This made it difficult to track and target individual bands in the DGGE patterns obtained from the two digester cultures for further analysis.
For this reason, several extensive analyses of foaming causes in full-scale digesters were carried out (see Analysis of foaming causes in full-scale digesters).
Manual excision of the protein spots of interest and tryptic digestion were carried out using an Ettan Digester (GE Healthcare, Uppsala, Sweden) and peptide analysis was carried out using a linear ion trap mass spectrometer (LTQ Mass Spectrometer Thermo-Finnigann Ltd, Hemel Hempstead, UK).
A financial analysis of biogas digesters in the pilot areas of the Tigray region was also conducted to ascertain whether biogas digesters were financially viable for households.
Analysis of samples from digester RTcSS, at three different time points (days 89, 224 and 402) showed a similar pattern, illustrating the stability over time and strengthening the hypothesis that the observed difference between this digester and RM and RS was caused by pre-treatment of the straw.
Quantitative elemental determinations were performed by firstly dissolving the solid samples with a CEM Mars microwave digester (Matthews, NC, USA), followed by analysis with a Thermo Scientific iCAP 6000 series inductively coupled plasma optical emission spectroscopy (ICP-OES, Thermo Scientific, England).
However, despite our analysis showing that biogas digester units can pay for themselves by increased yields and offsetting the costs associated with traditional fuels, farm households continue to use these traditional fuels.
The pathway for conversion of acetate to methane was determined by tracer analysis, involving incubation of digester sludge (20 mL) with [2-C]-acetate (final concentration 0.11 µCi/mL) and monitoring of labelled gases by scintillation counting as described by Schnürer and Nordberg [ 16].
A set of design recommendations for small-scale, cold-climate digesters is presented based on parametric analysis of the validated model for several key design parameters.
In the present work, we have performed a holistic analysis of seven different digesters at two distinct time points (2 × 9 reactors, sampled within 1 week) from Thuringia, Germany (Fig. 1; Table 1).
