In the present study, the influence of bioaugmentation strategy on co-treatment of 13% v/v reject water and municipal wastewater at decreasing temperature was evaluated. The experiment was performed in two equal laboratory sequencing batch reactors with the active volume of 8 L. Each one was operated using a 12-hour cycle at sludge retention time of 3 d. The SBR A was bioaugmented with a mixture of wild-living Bacteria and Archaea in a dose 0.25 ml. While the comparative reactor (SBR B) was non-bioaugmented, the Archaea product was replaced with an equal volume of dechlorinated tap water. The experiment was divided into 3 phases, each with a different temperature range (20, 15 and 10oC). The temperature reduction did not adversely affect the process performance in the bioaugmented and non-bioaugmented system. Significant removal efficiencies were achieved in both SBRs. The major differences were observed for the COD content in bioaugmented SBR at a temperature of 10oC. In this case, statistically lower concentrations in the effluent were observed in the bioaugmented system than in the non-bioaugmented one. Additionally, at a temperature of 10oC the improved process performance was observed in Archaea presence, but the differences were no of statistical significance.