Nitrogen and water recovery from animal slurries by a new integrated ultrafiltration, reverse osmosis and cold stripping process: a case study

The correct management of livestock manure represents one of the major challenge for the agricultural sector development, as it may ensure environmental and economic sustainability of livestock farming. In this work, a new treatment process called N-Free®, was monitored on two plants treating digested cattle manure (DCM) and digested swine manure (DSM). The process is characterized by sequential integration of solid/liquid separations, ultrafiltration, reverse osmosis and cold ammonia stripping. Solid and liquid streams were characterized regarding TS, TKN, N-NH4+, P and K content allowing to draw a complete mass balance. The main results were a substantial reduction of initial digestate volume (38 and 51% in DCM and DSM respectively) as clean water and a high N-NH4+ removal percentage (47 and 71% in DCM and DSM respectively), through cold ammonia stripping, allowing the production of up to 1.8m3 concentrated ammonium sulfate, every 100m3 of treated digestate. The concentrated streams, rich in either organic or mineral N, P and K, can be efficiently used for land application. The N-Free® technology demonstrated to be a valuable candidate for the path toward nutrient and water recycle, in a new sustainable agriculture and farming concept.