MINISTRY OF EDUCATION
AND TRAINING
VIETNAM ACADEMY OF
SCIENCE AND TECHNOLOGY
GRADUATE UNIVERSITY OF SCIENCE AND TECHNOLOGY
-----------------------------
Duong Van Nam
STUDY ON TREATMENT OF NATURAL RUBBER
PROCESSING WASTEWATER USING INTEGRATED
PHYSICOCHEMICAL AND BIOLOGICAL PROCESSES
Major: Environmental Engineering
Code: 9 52 03 20
SUMMARY OF ENVIRONMENTAL ENGINEERING
DOCTORAL THESIS
HA NOI, 2019
The thesis was performed at Graduate University of Science and
Technology, Vietnam Academy Science and Technology
Supervisor 1: Dr. Phan Do Hung
Supervisor 2: Assoc. Prof. Dr. Nguyen Hoai Chau
Reviewer 1: Assoc. Prof. Dr. Vu Duc Toan
Reviewer 2: Assoc. Prof. Dr. Cao The Ha
Reviewer 3: Assoc. Prof. Dr. Tran Thi Viet Nga
The thesis will be defended at the doctoral thesis committee at the
Academy level, meeting at the Graduate University of Science
and Technology - Vietnam Academy of Science and Technology
at ………… on………, 20…….
The thesis can be found in:
- The library of Graduate University of Science and Technology
- National Library of Vietnam
1
INTRODUCTION
1. Rationale of the thesis
Vietnam is one of the three leading countries in exploiting
and exporting natural rubber in the world. Annually, the natural
rubber processing (NRP) industry of Vietnam generates over 25
million cubic meters of wastewater. This is among the
wastewaters having a very high level of pollutants of organic
matter, nitrogen, phosphorus and total suspended solids (TSS).
Currently, wastewater treatment technologies being applied
in the natural rubber processing industry in Vietnam are mainly
the incorporation of a number of the following processes: rubber
latex decanting, flotation, UASB (Upflow Anaerobic Sludge
Blanket), oxidation ditches, aeration tanks, aerobic biological
filtration, algae ponds, and stationary ponds. These treatment
systems still exhibit many limitations such as inadequate
treatment efficiency, especially for organic matter, nitrogen and
phosphorous; large print foot and high energy requirement.
Although the NRP industry is one of five typical industries
(textile; NRP; pulp and paper; brewery; and leachate) generating
wastewater with high pollutant load, in Vietnam research on
treatment of NRP wastewater is still limited. So far, study on
appropriate technological processes for treating NRP wastewater
in Vietnam with approach to recover nutrients and energy using
integrated physicochemical and biological processes has not
been conducted.
2
From the above reasons, this thesis was conducted to study
and propose an appropriate technological process for treating the
NRP wastewater with the aim to simultaneously solve the
following problems: (1) Energy recovery (biogas containing CH4
as fuel); (2) Simultaneous recovery of nitrogen and phosphorus as
fertilizer for agriculture; (3) Modifycation of reactors and
integration of physicochemical and biological processes to
improve the system performance in the simultaneous removal of
organic and nutrients substances in NRP wastewater.
2. Objectives of the thesis
The objective of this study is to develop an energy and
nutrients recovering wastewater treatment process combining
physicochemical and biological methods for NRP wastewater.
3. Main research contents of the thesis
1) Overview of current technologies for treatment of NRP
wastewater;
2) Study on removal of organic substances and energy
recover from NRP wastewater by Expanded Granular Sludge
Bed (EGSB) reactor;
3) Study on simultaneous recovery of nitrogen and
phosphorus from NRP wastewater by Magnesium Ammonium
Phosphate (MAP) precipitation method;
4) Study on simultaneous removal of organic and nitrogen
substances from anaerobically treated NRP wastewater in
modified Sequencing Batch Reactors (SBRs);
5) Proposal of an energy and nutrients recovering wastewater
treatment process for NRP wastewater.
3
CHAPTER 1. LITERATURE REVIEW
This chapter presented the following contents: Overview of the
natural rubber processing industry; Characteristics of NRP
wastewater; The situation of study and treatment of NRP
wastewater in domestic and oversea; Wastewater treatment methods
related to the thesis; Existing problems in NRP wastewater
treatment in Vietnam; and Study orientation of the thesis.
