EP2201356A1 - Analyse d'eau - Google Patents

Analyse d'eau

Info

Publication number
EP2201356A1
EP2201356A1 EP08800162A EP08800162A EP2201356A1 EP 2201356 A1 EP2201356 A1 EP 2201356A1 EP 08800162 A EP08800162 A EP 08800162A EP 08800162 A EP08800162 A EP 08800162A EP 2201356 A1 EP2201356 A1 EP 2201356A1
Authority
EP
European Patent Office
Prior art keywords
chloride
oxidation
cod
oxygen demand
organic
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP08800162A
Other languages
German (de)
English (en)
Other versions
EP2201356A4 (fr
Inventor
Roger Knight
Elizabeth Reisman
Matthew Mccrum
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Aqua Diagnostic Pty Ltd
Original Assignee
Aqua Diagnostic Pty Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from AU2007905660A external-priority patent/AU2007905660A0/en
Application filed by Aqua Diagnostic Pty Ltd filed Critical Aqua Diagnostic Pty Ltd
Publication of EP2201356A1 publication Critical patent/EP2201356A1/fr
Publication of EP2201356A4 publication Critical patent/EP2201356A4/fr
Pending legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/18—Water
    • G01N33/1806—Biological oxygen demand [BOD] or chemical oxygen demand [COD]
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
    • G01N27/28—Electrolytic cell components
    • G01N27/30—Electrodes, e.g. test electrodes; Half-cells
    • G01N27/305—Electrodes, e.g. test electrodes; Half-cells optically transparent or photoresponsive electrodes

