- Email: [email protected]
Nitrogen removal in attached growth waste stabilization ponds of wastewater from a rubber factory
~
War. ScI. Tech. Vol. 40, No. I, pp. 45-52,1999
Pergamon
iCll999 Published by Elsevier Science Ltd on behalf of the IAWQ Pnnted in Great Britain. All rights reserved 0273-1223/99 $20.00 + 0.00
PH: S0273-1223(99)00362-5
NITROGEN REMOVAL IN ATTACHED GROWTH WASTE STABILIZATION PONDS OF WASTEWATER FROM A RUBBER FACTORY A. Rakkoed*, S. Danteravanich* and U. Puetpaiboon** • Faculty ofEnvironmental Management. Prince ofSongkla University, Hat Yai. Songkhla 901l2. Thailand .. Faculty ofEngineering. Prince ofSongkla University. Hat Yai, Songkhla 901l2, Thailand
ABSTRACT Nitrogen removal from wastewater from rubber factories using attached-growth waste stabilization ponds (AGWSP) was evaluated. Usually, wastewaters generated from rubber factories such as concentrated latex factories and rubber sheet factories contain a high amount of nitrogen originating from natural rubber and ammonia compounds added in the production processes. From an investigation of 3 rubber factories at Songkhla, Thailand, average concentrations of TKN, NHs-N and Org-N m raw factory wastewater were found to be 889, 578 and 311 mgll respectively. Two series of laboratory waste treatment ponds, waste stabilization ponds (WSP) and attached-growth waste stabilization ponds were investigated to compare the efficiency of nitrogen removal from wastewater from a concentrated latex factory. The wastewater fed to the experimental units was collected from the effluent of the anaerobic treatment pond at the factory. The experiments were conducted With hydraulic retention times (HRT) of 40 and 20 days. Another experiment run with an HRT of 40 days together with 50% recirculating of effluent was also conducted. Finally, an experiment run at an HRT of 4 days was carried out in order to observe the effect of shock loading. The results revealed that TKN, NHs-N and BODs removal efficiencies in AGWSP were higher than in control ponds (WSP). Increased removal efficiencies were achieved which resulted from an increase in biomass on media in the pond water. © 1999 Published by Elsevier Science Ltd on behalf of the IAWQ. All rights reserved
KEYWORDS Waste stabilization ponds; attached-growth; rubber wastewater; nitrogen removal; effluent, algae. INTRODUCTION The rubber industry is one of the most important industries in Southern Thailand. It usually generates large quantities of wastewater containing high concentrations of organic, nutrient and solid matter. In the rubber production process, especially in the manufacture of concentrated latex, an ammonia compound is added as a preservative agent. As a result the wastewater from rubber factories contains a high concentration of nitrogen. New standards for discharge of industrial effluent in Thailand were issued in 1996. The regulations permit a total nitrogen concentration of not more than 100 mgll in effluent. Investigation of the quantity and species of nitrogen in raw wastewater and treated effluent from concentrated latex factories was therefore 45
46
A. RAKKOED et al.
conducted to establish whether current treatment methods were likely to result in compliance with this standard. Waste stabilization ponds (WSP) have been extensively employed to treat rubber wastewater in Southern Thailand. WSPs incorporating attached-growth media, called attached-growth waste stabilization ponds (AGWSPs) have been recommended to be more efficient than standard WSPs in terms of organic material and nitrogen removal. In this study, experiments were conducted to investigate the performance efficiency of a laboratory-scale AGWSP unit in treating a high strength concentrated latex wastewater which was obtained after anaerobic pond treatment. METHODOLOGY Industrial wastewater investigation Wastewater samples were taken from 3 latex concentrate factories in Songkhla Province in Southern Thailand. These factories treat wastewater by using pond systems, such as anaerobic, facultative, and aerobic ponds as well as aerated lagoons. Wastewater samples were collected on 3 occasions during December 1996-March 1997. A total of 18 samples from 3 factories (nine composite samples of raw wastewater and nine grab samples of effluent) were collected for physical and chemical analysis. Wastewater samples were collected in bottles, preserved and kept in an ice box and transferred to the university for laboratory analysis. The following physical and chemical characteristics of wastewater samples collected from latex concentrate factories were examined : pH, COD, BODs, suspended solids, TKN, Org-N, NH3-N, NOrN and N02-N. Wastewater quality was determined following the procedures described by APHA, AWWA & WEF (1992). Small scale experiment
Experimental units. These experiments were carried out to determine the performance of nitrogen and organic removal in an AGWSP and a control WSP. A total of 6 small-scale ponds were constructed. Each pond was made of glass with working dimensions of 0.4 x 1.2 x 0.6 m3 (width x length x depth). The ponds were divided into two sets of three, one for AGWSP experiments and the other for WSP experiments. Each set of experimental units was composed of 3 ponds operated in series. The three WSP ponds were not installed with any baffles or media. In the AGWSP set, 3-5 em diameter brick media was laid at the bottom of the first pond to a depth of about 10 em. In the second pond, 160 pieces of 9 em diameter plastic media were installed in the pond in order to provide a surface for the attached biomass. The surface area of each 2 piece of plastic media is 530 cm • The third pond was without any media. All six units in the two sets of experiments were connected with the same pump. The arrangement of the laboratory scale experimental units is shown in Figure I. Experimental Condition. All pond units were located outdoors with an operating temperature range of 28-30°C. A wastewater feed of effluent from the anaerobic pond at a concentrated latex factory was applied to the experimental units. Initially, the six units were acclimatized for one month by being filled with wastewater collected from the anaerobic pond until the biofilm had developed and a steady state condition was reached. Steady state condition was considered to have occurred when the effluent COD concentrations were relatively constant for one cycle of hydraulic retention time (HRT). After this the treatment performance of each run was observed for 30-50 days. Two experiments were conducted with an HRT of 40 and 20 days respectively . A third experiment was run with the same wastewater feeding rate as the experiment for 40 days HRT but with 50% recirculation of effluent. A final experiment with a 4 day HRT was also investigated for 8 days in order to observe the effect of shock loading on the system. Influent and effluent samples collected from each small-scale experimental unit were regularly analyzed for COD, BODs, SS, TKN, NH3-N, and Org-N. All wastewater analyses were carried out according to the methods described in the Standard Methods (APHA, AWWA and WCF, 1992).
