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[CEJ-D-24-16977_R1.pdf](https://mdr.nims.go.jp/filesets/0dc014b2-8124-4810-9825-25115e048bfd/download)

## Creator

Cheng Zhang, Guangqi An, Yunxin Zhu, Xiang Sun, [Guoping Chen](https://orcid.org/0000-0001-6753-3678), Yingnan Yang

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[Creative Commons BY-NC-ND Attribution-NonCommercial-NoDerivs 4.0 International](https://creativecommons.org/licenses/by-nc-nd/4.0/)

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[Development of a sunlight adjustable parabolic trough reactor for 24-hour efficient photocatalytic wastewater treatment](https://mdr.nims.go.jp/datasets/78171cdc-0b78-4462-bc51-2c4abaa07315)

## Fulltext

1 1 Development of a Sunlight Adjustable Parabolic Trough Reactor for 24-hour 2 Efficient Photocatalytic Wastewater Treatment 3 4 5 6 Cheng Zhang a, b, Guangqi An b, Yunxin Zhu b, c, Xiang Sun b, Guoping Chen d, 7 Yingnan Yang b, * 8 9 10 a National Energy Key Laboratory for New Hydrogen-Ammonia Energy Technologies, 11 Foshan Xianhu Laboratory, Foshan 528200, China 12 b Graduate School of Life and Environmental Science, University of Tsukuba, 1-1-1 13 Tennodai, Tsukuba, Ibaraki 305-8572, Japan 14 c Department of Agriculture and Food Technology, Faculty of Bioenvironmental 15 Sciences, Kyoto University of Advanced Science, 1-1 Sogabecho Nanjo Otani, 16 Kameoka, Kyoto, 621-8555, Japan 17 d Research Center for Macromolecules and Biomaterials, National Institute for 18 Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 3050044, Japan 19 20 *Corresponding Author. Tel/Fax: +81 29 853465021 E-mail address: yo.innan.fu@u.tsukuba.ac.jp (Y.Yang)22 https://www2.cloud.editorialmanager.com/cej/viewRCResults.aspx?pdf=1&docID=291119&rev=1&fileID=7950915&msid=5db9e59d-d4cc-4061-9600-d1ffaec9765chttps://www2.cloud.editorialmanager.com/cej/viewRCResults.aspx?pdf=1&docID=291119&rev=1&fileID=7950915&msid=5db9e59d-d4cc-4061-9600-d1ffaec9765c2 Abstract: 23 Solar energy is the ideal energy source for activating photocatalysis. However, due 24 to the solar motion, achieving 24-hour solar-powered efficient photocatalytic reactions 25 remains a challenge. In this study, a Sunlight Adjustable Parabolic Trough Reactor (SA-26 PTR) integrated with flexible parabolic mirror and solar panel was developed. During 27 the daytime, flexible parabolic mirror could be rolled up under sunny condition or 28 expanded under cloudy condition, thus providing optimal light irradiance (1500 W·m-29 2) and temperature (rises yet below 55℃) for photocatalysis. Additionally, the solar30 panel behind the flexible parabolic mirror could generate solar-electricity. At night, the 31 stored solar-electricity could meet 100% power demands of UV lamp, enabling a 24-32 hour solar-powered photocatalytic process. Compared with traditional parabolic trough 33 reactor and inclined plate collector, SA-PTR exhibited higher treatment efficiency 34 against carcinogenic organic dyes (Rhodamine B, Methylene Blue, Methyl Orange), 35 antibiotic (Tetracycline) and pathogenic bacteria (Escherichia coli) during day and 36 night. Moreover, SA-PTR exhibited superior global deployability, economic advantage, 37 safety and lifetime. Therefore, SA-PTR, as a novel solar controllable 24-hour 38 operational photoreactor, is promising to be employed in real wastewater treatment 39 plant. 40 Keywords: 41 Sunlight adjustable parabolic trough reactor (SA-PTR); flexible parabolic mirror; 42 photocatalytic wastewater treatment; 24-hour continuous operation; whole-year 43 evaluation44 3 1. Introduction45 As human society progresses, a large amount of industrial, medical and domestic 46 wastewater has been discharged into water bodies [1–3]. Due to the presence of 47 carcinogenic organic dyes, antibiotics and pathogenic bacteria in wastewater, water 48 quality is deteriorating around the world [4]. Amid this water crisis, the UN strives to 49 achieve SDG 6 (Clean Water and Sanitation) [5], encouraging researchers to innovate 50 sustainable and efficient wastewater treatment systems. 51 In past decades, photocatalysis, a cost-effective wastewater treatment method 52 without secondary pollution, has been extensively studied [6–8]. Under the light 53 irradiation, photocatalyst could produce free electrons and holes with strong oxidation 54 and reduction [9], so as to decompose the organic pollutants. Solar energy, as an eternal, 55 eco-friendly and abundant energy [9], encompasses ultraviolet (UV) light, visible light 56 and infrared light [10]. Technically, high-energy UV and short-wave visible light 57 activate photocatalyst [8], while long-wave visible light and infrared light with strong 58 thermal effect could increase the temperature to promote the photocatalytic reaction 59 rate [11]. Therefore, the broad spectrum of sunlight makes it ideal for driving and 60 accelerating photocatalytic process [11]. 61 In the early explorations, Inclined Plate Collectors (IPC) were employed to 62 provide solar energy to photocatalysis [11,12]. IPC utilizes an inclined flat mirror to 63 passively capture sunlight, enabling photocatalytic reactions to occur within the 64 reaction tubes mounted on this mirror. However, since IPC could only passively receive 65 sunlight, its photocatalytic efficiency is generally limited by the inefficient acceptance 66 4 of solar energy [11]. It has been reported that sufficient light irradiance and favorable 67 temperature are prerequisites for promoting photocatalytic efficiency [13]. For example, 68 Reuterg̊ardh et al. demonstrated that 1000 W·m-2 light irradiance and temperatures 69 between 30-60℃ were conducive to efficient photocatalysis [14]. Zhang et al. also 70 reported that the light irradiance above 1000 W·m-2 and raised temperature (< 65℃) 71 were beneficial for the effective photocatalysis [11]. Nevertheless, the environmental 72 average light irradiance level is only around 500 W·m-2 [15], and the typical 73 environmental average temperature on earth is only 12℃ [16]. Therefore, solar energy 74 needs to be concentrated to achieve the optimal light irradiance and temperature 75 required for efficient photocatalytic reactions. 76 Parabolic Trough Reflector (PTR), as a typical light concentrator in solar thermal 77 projects [17], is not surprisingly employed to provide concentrated sunlight for 78 photocatalysis [18]. PTR used a parabolic mirror to focus incident sunlight onto the 79 reaction tube, which was located at its focal point. Its parabolic mirror size determines 80 the amount of concentrated solar energy. The larger the mirror, the more solar energy 81 could be concentrated [18]. Since PTR passively concentrates solar energy, it usually 82 concentrates over 30-70 times the amount of sunlight onto the reaction tube, which 83 provides ultra-high light irradiance [17,19]. However, violent recombination of 84 electrons and holes may occur under ultra-high illumination, which may limit the 85 photocatalytic efficiency [11,14,19]. Furthermore, the massive amount of concentrated 86 solar energy in PTR could lead to ultra-high temperatures of up to 400-500℃ [20], 87 potentially damaging the photocatalytic system and causing wastewater evaporation 88 5  [11]. Therefore, appropriate adjustment of concentrated solar energy is necessary to 89 achieve efficient photocatalytic reactions while mitigating issues caused by excessive 90 light irradiance and temperature. Recently, flexible mirrors with excellent bendability 91 have been developed for deployable space telescopes [21], as they could be shaped into 92 different forms as well as rolled up or expanded. Compared with glass mirrors, flexible 93 mirrors offer superior deployability while maintaining high reflectiveness [21]. If a 94 flexible parabolic mirror is used to replace the glass parabolic mirror which is currently 95 used in PTR, it could have the potential to change the mirror size by rolling or 96 expanding, thus adjusting the concentrated solar energy. In addition, it also has the 97 potential to reduce the cost and weight of photoreactor, which benefits the large-scale 98 deployment. To the best of our knowledge, a PTR utilizing flexible parabolic mirrors 99 to adjust concentrated solar energy for efficient photocatalytic reactions has not been 100 proposed yet. 101 Despite the potential of using a flexible parabolic mirror to adjust natural solar 102 energy during the daytime, achieving photocatalysis during nighttime remains a tricky 103 challenge. At present, photoreactors solely powered by solar energy for 24-hour 104 continuous photocatalytic reactions are still waiting to be explored [13]. The 105 breakthrough in this technology may be a boon for photocatalytic application in 106 industrial fields with high robustness requirements (such as wastewater treatment plant). 107 Notably, solar panel, as a device which converts solar energy into electrical power, 108 might be a solution to above issue. If a solar panel is integrated behind the flexible 109 parabolic mirror, during the daytime, the photoreactor could not only provide optimized 110 6 solar energy for photocatalysis, but also generate electrical power. During nighttime, 111 the solar-electricity could drive a lamp for activating photocatalyst, thus achieving 24-112 hour solar powered continuous photocatalytic reaction. 