MINISTRY
OF EDUCATION AND TRAINING

VIETNAM ACADEMY OF SCIENCE AND
TECHNOLOGY

GRADUATE UNIVERSITY OF SCIENCE AND TECHNOLOGY
-----------------------------

Le Cao Khai

RESEARCH ON THE LEACHATE TREATMENT BY
ELECTROCOAGULATION METHOD COMBINED WITH
BIOLOGICAL FILTRATION
Major: Environmental Engineering
Code: 9.52.03.20

SUMMARY OF ENVIRONMENTAL ENGINEERING
DOCTORAL THESIS

Hanoi - 2019


This thesis was done at:
-

Institute of Environmental Technology, Vietnam Academy of Science and Technology
Graduate University of Science and Technology - Vietnam Academy of Science and
Technology.

Supervisor 1: Assoc.Prof., Dr. Trinh Van Tuyen

Although, according to regulations, each landfill must have a leachate
treatment system, most of the current leachate treatment techniques in our
country still reveals many weaknesses neither the quality of treated water often
does not meet the effluent standards, especially the COD and nitrogen
parameters (VN standards 25: 2009/MONRE column B), nor difficult operation
and expensive cost. The reason comes from the leachate characteristics with the
complex composition and the continuous change by the landfill operating time.
The selection of inappropriate treatment technologies has resulted in nonresponding to discharge standards, while the leachate in landfills increases
continuously. Hence, it is necessary to find some appropriate technologies
which are able to handle all the daily leachate, improve current leachate
treatment systems and equip for the new landfills.
The option of combining electro-coagulation (EC) with biological filtration
(BF) is one of the promising solutions to increase the effectiveness of leachate
treatment. Unlike chemical coagulation, a large amount of coagulants must be
used, thus consuming a lot of chemicals as well as creating a great amount of
generated sludge, the EC process has the ability to remove effectively heavy
metals, phosphorus compounds, phenol compounds, hydrocarbons and several
pathogenic microorganisms, which are difficult to decompose by biological
methods. In addition, this process is also easy to automate and minimize the use
of chemicals thus reducing the amount of generated sludge. Meanwhile, the BF
process has the high treatment performance of suspended compounds (TSS),
total nitrogen (TN) and BOD5. In particular, the BF process on inexpensive
organic substrates such as peat, wood bark, and plastic have a higher treatment
efficiency than conventional BF processes. The reason is that the porous
organic substrates have a large specific surface area which is possible to absorb
a large amount of microorganisms, together with other physicochemical
processes, leading to very strong nitrate reduction. Combining two above
1.



Leachate is defined as any type of polluted liquid in the rubbish that
permeates through the garbage layers in landfills and entitles suspended solids,
dissolved colloids from solid wastes discharged into or outside the landfills.
The composition of the leachate varies widely depending on the composition
of the landfill waste and the landfill time. The pollutant content in leachate of the
new solid waste landfill is much higher than the old solid waste landfill. Because
in the old landfills, the content of easily biodegradable organic matter has been
mostly decomposed. Meanwhile, the leachate in the new landfills usually has a
low pH but very high content of COD, BOD5, nutrients, TDS and heavy metals. In
contrast to the new landfills, leachate in long-term landfills often has high pH (due
to increased methaneization) and the content of COD, BOD5, nutrients, TDS and
heavy metals decreases because most of the metals transfer to precipitate state as
pH increases. In particular, leachate in long-term landfills contains many high-


3
molecular compounds with many toxic chemicals that both cause dark color and
unpleasant odor, which are difficult to decompose by biological methods.
1.1.2. Impact of leachate on the environment and people
Leachate has high concentrations of pollutants such as: COD = 2000 70000 mg/l, BOD = 1200 - 27000 mg/l and many other toxics which can
permeate through the soil and contaminate the underground water sources as
well as surface water system. Bad odor in leachate can pollute the air
environment. Therefore, when leachate is discharged into the environment, it
will cause severe environmental pollution and affect public health.
1.2. Electrocoagulation overview
Mechanism of electrocoagulation process
“Electrocoagulation is an electrolysis method to treat contaminated water,
using direct current (DC) to corrode anode (usually aluminum or iron) and then
release coagulants (usually aluminum or iron ions) into the solution”.
When metal electrolysis occurs, the following processes occur:

studies with other electrodes are needed to find the optimum conditions for leachate
treatment with high efficiency and low operating costs. Therefore, the new direction
that the thesis focuses on is study on leachate treatment by the combination of iron
electrode EC and BF. The dissertation also compares the effectiveness of leachate
treatment by iron electrode EC process with aluminum electrode EC process.
Therefore, the study of leachate treatment by EC with BF is the direction
chosen in this thesis.
CHAPTER 2. STUDY OBJECT, SCOPE AND METHODS

