Two-step spent active carbon regeneration ­ by treatment with sodium hydroxide soln. and then washing with sodium metabisulphite soln.

In the 1 st step the spent C is treated successively with NaOH solns. having decreasing concns., respectively of 15-­, 10­-, 5-­, 2.25-­, 1 ­ and 0.5%, at 70 deg. C, for 2 hrs. for each treatment. In a 2nd step, the C is washed with 0.05% Na metabisulphite soln. at pH 1 .5. Washing is continued with an aq. soln. of 0.001 % Na metabisulphite, until the washing water reaches pH 4.5.