113 Therefore, in this study, a Sunlight Adjustable Parabolic Trough Reactor (SA-PTR) 114 for 24-hour photocatalytic operation was developed for the first time. The SA-PTR 115 features a flexible parabolic mirror that could change its size based on actual solar 116 conditions to adjust the concentrated sunlight. Additionally, a solar panel was highly 117 integrated with the mirror to power a UV lamp at night. The wastewater treatment 118 capability of SA-PTR was investigated through the removal of carcinogenic organic 119 dyes (Rhodamine B (Rh B), Methylene Blue (MB), Methyl Orange (MO)), antibiotics 120 (Tetracycline (TC)) and pathogenic bacteria (Escherichia coli (E. coli)) during daytime 121 and nighttime. Furthermore, the economic efficiency, long-term availability, wide 122 applicability and safety of the SA-PTR were also evaluated. 123 2. Materials and methods124 2.1. Identification of the optimal solar energy for efficient photocatalysis 125 To achieve high photocatalytic efficiency, the optimal solar energy that needs to 126 be concentrated by SA-PTR was first identified. In this step, Rh B solution (500 mL, 2 127 mg·L-1) was treated by photocatalyst in a batch reactor (Fig. S1a) under different solar 128 energy conditions. The TiO2-coated silica gel beads (HQC-21, Sinto V Ceracs) were 129 adopted as photocatalyst. The different solar energy conditions were provided by a 130 simulated solar lamp (XC-100, SERIC., Ltd) or the concentrated real sunlight. The 131 simulated solar lamp provided the light irradiance ranging from 0 to 2100 W·m-2, while 132 7 the concentrated real sunlight provided the light irradiance of 3000 and 4000 W·m-2. 133 The simulated solar lamp and the concentrated real sunlight have similar light spectrum 134 (Fig. S1b). During experiments, light irradiance was measured by pyranometer (LI-135 200R, LICOR) and temperature was measured by thermocouple (TR-71wf, TANDD). 136 The surrounding temperature was kept at 25°C. 137 2.2. Calculation of the mirror size in SA-PTR for providing the optimal solar 138 energy 139 To ensure the optimal light irradiance and reaction temperature, SA-PTR 140 employed a flexible parabolic mirror to adjust the concentrated solar energy. 141 Technically, when natural sunlight is intensive, the flexible mirror would be rolled up, 142 while during the period of weaker sunlight, the mirror would be expanded. The mirror 143 size of SA-PTR was calculated according to natural solar energy throughout the year in 144 Tsukuba area (36.1°N, Japan). The yearly natural solar energy I was calculated by Eq. 145 (1) [22].146 I = S × 0.7AM0.678                               ( 1 ) 147 where S represents the solar constant (= 1356 W·m-2). AM represents the air mass, 148 which could be calculated by Eq. (2) [23]. 149 AM = 1 / (sinα + 0.50572 × (α + 6.07995)-1.6364)                ( 2 )150 where α represents the solar elevation, which could be calculated by Eq. (3) [23]. 151 sinα = sinφ × sinδ + cosφ × cosδ × cosha                   ( 3 ) 152 where φ represents the latitude of Tsukuba area (= 36.1°N). ha represents the solar hour 153 angle, which is the number of degrees that the earth must rotate until the sun is directly 154 8 above the local meridian. δ represents the solar declination and could be calculated by 155 Eq. (4) [23]. 156 δ = 23.45° × π / 180° × sin(2π × (284 + n) / 365) ( 4 ) 157 The mirror size MS of SA-PTR was calculated by Eq. (5) according to the natural 158 solar energy. 159 MS = Optimal solar energy / I × WRT ( 5 ) 160 where WRT represents the width of reaction tube (= 20 mm) equipped in SA-PTR. 161 2.3. Manufacturing of SA-PTR for daytime operation 162 As the first step in the development of SA-PTR, it was manufactured for the lab-163 scaled wastewater treatment experiments during the daytime. A flexible parabolic 164 mirror described by Eq. (6) was equipped in SA-PTR for adjusting and concentrating 165 solar energy. 166 y2 = 2 × p × x ( 6 ) 167 where y and x are cartesian coordinate system parameters, and p (= 170 mm) is the 168 distance from the focal point to the corresponding directrix of the parabola. 169 Then, the arc length AL of the parabolic mirror of SA-PTR was calculated by Eq. 170 (7). 171 AL = p / 2 × (√2 × x / p × (1 + 2 × x / p) + ln (√2 × x / p + √1 + 2 × x / p)) ( 7 ) 172 For the SA-PTR manufacturing, all of its parts were purchased online or from local 173 hardware stores and manufactured according to the design blueprint. At the same time, 174 traditional PTR and IPC were also manufactured, serving as control reactors. The 175 equation of the parabolic mirror of PTR was consistent with that of SA-PTR. The mirror 176 9 size of PTR was the maximum mirror size of SA-PTR. All three reactors were operated 177 simultaneously under their optimum working conditions on a south-facing rooftop 178 located in Tsukuba area (= 36.1°N). The detailed information of PTR and IPC employed 179 in this study could be found in supplementary materials Text S1. 180 2.4. Verification of the sunlight adjustment capability of SA-PTR 181 After SA-PTR manufacturing, its ability to adjust the solar energy under real 182 sunlight was verified. The experiment was carried out on 2022-12-23 (winter solstice) 183 characterized by the lowest solar altitude angle, which presents the worst solar 184 condition during the year [11]. If SA-PTR could provide optimal solar energy on this 185 day, it could provide optimal solar energy during the yeartime. During the experiment, 186 1 L water was circulated inside the photoreactors. The solar energy and water 187 temperature in photoreactors were measured and recorded at 5-minute intervals. 188 2.5. Photocatalytic wastewater treatment experiments during daytime 189 In this study, carcinogenic organic dyes (Rh B, MB, MO), antibiotics (TC) and 190 pathogenic bacteria (E. coli) were targeted to evaluate the wastewater treatment 191 performance of photoreactors. Rh B, MB and MO were purchased from Wako Pure 192 Chemical Industries, Ltd. (Osaka, Japan). TC was purchased from Sigma–Aldrich Co., 193 Ltd. (Louisiana, USA). The E. coli was isolated from Matsumi Lake in Tsukuba, and 194 the preparation of E. coli solution could refer to previous study [15]. 195 Firstly, the degradation experiments of Rh B (1 L, 2 mg·L-1) were conducted under 196 sunny, cloudy and heavy snow conditions, respectively. Then, MB (1 L, 5 mg·L-1), MO 197 (1 L, 5 mg·L-1) and TC (1 L, 10 mg·L-1) were degraded under sunny days and cloudy 198 10 days, respectively. The concentrations of Rh B, MB, MO and TC were measured by a 199 spectrophotometer (UV-1600, Shimadzu, Japan) at their maximum absorption 200 wavelength of 554, 664, 465 and 267 nm, respectively. The Total Organic Carbon (TOC) 201 results were measured by a total organic carbon analyzer (TOC-L, Shimadzu, Japan). 202 The disinfection experiment for E. coli (0.3 L, 1.2×105 cfu·mL-1) was carried out under 203 typical sunny-cloudy condition. The concentration of E. coli was calculated by the 204 standard plate count method. The reaction rate k of degradation and disinfection 205 experiments were calculated according to the first-order reaction model Eq. (8). 206 - lnCtC0 = kt(8) 207 2.6. Evaluation of the whole-year daytime performance of photoreactors 208 The applicability of SA-PTR, PTR and IPC throughout the year during the daytime 209 was evaluated based on the natural meteorological data in Tsukuba area (= 36.1°N) in 210 2022. To calculate the light irradiance and reaction temperature provided by 211 photoreactors during the yeartime, solar energy conversion process in photoreactors 212 needs to be clarified. This analysis was based on the solar conditions on the vernal 213 equinox, a typical day when the length of daytime equals the length of the night [9], 214 which could represent the average solar conditions during the year. Firstly, the accurate 215 optical models of SA-PTR, PTR and IPC were created by a 3D modeling software 216 Solidworks [24]. Then, the optical simulations were performed by Tracepro software 217 to quantify the amount of solar energy harnessed by photoreactors [25]. When solar 218 energy is provided onto reaction tubes, a portion of solar energy would be converted 219 into internal energy for increasing temperature. The conversion ratio of solar energy 220 11 into internal energy could be calculated by Eq. (9). 221 Solar-internal conversion ratio =  Internal energy  Solar⁄ energy × 100% (9) 222 As the solar energy was provided to reaction tubes, some energy was also lost to 223 the environment in the form of heat. The computational fluid dynamics analysis was 224 carried out by Fluent software for analyzing the boundary heat flux distribution [26], 225 which refers to the heat loss in photoreactors. Accordingly, the solar energy loss ratio 226 of photoreactors could be calculated by Eq. (10). 227 Solar energy loss ratio =  Boundary heat flux  Solar⁄ energy × 100% (10) 228 Ultimately, the whole-year solar energy harnessed and the reaction temperatures 229 within the photoreactors were calculated utilizing meteorological data sourced from the 230 Japan Meteorological Agency [27]. 231 2.7. Wastewater treatment experiments during nighttime 232 After studying the daytime performance of SA-PTR, the wastewater treatment 233 experiments were further conducted at night. First, solar panels (maximum electrical 234 power generation = 50 W under 1.5 air mass) were integrated behind the flexible mirror. 235 The size of solar panel was similar with that of flexible mirror in SA-PTR, thus no extra 236 installation space was required. The solar panel was connected to a battery for energy 237 storage and subsequently supplied power to a UV lamp (FL10BLBX1, Tokyo Metal 238 Industry) mounted above the reaction tubes. During the nighttime experiments (2023-239 10-02 to 2023-11-03), Rh B, MB, MO, TC, E. coli were degraded or disinfected in SA-240 PTR. At the same time, in order to simulate the photocatalytic performance of PTR and 241 IPC (no solar-electricity generation capability) during the nighttime, dark condition 242 12  experiments were comparatively conducted. Other experiment conditions remained the 243 same as daytime experiments (as described in section 2.5). 