Proficiency test SPIL-2 (2018) Nitrogen parameters in wastewater (synthetic wastewater, effluent)

Transcription

1 Proficiency test SPIL-2 (2018) Nitrogen parameters in wastewater (synthetic wastewater, effluent) Quality Documentation July 2018

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3 Proficiency test SPIL-2 (2018) Quality Documentation July 2018 Eurofins Miljø A/S Smedeskovvej 38 DK-8464 Galten Denmark Tlf: Web: Client Client s representative Environmental laboratories Project Project No Proficiency test SPIL-2 (2018) Authors Date Peter Rerup Approved by Stine Ottsen Quality Documentation Report PRE SJN Revision Description By Approved Date Key words Analytical quality, assigned value, precision, trueness, homogeneity, stability, total nitrogen, ammonium, nitrite+nitrate, conductivity, ph, wastewater. Classification Open Internal Proprietary Distribution DANAK Eurofins: Stine Ottsen, Peter Rerup

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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 AND STABILITY OF SAMPLES CONCLUSION REFERENCES... 6 ANNEX A LIST OF PARTICIPANTS... 8 ANNEX B SAMPLE PREPARATION ANNEX C CONTROL OF SPIKE VALUES ANNEX D CONTROL OF RECOVERY ANNEX E CONCENTRATION LEVEL ANNEX F HOMOGENEITY AND STABILITY... 24

6 1 INTRODUCTION A proficiency test on the analysis of nitrogen parameters in wastewater was conducted on 17 May The proficiency test was organised by Eurofins Miljø A/S. 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 /1/ on 19 June

7 2 FEATURES OF THE PROFICIENCY TEST Participants in the proficiency test were a total of 57 laboratories from Denmark, Germany, Norway and Sweden. A list of participants is shown in Appendix A. The closing date for submission of results was 1 June All participants except laboratory no. 9, 15, 43, 54, and 57 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 synthetic wastewater, effluent. Sample preparation is described in Appendix B. Table 1 Samples in the proficiency test Sample name Parameters A1/B1 TN, NH 4, NO 2+3, NO 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 synthetic wastewater, effluent. The table also gives the expanded uncertainty of the assigned values. 2

8 Table 2 Assigned and spike value Parameter Abbreviation Unit Typical Range Assigned value Expanded uncertainty of assigned value Spike value Total nitrogen TN mg/l N Ammonium NH 4 mg/l N Nitrite+nitrate NO 2+3 mg/l N Nitrate NO 3 mg/l N Conductivity γ 25 ms/m ph ph Assigned and spike values The content of each parameter in each sample is given an assigned value for the sample with the lower content and a spike value, the spike value being the difference in concentration between the two samples of the sample pair. The assigned and spike values are both calculated from sample preparation for TN, NH 4 and NO 2+3. For conductivity and ph the assigned value is a consensus value for all laboratories based on the median and the spike value the difference between median values for the two samples in the sample pair 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 showed no significant difference between the two for most of the parameters. The test revealed a significant difference between the two for TN. The difference could be attributed to influence from laboratories using methods other than those prescribed by the Danish EPA. The test was repeated after exclusion of the results for method no. 3, 6, 9, 51, 71, 71A, 71B, and 72 and now showed no significant difference. The spike value is therefore kept unchanged 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 showed no significant difference between the two and the control of assigned value at Eurofins confirmed the value (Appendix E). 3

9 3 HOMOGENEITY AND STABILITY OF SAMPLES The homogeneity and stability of samples were tested using the following parameters as indicators: NH 4 NO 3 ph Combined homogeneity and stability test Homogeneity test Combined homogeneity and stability 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), 2. the between bottle standard deviation/variance (the contribution from heterogeneity) and 3. the between days concentration difference (the contribution from instability). Homogeneity is evaluated by comparing the between bottle variance to 0.3 * the standard deviation for evaluation of participants performance (0.3 σ ) specified by the Danish EPA /5/, whereas the stability is evaluated by comparing the concentration change of the samples to 0.3 σ. This test ensures that heterogeneity and instability 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 stability and homogeneity show that the samples are stable and homogeneous. 4

10 4 CONCLUSION The quality control performed, including test of sample stability and 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 TN 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. 5

11 5 REFERENCES /1/ Eurofins A/S, Proficiency test SPIL-2 (2018), 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 on quality criteria for environmental measurements, 24 October 2017 (in Danish). /6/ ISO 13528, Statistical methods for use in proficiency testing by interlaboratory comparison,

