Liquid–liquid membrane contactors incorporating surface skin asymmetric hollow fibres of poly(4-methyl-1-pentene) for ammonium recovery for liquid fertilisers

Abstract Two novel hollow-fibre liquid–liquid membrane contactor (HF-LLMC) modules named EF-010-A60 and EF-010-Q-A60 containing S-type (skin layer with low porosity) and Q-type (skin layer with higher porosity) fibres, respectively, with asymmetric, porous, and hydrophobic membranes made from poly(4-methyl-1-pentene) (PMP) were used for the efficient technology of ammonia from treated domestic wastewater to produce liquid fertilisers. The ammonia-rich stream was fed into the shell side of the HF-LLMC, while nitric acid or phosphoric acid were fed separately into the lumen to produce N-type (NO3–-NH4+) and N-P-type (NH4+-P2O5) fertilisers, respectively. The maximum NH3 recovery (>95%) was achieved in a closed-loop configuration with S-type fibres, while Q-type fibres showed a better performance in terms of the production of more concentrated N-type liquid fertiliser. With Q-type fibres, the highest values of N-P-type liquid fertilisers were achieved (8.0% N (NH4+) and 20.3% P2O5 (w/w)) using phosphoric acid, while the highest value of water flux across the PMP fibres was