WO2004024633A2

WO2004024633A2 - Dipping sensor for real-time bod monitoring of water

Info

Publication number: WO2004024633A2
Application number: PCT/KR2003/001872
Authority: WO
Inventors: Sung Hyun Nam; Hyung Joo Kim; Mi A Kim; Seol Hee Han; Ji Gu Jang; Sung Hye Shin; Su Mi Youn; Moon Sik Hyun
Original assignee: Korea Biosystems Corp.
Priority date: 2002-09-11
Filing date: 2003-09-09
Publication date: 2004-03-25
Also published as: AU2003261002A1; KR20040023170A; AU2003261002A8; WO2004024633A3; KR100483584B1

Abstract

Disclosed herein is a dipping sensor for real-time BOD monitoring of water which comprises: a biofuel cell 10 consisting of an anode 10a where organic substances are oxidized by enriched electrochemically active microorganisms, and a cathode 10b to which electrons generated from the anode 10a are transferred; a pretreatment unit 11 for preventing suspended substances; a rain and dust guard 14 to prevent rain and dust from being introduced into the biofuel cell 10; a buoy 15 provided in the biofuel cell 10 to float the biofuel cell 10 in water; a sensor direction-adjusting wing 18 to adjust the installation direction of the biofuel cell 10; a data collection-transmission unit 19 to transmit and receive data detected by the biofuel cell 10, and transmit the data to a data receiving unit 44; and a sinker 16 to fix the location of the biofuel cell 10 floating in the water.

Description

DIPPING SENSOR FOR REAL-TIME BOD MONITORING OF WATER

Technical Field

The present invention relates to a dipping sensor for real-time BOD monitoring of water which can measure in real time biochemical oxygen demand (hereinafter, referred to as "BOD") of water.

Background Art

Generally, there are 26 items for monitoring the water quality of rivers, such as biochemical oxygen demand (BOD), suspended solids (SS) and total phosphorus, etc. These items are selected depending on the necessity for the examination of the environmental water quality standards - and the water quality state of rivers (Monitoring of water pollutants in water treatment system and study on its application, 1999, Korea Institute of Science and Technology (KIST)). BOD is an important index of the level of water contamination, and is expressed as the amount of dissolved oxygen required for the biochemical oxidation of organic compounds for 5 days (Standard Methods for the examination of water and wastewaters, 1995, 19th Edition). However, the BOD measurement requires great experience and skill of operators, and has an uncertainty of 15~20% (Wilfrid et al, 2001, On-line monitoring of wastewater quality: a review, J. Chem. Technol. Biotechnol, 76 : 337-

348). Further, since the BOD measurement is performed over a five-day period, it is limited in prompt management of the BOD changes in water.

BOD sensors developed hitherto are generally in the form in which a dissolved oxygen-measuring electrode is coupled with a porous membrane onto which certain microorganisms are immobilized to measure the oxygen consumption rate in a sample. However, since these BOD sensors have a porous membrane onto which certain microorganisms are immobilized, they have disadvantages that the porous membrane must be changed frequently and additional elements, such as a separate converter, are needed (Monitoring techniques of water pollutants and study on its phenomena, 1998, Korea Institute of Science and Technology (KIST), 88-89).

In recent years, mediator-less biofuel cells have been developed. The biofuel cells can enrich microorganisms having electrochemical activities by using active sludge as an inoculum. The electric current generated from biofuel cells is directly proportional to the concentration of the supplied organic substances (see Byung-Hong Kim et al., 1999, microbial fuel cell without a mediator, The Microorganism and Industry, 25(2), 7-10). Based on this relationship, the present applicant developed devices for measuring BOD (Model: HABS-2000 and HABS- 2001) and sold them.

