Taste and odor assessment in the framework of water quality monitoring

1. Taste and odor assessment in the framework of water quality monitoring Dr. Frank Sacher DVGW-Technologiezentrum Wasser (TZW), Karlsruhe

2. Outline • Introduction • Regulation • Sensory perception • Analysis of taste and odor compounds • Chemical analysis of single compounds • Electronic instruments • Odorimetry • Procedures for determination of taste and odor • German Standard DIN 38403, part B1/2 • EN 1622 • Taste and odor determination at TZW • Conclusions

3. Council Directive 98/83/EC on the quality of water intended for human consumption • ANNEX I, Part C: Indicator parameters • (…) • Odour: Acceptable to consumers and no abnormal change • (…) • Taste: Acceptable to consumers and no abnormal change • (…) • ANNEX III: Specifications for the analysis of parameters • (…) • 3. Parameters for which no method of analysis is specified • Odour • Taste

4. German Drinking Water Directive (TrinkwV 2001) • ANNEX 3: Indicator parameters • (…) • Odor: Threshold number of 2 at 12 °C and of 3 at 25 °C Comment: Dilute stepwise with water free of smell and test for odor. • Taste: Acceptable to consumers and no abnormal change • (…) • ANNEX 5: Specifications for the analysis of parameters • (…) • 3. Parameters for which no method of analysis is specified • Odor • Taste

5. Summary: Directives on the quality of water intended for human consumption • For the parameters taste and odor Council Directive 98/83/EC does not give any parametric values nor does it specify any methods for analysis or any performance characteristics. • The German Drinking Water Directive gives a threshold value for odor but not for taste. It does also not specify any methods for analysis or any performance characteristics. • BUT: Taste and odor problems are among the most frequent and the most serious complaints from consumers.

6. Taste and odor complaints from consumers • Chlorine-like • Swimming pool-like • Ozone • Mineral oil-like • Muggy • Corky • Salty • … • In most cases source of complaints is difficult to determine

7. Taste and odor compounds in water • Algae-borne compounds (e.g. geosmine, MIB) • Phenols • Chlorophenols • Anisoles • Chloroanisoles • Hydrocarbons • Musk compounds (nitro musks, polycyclic musks) • Sulfur-containing compounds • Chlorine • Chlorine dioxide • Ozone • …

8. Sensory perception Single impressions optical olfactory tasty haptic aroma taste temperature texture look flavor Overall impression

9. Taste assessment

10. Analysis of taste and odor compounds • Chemical analysis of single compounds • Electronic tongues and electronic noses • Odorimetry

11. Chemical analysis of single compounds

12. Disadvantages of chemical analysis • Expensive • Labor intensive • Needs experienced personal • Time intensive • Laboratory-based method • Important compound might be missed

13. Disadvantages of Electronic Nose technology • Expensive • Not very sensitive • Needs experienced personal • Time intensive • Laboratory-based method • Correlation to human sensing is still limited • Not (yet) very reliable

14. Odorimetry • German Standard Method DIN 38403, part B1/2: Qualitative determination of taste; qualitative and quantitative determination of odor • German Standard Method DIN 38403, part B3 = EN 1622: Determination of the threshold odour number (TON) and threshold flavour number (TFN) • Laboratory methods • …

15. German Standard Method DIN 38403, part B1/2: General recommendations • Water sample has to be transferred into an odor-free glass bottle (in practice: an odor-free glass bottle is used for sampling) • For sample transport, glass bottle has to be filled completely and has to be sealed with a stopper made of glass or teflon • Cooling during sample transport is strongly recommended • Analysis has to be done as soon as possible after sampling • Testing can only be done if danger of poisoning (intoxication or contagion) can be excluded!!!(in practice: only drinking waters are tested for taste) • Testing for taste must always be done after testing for odor as odor perception can be interfered by taste perception

16. German Standard Method DIN 38403, part B1/2: Reporting of results for qualitative odor testing • Reporting of intensity: without weak/poor strong • Reporting of character: a) general: earthy muggy rotten corky… b) differentiated: chlorine-like fish-like mercaptane-like mineral oil-like… • Temperature of testing must always be reported!!!