47
Nitrogen removal in attached growth waste stabilization ponds of wastewater
RESULTS AND DISCUSSION Results of field survey The results of physical and chemical analysis of influent and effluent wastewater from three concentrated latex factories in Songkhla Province is shown in Table I. Influent wastewater was observed to contain high concentrations of organic matter, suspended solids and nitrogen. Within the 9 samples of raw wastewater, it was found that the COD and BODs values were in the range of 5,119-18,059 mg/I and 1,463-7,600 mg/l, respectively. The pH of wastewater was found to vary greatly from 5.20-9.08. The results displayed in Table 1 indicate that suspended solids content of wastewater is high, with a range of 800-4,667 mg/1. Nitrogen contents of 9 raw wastewater samples in terms of TKN, NH 3-N, Org-N, N03-N and N0 2-N were in the range of 455-1,686 mgll, 354-948 mg/I, 101-738 mg/l, <0.001-0.01 mg/I and <0.001-0.006 mg/I, respectively. The average concentrations of TKN, NH3-N and Org-N can be calculated to be 889, 578 and 311 mg/l, respectively. A high nitrogen content was thus detected in the concentrated latex wastewater. This was because nitrogen compounds are normally used for latex preservation in the factory. These results for the analysis of raw wastewater are consistent with Isa's report in 1991. Isa presented average concentrations of total nitrogen, ammonia nitrogen, COD and BODs oflatex concentrate wastewater in Malaysia were 602 mg/I, 466 mg/l, 4,849 mg/l, and 3,524 mgll, respectively.
wsr Unit
AGWSP Unit
wsr Unit: Waste stabilization pond AGWSP Unit: Attached-growth stabilization pond RW: Wastewater storage tank
Waskwlltcr Storage
~~Pump
I'ond Ijl
I'ond /11 7/'.
Pond /13
r r>
f ~o
em
1 12l/em - - - " "
120em--"'
1200m ------,..
rump
Figure I. Schematic outline of small-scale experimental units.
IOem
48
A . RAKKOEO et al.
Table I. Physical and chemical characteristics of influent and effluent from concentrated latex factories
Parameters I) PH 2) COD (rng/l) 3) BODs (rng/l)
4) SS (rng/l) 5) 6) 7) 8) 9)
TKN (rng/l) Org-N (rng/l) NH 3-N (mg/l) N03-N (rng/l) NOz-N (mg/I)
Raw Wastewater
Treated Effluent
5.20-9.08 5,119-18,059 1,463-7,600 800-4,66 7 455-1 ,686 101-738 354-948 <0.00 1-0.0 1 <0.00 1-0.006
7.93-8 .99 119-546 26- 78 80-3 16 17-324 7-61 5-263 <0.00 1-0.02 <0.00 1-0.5
After wastewater was treated by the pond system, the COD, BODs, S5 and nitrogen pollutants decreased. The removal efficiencies of COD, BODs, SS and nitrogen by the treatment pond system of the three rubber factories is shown in Fig 2. The removal efficiencies of COD, BODs and 55 were in the range of 97-99 %, 97-99 % and 86-96 %, respectively, whereas the removal efficiencies of TKN, NH 3-N and Org-N were at the values of 52-98 %, 44-99 % and 68-94 % , respectively. The efficiency of nitrogen removal of rubber wastewater treatment varied with the retention time of wastewater kept in the treatment ponds together with the number of treatment ponds utilized in each factory. If there are more treatment ponds used in the wastewater treatment process and a high retention time is provided, a greater percentage of nitrogen will be removed. New industrial effluent standards were issued in Thailand in 1996 . The standard requires the concentrations 'of industrial effluent to be not more than 120 mg/l , and 20 mg/I for COD and BOD ~. respectively, SS and TKN concentrations must not exceed values of 50 mg/l and 100 mg/l , respectivel y. Compared with these standards, it can be seen that the effluent from all three rubber factories does not meet the effluent standard criteria. Improved treatment performance is required to remove organ ic matter, suspended solids, and nitrogen content. 100
O( ()(
oc
x
I MN
F:It'If,,')' I
r
Fnctu r . 2
t~ll \ t4
-...... - -
~ N
I·'"'::'"'.' '':'J Fu. c tu rv .
Figure 2. The removal efficienc ies of eOD, BOD" S5, TKN, Org-N and NII ,·N of three rubber factories investigated in the study.
