Activated carbons were produced by chemical activation of hydrothermally carbonized (HTC) beer waste, with phosphoric acid as the activation agent. The activation was optimized within a full factorial design, using the outcome of 19 different experiments. Four different parameters (concentration of the acid, activation time, activation temperature, flow rate) were analyzed with respect to their influence on the median pore size. The concentration of H3PO4 had a strong positive effect on the median pore size. The specific surface areas of these activated carbons were similar to 1000 m(2)/g, which compared well commercially available activated carbons. The activated carbons had mostly large pores with a size of similar to 4 nm, and a significant amount of acid surface groups. Scanning electron microscopy (SEM) revealed that the morphology of the HTC beer waste changed significantly after the chemical activation. The capacity to adsorb methylene blue from aqueous solutions was 341 mg/g, for one of the activated carbons at pH 7. A Langmuir model described the uptake of the dye quite well, which suggested a homogeneous adsorption of Methylene Blue (MB).