title: Single-phase and two-phase anaerobic digestion of fruit and vegetable waste: comparison of start-up, reactor stability and process performance.
abstract: Single-phase and two-phase digestion of fruit and vegetable waste were studied to compare reactor start-up, reactor stability and performance (methane yield, volatile solids reduction and energy yield). The single-phase reactor (SPR) was a conventional reactor operated at a low loading rate (maximum of 3.5 kgVS/m3 d), while the two-phase system consisted of an acidification reactor (TPAR) and a methanogenic reactor (TPMR). The TPAR was inoculated with methanogenic sludge similar to the SPR, but was operated with step-wise increase in the loading rate and with total recirculation of reactor solids to convert it into acidification sludge. Before each feeding, part of the sludge from TPAR was centrifuged, the centrifuge liquid (solubilized products) was fed to the TPMR and centrifuged solids were recycled back to the reactor. Single-phase digestion produced a methane yield of 0.45 m3 CH4/kg VS fed and VS removal of 83%. The TPAR shifted to acidification mode at an OLR of 10.0 kgVS/m3 d and then achieved stable performance at 7.0 kgVS/m3 d and pH 5.5-6.2, with very high substrate solubilization rate and a methane yield of 0.30 m3 CH4/kg COD fed. The two-phase process was capable of high VS reduction, but material and energy balance showed that the single-phase process was superior in terms of volumetric methane production and energy yield by 33%. The lower energy yield of the two-phase system was due to the loss of energy during hydrolysis in the TPAR and the deficit in methane production in the TPMR attributed to COD loss due to biomass synthesis and adsorption of hard COD onto the flocs. These results including the complicated operational procedure of the two-phase process and the economic factors suggested that the single-phase process could be the preferred system for FVW.
authors.affiliation: INRA, UR50, Laboratoire de Biotechnologie de l'Environnement, Avenue des Etangs, Narbonne F-11100, France.
authors.forename: Rangaraj
authors.initials: R
authors.lastname: Ganesh
authors.affiliation: INRA, UR50, Laboratoire de Biotechnologie de l'Environnement, Avenue des Etangs, Narbonne F-11100, France. Electronic address: michel.torrijos@supagro.inra.fr.
authors.forename: Michel
authors.initials: M
authors.lastname: Torrijos
authors.affiliation: INRA, UR50, Laboratoire de Biotechnologie de l'Environnement, Avenue des Etangs, Narbonne F-11100, France.
authors.forename: Philippe
authors.initials: P
authors.lastname: Sousbie
authors.affiliation: Naskeo Environnment, 52 rue Paul Vaillant Couturier, F-92240 Malakoff, France.
authors.forename: Aurelien
authors.initials: A
authors.lastname: Lugardon
authors.affiliation: INRA, UR50, Laboratoire de Biotechnologie de l'Environnement, Avenue des Etangs, Narbonne F-11100, France.
authors.forename: Jean Philippe
authors.initials: JP
authors.lastname: Steyer
authors.affiliation: INRA, UR50, Laboratoire de Biotechnologie de l'Environnement, Avenue des Etangs, Narbonne F-11100, France.
authors.forename: Jean Philippe
authors.initials: JP
authors.lastname: Delgenes
mesh_terms: D000693:Anaerobiosis; D001673:Biodegradation, Environmental; D019149:Bioreactors; D005638:Fruit; D012037:Refuse Disposal / Q000379:methods* / Q000592:standards; D062611:Solid Waste / Q000032:analysis*; D014675:Vegetables
chemical_list: D062611:Solid Waste
keywords: Energy yield; Fruit and vegetable waste; Process stability; Single-phase process; Solids recirculation; Two-phase process