Results of laboratory experiments
Experiments run at 20 and 40 days HRT and 40 days HRT with 50% recirculation of effluent. Table 2 summarizes the average treatment performance of the small-scale WSP and AGWSP un its operated at three conditions of organic loading rate (25, 27 and 61 g COD /m 1-day ), The HRT of exper imental Run No . I and Run No.3 were 40 and 20 days, respectivel y. For experimental Run No .2, wastewater was fed with the sam e flow rate as Run No . I, but 50 % recirculation of effluent was carried out. This made the organic loading rate relatively sim ilar to experimental Run No .1, while the equivalent HRT was decreased to 27 days. The TKN
Nitrogen removal in attached growth waste stabilization ponds of wastewater
49 2-day
loading rate applied for the 3 experiments was calculated to be 6.3,7.6, and 13.2 g TKN/m second and third run, respectively.
for the first,
Table 2. Performance of small-scale experiments operated at 20 and 40 days HRT, and at 40 days HRT with the recirculation of 50% effluent COD
BOD~
S8
TKN
NIIJ-N
Ore-N
Influent Effluent from the first unit Effluent from the second unit Effluent from the third unit
1,990 235 248 379
1,418 66 35 56
89 63 50 118
507 290 128 38
474 258 105 16
33 32 23 22
Influent Effluent from the first unit • Effluent from the second unit • Effluent from the third unit Run II : HRT=40 days and 50% Recirculation of Effluent OLR=27 g COD/m 1-day NLR=7.6 g TKN/m 1-day
1,990 348 233 242
1,418 137 48 41
89 84 28 33
507 311 174 75
474 279 156 62
33 32 19 13
Influent Effluent from the first unit Effluent from the second unit Effluent from the third unit
2,088 244 133 159
1,518 70 25 24
72 61 72 62
586 321 148 51
554 299 135 41
32 22 13 10
Influent Effluent from the first unit • Effluent from the second unit • Effluent from the third unit Run III : IIRT=20 dar OLRc61.2 g COD/m -day NLR=13.2 g TKN/m1_day
2,088 366 210 130
1,518 128 48 23
72 142 80 40
586 302 181 71
554 272 156 61
32 31 24 9
2,448 340 134 185
1,652 71 23 36
59 69 33 87
531 297 128 39
495 283 125 26
23 18 8 13
2,448 455 318 201
1,652 150 67 46
59 94 145 119
531 336 162 54
495 316 145 43
23 17 21 13
Experimental Run Run I : HRT=40 da~s OLR=2S g COD/m -day NLR=6.3 g TKN/m 1-day AGWSP
• •
•
• WSP
•
•
AGWSP
•
•
•
•
WSP
• •
AGWSP
•
•
• •
Influent Effluent from the first unit Effluent from the second unit Effluent from the third unit
WSP
• •
Influent Effluent from the first unit Effluent from the second unit • Effluent from the third unit Note: HRT - Hydrauhc retention ume, OLR
•
Organic loadmg rate, NLR - TKN loading rate. All units are mg/l,
Data in Table 2 shown that the first two reactors of the AGWSP could remove organic matter (BOD, and COD) better than the first two reactors of the WSP. This was probably due to the effect of biomass growing on media in the ponds. The biofilm in the AGWSP promotes more biodegradation and as a result the BOD, and COD of the effluent are lower compared to the WSP. However, opposite results were observed for the last pond's effluent. The effluent of the last pond of the AGWSP was shown to have a higher BOD, and COD than the WSP in experiments number one and two. During the third run, the BOD, and COD of effluent from the AGWSP was lower than from the WSP. In the third run, there was more algae in the WSP
A. RAKKOED et al.
50
unit than in the AGWSP unit (see the SS data), and the presence of suspected algae in samples resulted in increased BOD and COD levels. It is evident from Table 2 that the WSP was inferior to the AGWSP with respect to nitrogen removal. This result is consistent with the study reported by Polprasert and Champrateep in 1989. They concluded that the AGWSP was more efficient than the WSP in the removal of organics, ammonia and heavy metal. Table 2 shows the nitrogen concentrations of effluent and influent in the forms of TKN, NH3-N and Org-N, Ammonia nitrogen was found to be the predominant nitrogen form in the influent and effluent from both the AGWSP and WSP. Within the loading rate range of 6.3-13.2 g TKN/m 2-day, TKN removal for the AGWSP was about 91-92%, whereas that of the WSP was about 85-89%. The ammonia nitrogen removal in the AGWSP was also found to be higher than in the WSP. 93-97 % removal of ammonia nitrogen was observed in the AGWSP and 87-91 % was found in the WSP. With respect to nitrogen removal in each pond, Table 3 shows that the ponds with either brick media or plastic media added can promote better nitrogen removal. As shown in Table 3, the removal ofTKN in the first two reactors of the AGWSP for the three experiments is in the range of 41-56%, while the WSP is in the range of 34-50%. NH3-N removal shows the same trend as TKN removal in the three experiments. NH 3-N removal from the first two ponds of the AGWSP was found to be from 41-59 %, and 35-54 % for the WSP. However, the percentage ofTKN and NH3-N removal in the last pond of both the AGWSP and WSP was found to be higher than in the first two ponds in each set. The TKN removal in the last pond of the three experiments in the AGWSP and the WSP system was observed to be 65-70% and 57-66 %, respectively, whereas, NH3-N removal in the last pond of both systems was found to range from 70-83% and 60-70 % in the AGWSP and WSP respectively. In this study, the recirculation of effluent was shown not to be significant in increasing the efficiency of nitrogen removal. Table 3. The removal percentage ofTKN and NH3"Nin each pond of three experiments Experiments
Pond #1
TKN Removal ( %) Pond #2
Pond #3
43 38
56 44
48 45 41 34
Pond #1
NH3"N Removal (%) Pond #2
Pond #3
70 57
45 40
59 44
83 60
54 40
65 60
46 51
54 42
70 61
56 50
70 66
41 35
56 54
79 70
Run #1
AGWSP WSP Run #2
AGWSP WSP Run #3
AGWSP WSP
Nitrogen is removed in several ways by wastewater treatment ponds. Organic nitrogen could be biodegraded by the biofilm bacteria to become NH3-N and eventually be taken up by algae in the pond. In this study, uptake of nitrogen by bacterial biomass in the attached-growth waste stabilization ponds was found to be one mode of nitrogen removal.
