Fabrication of low-cost ceramic microfiltration membranes with controllable pore size distribution using nanometer attapulgite for gravity-driven filtration of microplastic-contaminated roofing rainwater.

Rapid urbanization usually leads to water shortage and roofing rainwater contamination. Although rainwater recycling offers a potential solution to both issues, the complexity in rainwater quality and roofing environments warrants additional concerns. In present study, low-cost ceramic microfiltration membrane with controllable pore size distribution was successfully fabricated with nanometer attapulgite (NMA) and Al₂O₃ for efficiently treating microplastic-contaminated rainwater in gravity-driven membrane filtration (GDM). Both Al₂O₃ particle size and starch dosage were optimized for improving membrane porosity, permeability, and hydrophilicity. The decreasing theoretical fouling potential of NMA-Al₂O₃ membranes was attributed to the reduction in Lewis base sites which might interact with Lewis acid sites on foulants. The feasibility of NMA-Al₂O₃ membranes for treating rainwater in GDM was systematically assessed in terms of membrane fouling development, mechanism, and pollutant removal efficiency towards typical pollutants (e.g. humic-like substances and microplastics) in rainwater. Noteworthy, membrane pore size distribution could be precisely controlled for reliable microplastic removal and excellent water permeability (∼321 L/(m²·h)) with the waterhead of 0.2 m. Over the 140 L/m² NMA-Al₂O₃ membrane filtration of simulated rainwater in GDM, favorable organic removal efficiency (up to 93 %) and considerable permeability (up to 311 L/(m²·h)) were also achieved. Economic analysis further highlighted the cost-saving features of NMA-Al₂O₃ membrane filtration, which total material cost for industry-scale fabrication was only 65-75 $/m² and all energy required for roofing rainwater GDM treatment (6.81 × 10^-3 kWh/m³) was supplied by gravitational potential energy.