Definitions

  • This invention relates to a method for the determination of oxygen demand of water using photoelectrochemical cells.
  • the invention relates to a photoelectrochemical method of determining chemical oxygen demand in water samples having high chloride content, such as sea water.
  • BOD 5 biochemical oxygen demand
  • COD chemical oxygen demand
  • BOD 5 involves the use of heterotrophic microorganisms to oxidise organic material and thus estimate oxygen demand.
  • COD uses strong chemical oxidising agents such as dichromate or permanganate to oxidise organic material.
  • the BOD 5 analysis is carried out over five days and oxygen demand is determined by titration or with an oxygen probe. COD is determined by the measurement of dichromate or permanganate depletion by titration or spectrophotometry.
  • seawater is typically used in cooling towers to cool the condenser and for a number of other applications.
  • the monitoring of seawater is required to avoid potential environmental concerns related to its usage and discharge.
  • the ability to measure COD in seawater is an enormous industry application that is yet to be catered for.
  • Titanium(IV) oxide has been extensively used for the photooxidation of organic compounds.
  • TiO 2 is non- photocorrosive, non-toxic, inexpensive, relatively easily synthesised in its highly active catalytic nanoparticulate form, and is highly efficient in photooxidative degradation of organic compounds.
  • a problem encountered in conducting assays using this method is dealing with interference from competing oxidisable chemical species other than organic carbon. Filtration of samples reduces interference from many species but the presence of chloride still remains a significant interference that must be dealt with.
  • Chloride is commonly oxidized by photocatalysis to chlorine according to the following equation:
  • the produced chlorine can be readily converted into hypochlorite under UV illumination (Equation 2) and production of other possible products including CIO 2 " , CIO 3 ' and CIO 4 ' may also occur.
  • Equation 2 UV illumination
  • CIO 3 ' and CIO 4 ' may also occur.
  • the photoxidation kinetics of Cl " has proven to be slow.
  • the method involves the use of expensive and toxic chemicals and requiring separation.
  • the system will need a sophisticated component to achieve in situ separation of precipitated AgCI or Hg 2 CI 2 , which, on one hand will significantly undermine the accuracy and reliability of the system, and on the other hand will increase both the capital and operational costs.
  • Chloride is a problem for organic content measurement in aqueous samples as current methods of analysis can't easily distinguish between organic and chloride content and hence it creates an erroneous measurement.
  • WO2007/016740 discloses an improvement in the photoelectrochemical method for detecting chemical oxygen, previously described in WO2004/088305, which deals with the interference by chloride.
  • PCT/AU2007/000735 discloses a similar method for dealing with difficult to oxidise organic compounds.
  • the analytical signal is generated in exactly the same way as for the photoelectrochemical method disclosed in WO2004/088305.
  • the present invention provides a method of determining chemical oxygen demand in water samples containing chloride ions by a photoelectrochemical method in which the photo electrode is activated by light pulses and the pulse parameters and the light source intensity are set to favour oxidation of the organic species in the water sample and to suppress any oxidation signal from the chloride ions present in the sample.
  • the speed of organic oxidation and sensitivity may be optimised, without triggering chloride oxidation and the ensuing photocatalytic cyclic chloride oxidation reaction.
  • the measurement of 1 mg/L organic content is achievable in seawater.
  • the effectiveness of the method of this invention means that potassium Chloride may be used as the supporting electrolyte without compromising the effectiveness of the measurements.
  • the photohole is a very powerful oxidizing agent (+3.1 V) that will readily lead to the seizure of an electron from a species adsorbed to the solid semiconductor.
  • both organic compounds and water can be oxidized by the photoholes or surface trapped photoholes but usually organic compounds are more favorably oxidized, which leads to the mineralization of a wide range of organic compounds.
  • N and X represents a nitrogen and a halogen atom respectively.
  • the numbers of carbon, hydrogen, oxygen, nitrogen and halogen atoms in the organic compound are represented by y, m, j, k and q.
  • n refers to the number of electrons transferred during the photoelectrocatalytic degradation, which equals 4y ⁇ 2j+m-3k-q
  • i the photocurrent from the oxidation of organic compounds.
  • F is the Faraday constant
  • V and C are the sample volume and the concentration of organic compound respectively.
  • the measured charge, Q is a direct measure of the total amount of electrons transferred that result from the complete degradation of all compounds in the sample. Since one oxygen molecule is equivalent to 4 electrons transferred, the measured Q value can be easily converted into an equivalent O 2 concentration (or oxygen demand).
  • the equivalent COD value can therefore be represented as:
  • COD (mg I L of O 2 ) -Q— x 32000 l J 4FV
  • This COD equation can be used to quantify the COD value of a sample since the charge, Q, can be obtained experimentally and for a given photoelectrochemical cell, the volume, V, is a known constant.
  • the net charge by pulsing is calculated according to the Equation 3, where the charge of the last pulse, nominated as Q b iank is subtracted from each pulse and from this the sum of all pulses results in Q net (see Figure 4).
  • the present invention provides a photoelectrochemical assay apparatus to determine oxygen demand of a water sample which consists of a) a flow through measuring cell b) a photoactive working electrode and a counter electrode disposed in said cell, c) a UV light source, adapted to illuminate the photoactive working electrode in pulses d) a control means to control the pulsed illumination of the working electrode, the applied potential and the signal measurement 2008/001529
  • control means sets the duration of the pulse, the gap between pulses and the light intensity.
  • pulse duration is from 0.01 to 5 seconds and the interval between pulses is at least 1 second.
  • a reference electrode is also located in the measuring cell and the working electrode is a nanoparticulate semiconductor electrode, preferably titanium dioxide.