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13 ANNEX A LIST OF PARTICIPANTS Laboratory Town Country Analyseenheden, Institut for Agroøkologi, Aarhus Universitet Tjele Denmark AquaDjurs A/S Grenaa Denmark Biofos A/S København K Denmark Bjergmarken R/A, Fors Spildevand Roskilde Roskilde Denmark BlueKolding A/S Kolding Denmark CP Kelco, Spildevandslaboratoriet Ll. Skensved Denmark Eurofins Miljø A/S (3 participants) Vejen Denmark Faxe Forsyning Faxe Denmark Fors Spildevand Holbæk Holbæk Denmark Hedensted Spildevand A/S Daugård Denmark Hillerød Forsyning Spildevand A/S Hillerød Denmark Holstebro Centralrenseanlæg, Vestforsyning Spildevand Holstebro Denmark Kerteminde Forsyning - Spildevand A/S Kerteminde Denmark Klarforsyning, Køge-Egnens Renseanlæg Køge Denmark Melby Renseanlæg Liseleje Denmark Nyborg Renseanlæg Nyborg Denmark Næstved Central Renseanlæg, NK-Spildevand Næstved Denmark Provas Haderslev Denmark Ringkøbing-Skjern Forsyning A/S Skjern Denmark Rønne Renseanlæg Rønne Denmark Slagelse Renseanlæg (5 participants) Slagelse Denmark Spildevandslaboratoriet Esbjerg Denmark Svendborg Centralrenseanlæg Skårup Fyn Denmark Vandmiljø Randers A/S Randers SØ Denmark Vejle Renseanlæg Vejle Denmark Macherey-Nagel GmbH & Co KG Düren Germany Eurofins Environment Testing Norway AS Moss Norway NGIs Miljølaboratorium Oslo Norway Campus Roslagen, Utvecklingscentrum för Vatten Norrtälje Sweden GRYAAB AB Göteborg Sweden Hallsta Pappersbruk Hallstavik Sweden Holmen Paper AB Bravikens Pappersbruk Norrköping Sweden 8

14 Kalmar Vatten AB, VA-lab Kalmar Sweden Klippans Reningsverk Klippan Sweden Laboratoriet vid Smedjeholms avolppsreningsverk Falkenberg Sweden Mjölby Kommun Mjölby Sweden Motala Kommun Motala Sweden Nordic Sugar, Örtofta Sockerbruk Eslöv Sweden Nynäshamn Kommun, VA-avd. Laboratoriet Nynäshamn Sweden Preem AB Göteborg Göteborg Sweden Reningsverket Aggerud Karlskoga Sweden Smurfit Kappa Piteå Piteå Sweden St1 Refinery AB Göteborg Sweden Södra Cell AB Mönsterås Mönsterås Sweden Södra Cell AB, Värö Väröbacka Sweden Södra Cell Mörrum Mörrum Sweden Uddebo Laboratorium Luleå Sweden Vallviks Bruk Vallvik Sweden VIVAB Varberg Sweden Västervik Miljö & Energi AB, Vattenlaboratoriet Västervik Sweden Yara AB Köping Sweden 9

15 ANNEX B SAMPLE PREPARATION Stock solution Prepared from Concentration Stock TN g Disodium edetate, 2H 2 O milli-q water up to g TN: 1881 mg/kg N Stock NH g Ammonium chloride (NH 4 Cl) NH 4 : 2617 mg/kg N milli-q water up to g Stock NO g Potassium nitrate (KNO 3 ) NO 3 : mg/kg N milli-q water up to g Stock NaCl g Sodium chloride (NaCl) milli-q water up to g conductivity: c ms/m Sample Sample prepared from A1 B g stock TN g stock NH g stock NO g stock NaCl milli-q water up to kg 6.01 g stock TN 1.30 g stock NH g stock NO g stock NaCl Sample A1 up to kg Sample Sample prepared from A2/B g Potassium dihydrogen phosphate (KH 2 PO 4 ) g Disodium hydrogen phosphate, 2H 2 O (Na 2 HPO 4, 2H 2 O) milli-q water up to g TN mg/l N NH 4 mg/l N NO 3 mg/l N ph c Conductivity ms/m

16 ANNEX C CONTROL OF SPIKE VALUES Total nitrogen, mg/l N Control of differences within sample pairs Laboratory Difference AB UC A B A B UG Laboratory Difference AB UC No of labs., p 47 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 Difference for sample pair AB is significantly different from 0, and data should be corrected with the difference (in spike value), during execution of Cochran's test. 11

