90% of the color with optimum parameters. Jiang et al. achieved
comparable efficiency in their article [8]. According to WHO guidelines
for drinking water, drinking water should ideally have no visible
color [29]. Levels of color below 15 as true color units (TCO)
are acceptable to consumers. However, WHO does not give
health-based guideline for color in drinking water.
TOC removal with different cell constructions can be compared
when TOC concentration of the samples is presented as a function
of aluminum concentration dissolved from the electrodes (Fig. 3).
With pH 3, there was no significant effect if the aluminum originated
from either the anodes or the cathodes. TOC concentration
depended linearly on the aluminum concentration added to the
solution. In low pH (typically at pH < 6), the mechanisms of NOM
removal are mainly charge neutralization and compression of double
layer because hydroxides are not stable in this environment
[3,30]. It is interesting that TOC removal did not show any stabilization
at low concentrations, and it is possible that even lower
TOC concentrations could be achieved with longer treatment
times. Models show some errors for this pH, especially with Cell
C, which predicts stabilization of TOC concentration at approximately
6 mg/l.
Also, with pH 4 electrode construction did not have a significant
effect on the TOC removal per aluminum added. With pH 4, TOC removal
was not linear as a function of aluminum, but rather asymptotic,
and TOC removal stabilized at approximately 4 mg/l
concentration with the cell constructions tested. It seems that aluminum
concentrations higher than 8 mg/l were not effective. Final
pH was near neutral, and therefore metal hydroxides are the predominant
form of aluminum in the solution. Hydroxides form flocs,
and sweep coagulation and bridging are the predominant mechanisms
of the NOM removal. In adsorption, mechanism charged