The presence of bicarbonate affects the degradation efficiency of effluents containing aqueous methyldiethanolamine (MDEA) solution leaving the CO2 absorption/regeneration unit of natural gas processing units. In the present study the effect of bicarbonate at three different pH conditions of (acidic, neutral and alkaline) simulated MDEA solution were conducted, by the addition of six different concentration of NaHCO3 (0.025, 0.05, 0.075, 0.1, 0.125 and 0.15 M). The presence of bicarbonate increased the mineralization of MDEA when the reaction was conducted at neutral initial pH conditions, where as the MDEA mineralization was reduced when the reaction was conducted at alkaline pH condition.