H2O2 processes: A proof of concept

Journal Pre-Proof Tube-in-Tube Membrane Microreactor for Photochemical UVC/H2O2 Processes: A Proof of Concept Vítor J.P. Vilar, Pello Alfonso-Muniozguren, Joana P. Monteiro, Judy Lee, Sandra M. Miranda, Rui A.R. Boaventura PII: DOI: Reference:

S1385-8947(19)31744-9 https://doi.org/10.1016/j.cej.2019.122341 CEJ 122341

To appear in:

Chemical Engineering Journal

Received Date: Revised Date: Accepted Date:

30 April 2019 1 July 2019 25 July 2019

Please cite this article as: V.J.P. Vilar, P. Alfonso-Muniozguren, J.P. Monteiro, J. Lee, S.M. Miranda, R.A.R. Boaventura, Tube-in-Tube Membrane Microreactor for Photochemical UVC/H2O2 Processes: A Proof of Concept, Chemical Engineering Journal (2019), doi: https://doi.org/10.1016/j.cej.2019.122341

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JOURNAL PRE-PROOF 1

Tube-in-Tube Membrane Microreactor for Photochemical UVC/H2O2

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Processes: A Proof of Concept

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Vítor J.P. Vilara,*, Pello Alfonso-Muniozgurena,b, Joana P. Monteiroa, Judy Leeb, Sandra M.

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Mirandaa,*, Rui A.R. Boaventuraa

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aLaboratory

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(LSRE-LCM), Department of Chemical Engineering, Faculty of Engineering, University of

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Porto, Rua do Dr. Roberto Frias, 4200-465, Porto, Portugal

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and Process Engineering, University of Surrey, Guildford, GU27XH

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of Separation and Reaction Engineering-Laboratory of Catalysis and Materials

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*Corresponding

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Tel.: +351 220414937; E-mail address: [email protected] (Sandra M. Miranda)

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authors:

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Tel.: +351 918257824; E-mail address: [email protected] (Vítor J.P. Vilar)

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JOURNAL PRE-PROOF Abstract

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This work proposes a disruptive tube-in-tube membrane microreactor for the intensification of

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photochemical UVC/H2O2 processes, towards contaminants of emerging concern (CECs)

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removal from urban wastewaters. The main novelty of this system relies on the radial addition of

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H2O2 through the porous membrane into the annular reaction zone, providing a more

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homogeneous distribution of the injected chemical across the whole reactor length. The proposed

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novel reactor consists of a ceramic ultrafiltration membrane inner tubing and a concentric quartz

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outer tubing that compose the annulus of the reactor (path length of 3.85 mm). The ultrafiltration

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membrane is used as a dosing system to deliver small amounts of H2O2 into the annulus of the

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reactor. In the annulus, where a 2 mg/L of oxytetracycline (OTC) solution flows, UVC light is

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provided via four mercury lamps located externally to the outer tube. The helical motion of OTC

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solution around the membrane shell-side enhances H2O2 radial mixing. The efficiency of the

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photochemical UVC/H2O2 process was evaluated as a function of the OTC flowrate, H2O2 dose,

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H2O2 dosage method and water matrix. OTC removal efficiencies of 36% and 7% were

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obtained for a synthetic OTC solution and an urban wastewater fortified with the same OTC

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concentration, using a H2O2 dose of 15.8 mg/L. Besides providing a good performance using low

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UVC fluence (34 mJ/cm2) and reactor residence time (4.6 s), the reactor has the advantage of an

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easy upscaling into a real plant by integrating multiple parallel membranes into a single shell.

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Keywords: Tube-in-Tube Membrane Microreactor; UVC-H2O2; H2O2 Dosing Method; Process

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Intensification.

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JOURNAL PRE-PROOF 1. Introduction

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The occurrence of organic microcontaminants in aquatic ecosystems has become an emerging

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concern due to the inability of current treatment methods to remove such compounds [1]. These

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contaminants of emerging concern (CECs), even in concentrations of nanograms or micrograms,

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constitute a potential threat to both the ecosystem and human health [2]. Consequently, more

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efficient wastewater treatment methods are required to reduce the discharge of such compounds

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into the environment, mainly from urban wastewater treatment plants (WWTPs) [3].

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The use of advanced oxidation processes (AOPs) in general and particularly the combination of

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UVC/H2O2 have proved to be a suitable approach for the removal of CECs [4-6]. When

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combining H2O2 with UVC light, two moles of OH radicals are formed through the photolytic

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cleavage of one mole of H2O2 that lead to a chain reaction [7, 8], improving the performance of

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the individual processes [5, 9, 10]. Generally, the photoreactor comprises a cylindrical shell of

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stainless steel housing concentric quartz sleeves filled with UVC lamps [9, 11, 12]. The

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wastewater to be treated flows between the concentric tubes (annular reactor) [9, 11]. Oxidant is

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supplied upstream of the photoreactor inlet, with the help of static mixers, being able to improve

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the in line mixing of the chemical with the wastewater to be treated [9, 11]. The oxidant

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concentration decreases along the reactor length, due to its homolytic cleavage by UVC photons

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and its decomposition with organic and inorganic species present in the wastewater.