17 Ammonium, mg/l N Control of differences within sample pairs Laboratory Difference AB A B UC UG UG A B UC UG No of labs., p 37 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 12

18 Nitrite+nitrate, mg/l N Control of differences within sample pairs Laboratory Difference AB B B A - 29B UG No of labs., p 13 No of repl., n 2 d s² s t = p (d/s) Sign. level, p(t) No test statistics were found to be significant UG denotes a Grubbs outlier 13

19 Nitrate, mg/l N Control of differences within sample pairs Laboratory Difference AB A B A B UC UC UC No of labs., p 31 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 14

20 Conductivity, ms/m Control of differences within sample pairs Laboratory Difference AB A B UC A - 29B UC No of labs., p 19 No of repl., n 2 d s² 8.07 s 2.84 t = p (d/s) Sign. level, p(t) No test statistics were found to be significant UC denotes a Cochran outlier 15

21 ph, Control of differences within sample pairs Laboratory Difference AB UC A B UC UG A - 29B UC No of labs., p 45 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 16

22 ANNEX D CONTROL OF RECOVERY Total nitrogen, mg/l N Control of recovery, average of results Laboratory Sample pair AB UC A B A B UG Laboratory Sample pair AB UC No of labs., p 47 No of repl., n 2 m s² s Assigned value, µ 4.03 Recovery, % 99.4 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 17

23 Ammonium, mg/l N Control of recovery, average of results Laboratory Sample pair AB A B UC UG UG A B UC UG No of labs., p 37 No of repl., n 2 m s² s Assigned value, µ Recovery, % 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 18

24 Nitrite+nitrate, mg/l N Control of recovery, average of results Laboratory Sample pair AB B B A - 29B UG No of labs., p 13 No of repl., n 2 m s² s Assigned value, µ 1.57 Recovery, % 98.4 t = p (m-µ)/s Sign. level, p(t) No test statistics were found to be significant UG denotes a Grubbs outlier 19

25 Nitrate, mg/l N Control of recovery, average of results Laboratory Sample pair AB A B A B UC UC UC No of labs., p 31 No of repl., n 2 m s² s Assigned value, µ 1.52 Recovery, % t = p (m-µ)/s Sign. level, p(t) No test statistics were found to be significant UC denotes a Cochran outlier 20

26 Conductivity, ms/m Control of recovery, average of results Laboratory Sample pair AB A B UC A - 29B UC No of labs., p 19 No of repl., n 2 m s² s Assigned value, µ 178 Recovery, % 98.2 t = p (m-µ)/s Sign. level, p(t) No test statistics were found to be significant UC denotes a Cochran outlier 21

27 ph, Control of recovery, average of results Laboratory Sample pair AB UC A B UC UG A - 29B UC No of labs., p 45 No of repl., n 2 m s² s Assigned value, µ 7.23 Recovery, % 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 22

28 ANNEX E CONCENTRATION LEVEL Concentration level SPIL-2 (2018) Parameter Unit Sample Bottle no. I II Bottle Sample Assigned Spike Average Average value Measured Assigned Total nitrogen mg/l N A1 15 4,07 4,01 4,04 4,02 4,03 0,87 0, ,98 4,02 4, ,99 4,07 4,03 B1 5 4,85 4,92 4,89 4,90 4, ,89 4,85 4, ,92 4,94 4,93 Ammonium mg/l N A1 15 0,578 0,579 0,58 0,580 0,571 0,115 0, ,580 0,582 0, ,581 0,581 0,58 B1 5 0,695 0,695 0,70 0,695 0, ,695 0,694 0, ,695 0,696 0,70 Nitrite+nitrate / Nitrate mg/l N A1 15 1,59 1,61 1,60 1,61 1,57 0,28 0, ,61 1,63 1, ,61 1,59 1,60 B1 5 1,90 1,88 1,89 1,89 1, ,89 1,88 1, ,88 1,90 1,89 ph A2 2 7,21 7,21 7,21 7,21 7,23 0, ,21 7,22 7, ,22 7,21 7,22 B2 16 7,21 7,22 7,22 7,22 7, ,22 7,22 7, ,23 7,22 7,23 23

