Supporting information accompanying the manuscript:

Transcription

1 Supporting information accompanying the manuscript: Determination of COD in heterogeneous solid or semisolid samples using a novel method combining solid dilutions as preparation step followed by optimized closed reflux and colorimetric measurement Joan Noguerol-Arias 1 *, Angela Rodríguez-Abalde 1, Eva Romero-Merino 1, and Xavier Flotats 1,2 1 GIRO Technological Centre. Rambla Pompeu Fabra 1, E Mollet del Valles, Barcelona, Spain. 2 Department of Agrifood Engineering and Biotechnology, Universitat Politècnica de Catalunya (UPC), Parc Mediterrani de la Tecnologia Edifici D-4, E Castelldefels, Barcelona, Spain Corresponding author: joan.noguerol@giroct.irta.cat Table of content of SI Supporting Material and Methods..S2 Table S-1....S6 Table S-2....S6 Table S-3....S7 Table S-4....S7 Table S-5....S8 S-1

2 Supporting Material and Methods Materials Digestion of samples were carried out in 40 mm 300 mm glass digestion vessels and 635 mm jacket condensers with ground-glass joint, or in 13 mm x 100 mm borosilicate culture tubs, with TFE-lined screw caps, for open or closed reflux method, respectively. Erlenmeyer flasks of 100 ml nominal capacity and burettes of 10 ml nominal capacity were used for titrimetric method. Apparatus Digestion of samples were carried out at 150±2 ºC in a Bloc Digest-20 from J.P. Selecta (Spain) or LT 200 thermostat from Hach Lange (Germany), for open or closed reflux method, respectively. COD determinations using colorimetric method were carried out using a DR 2800 Spectrophotometer from Hach Lange. For theoretical COD determination, elemental analysis was carried out using a Truespec CHNS from Leco (USA). Lipids content was determined by an automatic soxhlet extraction system using a Soxtec 2050 from Foss (Denmark). Nitrogen NH 4 -N determination was carried out by automatic distillation Büchi B-324 unit (Switzerland), and automatic titration using a 702 SM Titrino from Metrohm (Switzerland). Reagents Potassium hydrogen phthalate (KHP): primary standard grade Panreac brand, standard for COD determination internationally accepted. Digestion reagent containing potassium dichromate (K 2 Cr 2 O 7 ) 0.24 or 0.5 N primary standard grade, mercuric sulfate (HgSO 4 ), and sulfuric acid 95-97%; and also sulfuric acid reagent containing 1% of silver sulfate (Ag 2 SO 4 ) in sulfuric acid 95-97% reagent grade Scharlau brand, were prepared following indications of Standard method 5220 B-open reflux 6. Ferroin solution M redox indicator and ferrous ammonium sulfate (FAS) solution 0.25 N, used for titrimetric method were prepared following the same indications. Sodium hydroxide solution 40% W/V extra pure, boric acid solution 4% W/V and hydrochloric acid solution 0.1 Mol/L (0.1 N) Scharlau brand were used for NH 4 -N determination. EDTA calibration sample LECO corporation brand was used for calibration of Truespec CHNS from LECO used for elemental analysis. n-hexane 96% reagent grade, ACS, Reag. Ph Eur Scharlau brand was used for lipids determination. All these reagents were used for theoretical COD determination. Samples Pig slaughterhouse waste (PSW) is a heterogeneous substrate characterized by high COD due to its high concentration of lipids and proteins. With the aim of increasing homogeneity, the samples were S-2