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Consequently, an oxidant concentration profile along the reactor length is observed, generating a

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non-homogenous reaction rate inside the photoreactor, limiting the length of reactors to be used

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in full-scale applications. In order to minimize radial and axial concentration gradients inside the

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annular reaction zone (ARZ) and thus, maximise the efficiency of the photochemical process,

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higher doses of oxidant in the feed stream are required. However, an excessive concentration of

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JOURNAL PRE-PROOF H2O2 can act as a radical scavenger (mainly in the reactor entrance) and higher amounts of

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residual oxidant are wasted and must be eliminated before the discharge of the treated water into

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the environment [11, 13]. Consequently, more efficient photoreactor configurations are required

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to achieve fast reaction rates in the entire annular reactor zone with low residual concentration of

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chemicals at the reactor outlet. An interesting approach is the use of membrane technology to

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provide the minimum amount of oxidant necessary for the reaction. Ozonation membrane

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contacting systems have been used to supply ozone on a continuous basis for water and

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wastewater treatment, showing high ozone transfer efficiencies [14-16]. However, this type of

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reactors has been mainly evaluated for chemical synthesis using gas/liquid reactions [17-24]. For

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example, Cui, et al. [25] proposed a continuous tube-in-tube membrane reactor for the catalytic

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N-oxidation of alkylpyridines with hydrogen peroxide, inspired by the idea of a tubular reactor

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with radial distribution of H2O2 given by Pineda-Solano, et al. [26]. No UV lamps were used in

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this case. A single tube-in-tube model, as well as a multiunit reactor bundle were proposed for

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real scale applications using a ceramic membrane for the segregated feeding of H2O2. Similarly,

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a liquid-liquid tube-in-tube semipermeable membrane microreactor was employed by Buba, et

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al. [27] for the synthesis of N-Methylated amino acids. For this experimental study, a Teflon AF

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2400 membrane was used as an improved mixing system, injecting the solvent by a syringe

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pump in the annulus of the reactor.

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Therefore, this work proposes a disruptive tube-in-tube membrane microreactor for the

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photochemical UVC/H2O2 process, allowing a controlled “titration” of small H2O2 doses along

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the reactor length, resulting in a more homogenous distribution of H2O2 molecules in the annular

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reaction zone. The efficiency of the photochemical UVC/H2O2 reactor was tested for the

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oxidation of oxytetracycline (OTC), a commonly antibiotic used as a model CEC, as a function

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JOURNAL PRE-PROOF of the OTC flowrate, H2O2 dosage (H2O2 stock solution concentration vs H2O2 dosing rate),

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H2O2 dosage method (radial permeation through the porous inner membrane or supplied

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upstream of the photoreactor inlet) and water matrix. The idea is to maximise per-pass pollutants

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conversion, while keeping H2O2 in the reactor outlet at a minimum. This would minimise (or

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even avoid) the use of subsequent treatment methods needed to remove residual H2O2, as well as

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the storage capacity and transportation costs of the chemical, maximising the efficient use of

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H2O2 in real WWTPs.

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2. Material and methods

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2.1. Reagents

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Oxytetracycline hydrochloride (OTC, MW = 496.89, 96% purity, CAS# 2058-46-0) was

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supplied by ThermoFisher and used as model pollutant. Hydrogen peroxide (HYPE-30P-1K0

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from Labbox, purity 30% (v/v)) was used as oxidant. Na2SO3 (Merck, p.a.) was added to samples

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for H2O2 elimination. Ammonium monovanadate (Merck, p.a.) was used to determine H2O2

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concentration. For OTC analysis by HPLC-DAD, acetonitrile, methanol and oxalic acid

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dehydrated were supplied by Merck. Pure water (Panice® reverse osmosis system) and ultrapure

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water (Millipore® Direct-Q system) were used to prepare the synthetic OTC solutions and the

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mobile phases for HPLC system, respectively. Methylene blue (provided by Merck) was used to

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prepare the solution for tracer experiments.

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The real wastewater sample was collected downstream from the secondary treatment of an urban

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wastewater treatment plant (WWTP) and kept refrigerated until use. The urban WWTP from

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Northern Portugal was designed to serve 260,000 population-equivalent with an average flowrate

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of 43,000 m3/day. Table 1 presents its main physicochemical characteristics. Feed solutions

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used in the experiments were prepared from pure water or the urban wastewater spiked with 2

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mg OTC per litter. Insert Table 1

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2.2.

