In RENURE project, stripping and scrubbing technology is used to recover nitrogen from animal manure in the form of ammonium nitrate or ammonium sulphate, depending on either nitric acid or sulphuric acid is used. This technology can be applied to the liquid fractions of either animal manure or digestate, or their mix. The process consists of two steps: in the stripping step, air is blown into the first compartment to remove the gaseous ammonia that is released from the thin fraction of manure or digestate due to increased pH and/or temperature; in the successive scrubbing step, the ammonia-rich air is sprayed with a strongly acidic solution to form the ammonium salts. The recovered ammonium salts usually have a slightly acidic pH (around 5-6), which is suitable for application in soils with neutral or alkaline pH. Given the status of manure in Nitrates Directive, application of these ammonium salts are limited to 170 kg N /ha/year, therefore the applied volume of ammonium salts haven't shown any negative effect on soil acidity yet, according to the current results. However, research is needed to monitor and evaluate the long-term impact.
During the stripping and scrubbing process, the amount of acids added to the manure is calculated based on the ammonium content of the manure, the targeted nitrogen content in the recovered products, the flow rate of the air and acids into the system. According to past research, approximately 7.7 kg 60% HNO3 (Brienza et al., 2023) or 7.3 kg of 50% H2SO4 (Brienza et al., 2021) is needed to recuperate 1 kg of N from the manure fractions. The market price of the acids varies, compared to nitric acid, sulphuric acid has a competitive price and is more commonly used for the NH3 washing step.
If you are interested in more details on the economic assessment, please feel free to check the wo scientific publications on the technology:
https://www.sciencedirect.com/science/article/pii/S0925857423000289#bb0045
https://www.sciencedirect.com/science/article/pii/S0959652621016279
