CaO2 as a pretreatment method for the removal of carbamazepine and primidone in waste activated sludge and improving the solubilization of sludge

Accepted Manuscript MP-UV/CaO2 as a pretreatment method for the removal of carbamazepine and primidone in waste activated sludge and improving the solubilization of sludge Ming Zheng, Yongmei Li, Qian Ping, Lin Wang PII:

S0043-1354(18)31027-3

DOI:

https://doi.org/10.1016/j.watres.2018.11.086

Reference:

WR 14305

To appear in:

Water Research

Received Date: 26 September 2018 Revised Date:

29 November 2018

Accepted Date: 30 November 2018

Please cite this article as: Zheng, M., Li, Y., Ping, Q., Wang, L., MP-UV/CaO2 as a pretreatment method for the removal of carbamazepine and primidone in waste activated sludge and improving the solubilization of sludge, Water Research, https://doi.org/10.1016/j.watres.2018.11.086. 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.

ACCEPTED MANUSCRIPT

CBZ/PMD

⦁𝐎𝐇

CaO2 +H2O

WAS

RI PT

UV

UV

EP

indirect photolysis

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⦁𝐎𝐇, 𝟑𝐃𝐎𝐌 𝟏𝐎 𝟐

∗

𝐎𝟐

𝟑𝐃𝐎𝐌 ∗

𝟏𝐎

direct photolysis

N O O C2H5

NH 2

O

NH 2

Mechanism

0

0

Time (h) MP-UV

1

10

MP-UV/CaO2 O C2H5

NH NH O

NH NH O

Experiment

N

𝟐

TE D

UV

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𝐎𝟐 DOM

MP-UV/CaO2

SC

𝐇𝟐 𝐎𝟐

MP-UV

1

C/C0

UV

WAS solubilization

𝐂𝐚(𝐎𝐇)𝟐

C/C0

CaO2

0

0

Time (h)

Result

10

Biodegradable substances

ACCEPTED MANUSCRIPT 1

MP-UV/CaO2 as a pretreatment method for the removal of carbamazepine and

2

primidone in waste activated sludge and improving the solubilization of sludge

3

Ming Zheng1, a, Yongmei Li*1, a, b Qian Pinga, Lin Wang a, b

4

a

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Science and Engineering, Tongji University, Shanghai 200092, China

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b

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P.R. China

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*Corresponding author

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Tel. +86-21 65982692; fax: +86 21 65986313

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State Key Laboratory of Pollution Control and Resources Reuse, College of Environmental

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SC

Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092,

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E-mail address: [email protected] (Y. Li).

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1

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Abstract

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These authors contributed equally to this work.

Medium-pressure ultraviolet light (MP-UV) combined with calcium peroxide

14

(CaO2) as a pretreatment technology for removing carbamazepine (CBZ) and

15

primidone (PMD) in waste active sludge (WAS) and improving the solubilization of

16

sludge were investigated. CBZ and PMD were effectively removed and the removal

17

fitted pseudo-first kinetics under MP-UV/CaO2 treatment with R2 > 0.97. The higher

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CaO2 dosage and lower initial volatile suspended solids (VSS) concentration were

19

conductive to the removal of CBZ and PMD. Of the CaO2 hydrolysates, Ca(OH)2

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played a more important role than H2O2 during MP-UV/CaO2 treatment. The removal

21

of the target compounds was attributed to direct photolysis and indirect photolysis

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1

ACCEPTED MANUSCRIPT caused by •OH, 3DOM*, and 1O2, in which •OH played a vital role with > 62.2%

23

contribution to the overall degradation rate. A model predicting the steady

24

concentration of •OH in WAS ([VSS] ≈ 8.6 g L-1) under MP-UV/CaO2 treatment with

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CaO2 dosage ranging from 0 to 0.5 g g-1-VSS was proposed and validated. Moreover,

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major intermediates of CBZ and PMD were detected and the probable transformation

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pathways during MP-UV/CaO2 treatment were proposed. In addition, MP-UV/CaO2

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promoted the sludge solubilization effectively. Considering both the pharmaceutical

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degradation and sludge solubilization, the optimum operation condition with 0.2

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g-CaO2 g-1-VSS combined with 7 h MP-UV irradiation is recommended. Under this

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condition, more than 92.3% of CBZ and 90.3% of PMD were removed, and soluble

32

chemical oxygen demand (SCOD) increased by 657% and 13.6% compared with sole

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10 h CaO2 (0.2 g g-1-VSS) treatment and 7 h MP-UV treatment, respectively.

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Keywords:

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carbamazepine (CBZ) and primidone (PMD); degradation pathway; sludge

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solubilization

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pretreatment;

waste

activated

sludge

(WAS);

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MP-UV/CaO2

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1

Introduction

Waste activated sludge (WAS) produced from wastewater treatment plants

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(WWPTs) are becoming a major concern with the urbanization in the world.

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Anaerobic digestion (AD) is claimed to be a highly cost-effective technology for

41

WAS stabilization in modern waste sludge treatment (Anjum et al. 2016). However,

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the persistent trace organic contaminants (TOrCs) are one of major concerned issues 2

ACCEPTED MANUSCRIPT during sludge treatment and application (Anjum et al. 2016). These TOrCs, including

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pesticides, industrial chemicals, pharmaceuticals and personal care products, could be

45

adsorbed onto sludge with concentration generally between ng g−1 and µg g−1 dry

46

weight (dw) (Liu and Wong 2013, Subedi et al. 2013, Wu et al. 2013), and difficult to

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be degraded during AD process (Stasinakis 2012), which were finally discharged to

48

the environment through landfill or land application of sludge, resulting in potential

49

harm to ecosystem and human health (Semblante et al. 2015). They may also pose an

50

inhibitation to AD; for example, Chen et al. (2008) reported methanogens were highly

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susceptible to TOrCs such as halogenated aliphatic, chlrophenols, and N-subsituted

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aromatic compounds. Therefore, these refractory TOrCs should be removed before

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AD.

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Recent years, pretreatment of WAS is adopted to remove the toxic TOrCs and

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improve the solubilization of sludge. It has been demonstrated that calcium peroxide

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(CaO2), as a slowly released oxidant, could help to remove some TOrCs and enhance

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the solubilization of sludge (Chen et al. 2016, Li et al. 2015, Lu et al. 2017, Zhang et

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al. 2015), because CaO2 can produce Ca(OH)2, H2O2, O2, hydroxyl radical (•OH) and

59

superoxide radical (O•  ) in moist media (Ma et al. 2007). Li et al. (2015) has reported

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that the addition of 0.2 g-CaO2 g-1 volatile suspended solids (VSS) during AD could

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decrease the total detection frequency of some TOrCs in the supernatant, and improve

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the sludge solubilization. Zhang et al. (2015) showed 0.25 g-CaO2 g-1-VSS effectively

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removed more than 50% of estrogens in WAS, and increased the soluble total organic

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ACCEPTED MANUSCRIPT carbon (STOC) by 25% after 7 d AD. Chen et al. (2016) demonstrated 0.025 g-CaO2

65

g-1-VSS enhanced the WAS dewaterability and broke the sludge floc through

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changing the extracellular polymeric substances. In addition, CaO2 has been proved as

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a good pretreatment to promote the subsequent AD to produce high quality short

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chain fatty acids (TSCFA) and methane (CH4) (Li et al. 2015, Ping et al. 2018, Zhang

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et al. 2015). Therefore, CaO2 was considered to be a good additive for WAS

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pretreatment. However, the previous investigation found 19 of the 29 organic

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pollutants detected in the supernatants of raw sludge samples were not removed by

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CaO2 treatment (Li et al. 2015). Our recent preliminary experiments also showed that

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CaO2 had little degradation effects on the typical

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Carbamazepine(CBZ) and primidone(PMD) (Fig. S2 in supporting information (SI)).

