A treatment process for remediating a contaminated liquid containing more than 5 ppm hydrogen sulfide, includes steps of: preparing a treatment solution containing an aqueous solution containing ≥1 hydroxide compound, in which a collective concentration of the ≥1 hydroxide compound in the aqueous solution is in a range of 35-55 weight percent and the aqueous solution constitutes at least 95% of the treatment solution; adding to the liquid an amount of an treatment solution sufficient to reduce a concentration of hydrogen sulfide in the contaminated liquid to ≤5 ppm based on stoichiometry of reactions between the ≥1 hydroxide compound and the hydrogen sulfide in the liquid; and dispersing the treatment solution in the liquid and allowing the treatment solution to react with the contaminated liquid for a period of time until a concentration of hydrogen sulfide in the liquid is reduced to ≤5 ppm.