Electrochemical to maintain a homogeneous solution in the

Electrochemical cell of required
volume was fabricated. Iron/Copper plates were used as electrodes (anodes and
cathodes) and arranged in bipolar configuration. EC reactor is filled with 1.5L
of raw sample, placed on magnetic stirrer. Electrodes were connected to the
positive and negative terminals of the DC power supply. Experiments were
carried out at different Voltages and at pre-optimized 9V, 430 Rpm for
different time intervals, different electrode material. Electrode spacing was
maintained 1cm using separating stand. The sample were retrieved from the
reactor was filtered using A1 filter paper and filtrate used for the
characterization.

 

1.2.      Batch
ECC studies

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Experiments were carried with 4 electrodes
arranged in bipolar condition. Only the outer electrodes were connected to the
DC power source to form bipolar system. Magnetic stirrer helped to maintain a
homogeneous solution in the batch reactor. Electrode plates were washed
manually using scrubber and then washed with 15% acid solution followed by
distilled water prior to use. The treated samples retrieved after each run were
filtered and the filtrate was used to analyze the change in different water
quality parameters.

 

1.3.       
Settling and Filterability

The mixture of sludge and supernatant
from EC process were mixed well, and resultant slurry used for settling and
filterability studies. Settling studies carried using graduated cylinder. The
well mixed slurry was homogenized before pouring in to cylinder and was allowed
to settle. The position of interface was measure as function of time. Each
settling experiment done up to 45 min time interval. The filterability of the sludge was tested using gravimetric
filter paper supported over funnel and graduated cylinder column. Dry Filter
paper weighed. A known volume of homogenized slurry was taken in a beaker and
poured in to the funnel. The volume of filtrate collected in the graduated
vertical cylinder with regular interval of time. Each filterability experiment
done up to 70-75min time interval. The cake formed in the funnel is removed
carefully and weighed.

 

1.4.       
Membrane Filtration

Membrane filtration done using membrane holding unit of size –
(L×W×D) – 12×5×17cms, made up of Perspex material, Peristaltic pump and
Membrane made up of Tubular PVDF membrane having Pore size 0.1µm, Membrane
area: 0.5sq.m and Size:  W×H = 13×16cms. Supernatant from batch ECC is
passed through membrane in submerged condition. Filtration process carried for
flow rate of 2.5L/hr. The filtrate was used to analyze the change in different
water quality parameters like COD, TS and TDS.

 

 

2.       
Results
and discussions

3.1. 
Batch ECC studies for different operating parameters using Fe electrodes

Batch ECC
experiments carried out to study COD degradation for different operating
conditions like various voltages with 2E, 90min ET and with 4E, 60min ET, 9V
and 2 different initial temperature of raw wastewater.

 

3.1.1.
COD degradation as a function of electrolysis time at different applied voltage
using 2E

Batch ECC experiments carried out
using 2 Fe electrodes for different operating conditions with 1V, 2V, 3V, 6V
& 8V, 90min ET.

Fig
2 COD degradation as a function of electrolysis time at different applied
voltage using 2Electrodes

 

The Fig 2 shows COD removal for 1V,
90min ET is 35.54% r, for 2V 90min ET is 71.6%, For 4V 90min ET is 76%, for 6V
90min ET is 80% and for 8V 90min ET 83%. For 8V, COD degradation almost
constant at 70, 80 and 90min ET.

 

3.1.2.
Effect of Initial Temperature on COD removal

Batch ECC experiment carried out for
the sample taken out from preservation having the initial temperature of 6oC
and for sample having room temperature 26oC using Iron electrodes
for different operating parameters with 4E, 9Volt, 430Rpm and 60min
Electrolysis time. The samples were taken out at time intervals of 5, 10, 15,
20, 30, 45 and 60mins in each set and the samples were filtered using A1 filter
paper. Filtered samples were used for analysis of COD. The Fig 3 shows the COD
degradation curves as a function of electrolysis time at starting temperature
of 6oC and 26oC.