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Therefore, combination of CaO2 with other technologies as a stronger pretreatment

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method should be considered.

refractory pollutants

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Previous investigations have proved photochemical AOPs were the common and

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effective methods to remove refractory TOrCs in water and WAS (Rosario-Ortiz et al.

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2010, Salihoglu et al. 2012, Yang et al. 2014, Yonar et al. 2006, Zhang and Li 2014,

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Zhang et al. 2018), especially the UV/H2O2 treatment, which has been used for the

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refectory TOrCs control (Yang et al. 2014). Besides, UV-based processes have also

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been used to enhance WAS stabilization (Anjum et al. 2016, Zhang and Li 2014). As

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CaO2 was considered as solid H2O2, CaO2 combination with UV irradiation

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(UV/CaO2) is assumed to have the similar oxidation power to UV/H2O2 to remove

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ACCEPTED MANUSCRIPT refractory pollutants in WAS. Furthermore, sole CaO2 and its hydrolysate Ca(OH)2

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have been proved to accelerate hydrolysis and acidification processes during WAS

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AD (Li et al. 2014, Li et al. 2015). Hence, combination of UV with CaO2 as a novel

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sludge pretreatment to remove TOrCs in WAS was investigated in this paper. CBZ

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and PMD were selected as the typical TOrCs in this study as they were frequently

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detected in wastewater (LQD-2300 ng·L-1) and wastewater sludge (LQD- 103 ng

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g-1-dw) for their wide application (Liu and Wong 2013, Oulton et al. 2010, Subedi et

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al. 2013) and their biological hazard (Keen et al. 2012, Krugel et al. 2017, Liu and

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Wong 2013).

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The aim of this study was to investigate the mechanism about combination of

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UV light generated by medium-pressure mercury lamp with CaO2 (MP-UV/CaO2) to

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remove CBZ and PMD in WAS and improve the sludge solubilization simultaneously.

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1) Factors influencing CBZ and PMD degradation during MP-UV/CaO2 treatment

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were investigated. 2) Effects of CaO2 hydrolysates combining with MP-UV on the

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degradation of the two target compounds were clarified. 3) To ascertain the

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degradation mechanisms of CBZ and PMD under MP-UV/CaO2 treatment, the main

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reactive radicals and their effects were identified, and the production of •OH at

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different CaO2 dose was modeled. 4) The intermediates of CBZ and PMD generated

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under MP-UV/CaO2 treatment were detected. 5) Effect of MP-UV/CaO2 pretreatment

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on sludge solubilization was evaluated and the optimal pretreatment conditions were

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recommended. This work explores the mechanisms and applicability of a new

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advanced treatment to remove the persistent TOrCs in sludge and promote the safe

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application of sludge.

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2

Materials and methods

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2.1 Chemicals

Calcium peroxide (CaO2, 75%), CBZ and PMD (> 97% purity) as well as

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scavengers including isopropyl alcohol (IPA), isoprene (IPE), superoxide dismutase

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(SOD), catalase (CAT), and 5,5-dimethyl-1-pyrroline N-oxide (DMPO) were

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purchased from Sigma-Aldrich (St. Louis, MO). Ca(OH)2, CaCl2, Na(OH)2, H2SO4,

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and H2O2 (30%, w/w) were of analytical grade and were provided by Sinopharm

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Chemical Reagent (Shanghai, China). All solvents used for instrumental analysis were

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of chromatographic purity and obtained from Sigma-Aldrich. Others were purchased

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from Sinopharm Chemical Reagent unless otherwise stated. The pure-water was

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prepared using a Milli-Q system (EMD Millipore, Billerica, MA, USA).

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2.2 WAS

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The sludge was obtained from the secondary sedimentation tank of a wastewater

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treatment plant (WWTP) in Shanghai, China, in which an anaerobic-anoxic-aerobic

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activated sludge process was used to remove nutrients. When the sludge was taken to

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the lab, it was filtered with a 1mm × 1 mm screen and settled for approximately 24 h

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at 4 ˚C prior to use. The characteristics of the concentrated sludge sample are shown

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in Table 1.

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2.3 Batch tests for the pretreatment of WAS using MP-UV/CaO2

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ACCEPTED MANUSCRIPT A merry-go-round photochemical reactor PhchemIIII (NBeT Co. Ltd, Beijing,

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China) equipped with medium-pressure mercury lamp (MP-UV) was used for the

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photoirradiation experiments. It contained 12 quartz tubes and the volume of each

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tube was 80 mL. The irradiant intensity of the MP-UV was 180 mW cm-2 and the

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irradiance spectra were measured by a spectroscope (USB2000+UV−vis, Oceanoptics,

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USA). The MP-UV lamp has relatively strong intensity at wavelength from 250 to

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440 (Fig. S1).

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WAS spiked with CBZ or PMD at 0.1 mg g-1-VSS was first mixed with CaO2 for

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2 min, and then were irradiated by MP-UV. Unless otherwise stated, 0.2 g-CaO2

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g-1-VSS was added. During the photoirradiation, each tube contained 50 mL sludge.

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Meanwhile, two control tests were set with one only adding 0.2 g-CaO2 g-1-VSS, and

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another using UV photoirradiation without CaO2.

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The degradation of CBZ and PMD were described using pseudo-first-order kinetics as follows (Eq. 1):

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ln C C  = −t

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where C is the residual concentration of CBZ or PMD, C0 is the initial concentration

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of CBZ or PMD, t is the reaction time in hour (h) and K is the pseudo-first-order

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kinetics constant representing the degradation rate constant in h-1.

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2.3.1

(1)

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Effects of CaO2 dosage, initial VSS concentration and initial pH

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Experiments evaluating effects of CaO2 dosage (from 0 to 0.5 g g-1-VSS), initial

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VSS concentration (from 4 to 16 g L-1) and initial pH values (from 1.83 to 12.12) on

7

ACCEPTED MANUSCRIPT CBZ and PMD degradation during UV/CaO2 treatment were conducted. The initial

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pH value was adjusted using NaOH and H2SO4 as appropriate for 2 min before

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pretreatment.

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2.3.2

Effects of CaO2 hydrolysates combined with MP-UV

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CaO2 can be hydrolyzed into Ca(OH)2 and H2O2 in WAS (Zhang et al. 2015).

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Experiments using Ca(OH)2 or H2O2 combining with MP-UV irradiation were

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conducted to ascertain effect of each hydrolysate on the removal of the target

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compounds. The Ca(OH)2 dosage was set at the same initial pH of 0.20 g-CaO2 (pH =

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9.05), and H2O2 were set at the equivalent amount of the hydrolysate of 0.20 g-CaO2

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g-1-VSS ([H2O2] =0.071 g g-1-VSS). In addition, CaCl2 (0.305 g g-1-VSS) was used to

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evaluate the effect of calcium ion. Like CaO2, each additive was first mixed with

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WAS for 2 min before irradiation.