  • the flow rate is adjusted to optimise the sensitivity of the measurements.
  • This cell design is based on that disclosed in application WO2004/088305 with a means to store the organic/electrolyte solution.
  • the sample collection device may include a filter to remove any large particulates, or precipitated substances, that may interfere with the operation of the cell.
  • the method of this invention may be combined with the organic addition method disclosed in WO2007/016740, the contents of which are incorporated herein by reference. The combination is useful when chloride content is high.
  • the limitation of the organic addition method is that some prior knowledge of the level of chloride or difficult to oxidise organics is required before the appropriate level of catalytic organics may be added.
  • the method embodied by this invention avoids this constraint by the use of pulsed light.
  • the reaction of the chloride is discriminated against by the pulsed waveform, and the COD may be determined in high saline matrices.
  • Figure 1 is a graph illustrating varying LED intensities applied to a 1 : 50 dilution of a seawater sample resulting in a chloride content of 425 mg/L Cl " ;
  • Figure 2 illustrates calibration, showing the linear relationship between concentration as COD and charge response for standards ranging from 0 - 50 mg/L COD in a background of 0 - 150 mg/L Cl " in the cell a. Pulsing technique, b. standard PeCOD analysis where there is a clear effect by a significant presence of chloride;
  • Figure 3 illustrates the signal response for saline and non-saline Potassium
  • KHP Hydrogen Phthalate
  • Figure 5 illustrates the influence of chloride presence on the analytical signal.
  • Figure 5a shows the normal response for KHP in the presence (upper trace) and absence (lower trace) of 1000 mg/L chloride with direct light;
  • Figure 5b shows the response for 5a above (chloride present) with a pulsed regime
  • Figure 6 illustrates the calibration over a concentration range for saline samples at various dilutions, with and without organic addition. Analyses were performed using a pulse of 0.1 sec on and 1 sec off;
  • Figure 7 illustrates the calibration over a concentration range for saline and non- saline sample; a.) comparing pulsed and non-pulsed methods, b.) Comparison of saline and non-saline samples for the pulsed analysis method. Analyses were performed using a pulse of 0.1 sec on and 1 sec off;
  • Figure 8 provides comparative data for COD (PeCODTM ) and BODsugar refinery samples in salt water;
  • FIG. 9 illustrates the relationship between PeCODTM COD and BOD values.
  • PeCODTM is the trademark of the applicant that is used to designate the water analysers made in accordance with WO2004/088305.
  • Figure 1 shows that when a dilution of 1 to 50 of seawater is made, resulting in a chloride content of 425 mg/L Cl " , and when the applied UV light level applied is low, the onset of chloride oxidation is delayed and a window of opportunity exists where organics can be oxidised prior to the oxidation of chloride. At a LED intensity of 20% it was observed that 5 mg/L of organic could be easily observed above the chloride content.
  • the sensors were made according to the colloidal method disclosed in
  • KCI is a common electrolyte used in electrochemistry, and subsequently the potential for its use as a replacement electrolyte to the currently used NaNO 3 was investigated. KCI is a good electrolyte (due to its enhanced ionic mobility) and potentially it can provide a high background of chloride that would mask any chloride present in a sample. Preliminary experiments investigated the ability to detect low COD concentrations in a 1M KCI electrolyte.
  • Figure 4a shows that 10 ppm of COD could be detected in KCI and hence a high chloride background using the pulsing technique. However, further tests showed the reproducibility to be poor and the ability of the signal to return to baseline could not be repeatedly achieved.
  • KHP Potassium Hydrogen Phthalate
  • the linearity and response over a concentration range was investigated for both saline and non-saline standards with Potassium Hydrogen Phthalate (KHP) in the range 0-300 mg/L. The responses are shown in Figure 3.
  • KHP Potassium Hydrogen Phthalate
  • Sodium perchlorate is a preferred electrolyte that for the PeCODTM instrument. It can achieve excellent linearity, use lower concentrations and is also hygroscopic. For this reason it was also investigated for its use in the application of analysis of COD in a chloride matrix.
  • the initial pulsing parameters in pulsing mode were 0.5 sees for the LED on time and 2.5 sees for the off time, which is a 1 :5 ratio.
  • Alteration of the pulsing settings to 0.1 sec on and 1 sec off resulted in a 1 :10 ratio, which resulted in improved signal-to-noise, and in observations which showed that these settings had the biggest effect in controlling the level of chloride oxidation.
  • Further studies showed that increased off time did not significantly improve the sensitivity and consequently it was decided to maintain the 0.1 on and 1.0 off time in order to also achieve increased sample throughput.
  • Example 1 The determination of COD in seawater is presented. Results obtained by the pulsing method are compared to results obtained without pulsing. Three examples are presented - COD analysis with direct light and no chloride present, COD with direct light and chloride present, and COD with pulsed light and chloride present.
  • Figure 5a shows the normal response obtained for COD determination of 10 mg/L KHP with direct light with and without chloride present (at 1000 mg/L). It will be seen that the tailing of the organic response down to its baseline is interrupted by the onset of the chloride oxidation. Since the response never returns to its baseline, the generation of an analytical signal is compromised.
  • Figure 5b shows the response for the solution analysed in 5a above, with the pulsed regime (chloride present).
  • the protocol was as follows: with the current settings at 0.1 on and 1.0 off time, linearity was tested for a range of dilutions with seawater samples (See Figure 6). A 1 :50 dilution of seawater without organic addition is seen to be preferred. Smaller dilutions are possible (i.e. 1:10), but they then require organic addition. With such high chloride backgrounds, and no organic present, chloride oxidation begins to dominate.
  • the Ti ⁇ 2 sensor life is extended due to pulsing efficiency of oxidation and the absence of chloride interference.

