- Email: [email protected]
Biological activated carbon treatment of effluent water from wastewater treatment processes of plating industries
ELSEVIER
Separations Technology 6 (1996) 147-153
Biological activated carbon treatment of effluent water from wastewater treatment processes of plating industries Yoshitake Suzuki”, Kazuhiro Mochidzuki”, Yasushi Takeuchi”, Yoshiteru Yagishitab, Tadashi Fukudab, Hideo Amakusab, Hiroshi Abeb “Department of Industrial Chemistry, Meiji University, l-l-l Higashi-Mita, Tama-Ku, Kawasaki 214, Japan ‘Sanshin Mfg. Co., Ltd., 2-22-2 Kamejima, Nakamura-Ku. Nagoya 453, Japan
Abstract Biological activated carbon treatment is applied to a type of wastewater collected from plating industries. The water contains small amounts of refractory organic pollutants, such as anionic surfactants, small amounts of heavy metals, such as cupric and chromic ions, and large amounts of sodium salts. It is found that the thickness of biofilm formed around activated carbon particles increases with time, even though the existence of heavy metals is unfavorable to the growth of microorganisms. As a result, about 50% of organic substances are removed from the water. Present removals for the ionic species of copper and chromium are about 80% and 30%, respectively. Heavy metals are removed from the wastewater by uptake in the bodies of microorganisms, while organic substances are removed by biological decomposition and partly by adsorption. Keywords:
Biological
activated
carbon,
Heavy metals, Plating
industries
wastewater,
Removal of organics, Wastewater
treatment
1. Introduction Plating processes including surface treatment of various metals are used widely, in the plating industry, the iron and steel manufacturing industry including metal processing, the motorcar manufacturing industry, and the electrical and electronics manufacturing industry. A special feature of wastewater discharged from these plating facilities is the presence of various harmful chemical substances [l]. Furthermore, these industries as well as need to consider their effect on the regional and global environment, to save source and energy [2]. Therefore, substances other than products and excess energy should be recovered as much as possible and reused. To meet with such requirements, various types of closed and semi-closed systems are being developed [3]. There are only a few industries, however, that adopted such systems mainly due to the incompatibility of these systems with small-scale industries [4]. Therefore, a novel treatment method, which requires lower construction and 0956-9618/96/$15.00
operating costs and can be adopted irrespectively of the size of the industry, should be developed. To meet this objective, it was found recently that the biological activated carbon (BAC) treatment, in which both adsorption and biological decomposition take place, has an advantage over conventional activated carbon treatment for the removal of organic substances [1,5,61. As the use of BAC treatment makes the whole facilities compact and the life of carbon longer, it has been attracting great attention as one of the most efficient advanced water treatment technologies, and is being applied to various treatment processes to remove pollutants. In general, the existence of heavy metals in the wastewater is very unfavorable to the growth of microorganisms. Actual industrial wastewater, such as that from the plating industry, often contains these ions. Even though heavy metal ions can be removed by physical-chemical treatment, e.g., coagulation and filtration, a part of them may remain in the water treated. When organic substances of lower concentra-
Q 1996 Elsevier Science Ireland Ltd. All rights reserved.
PII:SO956-9618(96)0015~~-6
Fig. 1. Flow diagram of physical-chemical
treatment
for a plating wastewater
tion coexist with such ions, conventional biological removal processes may not be effective. Therefore, as an alternative, the BAC treatment may be adopted to clean up the wastewater. In this paper, our results on BAC treatment of plating wastewater containing both heavy metals and organics are presented [5,6].
