Resource recovery from anaerobic digestate: struvite crystallisation versus ammonia stripping

The wide application of anaerobic digestion for the treatment of organic waste streams and high-loaded wastewater results in the production of high quantities of anaerobic effluents. Such effluents are characterised by high nutrient content, this is why struvite crystallisation and ammonia stripping have gained interest as routes to nitrogen and phosphorus recovery. Pros and cons of both technologies have been analysed in this paper. Ammonia stripping coupled with absorption proved to be a suitable technical solution for the recovery and valorisation of the nitrogen contained in waste streams. Laboratory-scale experiments result in more than 80% of ammonia recovery using this technique. However, since the crystallisation process can simultaneously remove and recover more than 90% P and N in stoichiometric ratio (according struvite formulation) from waste streams, it is considered the preferred technique. Both processes are environmentally friendly and cost-effective in large-scale facilities although economics slightly favour the struvite formation.