An apparatus for automatically monitoring water quality was first installed in the Noryaηjin and Tuck-island catchment areas, Seoul, Korea, 1974. Since then, the automatic monitoring apparatus has installed in main water source conservation areas and intake facilities in Korea, and used to continuously measure 5 items including pH, dissolved oxygen, temperature, turbidity and conductivity of water, and chemical oxygen demand (COD), concentrations of Cd, Pb, Cu, etc., and if needed, harmful substances (Study for monitoring and application of water pollutants in water treatment system, 1999, Korea Institute of Science and Technology (KIST)).

Since the Nakdong-river water pollution accident happened in Korea, in January 1994, the Ministry of Environment has continuously and automatically measured and monitored the water quality state of main water source protection areas and areas susceptible to environmental pollution accidents all over the country. Currently, the Ministry of Environment is promoting a project for installing an automated water quality measuring system to promptly cope with future water pollution accidents. The automated water quality measuring system is an intensive technique including design installation, operation management, maintenance, and quality control, operation of tele-metering system (TMS), etc. The Korea Institute of Environmental Research installed 20 automated water quality measuring systems from 1995 to 2000. Since 2000, the Korea Environmental Management Corporation has been installed the automated water quality measuring systems as a civil agency business. By 2005, 36 automated water quality measuring systems will be further installed to prepare against future water pollution accidents (see, related reference materials shown in the homepage of the Korea Ministry of Environment).

Accordingly, demand for sensors capable of measuring BOD in real time, a representative item for monitoring water quality, will be increased in the near future.

A recent study reports that when the BOD of an artificial wastewater was measured in real time in the continuous mode using a biofuel cell, there was a correlation between the measured BOD concentrations and electric current values

(LS. Chang et al., 2001, Continuous determination of BOD in wastewater using microbial fuel cell type of novel biosensor, Proceedings of the International Sensor Conference, 125-126, Seoul, Korea).

Disclosure of the Invention

Based on the results from the studies discussed above and social demands, it is an object of the present invention to provide a dipping sensor for real-time BOD monitoring of water which can monitor the BOD concentration of water in real time by modifying conventional biofuel cells.

According to the present invention, the above object can be accomplished by a dipping sensor for real-time BOD monitoring of water which comprises: a biofuel cell consisting of an anode where organic substances are oxidized by enriched electrochemically active microorganisms, and a cathode to which electrons generated from the anode are transferred; a pretreatment unit for preventing suspended substances from being introduced into the anode of the biofuel cell; a rain and dust guard arranged at the upper portion of the biofuel cell to prevent rain and dust from being introduced into the biofuel cell; a buoy provided in the biofuel cell to float the biofuel cell in water; a sensor direction-adjusting wing connected to the rear portion of the biofuel cell to adjust the installation direction of the biofuel cell; a data collection transmission unit provided on the biofuel cell to transmit and receive data detected by the biofuel cell and transmit the data to a data receiving unit located at a long distance from the biofuel cell; and a sinker connected to the biofuel cell to fix the location of the biofuel cell floating in the water.

The anode is arranged along the direction of water flow so that organic substances contained in the sample and electrochemically active microorganisms are directly reacted with each other.

The cathode and the anode are divided by an ion exchange membrane. For better efficiency, a membrane-electrode assembly(MEA) is used.

The cathode is exposed to the atmosphere to enable atmospheric oxygen to function as an oxidizing agent. The cathode includes a supporter for supporting a catalyst and a catalyst layer.

Platinum (Pt) in the cathode serves as the catalyst for the reduction of oxygen, and the supporter at which the reduction takes place is made of a porous carbon body.

The pretreatment unit is a cylindrical form in which a plurality of plates formed at the upper and lower portions cross each other at an angle of 45° in a direction opposite to the water flow. In addition, a plurality of holes are formed in the positions adjacent to the plurality of plates.

The data collection transmission unit includes a voltameter for measuring a voltage of the electric current generated in the biofuel cell, a signal converter for converting the measured voltage to a signal for wireless transmission, and a transmitter for transmitting the converted signal. The data receiving unit includes a receiver for receiving the data transmitted from the data collection transmission unit, a signal converter for converting the received signal to a voltage value in a particular mode, and a data interpreter for interpreting the converted voltage value and outputting a BOD value.

