Concentration ( ppm ) |
Physiological effect |
0.1 - 3 |
• Odour threshold |
3 - 10 |
• Offensive odour |
• Headache |
10 - 50 |
• Nausea |
• Throat & eye irritation |
50 - 100 |
• Eye injury |
the odour-causing compounds in the wastewater or cease their formation and / or release from solution .
Control options
The conventional classes of reactions used to control H 2
S are :
• Chemical oxidation through the use of a compound with a high oxidation potential , called an oxidant , such as hydrogen peroxide or sodium hypochlorite ( bleach )
100 - 300
300 - 500
• Conjunctivitis
• Respiratory tract irritation
• Olfactory paralysis
• Pulmonary oedema
• Imminent threat to life
• Using sulfide scavengers ( iron salts ), which interact with H 2
S and sequester the sulfur into a relatively insoluble form , such as ferric or ferrous chloride , thus removing it from the cycle entirely
500 - 1,000
1,000 - 2,000
Historically , odour and / or corrosion have been treated either through vapour-phase techniques , where the headspace of a system is treated , or liquid-phase techniques , where treatments target the liquid flow . Some of the former , like scrubbers , do not provide corrosion control , while some of the latter do .
• Strong nervous system stimulation
• Apnoea
• Immediate collapse with respiratory paralysis
• Risk of death
Table 1 – H 2 S health effects at different concentrations
The most common method of inducing liquid-phase treatment inside the collection system has been by dosing chemicals . A constant and continuous dose of chemical is fed from a large reservoir with a small pump into the collection system , typically at a manhole or pump station . These are meant to react with
• Adjusting the pH : because of the way that its ions dissociate in the aqueous phase , H 2
S will not be released from wastewater if the pH is at 9 or above
A common alternative is to use an oxygen source and sulfate substitute . In an anaerobic environment , the microbiology in a collection system will use oxygen from a nitrate ( NO 3
) molecule more readily than from a sulfate ( SO 4
) molecule . As a result , benign nitrogen is released rather than H 2
S . Chemicals like calcium or sodium nitrate are commercially available ‣
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