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2.3.3

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Effect of MP-UV/CaO2 treatment on solubilization of WAS Effect of MP-UV/CaO2 pretreatment on WAS solubilization was investigated.

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SCOD and VSS were measured to evaluate the sludge solubilization (Li et al. 2015).

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Specifically, 100 mL of sludge were first mixed well with various CaO2 dosage (from

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0 to 0.5 g g-1-VSS) for 2 min, and then exposed to MP-UV irradiation from 0 to 10 h.

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The change of SCOD was tested. The reductions of TSS and VSS after 10 h were

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measured. In addition, WAS treated by various CaO2 dosages without MP-UV

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irradiation were set as control tests.

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2.4 Analysis of reactive radicals

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2.4.1

Detection of the reactive radicals using scavengers H2O2, O2, •OH, triplet of dissolved organic matter (3DOM*), O2•–, singlet oxygen

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(1O2) and carbonate radical (CO3•–) may be produced in photochemical system upon

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adding CaO2 (Jasper and Sedlak 2013, Kozak and Włodarczyk-Makuła 2018, Ma et al.

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2007). To understand contributions of each reactive radical in the removal of CBZ

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and PMD, effects of scavengers of these reactive radicals were investigated. IPA (100

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mmol g-1-VSS) was used to quench •OH reactions (Jasper and Sedlak 2013). IPE (100

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mmol g-1-VSS) was used to quench

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(12.5⦁1000⦁unite (kU) g-1-VSS) was used to quench O2•– (Singh 1982). CAT (12.5

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kU g-1-VSS) was used to quench H2O2 (Keen et al. 2012). As 1O2 was mainly

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generated from the reaction between the dissolved oxygen and the 3DOM* (Haag and

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Hoigne 1986), sparging N2 (99.99%) can be used to evaluate the effects of 1O2 and O2

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on the removal of the target compounds (Jasper and Sedlak 2013). Scavengers were

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added into WAS and mixed evenly before irradiation.

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2.4.2

SC

DOM*(Jasper and Sedlak 2013). SOD

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EPR analysis

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Electron paramagnetic resonance (EPR, ESP300 (Bruker, Germany)) was also

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used to detect the main reactive radicals during MP-UV/CaO2 pretreatment.

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5,5-dimethyl-1-pyrroline N-oxide (DMPO) was used in trapping experiments. DMPO

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can trap •OH, O2•– and methyl radicals (•CH3), forming DMPO-OH signal with four

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split lines with the height ratio of 1:2:2:1, DMPO-OOH with a sextet EPR signal, and

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DMPO-CH3 with six split lines with same height ration, respectively (Barbierikova et

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ACCEPTED MANUSCRIPT al. 2018, Li et al. 2015, Lipovsky et al. 2012). DMPO-OOH can be easily converted

191

into DMPO-OH (Lipovsky et al. 2012). To identify whether the DMPO-OH signal

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was from the trapping of •OH by DMPO, SOD (12.5 kU g-1-VSS) and thiourea (~

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0.01 mol g-1-VSS) were used to quench O2•– and •OH, respectively (Li et al. 2015,

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Singh 1982). As the alkyl radical (•C-R) may be generated from the oxidation of

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contaminants to form DMPO-C-R which had the similar DMPO-CH3 signal feature

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(Zhang et al. 2015), EPR analysis for the oxidation of CBZ and PMD under

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MP-UV/CaO2 was also conducted ([CBZ]= 1mg g-1-VSS and [PMD]= 1mg g-1-VSS).

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2.4.3

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Detection of steady-state •OH concentrations

To confirm UV/CaO2 as a new effective AOP, steady-state concentrations of

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•OH ([•OH]ss) were calculated. [•OH]ss in WAS under MP-UV/CaO2 treatment (CaO2

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ranging from 0 to 0.5 g g-1-VSS) was measured using para-chlorobenzoic acid (pCBA)

202

as a probe ([pCBA]0 ≈ 0.1 mg g-1-VSS, , = 5 × 10 M  s  ) (Jasper

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and Sedlak 2013). Under these conditions, disappearance of pCBA exhibited

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pseudo-first-order kinetics (R2 > 0.97) with the degradation rate constant "#$% .

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Meanwhile, IPA (100 mmol L-1) was added to quench •OH during MP-UV/CaO2

206

treatment with the degradation rate constant "#$%,&'% (R2 > 0.95). [•OH]ss can be

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calculated using Eq. 2:

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" − ",() = ∙," +⦁OH-..

(2)

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where "#$% is the degradation rate constant under MP-UV/CaO2 in h-1, &'%,"#$% is

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the degradation rate constant under MP-UV/CaO2 with IPA quencher in h-1, /0,"#

%$10

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is the degradation rate constant caused by ⦁OH radical in h-1.

212

2.5 Sample preparation and analysis of CBZ, PMD and pCBA in sludge The sample preparation procedure for the analysis of CBZ, PMD and pCBA

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followed the method described by previous investigations (Jasper et al. 2014, Zhang

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et al. 2015). The details of the procedure are provided in SI materials. CBZ, PMD,

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and pCBA spiked in WAS were detected using a high performance liquid

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chromatography (HPLC) system (Agilent 1260 series). Details of the analytical

218

methods are provided in SI materials.

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2.6 Identification of transformation products of CBZ and PMD

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During UV/CaO2 treatment, CBZ and PMD may undergo structural alteration

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because of the electronic transition from an excited state to the ground state (direct

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photolysis) or photolytic transformation induced by reactive radicals generated by the

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UV-photons (indirect photolysis) (Kosjek et al. 2009). The transformation products of

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CBZ and PMD in WAS under MP-UV/CaO2 were investigated. Main intermediates

225

were analyzed using an Agilent 1290 series HPLC coupled to a 6500 Series

226

Accurate-Mass Quadrupole Time-of-Flight (LC-Q-TOF) and an Agilent 1290

227

UHPLC coupled to an Agilent 6460 triple quadrupole mass spectrometer (LC-QQQ).

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Details of the analytical methods are provided in SI materials. The samples of

229

intermediates were prepared as the same procedure of CBZ and PMD.

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2.7 Analytical Methods for other parameters

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The analytical methods for TCOD, SCOD, TSS, VSS, TS, VS, pH,

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Oxidation-Reduction Potential (ORP), TOC were all described in our previous

233

investigations (Li et al. 2015, Zhang et al. 2015).

3

Results and discussion

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3.1 MP-UV/CaO2 pretreatment for the degradation of CBZ and PMD

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3.1.1

Effect of CaO2 dosage

CBZ and PMD were well degraded under both MP-UV and M-UV/CaO2

238

treatments, and the addition of CaO2 obviously enhanced their removal (Fig. 1(a) and

239

(b)). The degradation of the target compounds under MP-UV or MP-UV/CaO2 was

240

due to direct and indirect UV photolysis. The indirect photolysis may be caused by

241

free reactive radicals (•OH, O• , 1O2, DOM*, ⦁CO1 etc.) generated from UV

242

light-activated

243

Włodarczyk-Makuła 2018). The significant improvement of degradation efficiency

244

upon CaO2 addition may be attributed to amounts of reactive radical generated from

245

CaO2 activated by UV light, especially •OH (reactions 3-5) (Kozak and

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Włodarczyk-Makuła 2018), which is a vital oxidative radical to remove

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micropollutants(Oulton et al. 2010, Rosario-Ortiz et al. 2010).

