Proficiency test SPIL-2 (2011) Nitrogenparameters in wastewater (sewage)

Transcription

1 Proficiency test SPIL-2 (2011) Nitrogenparameters in wastewater (sewage) Quality Documentation February 2013

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3 Proficiency test SPIL-2 (2011) Quality documentation February 2013 Smedeskovvej 38 DK-8464 Galten Denmark Tel: Fax: Web: Client Client s representative Environmental laboratories Project Project No Proficiency test SPIL-2 (2011) Authors Stine Jespersen Date Approved by Ulla Lund Quality Documentation Revision Description By Approved Date Key words Analytical quality, assigned value, precision, accuracy, homogeneity, stability, total nitrogen, Kjeldahl-N, ammonium, nitrite+nitrate, conductivity, ph, wastewater Classification Open Internal Proprietary Distribution DANAK Eurofins: Stine Ottsen, Ulla Lund No of copies 2 File

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5 CONTENTS 1 INTRODUCTION FEATURES OF THE PROFICIENCY TEST Sample preparation Statistical analysis of participants data Assigned and spike value Assigned and spike values Test of spike values Test of assigned values HOMOGENEITY OF SAMPLES CONCLUSION REFERENCES APPENDICES A List of participants... A-1 B Sample preparation... B-1 C Control of spike value... C-1 D Control of recovery... D-1 E Concentration level... E-1 F Homogeneity and stability... F-1

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7 1 INTRODUCTION A proficiency test on the analysis of nitrogenparameters in wastewater was conducted on 26 May The proficiency test was organised by Eurofins Miljø A/S according to agreement with Danish Accreditation, DANAK. The present report contains Eurofins documentation for the quality of the proficiency test. Results of the proficiency test including data from participating laboratories and statistical analysis of these data were issued in a report to all participants and DANAK /1/ on 27 June

8 2 FEATURES OF THE PROFICIENCY TEST Participants in the proficiency test were a total of 69 laboratories from Denmark, Norway and Sweden. A list of participants is shown in Appendix A. The closing date for submission of results was 14 June All participants had submitted their results before the dead-line. 2.1 Sample preparation The parameters covered in the proficiency test are listed in Table 2 as are the abbreviations used in this report. Four samples were dispatched for the proficiency test. The samples were sample pairs covering the parameters as described in Table 1. The matrix of the samples represented wastewater, in this case sewage. Sample preparation is described in Appendix B. Table 1 Samples in the proficiency test Sample name Parameters A1/B1 TN, Kjeldahl-N, NH 4, NO 2+3, γ 25 A2/B2 ph 2.2 Statistical analysis of participants data A split-level design was used. The data analysis was performed in accordance with ISO 5725: Accuracy (trueness and precision) of measurement methods and results (1994) /2/ and as described in detail in Spliid (1992) /3/. A short introduction to the statistics and a list of symbols and abbreviations used is given in Eurofins document Schedule for a proficiency test, which is available at Eurofins home page /4/. The statistical model used is based on the assumption that the variances for the two samples in a sample pair are identical. The assumption was tested (F-test, 95% confidence level) and the result was that the two variances may be assumed to be identical for all parameters. 2.3 Assigned and spike value An overview of the concentrations in the samples (the assigned values) and the difference in concentration between the two samples of a sample pair (spike value) are shown in Table 2 compared to the range of concentrations normally encountered in sewage. 2-1

9 Table 2 Assigned and spike value Parameter Abbreviation Unit Typical Range Assigned value Spike value Total nitrogen TN mg/l N Kjeldahl-N Kjeldahl-N mg/l N Ammonium NH 4 mg/l N Nitrite+nitrate NO 2+3 mg/l N < Conductivity γ 25 ms/m ph ph Assigned and spike values In order to ensure optimal use of the data, the assigned value is calculated as the average of the median for both samples in the sample pair after subtraction of the spike value. The spike values are calculated from sample preparation except for γ 25 where the spike value is the difference between median values for the two samples in the sample pair. The results for TN, Kjeldahl-N, and NO 2+3 are operationally defined. The assigned value is a consensus value based upon the median for method no. 1 and 2 (TN), method no. 1, 2 and 3 (Kjeldahl-N), and method no. 1, 2, 3, 4, and 5 (NO 2+3 ). A list of method identification numbers is found in the report to participants /1/. Assigned values for NH 4, γ 25 and ph are consensus values for all laboratories based on the median. Only eight laboratories submitted results for Kjeldahl-N, and only four laboratories used method no. 1 which is the method required by the Danish EPA /5/. The assigned and spike value were therefore also based upon method no. 2 and 3, and hence the stated values should be seen as indicative values Test of spike values A comparison was made (t-test, 95% confidence level) between the spike value and the difference in concentration between the two samples in the sample pair found from the laboratories results, see Appendix C. The test revealed a significant difference between the two for NO 2+3 and γ 25. For NO 2+3 the difference could be attributed to influence from laboratories using test kids instead of standardised methods. The test was repeated after exclusion of the results from laboratories using method no. 9, 61, and 71 and now showed no significant difference. For γ 25 the difference could be attributed to influence from a few laboratories. The test was repeated after exclusion of the results from laboratory no. 7 and 35 and now showed no significant difference Test of assigned values The assigned value and the average of the results obtained from all laboratories were also compared (t-test, 95% confidence level), see Appendix D. The test revealed a significant difference between the two for NO 2+3. Average recovery was %. The difference could be attributed to influence from laboratories using test kits instead of standard methods. The test was repeated after exclusion of the results from laboratories using method no. 9, 61, and 71 and now showed no significant difference. The assigned value is therefore kept unchanged. 2-2