Figure 2.1. Diagram of leachate treatment by EC combined with BF
2.1. Study object and scope
2.1.1. Study object
The pollutants in leachate (evaluated thoroughly several parameters
namely COD, ammonium, TSS, color).
Leachate used in the study was taken at the biological lake of the Nam
Son solid waste treatment complex - Soc Son - Hanoi and stored at 4oC.
2.1.2. Study scope
Study on contaminants treatment in leachate by EC method combined
with BF at laboratory scale.
The block diagram of the research system for leachate treatment in the
laboratory is shown in Figure 2.1.
2.2. Study Methods


5
2.2.2. Experimental method of electrocoagulation.
Experiments were conducted to find suitable conditions of current
density, electrolysis time, pH, electrode distance for leachate treatment.
2.2.3. Experimental methods of bio-filter
The experiments were conducted to find suitable conditions for aeration

electrolysis time on TSS treatment
density and electrolysis time on
efficiency
color treatment efficiency
The variation of pH during EC process is shown in Figure 3.5:

Thoi

Figure 3.5. The variation of pH in leachate during EC process by electrolysis time
Table 3.1. Impact of electrolysis time on COD, ammonium, TSS and color
treatment efficiency. (J= 3,896 mA/cm2)
Reaction
Treatment efficiency (%)
time (mins)
COD
Ammonium
TSS
Color
10
42,86
8,75
9,83
27,90
20
58,93
12,29
15,95
46,75
30
69,64

leachate. At current density J = 3,896 mA/cm2 (I = 3A), power consumption is
12,83 KWh/m3 leachate, when increasing current density to 4,545 and 5,194
mA/cm2, power consumption increases considerably, respectively to 18.08 and
24.67 KWh/m3 leachate. The results from Table 3.2 also show that COD,
ammonium, TSS and color performance at current density of J = 3,896 mA/cm 2
does not change significantly compared to J = 4,545 and 5,194 mA/cm 2. The
energy consumed to treat 1 m3 of leachate at J = 5,194 mA/cm 2 is almost double
that of J = 3,896 mA/cm2. Therefore, selecting the current density of J = 3,896
mA/cm2 is energy-efficient while the COD, ammonium, TSS and color
performance are not much lower than J = 4,545 and 5,194 mA/cm 2. Table 3.2
show that if the current density is smaller than 3,896 mA/cm 2, neither the power
consumption is low nor COD, ammonium, TSS and color treatment efficiencies
are small. Therefore, current density of J = 3,896 mA/cm2 is applied to the next
studies.
Table 3.2. Power consumption and COD, ammonium, TSS and color
Current
intensity
(A)

1,0
2,0
2,5
3,0
3,5
4,0

Current
density
(mA/cm2)


53,33
14,03
6,85
42,2
2,597
4,4
4,89
62,50
15,03
20,79
56,5
3,246
5,5
7,64
69,64
18,32
26,57
59,6
3,896
7,7
12,83
76,79
23,64
38,61
71,67
4,545
9,3
18,08
78,71
24,32

TSS treatment efficiency
color treatment efficiency
Table 3.3. The COD, ammonium, TSS and color
treatment efficiencies at different pH
(J = 3,896 mA/cm2, 60 mins electrolysis, electrodes distance of 1 cm)
Treatment efficiency (%)
pH
COD
Ammonium
TSS
Color
5
50,00
14,33
16,65
24,11
6
69,62
22,02
18,95
40,99
7
73,91
22,63
30,55
67,1
8
72,00
24,88
39,93

Table 3.4. COD, ammonium, TSS and color treatment efficiencies at different
electrodes distances (J = 3,896 mA/cm2, electrolysis time of 60 mins)
Electrodes
Treatment efficiency (%)
distance (cm)
COD
Ammonium
TSS
Color
1
76,79
23,64
38,61
71,67
3
63,71
20,38
27,21
64,2
5
50,00
14,85
21,1
44,1
7
45,65
10,54
8,02
28,5
Table 3.4 shows that at the electrode distance of 1 cm, the highest

on color treatment efficiency by iron
electrodes in comparison with
electrodes in comparison with
aluminum electrodes
aluminum electrodes
Electrode material is one of the parameters that directly affects the
electrolysis reactions taking place inside the solution. In each EC reaction, dissolved
anodes and flocculants play an important role to assess the method effectiveness.