244 3. Results and discussion 245 3.1. Optimal solar energy for efficient photocatalytic reaction 246 To identify the optimal solar energy for the efficient photocatalytic reaction, the 247 Rh B degradation experiments were carried out at the solar energy of 0-4000 W·m-2. 248 Figure 1a showed the change of reaction temperature under different solar energy 249 conditions. When the solar energy increased from 300 to 4000 W·m-2, the reaction 250 temperatures also increased. This might be due to the fact that the solar spectrum 251 includes long-wavelength visible light and infrared light, which possess significant 252 thermal effects [23]. The stronger the solar energy, the greater the increase in reaction 253 temperature.  254 To identify the optimal solar energy, the relationship between solar energy and 255 photocatalytic Rh B degradation reaction rate was studied and shown in Fig. 1b. As the 256 solar energy increased from 300 to 1500 W·m-2, the reaction rate increased rapidly 257 (from 0.0189 to 0.0374 min-1). Therefore, to achieve an efficient photocatalytic reaction, 258 it is reasonable to increase the solar energy from 300 to 1500 W·m-2. However, no 259 obvious increase in the degradation rate was found when the solar energy exceeded 260 1500 W·m-2. Many studies have reported that excessive light energy may increase the 261 recombination rate of electrons and holes generated by photocatalyst, thus limiting the 262 photocatalytic efficiency [14,19]. In addition, excessive solar energy may lead to 263 elevated reaction temperature (such as 77℃ at 4000 W·m-2, shown in Fig. 1a). At this 264 13  temperature, due to the vaporization of water, many photocatalysts could not contact 265 with pollutants (Fig. S2), which may limit the photocatalytic activity. Based on the 266 above results, SA-PTR was designed to provide the optimal 1500 W·m-2 solar energy 267 to achieve efficient photocatalytic reaction. 268 3.2. Design and manufacturing of SA-PTR for providing optimal solar energy 269 Due to the movement of the sun, the amount of natural solar energy reaching the 270 earth is constantly changing [11]. To provide the optimal solar energy (1500 W·m-2), a 271 flexible parabolic mirror was employed in SA-PTR, and the mirror size determining the 272 concentrated solar energy amount could be changed. 273 Figure 2a showed the variation of natural solar light irradiance in Tsukuba area 274 throughout the year. During the morning and afternoon, the natural sunlight is weaker, 275 while it is stronger in the noon. In addition, in winter, the natural sunlight irradiance is 276 lower, while in summer it is higher. As shown in Fig. 2b, the photocatalytic reaction 277 tubes were located at the focal point of the parabolic mirror. In order to achieve the 278 optimal 1500 W·m-2 solar energy in reaction tubes, the mirror size of SA-PTR was 279 changed according to real solar conditions. Figure 2c showed the variation of the 280 parabolic mirror size of SA-PTR throughout the year. In the morning and afternoon, the 281 size of flexible parabolic mirror needs to be increased, while at noon it needs to be 282 decreased. In addition, the mirror size needs to be larger in winter and smaller in 283 summer. Furthermore, the maximum and minimum mirror size were also calculated. 284 Since the natural sunlight is weakest at sunrise (or sunset) on the winter solstice 285 (December 23rd) during the year (Fig. 2a), the flexible parabolic mirror in SA-PTR 286 14 needs to be expanded to the maximum size (396 mm) to provide the optimal 1500 W·m-287 2 of solar energy. At noon on the summer solstice (June 21st), since natural solar energy 288 is strongest during the year (Fig. 2a), the mirror size needs to be rolled up to the 289 minimum size (54 mm). This adjustment ensured that SA-PTR could provide the 290 optimal 1500 W·m-2 solar energy for the photocatalytic reaction tubes during the year. 291 After determining the maximum and minimum parabolic mirror size, the structure 292 of SA-PTR for daytime operation was designed and shown in Fig. 3a. The SA-PTR 293 featured a flexible mirror attached to a parabolic arch supporting structure. The flexible 294 mirror could be magnetically attracted to the mirror supporting structure, forming a 295 paraboloid shape. The photocatalytic reaction tubes were installed at the focal point of 296 the parabolic mirror and filled with photocatalyst. The inlet and outlet of photocatalytic 297 reaction tubes connected with a pipeline, which was in turn connected to a water pump 298 and a 1 L storage bottle containing organic wastewater. As shown in Fig. 3b, to control 299 the concentrated solar energy at 1500 W·m-2 during the year, the flexible parabolic 300 mirror could be rolled up or expanded by the reel to control the mirror size from 301 minimum to maximum size (54-396 mm). The rotation of the reel could be controlled 302 by a stepper motor (Bipolar Nema 17), which was mounted on a railcar. The railcar has 303 wheels, which could move along the track installed on the mirror supporting structure. 304 A light sensor (GY-30) was installed near the photocatalytic reaction tubes to receive 305 the concentrated solar energy. The control system of the stepper motor in SA-PTR was 306 based on the Arduino system (Arduino UNO REV3 mainboard) and shown in Fig. 3c. 307 Arduino system is an open source compliable control system based on C language [28]. 308 15 When the concentrated solar energy is higher than 1500 W·m-2, the light sensor would 309 send the signal to the stepper motor for rolling up the flexible mirror, and the rail car 310 would move to the center point of the mirror support. When the concentrated solar 311 energy is lower than 1500 W·m-2, the flexible mirror would be expanded, and the rail 312 car would go to the far edge of the mirror support. While on cloudy days, due to the 313 low natural solar light irradiance at this time, the flexible parabolic mirror would be 314 expanded to its maximum size (396 mm) to concentrate the solar energy as much as 315 possible. The SA-PTR pictures of changed mirror size could be found in Fig. S3. 316 After the SA-PTR was designed and manufactured (Fig. S4a), the control reactors 317 PTR (Fig. S4b) and IPC (Fig. S4c) were also manufactured. The reflectivity of PTR 318 and IPC mirrors was similar to that of SA-PTR mirrors (shown in Fig. S5). Three 319 reactors were equipped with temperature sensors (TANDD, TR-71wf) and light 320 intensity sensors (UV-340 ultraviolet meter and LI-200R pyranometer). During the 321 experiments, the three reactors were installed on rooftops with the same light conditions 322 and were all oriented towards the incident direction of the solar rays. 323 3.3. Solar energy control capability of SA-PTR 324 The solar energy control capability of SA-PTR was verified on the winter solstice 325 (December 23rd, 2022), which was the day with the worst solar conditions during the 326 yeartime. The experiment lasted from 8:00 to 14:30, covering sunrise, morning, noon 327 and afternoon periods. As shown in Fig. 4a, the natural solar energy only varied in the 328 range of 26-549 W·m-2, which was insufficient to support the photocatalytic reactions329 effectively (Fig. 1b). For the IPC, which passively receives solar energy, provided the 330 16  slightly higher solar energy at 44-793 W·m-2, but still inadequate for efficient 331 photocatalysis (Fig. 1b). Though PTR could provide the solar energy up to 4587 W·m-332 2, the excessive light irradiance may hinder photocatalytic activity by inducing high 333 recombination rate of electrons and holes [14,19], which may inhibit the promotion of 334 photocatalytic activity. In contrast, the SA-PTR could stabilize the solar energy at the 335 optimal 1500 W·m-2 under various solar conditions by changing the parabolic mirror 336 size. During the period of weak natural light irradiance (8:00-8:30, shortly after sunrise), 337 the mirror size of SA-PTR was expanded to maximize the concentrated solar energy, 338 rapidly increasing the concentrated solar energy from 204 to about 1500 W·m-2. In the 339 following time with clear sky (8:30-10:15 and 10:40-14:30), by controlling the mirror 340 size, the concentrated solar energy could be effectively stabilized at the optimal 1500 341 W·m-2. Even during the period that temporary clouds blocked sunlight (10:20-10:35), 342 SA-PTR still provided 287-742 W·m-2 of solar energy, which was still more favorable 343 for photocatalytic reactions than the natural condition (170-361 W·m-2). Therefore, the 344 newly developed SA-PTR could effectively adjust the concentrated solar energy by 345 changing the mirror size. 346 The temperature was also recorded and shown in Fig. 4b. The natural temperature 347 was only 4.1-18.3℃, which was not effective for promoting the photocatalytic reaction 348 rate [11]. For IPC, since the provided solar energy was only slightly increased compared 349 to natural conditions, its temperature (5.2-22.3℃) was still unable to achieve efficient 350 photocatalytic reactions. Although the PTR provided a high temperature (67.7℃) by 351 concentrating a large amount of solar energy (up to 4587 W·m-2), excessive temperature 352 17  may cause wastewater evaporation and bubble generation (Fig. S2), which was 353 unfavorable for system operation [11]. While for the SA-PTR, by adjusting the solar 354 energy, not only provided the optimal and stable light irradiance of 1500 W·m-2, but 355 also quickly raised the reaction temperature to a suitable range of 30-48℃, which was 356 favorable for efficient photocatalytic reaction. 