10 3 HOMOGENEITY OF SAMPLES The homogeneity of samples was tested using the following parameters as indicators: NH 4 NO 2+3 ph Homogeneity test Homogeneity test Homogeneity test The results of control measurements are shown in Appendix F. The appendix also gives the results of the statistical evaluation of the control data. The data are analysed by analysis of variance (ANOVA) giving: 1. the standard deviation/variance for replicates (the contribution from analytical variability) and 2. the between bottle standard deviation/variance (the contribution from heterogeneity). Homogeneity is evaluated by comparing the between bottle variance to 0.15 * the maximum tolerated deviation from the assigned value specified by the Danish EPA /5/ ( sigma in the calculations is 0.5 times the maximum tolerated deviation). This test ensures that heterogeneity will not have negative influence on the evaluation of participant performance /6/. The appendix also shows the standard deviation within and between laboratories from the proficiency test to allow comparison between tests performed and average quality from participating laboratories. The tests for homogeneity show that the samples are homogeneous. 3-1

11 4 CONCLUSION The quality control performed, including test of sample homogeneity as well as test of recovery of spike and assigned values, shows that the samples and their assigned values are suitable for testing the proficiency of the participating laboratories for all parameters. The results are also suitable for estimation of the general quality of analyses among all participating laboratories. For NO 2+3 and γ 25 the participants could not recover the spike value. The difference between the calculated spike value and that found by the participants is small and the influence on evaluation of participant performance or estimation of general quality of analyses is insignificant. For NO 2+3 the participants did not recover the assigned value. Eurofins scrutiny of the combined evidence gave the conclusion that the assigned value is correct. The assigned value is therefore kept unchanged and it is recommended as the basis for evaluation of participating laboratories. For Kjeldahl-N the spike and assigned value are indicative as only a few laboratories submitted results. 4-1

12 5 REFERENCES /1/ Eurofins Miljø A/S, Proficiency test SPIL-2 (2011), Report to participants, June /2/ ISO , Accuracy (trueness and precision) of measurement methods and results Part 2: Basic method for the determination of repeatability and reproducibility of a standard measurement method, /3/ Spliid, H., Procedure and analysis of data for proficiency tests and environmental analyses, Report to Danish Environmental Protection Agency, 1994 (in Danish). /4/ Eurofins A/S, Schedule for a proficiency test, document may be downloaded from /5/ Ministry of Environment regulation no. 866 on quality criteria for environmental measurements performed by accredited laboratories, certified personnel etc., 1 July 2010 (in Danish). /6/ ISO 13528, Statistical methods for use in proficiency testing by interlaboratory comparison,

13 APPENDICES

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15 APPENDIX A List of participants

