Liquid fertilizer production by ammonia recovery from treated ammonia-rich regenerated streams using liquid-liquid membrane contactors

The nitrogen load on urban wastewater should be considered as a secondary resource for nitrogen-based fertilizers. From this point of view, ammonia-rich streams obtained from a regeneration step with zeolites using 70-80 g NaOH/L could contain up to 3.5-4.5 g NH3/L as well as other ionic species (Na+, K+, Ca2+, Mg2+) and dissolved organic matter (DOM). Thus, they could be treated to obtain a valuable product composed by ammonia for fertilizing applications. A sorption pre-treatment process was carried out to remove the residual amount of DOM and to reduce membrane fouling before processing with hollow fibres liquid-liquid membrane contactors (HF-LLMC). Polypropylene HF-LLMC was used to selectively extract ammonia in single or two-step configurations using different acid stripping solutions (H3PO4, HNO3 or a mixture of HNO3/H3PO4). For ammonia recovery, the ammonia mass transfer coefficient (K-m(NH3)) and water transport by HF-LLMC were determined. H3PO4 was found to be the best acid stripping solution by one-step HF-LLMC; the ammonia removal was 76% with a K-m(NH3) of 8.8 x 10(-7) m/s. Additionally, the ammonia was concentrated 26 times, and it was recovered as multi-nutrient liquid fertilizer (NP) composed of 7.8% N and 21.6% P2O5. Furthermore, ammonia recovery was increased, reaching values up to 94%, through two-step HF-LLMC, and again H3PO4 was used as stripping solution. Finally, water transport from the feed to the stripping phase was estimated to be 0.022 L/m(2)center dot h for one-step HF-LLMC with H3PO4. Finally, the use of UV-Vis and 2D-Fluorescence was shown to be a successful approach for monitoring pore wetting events.