357 The above experiments confirmed that SA-PTR could provide the optimal solar 358 energy and suitable reaction temperature by actively adjusting the mirror size even on 359 the winter solstice with the worst solar condition through the year. This lays a 360 foundation for SA-PTR to realize efficient photocatalytic wastewater treatment process 361 under real weather conditions. 362 3.4. Degradation of organic dyes under real weather conditions 363 After verifying the ability of SA-PTR to control solar energy, its wastewater 364 treatment performance was studied under different real solar conditions during the 365 daytime. Rh B, MB and MO, as a typical carcinogenic organic dyes [29], were chosen 366 as the wastewater models. Firstly, the Rh B experiments were conducted from 9:30 to 367 11:30 on several days with typical weather conditions, including sunny day (2023-01-368 08), temporarily cloudy day (2023-01-09) and heavy snowy day (2023-02-10), 369 respectively.  370 Figure S6a showed the light irradiance during the experiments. Under sunny 371 condition (2023-01-08), SA-PTR could effectively adjust the variable natural sunlight 372 (388-619 W·m-2) to the optimal solar energy 1500 W·m-2 by actively adjusting the 373 mirror size. In addition, on temporarily cloudy day (2023-01-09), SA-PTR could 374 18 provide the optimal solar energy when the cloud does not obscure the sunlight. When 375 clouds occasionally blocked solar rays, the SA-PTR mirror was expanded to the 376 maximum size to maximize the light irradiance (25-218 W·m-2), which was much more 377 favorable for photocatalytic reactions than natural sunlight (12-89 W·m-2). Furthermore, 378 even on a heavy snowy day (2023-02-10) when the sun was completely blocked, the 379 fully expanded mirror allowed SA-PTR to provide doubled solar light irradiance (12-380 27 W·m-2) for photocatalytic reactions, compared with natural sunlight (6-14 W·m-2). 381 Therefore, SA-PTR could effectively control the concentrated solar energy under 382 different weather conditions. Through the optimization of solar energy, the reaction 383 temperature in SA-PTR could be rapidly increased while lower than 55℃ under sunny 384 or temporarily cloudy conditions (Fig. S6b), thus promoting the photocatalytic reaction 385 and avoiding excessive temperature. Even on cold and snowy day, the temperature of 386 SA-PTR could reach 4.4-5.9℃, which was still higher than natural temperature (2.0-387 3.1℃). Therefore, SA-PTR could effectively adjust the sunlight under various typical 388 weather conditions, thus providing the optimized reaction temperature. However, 389 traditional PTR and IPC were unable to provide the optimal light irradiance and reaction 390 temperature under real weather conditions (shown in Fig. S6). For PTR, since it could 391 only concentrate the solar energy, it provided excessive light irradiance (up to 5324 392 W·m-2) and reaction temperature (up to 70.7℃) on the sunny and temporarily cloudy 393 days. While for IPC, its light irradiance (6-705 W·m-2) and reaction temperature (4.5-394 21.9℃) were only slightly higher than the natural sunlight (5-617 W·m-2) and ambient 395 temperature (4.1-15.4℃), respectively. 396 19 The Rh B degradations were carried out under real weather conditions and the 397 degradation processes were shown in Fig. 5a with the summarized reaction rate k (Table 398 1). Under sunny and temporarily cloudy conditions, the reaction rates of SA-PTR were 399 0.0338 and 0.0212 min-1, which were slightly higher than that of PTR, and 1.75 and 400 1.64 folds of IPC, respectively. This might be due to that SA-PTR could provide the 401 optimized solar energy (around 1500 W·m-2), thus effectively promoting the reaction 402 process. In addition, on heavy snowy day, the reaction rates of SA-PTR and PTR were 403 the same (0.0114 min-1). This was due to that when the sunlight was completely blocked, 404 the mirror of SA-PTR was fully expanded, making its light collection capacity equal to 405 that of PTR, resulting in similar performance. Compared to IPC, the reaction rate of 406 SA-PTR was doubled to that of IPC (0.0057 min-1) during heavy snow, likely due to 407 the more favorable light irradiance and reaction temperature provided by SA-PTR. 408 Furthermore, SA-PTR exhibited the highest TOC removal capacity under sunny 409 (81.7%), temporarily cloudy (56.9%) and snowy conditions (14.3%) (shown in Fig. S7), 410 indicating its ability to efficiently mineralize the organic pollutants. 411 To further evaluate the capacity of SA-PTR to treat the wastewater containing 412 different organic dyes, the degradation experiments of MB and MO under different 413 actual weather conditions were carried out. Figure S8a-b and Fig. S9a-b exhibited that 414 under sunny conditions (2023-02-16 and 2023-02-18), SA-PTR could always control 415 the solar energy near the optimal 1500 W·m-2 with suitable reaction temperature 416 (around 40℃). Even under the rainy and cloudy conditions (2023-02-13 and 2023-02-417 17, shown in Fig. S8c-d and Fig. S9c-d), SA-PTR could still maintain the optimized 418 20 light irradiance and temperature. Under these superior reaction conditions, SA-PTR 419 exhibited significantly improved MB and MO degradation efficiency (Fig. 5b-c). Under 420 sunny condition (2023-02-16 and 2023-02-18), the degradation rate of MB in SA-PTR 421 was 0.019 min-1, which was 1.10 folds of PTR and 1.42 folds of IPC, respectively 422 (Table 1). Besides, the degradation rate of MO in SA-PTR was 0.0094 min-1, which 423 was slightly higher than that of PTR and 2.94 folds of IPC, respectively (Table 1). While 424 during the undesired weather (2023-02-13 and 2023-02-17), the degradation rate of MB 425 in SA-PTR was 0.0099 min-1, which was almost similar with PTR and 1.46 folds of 426 IPC, respectively (Table 1). Additionally, the degradation rate of MO in SA-PTR was 427 0.050 min-1, which was also similar with PTR and 2.42 folds of IPC, respectively (Table 428 1). Therefore, the above results demonstrated that SA-PTR not only avoided the 429 negative effects of excessive light irradiance and temperature via sunlight adjustment, 430 but also realized efficient photocatalytic degradation of different organic dyes. 431 Moreover, considering the typical concentration of 5 mg·L-1 for MB or MO wastewater432 [30–32], which was consistent with this study, SA-PTR showed great potential for 433 treating typical organic dye wastewater in practice. 434 3.5. Antibiotic treatment and pathogenic bacteria disinfection under actual 435 sunlight 436 Antibiotics and pathogenic bacteria are also organic pollutants in wastewater, 437 which cause serious problems on human health [33,34]. To further evaluate the 438 capability of SA-PTR, the degradation and disinfection of typical antibiotic (TC) and 439 pathogenic bacteria (E. coli) were carried out under real sunlight. 440 21 Firstly, TC was degraded on a typical sunny day (2023-02-22) and cloudy 441 conditions (2023-02-23), respectively. Fig. S10a-b showed that SA-PTR provided the 442 optimal solar energy (around 1500 W·m-2) and reaction temperature (around 38℃) for 443 the photocatalytic degradation of TC by actively adjusting the mirror size under sunny 444 conditions. In addition, SA-PTR also provided the optimized light irradiance and 445 reaction temperature for TC degradation under cloudy weather (shown in Fig. S10c-d). 446 Under such favorable photocatalytic reaction conditions, the TC degradation 447 experiments were carried out (Fig. 6a). The TC reaction rate of SA-PTR on sunny day 448 was 0.0201 min-1, which was almost the same as that of PTR and 1.38 times that of IPC, 449 respectively (Table 1). Additionally, the TC degradation rate of SA-PTR under cloudy 450 condition reached 0.0182 min-1, which was also almost the same with that of PTR, and 451 1.34 folds of IPC, respectively (Table 1). These results suggested that the strategy of 452 providing optimal solar energy with SA-PTR could facilitate the photocatalytic 453 degradation process of antibiotics. Moreover, in this study, the antibiotic solution with 454 the concentration of 10 mg·L-1 was used, which was much higher than the TC 455 concentration (0.1 mg·L-1) in real hospital wastewater [35]. Therefore, the above results 456 implied that SA-PTR has application value in the treatment of real antibiotic wastewater. 457 Then, the disinfection experiment for pathogenic bacteria E. coli was conducted 458 under sunny-cloudy condition on a day (2023-03-01) near the vernal equinox. SA-PTR 459 could provide optimal solar energy when the sun was not blocked, and could provide 460 as much light energy as possible when the solar rays were weakened by clouds (Fig. 461 S11a). In addition, the reaction temperature in SA-PTR was also increased to the 462 22  suitable range (around 32℃), which could effectively facilitate the reaction process 463 (Fig. S11b). While for the PTR, on the one hand, it provided excessive light irradiance 464 (up to 6500 W·m-2), which may lead to the fast recombination of electrons and holes in 465 photocatalyst and could not increase photocatalytic efficiency. Therefore, as shown in 466 Fig. 6b, SA-PTR still achieved the highest sterilization rate (0.0024 min-1), which was 467 1.26 folds of PTR, and 2.67 folds of IPC (Table 1), respectively. In addition, the 468 concentration of pathogenic bacteria in real waterbody was only around 1 × 103 cfu·mL-469 1 [36], which was much lower than the concentration used in this study (1.2 × 105 470 cfu·mL-1). Therefore, SA-PTR could also have applicability in eliminating the 471 pathogenic bacteria in real waterbody. 