SYSTEM AND METHOD TO CONTROL H2O2 LEVEL IN ADVANCED OXIDATION PROCESSES

Abstract

The present invention relates to a bio-electrochemical system (BES) and a method of in-situ production and removal of H.sub.2O.sub.2 using such a bio-electrochemical system (BES). Further, the invention relates to a method for in-situ control of H .sub.2O.sub.2 content in an aqueous system of advanced oxidation processes (AOPs) involving in-situ generation of hydroxyl radical (OH) by using such a bio-electrochemical system (BES) and to a method for treatment of wastewater and water disinfection. The bio-electrochemical system (BES) according to the invention comprises:—an aqueous cathode compartment comprising a first cathode and a second cathode,—an aqueous anode compartment comprising an anode at least partly covered in biofilm, wherein the first cathode is connected to a first circuit and the second cathode is connected to a second circuit, wherein the first and the second circuit are connected to the system by an external switch.

Claims

1. A bio-electrochemical system (BES) comprising an aqueous cathode compartment comprising a first cathode and a second cathode, an aqueous anode compartment comprising an anode, which is at least partly covered in a biofilm, wherein the first cathode is connected to a first circuit and the second cathode is connected to a second circuit, and wherein the first and the second circuits are connected to the system by an external switch.

2-12. (canceled)

13. The bio-electrochemical system (BES) of claim 1; wherein the cathode compartment and the anode compartment are separated by a bipolar membrane.

14. The bio-electrochemical system (BES) of claim 1, wherein the first circuit comprises a microbial electrolysis cell (MEC) mode, and the second circuit comprises a microbial fuel cell (MFC) mode.

15. The bio-electrochemical system (BES) according to claim 1, wherein the first cathode comprises a graphite plate cathode and the second cathode comprises a Pt catalyst-coated cathode or a cathode coated with another catalyst.

16. The bio-electrochemical system (BES) according to claim 1, wherein the anode comprises carbon fibre, a carbon electrode material, or stainless steel.

17. The bio-electrochemical system (BES) according to claim 1, wherein the first circuit comprises a microbial fuel cell (MFC) comprising an anode.

18. The bio-electrochemical system (BES) according to claim 1, wherein the second circuit comprises an external resistor.

19. A method of in-situ production and removal of H.sub.2O.sub.2, comprising: providing a bio-electrochemical system (BES) comprising an aqueous cathode compartment comprising a first cathode and a second cathode, and an aqueous anode compartment comprising an anode, which is at least partly covered in biofilm; wherein the first cathode is connected to a first circuit and the second cathode is connected to a second circuit, and wherein the two circuits are connected by an external switch; applying voltage from a microbial fuel cell (MFC) to the first cathode, which induces H.sub.2O.sub.2 production; and producing electricity over the external resistor with the second cathode, which induces H.sub.2O.sub.2 removal.

20. The method according to claim 19, wherein the first circuit comprises the microbial fuel cell (MFC).

21. The method according to claim 19, wherein the second circuit comprises a resistor.

22. A method for treating a liquid or wastewater comprising: contacting a liquid or wastewater with a bio-electrochemical system (BES) comprising an aqueous cathode compartment comprising a first cathode and a second cathode, and an aqueous anode compartment comprising an anode, which is at least partly covered in biofilm; wherein the first cathode is connected to a first circuit and the second cathode is connected to a second circuit and, wherein the two circuits are connected by an external switch, applying voltage from a microbial fuel cell (MFC) to the first cathode, which induces H.sub.2O.sub.2 production; and producing electricity over the external resistor with the second cathode, which induces H.sub.2O.sub.2 removal from said liquid or waste water.

23. The method of claim 22, wherein said method is employed in an Advanced Oxidation Process.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] FIG. 1 shows a circuit for H.sub.2O.sub.2 production comprising a microbial electrolysis cell (MEC)

[0042] FIG. 2 shows a circuit for H.sub.2O.sub.2 removal comprising a microbial fuel cell (MFC)

[0043] FIG. 3 shows a bio-electrochemical system (BES) including a circuit for H.sub.2O.sub.2 production and a circuit for H.sub.2O.sub.2 removal.