29 ANNEX F HOMOGENEITY AND STABILITY PT: SPIL-2 Parameter: NH4 Unit: mg/l N Sigma: 0,038 Responsible for tests: IRL Homogeneity test Date: Stability test Date: Sample x(a) x(b) average sd sd^2 Sample x(a) x(b) B1-6 0,694 0,705 0,7 0,008 0,000 B1-5 0,695 0,695 B1-12 0,706 0,708 0,7 0,001 0,000 B1-34 0,695 0,694 B1-23 0,705 0,713 0,7 0,006 0,000 B1-77 0,695 0,696 B1-28 0,704 0,707 0,7 0,002 0,000 B1-31 0,707 0,706 0,7 0,001 0,000 B1-39 0,705 0,702 0,7 0,002 0,000 For stability B1-45 0,703 0,708 0,7 0,004 0,000 General average (y): 0,695 B1-55 0,706 0,701 0,7 0,004 0,000 /x-y/ = 0, B1-60 0,712 0,709 0,7 0,002 0,000 B1-69 0,705 0,712 0,7 0,005 0,000 B1-75 0,706 0,708 0,7 0,001 0,000 B1-80 0,710 0,711 0,7 0,001 0,000 Conclusions ss = 0, *sigma= 0,0114 For homogeneity /x-y/ = 0, General average (x) 0,7064 Analytical Is s w < 0,15*sigma Sample average sd (s x) 0,0032 quality YES Within-sample sd (s w): 0,0037 Between-samples sd (ss): 0,0019 Homogeneity: Is ss < 0.3*sigma? S L in the Proficiency Test: 0,0225 YES S R in the Proficiency Test: 0,0237 Stability: /x-y/ < 0.3*sigma? YES 24

30 PT: SPIL-2 Parameter: NO3 Unit: mg/l N Sigma: 0,105 Responsible for tests: IRL Homogeneity test Date: Sample x(a) x(b) average sd sd^2 B1-6 1,93 1,95 1,9 0,014 0,000 B1-12 1,96 1,95 2,0 0,007 0,00 B1-23 1,94 1,96 2,0 0,014 0,000 B1-28 1,95 1,94 1,9 0,007 0,000 B1-31 1,91 1,92 1,9 0,007 0,000 B1-39 1,92 1,94 1,9 0,014 0,000 B1-45 1,92 1,95 1,9 0,021 0,000 B1-55 1,95 1,96 2,0 0,007 0,000 B1-60 1,98 1,93 2,0 0,035 0,001 B1-69 1,95 1,96 2,0 0,007 0,000 B1-75 1,98 1,95 2,0 0,021 0,000 B1-80 1,97 1,94 2,0 0,021 0,000 Conclusions ss = 0, *sigma= 0,0315 For homogeneity /x-y/ = 0 General average (x) 1,95 Sample average sd (s x) 0,014 Within-sample sd (s w): 0,017 Between-samples sd (ss): 0,0072 Homogeneity: Is ss < 0.3*sigma? S L in the Proficiency Test: 0,102 YES S R in the Proficiency Test: 0,112 25

31 PT: SPIL-2 Parameter: ph Unit: Sigma: 0,1 Responsible for tests: IRL Homogeneity test Date: Stability test Date: Sample x(a) x(b) average sd sd^2 Sample x(a) x(b) B2-4 7,22 7,22 7,2 0,000 0,000 B2-16 7,21 7,22 B2-10 7,23 7,22 7,2 0,007 0,00 B2-51 7,22 7,22 B2-18 7,21 7,22 7,2 0,007 0,000 B2-70 7,23 7,22 B2-24 7,21 7,22 7,2 0,007 0,000 B2-32 7,22 7,22 7,2 0,000 0,000 B2-38 7,22 7,21 7,2 0,007 0,000 For stability B2-46 7,22 7,22 7,2 0,000 0,000 General average (y): 7,22 B2-52 7,21 7,22 7,2 0,007 0,000 /x-y/ = 0,0025 B2-60 7,21 7,22 7,2 0,007 0,000 B2-66 7,21 7,22 7,2 0,007 0,000 B2-74 7,22 7,21 7,2 0,007 0,000 B2-80 7,22 7,22 7,2 0,000 0,000 Conclusions ss = 0 0.3*sigma= 0,02 For homogeneity /x-y/ = 0,0025 General average (x) 7,22 Analytical Is s w < 0,15*sigma Sample average sd (s x) 0,003 quality YES Within-sample sd (s w): 0,006 Between-samples sd (ss): 0 Homogeneity: Is ss < 0.3*sigma? S L in the Proficiency Test: 0,039 YES S R in the Proficiency Test: 0,041 Stability: /x-y/ < 0.3*sigma? YES 26