472 The experimental results for the removal of organic dyes (Rh B, MB and MO), 473 antibiotics (TC) and pathogenic bacteria (E. coli) during the daytime indicated that the 474 newly developed SA-PTR could implement effective solar energy control under real 475 weather conditions. With such solar energy adjustment strategy, SA-PTR could be 476 expected to achieve efficient real wastewater treatment processes in future applications. 477 3.6. Assessment of whole-year daytime performance 478 The whole-year daytime performance of SA-PTR was evaluated at Tsukuba area 479 (36.1°N, Japan) based on the open-available database of the Japan Meteorological 480 Agency [27]. The solar energy conversion in photoreactors was calculated (as shown 481 in supplementary materials Text S2), and Fig. 7a-b showed the whole-year natural 482 sunlight irradiance and ambient temperature, respectively. Due to the solar movement 483 and seasonal changes, the maximum natural light irradiance was only 889 W·m-2, which 484 23 was much lower than the suitable 1500 W·m-2 (Fig. 1b). Due to the weak natural light 485 power, the highest ambient temperature was only 33.4℃, which could not effectively 486 promote the photocatalytic activity [11]. As for IPC, since it only passively receives 487 solar energy using an inclined mirror, it could only provide the solar energy of 0-1013 488 W·m-2 (Fig. 7c) and temperature lower than 37.8℃ (Fig. 7d), which were only slightly 489 improved compared with the natural conditions and unfavorable for efficient 490 photocatalytic process (Fig. 1b). Then, the PTR which passively concentrate solar light 491 using the parabolic mirror provided the solar energy up to 7500 W·m-2 (Fig. 7e) and the 492 excessive reaction temperature (near to 90℃) (Fig. 7f), which may cause the limitation 493 of the photocatalytic reaction [11], damage of equipment, evaporation of wastewater 494 [11] and the formation of undesired by-products [19]. Therefore, PTR may not be495 feasible for practical application in photocatalytic wastewater treatment. 496 To address the above issues, SA-PTR equipped with flexible parabolic mirror was 497 proposed in this study. On the one hand, it could concentrate solar energy. On the other 498 hand, it could adjust the concentrated solar energy amount by controlling the size of 499 flexible parabolic mirror. As shown in Fig. 7g-h, SA-PTR could adjust the concentrated 500 solar energy to the optimal 1500 W·m-2 under actual weather conditions. In this way, 501 the suitable reaction temperature could be achieved while avoiding the negative effects 502 caused by excessively high temperature. In addition, further calculation showed that as 503 long as the cloudage is less than 45%, the SA-PTR could provide the optimal 1500 504 W·m-2 solar energy to photocatalytic reaction (Table S1). Since such weather condition 505 accounts for 73.4% of the yeartime in Tsukuba area (Fig. S14), SA-PTR could have 506 24 excellent weather adaptability. 507 Then, the global whole-year applicability of SA-PTR was also evaluated by 508 assessing its performance at Ishigakijima (24.5°N) and Sapporo (43.1°N), which 509 represent the southernmost and northernmost points of Japan. As depicted in Fig. S15, 510 SA-PTR effectively controlled light irradiance and temperature within the optimal 511 range throughout the year in Sapporo by adjusting solar energy. This indicated the 512 potential of SA-PTR to achieve high-efficiency photocatalytic wastewater treatment in 513 Sapporo. Additionally, SA-PTR simulation at Ishigakijima (Fig. S16) demonstrated the 514 optimized solar energy by controlling the mirror size. Therefore, SA-PTR has the 515 potential to effectively adjust concentrated solar energy across Japan. Furthermore, 516 considering that the latitude of Japan encompasses the latitudes of the most densely 517 populated areas in the world (Fig. S17), SA-PTR could effectively adjust solar energy 518 and achieve efficient wastewater treatment at the global populated areas. 519 3.7. Nighttime operation of SA-PTR 520 The above results demonstrated that the developed SA-PTR could achieve 521 effective control of natural solar energy under real solar conditions, enabling efficient 522 photocatalytic treatment of different typical organic pollutants during the daytime. 523 However, for modern industrial facilities with high robustness requirements (such as 524 wastewater treatment plants), photocatalytic systems need to be operational not only 525 during the daytime, but also at nighttime. Nowadays, for solar-powered photocatalytic 526 systems, achieving 24-hour continuous operation remains a challenge. 527 It is worth noting that, since SA-PTR was designed to roll up the flexible mirror 528 25  (to provide optimal 1500 W·m-2) in sunny conditions, some spare spaces between 529 flexible mirror and framework of reactor were displayed (shown in Fig. 8a), allowing 530 sunlight to pass through. If a solar panel is integrated behind the flexible mirror, and a 531 UV lamp is installed above the reaction tube, it is possible to achieve the 24-hour 532 operation of SA-PTR. Figure 8b showed the working principle of SA-PTR during 533 daytime and nighttime. Under sunny conditions during the daytime, when natural solar 534 light irradiance is high, flexible mirror was rolled up to provide the optimal light 535 irradiance and temperature, which allowed the solar panel behind the mirror to receive 536 solar energy, thus generating and storing large amount of solar-electricity. Under 537 cloudy conditions during the daytime, flexible mirror was expanded to provide the light 538 irradiance and temperature as high as possible to maximize the photocatalytic efficiency. 539 At this time, since the expanded flexible mirror blocked the sunlight, few electrical 540 power was generated by solar panel. At night, the electrical power stored during the 541 daytime would power the UV lamp mounted over the reaction tube, ensuing the 542 continuous photocatalytic process 543 To verify whether the power generated by solar panel during the daytime could 544 cover the power requirement of UV lamp during the nighttime, the power 545 generation/consumption amount of SA-PTR for the whole-year time (2022) in Tsukuba 546 area has been calculated. Figure 8c presented the daily power generation capability of 547 SA-PTR. As can be seen, its power generation amount was greatly affected by the 548 season and weather. In winter (January, November and December), the solar-electricity 549 generation capability was weaker due to the short daytime hours and low solar altitude 550 26 angle. While in other seasons, more solar-electricity power could be generated owing 551 to longer daytime hours and higher solar altitude angles. Then, compared with the 552 power consumption of SA-PTR (Fig. 8d), its power generation amount (270,488 kJ) far 553 exceeded the consumption amount (182,304 kJ) in spring, summer and autumn. Even 554 in winter when solar radiation was the weakest, its power generation amount (58,393 555 kJ) still 100% satisfied the power consumption requirement (57,976 kJ). Therefore, the 556 SA-PTR combined with solar panel and UV lamp could achieve solar-powered 24-hour 557 continuous photocatalytic reactions during the whole-year time. 558 To investigate the 24-hour water purification performance of SA-PTR, 559 photocatalytic degradation experiments of different organic pollutants were further 560 carried out in SA-PTR during the nighttime. Figure 9a showed the Rh B degradation 561 results in SA-PTR and in dark condition during the nighttime (2023-10-02). The solar-562 electricity-powered UV lamp in SA-PTR could effectively activate the photocatalytic 563 reaction tube, so as to achieve Rh B degradation. While almost no Rh B was degraded 564 under the dark condition, implying the weak photocatalytic capability of traditional 565 PTR and IPC in the night. Similar results could be observed in Fig. 9b-e, which 566 demonstrated that the solar-electrical powered UV lamp equipped in SA-PTR could 567 achieve degradation of different organic pollutants (MB, MO, TC and E. coli) during 568 the nighttime (from 2023-10-11 to 2023-11-03), while PTR and IPC exhibited 569 negligible treatment efficiency toward organic pollutants. Interestingly, as shown in Fig. 570 9f, the degradation reaction rate of Rh B during the night operation of SA-PTR (0.0245 571 min-1) was similar with that during the daytime (0.0114-0.0338 min-1, shown in Table 572 27 1). What’s more, the degradation reaction rates of MB and TC in SA-PTR during 573 nighttime (0.0498 min-1 and 0.0259 min-1, respectively) were even much higher than 574 those in sunny conditions during the daytime (0.0172 min-1 and 0.0201 min-1, shown in 575 Table 1). On the other hand, the treatment efficiency of SA-PTR for MO and E. coli at 576 nighttime (0.00123 min-1 and 0.00024 min-1, respectively) were lower than those during 577 daytime (0.0051-0.0094 min-1 and 0.0024 min-1, respectively, shown in Table 1). 