Highly toxic, hydrogen sulphide (H2S) gas can be produced in large quantities in animal farms, industrial plants, sewers or sewage treatment plants, and has a distinctive and unpleasant rotten egg smell causing frequent odour complaints.
H2S gas is a consequence of anaerobic mechanisms at low pH which favour sulphate reducing bacteria (SRB), and results in the generation of this poisonous “rotten egg” gas in sewers.
People can usually smell hydrogen sulphide at very low concentrations in the air, ranging from 0.0005 to 0.3 parts per million (ppm). There is no way to tell whether concentrations of hydrogen sulphide are low or high by smell alone.
In fact, very hazardous concentrations (>100ppm) will temporarily eliminate ability to smell the gas. You should not rely on your nose to evaluate possible H2S danger!
Hydrogen sulphide levels can change based on a number of factors such as fluctuations from the source, or from changes in weather patterns.
In general, low pH and high temperature tend to favour evaporation of hydrogen sulphide, putting people and infrastructure at higher risks.
Odorous emissions from wastewater treatment plants (WWTPs) can create a nuisance for surrounding neighbourhoods. As population increases, houses are being built closer to WWTPs, with buffer zones around WWTPs that offer protection from unwanted odours decreasing. In many councils around
Australia, there is a growing pressure to control odorous emissions.
Emissions of odorous compounds increase during the summer months, not only because of increased H2S volatility (evaporation) but also because of an increase in anaerobic bacterial activity, as oxygen is less soluble at higher temperatures.
It is recommended that plant operators measure H2S more regularly in the summer months, and step up odour control measures, such as dosing ACTI-Mag magnesium hydroxide, which keeps the pH high and stops the formation of H2S from dissolved sulphides.
ACTI-Mag has a higher neutralising value per kilo when compared with caustic while being significantly safer to handle than other traditional alkalis, making it a very safe
and cost competitive option for hydrogen sulphide gas (H2S) control in sewers.