Effective removal of odor substances using intimately coupled photocatalysis and biodegradation system prepared with the silane coupling agent (SCA)-enhanced TiO2 coating method

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Effective Removal of Odor Substances Using Intimately Coupled Photocatalysis and Biodegradation System Prepared with the Silane Coupling Agent (SCA)-Enhanced TiO2 Coating Method Shiyuan Fu , Xinyu Zhao , Zhou Zhou , Mengyan Li , Liang Zhu PII: DOI: Reference:

S0043-1354(20)31104-0 https://doi.org/10.1016/j.watres.2020.116569 WR 116569

To appear in:

Water Research

Received date: Revised date: Accepted date:

6 August 2020 17 October 2020 24 October 2020

Please cite this article as: Shiyuan Fu , Xinyu Zhao , Zhou Zhou , Mengyan Li , Liang Zhu , Effective Removal of Odor Substances Using Intimately Coupled Photocatalysis and Biodegradation System Prepared with the Silane Coupling Agent (SCA)-Enhanced TiO2 Coating Method, Water Research (2020), doi: https://doi.org/10.1016/j.watres.2020.116569

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HIGHLIGHTS    

ICPB process is used for treatment of 2-MIB and GSM KH560 greatly enhanced the adhesion between photocatalysts and the carrier The outer photocatalysts protected the viability of internal biofilms 2-MIB and GSM removal rates in 12 h were maintained 86-90% even after 5 cycles

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Effective Removal of Odor Substances Using Intimately Coupled Photocatalysis and Biodegradation System Prepared with the Silane Coupling Agent (SCA)-Enhanced TiO2 Coating Method Shiyuan Fu a, #, Xinyu Zhao d, #, Zhou Zhou a, Mengyan Li e, Liang Zhu a, b, c, * a. Institute of Environmental Pollution Control and Treatment, Zhejiang University, Hangzhou 310058, China b. Zhejiang Province Key Laboratory for Water Pollution Control and Environmental Safety, Hangzhou 310058, China c. Zhejiang Provincial Engineering Laboratory of Water Pollution Control, 388 Yuhangtang Road, Hangzhou 310058, China d. Hangzhou No. 14 High School, Hanzhou 310006, China e. Department of Chemistry and Environmental Science, New Jersey Institute of Technology, Newark, New Jersey 07102, United States

#

These authors contributed equally to this work and should be considered co-first authors.

*

Corresponding author. Institute of Environmental Pollution Control and Treatment, Zhejiang

University No. 866 Yuhangtang Road, Hangzhou 310058, PR China. Tel (fax): +86 571 88982343. E-mail address: [email protected].

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Abstract Intimately coupled photocatalysis and biodegradation (ICPB) combining photocatalysis with microbial degradation is an attractive wastewater treatment technology. However, when prepared in conventional ways, the supported-photocatalysts aggregate frequently, detach easily from carriers, and prohibit the colonization of microorganisms inside the carriers. To overcome these challenges, silane coupling agent (SCA)-enhanced TiO2 coating method is developed in this study. The coupling agent γ-glycidoxypropyltrimethoxysilane (KH560) greatly enhanced the adhesion between photocatalysts and the carrier through ether and Ti-O-Si linkages. The dense TiO2 layer was firmly adhered to the carrier outer surface, and the loading amount reached 351.8±8.2 mg/g, over ten times higher than using the powder sintering method (31.5±2.4 mg/g). In the ICPB system

constructed

(KH560-TiO2-PU)

with carriers,

the

KH560-enhanced

removal

efficiencies

TiO2-supported of

two

polyurethane

model

odor

sponge

substances,

2-methylisoborneol (2-MIB) and geosmin (GSM), reached 88.9±0.3% and 85.0±1.0% in 12 h at an initial concentration of 500 ng/L respectively, which were 17.7±0.6% and 19.4±0.4% greater than those of the ICPB system prepared with the powder sintering method. After 5 operating cycles, the novel ICPB system remained stable with high 2-MIB and GSM removal efficiencies, reaching 89.9±0.8% and 86.1±0.2% respectively after 12h, while TiO2 peeling ratio was as low as 5.0±2.8%. Biofilms attached onto the carrier inner surface were resilient over the operating cycles with the increase of both richness and diversity of microbial communities. Analysis of biofilm microbial community and pollutant degradation pathways revealed the enhanced removal of 2-MIB and GSM in the novel ICPB system might be attributed to multiple factors. First, the alleviated aggregation and increased adhesion of photocatalysts onto carriers improved the overall 3

photocatalysis efficiency. Second, biofilm inside of the carrier was protected and the microbial activity was well remained. Third, photocatalytic intermediate products were efficiently biodegraded by the enriched functional microbial populations, such as Thauera and Flavobacterium, with little concern of excessive oxidation. Collectively, this research provides a new technological solution that synergizes photocatalysis and biodegradation for effective removal of odorous substances in polluted natural water.

Key words: Intimately coupled photocatalysis and biodegradation (ICPB); Silane coupling agent; TiO2; 2-methylisoborneol (2-MIB); Geosmin (GSM)

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1. Introduction Algae bloom triggered by eutrophication is attracting growing attention. It does not only cause the deterioration of aquatic ecosystems, but also produces odor substances during the growth and metabolism of algae (Suffet et al., 1996; Zhang et al., 2009), threatening water supply quality and public health (Wu et al., 2019). 2-Methylisoborneol (2-MIB) and geosmin (GSM) are two most frequently detected algal odorants in natural water (Asquith et al., 2018), and they can be detected easily at low levels by human olfactory sense concentrations (Davies et al., 2004), and have bio accumulation and toxicity (Gagne et al., 1999; Nakajima et al., 1996). Moreover, 2-MIB and GSM are both saturated cyclic tertiary alcohols, which are persistent and difficult to be removed by traditional water treatment processes, removing odor substances in polluted natural water bodies has become a difficult problem. Although 2-MIB and GSM can be removed by microbial degradation, the degradation rates are quite slow (Izaguirre et al., 1988; Yuan et al., 2012). Indiscriminately rapid chemical reactions of advanced oxidation processes (AOPs) usually lead to accumulation of toxic by-products and excessive residual of oxidation products (Collivignarelli et al., 2004; Wang et al., 2015; Yoon et al., 2007; Kim et al., 2016; Park et al., 2017), which cannot achieve complete mineralization of odorous substances. Intimately coupled photocatalysis and biodegradation (ICPB) may have the potential to repair the odorous substances-polluted natural water. ICPB system has been applied for the removal of a variety of refractory organic substances, in which photocatalysis and microbial degradation occur simultaneously (Li et al., 2011; Li et al., 2012a; Yan et al., 2013; Zhang et al., 2013; Xiong et al., 2017; Yu et al., 2020). Ultraviolet (UV) light is commonly used to excite photocatalysis (Marsolek 5

