2.3. Analytical methods
Samples of waste were taken weekly from the digester and analyzed
for dry solids content (DS – overnight drying at 105 C until
constant weight) and volatile solids content (VS – open-air calcination
at 550 C for 4 h). Water extractions were done in triplicates
by mixing for 2 h in 100 mL of deionised water for a given mass
of raw waste corresponding to 100 g of dry solids (L/S ratio of
10). The suspension was then filtered and analyzed for pH and volatile
fatty acids (VFA) concentration. Standard analytical methods
were employed when applicable (AFNOR NF ISO 11465, NF EN
12879 and NF T 90-008).
Volatile fatty acids were analyzed with an Agilent™ gas chromatograph
equipped with a flame-ionization detector (CPG–FID)
and an HP-FFAP column (30 m 0.25 mm).
Biogas was analyzed with an Agilent™ gas micro-chromatograph
equipped with a thermal conductivity detector (CPG–TCD),
a Poraplot U column (8 m 0.320 mm ID) for CO2 and H2S separation
and a Molsieve 5 Å column (10 m PPU 3 m) for O2, N2, and
CH4 separation.
All analyses were done in triplicates