Abstract
This review aims at summarizing the literature for the coupling of the biological process of anaerobic digestion (AD) with one of three thermal processes: gasification (Gs), pyrolysis (Py), and hydrothermal carbonization (HTC). These thermal processes are investigated as pre and/or post treatments for AD, aiming at reducing its main drawbacks. The different cases are considered separately, based on the thermal treatment that is coupled with the AD process: AD-Gs, AD-Py, and AD-HTC. For each group, up to three sub-cases are discussed: the thermal treatment of the digestate, the use of char from the thermal treatment as stabilizer and enhancer in the AD reactor, and the AD of the aqueous products of the thermal treatment (this last case is not available with Gs). When possible, the result of the different researches for each configurations are grouped for comparison. Finally, an overview of the most promising future research investigations is given.