Comparative study of methane production in a one-stage vs. two-stage anaerobic digestion process from raw tomato plant waste

Authors: RUIZ-AGUILAR, GRACIELA - University Of Guanajuato; NUNEZ-PALENIUS, HECTOR - University Of Guanajuato; Lovanh, Nanh; CAMARENA-MARTINEZ, SARAI - University Of Guanajuato

Submitted to: Energies
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/29/2022
Publication Date: 12/2/2022
Citation: Ruiz-Aguilar, G.M., Nunez-Palenius, H.G., Lovanh, N.C., Camarena-Martinez, S. 2022. Comparative study of methane production in a one-stage vs. two-stage anaerobic digestion process from raw tomato plant waste. Energies. 15(23). Article 9137. https://doi.org/10.3390/en15239137.
DOI: https://doi.org/10.3390/en15239137

Interpretive Summary: Population growth has resulted in a greater demand for food and energy, and at the same time, a greater generation of waste. Much of this organic waste is derived from agricultural activity and most is sent directly into landfills or burned together with other wastes. Globally in 2020, over 200 million tons of organic waste were generated worldwide and posed a serious environmental risk. A better way of utilizing these wastes and turn them into useful commodity is needed. Anaerobic digestion of these wastes is a viable technology that could turn these wastes into energy production and reduce biomass that requires landfills. In this study, a comparison of single stage versus a two stage anaerobic digestion system was carried out using tomato plant silage as feedstock. The results show that there is no significant different in methane gas production in the single stage versus the two stage anaerobic digestion systems. However, the two stage digestion system was able to produce hydrogen gas in addition to methane for energy production. Thus, a two stage anaerobic digestion system may be more advantageous in creating more fuel for energy production over the single stage system. Nevertheless, the single stage digestion may be a better option for simple operating system whereas the two stage digestion system may require more complex setup and operation.

Technical Abstract: An anaerobic digestion process carried out in two stages has certain advantages over the conventional process; among them the production of hydrogen in addition to methane and the increase in the degradation of the substrate. In several investigations the effectiveness of the implementation of this system for the treatment of lignocellulosic waste has been demonstrated, however, in other studies its implementation was not effective. In the present investigation, methane production was compared in a two-stage system vs. one-stage system from non-pretreated tomato plant residues. For this, different temperature (37 and 55 °C) and initial pH (5.5 and 6.5) conditions were evaluated during hydrolysis/acidogenesis and a single temperature (37 °C, without pH adjustment) during methanogenesis. At the same time, a one-stage treatment (37 °C, without pH adjustment) was run for comparison purposes. The two-stage treatment in which the highest production of hydrogen (12.4 mL/g VS) and methane (252.3 mL/g VS) was observed under the conditions of pH 6.5 and at 37°C. However, this energy production was statistically similar (P < 0.5) to the one-stage treatment (365.4 mL CH4/g VS); there were also no significant differences in the removal of volatile solids between the different treatments.