et al. 2008; Li et al., 2011; Li et al., 2012a), and refractory contaminants are decomposed by photocatalyst such as TiO2, and photocatalytic intermediate products can rapidly permeate into the carrier and be completely mineralized by the biodegradation of the biofilm attached to the carrier inner surface (Xiong et al., 2017). In ideal ICPB systems, photocatalysts are coated on the macroporous carrier (eg. polyurethane sponge) outer surface while microorganisms colonize on the inner surface (Li et al., 2012b). However, it remains challenging to achieve a tight and long-lasting adhesion of metal-based photocatalysts onto the hydrophobic outer surface of macromolecule carriers (Li et al., 2019). While photocatalysts were coated by conventional procedures, such as powder sintering and sol-gel methods, the photocatalysts has low load ratio and tend to aggregate, reducing their catalytic efficiencies. Detachment of photocatalysts from the carrier is also frequent due to low adhesion strength. Moreover, the photocatalysts are often coated on the carrier inner surface, which prohibits the colonization of microorganisms (Li et al., 2012b; Li et al., 2019; Ma et al., 2015). Silane coupling agents (SCAs) could improve the catalyst coating method because they have a strong “bridging” effect in combining organic and inorganic materials (Sang et al., 2017; Zheng et al., 2019). The molecular chemical structure of SCAs can be represented as Y-R-SiX3. The -X represents an alkoxy, acetoxy, halogen, etc., which can undergo a hydrolysis reaction to generate silanol hydroxyl groups (-Si-OH). Then, -Si-OH can chemically bond with the surface of inorganic materials. The -Y represents a vinyl, amino, epoxy, mercapto, etc., which can react with the polymer so that the silane can adhere to the surface of organic materials (Arkles, 1977). In this study, a modified SCA enhanced TiO2 coating method is developed, which greatly 6

improves the adhesion strength between photocatalysts and carriers. The ICPB system is used to remove 2-MIB and GSM for the first time to explore the feasibility of ICPB system for removing odor substances in polluted natural water. Firstly, the selection of SCAs and preparation conditions are optimized on the basis of the loading amount and adhesion strength of TiO2. The feasibility of this novel method is further evident by evaluating the accumulation of biofilm, the 2-MIB and GSM degradation efficiency, and the stability of the novel ICPB system. In addition, the removal mechanism of 2-MIB and GSM in the novel ICPB system is proposed based on the analysis of intermediate products, microbial activity and dominant bacteria.

2. Materials and methods 2.1 Chemicals and reagents 2-MIB (CAS: 2371-42-8) and GSM (CAS: 16423-19-1) were purchased from Sigma–Aldrich Co., USA. All other chemicals were analytically pure without requirement for further purification. Ultra-pure water was used throughout the experiment.

2.2 Carrier and TiO2 coating procedure optimization Polyurethane (PU) sponge was selected as the carrier with following characteristics: 3 mm × 3 mm × 3 mm, 60 ppi, a pore size of 100-300 μm, a porosity of about 87%, and 0.15 g per 100 pieces. Nanometer TiO2 was selected as the photocatalyst, provided by Shanghai Jiaotong University. The conventional process of bonding inorganic nano-powder material and organic material surface with SCA follows five steps (detailed in Section S1): 1) Hydrolysis of SCA; 2) Immersed 7

and blended with inorganic nano-powder material; 3) Heat curing; 4) Immersed and blended with organic materials; 5) Heat curing. As the heating temperature of the third step and the fifth step can be identical, a four-step preparation method waived the first heat step was developed (detailed in Section S1). The heating temperature was set at 65 °C and 150 °C, respectively. Three kinds of SCAs, KH550, KH560, and KH570, were compared. Four different coating procedures were carried out, including the five-step process at 65 °C (Five-65 °C), four-step process at 65°C (Four-65 °C), five-step process at 150 °C (Five-150 °C), and four-step process at 150 °C (Four-150 °C). The hydrolysis conditions were adjusted due to the differences in the optimal hydrolysis conditions of SCAs (Table S1). Carriers coated by the powder sintering method were prepared as the control (Tang et al., 2015).

2.3 Inoculation and microbial enrichment The inoculated activated sludge was collected from the secondary sedimentation tank of Hangzhou Qige Sewage Treatment Plant, and cultivated using a sequential batch aerobic activated sludge reactor with the influent of 1.2 kg COD/(m3∙d) and COD/NH3-N of 15: 1. The formulation of influent nutrient is shown in Table S2. The aerobic activated sludge reactor ran for 6 cycles per day. Each cycle (4 h) was divided into 4 stages: inflow for 5 minutes, aeration for 215 minutes, precipitation for 10 minutes, and drainage for 10 minutes, at a volume exchange ratio of 50%. After the sludge was acclimated and stabilized, the TiO2-supported sponges placed in a mesh bag were fixed in the activated sludge reactor for 12 d for microbial colonization. Then the carriers were cultured in a 250 mL Erlenmeyer flask on a shaker for 2 d.

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2.4 Reactor setup and experimental methods The ICPB reaction device with a working volume of 600 mL is shown in Fig. S1, and the configuration details are described in Section S2. The experiment was conducted at 25 °C. Each of the eight UV light source (SANKYO DENKI, Japan) had a power of 4 W and a characteristic peak of 254 nm. The intensity of the UV light received by the outer wall of the reactor was 2.5 mW/cm2 mimicking the exposure of sunlight (2.0-3.0 mW/cm2) as measured by an irradiator (ultraviolet light measurement mode 01080336, Beijing Normal University Illumination Electronic Instrument Factory, China). The Einstein constant was 1.11×10-7 einstein/(L∙s) with 254 nm as the average wavelength of ultraviolet light according to the Planck formula: F=

AλWT VhcNa

(1)

Where A and V are the light receiving area and light receiving volume respectively, F is the Einstein constant, λ is the light wavelength, h is the Planck constant, c is the speed of light, Na is the Avogadro constant, and WT is the light intensity. The initial 2-MIB and GSM concentrations of the degradation test were both ~500 ng/L, to simulate their occurrence in natural water. To compare with the performance of the novel ICPB system (ICPB-SCA), four control systems with different operating conditions were designed, including the ICPB system with powder sintering method (ICPB), photocatalysis (P) system, biodegradation (B) system, and adsorption (AD) system (Table 1). All the above systems were carried out in separate reactors of an identical device design (Fig. S1) at 25 °C.

2.5 Analytical methods Concentrations of 2-MIB and GSM and their intermediates were analyzed using headspace 9

solid-phase microextraction method (HS-SPME) in combination with gas chromatography–mass spectrometry (GC-MS) at the full scan mode (details in Section S3). TiO2 loading amount (calculated as Ti) was detected by ICP-MS (PerkinElmer NexION 300X) under specific conditions (plasma gas flow rate, 17.0 L/min; atomizing gas flow rate, 0.92 L/min; RF power, 1300 W; KED measurement mode; He gas flow rate, 3.0 mL/min; integration time, 1000 ms) (sample pretreatment steps in Section S4). X-ray diffraction spectroscopy (XRD, Dmax-2550PC, Japan) was used to characterize the TiO2 crystal form (Kobayashi et al., 2008). After spray-gold treatment, scanning electron microscope (SEM, Hitachi SU-8010, Japan) was used to observe the TiO2 loading form on the carrier surface. The ratio of TiO2 loading amount after and before the 12-hour mechanical stirring represented the adhesion strength of TiO2 when optimizing the coating method. Attenuated total reflection Fourier transform infrared spectrometer (ATI-FT-IR, AVA TAR370) was used to measure the infrared spectra of sponge carrier samples (Zhao et al., 2012). Colonized microbial morphology on the carrier surface was characterized by SEM (Hitachi SU-8010, Japan), according to our previous study (Zhang et al., 2018a). The biomass of living cells was characterized by ATP from microorganisms on the carrier inner surface using the Beyotime Enhanced ATP Assay Kit. The LIVE/DEADTM BaclightTM Bacterial Viability Kit was used to stain the dead and living cells, then CLSM (LSM 710) was used to obtain the proportion of dead and live cells on the inner carrier surface. The bacterial communities of attached biofilm were analyzed by the Illumina MiSeq sequencing technology (details of the sample collection in Section S5). DNA extraction, 16S rRNA gene PCR amplification and Illumina MiSeq sequencing were consistent with the previous study (Zhang et al., 2018b). 10

All measurements were performed in triplicate. The optimal TiO2 coating procedure was obtained through orthogonal experiment, and TiO2 loading amount and adhesion strength were used as visual analysis indexs.