16 Laboratory Town Country Analyseenheden Tjele Denmark AquaDjurs - Fornæs Renseanlæg Grenaa Denmark Bjergmarken R/A, Roskilde Forsyning Roskilde Denmark CP Kelco ApS, Spildevandslaboratoriet Ll. Skensved Denmark Eurofins Miljø A/S Vejen Denmark Faxe Forsyning Faxe Denmark Fredericia Spildevand A/S Fredericia Denmark Greve Forsyning Greve Denmark Hach Lange ApS Brønshøj Denmark Halsnæs Kommunale Forsyning A/S Liseleje Denmark Hedensted Spildevand A/S Daugård Denmark Holstebro Centralrenseanlæg, Vestforsyning A/S Holstebro Denmark Højvang Miljølaboratorium Dianalund Denmark Ikast-Brande Renseanlæg Ikast Denmark Kerteminde Forsyning - Spildevand A/S Kerteminde Denmark Kolding Spildevand A/S Bjert Denmark Korsør Renseanlæg Korsør Denmark LabVest I/S Holstebro Denmark Lynettefællesskabet I/S København K Denmark MILANA A/S Humlebæk Denmark Mølleåværkets Driftslaboratorium Lyngby Denmark Måløv Renseanlæg Måløv Denmark Nyborg Renseanlæg Nyborg Denmark Næstved Centralrenseanlæg Næstved Denmark Provas Haderslev Forsyningsservice Haderslev Denmark Randers Spildevand A/S Randers NØ Denmark Rensningsanlæg Øst, Esbjerg Esbjerg Denmark Rensningsanlæg Øst, Esbjerg, Spildevandslaboratoriet Esbjerg Denmark Ringkøbing-Skjern Forsyning A/S Skjern Denmark Ringsted Renseanlæg Ringsted Denmark Rønne Renseanlæg Rønne Denmark Skælskør Renseanlæg Skælskør Denmark Slagelse Renseanlæg Slagelse Denmark Sun Chemicals, E30 Køge Denmark Svendborg Centralrenseanlæg Skårup Fyn Denmark A-1

17 Sønderborg Renseanlæg Sønderborg Denmark Vejen Renseanlæg Vejen Denmark Vejle Centralrenseanlæg, Laboratoriet Vejle Denmark Statoil ASA, Kollsnes processanlegg Rong Norway Ernemar Laboratoriet Oskarshamn Sweden Eslöv Kommun Miljö och Samhällsbyggnad Eslöv Sweden Eurofins Environment Sweden AB Lidköping Sweden GRYAAB AB Göteborg Sweden Gästrike Vatten AB Skutskär Sweden Hallsta Pappersbruk Hallstavik Sweden Holmen Paper Norrköping Sweden Kalmar Vatten AB, VA-lab, Avloppsreningsverket Kalmar Sweden Klippans Reningsverk Klippan Sweden Käppalaverket Lidingö Sweden Laboratoriet vid Smedjeholms Arv Falkenberg Sweden Mjölby Kommun Mjölby Sweden Motala Kommun Motala Sweden Norrköping Vatten AB, Laboratoriet Slottshagens Reningsverk Norrköping Sweden NSVA/Öresundsverket Helsingborg Sweden Preem AB Göteborg Göteborg Sweden St1 Refinery AB Göteborg Sweden Tekniska förvaltningen, Avloppsverkets laboratorium Örebro Sweden Tekniska Verken i Linköping AB (publ), Division Vatten Linköping Sweden Uddebo Laboratorium Luleå Sweden VA SYD Bulltofta Vattenverk Malmö Sweden VA SYD Klaghamns Avloppsreningsverket Klagshamn Sweden VA SYD Källby Avloppsreningsverk Lund Sweden VA SYD Sjölundalaboratoriet Malmö Sweden VIVAB Varberg Sweden Västerviks Miljö & Energi AB, Vattenlaboratoriet Västervik Sweden Örtofta Sockerbruk Eslöv Sweden A-2

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19 APPENDIX B Sample preparation

20 Stock solution Prepared from Concentration Stock TN 6.00 g Disodium edetate, 2H 2 O TN: mg/kg N milli-q water up to g Stock NH g Ammonium chloride (NH 4 Cl) NH 4 : mg/kg N milli-q water up to g Stock NO g Potassium nitrate (KNO 3 ) milli-q water up to g NO 3 : mg/kg N Sample Sample prepared from A1 B1 850 g stock TN 600 g stock NH g stock NO 3 Filtered untreated water from Bramming Syd sewage treatment plant up to kg g stock TN g stock NH g stock NO 3 Sample A1 up to 55.0 kg TN mg/l N NH 4 mg/l N NO 3 mg/l N Conductivity ms/m a+9.47 b+4.49 c+1.32 d (a+9.47) (b+4.49) (b+1.32) e Sample Sample prepared from ph A2/B2 Filtered untreated water from Bramming Syd sewage treatment plant f B-1

21 APPENDIX C Control of spike value

22 Total nitrogen, mg/l N Control of differences within sample pairs Laboratory Difference AB UC UC A B A B No of labs., p 69 No of repl., n 2 d 0.13 s² 0.87 s 0.93 t = p (d/s) Sign. level, p(t) No test statistics were found to be significant UC denotes a Cochran outlier C-1

23 Kjeldahl nitrogen, mg/l N Control of differences within sample pairs Laboratory Difference AB A B A B - No of labs., p 8 No of repl., n 2 d 0.09 s² 1.30 s 1.14 t = p (d/s) Sign. level, p(t) No test statistics were found to be significant C-2