The review showed that the study and treatment of NRP
wastewater have attracted great attention in past decades in the
world and Vietnam as well, and achieved relatively good results.
However, previous studies have mainly focused on the treatment of
organic matter in wastewater without paying attention to the
treatment of nitrogen substances, as well as the recovery of energy
and nutrients.
CHAPTER 2. REMOVAL OF ORGANIC MATTER AND
RECOVERY OF ENERGY BY EGSB REACTOR
2.1. Materials and research methodology
1) Materials, chemicals, and equipment
Wastewater: Simulated wastewater (wastewater prepared from
coagulation process of natural rubber latex in the laboratory) was
used for the start-up period of EGSB reactor. Real NRP
wastewater was used for further studies.
Seed sludge: Anaerobic sludge from an UASB of Sai Gon - Me
Linh Brewery was used as seed sludge.
4
Experimental equipment: An EGSB reactor with a reaction
volume of 13.5 L and a height of 155 cm, divided into reaction
zone (I) and settling zone (II) as shown in Figure 2.3.
1. Control box
2. Wastewater tank
3. Wastewater supply pump
4. Scum breaking pump
5. Circulating pump
6. EGSB reactor
7. Treated wastewater tank
8. Gas measuring device
I. Reaction zone
II. Setting zone
Figure 2.3. Experimental EGSB system
2) Research methodology
Experimental procedure
Wastewater from the wastewater tank (2) was pumped into
the bottom of the EGSB reactor (6), flowed up through the sludge
bed in the reaction zone (I), entered the settling zone (II), then
flowed into the treated water tank (7). Volume of generated
biogas from the reactor was measured by the gas meter (8).
Experimental conditions
The EGSB reactor was started up with simulated wastewater
(27 days) and real NRP wastewater (60 days) by a gradual
increase in organic loading rate (OLR). After the steady state
reached, effects of OLR in the range of 7 – 20 kg CODm-3d-1 on
COD removal, biogas generation and the system stability were
investigated using the real NRP wastewater.
1
2 7 8
6
I …
….… ….. ..
… ….. ..
… ….. .. … ….. .. … ….. .. … ….. ..
… ….. ..
… ….. ..
… … ….. ..
II
3
4
5
5
2.2. Results and discussion
1) Development of anaerobic granular sludge
On day 27 On day 87
Figure 2.5. Anaerobic granules of EGSB reactor during start-up
period
The EGSB reactor start-up was performed for 87 days to
form anaerobic granules. After 27 days of starting, anaerobic
granules appeared, and particles with size of 0.5 - 1.0 mm
accounted for 38.5% of activated sludge in the EGSB reactor.
After 87 days, the amount and size of anaerobic granules in
EGSB reactor has increased significantly: at the lower part of the
sludge layer, the particles with dimensions of 0.5 - 1.0 mm and
1.0 - 2.0 mm accounted for 45.5% and 35.4%, respectively; in
the upper part of the sludge layer, these percentages were 62.6%
and 18%, respectively. The image of anaerobic granules on days
27 and 87 was shown in Figure 2.5.
2) COD removal
COD removal efficiency of the EGSB reactor after start-up
period was shown in Figure 2.8. The results showed that COD
treatment efficiency was quite stable in the experimental modes
and tended to decrease in the first days after an increase of OLR,
but quickly stabilized in each experimental mode (about 5 days).
In particular, when changing from mode (II) to mode (III) with a
6
large increase in OLR (from 11.3 to 17.7 kg CODm-3d-1), COD
removal efficiency dropped sharply, then gradually ascended but
fairly slowly. Sludge concentration in the EGSB reactor at this
period was still not high, therefore the effect of OLR was very
clear. COD removal efficiency in the modes (I), (II), (IV) and (V)
are all over 80%, and that at OLR 19 kg CODm-3d-1, was 82.5%.
Although this efficiency was lower than those at OLRs of 7.7 and
10.8 kg CODm-3d-1, it was also a relatively high.
