Emerging investigator series: onsite recycling of saline–alkaline soil washing water by forward osmosis: techno-economic evaluation and implication

Abstract

This study investigated the techno-economic feasibility of forward osmosis (FO) for onsite recycling of saline–alkaline soil washing water with an all-purpose liquid fertiliser as a draw solution. Commercially available polyamide thin-film composite and aquaporin FO membranes (denoted HTI and AQP membranes, respectively) were compared under different operating conditions. Results showed that the incorporation of aquaporin vesicles offered the AQP membrane better transport properties (i.e. higher water permeability and lower salt permeability) than the HTI membrane. Thus, the AQP membrane exhibited a much higher water flux and lower reverse solute flux than the HTI membrane in response to either an increase in operating temperature or draw solution concentration. In particular, the water flux of the AQP membrane enhanced from 20.2 to 42.4 L m⁻² h⁻¹ with a temperature increase from 25 to 40 °C. Although over 85% water recovery with effective retention of dissolved inorganic salts could be achieved by both FO membranes in concentration of saline–alkaline soil washing water, the AQP membrane was more techno-economically feasible in practice, mainly due to its higher water flux and lower capital and operational expenses. Nevertheless, the economic favourability of the AQP membrane (i.e. the total water cost) over the HTI membrane was largely determined by its membrane element cost.