*4.1.2. Effect of the photocatalyst dose*

The addition of catalyst to the solution resulted in a better bacterial inactivation than the control experiments. At low catalyst dose (0.1 g/L), the observed inactivation was not significant because of less availability of OH radicals to target a large number of bacteria. The increase in the photocatalyst dose to 0.25 g/L shows the possibility of an increase in the number of OH radicals sufficient enough to target the microorganism number, which improves bacterial inactivation. At 0.25 g/L, the maximum inactivation shows the maximum availability of OH radicals in the solution. When the photocatalyst loading is increased above 0.25 g/L, the inactivation process becomes slow where more bacterial colonies are detected for photocatalyst loading of 0.5 and 1.0 g/L. A high amount of catalyst in the solution results in turbidity increase that blocks the radiation to reach to microorganisms and other catalyst particles (shadowing or screening effect), which leads to a low rate of inactivation. The similar effect is observed for the UV photocatalytic inactivation [63, 64].