Figure 2.8. COD removal efficiency of EGSB reactor during
steady operation period OLR (kg CODm-3d-1): (I) = 7.7; (II) = 11.3; (III) = 17.7; (IV) = 19.0; (V) = 10.8
3) Biogas generation yield
Figure 2.13 showed that generated biogas amount increased
when OLR increased. The average generated biogas amount at
different OLR modes from (I) to (V) at standard conditions was
33.6, 44.5, 63.9, 76.6, and 44.2 L/day, respectively.
The results in Figure 2.15 showed that generated biogas
amount at standard conditions was directly proportional to the
amount of removed COD. The average biogas conversion yield
0
20
40
60
80
100
0
2000
4000
6000
8000
10000
85 95 105 115 125 135 145 155
CO
D r
em
ova
l eff
icie
ncy, %
CO
D, m
g/L
Operation time, day
COD in influent COD in effluent Efficiency
I II III IV V
7
at the standard conditions for all study modes was 0.37 L/kg
removed COD.
Figure 2.13. Generated biogas amount in the steady period OLR (kg CODm-3d-1): (I) = 7.7; (II) = 11.3; (III) = 17.7; (IV) = 19.0; (V) = 10.8
Figure 2.15. The relationship between the generated biogas
amount and the amount of removed COD
y = 0.371x
R² = 0.9174
0
20
40
60
80
100
50 100 150 200 250
Gen
era
ted
bio
ga
s a
mo
un
t a
t
sta
nd
ard
co
nd
itio
n, L
/da
y
Amount of removed COD, g COD/day
20
40
60
80
100
5
10
15
20
25
80 90 100 110 120 130 140 150 160
Gen
era
ted
bio
ga
s a
mo
un
t a
t
sta
nd
ard
co
nd
itio
n, L
/da
y
OL
R, k
g C
ODm
-3d
ay
-1
Operation time, day
OLR Amount of biogas
I II III IV IV
8
CHAPTER 3. RECOVERY OF NUTRIENTS BY MAP
PRECIPITATION
3.1. Materials and research methodology
1) Materials, chemicals and equipment
Wastewater: Wastewater used in this study was the effluent of
the EGSB reactor.
Chemicals: MgCl26H2O and H3PO4 were used as additional
magnesium and phosphate sources.
Equipment: A Jar-Test was used for MAP precipitation.
2) Research methodology
Experiments: MAP precipitation were performed at different pH
values and Mg2+ : NH4+ : PO4
3- molar ratios. After reaction, the
reaction solution was let to settle and filtrated to obtain the
precipitate. P-PO43-, N-NH4
+ and Mg2+ in the filtrate was analyzed
to determine treatment efficiency. The precipitate was washed,
dried, and used to determine MAP amount and composition of Mg,
N, and P elements in the MAP precipitate.
Analysis: MAP crystal dimension was determined by SEM
images. MAP composition was determined through EDX
spectrum analysis.
3.2. Results and discussion
1) MAP recovery without magnesium addition
NRP wastewater contained significant amounts of
magnesium, ammonium and phosphate. Therefore, increasing
wastewater pH to the appropriate value could result in MAP
precipitation by reaction (1.3).
Mg2+ + NH4+ + HPO4
2- + 6H2O MgNH4PO46H2O↓+ H+(1.3)
9
The results in Table 3.2 showed that phosphate-P removal
increased from 15.6% at pH 7.5 to 44.7% at pH 9.5 and tended
to slightly increase as pH continued to increase to 11.5. On the
other hand, ammonium-N removal increased from 3.6% at pH
7.5 to a maximum value of 13.1% at pH 9.5, and then gradually
decreased to 4.1% as the pH continued to increase to 11.5.
Table 3.2. P, N and Mg removal without magnesium addition
at different pH
pH
Concentration after MAP
precipitation (mg/L) Removal efficiency (%)
PO43-–P NH4
+–N Mg2+ PO43-–P NH4
+–N Mg2+
7.5 119 214 15.0 15.6 3.6 70.0
8.0 107 209 8.8 24.1 5.9 82.4
8.5 97 204 6.5 31.2 8.1 87.0
9.0 90 197 4.0 36.2 11.3 92.0
9.5 78 193 1.8 44.7 13.1 96.4
10.0 77 198 1.6 45.4 10.8 96.8
10.5 77 206 1.5 45.4 7.2 97.0
11.0 76 211 1.3 46.1 5.0 97.4
11.5 75 213 1.1 46.8 4.1 97.8
Because MAP is soluble in acidic environment, the suitable
environment for MAP precipitation is alkaline. However, in an
alkaline environment, Mg2+ also reacts with PO43- and OH- to
form precipitates of Mg3(PO4)2 and Mg(OH)2. Therefore, the
higher pH was, the more precipitates form, resulting in reduction
of the magnesium source for the MAP forming reaction. Thus,
when pH was over a certain value, ammonium-N removal
10
efficiency would decrease. This result explained why the MAP
precipitation optimally occured at a certain pH range.
