A treatment composition for remediating for remediating H.sub.2S and other contaminant(s) in contaminated gasses comprising: an aqueous hydroxide solution containing at least one hydroxide compound at a collective concentration of 35-55 weight percent of the aqueous hydroxide solution; at least one organic acid selected from the group consisting of fulvic acid and humic acid; and a chelating agent, wherein the aqueous hydroxide solution constitutes at least 80 wt % of the treatment composition, the at least one organic acid constitutes 0.1-3 wt % of the treatment composition, the chelating agent constitutes 0.1-6 wt % of the treatment composition, and a pH of the treatment composition is at least 12.0.

A treatment composition for remediating for remediating H.sub.2S and other contaminant(s) in contaminated gasses comprising: an aqueous hydroxide solution containing at least one hydroxide compound at a collective concentration of 35-55 weight percent of the aqueous hydroxide solution; at least one organic acid selected from the group consisting of fulvic acid and humic acid; and a chelating agent, wherein the aqueous hydroxide solution constitutes at least 80 wt % of the treatment composition, the at least one organic acid constitutes 0.1-3 wt % of the treatment composition, the chelating agent constitutes 0.1-6 wt % of the treatment composition, and a pH of the treatment composition is at least 12.0.

A treatment composition for remediating for remediating H.sub.2S and other contaminant(s) in contaminated gasses comprising: an aqueous hydroxide solution containing at least one hydroxide compound at a collective concentration of 35-55 weight percent of the aqueous hydroxide solution; at least one organic acid selected from the group consisting of fulvic acid and humic acid; and a chelating agent, wherein the aqueous hydroxide solution constitutes at least 80 wt % of the treatment composition, the at least one organic acid constitutes 0.1-3 wt % of the treatment composition, the chelating agent constitutes 0.1-6 wt % of the treatment composition, and a pH of the treatment composition is at least 12.0.

A treatment composition for remediating for remediating H.sub.2S and other contaminant(s) in contaminated gasses comprising: an aqueous hydroxide solution containing at least one hydroxide compound at a collective concentration of 35-55 weight percent of the aqueous hydroxide solution; at least one organic acid selected from the group consisting of fulvic acid and humic acid; and a chelating agent, wherein the aqueous hydroxide solution constitutes at least 80 wt % of the treatment composition, the at least one organic acid constitutes 0.1-3 wt % of the treatment composition, the chelating agent constitutes 0.1-6 wt % of the treatment composition, and a pH of the treatment composition is at least 12.0.

Sodium borohydride (NaBH.sub.4) may be used to removing carbonyl sulfide (COS) from a process stream containing it. The method involves contacting the process stream with an amount of effective of NaBH.sub.4 to react with the COS to form reaction products that may be removed by a process of washing away the reaction product by an aqueous basic compound and/or the reaction product having a higher boiling point than carbonyl sulfide which permits trapping the reaction product, such as in a caustic tower.