[0044] FIG. 4 shows the gradual decolourization kinetics of the methylene blue (MB) contaminated wastewater in the MEC circuit (or called MFC-MEC mode). Control 1:

[0045] Open circuit. Control 2: No aeration at cathode. Control 3: No Fe.sup.2+addition at the cathode. Control 4: replace of MFC power supply with 5 Ω resistor without change of cathode in the MEC circuit. Operation conditions: external resistance of 5 Ω (ohm); initial MB concentration of 50 mg/L; Fe.sup.2+concentration of 2 mmol/L; pH of 3.0.

[0046] FIG. 5 shows the gradual mineralization kinetics of the methylene blue (MB) contaminated wastewater in the MEC circuit (or called MFC-MEC mode). Control 1: Open circuit. Control 2: No aeration at cathode. Control 3: no Fe.sup.2+addition at the cathode. Control 4: replace of MFC power supply with 5 Ω resistor without change of cathode in the MEC circuit. Operation conditions: external resistance of 5 Ω (ohm); initial MB concentration of 50 mg/L; Fe.sup.2+concentration of 2 mmol/L; pH of 3.0.

[0047] FIG. 6 shows the current density generation in the MEC circuit (or called MFC-MEC mode) and MFC circuit (or named MFC-removal mode). Control 4: replace of MFC power supply with 5 Ω resistor without change of cathode in the MEC circuit. Operation conditions: external resistance of 5 Ω (ohm); initial MB concentration of 50 mg/L; Fe.sup.2+concentration of 2 mmol/L; pH of 3.0.

[0048] FIG. 7 shows the change of H.sub.2O.sub.2 concentration in the MEC circuit (or called MFC-MEC mode) and MFC circuit (or named MFC-removal mode). Control 1: Open circuit. Control 2: No aeration at cathode. Control 4: replace of MFC power supply with 5 Ω resistor without change of cathode in the MEC circuit. Control 5: No Fe.sup.2+and MB addition. Operation conditions: external resistance of 5 Ω (ohm); initial MB concentration of 50 mg/L; Fe.sup.2+concentration of 2 mmol/L; pH of 3.0.

DETAILED DESCRIPTION OF THE INVENTION

[0049] The system performance in terms of pollutant treatment, H.sub.2O.sub.2 generation and residual H.sub.2O.sub.2 removal has been investigated.

[0050] The Bioelectro-Fenton system according to the invention is capable of both H.sub.2O.sub.2 generation and residual H.sub.2O.sub.2 removal and the new system offers a method for treating water containing recalcitrant organic pollutants in a sustainable way and therefore makes it possible to reuse wastewater.

[0051] FIG. 1 shows a first circuit system comprising two chambers, an anode chamber 1 and a cathode chamber 2 the chambers are separated by a bipolar membrane (BPM). Microorganisms having bioelectro-chemical activity such as bacteria are present in the anode chamber, and organic material is added to the anode chamber in order to provide feed material for the microorganisms which then decompose the organic material to H.sup.+, electrons and CO.sub.2. Electrons are transferred to the cathode compartment through an external electric circuit. The bipolar membrane provides water dissociation and H+ ions travel to the cathode whereas OH— ions travel to the anode.

[0052] When organic material and air is added to the anode chamber, then an advanced oxidation process (AOP) will take place in the cathode chamber:

O.sub.2+2e.sup.−+2H.sup.+.fwdarw.H.sub.2O.sub.2   (1)

[0053] The system of FIG. 1 comprises a third chamber 3 which in the shown embodiment is a further anode chamber, which is a typical single chamber MFC. This further anode chamber provides energy to the advanced oxidation process taking place in the cathode chamber and can e.g. be replaced with another energy source, preferably a source of renewable energy such as e.g. solar energy or wind energy (electricity). The third chamber 3 is connected to the first chamber 1 via a proton exchange membrane and a carbon electrode in form of a membrane electrode assembly (MEA) which server as the membrane and cathode of the third chamber 3.

[0054] FIG. 2 shows a second circuit system comprising two chambers, an anode chamber 1 and a cathode chamber 2, the chambers are separated by a bipolar membrane (BMP). The anode is connected to the cathode through an external resistor.

[0055] In this second circuit the following process takes place:

H.sub.2O.sub.2+2e.sup.−+2H.sup.+.fwdarw.H.sub.2O

[0056] The cathode acts as electron acceptor for electrons produced by the reaction in the anode chamber.

