The increase in energy and fertilizer consumption makes it necessary to develop sustainable alternatives for
agriculture. Anaerobic digestion and digestates appeared to be suitable options. However, untreated digestates
still have high water content and can increase greenhouse gas emissions during storage and land application. In
this study, manure-derived digestate and solid fraction of digestate after separation were treated with a novel
solar drying technology to reduce their water content, combined with acidification to reduce the gaseous
emissions. The acidified digestate and acidified solid fraction of digestate recovered more nitrogen and ammonia
nitrogen than their respective non-acidified products (1.5–1.3 times for TN; 14 times for TAN). Ammonia and
methane emissions were reduced up to 94% and 72% respectively, compared to the non-acidified ones, while
N2O increased more than 3 times. Dried digestate and dried acidified digestate can be labeled as NPK organic
fertilizer regarding the European regulation, and the dried solid fraction and the improved dried acidified solid
fraction can be labeled as N or P organic fertilizer. Moreover, plant tests showed that N concentrations in fresh
lettuce leaves were within the EU limit with all products in all the cases. However, zinc concentration appeared
to be a limitation in some of the products as their concentration exceeded the European legal limitsinfo:eu-repo/semantics/publishedVersio