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Kozak

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CaO2

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CaO + 2H O → Ca6OH7 + H O

(3)

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2CaO + 2H O → 2Ca6OH7 + O ↑ (4)

250

H O + hv → 2 ∙ OH

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The kinetics fitting results of CBZ and PMD coincided well with the

252

pseudo-first-order kinetics (R2 > 0.97, Table S1), and the degradation rates (K) of

(5)

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ACCEPTED MANUSCRIPT CBZ and PMD are shown in Fig. 1(c). Although K value increased with increasing

254

CaO2, the tendency became retarded. In fact, the degradation of micropollutant in

255

WAS was the comprehensive outcome of multi-factors. On the one hand, CaO2

256

disrupted the WAS structure and increased sludge solubilization (Li et al. 2015),

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which may reduce UV-shading effect on micropollutant degradation. Furthermore, it

258

made the natural chelating agents (organic acids, amino acids, and hydroxamate

259

siderophores) and transition metals release from sludge cell disruption forming

260

modified-Fenton (Zhang et al. 2015), which could accelerate the production rate of

261

free radicals under MP-UV. Therefore, the degradation of CBZ and PMD was

262

improved. On the other hand, the over addition of CaO2 resulted in the increase of

263

TSS (Fig. S3) and DOM. They could compete with the target compounds for the UV

264

light and oxidants, which may retard the increase of K values of the target compounds.

265

Furthermore, the invariable UV intensity limited the linear formation of •OH with the

266

increase of CaO2. The excessive CaO2 caused a higher pH value (Fig. 1(d)), which

267

may increase the decomposition rate of H2O2 (reaction 6) and lowered •OH

268

concentration (reactions 7-10), and moreover, may reduce the •OH oxidation potential

269

(Buxton et al. 1988). Consequently, the increase of K value was retarded with the

270

overdose of CaO2 dosage. In all, 0.2 g-CaO2 g-1-VSS was considered as the suitable

271

CaO2 dosage for the degradation of the target compounds and the corresponding

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irradiation time for 90% of CBZ and PMD degradation was 5.8 h and 6.3 h,

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respectively.

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2H O → 2H O + O

(6)

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⦁OH + OH  → O∙ + H O

(7)

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  ⦁OH + O∙ → HO  ,  ≤ 2 × 10 L mol s

(8)

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H

⦁OH + H O → HO• + H O ⇄ O•  + H O

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• •  @ ⦁OH + HO  → OH + HO ⇄ O + H /H O

@

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(9) (10)

Fig. 1(d) shows final pH value increased with increasing CaO2 dosage. However,

280

at the same CaO2 dosage, the pH with MP-UV treatment was lower than that without

281

MP-UV. Because MP-UV/CaO2 treatment as a stronger AOP caused a greater degree

282

of WAS disruption, resulting in the release of more extracellular and intracellular

283

materials which may function as buffering agents. Meanwhile, the ORP increased

284

exponentially with the CaO2 dosage (R2 = 0.97, Table S2), and the curve has the

285

similar trends with K values of CBZ and PMD in Fig. 1(c) (R2 ≥ 0.99, Table S2). The

286

ORP increased little when CaO2 dosage was higher than 0.2 g g-1-VSS, indicating that

287

further addition of CaO2 could not increase the oxidation capacity any more.

288

3.1.2

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Effect of initial VSS concentration and pH

AC C

289

SC

279

The increase of VSS concentration has a significant suppression on the

290

degradation of CBZ and PMD under both MP-UV and MP-UV/CaO2 treatments (Fig.

291

2(a)). This is because the increase of VSS caused serious UV-screening. Meanwhile,

292

the increase of suspended organic matter, DOMs (e.g., humic acid), and inorganic

293

ions (e.g., Cl‾, NO3‾, NO2‾ CO32‾ and HCO3‾) may compete with CBZ and PMD for

294

reactive radicals during the treatment (Qiu et al. 2019). Moreover, the K values were

14

ACCEPTED MANUSCRIPT 295

fitted as an exponential function of initial VSS concentration very well (R2 ≥ 0.98)

296

(Table S3). According the fitting formulas, the degradation rates of the target

297

compounds under different VSS concentrations can be inferred. Fig. 2(b) showed both the extreme low and high initial pH values promoted the

299

degradation of CBZ and PMD under MP-UV treatment, and the increase of K values

300

under alkaline conditions were more significantly than those under acidic conditions.

301

Under MP-UV/CaO2 treatment, both the low and high initial pH induced a big

302

promotion to the removal of the target compounds. This can be explained as follows:

303

Firstly, previous investigation showed strong pH surroundings could increase the

304

WAS solubilization through rupturing the sludge structure and cells (Ruiz-Hernando

305

et al. 2014), and subsequently improve the efficacy of UV light on micropollutant

306

degradation. Secondly, the improvement of K under low pH was because the acidic

307

medium increased the release rate of H2O2 (reaction (11)) and the final H2O2 yield

308

from CaO2 (Wang et al. 2016), which finally facilitated the formation of •OH

309

(reactions (3-5)) to degrade CBZ and PMD. However, it should be noted that with the

310

addition of CaO2, pH increased to the alkaline condition irrespective of the initial pH

311

(Fig. S4). Unless the very high initial pH condition (pH 12), the initial alkaline

312

condition cannot significantly improve the degradation rates of CBZ and PMD under

313

MP-UV/CaO2 treatment (Fig. 2(b)). Therefore, there is no need to adjust the initial pH

314

of WAS under MP-UV/CaO2 treatment.

315

CaO + 2H @ → Ca@ + H O

AC C

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298

(11)

15

ACCEPTED MANUSCRIPT 316

3.2 The degradation mechanisms of CBZ and PMD during MP-UV/CaO2 treatment

317

3.2.1

Effect of CaO2 hydrolysates combined with MP-UV Combining CaO2 hydrolysates with MP-UV to remove the target compounds

319

was investigated. As shown in Fig. 3, when combining with MP-UV irradiation,

320

Ca(OH)2 promoted the removal of CBZ and PMD significantly, while CaCl2 and

321

H2O2 had little influence. Therefore, the alkaline condition caused by CaO2 played an

322

important role in the improvement of K during MP-UV/CaO2. Liquid H2O2 known as

323

an oxidant could promote the WAS solubilization and remove some contaminants

324

(Zhang and Li 2014). However, unlike CaO2, it is thermodynamically unstable and

325

easily decomposed to form water and oxygen. Therefore, liquid H2O2 is insignificant

326

in improving the degradation rate constants of the target compounds under MP-UV.

327

However, the slow release of H2O2 from CaO2 may lead to the persistence of H2O2 in

328

WAS as compared with liquid H2O2, resulting in the increase of ⦁OH from H2O2

329

photolysis; meanwhile, the alkaline condition caused by CaO2 can promote the sludge

330

disintegration, which can improve the UV utilization efficiency during the photolysis

331

of CBZ and PMD. Therefore, CaO2 played a significant promotion in the degradation

332

rate constants of the target compounds compared to H2O2 under MP-UV. Moreover,

333

compared with the MP-UV treatment, the increases of K values of the target

334

compounds (CBZ: ~ 0.235 h-1, PMD: ~0.215 h-1) by MP-UV/CaO2 treatment were

335

greater than the sum of the increases caused by MP-UV/Ca(OH)2 and MP-UV/H2O2

336

treatments (CBZ: ~0.102 h-1, PMD: ~0 .115 h-1). This indicates that during MP-UV

AC C

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318

16

ACCEPTED MANUSCRIPT 337

irradiation, using CaO2 was better than combination of Ca(OH)2 with H2O2 to

338

improve the degradation of micropollutants in WAS.

