During the electrolysis, the pH of the electrolyte
increased with increased electrolysis time, as seen by final
pH value, which was 7.60 for aluminum electrode and 9.62
for copper electrode in an electrolysis time of 30 minutes
(Fig. 3).
In case of a copper anode, pH increased dramatically in
the period of electrolysis and then gradually afterward.
Copper(II) species (5) produced by electrolytic dissolution
also caused the treated water to turn blue. Moreover, above 1
mg/L, copper would cause staining of laundry and sanitary
ware and it would lead to bitter taste in water [22].
Consequently, an aluminum anode was seen to be more
suitable for algae removal, and it was selected in further
experiments.
B. Effect of Agitation on Algae Removal Efficiency
An advantage of the ECEF process is that, if there is no
need for the external mixing during its operation, it can save
energy. So, in this study, the effect of the mixing rate on
algae removal was investigated by varying rotational speed
from 0 to 600 rpm. The initial pH of 7 and applied current
density of 20 A/m2
were kept constant for all trials. The
result indicated that the efficiency decreased with increasing
rotational speed, that is from 96.1% at 0 rpm to 25.1% at
600 rpm.
In an electrolysis reactor, the mixing of solution
originates from the electrolysis of water which produces
turbulence from the rising motion of oxygen and hydrogen
micro-bubbles.
Furthermore, it leads to a thermal density gradient. The
temperature of electrolyte solution near electrodes is higher,
due to the power input during the treatment process.
Heightened temperature could cause density difference with
the rest of bulk solution resulting in the occurrence of
circulation [23].
Therefore, agitation is a vital factor in algae removal.
The agitation during the operation should be carefully
calibrated not only to generate good mixing, but also to
Time (min)
0 10 20 30 40 50 60
pH
7.0
7.5
8.0
8.5
9.0
9.5
10.0
10.5
Copper anode
Aluminum anode
Figure 3. Variation of pH as a function of electrolysis time using different
anode materials (CD:20 A/m2
; initial pH:7).
sustain algal flocs forming without being broken apart as
well as to avoid the dispersion of micro-bubbles