Valorization of bio-fertilizer from anaerobic digestate through ammonia stripping process: A practical and sustainable approach towards circular economy

Anaerobic digestion is a technology, which converts biological wastes into biogas and biogas digestates (DIG); the latter is considered the main challenge for biogas producers. Recently, nutrient recovery technology from these DIG for bio-fertilizers production as an alternative for traditional chemical fertilizers is receiving increasing attention. This study aims to use two different biofertilizers based on DIG using ammonia striping technique which are liquid bio-based ammonium sulfate (BAS-L) and solid bio-based ammonium sulfate (BAS-S) fertilizers, besides the raw DIG and the conventional urea compound fertilizer (UCF) is used as a chemical fertilizer for comparison to produce solanaceous plants (eggplant). The agronomic effectiveness and economics of using these fertilizers are listed, and the results indicated that the eggplant yields using UCF and BAS-L were 62.65 tons/ha and 63.42 tons/ha, respectively, representing 24.5 % and 27.9 % higher than BAS-S and DIG, respectively. The agronomic efficiency (AEN) and the apparent recovery efficiency (AREN) of BAS-L fertilizer were the highest, reaching 44.8 kg DM/kg N and 7.9 %, respectively, which were significantly higher than the corresponding values of BAS-S and DIG. Furthermore, the economic benefits of various fertilizer applications were estimated and compared. The results showed that the theoretical net revenue of BAS-L fertilizer was 86065.03 $/ha, while BAS-S fertilizer and UCF were lower than BAS-L (56.7 % and 48.5 %, respectively), and the theoretical net revenue of direct application of DIG was 36958.95 $/ha. Therefore, BAS-L fertilizer has the best comprehensive fertilizer effect and economic benefits.