339

3.2.2

340

3.2.2.1 Identification by scavengers

RI PT

Contributions of reactive radicals on the degradation of CBZ and PMD

Fig. 4(a) and (b) reveal effects of reactive radical scavengers on the degradation

342

rate constants of the target compounds in WAS under MP-UV and MP-UV/CaO2

343

treatments, respectively. IPA (~ 0.1 mol L-1) can quench •OH almost completely

344

(reaction (12)), whereas reactions of O2•– and 1O2 are unaffected (Singh 1982).

345

Therefore, the significant decrease of K upon adding IPA indicates •OH played an

346

important role in CBZ and PMD degradation under MP-UV and MP-UV/CaO2

347

treatments. The sparged N2 was used to remove O2 and 1O2. Since sole O2 had no

348

effect on the removal of the target compounds in WAS (Fig. S5), the decrease of K

349

under N2-satuated conditions was attributed to the elimination of 1O2 under both

350

treatments. SOD, a O2•– scavenger, can react with •OH and 1O2 at 5.3×1010 M-1 s-1 and

351

2.5 ×109 M-1 s-1 , respectively (Singh 1982). Therefore, to eliminate the effects of •OH

352

and 1O2, the IPA was added and N2 was sparged in advance. The negligible decrease

353

of K upon adding SOD implies little contribution of O2•– to the removal of CBZ and

354

PMD. IPE , usually as 3DOM* scavenger, can react with •OH at 1.2×1010 M-1 s-1

355

(Huang et al. 2011); meanwhile, 3DOM* can be quenched by O2 (Jasper and Sedlak

356

2013). Therefore, the IPA was added before the reaction and N2 was saturated during

357

the reaction. The comparison between K values upon N2+IPA and N2+IPA+IPE

AC C

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341

17

ACCEPTED MANUSCRIPT additions indicates 3DOM* could promote CBZ and PMD degradation during the

359

treatments. When CAT, usually as H2O2 scavenger, was further added (the

360

N2+IPA+IPE+SOD+CAT group), it appeared no suppression on the degradation rate

361

constants of the target compounds under MP-UP treatment but a little suppression

362

under MP-UP/CaO2 treatment, which is inconsistent with aforementioned little effect

363

of sole H2O2 on the degradation of the target compounds (Fig. S5). Because H2O2

364

generated from CaO2 hydrolysis may improve the efficacy of UV light irradiation on

365

the target compounds via WAS disruption.

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358

366

⦁OH + 6CH1 7 CHOH → 6CH1 7⦁ COH + H O,  = 1.9 × 10 L mol s 

367

The degradations of CBZ and PMD in the condition with addition of N2+ IPA+

368

IPE +SOD + CAT during MP-UV and MP-UV/CaO2 treatments may be caused by

369

direct photolysis and indirect photolysis caused by CO3•– (Jasper and Sedlak 2013).

370

Previous investigation demonstrated that STIC was the main factor to impact the

371

production of CO3•– (Huang and Mabury 2000). Preliminary investigation showed

372

STIC was about 3-6 mmol L-1 and 3-9 mmol L-1 under MP-UV and MP-UV/CaO2

373

treatments, respectively; meanwhile, the effect of CO3•– on the target compounds was

374

negligible when the STIC (CO32–) was below 10 mmol L-1 (detailed data not shown

375

here). Moreover, the second-order reaction rates posed by CO3•–on the target

376

compounds was 1-3 orders of magnitude lower than the values posed by •OH on the

377

target compounds, and DOM could reduce the lifetime of CO3•–(Canonica et al. 2005,

378

Jasper and Sedlak 2013). Therefore, the contribution of CO3•– to the overall

AC C

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(12)

18

ACCEPTED MANUSCRIPT 379

degradation rates of the target compounds was negligible and the degradation of CBZ

380

and PMD with the addition of N2+ IPA+ IPE +SOD + CAT should be attributed to the

381

direct photolysis. The contributions of different reactive radicals to the overall degradation rates of

383

WAS spiked CBZ and PMD are shown in Fig. 4(c). The degradation of WAS spiked

384

CBZ was mainly induced by •OH (68%), 3DOM* (15%) and direct photolysis (6%)

385

under MP-UV/CaO2, while •OH (39%), 3DOM* (24%) and direct photolysis (23%)

386

under MP-UV. The degradation of WAS spiked PMD was mainly induced by •OH

387

(62%), 3DOM*(15%), 1O2(10%) and direct photolysis (8%) under MP-UV/CaO2,

388

while •OH (38%), 3DOM*(23%), 1O2(11%) and direct photolysis (21%) under

389

MP-UV treatment. The contribution of •OH was obviously increased under

390

MP-UV/CaO2 treatment than that under MP-UV treatment. This enhancement was

391

due to the large production of •OH upon adding CaO2. In our investigation, ⦁OH was

392

the main reactive radical to remove CBZ and PMD, but the contributions of direct

393

photolysis, 3DOM* and 1O2 increased as compared to previous investigation in water

394

(Jasper and Sedlak 2013). This was attributed to 1) the different sludge matrix from

395

aqueous matrix, and 2) the specific MP-UV lamp and the strong intense irradiance of

396

MP-UV.

397

3.2.2.2 Identification by EPR

AC C

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382

398

During EPR experiments, SOD was added to quench O2•– reaction with DMPO

399

to generate DMPO-OOH which is easily converted into DMPO-OH during

19

ACCEPTED MANUSCRIPT MP-UV/CaO2 treatment (Lipovsky et al. 2012). The quartet DMPO-OH signal from

401

the reaction between DMPO and ⦁OH indicates •OH generated during MP-UV/CaO2

402

treatment in Fig. 5(a). Fig. 5(b) shows a negligible trace of DMPO-OH signal and a

403

DMPO-OOH signal upon adding thiourea, a •OH quencher, which indicates the

404

generation of O2•– in WAS under MP-UV/CaO2 treatment. The weak DMPO-OH

405

signal may be transformed from DMPO-OOH. Fig. 5(c) displays the primary spectral

406

features of similar DMPO-CH3 upon adding the target compounds under

407

MP-UV/CaO2 treatment. According to previous investigation, the primary spectra

408

signal may be DMPO-C-R signal (Zhang et al. 2015). Furthermore, the DMPO-C-R

409

signal further confirmed the existence of •OH radicals because •OH can attack the

410

target compounds to produce •C-R which can transform DMPO into DMPO-C-R

411

(Lipovsky et al. 2012). Fig. 5(d) exhibits the DMPO-OH, DMPO-OOH and

412

DMPO-C-R signals in WAS under MP-UV/CaO2, indicating the existence of •OH,

413

O2–• and probable •C-R radicals in WAS during MP-UV/CaO2 treatment.

414

3.3 Modeling and validating the steady-state •OH concentration

SC

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EP

Since ⦁OH played a vital role in the degradation of CBZ and PMD under

AC C

415

RI PT

400

416

MP-UV/CaO2 treatment, [•OH]SS was further calculated using pCBA. The changes of

417

"#$% and &'%,"#$% under MP-UV/CaO2 treatment are shown in Fig. S6.

