NOVELTY - Washing solution, comprises an aqueous solution of many amines comprising (a) an absorber component based on a tertiary amine or a mixture of many tertiary amines, (b) a first activator from monoalkyl amines or dialkyl amines, individually or in combination, (c) a second activator from piperazine or piperazine derivative with at least a free hydrogen atom on one of the two nitrogen atoms, individually or in combination, and (d) the residual water.    USE - The washing solution is useful for removing carbon dioxide from biogas or sewage gas.    ADVANTAGE - The washing solution: exhibits improved washing performance and working capacity; and require less regeneration effort.    DETAILED DESCRIPTION - Washing solution comprises an aqueous solution of many amines comprising (a) an absorber component based on a tertiary amine or a mixture of many tertiary amines in a concentration of 30-60 wt.%, based on the total weight of the washing solution, (b) a first activator from monoalkyl amines or dialkyl amines, individually or in combination, in concentration of 1-10 wt.%, based on the total weight of the washing solution, (c) a second activator from piperazine or piperazine derivative with at least a free hydrogen atom on one of the two nitrogen atoms, individually or in combination, at a concentration of 0.01-10 wt.%, based on the total weight of the washing solution and (d) the residual water with the water content not greater than 60 wt.%, based on the total weight of the washing solution. An INDEPENDENT CLAIM is also included for separating carbon dioxide from biogas or sewage gas, comprising contacting the crude gas stream of the biogas or sewage gas with the washing solution within a wash column in counter-current, circulating the loaded washing solution, and subjecting it to at least one main-stage regeneration, where the content of carbon dioxide is reduced up to a value of at least 20 g/l, and the cleaned washing solution optionally together with fresh wash solution is again brought into contact with the crude gas stream.