A wash system for removing ammonia slip in a chilled ammonia-based CO2 removal system comprising a main absorber and regenerator, the wash system comprising: a wash vessel configured to receive at a bottom portion a CO2 lean flue gas subjected to the chilled ammonia-based CO2 removal system, and configured to receive a liquid for washing the CO2 lean flue gas from the main absorber; wherein the wash vessel comprises a first absorption stage and a second absorption stage and is configured such that a first portion of the washed liquid from the bottom of the wash vessel isrecycled to the first absorption stage and that the CO2 lean flue gas enters the wash vessel and passes through the first absorption stage prior to passing through the second absorption stage; a separation unit in series with the wash vessel and configured to receive a second portion of the washed liquid having an ammonia concentration from the wash vessel and physically separate the washed liquid into a first feed stream and a second feed stream, wherein the first feed stream has a decreased ammonia concentration relative to the ammonia concentration of the washed liquid and is recycled back to the second absorption stage of the wash vessel via liquid delivery system, and wherein the second feed stream has an increased ammonia concentration relative to the ammonia concentration of the washed liquid, wherein the separation unit is a nanofiltration or reverse osmosis unit; a stripper system in series with the separation unit and configured to receive the second feed stream with the increased ammonia concentration from the separation unit, wherein the stripper system comprises a stripper column and a reboiler in fluid communication therewith to remove ammonia from the second feed stream to produce an ammonia lean solution; and a conduit to combine at least a portion of the ammonia lean solution with the first feed stream. a wash vessel configured to receive at a bottom portion a CO2 lean flue gas subjected to the chilled ammonia-based CO2 removal system, and configured to receive a liquid for washing the CO2 lean flue gas from the main absorber; wherein the wash vessel comprises a first absorption stage and a second absorption stage and is configured such that a first portion of the washed liquid from the bottom of the wash vessel isrecycled to the first absorption stage and that the CO2 lean flue gas enters the wash vessel and passes through the first absorption stage prior to passing through the second absorption stage; a separation unit in series with the wash vessel and configured to receive a second portion of the washed liquid having an ammonia concentration from the wash vessel and physically separate the washed liquid into a first feed stream and a second feed stream, wherein the first feed stream has a decreased ammonia concentration relative to the ammonia concentration of the washed liquid and is recycled back to the second absorption stage of the wash vessel via liquid delivery system, and wherein the second feed stream has an increased ammonia concentration relative to the ammonia concentration of the washed liquid, wherein the separation unit is a nanofiltration or reverse osmosis unit; a stripper system in series with the separation unit and configured to receive the second feed stream with the increased ammonia concentration from the separation unit, wherein the stripper system comprises a stripper column and a reboiler in fluid communication therewith to remove ammonia from the second feed stream to produce an ammonia lean solution; and a conduit to combine at least a portion of the ammonia lean solution with the first feed stream.