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		The Purification of Biogas (GTZ, 1985, 33 p.)
			(introduction...)
			0. Introduction
			1. Properties of hydrogen sulphide
			2. The origins of hydrogen sulphide in biogas plants
			3. The effect of hydrogen sulphide on the biogas plant and the gas-utilization equipment
			4. Determination of the hydrogen sulphide content of biogas
			5. Methods for removing hydrogen sulphide from biogas
			6. Purifying absorbent
			7. Requirements on the absorbent
			8. The desulphurizing apparatus
			9. Operation procedures for gas desulphurization
			10. Summary
			Appendix

3. The effect of hydrogen sulphide on the biogas plant and the gas-utilization equipment

Fermentation inhibition

Dissolved H2S is contained in the fermentation slurry. An equilibrium is set up between the dissolved H₂S and the H₂S in the gas phase. The dissolved H₂S in high concentrations can be toxic to the bacteria in the slurry. It can inhibit the production of biogas and cause its composition to alter.
Remedies - put less sulphur-rich material in the plant, dilute with water. In less serious cases stir vigorously (to drive H₂S out of the slurry).

Corrosion by H₂S

The presence of H₂S gas in biogas makes it corrosive to metal parts. Iron is subject to surface attack, although not major corrosion. Galvanized parts are similarly subject to surface corrosion.
The effect on non-ferrous metals in components, such as pressure regulators, gas meters, valves and mountings, is much more serious. They are very quickly corroded. These materials also corrode in gas engines (seals and valves).

Corrosion by SO₂ from H₂S

The combustion product SO₂ combines with water vapour and badly corrodes the exhaust side of burners, gas lamps and engines. Burning biogas in stoves and boilers can also result in damage to the chimney.

Engines

The acid which is formed corrodes engine parts in the combustion chamber, exhaust system and in various bearings. This is enhanced by frequent starts, short running times and the relatively low temperatures when starting up and after cutting off the engine. The water cooling system also provides the means (water needed to form sulphuric acid) for corrosion.

Service life

Running engines with H₂S -containing gas can reduce the service time to the first general overhaul by about 10-15%.

Engine oil changes

The suphur content of biogas used in gas engines shortens the time between oil changes. SO₂ from combustion and water vapour both dissolve in the lubricating oil. The oil becomes acidic and its properties change. It loses its ability to lubricate and sometimes corrodes metal components. Under continuous operating conditions the interval between oil changes is reduced to 200 - 250 hours.

Cooking stoves

If biogas is burned for cooking and lighting in poorly ventilated rooms' the occupants