3 previously lyophilized, removing water content by sublimation. Then, samples were grinded by a small mincer in order to obtain a more homogeneous consistency. Other different solid or semi-liquid wastes (SSW) were also studied, such as solid fraction of sewage sludge from a municipal wastewater treatment plant, effluent from an anaerobic digestion reactor treating different organic waste, waste from an enzymatic hydrolysis process of animal byproduct and two different mixtures of animal by-products, meat and bone meal, pig manure and sewage sludge. In all these cases the substrates were not lyophilizated. Certified reference materials (CRM) used for final assessment of precision and accuracy were: - Sample CRM-1 was a sewage sludge provided by LGC Promochem as certified reference material (CRM ), produced and certified by Resource Technology Corporation (USA and UK). - Sample CRM-2 was also a sewage sludge produced by Resource Technology Corporation (USA and UK) and provided for characterization as a new certified reference material (CRM SeWS). Procedure APHA AWWA WPCF standard method 5220 B-open reflux titrimetric (SM-ORT) After joining the condenser in the digestion vessels and placing the vessels in the block heater fixed at 150 C for 2 h, the tubes were removed and cooled at room temperature. Finally, 25 ml of the digestion vessel were transferred to 100 ml Erlenmeyer flask, 25 ml of distilled water and one or two drops of ferroin indicator solution were added. Then, the excess of potassium dichromate was titrated with ferrous ammonium sulfate (FAS) 0.25 N until the color changes from blue-green to reddish-brown. A blank containing 50 ml of distilled water was run simultaneously for each group of samples. Calculation: the chemical oxygen demand of a dry solid sample was calculated using the following equation: COD ( g O 2 Kg 1 ( FAS ) = BL FAS W SAMPLE SAMPLE ) x N where FAS BL is the volume of FAS used in the titration of blank sample (ml); FAS SAMPLE is the volume of FAS used in the titration of the solid sample (ml); N FAS is the concentration of reducing reagent (N); and W SAMPLE is the weight of solid sample (g). Further raw sample was used to determine the substrate moisture and the dry sample weight. Kit LCK914 COD Method (LCK) The tubes were heated at 150 ºC for 2 h in a thermostat. After allowing the tubes to cool at room temperature, COD were determined by measuring the absorbance of the digested assay solution at 605 nm on a spectrophotometer, and interpolating in a standard curve (5 65 g O 2 Kg 1 ), with KHP as FAS x 8 S-3

4 the chemical standard reference and correlated to the COD level taking into account that the theoretical oxygen demand of substrate is mg O 2 mg 1. If samples, standards and blanks were run under same conditions, COD level in sample was calculated as follows: 1 COD ( g O2 Kg ) = where W SAMPLE : weight of solid sample (g). Calculations Interlaboratory study (PT) of COD mg O 2 in final volume x 200 W SAMPLE The performance of each laboratory in an interlaboratory study (PT) of COD measurements was assessed by the internationally accepted z-score calculated by the following equation: where X i is the experimental value, A is the assigned or true value and SD is the standard deviation. Theoretical oxygen demand (COD- theo ) The calculation of the COD-1 theo was determined, defining it as the stoichiometric amount of oxygen required to oxidize a compound to end products, mainly CO 2 and H 2 O, although other additional products should be produced when the organic compound contains heteroatom in the molecule. The chemical composition of KHP and two different lyophilizated pig substrates were determined by means of elemental analysis using a Leco Truespec CHNS. The data of chemical compositions was determined by three replicates samples of each substrate. Then, COD-1 theo was calculated using the empirical equation detailed in the ISO The calculation of the COD-2 theo was also determined, where COD-2 theo was estimated by the sum of the COD values coming from the protein and fat fractions, main constituents of the pig slaughterhouse waste used for this paper. Fat determination was carried out by an automatic soxhlet extraction system using a Soxtec 2050, by EPA method 9071b n-hexane extractable material (HEM) for sludge, sediment, and solid samples 2. Protein concentration was estimated from the organic nitrogen content using a factor of 6.38 g protein g -1 Norg, as suggested by AOAC 3. Organic nitrogen was estimated from elementary nitrogen analysis result determined using a Leco Truespec CHNS 4 and subtracting NH 4 -N. NH 4 -N was analyzed using a B-324 distillation unit from Büchi, by automatic titration using a 702 SM Titrino from Metrohm, by Standard Methods 4500-NH 3 B Preliminary Distillation Step and 4500-NH 3 C Titrimetric method 5. S-4