3. Results and discussion 3.1 Optimization of the SCA-enhanced TiO2 coating method 3.1.1 Optimization of SCAs and preparation steps of TiO2-supported carriers The four-step process and the coupling agent KH560 showed advantages in the TiO2 loading amounts (Fig. 1a). The amount of TiO2 loaded on the carrier surface by four-step process was significantly higher than that of the five-step process (2-3 times). It might be because the Y moieties of SCAs were destroyed by the direct heating during the first heat-curing step of the five-step process (Abdolmaleki et al., 2011), which subsequently reduced the coupling reaction between SCA and PU sponge. In the four-step preparation, high and stable TiO2 loading was achieved (196.516.1 mg/g, 65℃; 359.786.8 mg/g, 150℃) when KH560 was used as the coupling agent. As for KH550 or KH570, the TiO2 loading amounts were more sensitive to temperature than KH560. This is in part because the epoxy group of KH560 is more efficient to react with amino and carboxyl groups of the polymer chains on sponge surface and form a stable chemical cross-linkage. The reaction could occur over a broad range of catalysis temperatures, and the formed cross-linked structure was of high thermal stability (Li et al., 2014). Functional groups on the carrier surface at different conditions were characterized by 11

ATI-FT-IR (Fig. 1b, c, d). The unloaded PU carrier has tensile vibration peak and deformation vibration peak of N-H at 3295 cm-1 and 1641 cm-1, asymmetric and symmetrical tensile vibration peaks of C-H at 2971 cm-1 and 2869 cm-1, and tensile vibration peaks of C-O at 1103 cm-1. These peaks were detected in other TiO2-supported carrier surfaces, indicating that the polyurethane sponge carrier structure was not destroyed. Using three kinds of SCAs, the peak intensity at 2971 cm-1 and 2869 cm-1 increased, indicating the vibrational absorption peaks of the three SCAs molecular groups -CH2. Increase of the peak intensity at 1103 cm-1 was presumed to be the result of the superposition of Ti-O-Si stretching vibration and C-O stretching vibration, indicating that the hydroxyl group produced by the hydrolysis of the SCAs’ X groups and the hydroxyl group of TiO2 surface formed Ti-O-Si by dehydration reaction (Zhao et al., 2012). This observation demonstrated that three SCAs successfully adhered to TiO2. As for the connection to the surface of the PU carrier, the peaks at 3295 cm-1 and 1641 cm-1 increased while using KH550, indicating that the Y group (-NH2) of KH550 bonded with the sponge surface by forming N-H. While using KH560 as the coupling agent, the absorption peak intensity at 3295 cm-1 increased, indicating that the surface of the carrier had an O-H stretching vibration absorption peak; the peak strength of C-O tensile vibration peak at 1225 cm-1 increased, speculating that the epoxy functional group at the end of KH560 Y group (-OCH2CH(O)CH2) generated hydroxyl groups by the ring-opening reaction and bonded with the sponge surface by generating unsaturated ether bonds. KH570 increased the peak strength of the stretching vibration peaks at 3295 cm-1 and 1641 cm-1, indicating that the C=O or C=C at the end of the KH570 Y group (CH2=C(CH3)COO-) was still retained with no or little portion of chemical bonding with the functional groups of the carrier surface. 12

Anatase has the highest photocatalytic activity among all crystalline forms of TiO2 and is most widely used in photocatalysis (Bavykin et al., 2006; Kobayashi et al., 2008). According to the XRD spectrum (Fig. S2), the characteristic peaks of the anatase phase appeared at 2θ = 25.46°, 37.82°, 48.08°, 55.18°, and 62.74°, and the corresponding crystal planes were (101), (004), (200), (211) and (204), respectively, indicating that the nano-TiO2 used in this study was anatase TiO2. PU sponge had a characteristic peak only at 2θ = 19.88°. For the TiO2-supported carriers using different coating procedures, in addition to the characteristic peaks of the PU carrier at 2θ = 19.88°, the characteristic peaks of the anatase phase also appeared at 2θ = 25.46°, 37.82°, 48.08°, 55.18°, and 62.74°, identical to the nano-TiO2 powders. These results indicated that the anatase TiO2 crystal form was not affected by the adhesion with PU sponge carriers. Through the observation of supported-TiO2 on the sponge surface (Fig. S3), the aggregation of TiO2 was found to be significantly alleviated when the four-step preparation was employed. Especially when KH560 was used as the coupling agent, the carrier outer surface was coated with a layer of uniform and dense TiO2. The reason might be that SCA diminished the hydroxyl groups on the surface of the nanoparticles, which stabilized the nanoparticles and prevented the aggregation in organic solutions (Zhao et al., 2012; Matinlinna et al., 2018). Little TiO2 was observed on the carrier inner surface, creating TiO2–coated PU sponges ideal for supported-photocatalysis. Overall, our results confirmed the feasibility of a four-step method with KH560 as the SCA to produce TiO2–coated PU sponges since this approach obtained the better photocatalyst coating effect and provided a TiO2–free non-toxic inner surface for biofilm growth and acclimation. On the contrary, low TiO2 surface bonding and agglomeration still occurred in the five-step preparation and the powder sintering method. 13

3.1.2 Optimization of preparation conditions

KH560 and the four-step method were selected according to the above selection, with variables of the alcohol-water ratio of hydrolysis solution, hydrolysis time, concentration of KH560 and heat-curing temperature. Each variable was tested at three levels to design orthogonal experiments (Table 2). Visual analysis used TiO2 loading amount and adhesion strength as indexes (Table S3). Results of orthogonal experiments showed that all TiO2 loading amounts under different conditions were about 200 mg/g - 400 mg/g. Adhesion strength of all nine sets was strong. The TiO2 peeling ratios were lower than 5% except for the three sets (6: 1 of alcohol-water ratio, 24 h of hydrolysis time, 15% of C%KH560, 85 ℃; 8: 1 of alcohol-water ratio, 24 h of hydrolysis time, 25% of C%KH560, 65 ℃; 10: 1 of alcohol-water ratio, 24 h of hydrolysis time, 5% of C%KH560, 105 ℃) after 12-hour stirring. The order of effects of various factors on the index of TiO2 loading amount was: KH560 concentration, heat curing temperature, hydrolysis time, alcohol-water ratio of hydrolysis solution; the optimal conditions were determined as: alcohol-water ratio of hydrolysis solution of 8:1, hydrolysis time of 36 h, KH560 concentration of 15%, heat curing temperature of 85 °C. The order of effects of various factors on the index of TiO2 adhesion strength was: hydrolysis time, heat curing temperature, KH560 concentration, alcohol-water ratio of hydrolysis solution; the optimal conditions were determined as: alcohol-water ratio of hydrolysis solution of 8:1, hydrolysis time of 36 h, KH560 concentration of 25%, heat curing temperature of 85 °C. As the KH560 concentration had less effect on TiO2 adhesion strength, which was sufficiently high as 95.3% when the KH560 concentration was 15%. Therefore, the optimal KH560 concentration of 15% was selected. 14

Collectively, KH560-TiO2-PU carriers was prepared by KH560 and the four-step preparation method with alcohol-water ratio of hydrolysis solution of 8:1, hydrolysis time of 36 h, KH560 concentration of 15%, heat curing temperature of 85 °C. This TiO2-coated carrier was designated as “KH560-TiO2-PU carrier”. Compared with previous works, Li et al. (2012b) coated TiO2 onto the PU sponge by the low temperature sintering method, diluted method, diluted and no additive method respectively, and the loading amount was 0.3, 0.264, 0.24 g/g carrier (calculated as Ti) respectively. Li et al. (2019) used powder spraying method and sol-gel method respectively to coat BiOCl /Bi2WO6 / Bi to PU carrier, the weight loss rates after 60h were 73% and 96% respectively. The trimesic acid in the diluted method and the polyurethane waterproof coating in the powder spraying method was also used as a binder, but KH560-enhanced coating method had advantages in simultaneously achieving high TiO2 loading amount (0.352 g/g), thin and uniform catalytic layer and high loading strength.

