Upgrading of moist agro-industrial wastes by hydrothermal carbonization

This work focuses in the application of the hydrothermal carbonization (HTC) technology as a possible moist agro-industrial waste management treatment. Through this technique, olive mill, canned artichoke and orange wastes (OMW, CAW and OJW, respectively) were carbonized in a lab-scale high pressure reactor at different temperatures (200–250 °C) and durations (2, 4, 8 and 24 h) in order to obtain useful bioenergy feedstocks. The effect of the residence time and temperature on the properties of the bio-char obtained was studied through different characterization techniques. Material and energy balances were also performed to determine the potential energy saving of hydrothermal carbonization versus dry thermal treatments like torrefaction (TF). It is found that the moisture content of HTC-hydro-chars decreases as the temperature and duration increase, which implies that wet biomass can be upgraded and, at the same time, dewatered through HTC. The best results are found for the OMW, whose moisture content decreases from over 70% to less than 30% for the experiments carried out under the more severe conditions. Consequently, it is be possible to reach energy savings over 50% by using HTC instead of TF technologies. Regarding the hydro-char properties, the hydrothermal carbonization of the three organic wastes treated leaded to hydro-chars that present carbon contents and heating values closed to those of brown coal and great energy densifications, depending on the type of waste. Accordingly, it can be concluded that it is feasible to manage moist agro-industrial wastes via HTC, which is ostensibly more efficient than TF in terms of energy consumption.

Authors kindly wish to thank the Spanish Ministry of Economy and Competitiveness (INNPACTO Project IPT-2012-0565-310000) and the Spanish Ministry for Education and Science (contract grant number 8850828) for financial support. The author V. Benavente also thanks the Conselleria d’Educación, Cultura i Esport, for a Ph.D. grant (contract grant number ACIF/2014/275).