Fig
3 COD degradation curves as a function of electrolysis time at starting
temperature of 6oC and 26oC (COD 1280-1310mg/l, pH0
6.66)

 

Initial COD for initial wastewater
temperature of 6oC was 1280mg/L and initial COD for initial
wastewater temperature of 26oC was 1310mg/L. The plot show lower the
wastewater temperature favored less COD removal. At 20min ET maximum COD
removal was observed at ambient operating temperature 26oC; the rest
40min of total ET of 60min was allowed for floc formation and aggregation.

 

3.2.
Batch ECC studies on sludge floc formation at different ET, min

Separate batch ECC experiment carried
out for ET 5, 10, 15, 20, 30, 45 and 60min using Iron electrodes with 4E,
9Volt, 430Rpm. ECC treated slurry was kept under observation to see the sludge
formation. Treated slurry sample taken for analysis of TS of slurry and the
sample of treated supernatant was taken for analysis of TS of Supernatant.
Electrodes weighed before and after treatments. Initial and final pH of
solution in EC reactor was noted for each set of experiments. Fig 4 shows the Effect of Electrolysis Time
on Sludge floc formation.

Fig 4 Effect of Electrolysis Time on
Sludge floc formation

 

The plot
shows no sludge floc formation in 5, 10, 15, 20min of ET. After EC treatment
for each ET, when treated sample was kept under observation, no sludge
formation and no settling was observed. In 30min ET there was slight sludge
floc formed with a final dried weight of sludge of 0.5421g.  In 45 min ET and 60min ET Sludge formation
was higher with a final dried sludge weighing 1.7921g and 1.9201g respectively.

 

3.3.
Batch ECC studies on Electrode dissolution as a function of change in bulk
solution pH

Fig 4.4
shows the Electrode dissolution as a function of change in bulk solution pH. Electrode dissolution and pH change
of bulk solution during batch ECC showed step change in values during ECC.
Electrode dissolution curve shows two plateaus namely, plateau 1 from 5 to 30
min ET; and plateau 2 from 45 to 60 min ET. Bulk solution pH shift from 7.73 to
8.84 was observed between 15 to 20min ET during ECC 10 min prior to maximum
electrode dissolution between 30 and 45min respectively. Electrode dissolution
causes increase in the solids concentration in the bulk solution during ECC.

 

3.4.
Batch ECC studies on TS removal at different ET

Fig 5 shows
Effect of Electrolysis time on TS removal.
As can be seen from the curves, total solids (TS) were seen to increase in the
bulk solution during ECT from its initial value of 1425mg/L to 2457mg/L at the
end of ET of 60 min.  Sludge formation
begins at ~ 45min ET to reach stable levels at 60min. TS value in the
supernatant after 60min ECC was 706mg/L showing a total solids removal of ~51%.

 

Fig 4.4 Electrode dissolution and bulk
solution pH as a function of ET

Fig 5 Effect of TS removal on
Electrolysis time

3.5. Batch ECC studies for different
operating parameters using Cu electrode

Batch ECC
experiments carried out using Cu electrodes for various operating parameters to
see the effect of initial temperature on COD removal, Sludge formation for
different ET.

 

3.6.
Effect of Initial Temperature on COD removal

Batch ECC experiment carried out for
the sample taken out from preservation having the initial temperature of 6oC
and for sample having room temperature 26oC using Iron electrodes
for different operating parameters with 4E, 9Volt, 430Rpm and 60min
Electrolysis time. The samples were taken out at time intervals of 5, 10, 15,
20, 30, 45 and 60mins in each set and the samples were filtered using A1 filter
paper. Filtered samples were used for analysis of COD

 

Table 2 Residual COD in ECC treated
effluent for different initial temperature

Sl
No

ET,
min

COD
mgL-1
@60c

COD
mgL-1
@260c

1

0

1664

2240

2

5

928

896

3

10

896

768

4

15

864

768

5

20

768

704

6

30

704

640

7

45

640

582

8

60

608

512

 

Table 2 shows the residual COD in the
ECC treated effluent for different initial temperature of wastewater. It shows
the COD removal of 63% for 60c and 77% 260c at 60min ET.
Therefore 260c is an ambient initial temperature compared to
preservation temperature of 60c. Using Cu electrode removal
efficiency of COD is less and not reached discharge limit standard of 250 mgL-1.