Brief Description the Drawings

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a view schematically showing a dipping sensor of the present invention;

Fig. 2 is an assembly diagram schematically showing a cathode and an anode of a dipping sensor of the present invention;

Fig. 3 a is a three-dimensional view showing a pretreatment unit of a dipping sensor of the present invention;

Fig. 3b is a side cross-sectional view of the pretreatment unit shown in Fig. 3 a; Fig. 4 is a view schematically showing a data transmission and receiving system;

Fig. 5 is a graph showing changes in electric current values at various artificial wastewater concentrations;

Fig. 6 is a graph showing the relationship between the concentrations of an artificial wastewater and average electric current values;

Fig. 7 is a graph showing the relationship between the concentrations of an artificial wastewater and maximum electric current values;

Fig. 8a is a graph representing Coulomb generated at various artificial wastewater concentrations as the respective areas; Fig. 8b is a graph showing the relationship between the concentrations of an artificial wastewater and the amount of Coulomb generated; and

Fig. 9 is a graph showing changes in electric current values when a dipping sensor of the present invention is applied to a sample collected from Paldang lake,

Korea.

Best Mode for Carrying Out the Invention

Hereinafter, preferred examples of the present invention will be explained in more detail with reference to the accompanying drawings. As shown in Fig. 1, in accordance with a dipping sensor for real-time BOD monitoring of water of the present invention, a sample is introduced into an anode 10a of a biofuel cell 10 (dipping sensor) through a pretreatment unit 11, generates an electric current, and is then discharged from the biofuel cell 10 through a sample- discharging port 12 connected to the anode. The upper portion of a cathode 10b of the biofuel cell 10 is opened and thus the cathode 10b is exposed to atmosphere.

This exposure enables atmospheric oxygen to function as an oxidizing agent, which eliminates the need for the introduction of an additional oxidizing agent. A rain ^• dust guard 14 is disposed at the upper portion of the cathode 10b of the biofuel cell 10 to prevent rain and dust from being introduced into the cathode 10b. The biofuel cell 10 is floated in water by a buoy 15 provided on the cathode 10b, on which a data collection ^• transmission unit 19 for collecting and transmitting data is provided.

The biofuel cell 10 is composed of the anode 10a where organic substances contained in the sample are directly reacted with electrochemically active microorganisms, and the cathode 10b. The anode 10a is arranged along the direction of water flow so that the sample can be easily introduced. A membrane- electrode assembly is applied to the anode 10a and the cathode 10b of the biofuel cell 10. As the cathode 10b, a platinum catalyzed electrode is used (see Korean Patent Appln. No. 2001-75259 filed by the present applicant, "Biochemical fuel cells with installed membrane-electrode assembly"). At the anode 10a of the biofuel cell 10, enriched electrochemically active microorganisms oxidize organic substances contained in the sample to generate electrons. The generated electrons are transferred to the cathode 10b to generate an electric current, thereby allowing the biofuel cell 10 to function as a sensor. The cathode 10b of the biofuel cell 10 is exposed to atmosphere to enable atmospheric oxygen to function as an oxidizing agent. The cathode includes a supporter for supporting a catalyst and a catalyst layer. Platinum (Pt) in the cathode serves as the catalyst for the reduction of oxygen, and the supporter at which the reduction takes place is made of a porous carbon body, such as carbon paper or cloth. The use of this carbon body permits electrical continuity of Pt/C, smooth transfer of oxygen to pores filled with thin H₂O membranes, smooth transfer of H- ions to the Pt catalyst, etc., and proceeds well the electrochemical reaction in the electrodes, thereby improving the performance of the sensor.

The biofuel cell 10 used in the dipping sensor for real-time BOD monitoring of the present invention is shown in Fig. 2.

