Ladda ner rapporten - Avfall Sverige

aBStraCt
Today, several biogas plants are planned. Some are large-scale or in localizations that means a long
distance to croplands. The digestate indeed contain phosphorus and nitrogen but above all large
quantities of water, which makes it tempting to try to refine the product.
Low concentration of nutrients in the digestate means that the theoretically possible value is low which
sets high demand on resource consumption of the processes to be used. In this report you can find
ammonia stripping, evaporation, ultra filter + reverse osmosis and struvite precipitation, but there might
be other methods. None of these methods will generate a profit, but are dependent of that the alternative,
handling of not dewatered digestate, for some reason (e.g. transport distance) is to expensive.
Dewatering of digestate followed by reject water treatment with aim to transform the ammonia and
organic nitrogen to airborne nitrogen (disposal) has not been discussed in this report.
In this project, visits have been made to three full scale plants and one pilot plant. The techniques on
these plants have been ammonia stripping to ammonium sulphate, ammonia stripping to ammonia
nitrate, ultra filter + reverse osmosis and struvite precipitation (pilot plant). Any appropriate plant
where evaporation with developed energy recovery is used has not been found.
Both plants with ammonia stripping work satisfying as well as the struvite precipitation plant. Struvite
precipitation should be seen as a way to separate the phosphate from the reject water.
Ultra filter + Reverse Osmosis are a functioning technique, but the concentrate was too dilute to be
possible to transport any longer distance at the current facility.