Lab-scale prototype

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The proposed novel tube-in-tube reactor consists of an inner ceramic ultrafiltration membrane (γ-

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Al2O3 membrane from Inopor GmbH) and a quartz outer tubing (Figs. 1 and 2). The main

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characteristics of the tube-in-tube reactor are summarized in Table 2. The tube ends are tightly

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sealed by two movable polypropylene flanges (Fig. 1a). The membrane outlet is connected to a

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back-pressure regulator (BPR). The membrane is internally fed with the H2O2 stock solution

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using a syringe pump (Nexus 6000 from Chemyx Inc.). H2O2 solution permeates through the

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porous ceramic membrane, and contacts directly with the concurrently fed OTC stream in the

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annulus (Fig. 3). The bottom and top flanges have inlet and outlet pipes located perpendicularly

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to the OTC stream flow direction and tangentially to the quartz tube, in horizontal plane and at

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the top in opposite sides (Fig. 2b). This configuration induces a helical motion of the OTC

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stream around the membrane shell-side, as can be seen in Fig. 2c using a tracer solution. The

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fluid movement drags the small H2O2 drops from the membrane shell-side to the bulk of the

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ARZ. The OTC solution is pumped from a jacketed vessel (connected to a F12-MA chiller from

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Julabo) to the ARZ using a gear pump (model BVP-Z from Ismatec). Radiation is provided by

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four UVC lamps (Puritec HNS 6 W G5 from Osram) located externally to the quartz tube and

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with a nominal power of 6 W (λmax = 254 nm; useful power = 1.4 W). Photon flow (1.7 W)

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inside the ARZ was measured by H2O2 (35 mM) actinometry [28] (overall quantum yield, ΦT =

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1.11, molar absorptivity, P = 18.6 M-1 cm-1, path length, b = 3.85 mm). The setup is surrounded

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by an aluminium shell to avoid direct eye contact with UVC lamps.

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Insert Figure 1

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Insert Figure 2

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Insert Figure 3

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Insert Table 2 2.3. Experimental procedure

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The ceramic membrane was internally filled with the H2O2 stock solution, with the BPR fully

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open. After that, with the BPR fully closed, the syringe pump was used to gradually administer

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the H2O2 solution, until the first drops of H2O2 appeared in the shell side of the membrane. This

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indicates that the membrane pores are completely filled with the H2O2 solution. Then, 1 L of

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pure water was pumped through the ARZ to clean the membrane surface. Subsequently, 5 L of

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an OTC solution ([OTC]inlet = 2 mg/L; T = 25ºC) was pumped through the ARZ. At the same

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time, the syringe pump administered the H2O2 stock solution at low dosing rates and UVC lamps

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were turned on. Samples were collected at different periods until reaching steady state conditions

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and further analysed in terms of OTC and H2O2 concentration. Immediately after sample

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collection for OTC analysis, Na2SO3 in a Na2SO3:H2O2 molar ratio of 1:1 was added to quench

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H2O2.

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The concentration of hydrogen peroxide in the water flow side at the reactor outlet in the absence

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of reaction (without OTC), was first evaluated as a function of water inlet flow rate, H2O2 stock

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solution concentration and H2O2 dosing rate. After that, OTC oxidation tests were performed at

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different reaction conditions using the synthetic OTC solution and H2O2 permeation method: i)

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direct photolysis (no oxidant permeation), ii) only with H2O2 (absence of radiation) and iii)

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UVC/H2O2. The following operational conditions were tested: OTC solution inlet flow rate

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(Qinlet,OTC = 10, 20, 40, 60 or 80 L/h), H2O2 stock solution concentration ([H2O2]stock solution = 7.5,

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15 or 30 g/L) and H2O2 dosing rate (0.35, 0.50, 0.70, 1.4, 2.1, 2.8 or 3.5 mL/min). Assays with

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the real wastewater were performed at the following conditions: Qinlet,OTC = 40 L/h; [H2O2]stock

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solution

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The system performance was also evaluated using the conventional oxidant dosing method-

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supplied upstream of the photoreactor inlet (direct injection). Table 3 presents the experimental

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conditions used in all UVC/H2O2 tests.

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2.4. Analytical procedure

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OTC concentration was determined by HPLC using a Hitachi ELITE LaChrom (Merck-Hitachi,

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Tokyo, Japan), equipped with a L-2130 pump, a L-2200 autosampler, a L-2300 column oven, a

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Purospher® RP-18e 125–4 (5 μm) (Merck) column and a L-2455 DAD. A detailed description of

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the analytical method can be found elsewhere [29]. H2O2 concentration was determined by the

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metavanadate method (λ = 450 nm) [30]. Dissolved organic carbon (DOC), chemical oxygen

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demand (COD), total suspended solids (TSS), volatile suspended solids (VSS), total

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phosphorous, pH, temperature and turbidity, as well as inorganic anions and cations

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concentrations were assessed according to the procedures already described by Moreira, et al.