The initial molar ratio of Mg : PO43- in the wastewater was
0.46 : 1.0 (in MAP, it is 1.0 : 1.0), therefore, theoretically, the
maximum phosphate-P removal via the MAP precipitation was
46%. At pH 9.5, the removal efficiency of phosphate-P was
44.7%, rather high in comparison to theorical value.
at pH 9,5
at pH 11
Figure 3.3. SEM image of MAP crystal
at pH 9,5
at pH 11
Figure 3.4. EDX spectrum of the MAP precipitate
In this study, suitable pH for MAP recovery was about 9 -
10. At this range, MAP precipitation was clearly observed.
MAP crystals were easy to settle and could be observed with
the naked eyes, and had a large length of 300 - 383 µm. The
70,6 µm
383 µm
328µm
11
removal efficiencies of phosphate-P and ammonium-N at pH
9.5 were 44.7% and 13.1%, respectively. At pH 11, beside MAP
crystals with small size, hardly settable fine flocks also
appeared (Fig. 3.3). EDX spectrum (Figure 3.4) and data of
chemical composition showed that: the mass percentages of the
P, Mg and O elements in MAP at pH 9.5 were 14.3%, 10.8%
and 54.3%, respectively. These percentages were similar to
those in pure MAP. At pH 11, beside the above main elements,
there were many other elements such as C, Na, K and Ca in the
MAP precipitate. The mass percentages of P, Mg and O
elements were 7.4%; 6.0% and 44.2%, respectively.
2) MAP recovery with magnesium addition
In this study, the molar ratio of Mg2+ : NH4+ : PO4
3- in NRP
wastewater was 0.46 : 3.5 : 1.0, while this ratio in pure MAP was
1.0 : 1.0 : 1.0. Therefore, to improve the recovery of phosphate-
P, addition of external magnesium source was required.
Table 3.5 showed that removal efficiencies of phosphate-P
and ammonium-N reached the best value of 93.3% and 28,4%,
respectively, at the Mg2+ : PO43- molar ratio of 1.2 : 1.0.
Table 3.5. Effect of Mg2+: PO43- molar ratio on P and N removal
Mg2+ :
PO43-
molar
ratio
Concentration after MAP
precipitation (mg/L) Removal efficiency (%)
PO43-–P NH4
+–N Mg2+ PO43-–P NH4
+–N Mg2+
0.6 : 1 65.3 185 3.2 53.7 16.7 95.1
0.8 : 1 34.2 173 3.3 75.7 22.1 96.3
1.0 : 1 15.6 163 2.8 88.9 26.6 97.4
12
Mg2+ :
PO43-
molar
ratio
Concentration after MAP
precipitation (mg/L) Removal efficiency (%)
PO43-–P NH4
+–N Mg2+ PO43-–P NH4
+–N Mg2+
1.2 : 1 9.4 159 2.5 93.3 28.4 98.1
1.4 : 1 9.2 161 3.4 93.5 27.5 97.8
1.6 : 1 9.1 174 3.6 93.5 21.6 97.9
3) MAP recovery with addition of magnesium and phosphate
MAP recovery efficiency
In order to increase the of ammonium-N removal efficiency
and MAP recovery, it was necessary to add external sources of
magnesium and phosphate.