578 Kalaycıoğlu et al. also reported the similar phenomenon that the photocatalytic reaction 579 rate varied under the different light sources (sunlight and UV light) [30]. However, the 580 reason may need to be further studied in the future. The above results indicated that SA-581 PTR could provide superior light irradiance and reaction temperature for photocatalyst 582 via solar energy controlling, thus realizing efficient photocatalytic water purification 583 process during the daytime. At the same time, the power generated by SA-PTR under 584 real sunlight during the daytime was sufficient to meet the power requirements of 585 continuous 24-hour photocatalytic reaction. At night, SA-PTR could also achieve 586 effective photocatalytic degradation of different organic pollutants. 587 In comparison to the photoreactors reported so far, SA-PTR potentially offered 588 significant advantages in terms of light adjustability and all-weather operational 589 capability. For instance, the maximum irradiance achieved by IPC was limited to 800 590 W·m-2 [11], while V-groove-based photoreactors struggled with inefficient sunlight 591 harnessing, resulting in temperatures that rarely exceed 38°C [37]. This low solar 592 energy capture capacity renders them inadequate for achieving efficient photocatalytic 593 reactions. On the contrary, high-solar-concentrated photoreactors such as PTR, 594 28  Parabolic Dish Reflector (PDR), and Fresnel lens (FL) typically provided extreme light 595 irradiances of up to 15,000 W·m-2 and temperatures of up to 200-250°C [38,39]. 596 However, numerous studies have highlighted the drawbacks of these systems 597 [11,40,41]. Specifically, the rapid electron-hole recombination rate at high light 598 irradiances fails to enhance photocatalytic efficiency. Additionally, excessive 599 temperatures have detrimental effects on the reaction process. Despite Compound 600 Parabolic Collectors (CPC) could provide a suitable light irradiance of 1018-2083 W·m-601 2 for photocatalysis [42,43], certain shortcomings specific to CPC are also noteworthy. 602 One major drawback is the potential for localized excessive light irradiance and 603 overheating within certain regions of reaction tube [44]. The intricate mirror of CPC 604 may also lead to high manufacturing cost. Notably, the recently developed solar-605 energy-controllable Linear Fresnel Photoreactor (LFP) addressed above issues by 606 tracking and controlling sunlight to achieve an optimized light irradiance of 1000 W·m-607 2 and a suitable temperature (increased while lower than 65℃), which were favorable 608 for photocatalysis [11]. Nevertheless, its inability for night-time operation may limit its 609 all-weather functionality. Although Portela et al. introduced a CPC that incorporated 610 both solar and artificial lamp irradiation, allowing for daylight utilization and nighttime 611 operation, the energy source for the artificial lamp still relied on municipal power [45]. 612 Therefore, the developed SA-PTR could be a 24-hour solar-powered 613 photocatalytic reactor that could be efficiently operated during the whole-year time, 614 which laid the basis for its industrial large-scale application. 615 29 3.8. Economic analysis and application prospects of SA-PTR 616 One of the decisive factors determining whether a new technology could be 617 popularized and applied on a large scale is its economic advantages. In order to explore 618 the economic advantages of SA-PTR compared with traditional PTR and IPC, the 619 economic analysis based on the actual situation was carried out. In this study, SA-PTR, 620 PTR and IPC based photocatalytic systems located in Tsukuba area were proposed for 621 daily 1000 m3 organic wastewater treatment, respectively. Assuming a citizen uses 100 622 L of water per day, and 70% of the used water becomes wastewater, each of these 623 systems could provide water purification services for a community of 14,000 people. 624 As shown in Fig. 10a, the insoluble and large particles in city-generated sewage would 625 first be removed by a filtration/precipitation station for initial treatment. Then, the 626 remaining waste liquid containing refractory soluble organic pollutants would be sent 627 to the proposed SA-PTR, PTR and IPC based photocatalytic systems, respectively. 628 The estimated parameters of three photocatalytic systems for 1000 m3 wastewater 629 purification were listed in Table S2. The total length of the SA-PTR system which was 630 24-hour operational was evaluated to be 216 m. Although the photocatalytic reaction631 efficiency of PTR was close to that of SA-PTR (Table 1), it could only work during the 632 daytime (with an operational time of 12 h on average). Thus, in order to achieve the 633 same daily wastewater treatment capacity (1000 m3), the total length of the PTR system 634 needs to be doubled (432 m). Further, for IPC which could only work during the 635 daytime with low photocatalytic efficiency, an even larger scale (840 m) was required. 636 Notably, these differences in total length of the photocatalytic system would directly 637 30 impact the size of deployment area. For the SA-PTR system, its solar panel was highly 638 integrated behind the flexible mirror and did not require any extra installation space 639 outside the reactor body (Fig. 8a). Therefore, SA-PTR system only needs to occupy 640 about 1860 m2, which was much smaller than the PTR (3360 m2) and IPC (5280 m2) 641 systems, thus making SA-PTR gains the advantages in reducing land costs (Fig. 10b) 642 and improving deployment flexibility (such as rooftop deployment). Besides, as shown 643 in Fig. 10b, the smaller size of the SA-PTR system also significantly reduced the cost 644 of reaction components (photocatalyst, reaction tubes, etc.), mirror components (mirror 645 pylon, mirror panel, etc.) and flow components (pipes and pumps). Despite additional 646 electronic devices (mirror controlling system, solar panel, rechargeable battery, UV 647 lamp, etc.) were required to be equipped in SA-PTR system for solar energy adjustment 648 and 24-hour continuous operation, they might not significantly increase the overall 649 construction cost budget of the SA-PTR system owing to their low market price and 650 limited equipment demand. 651 In addition to the construction budget, the operation cost could also be an 652 important aspect of the economic analysis, which was closely related to the system 653 power requirement. Figure 10c compared the daily power requirements for SA-PTR, 654 PTR and IPC based photocatalytic systems. Traditional PTR and IPC based 655 photocatalytic systems require pump operation, and PTR further requires a solar 656 tracking system to maintain the vertical incidence of sunlight. Since PTR and IPC 657 cannot be integrated with solar panel, their pump and solar tracking system could only 658 rely on external artificial power supply, which lead to extensive annual power cost 659 31  (16,530 kW·h for PTR, 30,306 kW·h for IPC). While for the SA-PTR system coupled 660 with solar panel, despite additional electronic devices (for solar tracking/controlling and 661 UV lighting) increased its total annual power demand (72,156 kW·h), it could generate 662 86,222 kW·h solar-electrical power during the year, thus no any external artificial 663 power input was needed. Since all the energy for driving 24-hour continuous 664 photocatalytic reactions in SA-PTR come from free and eternal solar energy, its 665 sustainability and cost-effectiveness was highlighted. From the above results, it could 666 be seen that the SA-PTR system requires low budget for construction and zero power 667 cost for operation, thus enabling SA-PTR to have significant economic advantages over 668 PTR and IPC. 669 Furthermore, the innovative design of SA-PTR may bring some additional benefits. 670 For example, its flexible mirror could be rolled up to avoid structural damage during 671 extreme weather such as typhoons and hail. Its lightweight flexible mirror could also 672 lower the gravity center of system to avoid toppling during earthquakes. Moreover, 673 excessive reaction temperature and light irradiance could be avoided by adjusting solar 674 energy, thus reducing the aging and damage of system components (such as rubber 675 connecting pipes and water pump blades). It is noteworthy that at the present stage, the 676 photocatalyst used in SA-PTR is TiO2, which possesses low utilization ability of 677 sunlight and poor adsorption for organic pollutants [46,47]. One of the future 678 improvements may involve adopting solar-light-driven composite catalysts to enhance 679 photocatalytic activity [15,47,48]. Adsorption technology, as an effective approach of 680 contaminant removal [49,50], could also be leveraged to augment the performance of 681 32 SA-PTR. In particular, catalysts that possess excellent adsorption capabilities are 682 promising candidates for this purpose [51–53]. Based on the above perspectives, SA-683 PTR could be a novel 24-hour operational photoreactor with excellent photocatalytic 684 capability, industrial applicability, superior economic efficiency, high safety and long 685 lifetime, which is promising to be applied in wastewater purification globally. 686 4. Conclusions687 In this study, a 24-hour operational solar energy-controllable SA-PTR system was 688 pioneeringly developed. This innovative system incorporated a flexible parabolic 689 mirror, adaptively adjustable in size to harness optimal solar energy for photocatalytic 690 reactions during daytime. Notably, the SA-PTR even retained operational capability 691 during nighttime, independent of external power sources. Comparative assessments 692 with traditional PTR and IPC reactors revealed that the SA-PTR outperformed in the 693 removal of typical organic dyes, antibiotics and pathogenic bacteria, achieving superior 694 treatment efficiency day and night. Additionally, its excellent economic feasibility and 695 practical applicability make the SA-PTR a highly promising technology for widespread 696 implementation in global real-world wastewater treatment. 