Valorization of olive mill wastewater via autothermal reforming for hydrogen production

Abstract

Olive mill wastewater (OMW) is an effluent of the olive oil industry that is extremely pollutant. Current solutions are either costly or inefficient. In this study, autothermal reforming (ATR) is presented, for the first time, as a solution to this problem, capable of high organic load removal, renewable hydrogen production and thermally neutral operation. The tests were conducted with a ruthenium-nickel catalyst, doped with La2O3, on a SiO2 support. Different operating conditions were tested (T = 400–700 °C and O2/C = 0.0–0.5 mol O2.mol C−1) and a comparison with traditional reforming (TR) was provided. Characterisation of the catalyst was conducted through temperature-programmed oxidation and inductively coupled plasma - optical emission spectroscopy. The catalytic tests showed hydrogen yields – up to 66.8 % for TR and 52.0 % for ATR – with high rates of organic pollutant load removal (always above 98 %, as inferred from the total organic carbon analyses). Furthermore, an energy balance revealed that ATR releases high amounts of energy, up to 272 kJ·molOMW−1, whilst TR has high energy demand, of up to 360 kJ·molOMW−1. In terms of the amount of heat released during the reaction and the net calorific value of the hydrogen produced, it was found that the ATR at 500 °C with O2/C = 0.25 had the best performance, with a total output of 1695 kJ·molOMW−1.