Table 3.7. Effect of Mg2+ : NH4+ : PO4
3- molar ratio on P and N
removal efficiencies
Mg2+ : NH4+
: PO43-
molar ratio
Concentration after MAP
precipitation (mg/L) Removal efficiency (%)
PO43-–P NH4
+–N Mg2+ PO43-–P NH4
+–N Mg2+
0.6: 1.0: 1.0 214.0 154.3 8.2 56.5 30.5 96.4
0.8: 1.0: 1.0 117.0 138.6 9.6 76.2 37.6 96.8
1.0: 1.0: 1.0 36.5 106.5 11.3 92.6 52.0 97.0
1.2: 1.0: 1.0 27.4 61.2 13.2 94.4 72.4 97.1
1.4: 1.0: 1.0 19.6 42.4 15.6 96.0 80.9 97.1
1.6: 1.0: 1.0 15.2 56.4 22.7 96.9 74.6 96.3
1.8: 1.0: 1.0 14.3 97.1 28.4 97.1 56.3 95.9
The results in Table 3.7 showed that the highest ammonium-
N removal efficiency of 80.9% was obtained at Mg2+ : NH4+ :
PO43- molar ratio of 1.4 : 1.0: 1.0. As a result, the optimal Mg2+
13
: NH4+ : PO4
3- molar ratio for the simultaneous removal of both
ammonium-N and phosphate-P was 1.4 : 1.0 : 1.0. , at which the
phosphate-P, magie removal efficiencies, obtained MAP amount
were 96.0% and 97.1%, and 4,85 g/L wastewater, respectively.
Analyzation of obtained MAP product
MAP sample obtained at pH = 9.5 and Mg2+ : NH4+ : PO4
3-
molar ratio of 1.4 : 1.0 : 1.0 was taken for SEM and EDX
analysises to evaluate the crystal size and composition of the
MAP product. The results showed that the precipitate was clear
crystals, and had white color mixed with dark brown color and
many stains on its surface (Figure 3.12), possibly due to the
organic components in wastewater and/or other precipitates
formed during the MAP precipitation. The mass composition of
the P, Mg, O elements was 13.6%, 11.4%, 59.4% respectively.
This composition was nearly similar to that in pure MAP (12.6%,
9.9% and 65.3%). In addition, the precipitate also contained
11.2% C and other substances.
(a) (b)
Figure 3.12. MAP precipitate (a) and its SEM image (b)
14
CHAPTER 4. SIMULTANEOUS REMOVAL OF
ORGANIC MATTER AND NITROGEN IN MODIFIED
SBRs
4.1. Materials and research methodology
1) Materials, chemicals, and equipment
Wastewater: Wastewater in this study was the effluent of the
EGSB reactor.
Seed sludge: Activated sludge from an oxic/anoxic biological
tank of Hanoi Plastic Company was used as seed sludge.
Equipment: Two similar modified SBRs with an effective
volume and a working height of 15L and 1.34m, respectively,
were used (Figure 4.1).
1. Wastewater container
2. Wastewater supply pump
3. Wastewater supply pipe
4. Modified SBR
5. Automatic valve
6. Effluent tank
7. Air blower
8. Air flowmeter
9. Air diffuser
10. Controller
I. Oxic zone; II. Anoxic zone
Figure 4.1. Modified SBR system
2) Research methodology
Experimental procedure
Wastewater
2
8
7
1 6
Air
Eff
luen
t
3
10
9
4
5
I I
15
Two modified sequencing batch reactors (SBRs), R1 and
R2, specially configured to consist of both oxic and anoxic zones,
and be operated with only a single simultaneous oxic/anoxic
phase in each treatment batch were used. R1 was operated with a
constant aeration, by contrast, R2 was operated with an air flow
varied from a lower rate in the early period of the reaction phase
to a higher rate in the later period. The operating strategy for the
reactors was also modified to combine the drawing stage of the
treated water from the previous batch and the filling stage for the
new batch into the same phase. The reactors was operated in a
sequential three-step cycle mode (simultaneous drawing and
filling; reacting; and setting) as shown in Table 4.1.
Table 4.1. Operation mode of the modified SBRs
Reactor
Time for
simultaneous
drawing and
filling, min
Time of reaction phase,
min Setting time,
min Air flow
0,4 L/min
Air flow
2,0 L/min
R1 10
0 145 25
R2 55 90
Experimental conditions
Study on effects of OLR, ammonium-N loading rate
(ANLR) and nitrogen loading rate (NLR) on the performance of
R1 and R2 was performed in the OLR and NLR ranges of 0.52 –
1.61 kg CODm-3d-1 and 0.071 – 0.32 kg Nm-3d-1, respectively.