5 The COD values were obtained using different indexes obtained from the oxidations of a standard protein (C 5 H 7 NO 2 ) and glycerol trioleate as standard fat (C 57 H 104 O 6 ) 6, 7, that is, 1 g of protein is considered equivalent to 1.42 g COD and 1 g of fat equivalent to 2.90 g COD. SUPPORTING REFERENCES (1) ISO 10707, Water quality. Evaluation in an aqueous medium of the "ultimate" aerobic biodegradability of organic compounds. Method by analysis of biochemical oxygen demand (closed bottle test), (1994). (2) EPA Method 9071B, n-hexane extractable material (HEM) for sludge, sediment, and solid samples. Revision 2 April (3) AOAC Official Method , Nitrogen (Total) in Milk, Kjeldahl Methods, First Action 1991, Final Action 1994, AOAC International, 2006 (4) AOAC Official Method , Crude Protein in Meat and Meat Products Including Pet Foods, Combustion Method, First Action 1992, AOAC International, 2006 (5) 4500-NH 3 B Preliminary Distillation Step and 4500-NH 3 C Titrimetric method. APHA AWWA WPCF, Standard Methods for the Examination of Water and Wastewater, 21st edition, Washington, DC, (6) Angelidaki, I. Anaerobic Biodegradability of Macropollutants, Workshop on Harmonization of Anaerobic Biodegradation, Activity and Inhibition Assays, Lago d Orta, Italy, (7) Angelidaki, I. and Sanders, W. Reviews in Environmental Science and Bio/Technology, 2004, 3, S-5

6 Table S-1. Effect of Cr 2 O 7 K 2 concentration in the digestion reagent and of the digestion reagent / sulfuric acid reagent ratio on the slope and linear range of calibration curve for the SM-CRC method Cr 2 O 7 K 2 (N) V digestion /V sulfuric (ml) Slope Upper Linear Range (g O 2 Kg -1 ) Observations < / < < * < < 85 Cr 2 O 7 K 2 Precipitation / < 75 Cr 2 O 7 K 2 Precipitation < 65 Kit LCK 914 (**) < 60 (*) Concentration of reagents recommended in SM-CRC standard method (**) Unknown Table S-2. Lower and upper linear range (LR) of the optimized SM-CRC method, depending on the amount of weighted sample used Sample Weight (mg) Lower LR (g O 2 Kg -1 ) Upper LR (g O 2 Kg -1 ) ,300 S-6

7 Table S-3. TS, VS and elemental composition of two different substrates used for COD-1 theo assessment Sample TS (%) VS (%) Elemental composition (%) C H N O S Estimated formula PSW C 536 H 1138 N 19 O 116 S 1 PSW C 547 H 1047 N 33 O 95 S 1 Table S-4. Lipid and protein composition of two different substrates used for COD-2 theo assessment Sample Lipids COD Lipids (go 2 Kg -1 TS) N tot NH 4 -N N org Protein COD Protein (go 2 Kg -1 TS) PSW , PSW , S-7

8 Table S-5. Experimental COD values obtained from different substrates using SD/SM-CRC optimized method Sample Sample Type Dilution SSW-2 SSW-3 SSW-4 SSW-5 SSW-6 Solid fraction from a municipal sewage treatment plant Wasted enzymatically hydrolyzed animal byproducts Efluent of anaerobic reactor Mixture of animal byproducts and meat and bone meal Mixture of pig manure, sewage sludge and meat and bone meal COD (g O 2 Kg -1 TS) 2,356 2,423 2,316 2,142 2,248 2,126 1,417 1,281 1,324 1,606 1,568 1,638 1,927 1,877 1,967 Mean SD CV (%) 2, , , , , S-8