As shown in Fig. 2, the anode 10a includes an acrylic cylindrical body 20 in which a sample-input port 21 is formed, and an electrode 22 disposed inside the cylindrical body 20. As shown in Fig. 1, the pretreatment unit 11 is connected to the sample-input port 21 of the anode 10a of the biofuel cell 10 to filter suspended substances present in the sample. The pretreatment unit 11 can prevent the clogging of the anode 10a due to the suspended substances present in the sample. The sample introduced into the anode 10a through the pretreatment unit 11 directly contacts and reacts with the electrode 22 to oxidize organic substances contained in the sample due to the electrochemically active microorganisms enriched in the electrode 22. After reacting with the electrode 22, the sample is discharged from the biofuel cell 10 through the discharging port 12.

As shown in Fig. 2, the cathode 10b made of an acrylic plate includes an acrylic cylindrical body 24a and an upper open tube 24b disposed on the upper center of the cylindrical body 24a. Atmospheric oxygen can be introduced into an electrode 25 (electrode at the cathodic portion of the MEA (platinum-catalyzed carbon cloth)) through the upper open tube 24b. An acrylic or plastic screw 28 tightens the membrane-electrode assembly 25 (MEA), one element constituting the biofuel cell 10, and a water leakage-preventing silicone rubber interposed between the anode 10a and cathode 10b. The use of the platinum-catalyzed electrode as the cathode 10b of the biofuel cell 10 used in the present invention causes the chemical reactions in the electrode to proceed well, and lowers the internal resistance of the sensor. The membrane-electrode assembly 25 is interposed between the anode 10a and the cathode 10b, as shown in Fig. 2. A pair of platinum wires 26 have a diameter of about 0.5mm, one of which is connected to the electrode 22 of the anode 10a, and the other of which is connected to the cathodic portion of the membrane- electrode assembly 25. The electrons generated from the oxidation of organic substances in the anode 10a are transferred to the cathode 10b through the platinum wires 26 to generate an electric current.

Meanwhile, the sample introduced into the biofuel cell 10 is fed into the anode 10a through the pretreatment unit 11 in the form of a cylindrical body, as shown in Figs. 3a and 3b. The pretreatment unit is in a cylindrical form in which a plurality of plates 31 formed at the upper and lower portions cross each other at an angle of 45° in a direction opposite to the water flow. In addition, a plurality of holes 32 are formed in the positions adjacent to the plurality of plates 31. Suspended substances in water introduced into the pretreatment unit 11 are filtered by the plates 31 which cross each other, and are then discharged through the holes 32. As described above, the sample (water) filtered by the pretreatment unit 11 is introduced into the anode 10a of the biofuel cell.

Fig. 4 schematically shows a transmission and receiving system of the dipping sensor according to the present invention. The data collection ^• transmission unit 19 shown in Fig. 4 is provided in the biofuel cell 10. The data collection ^• transmission unit 19 includes a voltameter 41 for measuring a voltage of the electric current generated in the biofuel cell 10, a signal converter 42 for converting the measured voltage to a signal for wireless transmission, and a transmitter 43 for transmitting the converted signal.

The biofuel cell 10 includes a resistor having a resistance of 500Ω connected between the cathode 10b and the anode 10a. The voltage between both electrodes is determined by the voltameter 41 (DDN-032). The voltage measured by the voltameter 41 is converted to a signal for wireless transmission by the signal converter 42 (RS-232S method, self-manufactured) and transmitted to a data receiving unit 44 located at a long distance from the biofuel cell 10 by the transmitter 43 (RATA ION).

The data receiving unit 44 includes a receiver 45 (RATA ION) for receiving the data transmitted from the data collection transmission unit 19, a signal converter 46 (RS-232S method) for converting the received signal to a voltage value, and a data interpreter 47 for interpreting the converted voltage value and outputting a BOD value.

The data transmitted from the data collection ^• transmission unit 19 through the transmitter 43 are received by the receiver 45 of the data receiving unit 44. The signal received by the receiver 45 is converted to a voltage value by the signal converter 46 in the same method (RS-232S) as the data collection ^• transmission unit 19, and then is represented as a BOD value to output the BOD value. By using such a tele-metering system (TMS), users can monitor the BOD concentration of water at various sites in real time in their offices.