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  • Life Sciences & Earth Sciences (AREA)
  • Health & Medical Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Pathology (AREA)
  • Molecular Biology (AREA)
  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Electrochemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Biodiversity & Conservation Biology (AREA)
  • Biomedical Technology (AREA)
  • Emergency Medicine (AREA)
  • Food Science & Technology (AREA)
  • Medicinal Chemistry (AREA)
  • Investigating Or Analyzing Non-Biological Materials By The Use Of Chemical Means (AREA)
  • Investigating Or Analysing Materials By The Use Of Chemical Reactions (AREA)

Abstract

L'invention concerne un procédé permettant de déterminer la demande chimique en oxygène dans des échantillons d'eau contenant des ions chlorure par un procédé photo-électrochimique dans lequel la photo-électrode est activée par des impulsions lumineuses et les paramètres des impulsions et l'intensité de la source lumineuse sont réglés pour favoriser l'oxydation des espèces organiques présentes dans l'échantillon d'eau et pour supprimer toute oxydation de la part des ions chlorure présents dans l'échantillon. Le procédé contrôle la durée des impulsions, l'intervalle entre les impulsions et l'intensité lumineuse.
EP08800162A 2007-10-17 2008-10-17 Analyse d'eau Pending EP2201356A4 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
AU2007905660A AU2007905660A0 (en) 2007-10-17 Water Analysis
PCT/AU2008/001529 WO2009049366A1 (fr) 2007-10-17 2008-10-17 Analyse d'eau

Publications (2)

Publication Number Publication Date
EP2201356A1 true EP2201356A1 (fr) 2010-06-30
EP2201356A4 EP2201356A4 (fr) 2011-12-14

Family

ID=40566923

Family Applications (1)

Application Number Title Priority Date Filing Date
EP08800162A Pending EP2201356A4 (fr) 2007-10-17 2008-10-17 Analyse d'eau

Country Status (5)

Country Link
EP (1) EP2201356A4 (fr)
CN (1) CN101918823A (fr)
AU (1) AU2008314501B2 (fr)
WO (1) WO2009049366A1 (fr)
ZA (1) ZA201002406B (fr)

Families Citing this family (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2010132957A1 (fr) * 2009-05-22 2010-11-25 Aqua Diagnostic Holdings Pty Ltd Analyse de l'eau
DE102013108556A1 (de) * 2013-08-08 2015-02-12 Endress + Hauser Conducta Gesellschaft für Mess- und Regeltechnik mbH + Co. KG Verfahren und Analysegerät zur Bestimmung des chemischen Sauerstoffbedarfs einer Flüssigkeitsprobe
CN104132978A (zh) * 2014-07-24 2014-11-05 南京大学 一种基于双极电极的光催化产生电化学发光的装置
CN106970131B (zh) * 2017-03-28 2019-01-18 北京北大明德科技发展有限公司 一种光电催化型水溶有机物浓度传感器及制备方法
CN110487864B (zh) * 2019-09-03 2020-10-27 中南大学 一种水体中氯离子浓度的光电化学检测方法
CN111505068B (zh) * 2020-04-01 2021-07-30 中国科学院水生生物研究所 一种实时监测人工湿地中cod浓度的生物传感器方法和装置
CN112798533A (zh) * 2021-02-07 2021-05-14 深圳市中志环境科技有限公司 多因子水质监测仪及多因子水质监测方法

Family Cites Families (4)

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Publication number Priority date Publication date Assignee Title
US4963815A (en) * 1987-07-10 1990-10-16 Molecular Devices Corporation Photoresponsive electrode for determination of redox potential
DE19914810A1 (de) * 1999-03-31 2000-10-26 Forschungszentrum Juelich Gmbh Photoelektrochemischer Sensor
AU2003901589A0 (en) * 2003-04-04 2003-05-01 Griffith University Novel photoelectrichemical oxygen demand assay
CN101238364A (zh) * 2005-08-11 2008-08-06 水体检测有限公司 用光电化学方法进行水分析

Also Published As

Publication number Publication date
AU2008314501A1 (en) 2009-04-23
AU2008314501B2 (en) 2011-02-17
CN101918823A (zh) 2010-12-15
ZA201002406B (en) 2011-03-30
EP2201356A4 (fr) 2011-12-14
WO2009049366A1 (fr) 2009-04-23

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