Effect of shock loading on treatment performance. An experimental run with HRT of 4 days was investigated for 8 days after the experimental run No.3 was finished. In this experiment, the average organic loading rate aPl'lied to the AGWSP and WSP was 360 g COD/m 2-day and the nitrogen loading rate was 76.5 g TKN/m -day, Figure 3 shows the resulting treatment performance. The COD and BOD5 of effluent from the first pond of the WSP was found to rapidly increase at a higher rate than the AGWSP. The COD and BOD5 of effluent in last two ponds of both the AGWSP and WSP increased relative to time, but there was not much different in the pattern of change for the two systems. For nitrogen, it was observed that the change pattern of TKN and NH3-N concentrations of effluent from the 3 ponds of both the AGWSP and WSP were the same. The nitrogen concentration in terms of TKN and NH3-N was also found to increase relative to time. From this experiment, it was concluded that the first pond of AGWSP can cope with a shock loading better than the first pond in WSP, possibly as a result of the role ofbiofilm bacteria.
SI
Nitrogen removal in attached growth waste stabilization ponds of wastewater
This study was carried out with the small experimental units. Therefore, the depth of the experimental units might affect to the performance results of wastewater treatment system. Hence, it should be noted that experiments testing with larger ponds (2-3 times bigger size of testing units used in this study) under the conditions investigated in this study are recommended to further conduct. The verification with the larger scale will give more confidence in extending the results in a full scale rubber wastewater treatment plants.
,.... '000 100
,
Inn_
rm:tf .ll~.c'~' ,
-
.
r~1 8
...,
~
•
•
)
•
•
)
•
7
wSP
:~t
:
::=F~
•
,
I
S
1
I
•
•
I
•
)
•
•
•
•
• wSP
~I i i c; 0
1
•
•
•
,
•
•
•
•
,-:
•
•
; ;
..-
,
• 00,..
~,
!•
Days
,
1• 'I'
D8Y1
•
:d Days •
7
;:;:;;;:;DaYS
•
)
,
eI :-, :, I~
f
•
,
•
s
•
iunlJml
•
i
,
wSP
,.., llWdll.
Days
•
;~! • •
:
' HHl ~ lieU ~ 1oti'=l l~jlillll.Hiq 0."
""" rttll'l"Hj."
,
ffi!
AGWSP
s
)
....
j ;::: i i ; ; ; ~ § I~ , ~ t
,
a- ;
•
,
AGWSP
e-
"'&
•
•
•
s
,
-
..
.i·
tOO
D.Y'
Ion.-
,..,
'~L ...
'~I
•
7
,
,
•
'000 100
• § Days
!§
~::::
•
J
.000
i_
• Day.
;=+=r:; ; J
, ,
0
,.
,
•
s
AGWSP
F;
':
U~.~~_L~d.1oN·1~'fi'-f~
~.
,..,
:: ~L: I~ :
•
-
I
A-4
.-.
)
· :
AGWSP
: T : ,
• •
,
• •
: : : ::::
~
~
• ,
: •
::
·. : : . : :· --.---.
,
• ,
,
wSP
,
;
,
I Da\" ~
~
,
•
,
UIY'
• •
PO"~ NI Pond N2 Pond N3
Figure 3. The performance of treatment during shock loading experiment.
CONCLUSION The experimental results obtained from this study have demonstrated the superior performance of the AGWSP system over the WSP system in terms of nitrogen removal in the treatment of rubber wastewater. The main mechanisms causing improved nitrogen removal in the AGWSP are hypothesized to be biodegradation by and adsorption to the biofilm retained in the pond water. AGWSP appeared to show better nitrogen removal efficiency than the WSP, but it was not shown to be significantly better at organic removal for ponds in series as a result of algae growing in the last treatment pond, which acted as a selfpollutant. In order to develop appropriate technology which will allow industrial effluent standards to be met, it is recommended that further investigations are carried out on the aquatic pond weeds connected with stabilization pond systems, for example using water hyacinth to treat wastewater in the third pond. It is expected than better results will be observed in terms of overall organic and nitrogen removal caused by minimization of algae growth in the last treatment pond.
52
A. RAKKOED et al.
ACKNOWLEDGEMENT The figures created by Mr. Suthira Thongkao are gratefully acknowledged. The authors wish to express their sincere gratitude to Dr. Peter Burt for spending his valuable time in correcting this paper. REFERENCES APHA, AWWA and WEF (1992). Standard Methods for the Examination of Water and Wastewater, 18th ed., New York, American Public Health Association. Isa, Z. (1991). Effluent treatment technology in the rubber industry, ASEANIUNDP Workshop on Pollution Control in the Palm Oil and Rubber Industries, Department of Environment, Ministry of Science, Technology and Environment, Malaysia. Polprasert, C. and Champratheep, K. (1989). Heavy metal removal in attached-growth waste stabilization ponds. Water Res.; 23,
625-631. Shin, H. K. and Polprasert, C. (1987). Attached-growth waste stabilization pond treatment evaluation. Wat Sci. Tech., 19,
229-235. Shin, H. K. and Polprasert, C. (1988). Ammonia nitrogen removal in attached-growth ponds. J. Env Eng.. Am. Soc. Civ. Engrs.,
114,846-863.