Study on effect of COD/TN ratio on the performance of the
reactors was carried out in the COD/TN ratio range of 3.4 – 6.0.
16
4.2. Results and discussion
1) Effect of OLR on the COD removal
The results in Figure 4.4 showed that both R1 and R2
almost reached steady state after only one week from the startup.
The average COD removal efficiencies of both R1 and R2 in all
phases were quite stable and over 95%. There was no significant
difference in COD removal efficiency for both R1 and R2.
Figure 4.4. COD removal efficiency of modified SBRs OLR (kg CODm-3d-1): I = 0.52, II = 0.73, III = 0.90, IV = 1.19, V = 1.61
2) Effect of ANLR on the ammonium-N removal
The results in Figure 4.7 showed that the ammonium-N
removal of both R1 and R2 became stable after only one week
operation. Ammonium removal efficiencies of R1 and R2 were
almost the same, averagely over 99%. Average effluent
ammonium-N concentration was less than 1 mg/L.
0
20
40
60
80
100
0
500
1000
1500
2000
2500
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80
CO
D r
em
ova
l , %
CO
D, m
g/L
Thời gian vận hành, ngày
Influent COD Effluent COD_R1 Effluent COD_R2
Removal_R1 Removal_R2
I II III IV V
17
Figure 4.7. Ammonium-N removal efficiency of modified SBRs ANLR (kg ammonium-Nm-3d-1): I = 0.048, II = 0.064, III = 0.11, IV = 0.14, V = 0.21
3) Effect of NLR on the TN removal
Figure 4.10 showed that essential time for R1 and R2 to
achieve stable TN removal was 30 and 21 days, respectively.
Figure 4.10. TN removal efficiency of modified SBRs
NLR (kg Nm-3d-1): I = 0.070, II = 0.09, III = 0.16, IV = 0.21, V = 0.31
In the stationary period, the TN removal efficiency of R1
was quite high with an average of 88 - 92% in phases III – V. R2
was able to achieve a steady state faster than R1. The removal
efficiency of R2 was higher than that of R1, about 97% in phases
III and IV, and 94% in phase V.
96
97
98
99
100
0
100
200
300
400
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80
Hiệ
u s
uấ
t xử
lý
N-N
H4
+,
%
N-N
H4+,
mg
/L
Thời gian vận hành, ngày
effluent N-amoni_R1 Effluent N-amoni_R2 Influent N-amoni
I II III IV V
0
20
40
60
80
100
0
100
200
300
400
500
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80
T-N
rem
ova
l, %
TN
, m
g/L
Operation time, day
Influent T-N Efluent T-N_R1 Efluent T-N_R2
Removal_R1 Removal_R2
18
At the same NLR, the TN removal efficiency of R2 was
higher than that of R1. The TN concentration in the effluent of
R2 was significantly lower than that of R1, less than 25 mg/L in
all three experimental phases III - V, meanwhile, the TN
concentration in the effluent of R1 fluctuated within the range of
15 - 50 mg/L.
4) Effect of COD/TN ratio on COD removal
The results in Figure 4.13 showed that no significant
differences in the COD removal efficiencies versus COD/TN
ratio were observed. The COD removal efficiencies of both
reactors were similar, with an average of over 95%.
Figure 4.13. Effect of COD/TN ratio on COD removal
5) Effect of COD/TN ratio on ammonium-N and TN removal
The ammonium-N removal efficiencies of both reactors
were over 99%, and ammonium-N concentration in the effluent
was below 1 mg/L (Fig. 4.14).
TN removal efficiencies of both reactors tended to increase
when increasing in the COD/TN ratio. These results were
40
50
60
70
80
90
100
0
500
1000
1500
2000
2500
3000
3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0
CO
D r
em
ova
l, %
CO
D, m
g/L
COD/TN ratio
COD Influent
COD Effluent - R1
COD Effluent - R2
COD removal - R1
COD removal - R2
19
consistent with expectations, since a low COD/TN ratio leads to
a shortage of organic substrates for denitrification, resulting in
low TN removal (Figure 4.15).
