Aims: As a highly developed oxidation process, the solar photo-catalytic process is highly used to reduce the environmental pollutants. In addition, it most sufficiently analyzes many organic pollutants and pathogenic microbial agents, completely. The aim of this study was to determine the efficiency of the photo-catalytic process in the removal of microbial pollutant of the refinery wastewater of Gonabad Behshiran Dairy Factory.

Materials & Methods: In the cross-sectional study, samples of the refinery wastewater of Gonabad Behshiran Dairy Factory were prepared in spring and summer 2015. The processes were photolysis through concentrated sun light (P1), photo-catalytic at the presence of concentrated sun light (P2), photo-catalytic at the presence of normal sun light (P3), and photolysis with normal sun light (P4). Data was analyzed by SPSS 20 software using ANOVA.

Findings: Passing from spring to summer, there were increases in the intensity of solar radiation, UV, and IR, while there was more change in UV. Using concentrated sun light, microbial removal efficiency hugely increased in such a way that there was a significant correlation between radiation intensity and microbial removal efficiency in P2 and P3 processes.

Conclusion: Compared to normal sun light, the concentrated sun light considerably reduces microbial load. In addition, TiO₂ Nano-particles in photo-catalytic process lead to a higher disinfection rate.