418

According to Eq. 2, the [•OH]SS was calculated and shown in Fig. 6(a). The [•OH]SS

419

increased from 1.18×10-15 mol L-1 to 1.01 ×10-14 mol L-1 with CaO2 dosage increasing

420

from 0 to 0.5 g g-1-VSS. The mathematical fitting to the curves shows that [•OH]SS is

20

ACCEPTED MANUSCRIPT 421

an exponential function of CaO2 dosage([CaO2]) (Eq. 13, R2 = 0.99).

422

[•OH]SS = 1.22×10-14-1.01×10-14⦁exp(-3.06*[CaO2])

(13)

The [•OH]SS increased with the increase of CaO2 dosage but the tendency

424

became retarded. This is because the increase of CaO2 dosage would increase the

425

production of H2O2 (reaction 3) and pH, which finally increased the [•OH]SS under

426

UV activation (reaction 5). However, the UV irradiance was fixed and the increase of

427

CaO2 would increase the TSS concentration, which may block the UV irradiation and

428

retard the increase of •OH formation. This phenomena was in consistent with the

429

tendency of CBZ and PMD degradation described in section 3.1.1.

M AN U

SC

RI PT

423

To evaluate the applicability of the fitting formula of [•OH]SS (Eq. 13), predicted

431

degradation rates of the target compounds (∙/0,DEF"EGHI"JKILDMKI ) based on Eq. 14

432

were compared to the measured degradation rates (∙/0,DEF"EGHIFKNOGJKI ) of the

433

target compounds based on Eq. 15 ([CBZ] = 0.10 mg g-1-VSS, •,P = 9.1 ×

434

10 M  s  ; [PMD] =0.10 mg g-1-VSS, •,)QR = 6.7 × 10 M  s  ) (Jasper

435

and Sedlak 2013, Park et al. 2017). The measured #$U , &'%,#$U , 'VW and

436

&'%,'VW at different CaO2 dosages under MP-UV/CaO2 treatment are showed in Fig.

437

S6.

439

EP

AC C

438

TE D

430

∙/0,DEF"EGHI"JKILDMKI = /0,DEF"EGHI +⦁OH-..

(14)

∙/0,DEF"EGHIFKNOGJKI = DEF"EGHI − &'%,DEF"EGHI

(15)

440

where /0,DEF"EGHI is the degradation rates of the target compounds caused by ⦁OH

441

radical in h-1.

21

ACCEPTED MANUSCRIPT According to Eq. 14 and Eq. 15, when CaO2 dosage increased from 0 to 0.5 g

443

g-1-VSS, the predicted ∙/0,#$U increased from 0.0688 h-1 to 0.328 h-1, and the

444

measured ∙/0,#$U increased from 0.0709 h-1 to 0.330 h-1; the predicted ∙/0,'VW

445

was from 0.0507 h-1 to 0.242 h-1 corresponding to the measured ∙/0,'VW from

446

0.0541 h-1 to 0.243 h-1. ∙/0,DEF"EGHIFKNOGJKI of the target compounds under

447

MP-UV/CaO2 treatment agreed well with ∙/0,DEF"EGHI"JKILDMKI at various CaO2

448

dosage. The difference between them was less than 7% (Fig. 6(b)). Meanwhile, the

449

Pearson product-moment correlation coefficients between them were over 0.99.

450

Therefore, the fitting formula of [•OH]SS at various initial CaO2 dosage during

451

MP-UV/CaO2 treatment was considered reasonable. However, since the VSS is the

452

big influencing factor for MP-UV/CaO2 treatment, the effect of VSS on the ⦁OH

453

generation should be investigated in future.

454

3.4 The transformation products of CBZ and PMD

455

3.4.1

TE D

M AN U

SC

RI PT

442

EP

The transformation products of Carbamazepine The detected intermediates of CBZ are listed in Table S4. Their variations

457

detected by LC-QQQ during MP-UV/CaO2 treatment are shown in Fig. 7(a). During

458

MP-UV/CaO2 treatment, both the olefinic double bond in the central heterocyclic ring

459

and two outside aromatic rings can be attacked. Based on the transformation products

460

detected in WAS and the aforementioned degradation mechanism, a possible

461

degradation pathway for CBZ was proposed in Fig. 8(a).

462

AC C

456

The olefinic double bond was usually hydroxylated to form corresponding

22

ACCEPTED MANUSCRIPT 463

hydroxyl derivatives (Hu et al. 2009, Li et al. 2013, Tang et al. 2017) such as the

464

alcohol

465

10,11-dihydro-10,11-trans(cis)-dihydroxy-CBZ

466

(acridine-9-carboxaldehyde (AIC)) and ketone (i.e. oxcarbazepine). Therefore, the

467

hydration of the C10-C11 double bond of CBZ firstly occurred, forming CBZ-10OH

468

due to direct photolysis of CBZ (Chiron et al. 2006). The second predominant

469

pathway involved the heterocyclic ring contraction process (Chiron et al. 2006). The

470

reactive double bond was firstly attacked by oxidants to yield 10,11-

471

epoxycarbamazepine (CBZ-EP), which has been mentioned in many studies for water

472

or soil treatments (De Laurentiis et al. 2012, Kosjek et al. 2009, Li et al. 2013, Vogna

473

et al. 2004). Then, CBZ-EP was further oxidized into acridine-9-carboxaldehyde (AIC)

474

by •OH through the heterocyclic ring contraction with the loss of the CONH2 lateral

475

chain (Kosjek et al. 2009, Vogna et al. 2004). This contraction may take place via a

476

pinacol-type rearrangement for π-electron-rich heterocycles and convert an azepine

477

ring into an aromatic structure (Li et al. 2013). Finally, AIC was hydroxylated into

478

hydroxyacridine-9-carboxaldehyde (AIC-OH), or the carboxyaldehyde group of AIC

479

would cleavage to yield acridine (AI) (Kosjek et al. 2009). In addition, although

480

CBZ-DiOH was not detected here, previous investigation has showed CBZ-EP may

481

easily evolve into CBZ-DiOH during photooxidation and then undergo ring

482

contraction to yield AI via direct photolysis (De Laurentiis et al. 2012).

483

(10-hydroxy-10,11-dihydro-carbamazepine

(CBZ-10OH)

aldehyde

AC C

EP

TE D

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SC

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(CBZ-DiOH)),

and

The aromatic rings of CBZ can be attacked by •OH to form two stereoisomers

23

ACCEPTED MANUSCRIPT 484

(CBZ-OH): 2-hydroxy-carbamazepine and 3-hydroxy-carbamazepine. They can be

485

further hydroxylated into the dihydroxylated derivatives (CBZ-OH-OH) (De

486

Laurentiis et al. 2012, Miao et al. 2005). The dihydroxylated stereoisomers were

487

distinguished

488

2,7-dihydroxycarbamazepine

489

3,8-dihydroxycarbamazepine with the hydroxyl function on the different carbon site

490

of outside aromatic ring (De Laurentiis et al. 2012).

basis

of

the

retention

time,

which

may

be

RI PT

the

2,8-dihydroxycarbamazepine

and

SC

on

Fig. 7(a) shows the detected intermediates were almost degraded after 7 h

492

treatment by MP-UV/CaO2, which indicates MP-UV/CaO2 is effective in removing

493

CBZ and its intermediates. Previous investigations have also shown AI and AIC are

494

biodegradable (Kosjek et al. 2009), and the intermediates containing a hydroxyl and