11
The effect of electrolysis time on COD, ammonium, TSS and color
treatment efficiencies of iron and aluminum electrodes are shown in Table 3.5.
Table 3.5 shows that the COD, TSS and color treatment efficiencies of
iron electrodes are much higher than aluminum electrodes at all electrolysis
time. Whereas the ammonium removal efficiency of iron and aluminum
electrodes depends on the electrolysis time. Thus, it is clearly to choose the iron
electrodes for research on leachate treatment by EC.
Table 3.5. COD, ammonium, TSS and color treatment efficiencies with iron and
aluminum electrodes at different electrolysis time.
(J = 3,896 mA/cm2, electrodes distance of 1 cm)
Treaatment efficiency (%)
Electrolysis
time (mins)

COD

Amoni

TSS


6,71

27,90

19,90

20

58,93 17,24

11,71

8,19

15,95

9,12

46,75

32,91

30

69,64 22,41

14,06

11,34


27,1

71,67

58,98

80

79,29 44,83

24,79

30,24

38,97

29,1

79,39

66,64

Comparison the COD, ammonium, TSS and color treatment efficiencies
between iron and aluminum electrodes at different input pH of leachate.

Figure 3.18. Effect of pH on COD
treatment efficiency with iron and
aluminum electrodes


Al
5
50,00 18.72 14.33 15.87 16.65 13.8 24.11 22.5
6
69.62 35.9 22.02 23.57 18.95 15.24 40.99 35.7
7
73.92 44.83 22.63 25,56 30.55 22.97 67.04 60.2
8
72,00 43.58 24.88 26.46 39.93 35.83 72.19 65.13
9
62.90 30.76 19.22 22.48 19.26 13.05 50.70 45.63
10
43.75 14.2 11.23 15.76 15.74 11.38 34.58 30.32
Table 3.6 shows that the COD, TSS and color treatment performance
using iron electrode treatment efficiency are much higher than the aluminum
electrode at all pH values. Meanwhile, the ammonium removal efficiency of
aluminum electrode is higher than iron electrode. In acidic (pH < 7) and
alkaline (pH > 8) environments, COD, ammonium, TSS and color treatment
efficiency of both aluminum and iron electrodes are low. This phenomenon was
explained by Park et al. (2002): each type of metal ion in solution can create
different coagulants leading to different performance of pollutant treatment. For
example, the high alkali conditions in aluminum hydroxide and iron hydroxide
solutions exist in the form of Al(OH) 4and Fe(OH)4 respectively. These
hydroxides have poor flocculation activity, then, usually (except for some
polyaluminum products) the coagulant process is difficult to perform in an
acidic environment (Fe: pH = 4 - 5 and Al: pH = 5 - 6).
This result is the basis for selecting the input pH value of the leachate and
the appropriate electrode type. The initial pH 7 - 8 is chosen for both types of



electrodes are proved to be superior in COD, TSS and color removal


14
performance. Although the ammonium removal efficiency of the aluminum
electrode is higher than the iron electrode, it is not considerable. With the same
amount of removed pollutants, the consumed energy using iron electrodes can
be calculated to be smaller than that of aluminum electrode. The cost of the
electrodes is also an issue, as the iron electrodes is lower than the aluminum
electrodes. Therefore, iron electrodes were chosen for this study.
Comparing the results of study on COD, ammonium, TSS and color treatment
performance in leachate at appropriate conditions with previous studies is
shown in Table 3.8:
Comparing the results of the thesis with other studies shows that some leachate
indicators in this study have higher treatment efficiency and lower energy consumption.
Table 3.7. COD, ammonium, TSS and color treatment efficiencies between iron
and aluminum electrodes in different electrodes distances
(J = 3,896 mA/cm2, electrolysis time of 60 mins)
Treatment efficiency (%)
Electrodes
distance
COD
Amoni
TSS
Color
(cm)
Fe
Al
Fe
Al

conditions for the treatment are found: iron electrodes, J = 3,896 mA/cm 2, initial
pH = 7 - 8, the electrode distance of 1 cm, electrolysis time of 60 minutes.


15
Study results show that the EC process is a promising method for to treat
leachate. However, if only EC process is used, some parameters of the effluent
discharges have not met the discharge requirements. Further processing is required.
In this thesis, after EC process, treated water continues to be studied by BF treatment.
After the EC process, some of the pollutants remaining in leachate were: COD
< 30%, ammonium > 75%, TSS > 60% and color < 30% compared to the original.
Thus, ammonium and TSS are subject to treatment in the next biological process.
Table 3.8. Comparison the COD, ammonium, TSS and color treatment efficiencies in
different studies at selected conditions

COD

Amonium

TSS

Color

Thesis

71 - 77

24 - 25

38 - 40

12,5 – 19,6

Li X. et al (2011)

49,8

38,6

-

-

-

Catherine R. et al (2014)

-

-

-

80*

-

Top S. et al (2011)

45


-

Study

Treatment efficiency (%)

1.2 Study on leachate treatment by bio-filter method

Table 3.9. Some characteristics of NRR after EC process
used for input of BF process
No.
Parameters
Unit
After EC
1
pH
8,7 – 9,1
2
COD
mg/l
717 - 870
3
BOD5
mg/l
312 - 337
+
4
NH4 -N
mg/l
410 - 484