War. ScI. Tech. Vol. 40, No. I, pp. 45-52,1999
Pergamon
iCll999 Published by Elsevier Science Ltd on behalf of the IAWQ Pnnted in Great Britain. All rights reserved 0273-1223/99 $20.00 + 0.00
PH: S0273-1223(99)00362-5
NITROGEN REMOVAL IN ATTACHED GROWTH WASTE STABILIZATION PONDS OF WASTEWATER FROM A RUBBER FACTORY A. Rakkoed*, S. Danteravanich* and U. Puetpaiboon** • Faculty ofEnvironmental Management. Prince ofSongkla University, Hat Yai. Songkhla 901l2. Thailand .. Faculty ofEngineering. Prince ofSongkla University. Hat Yai, Songkhla 901l2, Thailand
ABSTRACT Nitrogen removal from wastewater from rubber factories using attached-growth waste stabilization ponds (AGWSP) was evaluated. Usually, wastewaters generated from rubber factories such as concentrated latex factories and rubber sheet factories contain a high amount of nitrogen originating from natural rubber and ammonia compounds added in the production processes. From an investigation of 3 rubber factories at Songkhla, Thailand, average concentrations of TKN, NHs-N and Org-N m raw factory wastewater were found to be 889, 578 and 311 mgll respectively. Two series of laboratory waste treatment ponds, waste stabilization ponds (WSP) and attached-growth waste stabilization ponds were investigated to compare the efficiency of nitrogen removal from wastewater from a concentrated latex factory. The wastewater fed to the experimental units was collected from the effluent of the anaerobic treatment pond at the factory. The experiments were conducted With hydraulic retention times (HRT) of 40 and 20 days. Another experiment run with an HRT of 40 days together with 50% recirculating of effluent was also conducted. Finally, an experiment run at an HRT of 4 days was carried out in order to observe the effect of shock loading. The results revealed that TKN, NHs-N and BODs removal efficiencies in AGWSP were higher than in control ponds (WSP). Increased removal efficiencies were achieved which resulted from an increase in biomass on media in the pond water. © 1999 Published by Elsevier Science Ltd on behalf of the IAWQ. All rights reserved
KEYWORDS Waste stabilization ponds; attached-growth; rubber wastewater; nitrogen removal; effluent, algae. INTRODUCTION The rubber industry is one of the most important industries in Southern Thailand. It usually generates large quantities of wastewater containing high concentrations of organic, nutrient and solid matter. In the rubber production process, especially in the manufacture of concentrated latex, an ammonia compound is added as a preservative agent. As a result the wastewater from rubber factories contains a high concentration of nitrogen. New standards for discharge of industrial effluent in Thailand were issued in 1996. The regulations permit a total nitrogen concentration of not more than 100 mgll in effluent. Investigation of the quantity and species of nitrogen in raw wastewater and treated effluent from concentrated latex factories was therefore 45
46
A. RAKKOED et al.
conducted to establish whether current treatment methods were likely to result in compliance with this standard. Waste stabilization ponds (WSP) have been extensively employed to treat rubber wastewater in Southern Thailand. WSPs incorporating attached-growth media, called attached-growth waste stabilization ponds (AGWSPs) have been recommended to be more efficient than standard WSPs in terms of organic material and nitrogen removal. In this study, experiments were conducted to investigate the performance efficiency of a laboratory-scale AGWSP unit in treating a high strength concentrated latex wastewater which was obtained after anaerobic pond treatment. METHODOLOGY Industrial wastewater investigation Wastewater samples were taken from 3 latex concentrate factories in Songkhla Province in Southern Thailand. These factories treat wastewater by using pond systems, such as anaerobic, facultative, and aerobic ponds as well as aerated lagoons. Wastewater samples were collected on 3 occasions during December 1996-March 1997. A total of 18 samples from 3 factories (nine composite samples of raw wastewater and nine grab samples of effluent) were collected for physical and chemical analysis. Wastewater samples were collected in bottles, preserved and kept in an ice box and transferred to the university for laboratory analysis. The following physical and chemical characteristics of wastewater samples collected from latex concentrate factories were examined : pH, COD, BODs, suspended solids, TKN, Org-N, NH3-N, NOrN and N02-N. Wastewater quality was determined following the procedures described by APHA, AWWA & WEF (1992). Small scale experiment
Experimental units. These experiments were carried out to determine the performance of nitrogen and organic removal in an AGWSP and a control WSP. A total of 6 small-scale ponds were constructed. Each pond was made of glass with working dimensions of 0.4 x 1.2 x 0.6 m3 (width x length x depth). The ponds were divided into two sets of three, one for AGWSP experiments and the other for WSP experiments. Each set of experimental units was composed of 3 ponds operated in series. The three WSP ponds were not installed with any baffles or media. In the AGWSP set, 3-5 em diameter brick media was laid at the bottom of the first pond to a depth of about 10 em. In the second pond, 160 pieces of 9 em diameter plastic media were installed in the pond in order to provide a surface for the attached biomass. The surface area of each 2 piece of plastic media is 530 cm • The third pond was without any media. All six units in the two sets of experiments were connected with the same pump. The arrangement of the laboratory scale experimental units is shown in Figure I. Experimental Condition. All pond units were located outdoors with an operating temperature range of 28-30°C. A wastewater feed of effluent from the anaerobic pond at a concentrated latex factory was applied to the experimental units. Initially, the six units were acclimatized for one month by being filled with wastewater collected from the anaerobic pond until the biofilm had developed and a steady state condition was reached. Steady state condition was considered to have occurred when the effluent COD concentrations were relatively constant for one cycle of hydraulic retention time (HRT). After this the treatment performance of each run was observed for 30-50 days. Two experiments were conducted with an HRT of 40 and 20 days respectively . A third experiment was run with the same wastewater feeding rate as the experiment for 40 days HRT but with 50% recirculation of effluent. A final experiment with a 4 day HRT was also investigated for 8 days in order to observe the effect of shock loading on the system. Influent and effluent samples collected from each small-scale experimental unit were regularly analyzed for COD, BODs, SS, TKN, NH3-N, and Org-N. All wastewater analyses were carried out according to the methods described in the Standard Methods (APHA, AWWA and WCF, 1992).
