Development of a continuous‐flow anaerobic co‐digestion process of olive mill wastewater and municipal sewage sludge

Abstract

BACKGROUNDOlive mill wastewater (OMW) represents an environmental problem due to its high organic load and relevant concentration of phenolic compounds (PCs). OMW treatment and disposal represents a relevant challenge and cost for olive mills and multi‐utilities in charge of waste management in Mediterranean countries. The goal of this study was to develop an anaerobic co‐digestion (co‐AD) process of OMW and sewage sludge (SwS) from municipal wastewater treatment.RESULTSDifferent volumetric OMW:SwS ratios up to 100% OMW were fed in continuous 1.7‐L bioreactors. The reactors fed with raw OMW (rOMW) performed better than those fed with OMW dephenolized by adsorption (dOMW). At a 23‐day hydraulic retention time, the best performances were obtained in the reactor fed with 25% rOMW, with a 105% increase in methane yield in comparison to the 100% SwS test. At a 40‐day hydraulic retention time, the reactor fed with 40% rOMW attained a 268 NLCH4/kgvolatile solids methane yield. The conversion of phenolic compoundsreached 70% when the hydraulic retention time was increased from 23 to 40 days. A cost–benefit analysis indicated that both rOMW co‐AD in existing digesters and phenolic compounds recovery from OMW followed by co‐AD of dOMW can lead to relevant additional revenues for the multi‐utilities in charge of wastewater management.CONCLUSIONThis work proves that, using the existing network of SwS anaerobic digesters, it is feasible to co‐digest the entire OMW production in regions characterized by intense olive oil production, thus attaining a relevant increase in methane production yield (a 144% increase in comparison to 100% SwS). © 2020 Society of Chemical Industry (SCI)

Increasing the Content of Olive Mill Wastewater in Biogas Reactors for a Sustainable Recovery: Methane Productivity and Life Cycle Analyses of the Process

“…In contrast with the results presented here, they yielded higher amounts of biogas and methane with lower quantities of OMWW. Bovina et al [ 51 ] reported an increase in biogas and methane yield with the increasing of OMWW content instead of sewage sludge, obtaining the best performances with 25% OMWW (with 1.01 ± 40 g.L −1 of polyphenols)—i.e., 116 NL.kg VS –1 of methane. Calabrò et al [ 52 ] used raw and concentrated OMWW with polyphenols values ranging between 1.1 ± 0.12 and 4.4 ± 0.03 g.L −1 in order to obtain up to 2 g.L −1 PPs in the blends they tested in batch under mesophilic conditions.…”

Analysis of energy return on investment of dry anaerobic digestion for low water alperujo with oxidative, thermal and alkaline pretreatments

“…However, these studies often focus on improving final yields without taking into account the use of energy resources, which is a key aspect when scaling up a process. It is therefore essential to ensure a quantification of the energy use in each technology to balance the associated costs and efficiency (Bovina et al, 2021). Consequently, the assessment of the energy cost of bioenergy utilization has been the subject of intensive research in recent years (Wang et al, 2021).…”

“…ALP use as a substrate for biogas production by WAD has been extensively studied on a laboratory scale (Borja et al, 1993; Boubaker & Cheikh Ridha, 2007; Bovina et al, 2021; Roig et al, 2006), but when the bioprocess is carried out on a larger scale, the high production costs and dependence on water make it an unsustainable alternative. Moreover, ALP contains 98% of the polyphenolic compounds ( PhC ) present in the olive fruit, a content that varies depending on the olive variety, the ripening of the stone fruit, the oil extraction system used and the storage time after extraction (Carmona et al, 2023; Solomakou & Goula, 2021).…”

Chemical Treatment of Bio-Derived Industrial Waste Filled Recycled Low-Density Polyethylene: A Comparative Evaluation

“…Therefore, it is extremely important to safely handle such materials [1,2]. It is estimated that one ton of olives is responsible for producing 0.6 tons of olive mill solid residue [3,4]. Olive pits (OP) are residues that form part of the solid wastes produced by the olive oil manufacturing industry during the processing and extraction of olive oil from olives [5,6].…”