Investigating the impact of surfactant-salt feed solution on PTFE membrane performance under varying feed and permeate temperatures in membrane distillation

Abstract

Membrane distillation (MD) is a temperature-driven technology suitable for treating industrial wastewater, especially when utilizing low-grade heat sources like waste heat or renewable energy. Despite its potential, large-scale application of MD faces challenges due to high energy demands and operational instability caused by membrane fouling and wetting, particularly when surfactants are present. This study evaluated the thermal performance of a lab-pilot MD system using two commercial PTFE membranes. Initial experiments used saline feed solutions at varying feed and permeate temperatures. Subsequent tests introduced a non-ionic surfactant (Triton X-100), with and without NaCl, to investigate membrane fouling and wetting behavior. Results showed that higher feed temperatures increased permeate flux across all conditions, but also accelerated fouling and wetting, thereby shortening operational time. Notably, in the absence of NaCl, membrane degradation occurred more slowly, resulting in more stable performance. The novelty of this study lies in revealing the combined effect of salinity and non-ionic surfactants on the fouling and wetting performance of commercially available PTFE membranes in membrane distillation. Using a comprehensive two-stage experimental approach, the work systematically correlates MD system performance with membrane degradation mechanisms under feed conditions representative of real industrial wastewater. This dual focus not only uncovers the interplay between surfactants and salts but also provides practically relevant insights into the reliability and applicability of PTFE membranes in industrial MD operations.