NOVELTY - Biocidal aqueous solution (I) comprises hydrogen peroxide (0.05-20% (w/w)), where (I) has a pH of 2-4, and an oxidation reduction potential (ORP) of 400-600 mV, and when (I) has a peroxide content of 0.05-0.5, 0.1-5 or 5-20% (w/w), then (I) has a conductivity of 100-500 (preferably 100-450), 100-450 (preferably 100-350) and 100-350 muSiemens/cm respectively.    USE - (I)/The composition is useful for any purpose where disinfecting, sanitizing, cleaning, bleaching and/or preservative activity is required. (I) is useful for disinfecting a substrate such as any surface, space, material, medical instrument or device, hospital equipment, and/or surface of walls, ceilings and floors, preferably where the presence of gram positive and/or gram negative pathogenic bacteria is suspected (all claimed).    ADVANTAGE - (I) has a biocidal activity against a broad spectrum of micro-organisms, including gram positive and/or gram negative bacteria and fungi. (I) provides at least a log 4 reduction using a European Norm EN 1040 conform assay against Escherichia coli, Rhodotorula rubra, Pseudomonas aeruginosa or Salmonella typhimurium for a 5 minute contact time. The pH, ORP and conductivity are measurable under conditions essentially without the presence of additional compounds in the solution. (I) has substantially no available free chlorine content (all claimed). (I) is environmental friendly and is safe. (I) has higher biocidal activity than the existing solutions. The glow discharge plasma or the corona discharge is operated in a pulse mode, which allows higher instantaneous powers to be applied without excessively heating the aqueous layer. The pulsed glow discharge plasma's and pulsed corona discharges are run reliably at low and high temperatures, in various gases and with a wide range of composition. The pulsed corona promises higher efficiency than other advanced oxidation processes.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) a composition comprising (I) and an additive;    (2) the preparation of (I) comprising placing an aqueous solution containing hydrogen peroxide (0.05-20%) in the form of a layer in a chamber suitable for a non-thermal electrical discharge treatment, positioning an electrode in the layer and an electrode with opposite potential in the gas phase above the layer, generating a non-thermal electrical discharge in the chamber, and subjecting the peroxide solution to the nonthermal electrical discharge to obtain an activated peroxide solution; and    (3) a method for disinfecting a substrate comprising contacting the substrate with (I).