Changes in the VOAs/TAC values during the AD of casein (blue line) and blood (red line).

<p>The protein loads administered at weekly intervals are indicated by the blue (casein) and red (blood) columns. The vertical black line denotes the end of the adaptation period, i.e. feeding with a constant, low protein dose. The gray area indicates the VOAs/TAC range under optimal operational conditions.</p

Biogas production from pig blood.

<p>The fed-batch reactors were fed with increasing amounts of protein at weekly intervals. The protein dosages are shown by red line. The columns indicate the specific biogas yield generated during each week. Dashed line indicates biogas productivity according to the batch test.</p

Changes induced in the Bacteria microbial community composition by adaptation to casein as sole carbon source.

<p>The relative abundances of the taxonomic groups were determined in week 0 (light-blue columns), week 5 (medium-blue columns), week 9 (dark-blue columns) and week 12 (purple columns).</p

Comparison of acetate accumulation during growth on casein (blue line) or on pig blood (red line) in fed-batch AD.

<p>The vertical black line indicates the end of the adaptation period, i.e. feeding with a constant, low protein dose.</p

The amino acids of proposed proton transfer pathway are highly conserved.

<p>T.r.: <i>Thiocapsa roseopersicina</i> HynL, A.v.: <i>Allochromatium vinosum</i> HydL, R.c.: <i>Rhodobacter capsulatus</i> HupL, M.c.: <i>Methylococcus capsulatus</i>, B.j.: <i>Bradyrhizobium japonicum</i> HupL, Rh.l.: <i>Rhizobium leguminosarum</i> HupL, R.e.: <i>Ralstonia eutropha</i> H16 HoxG, D.v.: <i>Desulfovibrio vulgaris</i> Miyazaki F HynB, D.g.: <i>Desulfovibrio gigas</i> HynB, D.f.: <i>Desulfovibrio fructosovorans</i> HynB. The upper and lower numbering refers to the large subunits of <i>T. roseopersicina</i> and <i>D. vulgaris</i> enzymes, respectively.</p

Scaling-up of AD of blood protein.

<p>Weekly average specific biogas yields were determined in completely stirred tank reactors of 5 L (blue columns) or 50 L (red columns). The X-axis indicates the weekly substrate doses for the 5 L (first number) and 50 L (second number) reactors. Note that both reactors were fed with the same amount of substrate for 3 weeks and the weekly dose was raised afterwards.</p

Changes induced in the Archaea microbial community composition by adaptation to pig blood as sole carbon source.

<p>The relative abundances of the taxonomic groups were determined on week 0 (light-brown columns), week 8 (medium-brown columns) and week 12 (dark-brown columns).</p

Bacterial strains.

<p>Indicated strains and plasmids are from Stratagene, La Jolla, CA, USA.</p

Accumulation of ammonium during the AD of casein (blue line) and pig blood (red line).

<p>The gray area indicates the ammonium-nitrogen concentration range under optimal operational conditions. The vertical black line denotes the end of the adaptation period, i.e. feeding with a constant, low protein dose.</p

Changes in the volatile fatty acid accumulation during the AD of casein.

<p>The colors indicate the acetate (blue), propionate (red), isobutyrate (green), butyrate (violet) and isovalerate (light blue) concentrations. The gray area illustrates the acetate concentration range under optimal operational conditions. The vertical black line denotes the end of the adaptation period, i.e. feeding with a constant, low protein dose (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0077265#pone-0077265-g001" target="_blank">Figures 1</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0077265#pone-0077265-g004" target="_blank">4</a>).</p