Biochemica OC-500 is a powerful non-chlorinating oxidizing agent useful in many water treating applications.

Odour Formation

Sulphide exists in wastewater in three forms; hydrogen sulphide gas (H₂S), non-volatile ionic species hydrogen sulphide (HS^–) and sulphide (S₂^–). The ratio of each of the three species H₂S, HS^– and S₂^– is dependent on the pH. At pH 6, 90% of the sulphide will be present as H₂S, and the higher the H₂S concentration the greater the tendency for it to volatilize.

Conversely at pH 10, 100% of the sulphide will be present as S₂.

Sulphides are produced by both biological and chemical action. They are produced biologically by anaerobic bacteria, and chemically by many industries including the chemical, petroleum, paper, and textile industries.

H₂S occurs naturally through the anaerobic decay of organic matter and is easily recognized by its characteristic rotten egg odour. In the absence of dissolved oxygen and in the presence of soluble Biological Oxygen Demand (BOD), Desulfovibrio desulfuricans (SRB) and other sulphate-reducing bacteria (SRB’s) convert the sulphate ion to sulphide:

SO₄^2- + Organic matter H₂S + CO₂

Many systems provide an environment that promotes the growth of a healthy biological community. H₂S formation in wastewater systems occurs primarily in the gelatinous slime layer (biofilm) that accumulates on pipe walls and in the sludge blankets of clarifiers and other solids processing units. The rate of sulphide production is dependent upon the concentrations of sulphate ions, organic matter, and dissolved oxygen, as well as other factors such as pH, temperature, retention time, stream velocity, and surface area.

Many industrial processes produce sulphide-containing gases and waste products. These are generated, for example, during petroleum refining, coal coking, black liquor evaporation in kraft pulping, viscose rayon manufacture and natural gas purification. In addition to their disagreeable “rotten egg” odour, sulphides are corrosive to concrete and are extremely toxic. These gases and wastes are frequently scrubbed with alkaline solutions and require treatment before discharge.

Treatment Alternatives

Sulphide can be removed from a system by precipitation with iron, or by oxidisation. Various oxidisers including chlorine, hydrogen peroxide, and potassium permanganate are commonly used for oxidation of sulphide.

Different treatment strategies are required depending on the application.

Biochemica OC-500

Unlike most oxidants, OC-500 may be used over a broad pH range to oxidize sulphide without the formation of colloidal sulphur, which can plug up equipment.

Biochemica OC-500 is effective where alternative oxidants don’t work, such as when rapid destruction of sulphide is important or the formation of halogenated by products prevents treatment with chlorine. Biochemica OC-500 reacts very rapidly with hydrogen sulphide gas or the sulphide ion.

Between pH 5-9, minimum 12 mg/L of OC-500 should be used to instantly oxidize 1 mg/L of sulphide to sulphate.

In wastewater systems where the odour causing sulphides are produced from colonies of bacteria metabolising sulphate, Biochemica OC-500 is an effective control strategy.

For further information please email: orders@biochemica.co.uk or call 0845 5045440.