Methane production from microalgae
C. kessleri and C. vulgaris grown in wastewater were recovered from
the PBR and anaerobically digested in order to evaluate their potential
as substrate for methane production. The methane production curves
from C. kessleri and C. vulgaris are shown in Fig. 4.
Themethane production was similar for bothmicroalgae species during
the first four days,becomingdifferent after thisperiod. On the6thday,
the methane production from C. vulgaris was 11% higher than from
C. kessleri. This difference progressively increased until the end of the experiment,
when it reached 20%. The final methane production from
C. kessleri and C. vulgariswere 346 ± 3 mLCH4/gVS and 415 ± 2 mLCH4/
gVS respectively. For C. kessleri, it has been reported 218 mLCH4/gVS
under mesophilic conditions; for C. vulgaris digestion, 240 mLCH4/gVS
and 286 mLCH4/gVS were reported after 28 days and 49 days mesophilic
conditions respectively [4]; however, there is no literature relating to
the anaerobic digestion of microalgae cultivated in wastewaters. These
methane productions were clearly exceeded in the present experiment.
What is more, the methane productions obtained are higher than those
reported for several microalgae species [4]. Evenmore interesting results
appear when comparing the methane production from microalgae with
substrates commonly used in anaerobic digestion, such as sewage sludge,
which under similar conditions produced around 350mLCH4/gVS [19]. The
methane production from several substrates such as municipal solid
wastes, swine manure,maize silage and straw, etc., was also exceeded [4].
The theoretical methane production resulted in 533 ± 5 mLCH4/gVS
and 567 ± 1 mLCH4/gVS for C. kessleri and C. vulgaris respectively. The
biodegradability resulted in 65% and 66% for C. kessleri and C. vulgaris respectively,
higher than the values reported for other microalgae species