Encroaching residential areas combined with a less tolerant general public has resulted in a significant increase in odour related complaints over recent years.

The presence of odour also suggests that municipal assets are being subjected to concrete corrosion from acid attack. These odour and corrosion problems can be controlled using Orica Watercare’s SulfaLockTM.

SulfaLock is a low viscosity, highly concentrated aqueous suspension of magnesium hydroxide. Magnesium hydroxide is a gentle alkali reagent that is widely used for acid neutralisation. It can also be applied very effectively to control odour and corrosion problems in sewage networks.

SulfaLock can be used in two ways: Direct addition for odour control - added directly to sewers or pump stations, SulfaLock HiGel controls odours by preventing the formation of hydrogen sulfide gas and other odorous sulphur based compounds from sewage.

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Sewer crown, pump stations and manhole spray for corrosion control – sprayed annually onto exposed concrete surfaces subject to acid corrosion, SulfaLock forms an alkaline coating which can completely eliminate further asset deterioration through acid corrosion.

Process

Most sewer odour problems are due to the presence of hydrogen sulfide gas, which is formed by the biological conversion of sulphates present within sewage to hydrogen sulphide.

At neutral pH, hydrogen sulfide gas is only slightly soluble in sewage and can freely evolve from the liquid phase as a gas.

Even at relatively low levels, hydrogen sulfide gas can result in odour problems. The addition of SulfaLock to increase sewage pH to above pH 8 significantly reduces the odour emanating from sewage collection systems.

SulfaLock achieves this in two ways:

  • The total sulphide concentration is reduced
  • The solubility of hydrogen sulfide gas is greatly increased.

Due to its limited solubility, the addition of SulfaLock can gently raise sewage pH to a maximum around pH 9, which corresponds to the maximum solubility of hydrogen sulphide and minimum odour.

This feature allows the addition of a large amount of alkalinity or buffering capacity to sewage without increasing sewage pH to very high levels.

This alkalinity remains within the system and is utilised as required in the sewage network and allows the odour control to be sprayed (annually or bi-annually) onto sewer crowns, walls, pumping stations, manholes or any other concrete surfaces exposed to hydrogen sulfide gas. SulfaLock forms a durable alkaline coating which can completely eliminate concrete corrosion.

Its unique fluid properties allow a coating to be built onto surfaces without excessive runoff. Unlike other coating technologies, the application of SulfaLock requires minimal surface preparation. Actual application can be performed on working sewer systems with manned entry or flow diversion usually not required.

Magnesium hydroxide has long been used to maintain pH during the nitrification process. Tests show that SulfaLock will not increase the amount of sludge that is produced in the treatment plant. Due to the cationic nature of SulfaLock, floc formation, settling rates and dissolved air flotation processes are all improved.

SulfaLock offers a safe, inexpensive alternative (or supplement) to continuous chemical addition. The acid corrosion common to many sewer collection systems is due to the formation of acid produced by the biological conversion of hydrogen sulfide gas to sulphuric acid. Exposed concrete surfaces with pH values below pH 5 are subject to severe degradation by acid corrosion.

Benefits of SulfaLock

  • Reduces odour complaints associated with sulphides in sewer networks and at treatment plants
  • Significant capital expenditure resulting from sulphide related corrosion can be deferred
  • Simple to use, based on pH and sewer flows
  • Safer working environment by reducing hydrogen sulfide gas
  • Performance of sewer treatment is enhanced by improved nitrifi-cation and improved flocculation and settling.