Main generating sources of wastewater in plating industries are washing processes from which the washing water is thrown away. On the other hand, plating solutions and other solutions used in acid treatment processes need to be discharged. These solutions, even though their quantities are small, may contain various harmful chemicals, such as concentrated cyanides and acids. Therefore, the water quality must be carefully monitored as serious accidents may occur under poor control of wastewater treatment. Treatment of plating wastewater is usually difficult. It is generally divided into three kinds of treatments, 1
Water
quality of an effluent
discharged from a wastewater
[1.3.7i
as shown in Fig. 1 [1,2,71. The first one discharged from a plating bath that contains high concentration cyanides and washing processes of the plating object. Consequently, these cyanides are decomposed by adding NaClO, NaOH and H,SO,. The second one contains Crh+ generated from plating processes in the case of chromium plating. Therefore, Ca(OH&, H,SO, and NaHSO, are added to reduce Crhi. The last one contains acids and alkalis added to neutralize a worn-out concentrated acid as well as solutions generated in the washing process after acid treatment. Therefore, sodium salts and sulfides of high concentrations remain in the wastewater, even though the quality meets with national and regional regulations
2. Water quality of plating wastewater
Table
and addition of BAC treatment
Dl. Plating wastewater also differs depending on the type of plating process used in the industry. In the following, we summarize two types of wastewater discharged from electroplating and electroless plating processes, respectively. Electroplating processes are divided into (a) pre-
treatment
facility of electroplating
process and that of a sample water used in this
work [5, 61 Component
Concentration
Component
[ppml
Concentration
Component
Concentration Lppml
[ppml
____~
_____.-.__
4 -
N.i) N.D.
SS
29.1
TOC
10.6
Zn’+
0.357
Pb’
COD
14.3
cu? +
0.275
Cl
662
NH,+
13.2
Nip’
0.21 I
so;--
6546
Cal’
32.4
Cd2
K’
55.5
Cr.1 +
0.00s
NO,
2.73
Na’
3455
Fe”‘
N.D.
NO,
72.4
Mg’+
7.04
co’+
N.D.
(pH[-I)
6.83
N.D.:
Not detected
Y. Suxki et al. /Separations
treatment, such as degreasing and washing, (b) plating, and (c) post-treatment. The degreasing solution is reused after purification [9]. An example of the quality data of a certain wastewater, discharged from the physical-chemical treatment facility shown in Fig. 1, is tabulated in Table 1 [5,6]. Metal ions, related directly to the electroplating process were removed well, while K+, Na+, and anionic ions were originated from reagents added to decompose some harmful substances or to neutralize the solution, remained. Part of the residual substances can be used as nutrients for microorganisms in the following biological treatment, but the presence of heavy metals may prohibit their growth. Electroless plating processes are often applied to the treatment of wastewater from high technology industries and the main procedure [lo] is as follows: (a) solvent extraction and removal of the solvent, (b) etching, (c) neutralization, id) catalyst application, (e) promotion of the catalytic activity, and (f) plating, respectively. In these sequential processes, various chemical reagents are used [l,ll]. Especially, EDTA (Ethylene-Diamine-Tetraacetic Acid) is used widely in the electroless plating of copper and palladium. Though treatment is applied to the wastewater, EDTA remains at higher concentrations 11,121, and the effluent water is at present discharged into the sea. This disposal method will not be possible from the beginning of 1996, therefore various ways are being investigated presently for the decomposition and removal of EDTA from such wastewater [ 121.
3. Raw water to be treated and activated carbons used
Raw water, which was used as a sample in this study, was already treated by a series of physicalchemical treatment as shown in Fig. 1 after collecting it from plating factories. Its quality is also shown in Table 1 and satisfies local regulations. Two kinds of commercial granular activated carbons were used. One was brown coal based, and the other was coconut shell based (referred here as Br-AC and Cot-AC, respectively). Physical properties of the two samples are shown in Table 2 [5,6].
Table 2 Physical properties cjf activated carbon used [5,6] .___. Process or plating bath
Br-AC
Raw material True density [kg/m’] B.E.T. specific surface area [m’/kg] Total pore volume [m’/kg] ______-
Brown 2.08 x 1.04 x 2.67 x
Cot-AC coal 101 10h lo-’
Coconuts shell 1.98x IO’ 1.34 x 10h 3.95 x 10-j
Trchndo~
6 (1996) I-I7--1.53
Raw Water Tank
I49
Aeration Tank
Fig. 2. Experimental
-Carbon
Bed
setup [5.h].
