Our green solution: Ammonium Sulphate

Ammonium sulphate is a byproduct of biomethane

Ammonium sulphate is a byproduct of the production of biomethane. It is used as a fertiliser in the agricultural industry. And has a lower carbon footprint than artificial fertiliser, making it environmentally friendly.

What is ammonium sulphate?

Ammonium sulfate is a chemical compound with the formula (NH4)2SO4. It is a white crystalline solid that is highly soluble in water. It is commonly used as a fertiliser to provide plants with nitrogen and sulfur. Ammonium sulfate is produced by the reaction of sulfuric acid and ammonia and is typically sold as a granulated powder. Ammonium sulfate is also used in the production of dyes and other chemicals.

A byproduct of biomethane?

The materials used to make biogas are organic waste streams, such as poultry manure. This material is being ‘fed’ to the anaerobic digester tanks (reactors) and is typically diluted with water (or with recycled liquids). This is necessary so that it can be pumped to and from the reactors. 

Some of the liquids for diluting the feed material are obtained by separating the digestate into solids and liquid fractions by means of a decanter centrifuge. The liquid fraction from the digestate is then used for diluting the feed material again. This continual recycling of liquids within the anaerobic digestion plant (AD) can lead to a build-up of ammonia within the reactors, inhibiting the anaerobic bacteria’s activity and reducing biogas production.

How do we make ammonium sulphate?

To reduce the ammonia levels within the reactors, the recycled liquids are first processed in an Ammonia Removal system called an ‘ammonia stripper’. In this process, the liquid digestate is heated, and the ammonia gas is removed from the liquids by spraying the digestate over a stream of air that carries away the volatile ammonia gas that is released from the heated liquids. 

The ammonia-rich air is then ‘washed’ in a separate stage with an acidic solution of sulphuric acid and water. This ‘scrubs’ the ammonia gas from the air and transfers it again into a liquid form that is called ‘ammonium sulphate’.

The two types of ammonium sulphate

There are two types of ammonium sulphate: ammonium sulphate liquid and ammonium sulphate crystal. The liquid sulphate is stored in large storage tanks and can be removed by road tankers to be used in other locations. The sulphate can be further processed in a crystallisation plant that evaporates the moisture to create an ammonium sulphate crystal. This crystal can be used as a dry fertiliser that is more concentrated. Therefore it is more efficient to transport than the ammonium sulphate solution.