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[31].

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3. Results and discussion

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3.1. H2O2 permeation

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Fig. 4 shows the H2O2 concentration profile on the water flow side (annular zone) at the outlet of

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the tube-in-tube reactor. H2O2 concentration increases with time until steady state conditions

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after t/ ≥ 90 ( is the space-time inside the illuminated ARZ). The H2O2 steady state

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concentrations are very similar to the theoretical values considering the annular flow rate, H2O2

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stock solution concentration and H2O2 dosing rate. A similar trend was observed when varying

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the annular flow rate, H2O2 stock solution concentration and H2O2 dosing rate (data not shown). Insert Figure 4

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3.2. Effect of the OTC annular flow rate

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The OTC concentration profiles at the outlet of the tube-in-tube reactor for different H2O2

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permeation doses, displayed in Fig. 4, show that steady state conditions are obtained after

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stabilisation of H2O2 in the reactor outlet (t/ ≥ 90), in agreement with the results reported in

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section 3.1. Therefore, the OTC conversion for all assays will be calculated by taking into

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account the OTC concentration in the inlet and outlet streams of the tube-in-tube reactor after t/

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≥ 100, corresponding to an OTC working volume of 5 L.

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The shaded areas in Fig. 4 correspond to the amount of H2O2 consumed during each reaction for

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the different H2O2 permeation doses. H2O2 concentration values in the reactor outlet at steady

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state conditions presents a variation between 0.3 and 2 mg/L, as it can be seen in Table 3.

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Beyond that, the amount of H2O2 that permeates the membrane pores and reaches the ARZ show

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also a variation, in average, of 5% between experiments. Therefore, the amount of H2O2 really

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consumed during the experiments cannot be rigorously calculated. Table 3 shows that a

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significant fraction (in average 75%) of the initial H2O2 added to the ARZ remains after UVC

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irradiation at the reactor outlet at steady state conditions. Sarathy, et al. [11] also reported that for

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an initial H2O2 concentration of 10 mg/L and 0.18 kWh/m3, over 90% of the H2O2 remained in

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the water after UVC/H2O2 treatment (Trojan UVSwift™ 4L12 reactor consisting of four

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medium-pressure mercury vapour lamps with a total power of 11.7 kW).

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Fig. 5 shows that: i) UVC light (UVC photolysis) was not able to break down efficiently the

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OTC molecules considering the low space time inside the ARZ; ii) H2O2 molecules (in the

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absence of UVC light) showed an oxidation power over OTC molecules, resulting in a maximum

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OTC conversion of 12%; iii) the combination of UVC light and H2O2 boosted the OTC oxidation

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efficiency, achieving values in average of 30%, mainly associated with the generation of

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hydroxyl radicals. Insert Figure 5

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Fig. 5 also shows the effect of the annular flow rate (Qinlet,OTC) in the OTC conversion using the

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same amount of H2O2 injected per unit time (10.5 mg H2O2 per min). The H2O2/UVC process led

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to higher OTC conversions with the increment of Qinlet,OTC from 10 to 20 L/h (Fig. 5), indicating

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a change in the hydrodynamic conditions inside the ARZ. A Re number of 1028 (Q = 20 L/h,  =

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9.1 s) allowed to a 1.5-fold increase on OTC conversion compared to a Re of 514 (Q = 10 L/h, 

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= 18.3 s). This can be explained by the poor mixing of H2O2 in the ARZ (the helical motion of

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water around the membrane shell-side only starts to occur for annular flow rates ≥ 20 L/h),

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decreasing the efficiency of H2O2 photolysis by the UVC light and further interaction of the

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reactive species and UVC photons with the OTC molecules, even in the presence of a higher

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H2O2 residual concentration and higher residence time.

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A decrease in OTC conversion can be observed for flow rates higher than 40 L/h (Re >2056;  <

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4.6 s). Under these mixing conditions, the limiting factors are the residence time and H2O2

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concentration in the ARZ. Fig. 6 shows also the effect of the degree of mixing and residence

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time on OTC oxidation (assay 14: Qinlet,OTC = 40 L/h, [H2O2]stock solution = 7.5 g/L, H2O2 dosing

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rate = 1.4 mL/min; assay 9: Qinlet,OTC = 80 L/h, [H2O2]stock solution = 15 g/L, H2O2 dosing rate = 1.4

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mL/min), considering the same concentration of H2O2 in the annular reaction zone at steady state

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conditions (15.8 mg/L). A 2.5-fold increase in OTC oxidation efficiency is observed when the

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flow rate decreased from 80 L/h to 40 L/h, showing that under these mixing conditions, the

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residence time is the limiting factor. Insert Figure 6

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Therefore, considering the highest OTC conversion (27±3%) at lower residual H2O2

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concentration, a feed flow rate of 40 L/h was selected for the next set of experiments. However,

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for Qinlet,OTC = 60 L/h, the addition of 24 mg H2O2 was requested per mg OTC oxidised, against

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29 mg H2O2 added per mg OTC oxidised for Qinlet,OTC = 40 L/h.