3.2 Removal of 2-MIB and GSM by the ICPB system with KH560-TiO2-PU carriers 3.2.1 Removal efficiencies of 2-MIB and GSM

For the 2-MIB removal at an initial concentration of 501.1±14.4 ng/L for 12 h, the ICPB-SCA system showed higher 2-MIB removal efficiency (Fig. 2a). In the first 0.5 h, 2-MIB removal in the AD system was close to those in other systems, indicating that the initial removal of 2-MIB was primarily due to adsorption. The 2-MIB concentration in AD system decreased to the plateau of 210 ng/L in 1 h, suggesting an equilibrium of adsorption and desorption; the final removal efficiency of the AD system was 60.2±1.6% within 12 h with 2-MIB concentration 15

leveled at 199.2±8.0 ng/L. The 2-MIB removal efficiency of the B system was 69.9±0.8%, slightly higher than the AD system. These results indicated that the most of 2-MIB loss was due to adsorption and only a small portion of 2-MIB was directly biodegraded in the B system. This concurs with previous studies revealing 2-MIB is recalcitrant for the biodegradation in the natural environment. 2-MIB removal efficiency of the P system reached 78.7±1.0% within 12 h with 2-MIB residual concentration of 106.8±4.9 ng/L, indicating the highly effective photocatalytic degradation of 2-MIB by nano-TiO2. In the ICPB-SCA system, the lowest 2-MIB concentration among all treatments (162±12.3 ng/L) was observed after 4 h, probably because the detaching of the biofilm on the carrier outer surface resulted in a larger UV-illuminating area for TiO2, which accelerated the photocatalytic reaction (Li et al., 2011; Dong et al., 2016; Xiong et al., 2017). In 12 h, 88.9±0.3% of the 2-MIB removal was achieved lingering 2-MIB concentration as low as 55.9±1.5 ng/L. The 2-MIB removal in the ICPB-SCA system was superior to the P system, that might be due to the biodegradation of the intermediates reduced the competition for photocatalytically generated free radicals, which made these free radicals more readily available to attack 2-MIB (Xiong et al. 2017). GSM removal with an initial concentration of 504.0±24.3 ng/L was observed in a similar fashion to 2-MIB in all tested systems (Fig. 2b). The removal efficiency of 39.3±1.5% in the AD system was similar to those in other systems in the first 0.5 h, indicating that adsorption dominated the early GSM removal. Later, it became stable around 49.0±0.7% in 12 h. The GSM concentration in the ICPB-SCA system was the lowest (224.5±3.2 ng/L) after 1 h among all treatments. After 12 h of reaction, the ICMB-SCA system had the highest GSM removal efficiency 16

of 85.0±1.0% with the final concentration reduced to 75.7±5.0 ng/L, higher than those in the P system (72.7±1.7%) and the B system (56.1±2.9%). The 2-MIB and GSM removal efficiencies of the ICPB system with the powder sintering method were 71.2%±2.7% and 65.6%±2.5%, respectively. Comparing with the ICPB system, the 2-MIB and GSM removal efficiencies of the ICPB-SCA system increased by 17.7±0.6% and 19.4±0.4% respectively, indicating that the KH560-TiO2-PU carriers significantly improved removal efficiency of odor substances. The novel ICPB system showed advantages compared with other processes for removing odor substances. Yuan et al. (2012) isolated four kinds of bacteria from biological activated carbon, the removal efficiencies of 2-MIB (515 ng/L) were in the range from 92.8% to 98.4%, but it needed 9-12 d. The biodegradation of 1-6.7 mg/L 2-MIB in mixed cultures took 5-14 d (Izaguirre et al., 1988). The UV/O3 system removed 90% of 2-MIB and GSM with an initial concentration of 200-500 ng/L within 2-3 minutes only, but caused incomplete mineralization and aldehydes accumulation (Collivignarelli et al., 2004). For the photocatalysis, TiO2 (P25) as the photocatalyst could remove 99% of GSM and 2-MIB (~10 nM) within 60 minutes (Lawton et al., 2003), and Fe-N co-doped TiO2 as the visible light photocatalyst could reduce the initial concentration of 1μg/L of GSM and 2-MIB to below 10 ng/L within 5h (Yuan et al., 2018). However, the directionless degradation of the photocatalysis also easily leads to incomplete mineralization of intermediates accumulation (Yoon et al., 2007; Kim et al., 2016; Park et al., 2017; Yuan et al., 2018).

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3.2.2 Stability of the ICPB system with KH560-TiO2-PU carriers Removal of both 2-MIB and GSM in the ICPB-SCA system maintained high stability over 5 operating cycles (Fig. 3a and b). The removal efficiencies of 2-MIB and GSM were 89.9±0.8% and 86.1±0.2% during the fifth 12-h cycle, respectively. 2-MIB concentration decreased to 8.9±2.8 ng/L with the degradation efficiency of 98.2±0.6% after 18 h in the fifth cycle. GSM concentration decreased to 9.2±1.0 ng/L achieving a degradation efficiency of 98.16±0.2% after 24h. After five cycles of operation, both of 2-MIB and GSM can be degraded to concentrations lower than 10 ng/L, meeting stringent standards indicated in the "Sanitary Standards for Drinking Water" (GB 5749 -2006, China). The TiO2 loading amount on carriers decreased slightly after 5 operating cycles (Fig. 3c), showing endured adhesion strength when KH560 was used as the adhesive agent. After the total of 5 running cycles of continuous operation, the loading amount was slightly reduced from the initial 351.8±8.2 mg/g to 334.2±10.0 mg/g, resulting in a peeling ratio as low as 5.0±2.8%. In contrast, when the powder sintering method was employed for TiO2 adhesion, the peeling ratio of 16.5% was observed after operating for 12 h with an initial loading amount of 31.5±2.4 mg/g. These results further confirmed KH560 enhanced and elongated TiO2 coating, which significantly increased the photocatalyst loading amount and adhesion strength between TiO2 and PU sponge carrier. Fig. 4a shows the photocatalysis and biofilm distribution on the carrier surface during 5 cycles in the ICPB-SCA system. Before the operation, both inner and outer surfaces of the KH560-TiO2-PU carrier were successfully enriched with a large amount of cocci and bacillus wrapped in extracellular polymeric substances. During the circle experiment, the photocatalyst 18

layer on the carrier outer surface was still firmly coated on the PU carrier, and the amount of biofilm colonized on the inner surface was constantly well maintained at a high level. It is worth noting that the biofilm on the outer surface gradually detached due to the influence of UV light and active oxygen radicals, which, as a result, exposed more photocatalysts to light illumination (Rittmann, 2018). This could partially explain the degradation efficiency of 2-MIB and GSM in the ICPB-SCA system exceeded control systems in the late stage of reaction (Li et al., 2011; Li et al., 2012b; Dong et al., 2016; Xiong et al., 2017). The Fig.4b shows that the characteristic peaks of the anatase phase still appeared at 2θ = 25.46°, 37.82°, 48.08°, 55.18°, and 62.74°, indicating that the anatase crystal form with high photocatalytic activity was not changed after 5 operating cycles. Therefore, the stability of the ICPB-SCA system was confirmed over multiple cycles of operation. KH560-enhanced TiO2 coating method made the TiO2 photocatalyst firmly coated on the PU carrier outer surface with strong adhesion strength, and active microorganisms colonized inside the carrier protected by the photocatalysts.