[0057] FIG. 3 shows a combined system according to the invention where both the first and the second circuits exist and where the first and the second circuits are joined so that the two circuits can be activated alternately i.e. first the first circuit is activated and the second circuit is disrupted, then the first circuit is disrupted and the second circuit activated. The combined system only comprises a single cathode chamber normally provided with two cathodes of different material.

Reactor Setup and Operation

[0058] The following experiments were carried out in a Bioelectro-Fenton system as shown in FIG. 3. This system comprises a H-type two-chamber BES consisted of two chambers 1 and 2 separated by a bipolar membrane (BMP) (diameter 15 mm, FuMA-Tech GmbH, Germany), which was constructed as described in: Y. Zhang, B. Min, L. Huang and I. Angelidaki, Appl Environ Microbiol, 2009, 75, 3389-3395.

[0059] The total volume and the working volume of each chamber of the two-chamber BES were 300 and 250 mL, respectively. The anode of chamber 1 was made of a carbon fiber brush (5.9 cm diameter, 6.9 cm length, Mill-Rose, USA), which was pretreated at 450° C. for 30 min and then pre-cultivated with mature biofilm in an MFC reactor before transferring to the BES reactor.

[0060] A graphite plate (projected surface area of 50 cm.sup.2) and a piece of carbon paper with a 0.5 mg-Pt cm.sup.−2 catalyst layer (projected surface area of 50 cm.sup.2) were both used as cathode of chamber 3. The distance between the anode and cathode electrodes was approximately 5 cm. A single-chamber air cathode MFC was constructed in chamber 3 based on the anode chamber of the H-type two-chamber BES. The anode electrode of chamber 3 was the same as that used in the two-chamber BES i.e. chamber 1. The Pt coated carbon paper working as cathode was hot pressed together with a proton exchange membrane as a membrane electrode assembly (MEA, 15 mm diameter). Electrical connections and pretreatment of electrodes were done as previously described in Y. Zhang and I. Angelidaki, Water Research, 2013, 47, 1827-1836 which is hereby incorporated by reference.

[0061] The two-chamber BES was operated alternately in two different modes i.e. MEC mode and MFC mode, by switching the external circuits. The two-chamber BES is in MEC mode when a switch 5 is connected and a switch 4 is disconnected whereas the two-chamber BES is in MFC mode when the switch 5 is disconnected and the switch 4 is connected.

[0062] In the MEC mode, the anode and the graphite plate cathode of the two-chamber BES is connected to the cathode and anode of the single-chamber MFC which served as power source to the former. The Pt-coated cathode was disconnected from the circuit. The anode chambers i.e. chamber 1 and 3 of both reactors was continuously fed with acetate modified domestic wastewater (1 g-COD/L, pH 7.8, conductivity 2.5 mS/cm) at a hydraulic retention time (HRT) of 8 h. The feeding was designed to avoid substrate limitation on anode performance. Methylene blue (MB), which is a common dye widely used for dyeing and printing, was used as model pollutant for this study. The cathode chamber 2 of the two-chamber BES was batch fed with synthetic wastewater containing 50 mg/L MB and 0.1 M Na.sub.2SO.sub.4, and the cathode pH was adjusted to 1.5, 3, 4, 5 or 7 using 0.5 M H.sub.2SO.sub.4 and 0.5 M NaOH.

[0063] Fe.sup.2+was added to the cathode chamber 2 at an initial concentration of 2 mmol/L.

[0064] The whole system was operated at an external resistance of 5 Ω, unless stated otherwise.

[0065] The cathode solution was continuously purged with air.

[0066] In the MFC mode, the anode and the Pt-coated cathode of the two-chamber BES was connected to the external resistor (5 Ω)), while the single-chamber MFC and the graphite cathode were disconnected from the external circuit.

[0067] Meanwhile, the aeration was stopped in the cathode chamber of the two-chamber BES. In general, the whole system was first operated in MEC mode to produce H.sub.2O.sub.2 by the Fenton-process, and then switched to MFC mode for removal of residual H.sub.2O.sub.2.

[0068] Control reactors were also setup and operated under the conditions specialized in following sections.

[0069] All experiments were carried out in duplicate at room temperature (25±5° C.).