24 Ammonium, mg/l N Control of differences within sample pairs Laboratory Difference AB UC A B A B 0.30 No of labs., p 68 No of repl., n 2 d s² 0.79 s 0.89 t = p (d/s) Sign. level, p(t) No test statistics were found to be significant UC denotes a Cochran outlier C-3

25 Nitrite+nitrate, mg/l N Control of differences within sample pairs Laboratory Difference AB UG A B UC UG A B No of labs., p 58 No of repl., n 2 d s² s t = p (d/s) Sign. level, p(t) *** * denotes that there is a significant difference (t-test, 5%-level) ** denotes that there is a significant difference (t-test, 1%-level) *** denotes that there is a significant difference (t-test, 0.1%-level) UC denotes a Cochran outlier UG denotes a Grubbs outlier C-4

26 Conductivity, ms/m Control of differences within sample pairs Laboratory Difference AB UC UC 41-42A - 42B UC UG A - 69B - No of labs., p 27 No of repl., n 2 d 0.20 s² 0.24 s 0.49 t = p (d/s) Sign. level, p(t) * * denotes that there is a significant difference (t-test, 5%-level) ** denotes that there is a significant difference (t-test, 1%-level) *** denotes that there is a significant difference (t-test, 0.1%-level) UC denotes a Cochran outlier UG denotes a Grubbs outlier C-5

27 ph, Control of differences within sample pairs Laboratory Difference AB UG UG A - 42B UC UG A - 69B No of labs., p 58 No of repl., n 2 d s² s t = p (d/s) Sign. level, p(t) No test statistics were found to be significant UC denotes a Cochran outlier UG denotes a Grubbs outlier C-6

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29 APPENDIX D Control of recovery

30 Total nitrogen, mg/l N Control of recovery, average of results Laboratory Sample pair AB UC UC A B A B No of labs., p 69 No of repl., n 2 m s² 4.39 s 2.10 Assigned value, µ 31.7 Recovery, % t = p (m-µ)/s Sign. level, p(t) No test statistics were found to be significant UC denotes a Cochran outlier D-1

31 Kjeldahl nitrogen, mg/l N Control of recovery, average of results Laboratory Sample pair AB A B A B - No of labs., p 8 No of repl., n 2 m s² 1.49 s 1.22 Assigned value, µ 30.1 Recovery, % t = p (m-µ)/s Sign. level, p(t) No test statistics were found to be significant D-2

32 Ammonium, mg/l N Control of recovery, average of results Laboratory Sample pair AB UC A B A B No of labs., p 68 No of repl., n 2 m s² 1.09 s 1.04 Assigned value, µ 24.7 Recovery, % t = p (m-µ)/s Sign. level, p(t) No test statistics were found to be significant UC denotes a Cochran outlier D-3

33 Nitrite+nitrate, mg/l N Control of recovery, average of results Laboratory Sample pair AB UG A B UC UG A B No of labs., p 58 No of repl., n 2 m s² s Assigned value, µ 1.31 Recovery, % t = p (m-µ)/s Sign. level, p(t) *** * denotes that there is a significant difference (t-test, 5%-level) ** denotes that there is a significant difference (t-test, 1%-level) *** denotes that there is a significant difference (t-test, 0.1%-level) UC denotes a Cochran outlier UG denotes a Grubbs outlier D-4

34 Conductivity, ms/m Control of recovery, average of results Laboratory Sample pair AB UC UC 41-42A - 42B UC UG A - 69B - No of labs., p 27 No of repl., n 2 m s² 0.77 s 0.88 Assigned value, µ 73.4 Recovery, % 99.7 t = p (m-µ)/s Sign. level, p(t) No test statistics were found to be significant UC denotes a Cochran outlier UG denotes a Grubbs outlier D-5

35 ph, Control of recovery, average of results Laboratory Sample pair AB UG UG A - 42B UC UG A - 69B No of labs., p 58 No of repl., n 2 m s² s Assigned value, µ 6.72 Recovery, % 99.8 t = p (m-µ)/s Sign. level, p(t) No test statistics were found to be significant UC denotes a Cochran outlier UG denotes a Grubbs outlier D-6

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37 APPENDIX E Concentration level