3.3 Proposed removal mechanisms of 2-MIB and GSM in the SCA-enhanced ICPB system 3.3.1 Intermediates of 2-MIB and GSM degradation

16 intermediate products in the ICPB-SCA system after 5-cycle degradation experiment were detected by GC-MS full scan analysis (Table S5), containing dehydrated products (4 species), terpenes (3 species), alcohols (5 species), esters (2 species), and organic acids (2 species). Fig. 5 shows the possible degradation pathways of 2-MIB and GSM in the novel ICPB system based on the analysis of intermediate products. 2-MIB and GSM were first converted by dehydration, and 19

then converted into terpenes, alcohols, esters, organic acids, and other biodegradable intermediate products through free radical attack. A variety of reactive oxygen species were produced in the TiO2 photocatalytic degradation, including h+, e-, ·OH, O2-, HO2· and H2O2 (Hashimoto et al., 2005), and hydroxyl radicals deoxidized most of the organic matters in water, which was proposed to play a decisive role in the photocatalytic oxidation (Marsolek et al., 2008; Fotou et al., 1996). The 2-MIB dehydration products, 2-methyl-2-bornene and 2-methylenebornane, and the GSM dehydration product, 1,4-dimethyl-admantane, were all detected in both ICPB-SCA and P systems. These dehydration products and alcohol, ethers, aldehydes and other subsequent products were also reported in previous UV photolysis experiments (Kim et al., 2016). Cyclopentene-type intermediate products exist in our systems, which were also detected in the previous study of photocatalytic degradation of 2-MIB (Yoon et al., 2007). However, Park et al. (2017) found that no GSM dehydration products were detected in the photo-Fenton removal process of 2-MIB and GSM, while 2-MIB dehydration products 2-methyl-2-bornene and 2-methylenebornane, ring-opening products butyl butyrate, 2-ethyl-1-hexanol and nonanal were obtained. Compared to the P system, four over-oxidized intermediate aldehydes products were missing in the ICPB-SCA system (Table S5), suggesting that immediate biodegradation avoided undesirable oxidation and aldehyde accumulation in photocatalysis (Yu et al., 2020). The indiscriminate and fast acting radicals of photocatalysis could produce a range of toxic, too oxidized, or unavailable for biodegradation products, and much of radicals would be spent reacting with already biodegradable organics (Marsolek et al., 2008). The aldehyde accumulation and incomplete mineralization of 2-MIB and GSM was also reported in a UV/O3 photocatalysis system (Collivignarelli et al., 2004). Our results indicated that the ICPB-SCA system could 20

effectively avoid the excessive oxidation and accumulation of the intermediate products that frequently occur in photocatalysis treatment systems. In the ICPB-SCA system, microorganisms might timely removed a portion of the biodegradable intermediate products to achieve final mineralization, and the chemical oxidant could more focus on the recalcitrant compounds. On the contrary, in the P systems, intermediates are likely to be excessively oxidized, forming and accumulating toxic aldehyde products. In order to analyze the roles of microorganisms in the biotransformation of odor substances and their intermediate products, microbial analysis was performed below.

3.3.2 Microbial activity and community of inner biofilm

ATP stores and transports energy for the vital activities and can be used to characterize the biomass of living cells. Fig. 6a shows that the ATP amount of biofilm in the ICPB-SCA system and the B system increased after 5 operating cycles from 74.1±0.9 ng/g to 117.2±5.7 ng/g and 99.1±0.7 ng/g, respectively. It suggested that the biofilm colonization in the interior of carriers was stable and the microbial activity remained well, although the biofilm on the sponge outer surface was detached in the ICPB-SCA system. Two reasons might lead to the increase of the ATP amount of biofilm in the ICPB-SCA system, one was that the microbial community structure succession inside the carrier maintained biomass and activity through self-regulation (Xiong et al., 2017); the second was that the various intermediates produced by photocatalysis provided a rich variety of carbon sources and improve the activity of biofilm (Yoon et al., 2007; Yuan et al., 2018). The CLSM images of biofilm in the carrier interior are shown in Fig. 6b. It was calculated 21

that the ratio of microbial live/dead cells of the ICPB-SCA system and the B system carrier decreased from 1.17±0.05 to 1.02±0.05 and 0.99±0.05, respectively. It also proved that the biofilm of the ICPB-SCA system was not significantly deactivated by the toxic effects of UV light and reactive oxygen free radicals (Li et al., 2012a). Microbial community analysis revealed the increase of diversity and richness of microorganisms in the attached biofilm. Shannon index and Simpson index represent biodiversity; Observed_species index, Chao1 index and ACE index represent species richness. The statistical results of the alpha diversity of the biofilm attached on carriers (Table S4) showed that the Observed_species index, Shannon index, Simpson index, Chao1 index and ACE index of the biofilm of novel ICPB system were 482, 6.36, 0.97, 490.37, and 491.18, respectively, all greater than those observed in the original biofilm before the operation, which were 465, 5.88, 0.96, 472.07, and 475.45, respetively. This suggests that the ICPB operation can improve the richness and diversity of the microbial communities in biofilms on the carrier surface. However, the microbial community in the B system only have Shannon and Simpson indexes (6.35 and 0.97, respectively) higher than those of the original biofilm; Observed_species, Chao1, and ACE indexes were 449, 450.67 and 452.40, respectively, all lower than those of the original biofilm. It showed that the microbial diversity on the sponge surface increased and the richness decreased in the B system. The differences between the ICPB-SCA system and the B system were probably due to that the microorganisms inside of the carrier were protected from the exposure to odorous substances and provided more bioavailable intermediate products according to the 2-MIB and GSM degradation pathway. The microbial community analysis of biofilms at the genus level is present in Fig. 6c and Fig. 22

S5 (community structure at phylum level in Fig. S4). The dominant genera on the carriers included Zoogloea, Thauera, Acinetobacter, Comamonas, Brevundimonas, and Flavobacterium. Zoogloea accounted for the highest proportion, reaching 22.2%, 19.9%, and 24.6% in original biofilm, B system biofilm, and ICPB-SCA system biofilm, respectively. Previous studies reported that Zoogloea spp. could secrete extracellular polymeric substances and grow in large quantities to form bacterial micelles, which not only had a bridging effect, but also improved the resistance of biofilms (Liu et al., 2010). Thus, dominance of Zoogloea spp. on the carrier surface promoted the microbial colonization and biofilm formation and increased the tolerance of the biofilm to handle influents of varying compositions. Thauera spp. were confirmed to play an important role in the conversion of terpenes and other refractory compounds (Hylemon et al., 1998), accounting for 14.8%, 12.0%, and 15.0% in the biofilms of original, B system, and ICPB-SCA system, respectively. The enrichment of Thauera spp. in the ICPB-SCA system biofilm was probably caused by the production of terpenoids from photocatalysis. Flavobacterium spp. was found with the ability of degrading 2-MIB (Egashira et al., 1992), accounting for 0.54%, 3.6% and 2.4% of the biofilms of original, B system, and ICPB-SCA system, respectively. In addition, Stenotrophomonas spp. and Sphingopyxis spp., which were previously reported with the ability to degrade odor substances (Hoefel et al., 2009; Zhou et al., 2011), were also enriched on carriers in B and ICPB-SCA systems, accounting for 0.24% and 0.15%, 0.15% and 0.16%, respectively. It indicated that a little odor substance could be directly utilized by the functional microorganisms in addition to the photocatalytic degradation in the ICPB-SCA system.

