Hydrogen sulphide corrosion is a common, well-documented problem in many waste water treatment systems. Hydrogen sulphide corrodes the metal and concrete pipes and tubing used for sewer systems. Hydrogen sulphide also attacks copper contacts and forms copper sulphide. Another danger of hydrogen sulphide is that when it forms in waste water, it is released as a gas and enters the atmosphere of the sewer.
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Lower the temperature of the system. The EPA reported that the production rate of sulphide is increased seven per cent or more for every Celsius degree up to 40 degrees Celsius.
Control your discharge. The potential for corrosion is lowered when sulphide-bearing wastes are controlled. High organic strength wastes lower the rate of sulphide generation. The same is true for wastes containing fats and oils and grease.
Oxidise the hydrogen sulphide in the waste water. This can be done by involving air or oxygen injection or by adding oxidising chemicals to the waste water. Air injection--such as direct injection or dissolution--is an inexpensive treatment. Oxygen injection is five times more soluble than air injection. It can be injected like an air injection or in a third manner--in a pressurised side stream. Hydrogen peroxide, chlorine and potassium permanganate are examples of oxidising chemicals. The cost of oxidising chemicals is higher than the injection methods.
Use a metallic salt, such as iron salt or zinc salt, to precipitate the hydrogen sulphide. The conversion of the dissolved sulphide into an insoluble precipitate prevents the release of hydrogen sulphide. The two soluble salts react in a solution, forming an insoluble product. That product separates from the liquid and is now referred to as a precipitate. Iron salt is economical; however, the dosages vary depending on the level of the hydrogen sulphide. The zinc salts are regulated.
Raise the pH level. Elevating the pH level causes the inactivation of the sulphide-reducing bacteria found in the slime layer. A higher concrete alkalinity reduces the corrosion rate, according to the Environmental Protection Agency (EPA). A high concrete alkalinity--for example, over nine on a pH scale--can also compromises the adhesive and bonding systems.
Tips and warnings
- These treatments are intended for a public sewer system. You should seek help from a professional if you have residential sewer problems.
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