The present invention unveils a process for removal of color (melanoidins) of the biomethanated spent wash (BSW) discharged from distilleries which utilize molasses as resource. The process precludes the application of any chemicals or catalysts and is a one-step high temperature oxidative precipitation in oxygen deficient environment using O2/air as oxidizing agent. The coloring compounds precipitated along with the reduction in viscosity, COD, BOD and TDS. It may further be possible to develop methods like RO or precipitation for potassium recovery from the potassium rich water for further application of potassium in manure.