9. Ammonia recovery from raw pig slurry in a vacuum evaporation field plant

RL4: Biobased fertilisers (N, P) and soil enhancers (OC) from agro-residues

Responsible partners: Institute of Agrifood Research and Technology, IRTA

Country: Barcelona, SPAIN

An illustration of ammonia recovery from raw pig slurry in a vacuum evaporation field plant.

TRL and Scale of set up:

This demo is considered to be at TRL 6-7 and has been set up at pilot evaporator at farm scale (6.3 m³). The objective of this trial is to evaluate the ammonia recovery efficiency of a pilot vacuum evaporation system from pig slurry. An ammonia salt solution that can be used as a fertiliser is recovered.

Research line and priority:

This demo solution is linked to Nutri2Cycle research line 4 (RL-4: Biobased fertilisers (N, P) and soil enhancers (OC) from agro-residues) and is one of the shortlist priority solutions i.e. sub-research line 7 (Pig manure processing and replacing mineral fertilizers).

Description of demo investigation:

Livestock manure needs processing to recover nutrients, especially phosphorus and nitrogen, to optimize its management. Ammonia recovery from livestock manure can produce marketable products, such as fertilisers that allow for nitrogen loop closure. The present demo investigation develops low-temperature vacuum evaporation for the recovery of ammonia from livestock manure to obtain a salt solution that can be used as a fertiliser. Compared to conventional ammonia stripping and absorption, vacuum stripping operates at a lower temperature because of lower heating requirements. The field pilot plant is located on a sow farm in the municipality of Navàs (Catalonia, Spain), which has a pig slurry treatment capacity of 10 m³d^-1, is composed of a solid-liquid separator, a 6.4 m³ evaporator, a liquid ring vacuum pump, and a lactic acid bubbler. Prior to entering the evaporator, pig slurry is stored in a closed raft, where temperature increasing is favoured by sun heating, and pH value is modified to a range of 9-11 with Ca(OH)₂. Each evaporation cycle lasts for 3 hours and is performed at a temperature of 40-45°C and 800 mbar of vacuum. When the vacuum is applied to an enclosed reactor, boiling point temperature decreases to the below normal boiling point, thus reducing energy cost because of lower heating requirement. In addition, gas-phase ammonia mass transfer is boosted by the suction effect of the applied vacuum. With this field plant, it is expected to recover more than 60% of the nitrogen content of the pig slurry from reusing it as a fertiliser and close the N cycle. The recovered ammonia can be in the form of ammonium sulphate, nitrate, or lactate salt solution, among others. Due to the plant simplicity, it is suitable to become an on-farm treatment for decentralised pig slurry management. This technology can be applied directly to raw livestock manure to avoid ammonia gas emissions to the atmosphere or as a subsequent step of an anaerobic digestion process.

How it addresses the Nutri2Cycle goals:

This demo investigation addresses the Nutri2Cycle goal as it involves a field plant, which is expected to recover more than 60% of the nitrogen content of the pig slurry to be reused as a fertiliser and close the nitrogen cycle. Furthermore, NH₃ emissions to the atmosphere are aimed to be reduced. The processed livestock manure, with lower nitrogen content, should be managed as fertilizer accordingly to its composition (e.g. new N/P ratio) or further processed (e.g., to recover P).