 

3.7.
Batch ECC studies on sludge floc formation at different ET min

Separate batch ECC experiment carried
out for ET 5, 10, 15, 20, 30, 45 and 60min using Iron electrodes with 4E,
9Volt, 430Rpm. ECC treated slurry was kept under observation to see the sludge
formation. It is observed that no sludge formation in 5, 10, 15, 20, 30 and
45min ET. For 60 min ET the sludge floc
formed with a final dried weight of sludge of 1.1477g. No clear
separation of solid /liquid interface is observed using Cu electrodes.

 

3.8. Batch ECC studies for different
electrodes on Settling, Filterability, Electrode dissolution and COD
degradation

Separate ECC
studies carried out for 3 different electrodes 4Fe, 4Al, 4Cu for 60min ET, and
9V. Settling and filterability studies carried on each set of experiments. Samples
were retrieved for the analysis of COD and Electrodes were weighed before and
after experiments.

 

3.9. Settling characteristics for
different electrodes

Settling
experiment carried out for ECC treated slurry using different electrodes. Fig 6
shows the settling characteristics for different electrodes

Fig 6 Settling characteristics for
different electrodes

 

The Fig 6
shows the volume of sludge settled interface (vs) time in minutes. As can be
seen from the curves Fe electrode showed better settling compared with Al and
Cu. Settling after Fe electrode conducted EC is quite faster, likely due to
different morphology of iron hydroxide particles, which are better defined and
higher density than Al hydroxide. Dotted line indicates band settling/ no
settling depending on the electrode material up to 15min for Cu and 5min for
Fe. Discrete and compression settling is seen to dominate all the four settling
regimes.

 

 

3.10. Filterability Characteristics of
sludge for different electrodes

Filterability
experiments carried out for BECC treated slurry using different electrodes. Fig
7 shows Filterability Characteristics of sludge for different electrodes as
sacrificial anodes.

Fig 7 Filterability Characteristics of
sludge for different electrodes

 

Fig 7 shows
the plot of 

  as a
function of volume, V. As can be seen from plot Fe electrode show better
filterability compared to Al and Cu. Cu electrode showed better compared to Al
electrode. Low filterability is ascribed to poor sludge formation or filter
blockage during filtration. Poor filtration using Cu electrode is may be due to
no separation of solid/liquid interface and for Al electrode may be due to the
gel floc formation which will be dispersed in slurry or gel particles get
entrapped into the filter medium which inhibit filtration. Pressure filtration
could possibly improve filtration in particular with Fe electrode.

 

3.11. Electrode dissolution for
different Electrodes

Separate ECC
studies carried out for 3 different electrodes 4Fe, 4Al, 4Cu for 60min ET, and
9V. Electrodes weighed
before and after treatments to observe the electrode consumption/ electrode
dissolution during treatment. Fig
8 shows Electrode dissolution for different Electrodes.

Fig 8 Electrode dissolution for
different Electrodes.

 

As can be
seen from plot, anode electrode dissolution is more and cathode is less for Fe,
Anode dissolution and cathode dissolution almost same for Al, and highest anode
dissolution and very less cathode dissolution for Cu compared to Fe & Al.

 

3.12. COD degradation for different
electrodes

Separate ECC
studies carried out for 3 different electrodes 4Fe, 4Al, 4Cu for 60min ET, and
9V. The samples were
taken out at time intervals of 15, 30, 45, and 60mins and the samples were
filtered using A1 filter paper. Filtered samples were used for analysis of COD.
Fig 9 shows COD degradation for
different electrodes

Fig 9 COD degradation for different
electrodes

 

Fig 9 shows
the plot of COD (vs) ET. As can be seen in plot Al electrode is better for COD
degradation compared to Fe & Cu. COD removal of 96% for Al, 95% for Fe
& for Cu 88.6%.  Use of Fe electrode
results in the formation of very fine brown particles and for Al electrode gel
floc formed which may cause less degradation of COD in Fe compared to Al. Using
Cu electrode very less COD degradation is may be due to partial treatment.

