10 things you need to know about monitoring Total Residual Oxidants

Transcription

1 10 things you need to know about monitoring Total Residual Oxidants WWEM 2014

2 Introduction Who we are? Palintest manufactures a range of advanced water and environmental testing equipment, and from its Tyneside base exports to over 100 countries across the globe. These products are used in a wide variety of applications to protect the environment and safeguard public health. Crucially Palintest are able to simplify testing for key water quality parameters, enabling critical water quality decisions to be made with confidence.

3 Agenda Total Residual Oxidants (TRO) Guidelines across the globe The problems of transient species Portable methods: DPD method Lissamine Green B method Other colorimetric methods Amperometric Sensor Laboratory methods: Amperometric Titration Ion Chromatography Spectrophotometric method Iodometric titration Implications on DWI guidelines for TRO?

4 What are they? Total Residual Oxidants Usually used in the context of chlorine dosing Can be applied to other oxidants e.g. Chlorine Dioxide and the DBP chlorate and chlorite Usually in the context of drinking water

5 What are they? Total Residual Oxidants Name Formula Structure Chlorite is the primary DBP (50 70%) Chlorate also produced (dependent on ph conditions) Chlorite and Chlorate can be introduced by the generator Most generators use chlorite or chlorate precursor chemicals Hypochlorite ClO Chlorite ClO 2 Chlorine Dioxide ClO 2 Chlorate ClO 3

6 10 things you need to know # 1 Total Residual Oxidants mean ClO 2, ClO 2 and ClO 3 (Within the context of chlorine dioxide dosing) (May include chlorine if chlorinated water is being treated with ClO 2 )

7 UK Guidelines Guidelines behind TRO DWI Guidelines Guideline 31 BS EN 12671: 2009 European Standard Chemicals used for treatment of water intended for human consumption. Chlorine dioxide generated in situ. Additional national Conditions: The combined concentration of chlorine dioxide, chlorite and chlorate should not exceed 0.5mg l 1 as chlorine dioxide in the water entering supply.

8 Guidelines throughout the world Guidelines behind TRO USEPA used as a international surrogate standard ClO 2 and ClO 2 monitored daily ClO 3 monitored monthly Maximum Disinfectant Residual Levels (defined under DBPR: 2002) 0.8mg/l ClO 2 1mg/l ClO 2

9 10 things you need to know # 2 DWI requirements are relatively stringent

10 What s the problem? Transient or Persistent? ClO 2 is highly volatile Samples should be taken in amber glassware Small headspace Minimal agitation Testing must be carried out on site and carefully

11 What s the problem? Transient or Persistent? ClO 2 and ClO 3 are persistent More suitable for sampling and off site analysis Off site analysis issues in real time decision making

12 10 things you need to know # 3 On site analysis is the best way of complying with DWI

13 Portable Methods DPD LGB Amaranth CPR ACVK ChlordioX Plus

14 Portable methods DPD The Palin system Blue Book method US EPA approved method Widely accepted method, e.g. EA, HSE No longer an AWWA Standard Method (21 st edition) A general oxidation method, i.e. not selective

15 Portable methods DPD Determination of ClO 2 (and ClO 2 possible) ClO 2 method difficult and time consuming Can result in negative values if chlorine present A difference method Concerns over chlorite and chloride interference Removal as AWWA Standard method

16 10 Things you need to know # 4 DPD method is no longer a AWWA standard method for chlorine dioxide

17 Portable methods Lissamine Green (LGB) US EPA Approved method ClO 2 specific ClO 2 determination possible with Horseradish peroxidase (HRP)

18 Portable methods Lissamine Green (LGB) Dye bleaching method for ClO 2 Time and temperature dependence Operator errors Addition of HRP for ClO 2 A difference method

19 Other Portable Colorimetric Methods Available Generally nonstandard methods for ClO 2 Useful for process optimisation Not so good for regulatory reporting No ability to quantify ClO 2 (or ClO 3 ) Amaranth Method Chlorophenol Red Method ACVK Method

20 Other Portable Colorimetric Methods Available Amaranth Method Popular in Europe Small test range Generally interferent free Dye bleaching method

21 Other Portable Colorimetric Methods Available Chlorophenol Red (CPR) Method Generally interferent free (ClO 2 can be an issue) Dye bleaching method

22 Other Portable Colorimetric Methods Available Acid Chrome Violet K (ACVK) Method Generally interferent free Dye bleaching method Method defined in BS EN 12671:2009

23 10 Things you need to know # 5 Other colorimetric methods are available

24 10 Things you need to know # 6 Colorimetric methods suffers from difficulties in the field

25 10 Things you need to know # 7 Photometric dye bleaching methods can lead to operator error

26 Portable Amperometric Sensor Method Patented Palintest technology for ClO 2 and ClO 2 US EPA Approved method The ONLY portable US EPA approved method for ClO 2 Enables compliance to US EPA requirements (daily monitoring of ClO 2 and ClO 2, monthly for ClO 3 ) Uses standard chemistry (similar to amperometric titration method) Not DWI (because of lack of ClO 3 )

27 Portable Amperometric Sensor Method Sequential test protocol Aims to simplify ClO 2 and ClO 2 determination Can carry out chlorine measurement ClO 2 is difference method (but not reliant on user) ClO 2 ClO 2

28 10 Things you need to know # 8 ChlordioX Plus enables compliance with most of DWI requirements

29 Laboratory methods Amperometric Titration Ion Chromatography Iodometric Titration Spectrophotometry Not portable, therefore no ClO 2 determination

30 Laboratory Methods Amperometric Titration Sequential titration method Titration with PAO or thiosulphate with ph control ClO 2, chlorine (free and combined), ClO 2 and ClO 3 possible Requires a skilled technician (especially for ClO 3 )

31 Laboratory Methods Ion Chromatography The best way to determine ClO 2 and ClO 3 No good for ClO 2 Requires specialist equipment Requires careful sample preparation Requires skilled technician

32 Spectrophotometry UV/Vis (λ = 360nm) spectrophotometry can be used for ClO 2 Laboratory Methods If ClO 2 present, can lead to interferences from intermediate species Some manufacturers offer this as a visible region test (λ = ~420nm) Interferences more prominent at longer λ But portable High limit of detection (not suitable for potable water) Really only suitable for standard solutions (of high concentration)

33 Laboratory Methods Iodometric titration Same sequential titration principle as amperometric titration Suffers from interferences when multiple oxidants are present Requires skilled technician Really only suitable for standard solutions (and how Palintest standardise solutions)

34 10 Things you need to know # 9 Laboratory methods are not conducive to complying with DWI guidelines

35 10 Things you need to know # 10 Is it possible to comply with the DWI guidelines?

36 Is it possible to comply with the DWI guidelines? Implications Careful monitoring and dosing control at generator Downstream monitoring must incorporate On line monitors Sampling for laboratory (IC) assessment Portable monitoring

37 Summary 10 Things you now know about TRO: 1. Total residual oxidants include ClO 2, ClO 2 and ClO 3 (and chlorine) 2. DWI regulations are relatively stringent 3. On site analysis is the only way of complying with DWI regulations 4. DPD is no longer a standard method 5. Other colorimetric methods are available 6. Colorimetric suffers from difficulties in the field 7. Photometric dye bleaching susceptible to operator error 8. ChlordioX Plus enables compliance with most of DWI requirements 9. Laboratory methods alone are not conducive to complying with DWI guidelines 10. It is difficult to comply with the current DWI guidelines

38 Questions Questions? For more information on this topic,