A method for treating carbonaceous material, the method includes a) providing a first carbonaceous material CM1 contaminated with micro-pollutants and/or microplastics, and providing a second carbonaceous material CM2 free of micro-pollutants or microplastics, b) subjecting the first carbonaceous material CM1 to hydrothermal gasification in a HTG reactor, thereby producing an inorganic solid residue, a first gaseous fraction G1 comprising CH4, CO, CO2 and H2 and a filtrate F1 free of micro-pollutants or microplastics optionally containing readily biodegradable carbons such as VFAs, c) subjecting the second carbonaceous material CM2 together with at least part of the filtrate F1 to an anaerobic treatment step in an anaerobic tank, leading to a digestate free of micro-pollutants or microplastics and optionally a second gaseous fraction G2 containing CH4 and CO2. An installation for treating carbonaceous material is also provided.