Abstract: In so-called rising main sewers in which sewage can be subjected to conditions when the supply of oxygen is deficient noxious sulphides can be produced which are a nuisance. The present invention provides a composition for the treatment of sewage so that the production of noxious sulphides is minimized under these conditions.The composition of the invention comprises an aqueous solution of ferric sulphate and ferric nitrate in amounts such that the molecular ratio of ferric sulphate to ferric nitrate is from 1:0.5 to 1:3. Optionally the composition may contain nitric acid in an amount of up to 2.5 molecules per molecule of ferric sulphate.These compositions are produced by reacting in aqueous solution nitric acid with ferrous sulphate in the absence of separately added sulphuric acid in such amounts that nitric acid is sufficient to produce the desired molecular ratio of ferric sulphate to ferric nitrate and the reaction is conducted at a temperature of at least 60.degree. C. and not greater than 100.degree.