47
Nitrogen removal in attached growth waste stabilization ponds of wastewater
RESULTS AND DISCUSSION Results of field survey The results of physical and chemical analysis of influent and effluent wastewater from three concentrated latex factories in Songkhla Province is shown in Table I. Influent wastewater was observed to contain high concentrations of organic matter, suspended solids and nitrogen. Within the 9 samples of raw wastewater, it was found that the COD and BODs values were in the range of 5,119-18,059 mg/I and 1,463-7,600 mg/l, respectively. The pH of wastewater was found to vary greatly from 5.20-9.08. The results displayed in Table 1 indicate that suspended solids content of wastewater is high, with a range of 800-4,667 mg/1. Nitrogen contents of 9 raw wastewater samples in terms of TKN, NH 3-N, Org-N, N03-N and N0 2-N were in the range of 455-1,686 mgll, 354-948 mg/I, 101-738 mg/l, <0.001-0.01 mg/I and <0.001-0.006 mg/I, respectively. The average concentrations of TKN, NH3-N and Org-N can be calculated to be 889, 578 and 311 mg/l, respectively. A high nitrogen content was thus detected in the concentrated latex wastewater. This was because nitrogen compounds are normally used for latex preservation in the factory. These results for the analysis of raw wastewater are consistent with Isa's report in 1991. Isa presented average concentrations of total nitrogen, ammonia nitrogen, COD and BODs oflatex concentrate wastewater in Malaysia were 602 mg/I, 466 mg/l, 4,849 mg/l, and 3,524 mgll, respectively.
wsr Unit
AGWSP Unit
wsr Unit: Waste stabilization pond AGWSP Unit: Attached-growth stabilization pond RW: Wastewater storage tank
Waskwlltcr Storage
~~Pump
I'ond Ijl
I'ond /11 7/'.
Pond /13
r r>
f ~o
em
1 12l/em - - - " "
120em--"'
1200m ------,..
rump
Figure I. Schematic outline of small-scale experimental units.
IOem
48
A . RAKKOEO et al.
Table I. Physical and chemical characteristics of influent and effluent from concentrated latex factories
Parameters I) PH 2) COD (rng/l) 3) BODs (rng/l)
4) SS (rng/l) 5) 6) 7) 8) 9)
TKN (rng/l) Org-N (rng/l) NH 3-N (mg/l) N03-N (rng/l) NOz-N (mg/I)
Raw Wastewater
Treated Effluent
5.20-9.08 5,119-18,059 1,463-7,600 800-4,66 7 455-1 ,686 101-738 354-948 <0.00 1-0.0 1 <0.00 1-0.006
7.93-8 .99 119-546 26- 78 80-3 16 17-324 7-61 5-263 <0.00 1-0.02 <0.00 1-0.5
After wastewater was treated by the pond system, the COD, BODs, S5 and nitrogen pollutants decreased. The removal efficiencies of COD, BODs, SS and nitrogen by the treatment pond system of the three rubber factories is shown in Fig 2. The removal efficiencies of COD, BODs and 55 were in the range of 97-99 %, 97-99 % and 86-96 %, respectively, whereas the removal efficiencies of TKN, NH 3-N and Org-N were at the values of 52-98 %, 44-99 % and 68-94 % , respectively. The efficiency of nitrogen removal of rubber wastewater treatment varied with the retention time of wastewater kept in the treatment ponds together with the number of treatment ponds utilized in each factory. If there are more treatment ponds used in the wastewater treatment process and a high retention time is provided, a greater percentage of nitrogen will be removed. New industrial effluent standards were issued in Thailand in 1996 . The standard requires the concentrations 'of industrial effluent to be not more than 120 mg/l , and 20 mg/I for COD and BOD ~. respectively, SS and TKN concentrations must not exceed values of 50 mg/l and 100 mg/l , respectivel y. Compared with these standards, it can be seen that the effluent from all three rubber factories does not meet the effluent standard criteria. Improved treatment performance is required to remove organ ic matter, suspended solids, and nitrogen content. 100
O( ()(
oc
x
I MN
F:It'If,,')' I
r
Fnctu r . 2
t~ll \ t4
-...... - -
~ N
I·'"'::'"'.' '':'J Fu. c tu rv .
Figure 2. The removal efficienc ies of eOD, BOD" S5, TKN, Org-N and NII ,·N of three rubber factories investigated in the study.
