Sewage Odour & Methane Gas More information


Odour
Sewage odour is generally a regulated cost to the industry. Sewage odour, mainly rotten egg (H2S) gas:
  • Is offensive
  • Upsets your Customers
  • Is a Health Hazard
  • An Occupational Health & Safety Risk
  • Can lead to heavy fines
  • Leads to costly infrastructure corrosion
  • Increases Greenhouse Gas Emissions
  • Is an explosive risk.


How and where are sewage odour and methane gas formed?


Sewage odour (H2S gas), dissolved sulfides (HS-) and methane gas (CH4) are formed in the biofilm / sediment (slimes) layer on the invert of the sewer pipe as shown in the photo’s below (see Ref: below)



Note how Biosol products have removed or reduced the biofilm / sediment or slimes complexes in the base of the sewer pipe. This means the cause of sewage odour, sulphide and methane gas generation within the sewer pipe has been eliminated or minimised. The rate of removal of the biofilm / sediment matrix (slimes complex) and thus the time interval to control sewage odour, corrosion and methane gas production depends on the:

  • Depth of the biofilm sediment matrix in the sewer main

  • Surface condition of the sewer pipe

  • Water scour velocity

  • Selected dose rate of the Biosol products

  • Length of the sewer main and the sustained water scour velocity for each pumping interval

  • Sediment inputs to the sewer.


In general sewer odour reductions will be observed within one month of dosing but where a combination of factors as shown in the list above occur, the process may take from 1 to 4 or 5 months to achieve optimal results.

Biosol Product out perform Magnesium Hydroxide.
A recent independent study undertaken by AWT Australia Pty Ltd, (industry consultants) for Western Water (Victoria, Australia), has show that Biosol products gave superior odour control when compared with magnesium hydroxide on the same sewer main. The detention times in the pressure main, range from about 16 - 24 hours. Sewage temperatures are in the mid 20 Celsius range during summer and autumn, ensuring a high potential for odour generation. Prior to Biosol dosing H2S levels exceeded 500ppm.

An example of Sewer odour reduction
The following graphs show the level of sewage odour reduction at a site in North Queensland Australia. Graph 1 Before Biosol “3”, dosing shows an average of 15.3ppm H2S gas and a maximum of 74.8ppm , Graph 2 After dosing with Biosol “3” shows an average of 0.8ppm H2S gas and a maximum of 3.6ppm at the same site. Note the ground temperature is generally around 30 Celsius, which means the odour generation potential is high.

Before Biosol Dosing - Odour level as shown by H2S gas - Daily average 15.3ppm Maximum 74.8ppm
Graph 1



After Biosol Dosing - Odour level as shown by H2S gas - Daily average 0.8ppm Maximum 3.6ppm
Graph 2



The reduced odour level as show by the graph 2, will have dramatically reduced sewage infrastructure corrosion. This ensures that the use of Biosol products is not a cost, but offers a substantial return on the investment from reduced infrastructure corrosion.

Sewage odour as a Health Issue

Sewage odour can range from a nuisance, objectionable odour to a serious health hazard, which kills a number of people every year. More information

Sewage odour as the cause of infrastructure corrosion
Sewage odour is the cause of most sewage infrastructure corrosion. It results from the conversion of hydrogen sulphide (H2S) gas to sulphuric acid (H2SO4). Stopping or minimising the formation of sewage odour, also minimises infrastructure corrosion from sulfuric acid. More information

Sulphide’s at the treatment plant
At the treatment plant, sulphides (HS) need to be converted to sulphates (SO4). That requires 4 atoms of oxygen for every sulfate molecule entering the treatment plant. Stopping or minimising the formation of sulfides in the sewage catchment by removing the biofilm sediment complexes as shown above, can save a lot of energy at the treatment plant in supplying this oxygen and thus save on cost and greenhouse gas emissions.

Biosol products are unique in that they treats the cause of sewage odour, infrastructure corrosion and methane gas production in sewers.

Most opposition products treat the symptom and not the cause.

Return to Sewers & Cost

References for above:
1 Bowker Robert P.G. et al. Design Manual, Odour and Corrosion in Sanitary Sewerage Systems and Treatment Plants Pg.9 United States EPA Publication N-497
Mishina,F., Nonaka, T., Hikosaka, Y., .Koga, M., Mori, T. “Microbial Corrosion of Concrete Pipes, H2S production from Sediments and Determination of Corrosion Rates”, Water Science and Technology WSTED4 Vol.23 No.7/9 p1275 1282, 1991.
3 Guisasola,A. et al. “Methane formation in sewer systems” WATER RESEARCH 42 (2008) 1421–1430