A solution to sewage system corrosion and problems related to the release of hydrogen sulphide

The second factor is usually a complex biochemical process. When the initial effluent has an acidic reaction and carries sulphur-containing compounds, for example, sulphates, hydrogen sulphide (H₂S) is released from water into the gas phase with the appearance of a strong unpleasant smell. The released gas is adsorbed on the concrete walls of the sewer and is gradually oxidized by thiobacteria to sulfuric acid (H₂SO₄), which begins to corrode the concrete, as evidenced by a drop in its pH. If this process is uncontrolled, then the result is the destruction of the sewer. The speed of this process depends on the concentration of hydrogen sulphide, the grade of concrete and the presence/absence of a protective layer.

Schematically, this process can be represented as follows:

One of the most effective solutions to this problem is to adjust the pH of wastewater from acidic to basic. As a result, the equilibrium of the reaction below shifts to the left, contributing to the formation of aqueous S^2- and not gaseous H₂S.

S^2-  + 2H⁺ = H⁺ + HS^- = H₂S↑

 Aqueous phase                              Gas phase

Below you can find a phase diagram showing the concentration of all substances depending on pH:

As can be seen at the pH of 8.5, the release of gaseous H₂S drops almost to zero. If there is no release of hydrogen sulphide into the gas phase, then there is no biochemical corrosion of the sewage system.

The MagTreat^® - S reagent by Brucite+ produced on the basis of natural magnesium hydroxide is the most effective and at the same time safe alkali, giving many more hydroxide ions than caustic soda (NaOH) for example.

The reagent also provides a very high buffering capacity of wastewater, which prevents the loss of alkalinity with time resulting in a pH decrease (acidification) after the dosing of the reagent into the system.

So how does it work? Typically, the reagent is introduced into the sewage system where the wastewaters are collected and starts its way to the municipal wastewater treatment plant. In this case, wastewater does not emit H₂S along its entire path and comes with an already optimum pH of 8-8.5 for biological treatment.

Magnesium hydroxide is classified as sparingly soluble in water. Inside wastewater with an acidic reaction MagTreat^® begins to dissolve gradually releasing magnesium cations and hydroxide anions that neutralize the acids. Due to its limited solubility, MagTreat^® is consumed gradually, providing the system with a “buffer effect”. Divalent Mg²⁺ cations are involved in the processes of coagulation, compaction of sewage sludge, and are also micronutrients for activated sludge bacteria. Due to the formation of insoluble or poorly soluble salts with various anions, MagTreat^® is used to precipitate phosphates, magnesium-ammonium phosphates, fluorides, and regulates the content of sulphides, resulting in the reduction of odour in the wastewater treatment plant. Hydroxide anions promote the precipitation of heavy metals in the form of insoluble hydroxides. Magnesium hydroxide forms insoluble magnesium-ammonium phosphate with phosphate and ammonium ions, decreasing the N and P load in wastewater.