Processes and systems are disclosed that relate to the removal of impurities and separation the light olefins from an MTO product vapor stream. Specifically, the processes and systems relate to recovery of light olefins during regeneration of an adsorber in an oxygenate removal unit. Processes and systems for recovering light olefins during regeneration of an adsorber in an oxygenate removal unit can include recycling residual effluent stream to an upstream operation unit upstream of the oxygenate removal unit. Processes and systems for recovering light olefins during regeneration of an adsorber in an oxygenate removal unit can also include recycling residual effluent gas produced by depressurizing residual effluent in the first adsorber, as well as preferably venting an effluent gas from the first adsorber to a compressor upstream of the oxygenate removal unit.