The results obtained confirm that hydrogen yields of a mixture
of organic waste depend largely on the specific carbohydrate content,
i.e. the presence of carbohydrate rich compounds. The three
mixtures used during hydrogen production tests were characterised
by similar TOC, COD and TKN values, but nevertheless resulted
in consistently different hydrogen yields. It can be deduced that
the source and type of organic fractions are the main factors affecting
hydrogen production rather than TOC, COD and TKN contents
of the organic waste.
The data obtained from BMP tests (Table 6) agree with observation
made from the data reported in Fig. 2. Samples characterised
by the highest hydrogen yields presented the lowest methane
potential productions and vice versa. Likewise, a higher variability
of hydrogen production was found compared to the variability of
data from BMP tests. These results confirm that the potential variability
of waste composition over time might represent a more
significant issue in the management of full-scale plant for the production
of biohydrogen, than the variability of methane potential
productions
the contrary the lowest hydrogen production potential was measured
for mixture Mix B characterised by the highest content of
MFC. Sample Mix C presented a hydrogen production yield that
was intermediate between the yields of the other two samples,
but nevertheless closer to the yield of sample Mix A. Taken
together, the fractions F, V and U constituted approximately 80%
of all samples referred to wet weight. A variation in amount of
the BP fraction from 19% to 12% (on wet weight basis) produced
a decrease in hydrogen production from 85 ml H2/gVS to 65 ml
H2/gVS. A further change from 12% to 2% (on wet weight basis)