Efficient recovery of ammonia from digestate by membrane distillation: Nano-FeOOH re-entry structure modification, anti-fouling, and anti-wetting performance

Abstract

The recovery of resources from wastewater has drawn worldwide attention, and digestate has the potential to produce amino fertilizers as an ammonia-rich carrier. Membrane distillation (MD) is an effective process to recover ammonia from digestate, but membrane fouling and wetting are identified as major challenges faced. However, the research to enhance membrane fouling resistance and ammonia transfer efficiency through membrane modification has seldom been explored. Herein, we fabricated FeOOH grafted membranes with superior resistance to wetting by simple hydrothermal synthesis and fluorination. The grafted re-entrant FeOOH nanoparticles and fluorosilanes were confirmed by SEM, EDS, FTIR, and XRD. The superior hydrophobicity of the modified film was confirmed by contact angle (CA = 152.9 ± 2.8°) analysis. The fouling growth behavior of the membrane surface was monitored in situ by optical coherence tomography (OCT), and the anti-fouling performance was proved to be superior to that of commercial polyvinylidene fluoride membrane (PVDF) (no fouling accumulation was detected for 6 h). The modified membrane achieved ammonia recovery flux of 3.89 ± 0.18 g/m2 h and high ammonia recovery of 95.2 ± 2.3% without wetting occurrence. Our research illustrates that the grafting of nano-FeOOH re-entrant structures facilitates the recovery of ammonia from highly concentrated ammonia wastewater without wetting and fouling, revealing its promising prospect in MD resource recovery.