23

3.3.3 The synergy of adsorption, photocatalysis and biodegradation in the SCA-enhanced ICPB system

Combining the analysis of 2-MIB and GSM degradation intermidiates with the changes of microbial activity and community structures, the synergy of adsorption, photocatalysis and biodegradation in the novel ICPB system is shown in Fig. 7. The odorous substances are first adsorbed rapidly on the surface of the sponge, and then produce the dehydration intermediate products, which are further ring-opened to generate biodegradable intermediates such as terpenes, alcohols, esters and organic acids with lower molecular weights through TiO2 photocatalysis. Some of biodegradable intermediates are converted by photocatalysis, but most of them are decomposed and utilized by active functional microorganisms enriched on the inner surface of carriers, such as Thauera spp., Flavobacterium spp., Stenotrophomonas spp., and Sphinopyxis spp. A little of 2-MIB and GSM is also directly degraded and utilized by microorganisms. Our novel ICPB system also exhibits multiple properties for the improvement of 2-MIB and GSM removal efficiencies. Firstly, the enhancement of the photocatalyst's adhesive strength and the reduction of the aggregation improved photocatalysis efficiency and promised long-term stability. The removal efficiencies of 2-MIB and GSM by the photocatalytic system using the new loading method were higher than those of the ICPB system using the powder sintering method. Secondly, the photocatalyst is only coated on the external surface of carriers, leaving the colonization space inside the carrier for biofilm acclimation. 2-MIB and GSM were toxic to aquatic organisms (Nakajima et al. 1996; Gagne et al., 1999), and UV light (Zhou et al., 2015; Zhou et al., 2018; Cai et al., 2019) and free radicals (Li et al., 2012b; Ma et al., 2015; Rittmann, 2018) have also been reported to destroy microorganisms and worsen the shedding of biofilms. 24

However, biofilm inside of the carrier was protected and the microbial activity was well remained in the SCA-enhanced ICPB system. Thirdly, due to the tight combination of biodegradation and photocatalyst, intermediate products can be exchanged rapidly, enriching more functional microorganisms such as Zoogloea spp., Thauera spp., Flavobacterium spp., Stenotrophomonas spp., and Sphinopyxis spp., which can degrade intermediate products such as terpenes, alcohols, esters and organic acids to avoid excessive oxidization.

4. Conclusions In summary, the preparation method of KH560-enhanced TiO2-supported PU sponge (KH560-TiO2-PU) carriers for the ICPB system was developed, which formed a uniform and dense TiO2 layer firmly coated on the carrier outer surface, and the colonization of microorganisms on the inner surface was well protected. The ICPB system was first applied to degrade 2-MIB and GSM, the novel ICPB system constructed with KH560-TiO2-PU carriers significantly improved removal efficiencies of 2-MIB and GSM, and the system maintained an exceptional removal efficiency and stability even after several operating cycles. Besides, the diversity and abundance of microorganisms were increased, enabling multiple pathways for 2-MIB and GSM removal and reducing the accumulation of photocatalytic intermediate products. This study proved the feasibility of the supported-photocatalyst preparation method, providing a new treatment technology for removing odorous substances in natural waters.

Acknowledgement This work was supported by the Major Science and Technology Program for Water Pollution 25

Control and Treatment (Grant number 2017ZX07201003), the National Natural Science Foundation of China (Grant number 51961125101), and Science and Technology Project of Zhejiang Province (Grant number 2018C03003). Thanks for the technical support from Professor Long Mingce’ group in Shanghai Jiaotong University.

References Abdolmaleki, A., Mallakpour, S., Borandeh, S., 2011. Preparation, characterization and surface morphology

of

novel

optically

active

poly(ester-amide)/functionalized

ZnO

bionanocomposites via ultrasonication assisted process. Applied Surface Science 257 (15), 6725-6733. https://doi.org/10.1016/j.apsusc.2011.02.112 Arkles, B., 1977. Tailoring surfaces with silanes. Chemtech 7 (12), 766-778. Asquith, E., Evans, C., Dunsta, R.H., Geary, P., Cole, B., 2018. Distribution, abundance and activity of geosmin and 2-methylisoborneol-producing Streptomyces in drinking water reservoirs. Water Research 145, 30-38. https://doi.org/10.1016/j.watres.2018.08.014 Bavykin, D.V., Friedrich, J.M., Walsh, F.C., 2006. Protonated titanates and TiO2 nanostructured materials: synthesis, properties, and applications. Advanced Materials 18 (21), 2807-2824. https://doi.org/10.1002/adma.200502696 Cai, H., Sun, L., Wang, Y., Song, T., Bao, M., Yang, X., 2019. Unprecedented efficient degradation of

phenanthrene

in

water

by

intimately

coupling

novel

ternary

composite

Mn3O4/MnO2-Ag3PO4 and functional bacteria under visible light irradiation. Chemical Engineering Journal, 369, 1078-1092. https://doi.org/10.1016/j.cej.2019.03.143 Collivignarelli, C., Sorlini, S., 2004. AOPs with ozone and UV radiation in drinking water: 26

contaminants removal and effects on disinfection byproducts formation. Water Science & Technology 49 (4), 51-56. http://dx.doi.org/10.2166/wst.2004.0218 Davies, J.M., Roxborough, M., Mazumder, A., 2004. Origins and implications of drinking water odours in lakes and reservoirs of British Columbia, Canada. Water Research, 38 (7), 1900-1910. https://doi.org/10.1016/j.watres.2004.01.008 Dong, S., Dong, S., Tian, X., Xu, Z., Ma, D., Cui, B., Ren, N., Rittmann, B.E., 2016. Role of self-assembly coated Er3+: YAlO3/TiO2 in intimate coupling of visible-light-responsive photocatalysis and biodegradation reactions. Journal of Hazardous Materials 302, 386-394. https://doi.org/10.1016/j.jhazmat.2015.10.007 Egashira, K., Ito, K., Yoshiy, Y., 1992. Removal of musty odor compound in drinking water by biological

filter.

Water

Science

&

Technology

25

(2),

307-314.

https://doi.org/10.2166/wst.1992.0066 Fotou, G., Pratsinis, S., 1996. Phtocatalytic destruction of phenol and salicylic acid with aerosol-made and commercial titania powders. Chemical Engineering Communications 151(1), 251-269. https://doi.org/10.1080/00986449608936551 Gagne, E., Ridal, J., Blaise, C., Brownlee, B., 1999. Toxicological effects of geosmin and 2methylisoborneol on rainbow trout hepatocytes. Bulletin of Environmental Contamination and Toxicology 63 (2), 174–180. https://doi.org/10.1007/s001289900963 Hashimoto, K., Irie, H., Fujishima, A., 2005. TiO2 photocatalysis: a historical overview and future prospects.

Japanese

Journal

of

Applied

Physics

44,

8269-8285.

https://doi.org/10.1143/JJAP.44.8269 Hoefel, D., Ho, L., Monis, P.T., Newcombe, G., Saint, C.P., 2009. Biodegradation of geosmin by a 27

novel Gram-negative bacterium; isolation, phylogenetic characterisation and degradation rate determination.

Water

Research

43

(11),

2927-2935.

https://doi.org/10.1016/j.watres.2009.04.005 Hylemon, P.B., Harder, J., 1998. Biotransformation of monoterpenes, bile acids, and other isoprenoids in anaerobic ecosystems. FEMS Microbiology Reviews 22 (5), 475-488. https://doi.org/10.1016/S0168-6445(98)00027-8 Izaguirre, G., Wolfe, R.L., Means, E.G., 1988. Degradation of 2-methylisoborneol by aquatic bacteria.

Applied

Environmental

Microbiology

54

(10):

2424-2431.

http://dx.doi.org/10.1128/AEM.54.10.2424-2431.1988 Kim, T., Moon, B., Kim, T., Kim, M., Zoh, K., 2016. Degradation mechanisms of geosmin and 2-MIB during UV photolysis and UV/chlorine reactions. Chemosphere 162, 157-164. https://doi.org/10.1016/j.chemosphere.2016.07.079 Kobayashi, A., Jiang, W., 2008. Properties of titania/hydroxyapatite nanostructured coating produced

by

gas

tunnel

type

plasma

spraying.

