Mesophilic and thermophilic anaerobic laboratory-scale digestion of Nannochloropsis microalga residues.

This paper studies methane production using a marine microalga, Nannochloropsis sp. residue from biodiesel production. Residue cake from Nannochloropsis, oils wet-extracted, had a methane potential of 482LCH4kg(-1) volatile solids (VS) in batch assays. However, when dry-extracted, the methane potential of residue cake was only 194LCH4kg(-1) VS. In semi-continuous reactor trials with dry-extracted residue cake, a thermophilic reactor produced 48% higher methane yield (220LCH4kg(-1)VS) than a mesophilic reactor (149LCH4kg(-1)VS). The thermophilic reactor was apparently inhibited due to ammonia with organic loading rate (OLR) of 2kgVSm(-3)d(-1) (hydraulic retention time (HRT) 46d), whereas the mesophilic reactor performed with OLR of 3kgVSm(-3)d(-1) (HRT 30d). Algal salt content did not inhibit digestion. Additional methane (18-33% of primary digester yield) was produced during 100d post-digestion.

Lipid profile characterization of wastewaters from different origins.

Lipids in wastewaters are potential raw material for renewable diesel, but may complicate biological treatment of wastewaters. The lipid composition of palm oil mill effluent (POME), chemithermomechanical pulp mill (CTMP) wastewater and municipal wastewater (MWW) was studied with a combination of thin-layer chromatography and nuclear magnetic resonance. Gravimetrically determined content of extracted lipids from the solids of POME and CTMP wastewater were 8.4 ± 1.2 g/L (19.6 ± 0.8% of dry weight) and 0.17-0.23 g/L (12.4-18.5%), respectively, while MWW contained 0.021 ± 0.002 g/L (9.3 ± 1.4%) of lipids. All lipid extracts contained mono-, di- and triacylglycerols (TAGs) and free fatty acids (FFAs). In POME, lipids were mostly TAGs (11.5 ± 0.2 µmol/10 mg of lipid extract). In CTMP and MWW lipid composition was more diverse than in POME containing also sterol derivatives and fatty acid methyl esters and the main lipids were FFAs.