Results of laboratory experiments
Experiments run at 20 and 40 days HRT and 40 days HRT with 50% recirculation of effluent. Table 2 summarizes the average treatment performance of the small-scale WSP and AGWSP un its operated at three conditions of organic loading rate (25, 27 and 61 g COD /m 1-day ), The HRT of exper imental Run No . I and Run No.3 were 40 and 20 days, respectivel y. For experimental Run No .2, wastewater was fed with the sam e flow rate as Run No . I, but 50 % recirculation of effluent was carried out. This made the organic loading rate relatively sim ilar to experimental Run No .1, while the equivalent HRT was decreased to 27 days. The TKN
Nitrogen removal in attached growth waste stabilization ponds of wastewater
49 2-day
loading rate applied for the 3 experiments was calculated to be 6.3,7.6, and 13.2 g TKN/m second and third run, respectively.
for the first,
Table 2. Performance of small-scale experiments operated at 20 and 40 days HRT, and at 40 days HRT with the recirculation of 50% effluent COD
BOD~
S8
TKN
NIIJ-N
Ore-N
Influent Effluent from the first unit Effluent from the second unit Effluent from the third unit
1,990 235 248 379
1,418 66 35 56
89 63 50 118
507 290 128 38
474 258 105 16
33 32 23 22
Influent Effluent from the first unit • Effluent from the second unit • Effluent from the third unit Run II : HRT=40 days and 50% Recirculation of Effluent OLR=27 g COD/m 1-day NLR=7.6 g TKN/m 1-day
1,990 348 233 242
1,418 137 48 41
89 84 28 33
507 311 174 75
474 279 156 62
33 32 19 13
Influent Effluent from the first unit Effluent from the second unit Effluent from the third unit
2,088 244 133 159
1,518 70 25 24
72 61 72 62
586 321 148 51
554 299 135 41
32 22 13 10
Influent Effluent from the first unit • Effluent from the second unit • Effluent from the third unit Run III : IIRT=20 dar OLRc61.2 g COD/m -day NLR=13.2 g TKN/m1_day
2,088 366 210 130
1,518 128 48 23
72 142 80 40
586 302 181 71
554 272 156 61
32 31 24 9
2,448 340 134 185
1,652 71 23 36
59 69 33 87
531 297 128 39
495 283 125 26
23 18 8 13
2,448 455 318 201
1,652 150 67 46
59 94 145 119
531 336 162 54
495 316 145 43
23 17 21 13
Experimental Run Run I : HRT=40 da~s OLR=2S g COD/m -day NLR=6.3 g TKN/m 1-day AGWSP
• •
•
• WSP
•
•
AGWSP
•
•
•
•
WSP
• •
AGWSP
•
•
• •
Influent Effluent from the first unit Effluent from the second unit Effluent from the third unit
WSP
• •
Influent Effluent from the first unit Effluent from the second unit • Effluent from the third unit Note: HRT - Hydrauhc retention ume, OLR
•
Organic loadmg rate, NLR - TKN loading rate. All units are mg/l,
Data in Table 2 shown that the first two reactors of the AGWSP could remove organic matter (BOD, and COD) better than the first two reactors of the WSP. This was probably due to the effect of biomass growing on media in the ponds. The biofilm in the AGWSP promotes more biodegradation and as a result the BOD, and COD of the effluent are lower compared to the WSP. However, opposite results were observed for the last pond's effluent. The effluent of the last pond of the AGWSP was shown to have a higher BOD, and COD than the WSP in experiments number one and two. During the third run, the BOD, and COD of effluent from the AGWSP was lower than from the WSP. In the third run, there was more algae in the WSP
A. RAKKOED et al.
50
unit than in the AGWSP unit (see the SS data), and the presence of suspected algae in samples resulted in increased BOD and COD levels. It is evident from Table 2 that the WSP was inferior to the AGWSP with respect to nitrogen removal. This result is consistent with the study reported by Polprasert and Champrateep in 1989. They concluded that the AGWSP was more efficient than the WSP in the removal of organics, ammonia and heavy metal. Table 2 shows the nitrogen concentrations of effluent and influent in the forms of TKN, NH3-N and Org-N, Ammonia nitrogen was found to be the predominant nitrogen form in the influent and effluent from both the AGWSP and WSP. Within the loading rate range of 6.3-13.2 g TKN/m 2-day, TKN removal for the AGWSP was about 91-92%, whereas that of the WSP was about 85-89%. The ammonia nitrogen removal in the AGWSP was also found to be higher than in the WSP. 93-97 % removal of ammonia nitrogen was observed in the AGWSP and 87-91 % was found in the WSP. With respect to nitrogen removal in each pond, Table 3 shows that the ponds with either brick media or plastic media added can promote better nitrogen removal. As shown in Table 3, the removal ofTKN in the first two reactors of the AGWSP for the three experiments is in the range of 41-56%, while the WSP is in the range of 34-50%. NH3-N removal shows the same trend as TKN removal in the three experiments. NH 3-N removal from the first two ponds of the AGWSP was found to be from 41-59 %, and 35-54 % for the WSP. However, the percentage ofTKN and NH3-N removal in the last pond of both the AGWSP and WSP was found to be higher than in the first two ponds in each set. The TKN removal in the last pond of the three experiments in the AGWSP and the WSP system was observed to be 65-70% and 57-66 %, respectively, whereas, NH3-N removal in the last pond of both systems was found to range from 70-83% and 60-70 % in the AGWSP and WSP respectively. In this study, the recirculation of effluent was shown not to be significant in increasing the efficiency of nitrogen removal. Table 3. The removal percentage ofTKN and NH3"Nin each pond of three experiments Experiments
Pond #1
TKN Removal ( %) Pond #2
Pond #3
43 38
56 44
48 45 41 34
Pond #1
NH3"N Removal (%) Pond #2
Pond #3
70 57
45 40
59 44
83 60
54 40
65 60
46 51
54 42
70 61
56 50
70 66
41 35
56 54
79 70
Run #1
AGWSP WSP Run #2
AGWSP WSP Run #3
AGWSP WSP
Nitrogen is removed in several ways by wastewater treatment ponds. Organic nitrogen could be biodegraded by the biofilm bacteria to become NH3-N and eventually be taken up by algae in the pond. In this study, uptake of nitrogen by bacterial biomass in the attached-growth waste stabilization ponds was found to be one mode of nitrogen removal.