Chemical, Electrochemical Analysis and Calculations

[0070] The concentration of MB was determined by UV-vis spectrophotometry (Spectronic 20D-F, Thermo Scientific) at 665 nm. H.sub.2O.sub.2 concentration was determined using the ceric sulfate titration method. Chemical oxygen demand (COD) was measured according to Standard Method. Total organic carbon (TOC) analysis was carried out with TOC Shimadzu TOC 5000 A. pH was measured with a PHM 210 pH meter (Radiometer).

[0071] The voltage (V) across on the external resistor was monitored with 30 min intervals using a digital multimeter (Model 2700, Keithley Instruments, Inc., Cleveland, Ohio, USA). Current (I), power (P=IV) and Coulombic efficiency (CE) were calculated as previously described. Current or power density was calculated based both on the projected surface area of cathode.

[0072] In describing the embodiments of the invention specific terminology will be resorted to for the sake of clarity. However, the invention is not intended to be limited to the specific terms so selected, and it is understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose.

[0073] When describing the embodiments of the present invention, the combinations and permutations of all possible embodiments have not been explicitly described. Nevertheless, the mere fact that certain measures are recited in mutually different dependent claims or described in different embodiments does not indicate that a combination of these measures cannot be used to advantage. The present invention envisages all possible combinations and permutations of the described embodiments.

EXAMPLES

[0074] The FIGS. 4-7 illustrate the performance of the above exemplified system.

[0075] FIG. 4 shows the gradual decolourization (C.sub.T/C.sub.0—MB concentration at time T/MB concentration at time 0) kinetics of the methylene blue (MB) contaminated wastewater in the MEC circuit (called MFC-MEC mode). The system is set up to only operate in H.sub.2O.sub.2 production mode, i.e. switch 5 is connected during all 16 hours of the experiment.

[0076] The operation conditions during these experiments are as follows: external resistance of 5 Ω; initial MB concentration of 50 mg/L; Fe.sup.2+concentration in cathode chamber: 2 mmol/L; pH in cathode chamber of 3.0.

[0077] In order to evaluate different parameters influence on the process 4 control experiments are conducted:

[0078] Control 1: Open circuit, this means that the anode and cathode were disconnected from both circuits (Switch 4 and 5 were not closed).

[0079] Control 2: No aeration at cathode i.e. the cathode chamber is closed, so no air or aeration is supplied to the cathode.

[0080] Control 3: No Fe.sup.2+addition at the cathode i.e. the system does not operate with a Fenton process.

[0081] Control 4: replace of MFC power supply with 5 Ω resistor without change of cathode in the MEC circuit.

[0082] The result indicates that the invented system can successfully in-situ generate H.sub.2O.sub.2 for an AOP such as Fenton process oxidizing the organic matters in the wastewaters.

[0083] FIG. 5 shows the gradual mineralization kinetics of the methylene blue (MB) contaminated wastewater in the MEC circuit (or called MFC-MEC mode). Control 1: Open circuit. Control 2: No aeration at cathode. Control 3: no Fe.sup.2+addition at the cathode. Control 4: replace of MFC power supply with 5 Ω resistor without change of cathode in the MEC circuit. Operation conditions: external resistance of 5 Ω; initial MB concentration of 50 mg/L; Fe.sup.2+concentration of 2 mmol/L; pH of 3.0.

[0084] FIG. 6 shows the current density generation in the MEC circuit (or called MFC-MEC mode) and MFC circuit (or named MFC-removal mode). Control 4: replace of MFC power supply with 5 Ω resistor without change of cathode in the MEC circuit. Operation conditions: external resistance of 5 Ω; initial MB concentration of 50 mg/L; Fe.sup.2+concentration of 2 mmol/L; pH of 3.0.

[0085] FIG. 7 shows the change of H.sub.2O.sub.2 concentration in the MEC circuit (called MFC-MEC mode) and MFC circuit (called MFC-removal mode). Control 1: Open circuit.

[0086] Control 2: No aeration at cathode. Control 4: replace of MFC power supply with 5 Ω resistor without change of cathode in the MEC circuit. Control 5: No Fe.sup.2+and MB addition. Operation conditions: external resistance of 5 C); initial MB concentration of 50 mg/L; Fe.sup.2+concentration of 2 mmol/L; pH of 3.0.