAN BCAN DCAN TCAN

4 2

FPTE

SBTE

6

10

8 7 6 5 4 3 2 1 0

d)

12

HANs ( µg/L)

c)

50

DBAA MBAA MCAA BCAA TCAA DCAA

Cl Cl 2 O 2 U V O U 3 V /C l Cl 2 Cl 2 O U 2 V O U 3 V /C l2

40

FPTE

b)

80

Cl Cl 2 O 2 U V O U 3 V /C l Cl 2 Cl 2 O U 2 V O U 3 V /C l2

TDBPs（ µg/L）

160

HAcAms CH TCNM HKs HANs THMs HAAs

HAAs ( µg/L)

a)

SBTE

FPTE

SBTE

Fig. 3 DBPs formation under the optimal disinfectant dosage in different disinfection processes (a) TDBPs; (b) HAAs; (c) THMs; (d) HANs; (e) HKs; (f) TCNM; (g) CH; (h) HAcAms

HAcAms CH TCNM HKs HANs THMs HAAs

2000 1500 1000 500

Cl Cl 2 O 2 U V O U 3 V /C l Cl 2 2 Cl O U 2 V O U 3 V /C l2

0

c)

TBM DBCM BDCM TCM

1000 THMFP ( µg/L)

SBTE

800 600 400 200

SBTE

FPTE

TCP DCP

10 8 6 4

f) TCNMFP( µg/L)

e)

12

SBTE

4 3 2

0

0 Cl Cl 2 O 2 U V O U 3 V /C l Cl 2 2 Cl O U 2 V O U 3 V /C l2

1

FPTE

SBTE

FPTE

SBTE

25

g)

h) HAcAmFP ( µg/L)

CH

TCAcAm DCAcAm

20 15 10 5 0

Cl Cl 2 O 2 U V O U 3 V /C l Cl 2 Cl 2 O U 2 V O U 3 V /C l2

400 350 300 250 200 150 100 50 0

TCNM

5

2 Cl Cl 2 O 2 U V O U 3 V /C l Cl 2 2 Cl O U 2 V O U 3 V /C l2

HKFP ( µg/L)

DBAN BCAN DCAN TCAN

6

14

CHFP( µg/L)

d)

SBTE

Cl Cl 2 O 2 U V O U 3 V /C l Cl 2 Cl 2 O U 2 V O U 3 V /C l2

18 16 14 12 10 8 6 4 2 0

Cl Cl 2 O 2 U V O U 3 V /C l Cl 2 2 Cl O U 2 V O U 3 V /C l2

0

FPTE

DBAA MBAA MCAA BCAA TCAA DCAA

FPTE

HANFP ( µg/L)

FPTE 1200

b)

FPTE

Cl Cl 2 O 2 U V O U 3 V /C l Cl 2 Cl 2 O U 2 V O U 3 V /C l2

TDBPFP（ µg/L）

2500

1600 1400 1200 1000 800 600 400 200 0

Cl Cl 2 O 2 U V O U 3 V /C l Cl 2 Cl 2 O U 2 V O U 3 V /C l2

a)

HAAFP ( µg/L)

3000

SBTE

FPTE

SBTE

Fig. 4 DBPFP under optimal disinfectant dosage in different disinfection processes (a) Total amount of DBPs; (b) HAAs; (c) THMs; (d) HANs; (e) HKs; (f) TCNM; (g) CH; (h) HAcAms

120

140 a)

100 80 60

UPW HWW FPE Cl2

40 20 0

ClO2 UV O3 UV/Cl2

Inhibition rate (%)

Inhibition rate (%)

140

120

b)

100 80 60 40 20

SBE ClO2 O3

Cl2 UV UV/Cl2

0 2 3 1 2 3 Time (day) Time (day) Fig. 5 The comparison of the effects of different disinfected effluents on the growth 1

inhibition rates of Chlorella vulgaris. (a) FPTE; (b) SBTE (UPW: Ultra-pure water)

Table 1 The experiment parameters of each disinfection process for FPTE and SBTE

FPTE

SBTE

Parameters Dosage (mg/L)

Cl2 30, 40, 50

ClO2 10, 20, 30

Reaction time

1h

1h

Dosage (mg/L)

15, 20, 25

5, 10, 15

Reaction time

1h

1h

UV / 10, 30, 50, 70 s / 10, 20, 30, 40 s

O3 30, 50, 70, 90 30 min

15 min

UV/Cl2 10, 20, 30 1h (UV:30 s) 4, 8, 12 1h (UV:15 s)

Table 2 The optimal parameters of each disinfection process for FPTE and SBTE

FPTE SBTE

Cl2 (mg/L)

ClO2 (mg/L)

UV (s)

O3 (mg/L)

30 15

10 5

70 30

30 10

UV/Cl2 (s) / (mg/L) 30 /10 15 /4

Graphical Abstract

Highlights The optimal parameters in five disinfection processes were determined. The amounts of total DBPs followed the order of Cl2 > UV/Cl2 > ClO2 > UV ≈ O3. The amounts of total DBPFP followed the order of UV/Cl2 > UV ≈ Cl2 > O3 > ClO2. The acute toxicity order of disinfected effluents was Cl2 > UV/Cl2 > ClO2 > UV > O3. Most of DBPs and DBPFP except TCNMFP were lower in SBTE than those in FPTE.

Author Statement The work described has not been submitted elsewhere for publication, in whole or in part, and all the authors listed have approved the manuscript that is enclosed.

Declaration of Interest Statement The authors declared that they have no conflicts of interest to this work. The authors declare that they do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted.