Proficiency test SPIL-4 (2016) Nitrogen parameters in wastewater (effluent)

Transcription

1 Proficiency test SPIL-4 (2016) Nitrogen parameters in wastewater (effluent) Quality Documentation January 2017

2

3 Proficiency test SPIL-4 (2016) Quality Documentation January 2017 Eurofins Miljø A/S Smedeskovvej 38 DK-8464 Galten Denmark Tlf: Fax: Web: Client Client s representative Environmental laboratories Project Project No Proficiency test SPIL-4 (2016) Authors Maj-Britt Fruekilde Date Approved by Stine Ottsen Quality Documentation Report MBF SJN SJN Revision Description By Checked Approved Date Key words Analytical quality, assigned value, precision, trueness, homogenity, stability, total nitrogen, ammonium, nitrite+nitrate, conductivity, ph, wastewater Classification Open Internal Proprietary Distribution DANAK Eurofins: Maj-Britt Fruekilde, Stine Ottsen

4

5 CONTENTS 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 November 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 December

7 2 FEATURES OF THE PROFICIENCY TEST Participants in the proficiency test were a total of 62 laboratories from Denmark, Norway and Sweden. A list of participants is shown in Appendix A. The closing date for submission of results was 2 December All participants except laboratory No. 11 and 32 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 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 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 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. 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 assigned value for TN is operationally defined and is a consensus value based upon the median for method no. 2, 3 and 7. A list of method identification numbers is found in the report to participants /1/. Assigned values for NH 4, NO 2+3, NO 3, conductivity, and ph are consensus values for all laboratories based on the median. The assigned value for NO 3 (2.03 mg/l N) is higher than the assigned value for NO 2+3 (1.90 mg/l N). This is due to differences in results obtained from standard methods and test kit methods 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 except for TN. 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. 6, 9, 51, 71, 71A, 71B, and 72 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 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 Combined homogeneity and stability 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), 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. 5

11 5 REFERENCES /1/ Eurofins A/S, Proficiency test SPIL-4 (2016), Report to participants, December /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, 29 December 2015 (in Danish). /6/ ISO 13528, Statistical methods for use in proficiency testing by interlaboratory comparison,

12 7 A NNEXES

13 ANNEX A LIST OF PARTICIPANTS Laboratory Town Country AquaDjurs Grenaa Denmark Biofos A/S København K Denmark Bjergmarken R/A, Roskilde Forsyning Roskilde Denmark BlueKolding A/S Kolding Denmark CP Kelco ApS, Spildevandslaboratoriet Ll. Skensved Denmark Din Forsyning Spildevandslaboratorium Esbjerg Denmark Eurofins Miljø A/S Vejen Denmark Faxe Forsyning Faxe Denmark FORCE Technology Holstebro Holstebro Denmark FORS Spildevand Holbæk Holbæk Denmark Frisenette Aps Knebel Denmark Halsnæs Spildevand A/S Liseleje Denmark Hedensted Spildevand A/S (2 participants) Daugård Denmark Holstebro Centralrenseanlæg, Vestforsyning A/S Holstebro Denmark Højmarklaboratoriet A/S Lem St. Denmark Kerteminde Forsyning - Spildevand A/S Kerteminde Denmark Køge-Egnens Renseanlæg Køge Denmark Mosede Renseanlæg - Klarforsyning Greve Denmark Mølleåværkets Driftslaboratorium Lyngby Denmark Nyborg Renseanlæg Nyborg Denmark Næstved Central Renseanlæg, NK-Spildevand Næstved Denmark Provas Haderslev Forsyningsservice A/S Haderslev Denmark Randers Spildevand A/S Randers SØ Denmark Ringkøbing-Skjern Forsyning A/S, Spildevand Skjern Denmark Slagelse Renseanlæg (5 participants) Slagelse Denmark Spildevandslaboratoriet Esbjerg Denmark Svendborg Centralrenseanlæg Skårup Fyn Denmark Vandrens - Stigsnæs Industripark A/S Skælskør Denmark Vejen Renseanlæg Vejen Denmark Vejle Spildevand A/S Vejle Denmark Aalborg Renseanlæg Vest Ålborg Denmark NGI Miljølaboratorium Oslo Norway Arctic Paper Munkedals AB Munkedal Sweden Ernemar Laboratorium Oskarshamn Sweden 8

14 Laboratory Town Country GRYAAB AB Göteborg Sweden Holmen Paper AB Bravikens Pappersbruk Norrköping Sweden Kalmar Vatten AB, VA-lab Kalmar Sweden Kristianstad Kommun Kristianstad Sweden Käppalaverket Lidingö Sweden Mjölby Kommun Mjölby Sweden Motala Kommun Motala Sweden NSVA/Öresundsverket Helsingborg Sweden Nynäshamn Kommun, VA-avdelningen Nynäshamn Sweden Perstorp Oxo AB Stenungsund Sweden Preem AB Göteborg Göteborg Sweden Preemraff Lysekil Lysekil Sweden Rottneros Bruk AB Rottneros Sweden Smurfit Kappa Piteå Piteå Sweden St1 Refinery AB Göteborg Sweden Stora Enso Paper Hyltebruk Sweden Södra Cell Mörrum Mörrum Sweden Tekniska förvaltningen, Verksamhetsstöd VA, Laboratoriet Örebro Sweden Uddebo Laboratorium Luleå Sweden Vallviks Bruk AB Vallvik Sweden Västerviks Miljö & Energi AB, Vattenlaboratoriet Västervik Sweden Växjö Kommun, Tekn. Förvaltn. VA-Lab. Växjö Sweden Yara AB Köping Sweden 9

15 ANNEX B SAMPLE PREPARATION Stock solution Prepared from Concentration Stock TN 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 A g stock NH g stock NO g stock TN Sample B1 up to kg B g stock NH 4 0 g stock NO g stock TN filtered water from Ribe sewage treatment plant up to kg TN mg/l N NH 4 mg/l N (c+0.377) (a ) NO 3 mg/l N b Conductivity ms/m c a b d e Sample Sample prepared from A2/B2 Filtered treated wastewater from Ribe sewage treatment plant. ph f 10

16 ANNEX C CONTROL OF SPIKE VALUES Total nitrogen, mg/l N Control of differences within sample pairs Laboratory Difference AB A B UC A B A B A B A B A B No of labs., p 60 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 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 A B A B A B A B A B UG UG No of labs., p 52 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 A - 18B A B A - 34B A - 38B A B A B UC No of labs., p 21 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 13

19 Nitrate, mg/l N Control of differences within sample pairs Laboratory Difference AB UC 18A UC 18B UC A B A B A B A - 42B A - 50B UC No of labs., p 33 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 UG 18A - 18B UC UC 31A B A - 34B A - 38B A - 42B A - 50B UC UG No of labs., p 22 No of repl., n 2 d 0.22 s² 0.27 s 0.52 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 15

21 ph, Control of differences within sample pairs Laboratory Difference AB A B UG A B A B A - 38B A B A B UG No of labs., p 55 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 16

22 ANNEX D CONTROL OF RECOVERY Total nitrogen, mg/l N Control of recovery, average of results Laboratory Sample pair AB A B UC A B A B A B A B A B No of labs., p 60 No of repl., n 2 m s² s Assigned value, µ 3.18 Recovery, % 99.1 t = p (m-µ)/s Sign. level, p(t) No test statistics were found to be significant UC denotes a Cochran outlier 17

23 Ammonium, mg/l N Control of recovery, average of results Laboratory Sample pair AB A B UC A B A B A B A B A B UG UG No of labs., p 52 No of repl., n 2 m s² s Assigned value, µ Recovery, % 97.9 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 A - 18B A B A - 34B A - 38B A B A B UC No of labs., p 21 No of repl., n 2 m s² s Assigned value, µ 1.90 Recovery, % t = p (m-µ)/s Sign. level, p(t) No test statistics were found to be significant UC denotes a Cochran outlier 19

25 Nitrate, mg/l N Control of recovery, average of results Laboratory Sample pair AB UC 18A UC 18B UC A B A B A B A - 42B A - 50B UC No of labs., p 33 No of repl., n 2 m s² s Assigned value, µ 2.03 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 UG 18A - 18B UC UC 31A B A - 34B A - 38B A - 42B A - 50B UC UG No of labs., p 22 No of repl., n 2 m s² s 3.35 Assigned value, µ 82 Recovery, % 98.9 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 21

27 ph, Control of recovery, average of results Laboratory Sample pair AB A B UG A B A B A - 38B A B A B UG No of labs., p 55 No of repl., n 2 m s² s Assigned value, µ 7.78 Recovery, % 99.8 t = p (m-µ)/s Sign. level, p(t) No test statistics were found to be significant UG denotes a Grubbs outlier 22

28 ANNEX E CONCENTRATION LEVEL Parameter Unit Sample Bottle no. I II Bottle Sample Assigned Spike Average Average value Measured Assigned Total nitrogen mg/l N A1 15 3,70 3,70 3,70 3,70 3,81 0,66 0, ,61 3,71 3, ,73 3,75 3,74 B1 13 3,09 2,98 3,04 3,04 3, ,12 3,02 3, ,04 2,98 3,01 Ammonium mg/l N A1 15 0,235 0,235 0,24 0,235 0,236 0,075 0, ,234 0,236 0, ,235 0,235 0,24 B1 13 0,163 0,164 0,16 0,160 0, ,159 0,157 0, ,160 0,159 0,16 Nitrate mg/l N A1 15 2,54 2,56 2,55 2,56 2,42 0,40 0, ,55 2,56 2, ,56 2,57 2,57 B1 13 2,15 2,16 2,16 2,15 2, ,14 2,17 2, ,16 2,14 2,15 ph A2 6 7,76 7,79 7,78 7,77 7,78 0, ,74 7,77 7, ,78 7,77 7,78 B2 12 7,73 7,74 7,74 7,73 7, ,71 7,72 7, ,74 7,74 7,74 23