Vacuum

83

(1),

86-91.

https://doi.org/10.1016/j.vacuum.2008.03.070 Li, B., Li, S.M., Liu, J.H., Yu, M., 2014. The heat resistance of a polyurethane coating filled with modified

nano-CaCO3.

Applied

Surface

Science

315,

241-246.

https://doi.org/10.1016/j.apsusc.2014.07.022 Li, F., Lan, X., Wang, L., Kong, X., Xu, P., Tai, Y., Liu G., Shi, J., 2019. An efficient photocatalyst coating strategy for intimately coupled photocatalysis and biodegradation (ICPB): Powder spraying

method.

Chemical

Engineering

https://doi.org/10.1016/j.cej.2019.123092 28

Journal

383,

123092.

Li, G., Park, S., Kang, D., Krajmalnik-Brown, R., Rittmann, B.E., 2011. 2, 4, 5-Trichlorophenol degradation using a novel TiO2-coated biofilm carrier: roles of adsorption, photocatalysis, and

biodegradation.

Environmental

science

&

technology

45

(19),

8359-8367.

https://doi.org/10.1021/es2016523 Li, G., Park, S., Rittmann, B., 2012a. Degradation of reactive dyes in a photocatalytic circulating‐ bed

biofilm

reactor.

Biotechnology

&

Bioengineering

109

(4),

884-893.

http://dx.doi.org/10.1002/bit.24366 Li, G., Park, S., Rittmann, B., 2012b. Developing an efficient TiO2-coated biofilm carrier for intimate coupling of photocatalysis and biodegradation. Water Research 46 (19), 6489-6496. https://doi.org/10.1016/j.watres.2012.09.029 Liu, Y., Kong, Y., Zhang, R., Zhang, X., Wong, F., Tay, J., Zhu, J., Jiang, W., Liu, W., 2010. Microbial population dynamics of granular aerobic sequencing batch reactors during start-up and

steady

state

periods.

Water

Science

&

Technology

62

(6),

1281-1287.

https://doi.org/10.2166/wst.2010.408 Lawton, L., Robertson, P., Robertson, R., Bruce, F., 2003. The destruction of 2-methylisoborneol and geosmin using titanium dioxide photocatalysis. Applied Catalysis B: Environmental 44 (1), 9-13. https://doi.org/10.1016/S0926-3373(03)00005-5 Ma, D., Zou, D., Zhou, D., Li, T., Dong, S., Xu, Z., Dong, S., 2015. Phenol removal and biofilm response in coupling of visible-light-driven photocatalysis and biodegradation: Effect of hydrothermal treatment temperature. International Biodeterioration & Biodegradation 104, 178–185. https://doi.org/10.1016/j.ibiod.2015.06.004 Marsolek, M.D., Torres, C.I., Hausner, M., Rittmann B.E., 2008. Intimate coupling of 29

photocatalysis and biodegradation in a photocatalytic circulating-bed biofilm reactor, Biotechnology and Bioengineering 101 (1), 83–92. https:// doi: 10.1002/bit.21889 Matinlinna, J.P., Lung, C.Y.K., Tsoi, J.K.H., 2018. Silane adhesion mechanism in dental applications and surface treatments: A review. Dental Materials 34 (1), 13-28. https://doi.org/10.1016/j.dental.2017.09.002 Nakajima, M., Ogura, T., Kusama, Y., Iwabuchi, N., Imawaka, T., Araki, A., Sasaki, T., Hirose, E., Sunairi, M., 1996. Inhibitory effects of odor substances, geosmin and 2-methylisoborneol, on early

development

of

sea

urchins.

Water

Research

30

(10),

2508-2511.

https://doi.org/10.1016/0043-1354(96)00104-2 Park, J., Nam, H., Choi, J., Ha, J., Lee, S., 2017. Oxidation of geosmin and 2-methylisoborneol by the photo-Fenton process: Kinetics, degradation intermediates, and the removal of microcystin-LR and trihalomethane from Nak-Dong River water, South Korea. Chemical Engineering Journal 313, 345-354. https://doi.org/10.1016/j.cej.2016.12.086 Rittmann, B., 2018. Biofilms, active substrata, and me. Water Research 132, 135-145. https://doi.org/10.1016/j.watres.2017.12.043 Sang, J., Aisawa, S., Miura, K., Hirahara, H., Jan, O., Jozef, P., Pavol, M., 2017. Adhesion of carbon steel and natural rubber by functionalized silane coupling agents. International Journal of Adhesion & Adhesives 72, 70-74. https://doi.org/10.1016/j.ijadhadh.2016.10.008 Suffet, I., Corado, A., Chou, D., McGuire, M., Butterworth, S., 1996. AWWA taste and odor survey.

Journal‐American

Water

Works

Association

88

(4),

168-180.

https://doi.org/10.1002/j.1551-8833.1996.tb06542.x Tang, Y., Zhang, Y., Yan, N., Liu, R., Rittmann, B.E., 2015. The role of electron donors generated 30

from UV photolysis for accelerating pyridine biodegradation. Biotechnology & Bioengineering 112 (9), 1792-1800. https://doi.org/10.1002/bit.25605 Wang, D., Bolton, J.R., Andrews, S.A., Hofmann, R., 2015. Formation of disinfection by-products in the ultraviolet/chlorine advanced oxidation process. Science of the Total Environment 518, 49-57. https://doi.org/10.1016/j.scitotenv.2015.02.094 Wu, X., Noss, C., Liu, L., Lorke, A., 2019. Effects of small-scale turbulence at the air-water interface on microcystis surface scum formation. Water Research 167, 115091. https://doi.org/10.1016/j.watres.2019.115091 Xiong, H., Zou, D., Zhou, D., Dong, S., Wang, J., Rittmann, B.E., 2017. Enhancing degradation and mineralization of tetracycline using intimately coupled photocatalysis and biodegradation (ICPB). Chemical Engineering Journal 316, 7-14. https://doi.org/10.1016/j.cej.2017.01.083 Yan, N., Chang L, Gan L, Zhang, Y., Liu, R., Rittmann, B.E., 2013. UV photolysis for accelerated quinoline biodegradation and mineralization. Applied Microbiology & Biotechnology 97 (24), 10555-10561. https://doi.org/10.1007/s00253-013-4804-2 Yoon, S., Lee, Y., Cho, W., Koh, I., Yoon, M., 2007. Synthesis of TiO2-entrapped EFAL-removed Y-zeolites: Novel photocatalyst for decomposition of 2-methylisoborneol. Catalysis Communications 8 (11), 1851-1856. https://doi.org/10.1016/j.catcom.2007.02.027 Yu, M., Wang, J., Tang, L., Feng, C., Liu, H., Zhang, H., Peng, B., Chen, Z., Xie, Q., 2020. Intimate coupling of photocatalysis and biodegradation for wastewater treatment: Mechanisms, recent advances and environmental applications. Water Research 175, 115673. https://doi.org/10.1016/j.watres.2020.115673 Yuan, R., Zhou, B., Shi, C., Yu, L., Zhang, C., Gu, J., 2012. Biodegradation of 2-methylisoborneol 31

