Towards the circular economy — Sustainable fouling mitigation strategies in ultrafiltration of secondary effluent

Membrane separation is an emerging technology for secondary effluent (SE) recycling as an alternative water source. However, SE contains secondary metabolites which form a film on membrane surfaces, leading to a decrease in hydraulic capacity. This is an extensive study of the effect of fouling on UF performance, with a detailed analysis of foulants composition and morphology, and the evaluation of the most effective – either physical or chemical – UF membrane regeneration methods. The paper also investigates FNA (recycled from WWTPs) as an alternative acidic UF membrane cleaning agent. In the UF-DE mode, the most effective backwashing configuration was 1 s every 1 min, where relative membrane permeability decreased by 54% after 4-h, which indicated the presence of physically irreversible fouling after SE separation. An acidic-alkaline cleaning procedure in which the contribution of irreversible fouling was 13% resulted in a 100% efficiency of UF membrane regeneration. The results confirmed that recycled FNA is as efficient as pure reagent-nitric acid V and that the use of FNA can reduce the costs of chemical cleaning by 60%. To fit in with the idea of the circular economy, we proposed a new strategy of reusing spent acidic solutions as an alternative fertiliser.