A Systematic Study of Ammonia Recovery from Anaerobic Digestate Using Membrane-Based Separation.

Ammonia recovery from synthetic and real anaerobic digestates was accomplished using hydrophobic flat sheet membranes operated with H 2 SO 4 solutions to convert ammonia into ammonium sulphate. The influence of the membrane material, flow rate (0.007, 0.015, 0.030 and 0.045 m 3 h -1 ) and pH (7.6, 8.9, 10 and 11) of the digestate on ammonia recovery was investigated. The process was carried out with a flat sheet configuration at a temperature of 35 °C and with a 1 M, or 0.005 M, H 2 SO 4 solution on the other side of the membrane. Polytetrafluoroethylene membranes with a nominal pore radius of 0.22 µm provided ammonia recoveries from synthetic and real digestates of 84.6% ± 1.0% and 71.6% ± 0.3%, respectively, for a membrane area of 8.6 × 10 -4 m 2 and a reservoir volume of 0.5 L, in 3.5 h with a 1 M H 2 SO 4 solution and a recirculation flow on the feed side of the membrane of 0.030 m 3 h -1 . NH 3 recovery followed first order kinetics and was faster at higher pHs of the H 2 SO 4 solution and recirculation flow rate on the membrane feed side. Fouling resulted in changes in membrane surface morphology and pore size, which were confirmed by Atomic Force Microscopy and Air Displacement Porometry.