by bacteria enriched from biological activated carbon. Frontiers of Environmental Science Engineering 6 (5), 701-710. https://doi.org/10.1007/s11783-011-0367-6 Yuan, R., Wang, S., Liu, D., Shao, S., Zhou, B., 2018. Effect of the wavelength on the pathways of 2-MIB and geosmin photocatalytic oxidation in the presence of Fe-N co-doped TiO2. Chemical Engineering Journal 353, 319-328. https://doi.org/10.1016/j.cej.2018.07.123 Zhang, Y., Chang, L., Yan, N., Tang, Y., Liu, R., Rittmann, B.E., 2013. UV photolysis for accelerating pyridine biodegradation. Environmental Science & Technology 48 (1), 649-655. https://doi.org/10.1021/es404399t Zhang, T., Li, L., Song, L., Chen, W., 2009. Effects of temperature and light on the growth and geosmin production of Lyngbya kuetzingii (Cyanophyta). Journal of Applied Phycology 21 (3), 279-285. https://doi.org/10.1007/s10811-008-9363-z Zhang, Z., Yu, Z., Zhu, L., Yu, H., Dai, X., Xu, X., Alvarezc, P., 2018a. Gradient reduced aeration in an enhanced aerobic granular sludge process optimizes the dominant microbial community and its function. Environmental Science: Water Research & Technology 4 (5), 680-688. https://doi.org/10.1039/C7EW00562H Zhang, Z., Yu, Z., Dong, J., Wang, Z., Ma, K., Xu, X., Alvarezc, P., Zhu, L., 2018b. Stability of aerobic granular sludge under condition of low influent C/N ratio: Correlation of sludge property

and

functional

microorganism.

Bioresource

Technology

270,

391-399.

https://doi.org/10.1016/j.biortech.2018.09.045 Zhao, J., Milanova, M., Warmoeskerken, M.M., Dutschk, V., 2012. Surface modification of TiO2 nanoparticles with silane coupling agents. Colloids Surfaces A: Physicochemical Engineering Aspects 413, 273-279. https://doi.org/10.1016/j.colsurfa.2011.11.033 32

Zheng, W., Tang, C., Xie, J., Gui, Y., 2019. Micro-scale effects of nano-SiO2 modification with silane coupling agents on the cellulose/nano-SiO2 interface. Nanotechnology 30 (44), 445701. https://doi.org/10.1088/1361-6528/ab3546 Zhou, B., Yuan, R., Shi, C., Yu, L., Gu, J., Zhang, C., 2011. Biodegradation of geosmin in drinking water by novel bacteria isolated from biologically active carbon. Journal of Environmental Sciences 23 (5), 816-823. https://doi.org/10.1016/S1001-0742(10)60458-5 Zhou, D., Xu, Z., Dong, S., Huo, M., Dong, S., Tian, X., Cui, B., Xiong, H., Li, T., Ma, D., 2015. Intimate coupling of photocatalysis and biodegradation for degrading phenol using different light types: visible light vs UV light. Environmental Science &Technology 49 (13), 7776-7783. https://doi.org/10.1021/acs.est.5b00989 Zhou, D., Dong, S., Ki, D., Rittmann, B.E., 2018. Photocatalytic-induced electron transfer via anode-respiring bacteria (ARB) at an anode that intimately couples ARB and a TiO2 photocatalyst.

Chemical

Engineering

https://doi.org/10.1016/j.cej.2018.01.094

33

Journal

338,

745-751.

Figures Fig. 1. (a) The amount of TiO2 (calculated as Ti) adhering to the surface of PU sponge carrier using different SCAs, preparation steps and heating temperature. "Four" means the four-step method, "Five" means the five-step method. ATI-FTIR spectra of carrier surface using (b) KH550, (c) KH560 and (d) KH570 as coupling agents. Fig. 2. Removal of (a) 2-MIB and (b) GSM in ICPB-SCA, ICPB, P, B, and AD systems. Error bars represent standard deviations among triplicates.

Fig. 3. Concentration of (a) 2-MIB (b) GSM in the ICPB-SCA system over 5 operating cycles. (c) TiO2 loading amount (calculated as Ti) on the surface of KH560-TiO2-PU carrier of origin (O) and after each operating cycle. The vertical lines are the error bars representing standard deviations among triplicates.

Fig. 4. (a) SEM images of outer and inner surfaces of KH560-TiO2-PU carriers in the ICPB-SCA system over 5 operating cycles. (b) XRD spectra of KH560-TiO2-PU carrier surface after 5 operating cycles. Fig. 5. The possible degradation pathways of 2-MIB and GSM in ICPB system.

Fig. 6. (a) ATP amount, (b) the CLSM images of carrier’s inner surface and (c) relative abundance of microbial genera in biofilms attached to the carrier surface in B and ICPB-SCA systems before (O) and after 5-cycle degradation experiment. The bacteria relative abundances greater than 0.1% are showed. Fig. 7. The synergy of photocatalysis and biodegradation in the SCA-enhanced ICPB system.

34

Figure 1

(a)

(b)

(c)

(d)

Fig. 1. (a) The amount of TiO2 (calculated as Ti) adhering to the surface of PU sponge carrier using different SCAs, preparation steps and heating temperature. "Four" means the four-step method, "Five" means the five-step method. ATI-FTIR spectra of carrier surface using (b) KH550, (c) KH560 and (d) KH570 as coupling agents.

35

Figure 2

(a)

(b)

Fig. 2. Removal of (a) 2-MIB and (b) GSM in ICPB-SCA, ICPB, P, B, and AD systems. Error bars represent standard deviations among triplicates.

36

Figure 3

(a)

(b)

(c)

Fig. 3. Concentration of (a) 2-MIB (b) GSM in the ICPB-SCA system over 5 operating cycles. (c) TiO2 loading amount (calculated as Ti) on the surface of KH560-TiO2-PU carrier of origin (O) and after each operating cycle. The vertical lines are the error bars representing standard deviations among triplicates. 37

Figure 4

(a) Outer surface before operation

Inner surface before operation

Outer surface 1st cycle

Outer surface 1st cycle

Microbes

TiO2

Inner surface 5th cycle

Outer surface 5th cycle

Microbes

TiO2

(b)

Fig. 4. (a) SEM images of outer and inner surfaces of KH560-TiO2-PU carriers in the ICPB-SCA system over 5 operating cycles. (b) XRD spectra of KH560-TiO2-PU carrier surface after 5 operating cycles. 38

Figure 5

Fig. 5. The possible degradation pathways of 2-MIB and GSM in ICPB system.

39

Figure 6 (a)

(b)

O

B

ICPB-SCA

(c)

Fig. 6. (a) ATP amount, (b) the CLSM images of carrier’s inner surface and (c) relative abundance of microbial genera in biofilms attached to the carrier surface in B and ICPB-SCA systems before (O) and after 5-cycle degradation experiment. The bacteria relative abundances greater than 0.1% are showed.

40

Figure 7

Fig. 7. The synergy of adsorption, photocatalysis and biodegradation in the SCA-enhanced ICPB system.

41

Tables Table 1. Operating condition for ICPB-SCA, ICPB, P, B, and AD systems.

Table 2. Variables and levels of orthogonal experiment.

Table 1. Operating condition for ICPB-SCA, ICPB, P, B, and AD systems. Treatment or control systems Conditions ICPB-SCA

ICPB

P

B

AD

Coating method

SCA-TiO2

powder sintering

SCA-TiO2

SCA-TiO2

TiO2-supported

Yes

Yes

Yes

Yes

Yes

Microbial-colonized

Yes

Yes

No

Yes

No

UV light source

Yes

Yes

Yes

No

No

SCA-TiO2

Table 2. Variables and levels of orthogonal experiment. Alcohol-water ratio

Hydrolysis time

of hydrolysis solution

(h)

C%KH560

T

Levels (%)

(℃)

1

6: 1

12

5

65

2

8: 1

24

15

85

3

10: 1

36

25

105

42

GRAPHICAL ABSTRACT

43