38 Concentration level SPIL-2 (2011) Parameter Unit Sample Bottle no. I II Bottle Sample Assigned Spike Average Average value Measured Assigned Total nitrogen mg/l N A ,1 34,3 34,7 34,7 31,7 4,1 3,7 B ,5 37,0 38,8 38,8 35,4 Ammonium mg/l N A ,3 22,0 22,2 22,2 24,7 3,0 2,7 B ,2 25,0 25,1 25,1 27,4 Nitrite+nitrate mg/l N A1 79 1,50 1,52 1,51 1,51 1,31 0,1 0,14 E-1 B1 78 1,63 1,62 1,62 1,62 1,45 ph A2 85 6,82 6,83 6,83 6,83 6, B2 81 6,81 6,84 6,83 6,83 6,72

39 APPENDIX F Homogeneity and stability

40 PT: SPIL-2 Parameter: NH4 Unit: mg/l N Sigma: 2,6 2*s T max Responsible for tests: AGK 10% level or 2*S T max Homogeneity test Date: Sample x(a) x(b) average sd sd^2 B1-3 26,4 26,1 26,3 0,212 0,045 B ,4 26,3 26,4 0,071 0,005 B , ,1 0,141 0,020 B , ,0 0,000 0,000 B ,1 26,3 25,7 0,849 0,720 B , ,7 0,495 0,245 B , ,1 1,273 1,620 B ,0 25,9 26,0 0,071 0,005 B ,7 25,5 25,1 0,566 0,320 B ,2 26,2 25,7 0,707 0,500 B ,3 26,3 26,3 0,000 0,000 B ,4 25,7 26,1 0,495 0,245 Conclusions ss = 0,15 0.3*sigma= 0,78 For homogeneity General average (x) 25,9 Analytical Is s w < 0,15*sigma Sample average sd (s x ) 0,422 quality NO Within-sample sd (s w ): 0,557 Between-samples sd (ss): 0,151 Homogeneity: Is ss < 0.3*sigma? S L in the Proficiency Test: 0,94 YES S R in the Proficiency Test: 1,13 F-1

41 PT: SPIL-2 Parameter: NO2+3 Unit: mg/l N Sigma: 0,1664 2*s T max Responsible for tests: AGK 10% level or 2*S T max Homogeneity test Date: Sample x(a) x(b) average sd sd^2 B1-3 1,507 1,629 1,568 0,086 0,007 B1-10 1,657 1,698 1,678 0,029 0,001 B1-17 1,671 1,682 1,677 0,008 0,000 B1-23 1,672 1,681 1,677 0,006 0,000 B1-32 1,671 1,711 1,691 0,028 0,001 B1-42 1,643 1,535 1,589 0,076 0,006 B1-50 1,661 1,701 1,681 0,028 0,001 B1-60 1,690 1,689 1,690 0,001 0,000 B1-68 1,669 1,689 1,679 0,014 0,000 B1-73 1,701 1,688 1,695 0,009 0,000 B1-80 1,678 1,658 1,668 0,014 0,000 B1-91 1,658 1,691 1,675 0,023 0,001 Conclusions ss = 0, *sigma= 0,0499 For homogeneity General average (x) 1,66 Analytical Is s w < 0,15*sigma Sample average sd (s x ) 0,041 quality NO Within-sample sd (s w ): 0,0375 Between-samples sd (ss): 0,0310 Homogeneity: Is ss < 0.3*sigma? S L in the Proficiency Test: 0,097 YES S R in the Proficiency Test: 0,117 F-2

42 PT: SPIL-2 Parameter: ph Unit: Sigma: 0,6928 2*s T max Responsible for tests: AGK 10% level or 2*S T max Homogeneity test Date: Sample x(a) x(b) average sd sd^2 A1-1 6,96 7,00 6,98 0,03 0,001 A1-9 6,92 7,05 6,99 0,09 0,01 A1-17 6,89 6,90 6,90 0,01 0,000 A1-25 6,95 7,00 6,98 0,04 0,001 A1-33 6,90 6,98 6,94 0,06 0,003 A1-41 7,06 6,90 6,98 0,11 0,013 A1-49 6,88 6,88 6,88 0,00 0,000 A1-57 6,90 6,95 6,93 0,04 0,001 A1-65 6,90 6,91 6,91 0,01 0,000 A1-73 6,88 6,89 6,89 0,01 0,000 A1-83 6,89 6,88 6,89 0,01 0,000 A1-91 6,88 6,92 6,90 0,03 0,001 Conclusions ss = 0, *sigma= 0,21 For homogeneity General average (x) 6,93 Analytical Is s w < 0,15*sigma Sample average sd (s x ) 0,042 quality YES Within-sample sd (s w ): 0,049 Between-samples sd (ss): 0,0238 Homogeneity: Is ss < 0.3*sigma? S L in the Proficiency Test: 0,228 YES S R in the Proficiency Test: 0,256 F-3