Studies show chemical dosing is the most effective form of odour control
Municipal waste water is notorious for generating odours that affect the surrounding community. Most of these complaints relate to the pungent rotten egg smell associated with the release of H2S gas.
Some odour control methods are designed to mask the odour, but this just hides the problem rather than deal with it at its source. Any slight deviation in the concentration of H2S or the masking agent will cause the odour to become noticeable again. Odour neutralising agents are one step better because they drop odour particles from the air. But these systems are still trying to manage an odour problem that has already been created.
Carbon or biofilters can be installed on the vapour source (e.g. stacks) to scrub the vapours of any odour particles before they are released. But the best form of odour defence is to prevent the formation of odour producing gases in the first place.
Chemical dosing systems attack the odour problem at its source, before it reaches the atmosphere. This is the the most effective way to deal with waste water and keep on friendly terms with your neighbours.
The power of chemical dosing systems
The different chemicals used for odour control each act in a different way and are suitable for specific applications. It is important to understand the dynamics of your application to determine which is the best fit for your needs. Below are three examples where chemical dosing has been used cost effectively.
1. Tugun-Elenora system
A survey of chemical dosing use in Australia produced some interesting results. While magnesium hydroxide has more individual dosing points than any other dosing chemical, iron salts are being used to treat 66 per cent of the sewerage under the survey by volume.
Recommendations are to use more mathematical models to determine the best chemical for each system and the optimum dosing point.
2. Midcoast Water
MidCoast Water developed a trial for magnesium oxide dosing when the cost of using potable water to reduce septicity became unsustainable costs, and wastage of valuable resources. Some pump stations operate very sporadically in off peak seasons creating the perfect environment for septic conditions.
The trial was highly successful and even extended the life of their carbon filters on the vent stack. Combining the magnesium hydroxide dosing with vent stack filtering, has improved the operational costs and odour issues for MidCoast Water.
3. Yarra Water
Another case study shows it is possible to optimise dosing rates to minimise the costs of chemical dosing. At Yarra Water, pH probes and H2S sensors were installed in the sewer network to measure the effectiveness of the magnesium hydroxide dosing system.
Once a detailed study of the data had been completed, the operator was able to optimise chemical dosing through controlling the speed of the dosing pumps. This led to an operational cost saving of 20 to 30 per cent.
How do chemical dosing systems work?
Production of H2S in waste water is the result of bacteria feeding on the organic material in a septic environment. Bacteria feed on sulphates, which cause free sulphides to be released. These combine with Hydrogen to form H2S.
Chemical dosing systems act on the chemical balance of waste water before H2S is produced, thus eliminating the source of bad odours.
Ferrous dosing systems
Ferrous dosing systems act on the sulphides in the system before H2S is formed. They react with ferrous chloride to form iron sulphide, which precipitates out of the sewerage stream. Because the sulphides are now bound to the iron, H2S is not formed and no odours are released.
Ferrous dosing systems can be used upstream of the septic conditions or into the septic conditions and still be effective. Ferrous chloride’s residual properties make it suitable for treating long pipelines with a single dosing point
Calcium nitrate dosing systems
Calcium nitrate must be dosed upstream of any septic conditions in the sewerage network. Nitrates act as an alternative source of food for the bacteria, reducing their consumption of sulphates in the system. Fewer sulphates consumed means less sulphides produced and therefore a reduction in the formation of H2S.
Magnesium hydroxide dosing systems
Magnesium hydroxide dosing systems act on the sulphides in solution to prevent the formation of H2S gas. From a chemical perspective, the magnesium hydroxide raises the pH of the sewerage stream to above 8. At this pH, hydrogen sulphide remains in solution and does not progress to the formation of H2S. The overall effect is a significant reduction in odours.
Magnesium hydroxide dosing systems are ideal for waste water treatment where the pH is acidic or when the flow is very turbulent. A turbulent flow of waste water without any chemical dosing causes H2S to be released into the gaseous state and thus into the atmosphere. Magnesium sulphate keeps the hydrogen sulphide in solution even with a turbulent flow.
Contact OdourPro for more information about chemical dosing for odour control
OdourPro has extensive experience in chemical dosing odour control systems. We supply ferrous, calcium nitrate and magnesium hydroxide dosing units. Our technical experts and proven solutions can help your business overcome the challenges of odours emitted from sewers.
OdourPro on 21 November 2016
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