Biogas and Volatile Fatty Acids Production: Temperature as a Determining Factor in the Anaerobic Digestion of Spirulina platensis

This investigation compared the digestion in completely stirred tank reactor (CSTR) of Spirulina platensis at two digestion temperatures (25 and 35 degrees C). This comparison was conducted in terms methane production, organic matter (COD) removal, volatile fatty acids (VFAs) production and nitrogen mineralization. In mesophilic range, 42%tCOD removal and methane yield of 107 mL CH4 g VSin(-1) was attained. Due to the high digestate ammonium concentration, methane yield diminished along digestion time and VFAs accumulated. At 25 degrees C, methane production was negligible while 23%tCOD was removed. Ammonium concentration and nitrogen mineralization (+/- 70%) remained as high as in mesophilic range and thus, VFAs accumulation was also observed at 25 degrees C. Low temperature digestion shifted, however, the VFAs profile. This study shows that S. platensis might not be an optimum substrate for biogas production due to their high protein content. Nevertheless, VFAs can be used as building blocks for the production of fuels or chemicals.