Mode 2:
45/75

Mode 3:
30/90

Mode 4:
15/105

Figure 3.26. Effect of aeration modes on COD treatment efficiency
3.2.1.2. Effect of aeration modes on ammonium treatment efficiency

Mode 1:
60/60

Mode 2:
45/75

Mode 3:
30/90

Mode 4:
15/105

Figure 3.27. Effect of aeration modes on ammonium treatment efficiency
3.2.1.3. Effect of aeration modes on nitrate treatment efficiency


17


18
Mode 4:
15/105

Mode 1:
30/90

Mode 2:
45/75

Mode 3:
30/90

Figure 3.30. Effect of aeration modes on color treatment efficiency
Table 3.10 shows that, when reducing aeration time, COD, ammonium and
color treatment efficiencies decrease, however, TSS treatment efficiency
increases. Thus, mode 1 aeration/non-aeration time = 60/60 minutes has the
highest treatment efficiency for COD, ammonium and color, but the output
nitrate concentration is too large compared to the prescribed standards. Whereas
at mode 4 aeration/non-aeration time = 15/105 minutes, the nitrate concentration
is around 44 mg/l. If aeration time continues to reduce in one cycle, it is a rule
that the system's ability to handle nitrogen is better but the COD, ammonium and
color removal performance are low. The operating cost of anaerobic - aerobic BF
system mostly comes from the cost of aeration. Therefore, the shorter aeration
time in a cycle, the lower energy cost. In terms of treatment efficiency in modes
(especially with nitrogen treatment) and aeration cost, aeration/non-aeration
mode = 15/105 minutes is chosen for further studies.
Table 3.10. COD, ammonium, nitrate, TSS and color treatment efficiencies under
different aeration modes


254,5 ±
14,70
160,32 ±
8,44
43,64 ± 1,16

TSS (%)

Color (%)

84,36 ±
0,66
87,39 ±
0,52
89,20 ±
0,57
91,07 ±
0,52

55,13 ±
1,81
46,03 ±
1,14
39,09 ±
1,61
34,75 ±
1,30


19

7: 6 lít

Mode
8: 7 lít

Figure 3.31. Effect of input loads on COD treatment efficiency
(aeration/non-aeration mode: 15/105 mins)
3.2.2.2. Effect of input loads on ammonium treatment efficiency


20

Mode
4: 3 lít

Mode
5: 4 lít

Mode
6: 5 lít

Mode
7: 6 lít

Mode
8: 7 lít

Figure 3.32. Effect of input loads on ammonium treatment efficiency
(aeration/ non-aeration mode: 15/105 mins)
3.2.2.3. Effect of input loads on nitrate treatment efficiency

6: 5 lít

Mode
7: 6 lít

Mode
8: 7 lít

Figure 3.34. Effect of input loads on TSS treatment efficiency
(aeration/ non-aeration mode: 15/105 mins)
3.2.2.5. Effect of input loads on color treatment efficiency

Mode 4:
3 lít

Mode 5:
4 lít

Mode 6:
5 lít
Mode 7:
6 lít

Mode 8:
7 lít

Figure 3.35. Effect of the input loads on the color treatment efficiency
(aeration/ non-aeration mode: 15/105 mins)
Table 3.11 shows that, when the input load increases, the treatment
efficiencies of COD, ammonium, TSS, color all decrease. Mode 4 shows the lowest

Amoni

Load
kg/m3
day

Treatment
efficiency
(%)

Load
kg/m3
ngày

Amonium
treatment
efficiency
(%)

0,120 ±
0,004

77,46 ±
1,22

0,066 ±
0,0013

99,21 ±
0,03


0,136 ±
0,0022

0,280 ±
0,0061

73,77 ±
0,65

0,157 ±
0,0011

Nitrate
Inlet

TSS

Color

Load
kg/m3
ngày

Treatment
efficiency
(%)

Treatment
efficiency

0,0025

86,46 ±
0,48

28,32 ±
0,60

98,94 ±
0,02

48,17
± 0,46

0,153 ±
0,032

85,01 ±
0,45

24,03 ±
0,44

98,88 ±
0,01

49,55
± 0,70

0,179 ±


Thesis
EC (Fe)

BF

BF

EC (Mg)

EC (Al)

BF

COD

71 - 77

73,77 ± 0,65

-

53

37 ± 2

42 ± 7

BOD



Color

71 - 72

16,7 ± 0,75

85

60 ± 13

-

Energy/m3
NRR (KWh)

12,83

-

-

1,23 US$

-

-

Figure 3.36 shows the total treatment efficiencies of COD, ammonium,
TSS and color are about 91.7; 97.77; 87.65 and 75.89% respectively. Thus,

1,3 – 2,1