Impact of drought and water conservation on H2S formation in sewer pipes

Yuan, C 2010, Impact of drought and water conservation on H2S formation in sewer pipes, Masters by Research, Civil, Environmental and Chemical Engineering, RMIT University.

Document type: Thesis
Collection: Theses

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Title Impact of drought and water conservation on H2S formation in sewer pipes
Author(s) Yuan, C
Year 2010
Abstract One of the main problems associated with the transportation of sewage in sewer pipes has been the formation of hydrogen sulphide (H2S). In addition to being an odour nuisance, H2S emissions exceeding 1 mg/L are categorised as a health risk and can enhance corrosion potential in concrete sewer pipes.

The main processes involving sulphur in gravity sewers are sulphide generation and emission of hydrogen sulphide into the sewer atmosphere. H2S is produced from sulphate present in sewage through reduction reactions by sulphate-reducing bacteria. As the average pH of sewage is normally around 7, sulphide usually exists in the form of HS- ions and aqueous H2S. When certain conditions apply, aqueous H2S crosses the air-water interface and diffuses into the sewer pipe atmosphere. Many researchers have examined the formation and emission of H2S and have developed models to predict the concentration of sulphide both in sewage and sewer pipe atmosphere. The formation and emission of H2S in sewer systems is governed by a large number of factors. These factors include temperature, pH, hydraulic conditions (i.e. sewage velocity), sewage characteristics and ventilation.

In recent years, Australia has suffered from drought, which has led to a number of water conservation practices being implemented throughout the country. In Melbourne alone, a number of water restrictions have been put in place by the government. These new restrictions have led to reductions in quantities of sewage flowing through the sewers, which in turn have had a major impact on hydraulics in sewer pipes. This reduction in quantity of sewage has reduced flushing of the system and is likely to affect the characteristics of sewage and consequently increase potential problems of safety, odour and corrosion due to the build-up of hydrogen sulphide within the sewer.

Results showed that using synthetic toilet sewage that contained 29.5 mg/L sulphate, a higher aqueous sulphide concentration was measured compared to that at 18.2 mg/L. the aqueous sulphide concentration increased by 89.3% with the 11.3 mg/L increase in the sulphate concentration. Similarly, a higher CODs concentration, 36.8% increase was obtained with a 21.4% increase in the aqueous sulphide concentration. Increasing the sewage velocity by 85.7% increased the sulphide build-up rate by 15.4%.

The concentrations of sulphide predicted using the two-phase model were in agreement with those measured using the laboratory sewer pipe in terms of trend but agreement in terms of value varied. The predictions of H2S in the atmosphere were higher by 50 to 85% than measured concentrations. The model was also used to predict the sulphide concentrations at different sewage conditions.

Degree Masters by Research
Institution RMIT University
School, Department or Centre Civil, Environmental and Chemical Engineering
Keyword(s) sewer pipes
drought and water conservation
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Created: Fri, 23 Jan 2015, 10:28:35 EST by Denise Paciocco
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