In this Example, changes in electric current values generated when artificial wastewater adjusted at various concentrations was introduced into the dipping sensor of the present invention, were examined. Sludge for wastewater treatment collected from the Jung Nang sewage treatment plant, Seoul, Korea, was used as an inoculum to enrich electrochemically active microorganisms in the anode compartment of the sensor, and then the artificial wastewater was continuously introduced into the dipping sensor of the present invention.

A resistor included in the biofuel cell 10 had a resistance of 500Ω. The amount of voltage generated from the cell 10 was measured by a voltameter (DDN-

032), the measured voltage signals were converted using the RS-232S method, and the converted voltage values were received. At this time, the voltage values were measured at an interval of 120 seconds. The dipping sensor was installed in a water bath (size: 120 x 60 x 100(cm)) in which the BOD concentrations of the artificial wastewater were adjusted to 10, 20, 40 and 50ppm using glucose and glutamic acid. At this time, the electric current values generated from the dipping sensor were measured. The results are shown in Fig. 5. As an artificial wastewater at a different concentration was fed into the bath, the electric current values gradually increased and reached a maximum electric current value. The relationship between the average electric current values measured for about 17 hours and the BOD concentrations are shown in Fig. 6. As a result of regression, a linear relationship was exhibited. The regression coefficient (r²) was about 0.98, which implies a high proportion.

Fig. 7 shows the relationship between the concentrations of the artificial wastewater and obtained maximum electric current values. The BOD concentrations of the artificial wastewater were linearly proportional to the obtained maximum electric current values until the BOD concentration reached 40ppm or lower. At the BOD concentration of 40~50ppm or higher, the electric current values were about 1mA, which thereafter did not increase any further. The electric current values generated at the respective BOD concentrations of the artificial wastewater for a given time (about 17 hours) were accumulated (see Fig. 8a), and then expressed in Coulomb. As a result, the amount of electric current was about 34Coulomb at lOppm, about 42Coulomb at 20ppm, 50Coulomb at 40ppm and about 58Coulomb at 50ppm, respectively and a linear correlation between Coulomb and BOD was produced (see Fig. 8b).

In this Example, electric current values generated when the dipping sensor of the present invention was applied to sites, were measured. In the manner similar to in Example 1, sludge for wastewater treatment collected from the Jung Nang sewage treatment plant, Seoul, Korea, was used as an inoculum to enrich electrochemically active microorganisms in the artificial wastewater, and then the artificial wastewater was continuously introduced into the dipping sensor of the present invention. After enrichment was completed, the dipping sensor was installed at the upper stream of Paldang lake, Korea, a water source protection area, to examine changes in the generated electric current values. The results are shown in Fig. 9. The amount of voltage generated from the cell was measured by a voltameter (DDN- 032), the measured voltage signals were converted using the RS-232S method, and the converted voltage were received values. At this time, the voltage values were measured at an interval of 120 seconds. The measured BOD concentrations are summarized in Table 1 below. With a sample having a BOD₅ concentration of 3.8±0.5ppm, the average electric current and the amount of electric current (Coulomb) generated for 17 hours were 0.52mA and 31.04Coulomb, respectively. As a result of regression of the electric current values (Coulomb = 0.57 x BOD concentration + 29.06), the BOD value of Paldang sample was 3.47ppm. BOD value measured by a BOD measuring instrument (HABS-2000, Korea Biosystems, Korea) using the biofuel cell 10 was 3.5±0.1ppm, which was almost the same as the BOD concentration measured after the sample was fed. The difference from the BOD₅ concentration was about 0.3ppm, which is within the error range. This result indicates that the dipping sensor of the present invention is applicable to field.

