Spent caustic wastewater treatment using direct contact membrane distillation with electroblown styrene-acrylonitrile membrane

Abstract

Spent caustic is classified as a highly polluted and high-risk hazardous wastewater, which severely threatens the environment. In this work, a novel approach was proposed to treat the neutralized spent caustic wastewater using an electroblown nanofibrous styrene-acrylonitrile (SAN) membrane for direct contact membrane distillation (DCMD). The obtained results revealed that the permeate flux of the SAN membrane was lower compared to the commercial polytetrafluoroethylene (PTFE) membrane owing to the thicker structure. The higher surface hydrophobicity of the SAN membrane limited the intrusion of the feed water into the membrane pores. Therefore, extremely pure permeate water was produced. Stable permeate flux (12.03 kg/m2 h) and rejection factor (99.98%) were achieved for the hot-pressed SAN membrane during 96 h continuous DCMD test. Water contact angle of ˃ 90° was remained for both PTFE and SAN membranes, showing that DCMD performance was considerable even after 96 h operation. Besides, the chemical oxygen demand and sulfide removal factor for the fabricated membrane were 99.2 and 99.99%, respectively. Overall, the neutralization followed by the DCMD process can be considered as a proper alternative for treating the spent caustic wastewater.