Citation: Limonti, C.; Curcio, G.M.; Siciliano, A.; Le Pera, A.; Demirer, G.N. Kinetic Study of Anaerobic Digestion of Compost Leachate from Organic Fraction of Municipal Solid Waste. Fermentation 2023, 9, 297. https://doi.org/10.3390/ fermentation9030297 Academic Editor: Mohammad Taherzadeh Received: 16 February 2023 Revised: 15 March 2023 Accepted: 16 March 2023 Published: 18 March 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). fermentation Article Kinetic Study of Anaerobic Digestion of Compost Leachate from Organic Fraction of Municipal Solid Waste Carlo Limonti 1 , Giulia Maria Curcio 1 , Alessio Siciliano 1, * , Adolfo Le Pera 2 and Goksel N. Demirer 3 1 Laboratory of Sanitary and Environmental Engineering, Department of Environmental Engineering, University of Calabria, 87036 Rende (CS), Italy 2 Calabra Maceri e Servizi SpA, 87036 Rende (CS), Italy 3 School of Engineering & Technology, Institute for Great Lakes Research, Central Michigan University, Mt. Plesant, MI 48859, USA * Correspondence: alessio.siciliano@unical.it Abstract: The anaerobic digestion (AD) of compost leachate has been scarcely investigated and, to the best of our knowledge, no previous work has analyzed the kinetics of the process in completely stirred tank reactors (CSTR). To overcome this lack of knowledge, the present work aimed to deepen the study of the AD of compost leachate in CSTR and to identify the kinetics that can represent the process evolution under different operating conditions. In this regard, an experimental investigation was carried out on a laboratory anaerobic pilot plant that worked in semi-continuous mode under mesophilic conditions. After the start-up phase, the digester was fed with organic loading rates (OLR) between 4 and 30 g COD /Ld. The chemical oxygen demand (COD) removal ranged between 80 and 85% for OLR values up to 20 g COD /Ld and, then, it was observed as 54% at 30 g COD /Ld. The deterioration of process performance was caused by an excessive generation of volatile fatty acids leading to a decrease of methane production yield from 0.32–0.36 L CH4 /g CODremoved at 20 g COD /Ld, to 0.23–0.26 L CH4 /g CODremoved at 30 g COD /Ld. Using kinetic analysis, the Monod model was shown to be quite accurate in modelling the trends of COD degradation rates for OLR values up to 20 g COD /Ld. On the other hand, a better fit was achieved with the Haldane model at 30 g COD /Ld. The conducted modelling allowed to identify the kinetic parameters for each model. The detected results could help in the management and design of the digesters for the treatment of compost leachate. Keywords: anaerobic digestion; biogas; compost leachate; kinetic; methane; modeling 1. Introduction Composting is the most widely used technology for the treatment and valorization of the organic fraction of municipal solid waste (OFMSW) [1–3]. This process transforms the OFMSW into a stabilized product free of pathogens [4–6]. The produced compost can be used as an organic soil conditioner as it is rich in N, K, and P, all beneficial nutrients for plant growth [7,8]. However, large volumes of leachate are generated during the biochemical stabilization process of organic matter [9–11]. Leachate is generated from the water contained in the composted matrix, the water produced during the stabilization process, the water added during the process to regulate the moisture content of the heaps, and finally, where the composting process takes place outdoors, from rainwater [12,13]. The leachate quantities generated depend on the type of treatment plant and the composition of the composted organic matrix [14,15]. For example, recent studies indicated that the production of leachate from OFMSW varies between 75 and 100 L/ton [16], whereas from composting matrices composed essentially of urban green waste and garden clippings, the quantities generated fall between 5 and 50 L/ton [17]. Furthermore, the chemical– physical composition of compost leachate shows an extreme variability depending on the type of organic matrix and composting process, which makes it difficult to choose an appropriate treatment capable of effectively removing the contaminants. In this regard, Fermentation 2023, 9, 297. https://doi.org/10.3390/fermentation9030297 https://www.mdpi.com/journal/fermentation