The Dungerwek process uses vapour scrubbers to remove ammonia from the gas phase. By adding H2SO4 this ammonia is converted into ammonium sulphate and then concentrated. The negative pressure required for energy-efficient evaporation is generated by a vacuum pump. This pump is connected to the pressure side of the gas compartment of the biogas plant ensuring that any residual gases emerging from the digestate are safely fed back into the biogas plant. There they are either metabolised microbiologically (e.g. H2S that could occur is converted into sulphur) or burnt in the CHPS (CH4).
This digestate is now highly concentrated and contains all the nutrients also contained in the untreated, not yet concentrated, digestate. The nitrogen contained in the digestate can be stored separately as liquid fertiliser or added directly to the digestate.
2 NH3 + H2SO4 [NH4]2SO4