Filtering H2S from air

Hydrogen sulphide (H2S) smells of rotten eggs and is colourless. It forms where organic matter breaks down, as in wastewater treatment plants. Chemical processes and refining also produce H2S. Breathing it in can damage your health. The gas also attacks metal parts. You remove it from the air with carbon that has an alkaline impregnation, with chemisorption media or with an alkaline scrubber.

Next step: Ask for a test filter

What the Health Council of the Netherlands says

In 2006 the Health Council of the Netherlands (Gezondheidsraad) gave advice on H2S in the workplace. Some points from that advice:

The odour threshold is 0.18 mg/m³. So you can smell H2S at a very low concentration.
The Dutch MAC value (maximum workplace concentration) at that time was 10 ppm (14 mg/m³), averaged over 8 hours.
The Council recommended 2.3 mg/m³ (about 1.6 ppm) as an average over an 8-hour working day.
H2S is flammable and can explode in air.

Source: Health Council of the Netherlands, Hydrogen sulphide (zwavelwaterstof), 13 July 2006.

In sewers and manholes you often work in a confined space, with a risk of suffocation and poisoning.

Which filters remove H2S from air?

Technique	How it works	Removal according to iplo.nl
Activated carbon	the gas sticks to the carbon; plain carbon captures H2S to a lesser extent than odour and VOCs	95 to 99 per cent, residual emission 1 to 10 mg/Nm³
Activated carbon with an alkaline impregnation	H2S is an acid gas; the alkali binds it chemically
Carbon with potassium iodide (KI)	raises the uptake capacity; H2S is oxidised to SO2
Chemisorption media	alumina with potassium permanganate; binds H2S, SO2 and mercaptans, among others
Alkaline scrubber	H2S dissolves in a scrubbing liquid with caustic	90 to 95 per cent, residual emission below 15 mg/Nm³

Residual emission is what is still in the air after the filter. It is given in mg/Nm³: milligrams per cubic metre of air, converted to a fixed temperature and pressure so that measurements can be compared. iplo.nl is the Dutch government's information point on environmental rules.

With impregnated carbon, the reaction with H2S is almost irreversible. An alkaline scrubber is used mainly in sludge processing, sewage pumping stations and wastewater treatment plants, for inlet concentrations of 1,500 to 15,000 mg/Nm³.

For a high load, as at pumping stations, treatment plants and sludge processing, there is the deep bed scrubber. Versions go up to a flow rate of 6,500 m³/h. See Filter installations.

H2S and corrosion

H2S is one of the acid gases that attack electronics. Ducts and fans suffer from it too. Want to know how corrosive the air in a technical room is? See Corrosion protection.

Where is H2S released?

Wastewater treatment plants: the air extracted from sludge storage and digestion.
Petrochemicals and other chemical industry, coke ovens, the viscose rayon industry and tanneries.
Biogas plants.
Ships, from the black-water (sewage) tanks.

Do you work at a sewage pumping station or treatment plant? That is the subject of our site on odour at sewage pumping stations and our site on odour at treatment plants. For H2S in biogas: our site on biogas cleaning.

How do you know how much medium you need?

A one-off gas analysis is a snapshot. A test filter on a side stream shows over a longer period which medium works and how long it lasts. See Filter unit rental.

Next step: Ask for a test filter