 

3.13.
Change in water quality for ECC treated effluent followed by membrane
filtration

After batch ECC experiments using Fe
electrodes at 9V, 60min run the EC treated supernatant was further passed
through a membrane filtration unit having membrane of pore size 0.1µm to refine
the ECC treated effluent for possible enhancement of water quality. Removal of
TS, TSS, TDS and COD were studied for membrane treated effluent to attain the
desired water quality parameters. Table 3 shows the characterization of ECC effluent and membrane filtration.

 

 

 

 

Table 3 Characterization of ECC
effluent and membrane filtration

Sl No

Parameters

Unit

Raw wastewater

ECC Effluent

Membrane Filtration Effluent

Values

Values

% removal

Values

% removal

1

COD

mgL-1

4800

224

95.3%

42

99%

2

TS

mgL-1

2600

1140

56%

90

96.5%

3

TSS

mgL-1

314

260

17.2%

0

100%

4

TDS

mgL-1

2286

446

80.4%

90

96%

 

Initial COD
of textile wastewater was 4800 mgL-1 which came to very
low level of 42 mgL-1 after membrane filtration. ECC showed 95.3%
COD removal, 56% TS removal, 17.2% TSS removal and 80.4% removal of TDS.
Membrane filtration showed 99% removal of COD, 100% TSS removal, 96.5% of
removal of TS and 96% of TDS removal. ECC will remove colour and COD, TS of
about 80% effectively but iron electrode will give light brown colour to the
treated water. To refine these deficiencies membrane filtration can be used.

 

3.14.
Point of zero charge (pHpzc)

Point of zero charge (pHpzc) for EC
generated sludge treating textile wastewater for both iron and aluminum was
done using ‘solid addition method’. Fig 4.10 shows point of zero charge.

Fig 4.10 Point of Zero Charge

 

The plot shows point of zero charge (pHpzc)
for EC generated sludge treating textile wastewater for both iron and aluminum
was done using ‘solid addition method’. The zero value of ?pH lies at the pH0
value of 8.70 for iron electrodes and 9.41 for aluminum electrodes, which is
considered as the pHpzc of the dried sludge obtained from the batch
treatment of raw textile wastewater.

 

3.       
Conclusions

Iron electrodes with 4 electrode
configuration provided maximum COD removal ranging from 70-88% at initial
wastewater temperatures of 6oC and 26oC from its initial
COD value of ~1270mg/L. Copper electrodes with 4
electrode configuration showed less COD removal efficiency compared to Iron
electrode due to no solid liquid separation during treatment even though
maximum electrode dissolution.  Al electrode is better for COD degradation compared to Fe and Cu. COD
removal of 96% for Al, 95% for Fe & for Cu 88.6%.  Dry sludge was of the order of   0.36, 1.19, and 1.28kg/m3 of raw
textile wastewater treated which is less compared to other treatment methods.  Fe electrode showed better settling compared with Al and Cu. This may
likely due to, different morphology of iron hydroxide particles, which are
better defined and higher density than Al hydroxide. And also use of iron electrode often results in the formation of very
fine brown particles which are more prone to settling than gel floc formed with
Al. Fe electrode showed better filterability compared to Al and Cu.

The zero value of ?pH lies at the pH0
value of 8.70 for iron electrodes and 9.41 for aluminum electrodes, which is
considered as the pHpzc of the dried sludge obtained from the batch
treatment of silk textile wastewater. TS
value in the supernatant after 60min ECC showing a total solids removal of
~56%. Membrane filtration showed 99% removal of COD, 100% removal of TSS, 96.5%
of removal of TS and 96% of TDS removal and can be used for reclamation
purposes. Hence the overall studies confirmed that combined treatment of
Electrochemical coagulation and membrane filtration is efficient in degradation
of organics from silk textile wastewater.

 

Acknowledgement

The author wish to thank JSS
Mahavidyapeetha, Mysuru, Karnataka, Sri Jayachamarajendra College of
Engineering, Mysuru, JSSTI campus, Mysuru, Karnataka and JSS Academy of
Technical Education, Bengaluru, Karnataka for extending laboratory facilities
to carry out this research work.