Common municipal wastewater treatment problems and how to fix them
As urban areas grow in our major cities, services and infrastructure also increase. Wastewater networks is one such system that is growing along with our cities. Wastewater must be pumped via pump stations and rising mains to treatment plants before it is released into Australian waterways. This network of piping through urban and commercial districts creates the opportunity for odour complaints.
Every manhole, pump station, and treatment plant inlet structure is a potential source of emissions and therefore odour complaints. Here are some common municipal wastewater problems along with their solutions.
The formation and release of H2S
The primary source of odour complaints from municipal wastewater systems is the formation and release of H2S gas. Bacterial action in the wastewater causes sulphates to be converted to sulphides and then to H2S. This gas has a “rotten egg” smell, which is noticeable to the human olfactory system even at very low levels.
There are two main treatment options for H2S odours liquid phase treatment and gas phase treatment. There are treatment methods available for each:
|Liquid Phase Treatment Options||Gas Phase Treatment Options|
Ferrous Chloride Dosing
Magnesium Hydroxide Dosing
Calcium Nitrate Dosing
Liquid phase treatment
Liquid phase treatment is accomplished by dosing a chemical reactant into the wastewater piping network. Different chemicals affect the bacterial activity in the waste water in different ways, but their common result is a reduction in the formation of H2S gas being released to the atmosphere.
Reacts with sulphides in wastewater to form iron sulphide, which precipitates out of solution. With the removal of sulphides, H2S cannot be formed and therefore cannot be released into the atmosphere. Ferrous Chloride can be dosed anywhere in the wastewater network, even after the action of bacteria has caused septicity. It is a very effective chemical dosing solution, but care must be taken when handling Ferrous Chloride, which is classified as a dangerous substance.
Raises the pH of wastewater to a level of approximately 8.5. The alkaline characteristic of the solution inhibits bacterial action in the wastewater, thus breaking the chain of reactions that form H2S. Under alkaline conditions, dissolved sulphides also remain in the solution, and conversion to H2S gas is inhibited. Magnesium Hydroxide is best dosed as far upstream as possible to take effect before the wastewater turns septic.
This can offer an alternative source of oxygen to bacteria, rather than the sulphates in wastewater. Bacteria feed on the nitrates from the chemical additive, which breaks the chain of reactions that form H2S. Calcium Nitrate must be dosed as far upstream in the network as possible to prevent the wastewater from turning septic.
Gas phase treatment
Gas phase treatment is accomplished by treating the gas as it leaves the wastewater system so that it is stripped of H2S as it enters the atmosphere.
Using activated carbon technologies, carbon filtration removes up to 99.5 per cent of H2S from gas as it passes through the filter. The carbon filter has millions of pores between the carbon atoms, which attract H2S molecules. This process is called adsorption and results in H2S molecules being trapped in the carbon filter. Once all the sites are used, the filter is spent and needs to be replaced. OdourPro supplies carbon filtration systems in smaller passive units or larger extraction systems.
This uses micro-organisms to remove H2S. Up to 95 per cent of H2S molecules are removed from the gas as it passes through the filter. Biofiltration media beds must be kept at ideal conditions for the micro-organisms by keeping them moist. Gases are released from the system via a vent stack.
The emission of odorous volatile organic compounds
H2S is not the only source of odour from municipal wastewater systems. Volatile Organic Compounds (VOCs) are also noticeable as irritants to the human olfactory system. VOCs cannot be treated by chemical dosing systems in the liquid phase, they can only be treated by gas phase filtration.
Using double treatment
Both activated carbon filters and biofilters are effective to remove VOCs along with H2S. For this reason, gas phase treatment is often implemented along with chemical dosing. This double treatment captures all potential sources of odour.
It is also possible to implement a hybrid gas phase treatment solution using carbon filter and biofiltration. This solution is effective for persistent odour problems leading to poor relationships with the surrounding community.
Contact OdourPro for more information about municipal wastewater problems and their solutions
OdourPro has more than 25 years of experience in providing solutions for municipal wastewater. We supply chemical dosing systems for liquid phase treatment. Our carbon filtration and biofiltration technology for gas phase treatment is state of the art.
Find out more about our municipal wastewater odour solutions or call our expert team on 1800 510 704 today to arrange a consultation.
OdourPro on 21 November 2016
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