Chemical compositions and treatment systems and treatment methods using same for remediating H2S and other contaminants in fluids, including liquids,gasses and mixtures thereof

A treatment composition for remediating H2S and other contaminant(s) in contaminated gases 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 0.1-5 wt % of the treatment composition, the chelating agent constitutes 0.1-5 wt % of the treatment composition, and a pH of the treatment composition is at least 12.0, wherein the treatment composition does not include metals apart from any metals contained in the at least one hydroxide compound.