[Table 1]

Industrial Applicability

According to the dipping sensor of the present invention, since the anode is opened and thus directly contacts a sample, the monitoring of BOD concentration in real time is facilitated, compared to conventional water quality monitoring systems which comprise collecting a sample and analyzing it to measure the BOD concentration.

In addition, the use of the membrane-electrode assembly and the platinum- catalyzed electrode makes the chemical reaction of the electrodes vigorous, thereby improving the sensitivity of the sensor. Furthermore, since the upper portion of the cathode of the biofuel cell is opened, atmospheric oxygen can function as an oxidizing agent. Accordingly, units for feeding water and air into the cathode for maintaining the potential difference of the sensor can be eliminated, which makes the structure of the sensor simple.

Moreover, the buoy and sinker can keep the dipping sensor balanced in the water, and the sensor direction-adjusting wing is arranged in a direction opposite to the water flow, thereby stably monitoring the BOD concentration of water without being effected by water flow. By combining the dipping sensor with a tele- metering system (TMS), users can monitor the BOD concentration of water at various sites in real time in their offices.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

Claims:

1. A dipping sensor for real-time BOD monitoring of water, comprising: a biofuel cell 10 consisting of an anode 10a where organic substances are oxidized by enriched electrochemically active microorganisms, and a cathode 10b to which electrons generated from the anode 10a are transferred; a rain and dust guard 14 arranged at the upper portion of the biofuel cell 10 to prevent rain and dust from being introduced into the biofuel cell 10; a buoy 15 provided in the biofuel cell 10 to float the biofuel cell 10 in water; a sensor direction-adjusting wing 18 connected to the rear portion of the biofuel cell 10 to adjust the installation direction of the biofuel cell 10; a data collection transmission unit 19 provided on the biofuel cell 10 to transmit and receive data detected by the biofuel cell 10, and transmit the data to a data receiving unit 44 located at a long distance from the biofuel cell 10; and a sinker 16 connected to the biofuel cell 10 to fix the location of the biofuel cell 10 floating in the water.

2. The dipping sensor for real-time BOD monitoring of water according to claim 1, further comprising a pretreatment unit 11 connected to the input port 21 of the anode 10a of the biofuel cell 10 to filter suspended substances present in the sample.

3. The dipping sensor for real-time BOD monitoring of water according to claim 1, wherein the anode 10a is arranged along the direction of water flow so that organic substances contained in the sample and electrochemically active microorganisms are directly reacted with each other.

4. The dipping sensor for real-time BOD monitoring of water according to claim 1, wherein a membrane-electrode assembly (MEA) is applied to the anode 10a and the cathode 10b to assemble a membrane and the electrodes.

5. The dipping sensor for real-time BOD monitoring of water according to claim 1, wherein the cathode 10b is exposed to atmosphere to enable atmospheric oxygen to function as an oxidizing agent, and includes a supporter for supporting a catalyst and a catalyst layer.

6. The dipping sensor for real-time BOD monitoring of water according to claim 5, wherein the catalyst is platinum (Pt) and catalyzes the reduction of oxygen, and the supporter at which the reduction takes place is made of a porous carbon body.

7. The dipping sensor for real-time BOD monitoring of water according to claim 2, wherein the pretreatment unit 11 is a cylindrical form in which a plurality of plates 31 formed at the upper and lower portions cross each other at an angle of 45° in a direction opposite to the water flow, and a plurality of holes 32 are formed in the positions adjacent to the plurality of plates 31.

8. The dipping sensor for real-time BOD monitoring of water according to claim 1, wherein the data collection ^• transmission unit 19 includes a voltameter 41 for measuring a voltage of the electric current generated in the biofuel cell 10, a signal converter 42 for converting the measured voltage to a signal for wireless transmission, and a transmitter 43 for transmitting the converted signal; and the data receiving unit 44 includes a receiver 45 for receiving the data transmitted from the data collection transmission unit 19, a signal converter 46 for converting the received signal to a voltage value, and a data interpreter 47 for inte reting the converted voltage value and outputting a BOD value.