697 Acknowledgement 698 This work was supported by Scientific Research (B) 22H03778 and Grant-in-Aid 699 for Exploratory Research 21k19628 from Japan Society for the Promotion of Science. 700 References 701 [1] L. Bergamonti, C. Bergonzi, C. Graiff, P.P. Lottici, R. Bettini, L. Elviri, 3D702 printed chitosan scaffolds: A new TiO2 support for the photocatalytic 703 33 degradation of amoxicillin in water, Water Res. 163 (2019) 114841. 704 https://doi.org/10.1016/j.watres.2019.07.008. 705 [2] J. He, J. Cheng, I.M.C. Lo, Green photocatalytic disinfection of real sewage:706 efficiency evaluation and toxicity assessment of eco-friendly TiO2-based 707 magnetic photocatalyst under solar light, Water Res. 190 (2021) 116705. 708 https://doi.org/10.1016/j.watres.2020.116705. 709 [3] A. Taweesan, T. Kanabkaew, N. Surinkul, C. Polprasert, Convenient solutions710 to inconvenient truth : Domestic wastewater management-based approaches to 711 sustainable development goal no . 6, Environ. Sustain. Indic. 18 (2023) 100255. 712 https://doi.org/10.1016/j.indic.2023.100255. 713 [4] M.M.M. Syeed, S. Hossain, R. Karim, M. Faisal, M. Hasan, R. Hayat,714 Environmental and Sustainability Indicators Surface water quality profiling 715 using the water quality index , pollution index and statistical methods : A critical 716 review, Environ. Sustain. Indic. 18 (2023) 100247. 717 https://doi.org/10.1016/j.indic.2023.100247. 718 [5] K. Obaideen, N. Shehata, E. Taha, M. Ali, The role of wastewater treatment in719 achieving sustainable development goals (SDGs) and sustainability guideline, 720 Energy Nexus. 7 (2022) 100112. https://doi.org/10.1016/j.nexus.2022.100112. 721 [6] J. Ming, N. Liu, Q. Ma, A. Sharma, X. Sun, N. Kawazoe, G. Chen, Y. Yang,722 Bactericidal process and practicability for environmental water sterilization by 723 solar-light-driven Bi2WO6-based photocatalyst, J. Water Process Eng. 47 (2022) 724 102713. https://doi.org/10.1016/j.jwpe.2022.102713. 725 34 [7] Y. Zheng, X. Hu, F. Deng, J. Li, D.D. Dionysiou, X. Luo, Enhanced726 photocatalytic oxidizing ability of Zn1-xIn2x/3S solid solution via band structure 727 by composition regulation, Sep. Purif. Technol. 255 (2021) 117726. 728 https://doi.org/10.1016/j.seppur.2020.117726. 729 [8] A. Sharma, N. Liu, Q. Ma, H. Zheng, N. Kawazoe, G. Chen, Y. Yang, PEG730 assisted P/Ag/Ag2O/Ag3PO4/TiO2 photocatalyst with enhanced elimination of 731 emerging organic pollutants in salinity condition under solar light illumination, 732 Chem. Eng. J. 385 (2020) 123765. https://doi.org/10.1016/j.cej.2019.123765. 733 [9] C. Zhang, J. Ming, X. Sun, Y. Zhu, G. An, G. Chen, Y. Yang, Development of734 a green and efficient photocatalytic mesh microalgae biorefinery (PMMB) 735 system for sustainable biomass conversion under real solar light, Chem. Eng. J. 736 466 (2023) 143260. https://doi.org/10.1016/j.cej.2023.143260. 737 [10] H.M.F. Shakir, A. Ali, U. Zubair, T. Zhao, Z.A. Rehan, Fabrication of low738 emissivity paint for thermal / NIR radiation insulation for domestic applications, 739 Energy Reports. 8 (2022) 7814–7824. 740 https://doi.org/10.1016/j.egyr.2022.05.287. 741 [11] C. Zhang, N. Liu, J. Ming, A. Sharma, Q. Ma, Z. Liu, G. Chen, Y. Yang,742 Development of a novel solar energy controllable Linear fresnel photoreactor 743 (LFP) for high-efficiency photocatalytic wastewater treatment under actual 744 weather, Water Res. 208 (2022) 117880. 745 https://doi.org/10.1016/j.watres.2021.117880. 746 [12] C. Liu, Z. Lei, Y. Yang, Z. Zhang, Preliminary trial on degradation of waste747 35 activated sludge and simultaneous hydrogen production in a newly-developed 748 solar photocatalytic reactor with AgX/TiO2-coated glass tubes, Water Res. 47 749 (2013) 4986–4992. https://doi.org/10.1016/j.watres.2013.05.040. 750 [13] C. Zhang, N. Li, G. An, Review of Concentrated Solar Power Technology751 Applications in Photocatalytic Water Purification and Energy Conversion: 752 Overview, Challenges and Future Directions, Energies. 17 (2024) 1–24. 753 https://doi.org/https:// doi.org/ 10.3390/en17020463. 754 [14] L.B. Reuterg̊ardh, M. Iangphasuk, Photocatalytic decolourization of reactive azo755 dye: A comparison between TiO2 and CdS photocatalysis, Chemosphere. 35 756 (1997) 585–596. https://doi.org/10.1016/S0045-6535(97)00122-7. 757 [15] N. Liu, Q. Zhu, N. Zhang, C. Zhang, N. Kawazoe, G. Chen, N. Negishi, Y. Yang,758 Superior disinfection effect of Escherichia coli by hydrothermal synthesized 759 TiO2-based composite photocatalyst under LED irradiation: Influence of 760 environmental factors and disinfection mechanism, Environ. Pollut. 247 (2019) 761 847–856. https://doi.org/10.1016/j.envpol.2019.01.082. 762 [16] A. Volvach, G. Kurbasova, L. Volvach, Heliyon Analysis and numerical763 simulation of temperature measurements made on earth and from space, Heliyon. 764 9 (2023) e12999. https://doi.org/10.1016/j.heliyon.2023.e12999. 765 [17] J. Macedo-Valencia, J. Ramírez-Ávila, R. Acosta, O.A. Jaramillo, J.O. Aguilar,766 Design, construction and evaluation of parabolic trough collector as 767 demonstrative prototype, Energy Procedia. 57 (2014) 989–998. 768 https://doi.org/10.1016/j.egypro.2014.10.082. 769 36 [18] S. Malato, J. Blanco, A. Vidal, C. Richter, Photocatalysis with solar energy at a 770 pilot-plant scale: An overview, Appl. Catal. B Environ. 37 (2002) 1–15. 771 https://doi.org/10.1016/S0926-3373(01)00315-0. 772 [19] R.J. Braham, A.T. Harris, Review of major design and scale-up considerations773 for solar photocatalytic reactors, Ind. Eng. Chem. Res. 48 (2009) 8890–8905. 774 https://doi.org/10.1021/ie900859z. 775 [20] V.K. Jebasingh, G.M.J. Herbert, A review of solar parabolic trough collector,776 Renew. Sustain. Energy Rev. 54 (2016) 1085–1091. 777 https://doi.org/10.1016/j.rser.2015.10.043. 778 [21] B. You, D. Liang, X. Yu, X. Wen, Deployment dynamics for flexible deployable779 primary mirror of space telescope with paraboloidal and laminated structure by 780 using absolute node coordinate method, Chinese J. Aeronaut. 34 (2021) 306–319. 781 https://doi.org/10.1016/j.cja.2020.07.012. 782 [22] H.P. Garg, G. Datta, Fundamentals and characteristics of solar radiation, Renew.783 Energy. 3 (1993) 305–319. https://doi.org/10.1016/0960-1481(93)90098-2. 784 [23] Y. Baghzouz, Sunlight and its Properties, (2011). 785 http://www.egr.unlv.edu/~eebag/Sunlight and its Properties.pdf. 786 [24] H. Zhang, T. Li, Z. Li, Modeling in SolidWorks and analysis of temperature and787 thermal stress during construction of intake tower, Water Sci. Eng. 2 (2009) 95–788 102. https://doi.org/10.3882/j.issn.1674-2370.2009.01.009.789 [25] G. Cardona, R. Pujol-Nadal, OTSun, a python package for the optical analysis790 of solar-thermal collectors and photovoltaic cells with arbitrary geometry, PLoS 791 37 One. 15 (2020) 1–15. https://doi.org/10.1371/journal.pone.0240735. 792 [26] G. Xu, Y. Huang, Y. Quan, Q. Yin, Case Studies in Thermal Engineering Effect793 of thin-film sensors on local heat transfer in convective heat flux measurement, 794 Case Stud. Therm. Eng. 49 (2023) 103189. 795 https://doi.org/10.1016/j.csite.2023.103189. 796 [27] M. Borowitz, Japan Meteorological Agency, Open Sp. (2018).797 https://doi.org/10.7551/mitpress/10659.003.0018. 798 [28] H.K. Kondaveeti, N.K. Kumaravelu, S.D. Vanambathina, S.E. Mathe, S.799 Vappangi, A systematic literature review on prototyping with Arduino: 800 Applications, challenges, advantages, and limitations, Comput. Sci. Rev. 40 801 (2021) 100364. https://doi.org/10.1016/j.cosrev.2021.100364. 802 [29] L.M. Skjolding, L. v. G. Jørgensen, K.S. Dyhr, C.J. Köppl, U.S. McKnight, P.803 Bauer-Gottwein, P. Mayer, P.L. Bjerg, A. Baun, Assessing the aquatic toxicity 804 and environmental safety of tracer compounds Rhodamine B and Rhodamine 805 WT, Water Res. 197 (2021) 117109. 806 https://doi.org/10.1016/j.watres.2021.117109. 807 [30] Z. Kalaycıoğlu, B. Özuğur Uysal, Ö. Pekcan, F.B. Erim, Efficient Photocatalytic808 Degradation of Methylene Blue Dye from Aqueous Solution with Cerium Oxide 809 Nanoparticles and Graphene Oxide-Doped Polyacrylamide, ACS Omega. 8 810 (2023) 13004–13015. https://doi.org/10.1021/acsomega.3c00198. 811 [31] Q. Ma, J. Ming, X. Sun, H. Zhang, G. An, N. Kawazoe, G. Chen, Y. Yang,812 Photocatalytic degradation of multiple-organic-pollutant under visible light by 813 38 graphene oxide modified composite: degradation pathway, DFT calculation and 814 mechanism, J. Environ. Manage. 347 (2023) 119128. 815 https://doi.org/10.1016/j.jenvman.2023.119128. 816 [32] R.A. Putri, S. Safni, N. Jamarun, U. Septiani, Kinetics study and degradation817 pathway of methyl orange photodegradation in the presence of C-N-codoped 818 TiO2 catalyst, Egypt. J. Chem. 63 (2020) 563–575. 819 https://doi.org/10.21608/ejchem.2019.14543.1883. 820 [33] F. Biancullo, N.F.F. Moreira, A.R. Ribeiro, C.M. Manaia, J.L. Faria, O.C. Nunes,821 S.M. Castro-silva, A.M.T. Silva, Heterogeneous photocatalysis using UVA-822 LEDs for the removal of antibiotics and antibiotic resistant bacteria from urban 823 wastewater treatment plant effluents, Chem. Eng. J. 367 (2019) 304–313. 824 https://doi.org/10.1016/j.cej.2019.02.012. 825 [34] E. Rodríguez, Pilot-scale regeneration of wastewater through intensified sulfate826 radical-based advanced oxidation processes (PMS/UV-A, PMS/H2O2/UV-A, 827 and PMS/O3): Inactivation of bacteria and mechanistic considerations, Chem. 828 Eng. J. 469 (2023) 143859. https://doi.org/10.1016/j.cej.2023.143859. 