Solar-Driven interfacial evaporation for decentralized direct potable reuse of domestic wastewater

Water scarcity in arid areas requires the exploitation of unconventional water resources like domestic wastewater (DWW). Although direct potable reuse (DPR) of DWW as an alleviation is mature based on membrane and advanced oxidation, it is energy- and carbon-intensive with requirement of well-developed infrastructure. Recently, emerging solar-driven interfacial evaporation for sustainable freshwater reclamation has been practiced on seawater desalination but its feasibility of DPR from DWW has not been investigated. Herein, a solar-absorber of b-TiO₂-DW was constructed by coating delignified wood (DW) with black reduced TiO₂ (b-TiO₂) to conduct DPR from DWW in a solar-thermal system, wherein b-TiO₂-DW with anisotropic thermal conductivities and enhanced sunlight absorption facilitates DWW evaporation at air–water interfaces with a DRP rate of ∼1.25 kg·h⁻¹·m⁻²-absorber in ∼97.5 % photothermal conversion efficiency and ∼90 % evaporation efficiency under simulated illumination (100 mW·cm⁻²) in the lab. For real solar illumination outdoors (0.8–87.2 mW·cm⁻², 10 h), DRP rate reaches ∼7.65 kg·day⁻¹·m⁻² that can satisfy the demand of daily drinking water for 2–3 persons. The moderate temperature at evaporation interfaces, physical adsorption, and reactive oxygen species generated by b-TiO₂-DW synergistically inhibit conventional and emerging (in)volatile contaminants into PRW and prevent biofouling on absorbers. A life cycle assessment (10-years life-cycle amortization) shows that solar-thermal system has lower cost ($ ∼0.027 kg⁻¹ PRW) and carbon footprint (∼0.085 kg CO₂-eq·kg⁻¹ PRW) than current technologies ($ 0.25–1.14 kg⁻¹ PRW and 0.67–1.17 kg CO₂-eq·kg⁻¹ PRW). Although DPR efficiency of solar-thermal system needs further enhancement, its flexibility indicates a promising scenario for decentralized DPR in undeveloped areas with laggard infrastructures.