Abstract
Olive mill wastewater (OMW) presents high environmental impact due to the fact of its elevated organic load and toxicity, especially in Mediterranean countries. Its valorization for simultaneous pollutants degradation and green energy production is receiving great attention, mainly via steam reforming for hydrogen generation. Following previous works, the present research goes into detail about OMW valorization, particularly investigating for the first time the potential benefits of OMW–bioethanol mixtures co-reforming for ultra-pure hydrogen production in Pd-membrane reactors. In this manner, the typical large dilution of OMW and, hence, excess water can be used as a reactant for obtaining additional hydrogen from ethanol. Fresh OMW was previously conditioned by filtration and distillation processes, analyzing later the effect of pressure (1–5 bar), oxidizing conditions (N2 or air as carrier gas), gas hourly space velocity (150–1500 h−1), and alcohol concentration on the co-reforming process (5–10% v/v). In all cases, the exploitation of OMW as a source of environmentally friendly hydrogen was demonstrated, obtaining up to 30 NmL·min−1 of pure H2 at the most favorable experimental conditions. In the membrane reactor, higher pressures up to 5 bar promoted both total H2 production and pure H2 recovery due to the increase in the permeate flux despite the negative effect on reforming thermodynamics. The increase of ethanol concentration also provoked a positive effect, although not in a proportional relation. Thus, a greater effect was obtained for the increase from 5% to 7.5% v/v in comparison to the additional improvement up to 10% v/v. On the contrary, the use of oxidative conditions slightly decreased the hydrogen production rate, while the effect of gas hourly space velocity needs to be carefully analyzed due to the contrary effect on potential total H2 generation and pure H2 recovery.
Highlights
Olive oil is highly appreciated for its flavor and proven health benefits, and it represents a fundamental economic component of European Mediterranean countries, especially Spain, Italy, and Greece, where most of the olive farms are concentrated [1]
All experimentsDetails were performed using home-made equipment with a hydrogen perm-selective finger-typeAll membrane operating as simple gas separatorequipment or, in casewith of combining with some catalyst experiments were performed using home-made a hydrogen perm-selective pellets, membrane reactoroperating for reforming tests details about the experimental finger-type membrane as simple gas(Figure separator1)
A concentration step was performed with the aim of partially reducing the water content of the Olive mill wastewater (OMW) and, to improve the energy requirements of the reforming process. This concentration treatment was based on the distillation of the raw OMW into different fractions, removing those containing a negligible amount of organic compounds
Summary
Olive oil is highly appreciated for its flavor and proven health benefits, and it represents a fundamental economic component of European Mediterranean countries, especially Spain, Italy, and Greece, where most of the olive farms are concentrated [1]. Trying to mitigate the negative effects of OMW on the environment, two different strategies can be considered: (i) conventional water treatments for domestic and industrial wastewaters including physical–chemical [7,8], biological [9,10,11,12,13], and advanced processes such as photocatalytic or electro-hydrolysis reactions [14,15,16,17,18]; or (ii) valorization for green energy production [1,19,20,21] The latter alternative represents a very promising approach to cover future worldwide energy needs in a sustainable way, obtaining renewable and distributed energy while potentially harmful wastes are removed [22]. A similar strategy was considered in this work but replacing, for the first time, the methane with ethanol in the OMW membrane reformer
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