495

carbonyl groups such as AIC-OH can be mineralized by micro-organisms found in

496

activated sludge (Keen et al. 2012). Therefore, the CBZ products produced in

497

MP-UV/CaO2 treatment was biodegradable

498

3.4.2

TE D

EP

The transformation products of Primidone

AC C

499

M AN U

491

The detected intermediates of PMD are listed in Table S5, and their variations

500

detected by LC-QQQ are shown in Fig. 7(b). Fig. 8(b) reveals a possible degradation

501

pathway for PMD in WAS under MP-UV/CaO2. Phenobarbital (PBB) and

502

hydroxyl-primidone (PMD-OH) were first detected during reaction, which suggested

503

the attack of •OH on the pyrimidine ring and the aromatic ring of PMD. This result

504

was consistent with previous investigations for PMD in water under UV photolysis

24

ACCEPTED MANUSCRIPT (Sijak et al. 2015) and electron beam radiolysis (Liu et al. 2015). PMD may also

506

undergo the cleavage of N[1]–C[2] bond and N[3]–C[2] bond of pyrimidine ring to

507

form phenylethylmalonamide (PEMA) (Mac Leod et al. 2008). Moreover, both PBB

508

and PMD-4OH may be oxidized by •OH to form 4-hydroxyphenobarbital (PBB-4OH).

509

In addition, the dipeptide bonds on the heterocyclic ring of PBB can be hydrolyzed to

510

form PEMA. As shown in Fig. 7(b), MP-UV/CaO2 is also considered to be an

511

effective pretreatment method to remove PMD and its intermediates because of the

512

disappearance of PMD intermediates in 7 h reaction.

M AN U

SC

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505

MP-UV/CaO2 process efficiently removed CBZ and PMD as well as their

514

intermediates. However, due to the complexity of organic constituents in sludge, there

515

may exist other incomplete intermediates, which may lead to environmental problem

516

and need to be further treated. Similar problems was also mentioned in the

517

investigation to CBZ degradation in soil (Li et al. 2013). Previous investigations have

518

shown the combination of oxidation and biotransformation has the potential to

519

synergistically mineralize persistent contaminants and their incomplete intermediates

520

in water (Keen et al. 2012, Watts and Linden 2008). For example, UV treatment

521

followed by aerobic or anoxic activated-sludge treatment can remove CBZ and its

522

final such as acridine and 9(10H)-acridone in wastewater (Kosjek et al. 2009);

523

UV/H2O2 treatment followed by a mixed bacterial inoculum from activated sludge

524

processes can mineralize CBZ and its oxidation products (Keen et al. 2012).

525

Therefore, UV/H2O2 process followed by a biofilm-mediated biofiltration process

AC C

EP

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513

25

ACCEPTED MANUSCRIPT have been proposed for the treatment of recalcitrant contaminants in water (Keen et al.

527

2012, Metz et al. 2011). In this study, we proved that MP-UV/CaO2 is effective in

528

eliminating CBZ and PMD in sludge, it can be followed by the subsequent anaerobic

529

fermentation treatment, which means the incomplete intermediates may be finally

530

degraded. However, the detailed biotransformation of these incomplete intermediates

531

during the AD should be investigated in future research.

532

3.5 Effect of MP-UV/CaO2 pretreatment on the solubilization of sludge

SC

RI PT

526

Fig. 9(a) shows SCOD increased drastically within 2 h, and then slowly to the

534

maximum SCOD (SCODmax) after 7 h reaction during MP-UV/CaO2 treatment. The

535

SCODmax increased with increasing CaO2 dosage, while overdose of CaO2 and

536

MP-UV irradiation did not help much to increase SCOD. Fig. 9(b) shows TSS and

537

VSS reduced more than 17.6% and 21.6% after 10 h MP-UV irradiation, respectively.

538

VSS reduction increased slowly with the increase of CaO2 dosage; however, TSS

539

reduction increased first and then decreased. The maximum of TSS reduction

540

occurred at CaO2 of 0.2 g g-1-VSS. This is because the increase of CaO2 dosage can

541

also increase the suspended solid (Fig. S3). Overall, 7 h MP-UV/0.2 g-CaO2 g-1-VSS

542

was considered as the optimum irradiation time for sludge disintegration. With this

543

treatment, SCODmax was 13.6% greater than that under 7h MP-UV. Moreover,

544

SCODmax with MP-UV treatment were much greater than those with sole CaO2

545

treatment. SCODmax increased by 657% under 7h MP-UV/0.2 g-CaO2 and 566 %

546

under 7h MP-UV as compared to that under sole 10 h CaO2 treatment (98.8 mg

AC C

EP

TE D

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533

26

ACCEPTED MANUSCRIPT g-1-VSS) (Fig. 9(c)). Therefore, both MP-UV and MP-UV/CaO2 could serve as quick

548

methods to promote the sludge solubilization. However, comprehensively considering

549

the degradation of pharmaceutical degradation and sludge solubilization, the operation

550

condition with 7 h MP-UV/0.2 g-CaO2 g-1-VSS is recommended. In this condition,

551

CBZ and PMD were removed by 92.3% and 90.2%, respectively.

RI PT

547

Although MP-UV/CaO2 performed very well in the removal of toxic TOrCs, the

553

consumption of chemicals and energy should be considered. Given the water content

554

of WAS is 99.5%-99.2%, VSS/TS = 0.6-0.7 and the optimum dosage of CaO2 is 0.2 g

555

g-1-VSS, the CaO2 consumption is about 0.6-1.1 kg/ton WAS. According to Title 22

556

of California Code of Regulations, 0.5-log removal (68.4%) was needed for the

557

removal of CBZ and PMD in advanced oxidation processes(Park et al. 2017),

558

indicating the time for CBZ and PMD removal is 1.3- 3.1 h, when TS was from 7-15

559

g L-1. Therefore, the energy consumption (EPT) and the increase of the effective

560

energy (∆EB) of MP-UV/CaO2 (compared to control group without any treatment)

561

was 73-174 kWh/m3 and 2.6-5.6 kWh/m3, respectively. As compared to ultrasounds

562

with EPT at 16.6–117.9 kWh/m3 and ∆EB at 1.5-7.4 kWh/m3, microwaves with EPT

563

at 37.5-150 kWh/m3 and ∆EB at 5.3-7.4 kWh/m3, etc. (Table S6), MP-UV/CaO2 does

564

not show obvious advantage as an energetically self-sufficient pretreatment. However,

565

this pretreatment mainly aims to remove the refractory TOrCs in WAS. Therefore,

566

MP-UV/CaO2 as a new AOP to pretreat WAS is worthwhile studying, and

567

furthermore, the subsequent AD after MP-UV/CaO2 need to be investigated in future,

AC C

EP

TE D

M AN U

SC

552

27

ACCEPTED MANUSCRIPT 568

especially in a full-scale WWTP.

4

Conclusion

570

MP-UV/CaO2 was an effective pretreatment method to remove CBZ and PMD in

571

WAS. The degradation of CBZ and PMD followed the pseudo-first-order kinetics.

572

Higher CaO2 dosage and lower VSS concentration were conductive to the removals of

573

CBZ and PMD.