Figure 4.14. Effect of COD/TN ratio on ammonium-N removal
Figure 4.15. Effect of COD/TN ratio on TN removal efficiency
The mean TN removal efficiency for reactor R1 increased
from 70% to 92% when raising the COD/TN ratio from 3.4 to
6.0; meanwhile, that of reactor R2 increased from 80% to 97%.
The results in Figure 4.15 also showed that TN removal
efficiency of R2 was remarkably higher than that of R1 at all
COD/TN ratios investigated.
94
95
96
97
98
99
100
0
100
200
300
400
500
600
3.0 3.5 4.0 4.5 5.0 5.5 6.0
N-a
mo
niu
m r
em
ova
l, %
N-a
mo
niu
m,
mg
/L
Tỉ lệ COD /TN
N-amoni Influent
N-amoni Effluent - R1
N-amoni Effluent - R2
Removal - R1
Removal - R2
20
40
60
80
100
3.0 3.5 4.0 4.5 5.0 5.5 6.0
TN
rem
ova
l, %
COD/TN ratio
R1 R2
20
CHAPTER 5. PROPOSAL OF AN APPROPRIATE
TREATMENT PROCESS FOR NRP WASTEWATER
5.1. Proposed treatment process
Through the results achieved in this study, an energy and
nutrients recovering wastewater process for NRP wastewater
integrating physicochemical and biological processes was
proposed in Figure 5.1.
Figure 5.1. Proposed appropriate treatment process for NRP
wastewater
5.2. Process material balance
Based on results of the material balance (Table 5.1 and
Figure 5.2), the proposed process could ensure that the effluent
quality could meet the discharge requirements according to the
Vietnam Regulation QCVN 01-MT: 2015 BTNMT. In addition,
with the scale of Ha Tinh Rubber Factory, about 320 kg MAP per
day could be recovered each day. The biogas amount that could
be recovered daily is about 352 Nm3, equivalent to around 200
Nm3 methane. In terms of energy, it is equivalent to about 200 kg
of oil or nearly 2,000 kWh.
Rubber latex
seperating
pond
Equalizati
on tank
EGSB MAP
prepicipation
Product drying
furnace
Intermediate
tank
Bio
ga
s
Wastewater
Efluent Modified
SBR
Stationa
ry pond
MAP
product
21
Table 5.1: Influent parameters, calculation results for effluent
Parameters Unit Influent (1) Effluent (6)
COD mg/L 6,480 74.2
TN mg/L 285 31.0
TP mg/L 186 24.8
SS mg/L 500 50.0
Figure 5.2. Results of calculating the material balance
352 Nm3/ngày
Wastewater
(1) (2) (3) MAP
220,0 232,7 232,7 320 kg MAP/ngày
(4) 232,7
(5) (6) 212,1
232,7 Effluent
(7)
20,6 Sludge
overflow wastewater (8) Sludge (9)
12,7 7,9
Note: Number in diagram is flow by cubic metter per day
Điểm (1) (2) (3) (4) (5) (6) (7) (8) (9)
Q, m3/day 220 232,7 232,7 232,7 232,7 212,1 20,6 12,7 7,9
Q, m3/h 9,2 9,7 9,7 9,7 9,7 8,8 0,9 0,5 0,3
COD, mg/L 6480 6181,6 1854,5 1483,6 1483,6 74,2 - 1000,0 -
LCOD, kg/day 1426 1438,3 431,5 345,2 345,2 15,7 - 12,7 -
TN, mg/L 285 376,1 376,1 309,9 309,9 31,0 - 100,0 -
LTN, kg/day 63 87,5 87,5 72,1 72,1 6,6 - 1,3 -
TP, mg/L 186 177,2 177,2 35,4 35,4 24,8 - 24,8 -
LTP, kg/day 41 41,2 41,2 8,2 8,2 5,3 - 0,3 -
SS, mg/L 500,0 500,0 200,0 200,0 200 50,0 8000,0 500,0 20000,0
LSS, kg/day 110,0 116,3 46,5 46,5 46,5 10,6 164,7 6,3 158,4
Materials balance
MAP prepicipateDetention
tankEGSB
Intermediate tankModified
SBR
Slude
tank
Biogas
22
CONCLUSIONS AND RECOMMENDATIONS
Conclusions
1) Generation of granular sludge in ESGB reactor after 3 months
startup was successfully performed. The reactor could be stably
operated in the OLR range of 7 - 20 kg CODm-3d-1 with average
COD removal of over 80%. Biogas conversion yield for NRP
wastewater was 0.37 L/g removed COD.
