Harmonization of VFAs measurement by GC: something more than R2 to evaluate the calibration function

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.Peer Reviewe

Towards a standardization of biomethane potential tests

8 PáginasProduction of biogas from different organic materials is a most interesting source of renewable energy. The biomethane potential (BMP) of these materials has to be determined to get insight in design parameters for anaerobic digesters. A workshop was held in June 2015 in Leysin Switzerland to agree on common solutions to the conundrum of inconsistent BMP test results. A discussion covers actions and criteria that are considered compulsory ito accept and validate a BMP test result; and recommendations concerning the inoculum substrate test setup and data analysis and reporting ito obtain test results that can be validated and reproduced.The workshop in Leysin, Switzerland, has been financed by the Swiss Federal Office for Energy, and co-sponsored by Bioprocess Control Sweden AB, Lund, Sweden. The authors thank Alexandra Maria Murray for editing the English

Genotoxic effect induced by hydrogen peroxide in human hepatoma cells using comet assay

Background: Hydrogen peroxide is a common reactive oxygen intermediate generated by variousforms of oxidative stress. Aims: The aim of this study was to investigate the DNA damage capacity ofH2O2 in HepG2 cells. Methods: Cells were treated with H2O2 at concentrations of 25 μM or 50 μM for5 min, 30 min, 40 min, 1 h or 24 h in parallel. The extent of DNA damage was assessed by the cometassay. Results: Compared to the control, DNA damage by 25 μM and 50 μM H2O2 increasedsignificantly with increasing incubation time up to 1 h, but it was not increased at 24 h. Conclusions:Our Findings confirm that H2O2 is a typical DNA damage inducing agent and thus is a good modelsystem to study the effects of oxidative stress. DNA damage in HepG2 cells increased significantlywith H2O2 concentration and time of incubation but later decreased likely due to DNA repairmechanisms and antioxidant enzyme

Enhancing solubilisation and methane production kinetic of switchgrass by microwave pretreatment

This study investigated the effects of microwave pretreatment of switchgrass in order to enhance its anaerobic digestibility. Response surface analysis was applied to screen the effects of temperature and time of microwave pretreatment on matter solubilisation. The composite design showed that only temperature had a significant effect on solubilisation level. Then the effects of the microwave pretreatment were correlated to the pretreatment temperature. The sCOD/tCOD ratio was equal to 9.4% at 90 \ub0C and increased until 13.8% at 180 \ub0C. The BMP assays of 42 days showed that microwave pretreatment induced no change on the ultimate volume of methane but had an interesting effect on the reaction kinetic. Indeed, the time required to reach 80% of ultimate volume CH4 is reduced by 4.5 days at 150 \ub0C using the microwave pretreatment.Peer reviewed: YesNRC publication: Ye

Harmonization of the quantitative determination of volatile fatty acids profile in aqueous matrix samples by direct injection using gas chromatography and high-performance liquid chromatography techniques: Multi-laboratory validation study

The performance parameters of volatile fatty acids (VFAs) measurements were assessed for the first time by a multi-laboratory validation study among 13 laboratories. Two chromatographic techniques (GC and HPLC) and two quantification methods such as external and internal standard (ESTD/ISTD) were combined in three different methodologies GC/ESTD, HPLC/ESTD and GC/ISTD. Linearity evaluation of the calibration functions in a wide concentration range (10-1000mg/L) was carried out using different statistical parameters for the goodness of fit. Both chromatographic techniques were considered similarly accurate. The use of GC/ISTD, despite showing similar analytical performance to the other methodologies, can be considered useful for the harmonization of VFAs analytical methodology taking into account the normalization of slope values used for the calculation of VFAs concentrations. Acceptance criteria for VFAs performance parameters of the multi-laboratory validation study should be established as follows: (1) instrument precision (RSDINST≤1.5%); (2) linearity (R2≥0.998; RSDSENSITIVITY≤4%; REMAX≤8%; REAVER≤ 3%); (3) precision (RSD≤1.5%); (4) trueness (recovery of 97-103%); (5) LOD (≤3mg/L); and (6) LOQ (10mg/L

Biochemical methane potential (BMP) of solid organic materials: results obtained from an international interlaboratory study

IWA-487