Stripping and scrubbing of ammonium using common fractionating columns to prove ammonium inhibition during anaerobic digestion

Abstract

Anaerobic digestion to produce biogas is generally considered as one of the most sustainable technologies for the production of renewable energy. During this microbial process, organically bound nitrogen is released as ammonium that ends up in the digestate and finally may inhibit the process. In this study, it is investigated if ammonium can be removed and recovered out of the liquid fraction of a thermophilic digestate from a potato processor. This is achieved at laboratory scale through an easy and self-designed stripping and scrubbing process using Vigreux and Dufton columns, which are commonly used laboratory fractionating columns. The stripping is performed at pH 8.5 and at 323.15 K (50 °C), which results in the volatilization of the ammonium present in ammonia. Subsequently, the stripping gas charged with ammonia is put into contact with a sulphuric acid solution, resulting in (NH4)2SO4, which can be used as an N–S fertilizer. In addition, the digestion experiments have demonstrated that the biogas yield is 36% higher after removal of the ammonium from the digestate compared to the untreated digestate.