The rapid growth in world population brings with it the need for improvement in the current technology for water purification, in order to provide adequate potable water to everyone. Although an advanced oxidation process has been used to purify wastewater, its action mechanism is still not clear. Therefore, in the present study we treat dye-polluted water with gamma rays and dielectric barrier discharge (DBD) plasma. We study the wastewater treatment efficiency of gamma rays and DBD plasma at different absorbed doses, and at different time intervals, respectively. Methyl orange and methylene blue dyes are taken as model dyes. To understand the effects of environment and humidity on the decolorization of these dyes, we use various gas mixtures in the DBD plasma reactor. In the plasma reactor, we use the ambient air and ambient air + other gas (oxygen, nitrogen, and argon) mixtures, respectively, for the treatment of dyes. Additionally, we study the humidity effect on the decolorization of dyes with air plasma. Moreover, we also perform plasma simulation in different environment conditions, to understand which major radicals are generated during the plasma treatments, and determine their probable densities.