Identification and assay of microbial fatty acids during co-composting of active sewage sludge with palm waste by TMAH-thermochemolysis coupled with GC-MS

Abstract

The fatty acids of two composts of active sludge with palm tree waste were investigated by thermochemolysis coupled to gas chromatography-mass spectrometry. This method (tetramethylammonium hydroxide-pyrolysis-gas chromatography-mass spectrometry) allowed the direct determination of total fatty acids (analysed as fatty acid methyl esters: FAMEs) present in the organic matter of the samples without any separation procedures. Mixture A was 1/3 sludge+2/3 palm waste and mixture B was 1/2 sludge+1/2 palm waste. The level of FAMEs rose by 8.4–33.3% and 10.8–13.4% in mixtures A and B, respectively, after 6 months of co-composting. Branched FAMEs of bacterial origin (iC15:0) rose during the thermophilic phase, in mixture A the aC17:0/aC15:0 ratio increased during the co-composting process, also in mixture B the aC16:0/C16:0 ratio rose but only during the thermophilic phase. All the FAMEs identified showed a drop at the end of co-composting except for C18:0 and C16:0. The stabilisation phase was characterised by a significant rise in the length of the aliphatic chains; the carbon preference index thus increased at the end of the composting process, indicating that the final product was proportionally richer in fatty acids of plant origin.