Monoethanolamine (MEA) has been widely used for the removal of carbon dioxide and hydrogen sulfide in natural gas processing plant. However, during the treatment process of wastewater at Petronas Chemical Olefins Glycol Derivates (PCOGD), a small amount of amine (MEA) gets carried over from the process plant causing spikes in ammonia. Therefore, treatment of MEA-contaminated wastewater is a major concern in most amine sweetening plants. The objective of this study is to determine the impact of MEA on removal of nitrogen compounds using two trains of activated sludge treatment system. In this study, MEA wastewater was treated via a bench-scale of two trains that consist of three reactors known as reactor A1T1, A2T1, and A1T2. Train 1 will have two bench-scale activated sludge systems connected in series which is reactor A1T1 and reactor A2T1, while Train 2 is consisted of a single bench-scale activated sludge system which are reactor A1T2. The raw influent wastewater from PCOGD will be fed with varying concentrations of MEA (50, 100, 500, and 1000 mg/L). Influent and effluent samples were monitored for pH value, alkalinity, ammonia, and Total Kjeldahl Nitrogen. Based on the result, it can be observed that the addition of MEA decreases the percentage removal of nitrogen and slows down the nitrification process in all reactors. Throughout the study, Train 1 performed slightly better than train 2 since the impact of MEA was absorbed by the first reactor in train 1. However, alkalinity must be added and maintained to provide for nitrification in the second reactor. This study indicates that using activated sludge system to remove MEA contaminants from wastewater is both feasible and desirable. © 2023, The Author(s), under exclusive license to Springer Nature Switzerland AG.