Biogas and Volatile Fatty Acids Production: Temperature as a Determining Factor in the Anaerobic Digestion of Spirulina platensis
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This investigation compared the digestion in completely stirred tank reactor (CSTR) of Spirulina platensis at two digestion temperatures (25 and 35 °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 °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 °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.
KeywordsAnaerobic digestion Spirulina Inhibition VFAs Methane
The authors wish to thank the Spanish Ministry of Economy and Competitiveness for the financial support provided through the Grants ENE2013-45416-R and RYC-2014-16823. We would also like to acknowledge the Community of Madrid for the support offered in the framework of the project INSPIRA-1 (S2013/ABI-2783) and in addition to the WWTP of Valladolid (Spain) for kindly suppling the anaerobic sludge samples.
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