Anaerobic digestion of organic matter represents an important factor for economical management of municipal sewage plants. On the other hand, efficient anaerobic digestion does not only represent a suitable solution for sludge disposal, but also provides additional energy gain from biogas use in cogeneration. In the present chapter, the results of a lab-scale investigation of sewage sludge treatment in separate two-phase anaerobic digesters, are described. The first series of digesters was used for hydrolysis, acidification and acetogenesis, whereas the second one was employed for methanogenesis. The same raw mixed sludge (primary and secondary) was used to feed the first series of digesters. Cultures samples were taken daily from both digesters and chemically analyzed to monitor the fermentation process and to confirm steady-state conditions. Soluble chemical oxygen demand (SCOD), total suspended solids (TSS), volatile suspended solids (VSS) and volatile fatty acids (VFA) significantly differed in both digesters, being considerable higher in the acetogenic digesters. In contrast, the low SCOD and VFA values found in methanogenic digesters, indicated that a part of organic matter was converted into methane. VFA mainly consisted of acetic, propionic, iso-butyric, butyric, iso-valeric, valeric and caproic and they prevailed in acetogenesis; this implied that homoacetogenic and acetate/butyrate fermentations were predominant in this process. In methanogenesis, acetate and n-butyrate were completely degraded, while propionate degradation seemed to be time-dependent. These lipid and fatty acid variations were also supported by the FT-IR spectra of sludges. Scanning electron microscopy analysis evinced that sludges from acetogenic and methanogenic digesters were characterized by a different morphology. In acetogenesis, the sludge surface was densely packed with a smooth regular surface, probably due to the high content of lipids produced in this process phase. In methanogenesis, the porous spatial arrangement of the sludge surface was a less stable structure with broken parts and an irregular fissured surface, confirming the gas production.
A CHEMICAL AND STRUCTURAL STUDY OF SEWAGE SLUDGES FROM A TWO PHASE ANAEROBIC DIGESTION PLANT
FRANCIOSO, ORNELLA;RODRIGUEZ ESTRADA, MARIA TERESA;SAVIOLI, STEFANO;PISI, ANNAMARIA;PALENZONA, DOMENICO
2011
Abstract
Anaerobic digestion of organic matter represents an important factor for economical management of municipal sewage plants. On the other hand, efficient anaerobic digestion does not only represent a suitable solution for sludge disposal, but also provides additional energy gain from biogas use in cogeneration. In the present chapter, the results of a lab-scale investigation of sewage sludge treatment in separate two-phase anaerobic digesters, are described. The first series of digesters was used for hydrolysis, acidification and acetogenesis, whereas the second one was employed for methanogenesis. The same raw mixed sludge (primary and secondary) was used to feed the first series of digesters. Cultures samples were taken daily from both digesters and chemically analyzed to monitor the fermentation process and to confirm steady-state conditions. Soluble chemical oxygen demand (SCOD), total suspended solids (TSS), volatile suspended solids (VSS) and volatile fatty acids (VFA) significantly differed in both digesters, being considerable higher in the acetogenic digesters. In contrast, the low SCOD and VFA values found in methanogenic digesters, indicated that a part of organic matter was converted into methane. VFA mainly consisted of acetic, propionic, iso-butyric, butyric, iso-valeric, valeric and caproic and they prevailed in acetogenesis; this implied that homoacetogenic and acetate/butyrate fermentations were predominant in this process. In methanogenesis, acetate and n-butyrate were completely degraded, while propionate degradation seemed to be time-dependent. These lipid and fatty acid variations were also supported by the FT-IR spectra of sludges. Scanning electron microscopy analysis evinced that sludges from acetogenic and methanogenic digesters were characterized by a different morphology. In acetogenesis, the sludge surface was densely packed with a smooth regular surface, probably due to the high content of lipids produced in this process phase. In methanogenesis, the porous spatial arrangement of the sludge surface was a less stable structure with broken parts and an irregular fissured surface, confirming the gas production.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