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3.3. Effect of H2O2 stock solution concentration

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The effect of H2O2 stock solution concentration in OTC conversion was evaluated by

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maintaining the amount of H2O2 injected per unit time (10.5 mg H2O2 per min) for a Qinlet,OTC =

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40 L/h. According to Table 1 (Assays 1, 6 and 14), the OTC conversion remains on average near

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30% for all conditions. This indicates that the helical motion of water around the membrane

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shell-side drags rapidly the small H2O2 drops from the membrane shell-side to the bulk,

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improving the radial mixing homogeneity within the ARZ. This minimises local points near the

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membrane surface with much higher oxidant concentration than in ARZ bulk.

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3.4. Effect of H2O2 dosage

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As concluded by Crittenden, et al. [32], “there exists an optimum hydrogen peroxide dosage for

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each set of reactor conditions with regard to the organic pollutant removal efficiency of the

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H2O2/UV process“. Thus, the concentration of H2O2 in the reactor annulus was varied while

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maintaining an OTC annular flow rate of 40 L/h (Fig. 6a). This was carried out by modifying the

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H2O2 stock solution concentration and H2O2 dosing rate. Overall, OTC conversion increases with

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the increment on H2O2 concentration in the ARZ until 15.8 mg/L. An increment on H2O2 doses

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JOURNAL PRE-PROOF until 31.5 mg/L led to a similar OTC conversion (Fig. 6a.1). In fact, H2O2 in excess can act as

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hydroxyl radical scavenger [33, 34].

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In order to increase the treatment capacity, the OTC inlet flow rate was increased to 80 L/h.

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Under these conditions, to achieve an OTC conversion near 30%, an H2O2 concentration in the

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ARZ of 39.4 mg/L was required, resulting in a much higher residual H2O2 concentration (Fig.

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6b.2).

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Considering the above and taking into account both OTC conversion and residual H2O2 as

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reactor performance parameters, the best approach was obtained with a OTC inlet flow rate of 40

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L/h and H2O2 concentration in the ARZ of 15.8 mg/L.

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3.5. Effect of H2O2 dosage method

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The H2O2 radial permeation through the porous inner membrane was compared to the

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conventional supply of the chemical upstream of the photoreactor inlet (direct injection). The

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direct injection was carried out using a H2O2 dosing rate of 1.4 mL/min and a H2O2 stock

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solution of 7.5 g/L. Similar OTC conversion and H2O2 residual concentrations were obtained

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using both oxidant dosage methods. This can be related to a nearly constant axial oxidant

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gradient in the ARZ, as a result of the low H2O2 consumption (short reaction time - 4.6 s and low

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UVC fluence - 34 mJ/cm2). However, in full-scale applications, using powerful UVC lamps, the

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oxidant is rapidly consumed along the reactor length (> 1 m), due to its homolytic cleavage by

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UVC photons and its decomposition with organic and inorganic species present in the

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wastewater. Consequently, an axial oxidant profile will be generated when using tube lengths in

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the order of 1 m, resulting in different OTC conversion rates across the reactor length. This

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behaviour imposes a limit on the reactors length to be used in full-scale applications. In order to

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minimise radial and axial oxidant gradients inside the ARZ and thus, maximise the efficiency of

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JOURNAL PRE-PROOF the photochemical process, higher doses of oxidant in the feed stream are required. However, an

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excessive concentration of H2O2 can act as a radical scavenger mainly in the reactor entrance and

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higher amounts of residual oxidant are wasted and must be eliminated before the discharge of the

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treated water into the environment. Therefore, the uniform addition of H2O2 to the reaction zone

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through “virtually” unlimited dosing points along the membrane shell side can enhance the

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transformation rate of target contaminants and can also minimise the residual H2O2 concentration

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in the reactor outlet.

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3.6. Effect of water matrix

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In order to test this best approach for real applications, OTC removal by the photochemical

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UVC/H2O2 system was also evaluated for an urban wastewater after secondary treatment

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fortified with 2 mg/L of OTC (Fig. 7). Paralleling the reaction rates in both matrices, a

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substantial decrease in OTC conversion was observed in the presence of the real wastewater,

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adding the same H2O2 amount to the ARZ (15.8 mg/L). This is mainly related to the presence of

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light absorbing (low UVC transmittance) and reactive oxygen scavenger species, such as natural

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organic matter (NOM) and bicarbonates [35]. Although the OTC conversion using the real

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wastewater almost doubled with the increment on [H2O2]ARZ from 15.8 to 23.6 mg/L, the

