Isolating the Salt and Oil Discharging Area Enables the Continuous and Effective Purification of Saline Oily Wastewater

Abstract

Solar-driven interfacial evaporation holds promise for clean water production and wastewater treatment. However, simultaneously achieving the oil resistance and salt tolerance of evaporators remains challenging. In response, we proposed a self-rotating interfacial solar evaporator (SSE) with a superhydrophilic and underwater superoleophobic polydopamine/polypyrrole-coated nonwoven fabric (PDA/PPy-NF) layer. Such an SSE can isolate the salt and oil discharging areas, thus achieving continuous demulsification and crystallization by designedly guiding self-cleaning. Based on the torque balance theory, we established a self-cleaning cycle prediction model for an SSE. After optimizing the interface wettability, the SSE presented a high long-term evaporation rate of 1.86 kg m^–2 h^–1 under 1 sun, with a more than 99% oil and salt removal ratio. Taking Tianjin as an example, it is estimated that an SSE can produce freshwater with a high daily average rate of 5.5–6.5 kg m^–2, and 1 m² of an SSE can meet the daily drinking water supply for at least two adults. In conclusion, an SSE can be regarded as an ideal solution for treating saline oily wastewater, and this work is expected not only to expand the application scope of solar evaporators but also address the current water–energy challenges, thereby accelerating the realization of the Sustainable Development Goals.