29 ANNEX F HOMOGENEITY AND STABILITY PT: SPIL-4 Parameter: NH4 mg/l Unit: N Sigma: 0,036 Responsible for tests: IRL/HEW Homogeneity test Date: Stability test Date: Sample x(a) x(b) average sd sd^2 Sample x(a) x(b) A1-3 0,233 0,236 0,2 0,002 0,000 A1-15 0,235 0,235 A1-7 0,235 0,232 0,2 0,002 0,00 A1-41 0,234 0,236 A1-13 0,236 0,238 0,2 0,001 0,000 A1-85 0,235 0,235 A1-23 0,234 0,238 0,2 0,003 0,000 A1-29 0,236 0,238 0,2 0,001 0,000 A1-39 0,232 0,236 0,2 0,003 0,000 For stability A1-49 0,237 0,240 0,2 0,002 0,000 General average (y): 0,235 A1-55 0,238 0,238 0,2 0,000 0,000 /x-y/ = 0, A1-64 0,235 0,238 0,2 0,002 0,000 A1-69 0,239 0,243 0,2 0,003 0,000 A1-80 0,235 0,236 0,2 0,001 0,000 A1-86 0,235 0,235 0,2 0,000 0,000 Conclusions ss = 0,002 For homogeneity /x-y/ = 0, General average (x) 0,24 Analytical Is s w < 0,15*sigma Sample average sd (s x) 0,002 quality YES Within-sample sd (s w): 0,002 Between-samples sd (ss): 0,0016 Homogeneity: S L in the Proficiency Test: 0,018 YES S R in the Proficiency Test: 0,019 Stability: Is ss < 0.3*sigma? /x-y/ < 0.3*sigma? YES 0.3*sigma = 0,01 24

30 PT: Parameter: SPIL-4 NO3 Unit: mg/l Sigma: 0,136 Responsible for tests: IRL/HEW Homogeneity test Date: Stability test Date: Sample x(a) x(b) average sd sd^2 Sample x(a) x(b) A1-3 2,52 2,56 2,5 0,028 0,001 A1-15 2,54 2,56 A1-7 2,49 2,57 2,5 0,057 0,003 A1-41 2,55 2,56 A1-13 2,53 2,58 2,6 0,035 0,001 A1-85 2,56 2,57 A1-23 2,51 2,53 2,5 0,014 0,000 A1-29 2,50 2,56 2,5 0,042 0,002 A1-39 2,49 2,53 2,5 0,028 0,001 For stability A1-49 2,49 2,5 2,5 0,007 0,000 General average (y): 2, A1-55 2,50 2,53 2,5 0,021 0,000 /x-y/ = 0,035 A1-64 2,53 2,55 2,5 0,014 0,000 A1-69 2,52 2,49 2,5 0,021 0,000 A1-80 2,53 2,48 2,5 0,035 0,001 A1-86 2,52 2,51 2,5 0,007 0,000 Conclusions ss = 0 For homogeneity /x-y/ = 0,035 General average (x) 2,5 Sample average sd (s x) 0,018 Within-sample sd (s w): 0,030 Between-samples sd (ss): 0 Homogeneity: S L in the Proficiency Test: 0,14 YES S R in the Proficiency Test: 0,145 Stability: Is ss < 0.3*sigma? /x-y/ < 0.3*sigma? YES 0.3*sigma = 0,04 25

31 PT: Parameter: SPIL-4 ph Unit: Sigma: 0,072 Responsible for tests: IRL/HEW Homogeneity test Date: Sample x(a) x(b) average sd sd^2 B2-8 7,98 8,00 8,0 0,014 0,000 B2-15 7,97 8,01 8,0 0,028 0,00 B2-20 7,96 8,01 8,0 0,035 0,001 B2-27 7,99 8,00 8,0 0,007 0,000 B2-33 8,02 7,98 8,0 0,028 0,001 B2-41 7,99 7,94 8,0 0,035 0,001 B2-46 7,98 8,01 8,0 0,021 0,000 B2-53 7,95 7,98 8,0 0,021 0,000 B2-58 8,00 8,03 8,0 0,021 0,000 B2-65 8,01 8,02 8,0 0,007 0,000 B2-70 8,02 8,00 8,0 0,014 0,000 B2-84 8,01 7,99 8,0 0,014 0,000 Conclusions ss = 0,004 For homogeneity /x-y/ = 0 General average (x) 7,99 Sample average sd (s x) 0,017 Within-sample sd (s w): 0,023 Between-samples sd (ss): 0,0041 Homogeneity: S L in the Proficiency Test: 0,152 YES S R in the Proficiency Test: 0,161 Is ss < 0.3*sigma? 0.3*sigma = 0,02 26