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residual H2O2 concentration increased in a similar extend. Therefore, a much higher amount of

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oxidant is required to overcome those effects and achieve OTC conversions similar to the

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synthetic solution. However, it is important to highlight that the aforementioned results were

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obtained using a low UVC fluence (45 mJ/cm2), being significantly lower than those used in real

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treatment plants (600-1000 mJ/cm2) [36]. Insert Figure 7

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4. Conclusions

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JOURNAL PRE-PROOF This study proves the viability of using tube-in-tube membrane microreactors, with radial

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addition of H2O2, to promote photochemical UVC/H2O2 oxidation processes for CECs removal

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from urban wastewaters. The ceramic membrane is internally fed with the H2O2 stock solution;

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H2O2 permeates through the porous membrane, and contacts with the concurrently fed

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wastewater in the annulus; resulting in a controlled oxidant “titration” to the ARZ. The helical

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motion of water around the membrane shell side enhances H2O2 radial dispersion. The more

298

homogenous axial and radial distribution of H2O2 molecules in the ARZ enhances the

299

transformation rate of target contaminants, while keeping H2O2 in the reactor outlet at a

300

minimum.

301

The tube-in-tube membrane microreactor showed an OTC conversion near 36% for a synthetic

302

solution containing an OTC concentration of 2 mg/L, resulting in a residual H2O2 near 14 mg/L

303

(H2O2 dose of 15.8 mg/L). Although lower OTC conversions were observed for an urban

304

wastewater after secondary treatment (fortified with the same amount of OTC), it is important to

305

mention that a low UVC fluence (45 mJ/cm2) was applied when comparing to those used in real

306

treatment plants (600-1000 mJ/cm2).

307

The authors would like to highlight that this type of reactor configuration can be used to promote

308

different chemical, catalytic, electrocatalytic and photo-driven processes, through the dosing of

309

any kind of oxidant (either gas or liquid) or catalyst solutions along the reactor length. At the

310

same time, the proposed set-up could be easily scaled-up by integrating multiple parallel

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membranes into a single shell. In order to provide a better light distribution in the ARZ, multiple

312

concentric quartz sleeves filled with UVC lamps can be incorporated parallel to several

313

membranes.

314

Acknowledgements

14

JOURNAL PRE-PROOF This work was financially supported by: i) Project NOR-WATER funded by INTERREG VA

316

Spain-Portugal cooperation programme, Cross-Border North Portugal/Galiza Spain Cooperation

317

Program (POCTEP) and ii) Project POCI-01-0145-FEDER-006984 – Associate Laboratory

318

LSRE-LCM funded by FEDER funds through COMPETE2020 - Programa Operacional

319

Competitividade e Internacionalização (POCI) – and by national funds through FCT - Fundação

320

para a Ciência e a Tecnologia. Vítor J.P. Vilar acknowledge the FCT Individual Call to Scientific

321

Employment Stimulus 2017 (CEECIND/01317/2017).

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of gas-liquid transformations using a tube-in-tube reactor, Acc Chem Res 48 (2015) 349-362.

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Engineering Chemistry Research 56 (2017) 3822-3832.

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inherently safer design and operation of batch and semi-batch processes: The N-oxidation of

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alkylpyridines, Journal of Loss Prevention in the Process Industries 25 (2012) 797-802.

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[27] A.E. Buba, S. Koch, H. Kunz, H. Löwe, Fluorenylmethoxycarbonyl-N-methylamino Acids

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Synthesized in a Flow Tube-in-Tube Reactor with a Liquid-Liquid Semipermeable Membrane,

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European Journal of Organic Chemistry 2013 (2013) 4509-4513.

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V.J.P. Vilar, Overcoming limitations in photochemical UVC/H2O2 systems using a mili-

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photoreactor (NETmix): Oxytetracycline oxidation, Science of The Total Environment 660

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(2019) 982-992.

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[30] R.F.P. Nogueira, M.C. Oliveira, W.C. Paterlini, Simple and fast spectrophotometric

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determination of H2O2 in photo-Fenton reactions using metavanadate, Talanta 66 (2005) 86-91.

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[31] F.C. Moreira, J. Soler, M.F. Alpendurada, R.A.R. Boaventura, E. Brillas, V.J.P. Vilar,

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Tertiary treatment of a municipal wastewater toward pharmaceuticals removal by chemical and

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electrochemical advanced oxidation processes, Water Research 105 (2016) 251-263.

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[32] J.C. Crittenden, S. Hu, D.W. Hand, S.A. Green, A kinetic model for H2O2/UV process in a

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completely mixed batch reactor, Water research 33 (1998) 2315-2328.

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[33] Z. Shu, J.R. Bolton, M. Belosevic, M. Gamal El Din, Photodegradation of emerging

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micropollutants using the medium-pressure UV/H2O2 Advanced Oxidation Process, Water

415

Research 47 (2013) 2881-2889.