Effect of shock loading on treatment performance. An experimental run with HRT of 4 days was investigated for 8 days after the experimental run No.3 was finished. In this experiment, the average organic loading rate aPl'lied to the AGWSP and WSP was 360 g COD/m 2-day and the nitrogen loading rate was 76.5 g TKN/m -day, Figure 3 shows the resulting treatment performance. The COD and BOD5 of effluent from the first pond of the WSP was found to rapidly increase at a higher rate than the AGWSP. The COD and BOD5 of effluent in last two ponds of both the AGWSP and WSP increased relative to time, but there was not much different in the pattern of change for the two systems. For nitrogen, it was observed that the change pattern of TKN and NH3-N concentrations of effluent from the 3 ponds of both the AGWSP and WSP were the same. The nitrogen concentration in terms of TKN and NH3-N was also found to increase relative to time. From this experiment, it was concluded that the first pond of AGWSP can cope with a shock loading better than the first pond in WSP, possibly as a result of the role ofbiofilm bacteria.
SI
Nitrogen removal in attached growth waste stabilization ponds of wastewater
This study was carried out with the small experimental units. Therefore, the depth of the experimental units might affect to the performance results of wastewater treatment system. Hence, it should be noted that experiments testing with larger ponds (2-3 times bigger size of testing units used in this study) under the conditions investigated in this study are recommended to further conduct. The verification with the larger scale will give more confidence in extending the results in a full scale rubber wastewater treatment plants.
,.... '000 100
,
Inn_
rm:tf .ll~.c'~' ,
-
.
r~1 8
...,
~
•
•
)
•
•
)
•
7
wSP
:~t
:
::=F~
•
,
I
S
1
I
•
•
I
•
)
•
•
•
•
• wSP
~I i i c; 0
1
•
•
•
,
•
•
•
•
,-:
•
•
; ;
..-
,
• 00,..
~,
!•
Days
,
1• 'I'
D8Y1
•
:d Days •
7
;:;:;;;:;DaYS
•
)
,
eI :-, :, I~
f
•
,
•
s
•
iunlJml
•
i
,
wSP
,.., llWdll.
Days
•
;~! • •
:
' HHl ~ lieU ~ 1oti'=l l~jlillll.Hiq 0."
""" rttll'l"Hj."
,
ffi!
AGWSP
s
)
....
j ;::: i i ; ; ; ~ § I~ , ~ t
,
a- ;
•
,
AGWSP
e-
"'&
•
•
•
s
,
-
..
.i·
tOO
D.Y'
Ion.-
,..,
'~L ...
'~I
•
7
,
,
•
'000 100
• § Days
!§
~::::
•
J
.000
i_
• Day.
;=+=r:; ; J
, ,
0
,.
,
•
s
AGWSP
F;
':
U~.~~_L~d.1oN·1~'fi'-f~
~.
,..,
:: ~L: I~ :
•
-
I
A-4
.-.
)
· :
AGWSP
: T : ,
• •
,
• •
: : : ::::
~
~
• ,
: •
::
·. : : . : :· --.---.
,
• ,
,
wSP
,
;
,
I Da\" ~
~
,
•
,
UIY'
• •
PO"~ NI Pond N2 Pond N3
Figure 3. The performance of treatment during shock loading experiment.
CONCLUSION The experimental results obtained from this study have demonstrated the superior performance of the AGWSP system over the WSP system in terms of nitrogen removal in the treatment of rubber wastewater. The main mechanisms causing improved nitrogen removal in the AGWSP are hypothesized to be biodegradation by and adsorption to the biofilm retained in the pond water. AGWSP appeared to show better nitrogen removal efficiency than the WSP, but it was not shown to be significantly better at organic removal for ponds in series as a result of algae growing in the last treatment pond, which acted as a selfpollutant. In order to develop appropriate technology which will allow industrial effluent standards to be met, it is recommended that further investigations are carried out on the aquatic pond weeds connected with stabilization pond systems, for example using water hyacinth to treat wastewater in the third pond. It is expected than better results will be observed in terms of overall organic and nitrogen removal caused by minimization of algae growth in the last treatment pond.
52
A. RAKKOED et al.
ACKNOWLEDGEMENT The figures created by Mr. Suthira Thongkao are gratefully acknowledged. The authors wish to express their sincere gratitude to Dr. Peter Burt for spending his valuable time in correcting this paper. REFERENCES APHA, AWWA and WEF (1992). Standard Methods for the Examination of Water and Wastewater, 18th ed., New York, American Public Health Association. Isa, Z. (1991). Effluent treatment technology in the rubber industry, ASEANIUNDP Workshop on Pollution Control in the Palm Oil and Rubber Industries, Department of Environment, Ministry of Science, Technology and Environment, Malaysia. Polprasert, C. and Champratheep, K. (1989). Heavy metal removal in attached-growth waste stabilization ponds. Water Res.; 23,
625-631. Shin, H. K. and Polprasert, C. (1987). Attached-growth waste stabilization pond treatment evaluation. Wat Sci. Tech., 19,
229-235. Shin, H. K. and Polprasert, C. (1988). Ammonia nitrogen removal in attached-growth ponds. J. Env Eng.. Am. Soc. Civ. Engrs.,
114,846-863.