title: Anaerobic digestion of wastewater derived from the pressing of orange peel generated in orange juice production.
abstract: A study of the anaerobic digestion of wastewater from the pressing of orange peel generated in orange juice production was carried out in a laboratory-scale completely stirred tank reactor at mesophilic temperature (37 degrees C). Prior to anaerobic treatment the raw wastewater was subjected to physicochemical treatment using aluminum sulfate as a flocculant and to pH reduction using a solution of sulfuric acid. The reactor was batch fed at COD loads of 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, and 5.0 g of COD. The process was very stable for all of the loads studied, with mean pH and alkalinity values of 7.5 and 3220 mg of CaCO3/L, respectively. The anaerobic digestion of this substrate was found to follow a first-order kinetic model, from which the specific rate constants for methane production, K(G), were determined. The K(G) values decreased considerably from 0.0672 to 0.0078 L/(g h) when the COD load increased from 1.5 to 5.0 g of COD, indicating an inhibition phenomenon in the system studied. The proposed model predicted the behavior of the reactor very accurately, showing deviations of <5% between the experimental and theoretical values of methane production. The methane yield coefficient was found to be 295 mL of CH4 STP/g of COD removed, whereas the mean biodegradability of the substrate (TOC) was 88.2%. A first-order kinetic model for substrate (TOC) consumption allowed determination of the specific rate constants for substrate uptake, K(C), which also decreased with increasing loading, confirming the above-mentioned inhibition process. Finally, the evolution of the individual volatile fatty acid concentrations (acetic, C2; propionic, C3; butyric, C4; isobutyric, iC4; valeric, C5; isovaleric, iC5; and caproic, C6) with digestion time for all loads used was also studied. The main acids generated were acetic and propionic for all loads studied, facilitating the conversion into methane.
authors.affiliation: Departamento de Química InorgAnica e Ingeniería Química, Facultad de Ciencias, Universidad de Córdoba, Campus Universitario de Rabanales, Edificio C-3, Ctra. Madrid-CAdiz, Km 396, 14071 Córdoba, Spain.
authors.forename: José Angel
authors.initials: JA
authors.lastname: Siles
authors.forename: María
authors.initials: M
authors.lastname: de Los Angeles Martín
authors.forename: Antonio
authors.initials: A
authors.lastname: Martín
authors.forename: Francisco
authors.initials: F
authors.lastname: Raposo
authors.forename: Rafael
authors.initials: R
authors.lastname: Borja
mesh_terms: D000693:Anaerobiosis; D001628:Beverages; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D032084:Citrus sinensis / Q000737:chemistry*; D005511:Food Handling; D005638:Fruit / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008697:Methane / Q000737:chemistry; D014866:Waste Products; D014867:Water / Q000737:chemistry*
chemical_list: D014866:Waste Products; D014867:Water; D008697:Methane