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417

and reaction mechanism of advanced oxidation of 4-nitrophenol in water by a UV/H2O2 process,

418

Journal of Chemical Technology & Biotechnology 78 (2003) 788-794.

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[35] B.A. Wols, C.H.M. Hofman-Caris, Review of photochemical reaction constants of organic

420

micropollutants required for UV advanced oxidation processes in water, Water Research 46

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(2012) 2815-2827.

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[36] C.P. James, E. Germain, S. Judd, Micropollutant removal by advanced oxidation of

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microfiltered secondary effluent for water reuse, Separation and Purification Technology 127

424

(2014) 77-83.

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425

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19

JOURNAL PRE-PROOF Figure Captions

428

Figure 1. Photographs of the tube-in-tube reactor a) and respective components (b): 1 -

429

polypropylene flanges; 2 – quartz outer tube; 3 - γ-Al2O3 ultrafiltration membrane inner tube; 4 -

430

UVC lamp.

431

Figure 2. a) Reactor scheme; b) Reactor flanges design; c) Images of the helical motion of the

432

tracer solution (methylene blue dye solution) in the annular reaction zone.

433

Figure 3. Sketch of the proposed setup.

434

Figure 4. a) H2O2 concentration profiles (open symbols) on the water flow (Qinlet,water = 40 L/h)

435

side at the reactor outlet in the absence of UVC light; b) OTC (full symbols) and H2O2 (semi-

436

filled symbols) concentration profiles on the water flow (Qinlet,OTC = 40 L/h) side at the reactor

437

outlet in the presence of UVC light. [H2O2]stock solution = 7.5 g/L; H2O2 dosing rate (mL/min) = 0.7

438

( ,

439

Figure 5. a) Effect of the annular flow rate in the OTC conversion at steady state conditions; b)

440

Residual H2O2 concentration vs Qinlet,OTC: [H2O2]stock

441

mL/min.

442

permeation).

443

Figure 6. Effect of the H2O2 dosage in the ARZ on OTC conversion at steady state conditions

444

for two inlet flow rates: a.1 and a.2: Qinlet,OTC = 40 L/h, [H2O2]stock solution = 7.5 g/L ( ), 15 g/L (

,

); 2.1 ( ,

,

).

AL

); 1.4 ( ,

- UVC/H2O2;

solution

= 15 g/L; H2O2 dosing rate = 0.7

- H2O2 (absence of radiation);

- UVC photolysis (no oxidant

JO

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,

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427

445

), 30 g/L ( ); b.1 and b.2: Qinlet,OTC = 80 L/h, [H2O2]stock solution = 15 g/L ( ).

446

Figure 7. OTC conversion a) and residual H2O2 concentration b) for synthetic ( ) and real

447

matrices ( ) fortified with 2 mg OTC per liter at steady state conditions: Qinlet,OTC = 40 L/h;

448

[H2O2]stock solution = 7.5 g/L; H2O2 dosing rate = 1.4 or 2.1 mL/min.

20

JOURNAL PRE-PROOF Figures

450

Figure 1

E-

PR

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449

PR

451

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JOURNAL PRE-PROOF Figure 2

454

JO

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453

22

JOURNAL PRE-PROOF Figure 3

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457

460 461

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463 464 465 466

23

JOURNAL PRE-PROOF Figure 4

45 40

0.8

35 23.6 15.8

0.2

7.9

O O

0.4

25

PR

0.6

F

30

0.0 20

40

60

PR

0

E-

[OTC]Outlet/[OTC]Inlet

1.0

[H2O2]Outlet (mg/L)

467

80

20 15 10 5 0

100

AL

t/

468

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469

24

JOURNAL PRE-PROOF Figure 5

30 20 10 0

10

20 40 60 QInlet,OTC (L/h)

80

O

30

F

80

(b)

40

O

(a)

PR

20 10 0 20

40

PR

10

E-

1-[OTC]Outlet/[OTC]Inlet (%)

100

[H2O2]Residual (mg/L)

470

60

80

AL

QInlet,OTC (L/h)

471

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JOURNAL PRE-PROOF Figure 6 Qinlet,OTC = 40 L/h

F

30

1-[OTC]Outlet/[OTC]Inlet (%)

90

40 30

O

20

O

20 10

PR

0

(b.2)

(a.2)

20

10 5 7.9

15.8

22.5

23.6

[H2O2]ARZ (mg/L)

30 25 20

7.9

15 10 5 15.8

23.6

31.50

39.4

0

[H2O2]ARZ (mg/L)

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31.5

0

35

PR

15

10

40

E-

25

0

475

100

(b.1)

90

30

[H2O2]Residual (mg/L)

(a.1)

AL

1-[OTC]Outlet/[OTC]Inlet (%)

