Valorization of the complex organic waste in municipal solid wastes through the combination of hydrothermal carbonization and anaerobic digestion

Abstract

Municipal Solid Wastes (MSW) consist of the valorizable inorganic fraction, i.e., Refuse Derived Fuel, and the organic fraction which also can be valorized. However, the separated organic fraction, which is known as Complex Organic Waste (COW), contains traces of glass, plastics, non-ferrous metals, and stones. Thus, the aim of this work was to determine the value of the COW that comes from a MSW separation plant through the combination of Hydrothermal Carbonization (HTC) and Anaerobic Digestion (AD) for the production of biofuels. COWs were conditioned to undergo HTC for 1 h at 180 °C and 190 °C. HTC liquid was used as a substrate operating an Anaerobic Hybrid Reactor (AHR) in continuous mode with 5 gCOD/Ld at 35 ± 2 °C. The hydrochar contained on average (dry matter): (180 °C) 30.44 % carbon and 15.47 MJ/kg and (190 °C) 40.44 % carbon and 17.60 MJ/kg. The AHR removed more than 93 % (COD) reaching 0.34 LCH₄ at STP/gCOD_rem, and no inhibitory effects were observed. The coupling of HTC with AD at low temperatures for short times turned out to be a promising alternative for the valorization of COW, i.e., it produced 10,888 MJ (94 % HTC and 6 % AD) per metric ton of COW.