Odour mitigation to minimise sewer corrosion

Western Water owns and operates over 1000km of sewer mains in Victoria, Australia. Corrosion of these sewerage networks represents a huge ongoing cost to both maintain and replace damaged assets. Odours within sewerage networks are associated with the anaerobic generation of hydrogen sulphide (H2S) gas, a key component in the corrosion of concrete structures. In early 2009 a trial chemical dosing regime was initiated in order to remediate both the odours and their underlying causes within the sewerage network in order to reduce the corrosive potential within a part of Western Water’s network.

AWT carried out a process analysis of the odour generation potential in the sewerage network, a review of the different chemicals available and their potential effect on odour generation as well as potential “side effects” on reticulation and treatment systems, and then carried out the dosing trials themselves. Measurement of the H2S was carried out during the different phases of the trial and the data from this analysed to determine the profiles of H2S throughout the day as well as correlation between the H2S concentrations and the pump-outs from the two pump stations that feed the outfall.

The existing dosing regime (Biosol) was compared to another chemical dosing trial (magnesium hydroxide) at the same site during January 2010 to compare directly the odour reduction. This was evaluated in terms of pump station pump-outs, sewer retention time, a small wastewater characterisation study and H2S gas production in the downstream gravity main.

This found that magnesium hydroxide was capable of reducing odours to significantly improved levels. The difference in temperatures during the two periods meant that the results were not directly comparable however, they would indicate that magnesium hydroxide has the potential to be as effective as the proprietary chemical dose.