Despite advances in sewage treatment odour control, odour from primary treatment remains a significant problem. Odour is emitted from the tank surface and the peripheral weirs and generally increases as sewage flows through a primary tank, aided by the retention of a sludge blanket and the return of odorous sludge liquors. Control strategies for such odours are difficult to develop because of a number of areas of uncertainty:
- It is unclear if odour levels in primary tank effluent follow similar rapid decay patterns to H2S.
- Storm tanks often have zero H2S emissions despite high levels throughout much of the tank storm-water.
- H2S levels can fluctuate over short time scales around a primary tank, shorter than expected from the retention time. In many tanks an odour gradient exists: high at the bottom, lower at the top. Mixing, bringing deep layers to the surface, could therefore cause odour levels to fluctuate rapidly.
- Storing sludge in a primary tank, deliberately or otherwise, seems to greatly increase the odour potential of the settled sewage. However, reducing sludge levels does not always reduce emissions. The age and history of the stored sludge may be very important in determining build up of sulphate reducing capability.
- Emissions from primary tanks can be greater than expected from the odour or H2S levels of the liquid. Bubbles, dislodged by the scraper mechanism, rising directly from the sludge layer, may cause this.
This programme aims to reduce these uncertainties through investigations with the overall objective of identifying improved, effective odour abatement strategies.
Benefits to Clients
- More cost effective odour abatement strategies for primary treatment.
- Targeted identification of risk of odour from primary treatment.