Abstract
Water scarcity necessitates sustainable solutions, particularly the reuse of greywater for irrigation. However, contaminants in greywater limit their direct application, and conventional treatment methods pose challenges such as complexity and harmful by-products. Membrane technology, specifically thin-film composite (TFC) membranes, provides an efficient alternative for greywater treatment. Despite their advantages, TFC membranes suffer from reduced permeate flux, lower rejection efficiency, and fouling. This study addresses these limitations by incorporating Zeolitic Imidazolate Framework-8 (ZIF-8) and its amine-functionalized derivative (NH2-ZIF-8) into cellulose acetate-supported TFC (CA-TFC) membranes via in-situ interfacial polymerization.
The synthesized ZIF-8 and NH2-ZIF-8 nanoparticles were introduced at varying concentrations (0.1-2.0 wt.%), with CA-TFC/NH2-ZIF-8 (0.5 wt.%) demonstrating the most promising performance. Membrane hydrophilicity improved, with the contact angle decreasing from 91.7° (pristine CA-TFC) to 70.0°, a 24% reduction. Permeability was significantly enhanced, as the water flux increased from 8.90 L/m2.h to 23.56 L/m2.h. The membrane achieved high rejection rates (up to 96%) for metal ions such as Ca, Fe, K, Na, Mg, Zn, and Cu, while Al³⁺ and Mn²⁺ showed lower rejection efficiencies (<55%). Fouling resistance was also improved, with a fouling recovery ratio (FFR) increase of up to 36%.
Treated river greywater and synthetic laundry greywater (TPGW) exhibited reduced metal concentrations, meeting irrigation standards. Seed germination tests using mustard seeds demonstrated an 81% germination rate for treated TPGW, compared to 43% for untreated TPGW, while RGW germination rates improved by 15%, aligning closely with tap water controls. Elemental analysis confirmed that metal concentrations in plant tissues remained within safe limits, supporting the feasibility of using treated greywater for irrigation without adverse effects on plant growth.
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These findings highlight the effectiveness of CA-TFC/NH2-ZIF-8 (0.5 wt.%) composite membranes in reclaiming greywater for agricultural applications. The membrane not only enhances water quality but also creates conditions conducive to healthy seed germination and plant growth. This study demonstrates the potential of modified TFC membranes as a sustainable approach for greywater treatment, promoting water reuse in water-scarce regions.