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Anaerobic digestion is sensitive to many environmental factors requiring a robust control of this process. One of the analytical measurements considered as key parameter is the volatile fatty acids (VFAs) content. Total amount of volatile acids (TVFA) to control the relative changes over time has been suggested as a useful tool. However, TVFA does not provide sufficient information to reveal the overall reactor performance, and individual components have been considered of particular interest. Although some attempts have been described as on-line measurements for individual VFAs, normally they are determined by off-line chromatographic techniques (GC and HPLC). A previous interlaboratory study showed the lack of harmonization in the analytical methodologies dealing to individual VFAs, and giving an overall analytical performance rather poor. One of the reasons to justify these results was the inappropriate calibration procedures. It is widely used to check the linearity of the calibration curves based on the correlation and determination coefficients. However, these statistical parameters are erroneously interpreted. The objective of this interlaboratory study was to achieve the harmonization of results. By this way, the use of internal standard methodology (ISTD) should be useful to obtain accurate calibration functions. In addition, five different statistical parameters such as lack of fit test, residual standard deviation, relative standard deviation of the slope, relative standard deviation of the sensitivity and relative error were proposed to evaluate the linearity of calibration curves. Of these, lack of fit was unable to detect appropriately the linearity mainly due to its sensitivity to the precision of analytical results. The rest of statistical parameters reported could be considered as starting point for comparative purposes, being useful as acceptance criteria. The principal advantage of the GC/ISTD analytical methodology was the normalization of the slopes obtained by the participating laboratories, being very helpful to the harmonization of results.

International audience; BACKGROUND: This paper describes results obtained for different participating research groups in an interlaboratory study related to biochemical methane potential (BMP). In this research work, all experimental conditions influencing the test such as inoculum, substrate characteristics and experimental conditions were investigated. The study was performed using four substrates: three positive control substrates (starch, cellulose and gelatine), and one raw biomassmaterial (mung bean) at two different inoculum to substrate ratios (ISR). RESULTS: The average methane yields for starch, cellulose, gelatine and mung bean at ISR of 2 and 1 were 350 ± 33, 350 ± 29, 380 ± 42, 370 ± 36 and 370 ± 35 mL CH4 g−1 VSadded, respectively. The percentages of biotransformation of these substrates into methane were 85 ± 8, 85 ± 7, 88 ± 9, 85 ± 8 and 85 ± 8%, respectively. On the other hand, the first-order rate constants obtained from the experimental datawere 0.24±0.14, 0.23±0.15, 0.27±0.13, 0.31±0.17 and 0.23±0.13 d−1, respectively. CONCLUSION: The influence of inocula and experimental factors was nearly insignificant with respect to the extents of the anaerobic biodegradation, while the rates differed significantly according to the experimental approaches.

This paper describes the results obtained for different participating research groups in an interlaboratory study related to the biochemical methane potential (BMP). In this research work, the full experimental conditions influencing the test such as inoculum, substrate characteristics and experimental conditions were reported. The study was performed using 4 samples: 3 reference substrates (starch, cellulose and gelatine), and 1 raw material (mung bean). The BMP of mung bean was carried out at two inoculum to substrate ratios (ISR), specifically 2 and 1. The methane yields of reference substrates for starch, cellulose and gelatine were 352±33, 353±29 and 382±42 mL/g VSadded, respectively. The percentages of biotransformation of these substrates into methane were 85±8, 85±7 and 88±10%, respectively. On the other hand, the values of methane yields and biodegradability for MB were 373±35 mL CH4/g VSadded and 86±8%, respectively. In addition, the anaerobic digestion of the raw material elected did not show influence on the ISR in the extent of the biotransformation.

Chemical oxygen demand (COD) is a critical analytical parameter in waste and wastewater treatment, more specifically in anaerobic digestion, although little is known about the quality of measuring COD of anaerobic digestion samples. Proficiency testing (PT) is a powerful tool that can be used to test the performance achievable in the participants laboratories, so we carried out a second PT of COD determination in samples considered ‘‘difficult’’ to analyze (i.e. solid samples and liquid samples with high concentrations of suspended solids). The results obtained (based on acceptable z-score values) may be considered satisfactory. When compared with the results of a previous similar scheme, the overall performance improved by around 30%, again demonstrating that analytical performance can be improved by regular participation in PT.

P06.01 Chemical oxygen demand (COD) is a critical analytical parameter in the field ofwaste and wastewater treatment processes, and more specifically in anaerobicdigestion processes. However, little is known about the COD measurement quality ofanaerobic digestion samples. Taking into account the lack of a general standardmethod and high quality certified reference materials (CRMs), currently thetraceability of the COD determination in such samples is not easy to check.Proficiency testing (PT) is a powerful tool that can be used to test the performancethat the participant’s laboratories can achieve. Two PTs related with CODdetermination have been organised, and the results reported have been compared;showing the importance of continuous participation in proficiency testing (PT)schemes in order to improve the results obtained.