SC

RI PT

569

Of the hydrolysates of CaO2, Ca(OH)2 played a more important role than H2O2

575

during MP-UV/CaO2 treatment. Using CaO2 is better than using Ca(OH)2 and H2O2

576

for the removal of CBZ and PMD under MP-UV irradiation. The degradation of CBZ

577

and PMD was mainly attributed to UV direct photolysis and indirect photolysis

578

caused by •OH, 3DOM*, and 1O2. Considering MP-UV/CaO2 as a new AOP, a model

579

for predicting [•OH]SS was proposed with CaO2 dosage ranging from 0 to 0.5 g

580

g-1-VSS.

EP

TE D

M AN U

574

Major transformation products of CBZ and PMD were identified and the

582

degradation pathways were proposed for the MP-UV/CaO2 treatment of WAS. Most

583

intermediates of CBZ and PMD were well removed after 7 h MP-UV/CaO2.

584

Additionally, these intermediates are biodegradable, which means MP-UV/CaO2 as a

585

good pretreatment method for WAS AD.

AC C

581

586

MP-UV/CaO2 was effective in promoting the sludge solubilization. Considering

587

both the degradation of CBZ and PMD and the sludge solubilization, the optimal

588

operation condition with 0.2 g-CaO2 g-1-VSS and 7 h MP-UV irradiation is 28

ACCEPTED MANUSCRIPT recommended. Under this condition, CBZ and PMD were removed by 92.3% and

590

90.2%, respectively and SCOD increased by 657% and 13.6% compared with sole 10

591

h CaO2 treatment and 7 h MP-UV treatment, respectively, indicating this technology

592

may be used for the subsequent AD to produce high quality SCFAs and CH4 in future.

593

Acknowledgments

This work was supported by the National Natural Science Foundation of China (No. 51578392).

596

Appendix A. Supplementary data

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Supplementary data of this article can be found in the online version. References

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ACCEPTED MANUSCRIPT Table 1. Characteristics of the raw waste activated sludge samples. Mean valuea

pH

6.9 ± 0.1

TS (total solid) (mg L-1)

13007 ± 95

VS (volatile solid) (mg L-1)

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Parameters

8853 ± 74

VSS (volatile suspended solid) (mg L-1)

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TCOD (total chemical oxygen demand) (mg L-1)

12647 ± 21

SC

TSS (total suspended solid) (mg L-1)

8600 ± 14

9105.9 ± 70.1 1093 ± 45

SCOD (soluble chemical oxygen demand) (mg L-1)

66.5 ±3.2

STOC(soluble total organic carbon) (mg L-1)

10.02

STIC(soluble total inorganic carbon) (mg L-1)

38.02

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Total carbohydrate (as COD) (mg L-1)

9.7 ±0.9

TN (total nitrogen in sludge supernatant) (mg L-1)

5.9 ± 0.2

TP (total phosphorus in sludge supernatant) (mg L-1)

6.9 ± 0.1

Data are shown as arithmetic mean of three replicates ± standard deviation.

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TSCFA (total short-chain acids in sludge supernatant) (mg L-1)

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Fig. 1. (a) The degradation of CBZ under MP-UV/CaO2; (b) the degradation of PMD

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under MP-UV/CaO2; (c) effect of CaO2 dosage on pseudo-first-order kinetics constant K values of CBZ and PMD; (d) the ORP values at the 5th h during MP-UV/CaO2

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treatment and the pH values after 10 h CaO2 or MP-UV/CaO2 treatments. ([CBZ] =

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0.1 mg g-1-VSS, [PMD] = 0.1 mg g-1-VSS)

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Fig. 2. Effect of (a) initial VSS concentration and (b) pH value on the degradation rate

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constant (K) of CBZ and PMD under MP-UV and MP-UV/CaO2 treatments. ([VSS] = 8.6 g L-1, [CaO2] = 0.2 g g-1-VSS, [CBZ] = 0.1 mg g-1-VSS, [PMD] = 0.1 mg

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g-1-VSS)

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Fig. 3. K values of CBZ and PMD in WAS under different treatments and the

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corresponding pH values after reaction (right Y-coordinate). ([CaO2] = 0.2 g g-1-VSS; [H2O2] = 0.071 g g-1-VSS, [CaCl2] = 0.305 g g-1-VSS; the Ca(OH)2 dosage was set at pH = 9.05 adjusted with Ca(OH)2; [CBZ] = 0.1 mg g-1-VSS, [PMD] = 0.1 mg

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g-1-VSS).

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Fig. 4. Effect of scavengers of reactive radicals on the degradation rates (K) of CBZ

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and PMD in WAS under: (a) MP-UV and (b) MP-UV/CaO2 treatments, respectively; (c) contribution of direct and indirect photolysis (•OH, O2•–, O21, 3DOM* and H2O2)

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on CBZ and PMD degradation under these two treatments. ([IPA] = 100 mmol g-1-VSS, [IPE] = 100 mmol g-1-VSS, [SOD] = 12.5 kU g-1-VSS, [CAT] = 12.5 kU

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g-1-VSS, [CaO2] = 0.2 g g-1-VSS, [CBZ] = 0.1 mg g-1-VSS, [PMD] = 0.1 mg g-1-VSS)

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Fig. 5. EPR spectrum of reactive radicals released during the MP-UV/CaO2 treatment

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of WAS with DMPO spin trap: (a) WAS containing SOD (O2•– quencher, 12.5 kU g-1-VSS), (b) WAS containing thiourea (•OH quencher, ~ 0.1 mol L-1) (c) WAS

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containing CBZ (1mg g-1-VSS) and PMD (1mg g-1-VSS), and (d) WAS without

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additives. ([VSS] = 8.6 g L-1, [CaO2] = 0.2 g g-1-VSS)

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Fig. 6. (a) Measured [•OH]SS and (b) predicted and measured pseudo-first-order constants of CBZ and PMD caused by •OH in WAS under MP-UV/CaO2 treatment.

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(measured value: K•OH,CBZ (⧯) and K•OH,PMD (⧳); predicted value: K•OH,CBZ (―) and

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K•OH,PMD (―))

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Fig. 7. Variations of the intermediates of (a) CBZ and (b) PMD in WAS detected by

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g-1-VSS, [PMD] =1 mg g-1-VSS)

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LC-QQQ during MP-UV/CaO2 treatment. ([CaO2] = 0.2 g g-1-VSS, [CBZ] =1 mg

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ACCEPTED MANUSCRIPT Fig. 8. Proposed degradation pathways of (a) CBZ and (b) PMD in WAS under MP-UV/CaO2 treatment. The braces mean intermediates which have the same number of hydroxyl on the different carbon site; short dash line indicates the bond broken;

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uppercase letters under chemical structure indicates intermediates abbreviation.

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Fig. 9. When CaO2 dose increased from 0 to 0.50 g-CaO2 g-1-VSS, (a) the change of SCOD during MP-UV/CaO2 treatment; (b) the reduction of TSS and VSS after 10 h MP-UV/CaO2 treatment; (c) the SCODmax under 10 h sole CaO2 and 7h MP-UV/CaO2 treatments. ([VSS] = 10.72 g L-1)

ACCEPTED MANUSCRIPT Highlights MP-UV/CaO2 can promote CBZ/PMD removal and sludge solubilization




Major reactive radicals under MP-UV/CaO2 were identified




A model predicting [•OH]SS under MP-UV/CaO2 was proposed and validated




Ca(OH)2 was more important than H2O2 for CBZ/PMD removal under

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MP-UV/CaO2

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The transformation pathways of CBZ and PMD in WAS were proposed

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