The 5 times dilution has an initial COD of 9600 mg/L which
was suitable for Rps. palustris TN1. DFE of the non-dilution to 5
times dilution had a dark yellow color and a series decreased
to a light yellow color. This studied implied that the lighter
color of DFE from the higher dilution resulted in higher
hydrogen production. The possible reason was that light could
easily pass through the medium compared to the non-dilution
of DFE which had a dark yellow color. Thus, the lightest color
of 5 times dilution of DFE exhibited the highest hydrogen
production. These results were similar to those using an olive
mill wastewater in which the lighter color from higher dilution
could increase the hydrogen production [26].