title: Co-treatment of fruit and vegetable waste in sludge digesters. An analysis of the relationship among bio-methane generation, process stability and digestate phytotoxicity.
abstract: The co-digestion of a variable amount of fruit and vegetable waste in a waste mixed sludge digester was investigated using a pilot scale apparatus. The organic loading rate (OLR) was increased from 1.46 kg VS/m(3) day to 2.8 kg VS/m(3) day. The hydraulic retention time was reduced from 14 days to about 10 days. Specific bio-methane production increased from about 90 NL/kg VS to the maximum value of about 430 NL/kg VS when OLR was increased from 1.46 kg VS/m(3) day to 2.1 kg VS/m(3) day. A higher OLR caused an excessive reduction in the hydraulic retention time, enhancing microorganism wash out. Process stability evaluated by the total volatile fatty acids concentration (mg/l) to the alkalinity buffer capacity (eq. mg/l CaCO3) ratio (i.e. FOS/TAC) criterion was <0.1 indicating high stability for OLR <2.46 kg VS/m(3 )day. For higher OLR, FOS/TAC increased rapidly. Residual phytotoxicty of the digestate evaluated by the germination index (GI) (%) was quite constant for OLR<2.46 kg VS/m(3)day, which is lower than the 60% limit, indicating an acceptable toxicity level for crops. For OLR>2.46 kg VS/m(3) day, GI decreased rapidly. This corresponding trend between FOS/TAC and GI was further investigated by the definition of the GI ratio (GIR) parameter. Comparison between GIR and FOS/TAC suggests that GI could be a suitable criterion for evaluating process stability.
authors.affiliation: LAR - Dipartimento di Ingegneria - University of Perugia, Via G. Duranti 67, 06125 Perugia, Italy. Electronic address: francesco.dimaria@unipg.it.
authors.forename: Francesco
authors.initials: F
authors.lastname: Di Maria
authors.affiliation: LAR - Dipartimento di Ingegneria - University of Perugia, Via G. Duranti 67, 06125 Perugia, Italy.
authors.forename: Alessio
authors.initials: A
authors.lastname: Sordi
authors.affiliation: LAR - Dipartimento di Ingegneria - University of Perugia, Via G. Duranti 67, 06125 Perugia, Italy.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Cirulli
authors.affiliation: Dipartimento di Ingegneria Civile ed Ambientale, Via G. Duranti 67, 06125 Perugia, Italy.
authors.forename: Giovanni
authors.initials: G
authors.lastname: Gigliotti
authors.affiliation: Dipartimento di Scienze Agrarie, Alimentari e Ambientali, Borgo XX Giugno 74, 06121 Perugia, Italy.
authors.forename: Luisa
authors.initials: L
authors.lastname: Massaccesi
authors.affiliation: Dipartimento di Ingegneria Civile ed Ambientale, Via G. Duranti 67, 06125 Perugia, Italy.
authors.forename: Mirko
authors.initials: M
authors.lastname: Cucina
mesh_terms: D019149:Bioreactors; D005735:Garbage; D018525:Germination; D031220:Lepidium sativum; D008697:Methane / Q000032:analysis*; D018675:Toxicity Tests; D018505:Waste Management; D014866:Waste Products / Q000009:adverse effects*
chemical_list: D014866:Waste Products; D008697:Methane
keywords: Anaerobic co-digestion; Biomethane; FOS/TAC; Fruit and vegetable waste; Germination index; Organic loading rate; Waste mixed sludge