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Sources of Odour in Municipal Wastewater

Flowsheet for Municipal Wastewater Odour

Odours arising from Municipal Wastewater Treatment Plants

70% of all the number of Odour Control System installations are installed on Municipal Wastewater Treatment Plants. Also the probability of the sewer network and wastewater treatment plant generating significant odours doubles as the average wastewater temperature increases by 1.7 C.

The problem of odour management starts within the sewer network. Rising mains are known to generate three times the odour than the equivalent capacity gravity main. That odour gets released either at the pump station or at the manhole when the flows change to gravity flows. Hydrogen Sulphide is generated within the sewer network by slimes that grow on the surface of the sewer pipe and therefore is very dependent on:

The wastewater treatment plants operate over a large expanse and are above ground with many channels and operating processes. To contain the odours an extensive cover and ducting system is required. While most wastewater treatment plants are situated away from the housing areas. The demand for land has not made this option always available and it is therefore important that covering and extraction is considered when designing the wastewater treatment plant.

Managing odour control on Wastewater Treatment Plants

The inlet works and the sludge handling area are two separate areas of the wastewater process that produce odours. They are physically separate and the characteristics of the odour profile for each are totally different. It is therefore important to treat both these areas separately.

Biological odour control works well when there is a consistent feed and when there is one dominant chemical species present in the air stream. Mixing of the inlet works air, mostly composed of hydrogen sulphide contaminants and Biosolids plant air dominated by ammonia contaminants generally produces an unsatisfactory result and two separate systems should be installed. This also assists in the air flow balancing of the system as there is no large length of ducting bridging the Inlet Works and the Biosolids Plant.

When you place a cover on an open channel, it will immediately reduce the odour emissions from that channel by around 80%. To achieve 99.9% requires air extraction that maintains a low pressure zone on the underside of the cover. A number of cover designs have failed because the extraction rate is insufficient to maintain the low-pressure zone. The key factors that govern cover performance is the sealing arrangement around the covers and the extraction rate.

The options for most cost-effective system to manage odour is to consider:

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