829 [35] B. Gao, W. Chen, J. Liu, J. An, L. Wang, Y. Zhu, M. Sillanpää, Continuous830 removal of tetracycline in a photocatalytic membrane reactor (PMR) with 831 ZnIn2S4 as adsorption and photocatalytic coating layer on PVDF membrane, J. 832 Photochem. Photobiol. A Chem. 364 (2018) 732–739. 833 https://doi.org/10.1016/j.jphotochem.2018.07.008. 834 [36] N. Liu, J. Ming, A. Sharma, X. Sun, N. Kawazoe, G. Chen, Y. Yang, Sustainable835 39 photocatalytic disinfection of four representative pathogenic bacteria isolated 836 from real water environment by immobilized TiO2-based composite and its 837 mechanism, Chem. Eng. J. 426 (2021) 131217. 838 https://doi.org/10.1016/j.cej.2021.131217. 839 [37] O.A. McLoughlin, S.C. Kehoe, K.G. McGuigan, E.F. Duffy, F. Al Touati, W.840 Gernjak, I. Oller Alberola, S. Malato Rodríguez, L.W. Gill, Solar disinfection of 841 contaminated water: A comparison of three small-scale reactors, Sol. Energy. 77 842 (2004) 657–664. https://doi.org/10.1016/j.solener.2004.07.004. 843 [38] R. Ma, H. Su, J. Sun, D. Li, Z. Zhang, J. Wei, Concentrating photo-thermo-844 organized single-atom and 2D-raft Cu catalyst for full-spectrum solar harmonic 845 conversion of aqueous urea and urine into hydrogen, Appl. Catal. B Environ. 315 846 (2022) 121493. https://doi.org/10.1016/j.apcatb.2022.121493. 847 [39] T. Sano, N. Negishi, K. Takeuchi, S. Matsuzawa, Degradation of toluene and848 acetaldehyde with Pt-loaded TiO2 catalyst and parabolic trough concentrator, Sol. 849 Energy. 77 (2004) 543–552. https://doi.org/10.1016/j.solener.2004.03.018. 850 [40] N. Askari, M. Beheshti, D. Mowla, M. Farhadian, Facile construction of novel851 Z-scheme MnWO4/Bi2S3 heterojunction with enhanced photocatalytic852 degradation of antibiotics, Mater. Sci. Semicond. Process. 127 (2021) 105723. 853 https://doi.org/10.1016/j.mssp.2021.105723. 854 [41] J.M. Herrmann, Heterogeneous photocatalysis: State of the art and present855 applications, Top. Catal. 34 (2005) 49–65. https://doi.org/10.1007/s11244-005-856 3788-2. 857 40  [42] F. Cao, Q. Wei, H. Liu, N. Lu, L. Zhao, L. Guo, Development of the direct solar 858 photocatalytic water splitting system for hydrogen production in Northwest 859 China: Design and evaluation of photoreactor, Renew. Energy. 121 (2018) 153–860 163. https://doi.org/10.1016/j.renene.2018.01.016. 861 [43] P. Muñoz-Flores, P.S. Poon, C.O. Ania, J. Matos, Performance of a C-containing 862 Cu-based photocatalyst for the degradation of tartrazine: Comparison of 863 performance in a slurry and CPC photoreactor under artificial and natural solar 864 light, J. Colloid Interface Sci. 623 (2022) 646–659. 865 https://doi.org/10.1016/j.jcis.2022.05.042. 866 [44] K.S. Ochoa-Gutiérrez, E. Tabares-Aguilar, M.Á. Mueses, F. Machuca-Martínez, 867 G. Li Puma, A Novel Prototype Offset Multi Tubular Photoreactor (OMTP) for 868 solar photocatalytic degradation of water contaminants, Chem. Eng. J. 341 869 (2018) 628–638. https://doi.org/10.1016/j.cej.2018.02.068. 870 [45] R. Portela, S. Suárez, R.F. Tessinari, M.D. Hernández-Alonso, M.C. Canela, B. 871 Sánchez, Solar/lamp-irradiated tubular photoreactor for air treatment with 872 transparent supported photocatalysts, Appl. Catal. B Environ. 105 (2011) 95–873 102. https://doi.org/10.1016/j.apcatb.2011.03.039. 874 [46] N. Liu, R. Qi, X. Sun, N. Kawazoe, G. Chen, Y. Yang, Synthesis and 875 characterization of 3D-zeolite–modified TiO2-based photocatalyst with 876 synergistic effect for elimination of organic pollutant in wastewater treatment, 877 Front. Environ. Sci. 10 (2022) 1–12. 878 https://doi.org/10.3389/fenvs.2022.1009045. 879 41 [47] X. Sun, J. Ming, Q. Ma, C. Zhang, Y. Zhu, G. An, G. Chen, Y. Yang, Fabrication880 of optimal oxygen vacancy amount in P/Ag/Ag2O/Ag3PO4/TiO2 through a green 881 photoreduction process for sustainable H2 evolution under solar light, J. Colloid 882 Interface Sci. 645 (2023) 176–187. https://doi.org/10.1016/j.jcis.2023.04.085. 883 [48] Q. Ma, X. Hu, N. Liu, A. Sharma, C. Zhang, N. Kawazoe, G. Chen, Y. Yang,884 Polyethylene glycol (PEG)-modified Ag/Ag2O/Ag3PO4/Bi2WO6 photocatalyst 885 film with enhanced efficiency and stability under solar light, J. Colloid Interface 886 Sci. 569 (2020) 101–113. https://doi.org/10.1016/j.jcis.2020.02.064. 887 [49] E. Sharifpour, E. Alipanahpour Dil, A. Asfaram, M. Ghaedi, A. Goudarzi,888 Optimizing adsorptive removal of malachite green and methyl orange dyes from 889 simulated wastewater by Mn-doped CuO-Nanoparticles loaded on activated 890 carbon using CCD-RSM: Mechanism, regeneration, isotherm, kinetic, and 891 thermodynamic studies, Appl. Organomet. Chem. 33 (2019) 1–14. 892 https://doi.org/10.1002/aoc.4768. 893 [50] E.A. Dil, M. Ghaedi, G.R. Ghezelbash, A. Asfaram, A.M. Ghaedi, F. Mehrabi,894 Modeling and optimization of Hg2+ ion biosorption by live yeast: Yarrowia 895 lipolytica 70562 from aqueous solutions under artificial neural network-genetic 896 algorithm and response surface methodology: Kinetic and equilibrium study, 897 RSC Adv. 6 (2016) 54149–54161. https://doi.org/10.1039/c6ra11292g. 898 [51] E. Alipanahpour Dil, M. Ghaedi, A. Asfaram, F. Mehrabi, A.A. Bazrafshan, L.899 Tayebi, Synthesis and application of Ce-doped TiO2 nanoparticles loaded on 900 activated carbon for ultrasound-assisted adsorption of Basic Red 46 dye, 901 42  Ultrason. Sonochem. 58 (2019) 104702. 902 https://doi.org/10.1016/j.ultsonch.2019.104702. 903 [52] E. Alipanahpour Dil, M. Ghaedi, A. Asfaram, F. Mehrabi, F. Sadeghfar, Efficient 904 adsorption of Azure B onto CNTs/Zn:ZnO@Ni2P-NCs from aqueous solution in 905 the presence of ultrasound wave based on multivariate optimization, J. Ind. Eng. 906 Chem. 74 (2019) 55–62. https://doi.org/10.1016/j.jiec.2018.12.050. 907 [53] R. Bagheri, M. Ghaedi, A. Asfaram, E. Alipanahpour Dil, H. Javadian, RSM-908 CCD design of malachite green adsorption onto activated carbon with 909 multimodal pore size distribution prepared from Amygdalus scoparia: Kinetic 910 and isotherm studies, Polyhedron. 171 (2019) 464–472. 911 https://doi.org/10.1016/j.poly.2019.07.037. 912  913 Table 1 Summary of experimental information and reaction rates in IPC, PTR and SA-PTR. Weather condition Treatment target Reaction rate k (min-1) Reaction rate comparison (folds) IPC PTR SA-PTR kSA-PTR/kIPC kSA-PTR/kPTR Sunny Rh B 0.0193 0.0318 0.0338 1.75 1.06 Temporarily cloudy Rh B 0.0127 0.0209 0.0212 1.64 1.01 Snowy Rh B 0.0057 0.0114 0.0114 2.00 1.00 Sunny MB 0.0134 0.0172 0.0190 1.42 1.10 Rainy MB 0.0067 0.0100 0.0098 1.46 0.98 Sunny MO 0.0032 0.0091 0.0094 2.94 1.03 Cloudy MO 0.0021 0.0050 0.0051 2.42 1.04 Sunny TC 0.0141 0.0195 0.0201 1.38 1.03 Cloudy TC 0.0135 0.0184 0.0182 1.34 0.99 Cloudy-sunny E. coli 0.0009 0.0019 0.0024 2.67 1.26 https://www2.cloud.editorialmanager.com/cej/download.aspx?id=7950957&guid=ac0d9e7e-2efe-4fe0-a7c2-14d7fa9980a4&scheme=1https://www2.cloud.editorialmanager.com/cej/download.aspx?id=7950957&guid=ac0d9e7e-2efe-4fe0-a7c2-14d7fa9980a4&scheme=1Fig. 1. (a) Variation of reaction temperature under different solar energy; (b) relationship between Rh B degradation reaction rate and solar energy.FigureFig. 2. (a) Whole-year natural solar energy at Tsukuba area (36.1°N, 140.1°N); (b) schematic diagram of mirror width in SA-PTR; (c) whole-year mirror size in SA-PTR for providing the optimal solar energy of 1500 W·m-2.Fig. 3. Design of SA-PTR for solar energy controlling during the daytime. (a) Structure of SA-PTR; (b) control system of SA-PTR; (c) adjustment of mirror size in SA-PTR for providing the optimal 1500 W·m-2.Fig. 4. Solar energy adjustment under typical sunny weather condition (2022-12-23, from 8:00 to 14:30). (a) Light irradiance; (b) temperature. Fig. 5. Organic dye degradation experiments under different real weather conditions. (a) Rh B; (b) MB; (c) MO. Fig. 6. (a) TC degradation and (b) E.coli disinfection experiments under real weather conditions. Fig. 7. Evaluation of the light irradiance and temperature in IPC, PTR and SA-PTR during the whole-year time (2022) in Tsukuba area. (a-b): Natural light irradiance and temperature; (c-d) light irradiance and temperature in IPC; (e-f) light irradiance and temperature in PTR; (g-h) light irradiance and temperature in SA-PTR. Data source of natural light and temperature in Tsukuba area in 2022: Japan Meteorological Agency.  Fig. 8. 24-hour operational SA-PTR. (a) Solar panel and UV lamp integrated in SA-PTR; (b) working principle of SA-PTR for daytime (sunny and cloudy conditions) and nighttime operations; (c) daily power generation capability of SA-PTR; (d) yearly power generation and consumption of SA-PTR. All results were calculated based on the 2022 real weather data of Tsukuba obtained from Japan Meteorological Agency. Fig. 9. Comparative experiments of organic pollutants treatment during nighttime in SA-PTR and in dark condition. (a) Rh B degradation (2023-10-02); (b) MB degradation (2023-10-11); (c) MO degradation (2023-10-14); (d) TC degradation (2023-10-12); (e) E. coli disinfection (2023-11-03); (f) reaction rates of different targets treatment in SA-PTR and in dark condition.     Fig. 10. Economic analysis of SA-PTR, PTR and IPC. (a) Schematic diagram of the proposed SA-PTR, PTR and IPC based photocatalytic systems for daily 1000 m3 organic wastewater treatment in Tsukuba area; (b) evaluation on the construction budgets and (c) estimation of the yearly power requirement of SA-PTR, PTR and IPC based photocatalytic systems. All results were calculated based on the 2022 real weather data of Tsukuba obtained from Japan Meteorological Agency.