Abstract
Olive oil and pig productions are important industries in Portugal that generate large volumes of wastewater with high organic load and toxicity, raising environmental concerns. The principal objective of this study is to energetically valorize these organic effluents—piggery effluent and olive mill wastewater—through the anaerobic digestion to the biogas/methane production, by means of the effluent complementarity concept. Several mixtures of piggery effluent were tested, with an increasing percentage of olive mill wastewater. The best performance was obtained for samples of piggery effluent alone and in admixture with 30% of OMW, which provided the same volume of biogas (0.8 L, 70% CH4), 63/75% COD removal, and 434/489 L CH4/kg SVin, respectively. The validation of the process was assessed by molecular evaluation through Next Generation Sequencing (NGS) of the 16S rRNA gene. The structure of the microbial communities for both samples, throughout the anaerobic process, was characterized by the predominance of bacterial populations belonging to the phylum Firmicutes, mainly Clostridiales, with Bacteroidetes being the subdominant populations. Archaea populations belonging to the genus Methanosarcina became predominant throughout anaerobic digestion, confirming the formation of methane mainly from acetate, in line with the greatest removal of volatile fatty acids (VFAs) in these samples.
Highlights
The food industry is an economically important industrial sector [1], in which segments, such as olive oil and animal productions, play a relevant contribution
olive mill wastewaters (OMW) and Piggery effluent (PE) are substrates that contain very high concentrations of organic compounds (106 and 93 g/L chemical oxygen demand (COD), respectively), as shown in Table 2, what indicates a great potential for the production of biogas/methane
The concept of complementarity of effluents was successfully applied to the anaerobic digestion of piggery effluent, using the olive mill wastewater as complement, under mesophilic and batch conditions
Summary
The food industry is an economically important industrial sector [1], in which segments, such as olive oil and animal productions, play a relevant contribution. OMW has a high chemical oxygen demand COD content, usually up to 200 g/L, an acidic pH (between 4 and 6), and high content in solid matter (up to 20 g/L) [4,5,6,7] It contains minerals (potassium, sodium, and calcium), fermentable proteins, resinous and serous substances, vitamins, and small amounts of olive oil [3,8,9]. The phenolic compounds are phytotoxic and microbial inhibitors [8,10,11] This effluent contains water (80–95%) and is rich on sugars (fructose, mannose, glucose, saccharose, sucrose, among others), long chain and volatile fatty acids. The composition of this wastewater changes with the type and region of origin of the olives, the ripeness of the olives, and the way of processing and handling
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