Solar-driven membrane distillation is an innovative technology with low energy consumption as localised heating at membrane surfaces distillation has provided a means to mitigate the influence of temperature polarisation. However, it still suffers from several challenges, including membrane fouling. This study aimed to investigate the impact of biofouling in photothermal membrane distillation (P-MD) using treated effluent from a wastewater treatment plant. Scanning Electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) analysis revealed the initial deposition of EfOM on the membrane surface through adsorption leading to initial flux decline and development of conditioning film. Microbial community analysis showed an initial inactivation with exposure to solar radiation; however, the insensitivity of Proteobacteria and Bacteroidetes to temperature and ultraviolet radiation allowed them to survive. Additionally, the presence of EfOM and solar radiation facilitated the emergence of Actinobacteriota and Cyanobacteria, which developed various defence strategies against UV and proliferated. This resulted in the development of a dense foulant layer, leading to a steady decline in flux.