Isochrysis galbana and Selenastrum capricornutum, marine and freshwater microalgae species respectively,
were co-digested with sewage sludge under mesophilic and thermophilic conditions. The substrates
and the temperatures significantly influenced biogas production.
Under mesophilic conditions, the sewage sludge digestion produced 451 ± 12 mLBiogas/gSV. Furthermore,
all digesters were fed with I. galbana, or mixed with sludge, resulting in an average of
440 ± 25 mLBiogas/gSV. On the contrary, S. capricornutum produced 271 ± 6 mLBiogas/gSV and in the
mixtures containing sludge produced intermediate values between sludge and microalgae production.
Under thermophilic conditions, the sewage sludge digestion achieved yet the highest biogas yield,
566 ± 5 mLBiogas/gSV. During co-digestion, biogas production decreased when the microalgae content
increased, and for I. galbana and for S. capricornutum it reached minimum values, 261 ± 11 and
185 ± 7 mLBiogas/gSV, respectively. However, no evidence of inhibition was found and the low yields were
attributed to microalgae species characteristics.
The methane content in biogas showed similar values, independently from the digested substrate,
although this increased by approximately 5% under thermophilic condition