Preliminary research on activated sludge potassium efflux (GGKE – glutathione-gated potassium efflux) as a result of peroxyacetic acid (PAA) dosing were performed. Similar to the case of chlorine dosing, the PAA dosing causes initiation of bacteria defense mechanisms related to the transformations of gluthathione tripeptide, resulting in the increase of potassium ion concentrations in the activated sludge environment. In the range of biomass concentration from 6.035 g_MLSS/l to 9.331 g_MLSS/l and applied peroxyacetic acid doses from 0.12 mg PAA/g_MLSS to 3.55 mg PAA/g_MLSS, the increase of potassium ions K⁺ concentration in the activated sludge environment after 10 minutes of reaction in batch varied from approximately 3 mg/l to 40 mg/l. The elementary increase of potassium ion concentrations (mg K⁺/g_MLSS· l) was dependant on reaction time and the PAA dose. The elementary increase values varied from 0.5 mg K⁺/(g_MLSS· l) for the dose of 0.3 mg PAA/g_MLSS and 5 minutes reaction time to 4 mg K⁺/(g_MLSS· l) for 2.5 mg PAA/g_MLSS and reaction time equal to 20 minutes.