Odour Control for Municipal Wastewater
Municipal wastewater is notorious for bad odours. As residential areas expand, and neighbours live closer to wastewater treatment plants, there is more and more public pressure to eliminate wastewater odours.
Odour compounds are not only a nuisance factor for neighbours, they are also a health and safety hazard. H2S is a primary culprit. This chemical compound corrodes piping which leads to increased maintenance costs and the possibility of pipe failure. In high concentrations, it can actually be fatal for workers who enter sewerage manholes, pump stations, or piping networks.
The sources of odour
The most common odour compound in wastewater systems is H2S. Bacteria feeding on liquid and solid wastes obtain their oxygen from sulphate ions (SO4) present in the wastewater stream, which creates septic or anaerobic conditions.
H2S, generated by the bacteria, is released into the air thus resulting in the well-known 'rotten egg' smell associated with sewage. Other compounds present in wastewater that contribute to odour problems include mercaptans, amines, and ammonia.
Within a wastewater system, there are some point sources that are more likely to result in odour problems than others. Dewatering and treatment plants use turbulence, pH, and temperature adjustment as part of the process. The most common odour release point is at the discharge point of rising mains.
All of these could accelerate production of odours and result in complaints from neighbours. Sources of odour from wastewater treatment plants, pump stations, and rising mains can all be treated by collecting the vapours and filtering them before releasing them into the atmosphere.
Other treatment options within the network itself include chemical or micronutrient dosing, which minimises the bacterial activity and, consequently, reduces the production of H2S.
Liquid phase dosing
The purpose of liquid phase dosing is to either prevent the formation of dissolved sulphides or to prevent dissolved sulphides converting to H2S gas. Traditional methods involve chemical dosing using one of three types of chemicals:
Calcium Nitrate offers an alternative source of oxygen to the sulphates present in wastewater. As bacteria use this alternate feed, they no longer produce H2S, thereby reducing odours.
Ferrous Chloride reacts with dissolved sulphides converting them to an iron sulphide precipitate so that they cannot form H2S gas.
Magnesium Hydroxide changes the pH of wastewater. By raising pH to 8.5, magnesium hydroxide creates an environment that is no longer conducive to bacterial reduction of dissolved sulphides. Also, at this level of pH, dissolved sulphides remain in solution so that formation of H2S gas is significantly reduced.
However, there are also micronutrient additives which can be used to dose wastewater systems. These micronutrients cultivate facultative bacteria through the nutrients they provide. Facultative bacteria break down organic matter without the release of H2S and its associated odour.
Gas phase filtration
Activated carbon contains a vast number of active sites that trap VOCs or toxic vapours. Up to 99 per cent of harmful materials are removed from vapour streams by active carbon filters. Both passive or fan-assisted models are available.
Biofilters trap odour contaminants in the moisture on the surface of the filter medium. Bacteria then break these compounds down.
Hybrid filters use both biofiltration technology and activated carbon in series to maximise the effectiveness of odour reduction.
Over the last 20 years, OdourPro has designed and constructed approximately 100 chemical dosing units for Australian wastewater authorities.
The Central Coast Council in the Gosford area has implemented ten chemical dosing facilities with another eight in progress. Hunter Water also implemented chemical dosing at the Windermere Park rising main. Both of these projects have resulted in odour-reduction of at least 95 per cent.
As well as chemical dosing, Hunter Water implemented a carbon filter at its Thornton No. 4 pump station. The same approach was taken at the Brooms Head Caravan Park in Clarence Valley. Holiday makers now enjoy an odour-free experience due to the effectiveness of this system.
Eurobodalla Council opted for a biofilter at the Surf Beach pump station, and chose to partner with OdourPro for this project due to our track record and expertise.
OdourPro is the supplier of choice for your municipal wastewater odour solutions. We have the technical expertise and industry experience to identify sources of odour and the most effective solutions. OdourPro provides ongoing services to maintain odour control equipment and to monitor performance.
OdourPro on 21 November 2016
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