2) Applicability and appropriate conditions for MAP
precipitation in the nutrient recovery from the NRP wastewater
were clarified. The optimal pH for MAP precipitation was 9.5, at
which nearly 45% of phosphate-P in NRP wastewater could be
recovered without addition of magnesium source. In the case of
magnesium addition, the optimal Mg2+ : PO43- molar ratio and
phosphate-P removal efficiency were 1.2 : 1.0 and 93.3%,
respectively. When both magnesium and phosphate were added,
the optimal Mg2+ : NH4+ : PO4
3- molar ratio was 1.4 : 1.0 : 1.0, at
which the removal efficiencies of phosphate-P and ammonium-
N, and the obtained MAP amount were 97.1% and 80.9%, and
and 4,85 g/L wastewater respectively.
3) A new modified SBR capable of effectively and
simultaneously removing organic and nitrogen substances from
NRP wastewater was successfully developed. The performance
of the reactor was significantly improved compared to
conventional SBRs and nitrification/denitrification reactors. At
OLRs of 0.9 - 1.6 kg CODm-3d-1 and NLRs of 0.16 - 0.31 kg
Nm-3d-1, average removal efficiencies of COD, ammonium-N
and TN were 97 %, nearly 100% and 94 - 97%, respectively. The
23
optimal COD/TN ratio for the reactor was in the range of 5 - 6,
relatively low compared to that for conventional SBRs and other
nitrification/denitrification reactors. Average concentrations of
COD, ammonium-N and TN in effluent were below 70 mg/L,
less than 1 mg/L and less than 30 mg/L, respectively, satisfying
the Vietnamese regulation.
4) A new energy and nutrients recovering wastewater treatment
process integrating physicochemical and biological processes for
NRP wastewater was proposed. The features of the process are: (1)
energy saving and recoverable; (2) N and P nutrients recoverable;
(3) organic matter and nutrients simultaneously removable.
Recommendation
1) Further study on microorganism composition and activity of
anaerobic sludge in EGSB reactor, as well as evaluate the
performance of EGSB reactor at OLR above 20 kg COD m-3d-1.
2) Study in pilot scale to complete the proposed technological
process and fully evaluate economic-technical indicators.
NEW CONTRIBUTIONS OF THE THESIS
1) Generation of granular sludge in an EGSB reactor treating
natural rubber processing wastewater was successfully
performed. Applicability, appropriate technological conditions,
as well as energy recovery potential of EGSB reactor in the
treatment of the NRP wastewater were evaluated.
2) Applicability and suitable conditions for MAP precipitation
in the recovery of nitrogen and phosphorus from NRP
wastewater were clarified.
24
3) A new modified SBR capable of effectively and
simultaneously removing organic and nitrogen substances from
NRP wastewater with a simplified operation procedure and high
energy saving potential was successfully developed. The
performance of the modified SBR was significantly improved
compared to conventional SBRs.
4) A new energy and nutrients recovering wastewater treatment
process integrating physicochemical and biological processes for
NRP wastewater was proposed.
LIST OF PUBLICATIONS
1. Duong Van Nam, Phan Do Hung, Nguyen Hoai Chau, Dinh
Van Vien, Study on phosphorus recovery from natural rubber
processing wastewater by struvite precipitation method. Journal of
Agriculture and Rural Development, No. 21, 11/2017, pp 82 - 87.
2. Duong Van Nam, Phan Do Hung, Nguyen Hoai Chau, Dinh
Van Vien, High performance modified SBR for simultaneous
removal of organic and nitrogen matters from rubber latex
processing wastewater. Vietnam Journal of Science and
Technology B, Volume 22, No. 11, November 2017, pp 48 - 53.
3. Duong Van Nam, Nguyen Hoai Chau, Hamasaki Tatsuhide,
Dinh Van Vien, Phan Do Hung, Effect of COD/TN ratio and
loading rates on performance of modified SBRs in simultaneous
removal of organic matter and nitrogen from rubber latex
processing wastewater. Vietnam Journal of Science and
Technology 56 (2) (2018), p. 236 - 245.
