Surface modified basalt membrane as a photothermal material for improved oily wastewater solar evaporation

Oily wastewater is produced from many processes in petrochemical, food, pharmaceutical, mining, and metal industries. Proper management of oily wastewater discharges is required to mitigate their environmental impacts. Basalt fabric has been reported as being uniquely suitable for oily wastewater purification via solar evaporation due to its robust structure and surface chemistry. In this study, an efficient, low-cost, and scalable 3D photothermal evaporator was prepared by surface modification of basalt fabric with TiO₂ nanoparticles for oily wastewater treatment and solar steam generation. The basalt membrane was coated with two types of TiO₂ (Degussa P25 and nitrogen-doped TiO₂) to enhance its hydrophilicity and photocatalytic properties important for fouling control. The basalt membranes were then tested for their impacts on water evaporation under various salinities and concentrations of gasoline constituents and crude oil. In pure water, the modified membrane system achieved an evaporation rate of 1.65 kg‧m⁻²‧h⁻¹ under 1 sun irradiation, which is higher than the theoretical value of 1.47 kg‧m⁻²‧h⁻¹ due to the 3D nature of the structure capable of harvesting energy from the environment. Crude oil significantly decreased the evaporation rate of the unmodified basalt membrane. However, the coating of TiO₂ nanoparticles was found to ameliorate the fouling effect by increasing the membrane evaporation efficiency from 0.75 kg‧m⁻²‧h⁻¹ to 1.42 kg‧m⁻²‧h⁻¹ in a 2.0 g/L oily water composition. This technology is promising as a new approach to manage oily wastewater storage tanks and evaporation ponds in industry in addition to improving the efficiency of resource recovery.