17. German Standard Method DIN 38403, part B1/2: Reporting of results for qualitative taste testing • Reporting of intensity: without weak/poor strong • Reporting of character: a) general: salty sour bitter sweet… b) differentiated: chlorine-like fish-like soap-like…

18. DIN 38403, part B3 = EN 1622Determination of TON and TFN • TON = Threshold odour number A = Volume of water sample B = Volume of water sample for comparison (free of odor) • TFN = Threshold flavour number A = Volume of water sample B = Volume of water sample for comparison (free of taste)

19. Practical problems with taste and odor determination • Results may depend on the person performing the test and on the conditions during testing • Temperature • Draft • Noise • Presence of other people • Test has to be performed under standardized conditions!!! • Trained personal • Quiet and air-conditioned laboratories

20. TZW procedure for qualitative odor determination (1) • Sampling is done in 500 mL glass bottles with a glass stopper • Samples are stored at 4 °C until analysis • Analysis is done within 24 h after arrival of the samples in the lab • At beginning of analysis half of the volume of the sampling bottle is decanted (and used for the determination of other parameters)

21. TZW procedure for qualitative odor determination (2) • Glass bottles are tempered for 30 min in a water-bath at 25°C

22. TZW procedure for qualitative odor determination (3) • The bottle is taken from the water-bath and vigorously shaken • The stopper is removed and the smell is immediately tested by the test person • If an odor is detected, a second person smells as well

23. Procedure for quantitative odor determination • Principle: if in a water sample an odor has been qualitatively determined, the sample is diluted by odor-free water until no odor can be detected anymore • Only odor intensity is taken into account!!! • Threshold odor number: TON = Total volume after dilution/Volume of water sample

24. TZW procedure for quantitative odor testing: Pre-testing • A quantitative test is only performed if qualitative testing was positive • Different volumes (0.2 mL, 2 mL, 20 mL, 200 mL) of the water sample are diluted in odor-free 500 mL glass bottles with odor-free water (tap water from Karlsruhe) to a final volume of 200 mL • Following the procedure for qualitative odor determination all samples are tested, starting from the highest diluted sample • A odor-free water sample is tested for comparison • If even the highest diluted sample exhibits a perceptible odor, 2 mL of the diluted sample containing 2 mL of the original water are diluted with odor-free water up to 200 mL

25. TZW procedure for quantitative odor testing: Final testing • Final testing is done with the most diluted sample that exhibited a perceptible odor during pre-testing • Different volumes of this diluted water sample are further diluted with odor-free water to a final volume of 200 mL • E.g. 13, 10, 7, 5, 4, 3 mL of the original water are further diluted to 200 mL if the sample containing 20 mL of original water did exhibit a perceptible odor during pre-testing • Based on the volume of water sample in the tested water that exhibited no perceptible odor (while the sample less diluted did), the Threshold Odor Number is calculated

26. Calculation of TON

27. Practical procedure for taste testing • Only drinking waters are tested for taste (no raw waters, no waters during treatment) • Only qualitative determination of taste, no quantitative determination (TFN) • If a drinking water sample exhibits a perceptible taste, the procedure is immediately stopped and the operator of the treatment plant is contacted!!!

28. Training of personal - Odor • Test solutions are used for training • The test solutions are tested together with odor-free samples • The person has to identify unambiguously the test solutions among all samples

29. Training of personal - Taste • Test solutions are used for training • The test solutions are tested together with odor-free samples • The person has to identify unambiguously the test solutions among all samples and has to identify the taste characteristics

30. Conclusions • Compliance with recommendations of European on national Drinking Water Directives with regard to taste and odor is essential for water suppliers to keep the trust of the consumers • Testing of taste and odor is difficult and can easily become subjective • Sensory-based methods are still “the best available technology” • More advanced technologies as gas chromatography or Electronic nose & tongue technology might be helpful but can not (yet) be used on routine bases • Standardization of the methods for taste and odor testing is essential!!!!