The study aimed to treat Methylene Blue colour in wastewater flow by apply H₃PO₄ agent activated carbon material which was prepared from Macadamia nutshell, and then denatured with H₂O₂ agent at the ratio of H₂O₂ : activated carbon = 10 : 1. The study results show that the Methylene Blue adsorption capacity reaches value of 1 g / 265 mg Methylene Blue at optimal conditions of 20% concentration and 30 soaking hours. Analysis results of infrared spectra showed that the coal is modified by H₂O₂ agent presents the functional groups of –OH, Carboxylic functional group C=O, group C=H in NH₃, C–N group in Amine aliphatic or in Alcohol or Phenol and C–O bonding. Modified coal by H₂O₂ oxidation agent has the Methylene Blue color treatment efficiency of 99.07%, corresponding to the original colour of 449.67 Pt-Co at the respective optimal conditions of pH = 9, the dosage of 1 g/L, and the treatment time of 60 minutes. The study results are similar to previous research results that strongly confirm the ability to apply the mentioned modified coal to treat Methylene Blue colour in the wastewater flow.