100

Qinlet,OTC = 80 L/h

[H2O2]Residual (mg/L)

473

26

JOURNAL PRE-PROOF 476

Figure 7

100

50

20 15 10

F

90

(b)

25

5 0

O

[H2O2]Residual (mg/L)

15.8

40

23.6

O

[H2O2]ARZ (mg/L)

PR

30 20 10 0

PR

15.8

E-

1-[OTC]Outlet/[OTC]Inlet (%)

(a)

23.6

[H2O2]ARZ (mg/L)

AL

477

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JOURNAL PRE-PROOF 479

Tables

480 481

Table 1. Main physicochemical characteristics of the real wastewater sample collected after the secondary settling tank of an urban WWTP. Parameters (units) Pale yellow

Odor

n.d.a

Turbidity (NTU)

7.1

pH

8.1

Temperature (°C)

24

O

O 285

PR

Alkalinity (mg CaCO3/L)*

F

Color

23.4

Chemical oxygen demand (mg/L)

117

Transmittance at 254 nm (%)

54

E-

Dissolved organic carbon (mg/L)

2.7

Volatile suspended solids (mg/L)

0.68

PR

Total suspended solids (mg/L)

1.1

Nitrite – N-NO2- (mg/L)

0.2

Nitrate – N-NO3- (mg/L)

< 0.1

Chloride – Cl- (mg/L)

167

Sulfate – SO42- (mg/L)

78

Phosphate – PO43- (mg/L)

12.6

Total Phosphorous – P (mg/L)

4.1

U

*Alkalinity value considering that for the pH of the wastewater, the inorganic carbon is mainly in the form of bicarbonate; n.d. – not detected.

JO

482 483 484

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Ammonium – N-NH4+ (mg/L)

28

JOURNAL PRE-PROOF Table 2. Characteristics of the tube-in-tube reactor. Components

Characteristics Ø External Ø Internal Total length Illuminated length

3.2 cm 2.8 cm 20 cm 17.4 cm

Ultrafiltration membrane γ–Al2O3 (Cut-off: 20 kDa)

Ø External Ø Internal Total length Illuminated length Pore size Porosity

2.03 cm 1.55 cm 20 cm 17.4 cm 10 nm 30 - 55 %

ARZ volume

Total Illuminated

ENominal power Useful power Number of lamps

58.4 cm3 50.8 cm3 6W 1.4 W 4

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R N

AL

PR

UVC lamp (Puritec HNS 6 W G5, λmax = 254 nm)

PR

O

O

F

Quartz tube

29

JOURNAL PRE-PROOF

[H2O2]ARZ (mg/L)

0.35

15.8

0.50

22.5

0.70

31.5

Synthetic OTC solution

15

7.5

UW fortified with OTC

26

31±2

10±2

1

40

28±1

16±2

2

48

33±2

21.8±0.3

3

18±3

41±1

4

27±4

25±2

5

29

27±3

10±3

6

24

22±3

6.8±0.5

7

52

8±1

2.4±0.7

8

74

11±3

10±0.5

9

49

24±4

18.9±0.5

10

58

27±1

27±2

11

59

33±1

36.7±0.5

12

25

16±3

5.6±0.7

13

22

36±2

14.3±0.7

14

36

32±2

22.8±0.3

15

121

6.5±0.5

12±1

16

97

12±1

21±2

17

30

39±2

16±3

18

4.6

2056

10

18.3

514

171

31.5

20

9.1

1028

59

15.8

40

4.6

2056

10.5

60

3.0

3084

7.9

80

2.3

4112

15.8

2.1

23.6

2.8

31.5

3.5

39.4

0.70

7.9

1.4

15.8

2.1

23.6

2.1

Experiment number

63.0

1.4

1.4

7.5

[H2O2]Residual (mg/L)

80

2.3

40

4.6

15.8 23.6

40

4.6

O

0.70

Efficiency (%)

O

15

40

mgH2O2/mgOTC

4112

E-

30

QInlet,OTC τ (s) Re (L/h) Radial Permeation

F

H2O2 dosing rate (mL/min)

PR

[H2O2]stock solution (g/L)

PR

Table 3. Experimental conditions used in all UVC/H2O2 tests.

2056

2056

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Direct Injection

1.4

R N

7.5

U

Synthetic OTC solution

15.8

40

4.6

2056

30

E-

PR

O

O

F

JOURNAL PRE-PROOF

Highlights

PR

- Tube-in-tube membrane microreactor for photochemical UVC/H2O2 oxidation systems; - Radial addition of H2O2 through the porous membrane into the annular reaction zone;

AL

- “Virtually” unlimited number of H2O2 dosing points across the membrane length; - Helical motion of water around the membrane shell-side enhances H2O2 radial mixing;

U

R N

- More homogenous axial and radial distribution of H2O2 in the annular reaction zone.

31

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32