4. Feasibility of BAC treatment for a plating wastewater
To study if BAC treatment is applicable to the wastewater from plating factories, the formation of biofilm onto activated carbon particles’ surfaces was investigated. The experimental set-up is shown in Fig. 2 [5,61. A synthetic wastewater containing cupric ion, A, whose components are listed in Table 3 [5,6], was used instead of the actual plating wastewater, and Br-AC was selected. 1.0 X lo-’ kg of the activated carbon particles were inoculated with floe, in which microorganisms acclimatized to the other synthetic wastewater of cupric ion free (designated as B) existed, and were packed in a glass column (2.5 x lo-’ m in internal diameter). The synthetic water, A, was fed to an aeration tank (6.0 X 10m4 m”) at a feed rate of 6.0 x lo-” m”/h and was aerated. Then, the water was fed to the activated carbon bed of 4.7 x lo-’ m in height at 6.0 X 10d3 m3/h, and a part of the effluent water from the bed was recycled to the aeration tank while allowing overflow. This experiment was performed at 303 K. Similarly, a synthetic wastewater B was, also, used as a control. As a result, biofilm formed around particles’ surfaces as shown in Fig. 3 [1,6]. The removal ratio of phenol under existence of cupric ion was smaller than the case of cupric ion free. The thickness of the film was 1 x 10-j m after about 20 h and it increased gradually, however it was only about 30% of the value achieved under the cupric ion free solution. This shows that microorganisms can grow even under the presence of metal ions indicating the ability of decomposing organics. Fig. 4 [1,5,6] shows changes in the concentrations of TC (total carbon), IC (inorganic carbon) and TOC (total organic carbon) with time, respectively. In this case, the actual plating wastewater, as shown in Table 1, and an activated carbon, Br-AC, were used and the experiment was performed by using a batch system,
Water
quality
of two kinds of synthetic
Mg’+
wastewater
0.6
[5.6]
(pH[ ~ I)
0.6
which was accomplished by stopping the feed to the aeration tank, and allowing overflow from the tank as shown in Fig. 2. It was thought that most of organic substances were removed by adsorption on the activated carbon until 50 h elapsed, because the change of TOC was similar to that of TC. After that, while the concentration of TC was kept constant, the concentration of TOC decreased and IC concentration increased. A large concentration change in terms of TOC that occurred after 50 h seems to be caused by the biological decomposition and, consequently, the organic substances decompose to inorganic carbon. From these results, it is concluded that BAC treatment may be applied to clean actual plating wastewater that contains organic pollutants, small amounts of heavy metals, and sodium salts of high concentration. 5. Continuous
treatment
of the plating waste water
5.1. Experimental
Continuous treatment of an actual plating wastewater was performed using the experimental apparatus
6.6
8.0
shown in Fig. 2. The wastewater (hereafter, described simply as raw water), already subjected to various kinds of physical-chemical treatment as shown in Fig. 2, was aerated in the aeration tank, then fed to a BAC column and a part of the effluent water was fed back to the tank while allowing overflow. Experimental conditions are shown in Table 4 [5,6]. In Runs 1 and 4, BAC, whose surface had been covered with biofilm acclimatized to the raw water, was used. On the other hand, in Runs 2, 3-l and 3-2, an original activated carbon was simply packed in the column, and biofilm was allowed to form onto the particles’ surfaces. In Run 3-3, BAC column after used in Run 3-l was reused. In Runs 3-l-3-3, the circulation of up-flow with higher flow rates was employed to expand carbon bed, while the circulation was done using down-flow in other runs. At certain time intervals, water samples of 1.0 X lo-’ m3 each were collected from the aeration tank and the same volume of raw water was added afterwards. Changes in TOC, metal ions, pH, etc. with time were measured by a TOC analyzer (TOC-500;
a) With the presence of cupric ion
b) Without the presence of cupric ion Fig. 3. Influence
of the cupric
ion on changes
0 in biofilm
thickness
with time II.61.
1
2mm
0
50
100 Time [hrs]
150
200
0
50
100 Time [hrs]
150
200
Fig. 4. Biological decomposition of organ& in the actual plating wastewater by a batch method [1,5,6]. (a) Changes of C/C,, for TC and TOC (b) Changes of concentration for TC, IC and TOC.
Shimadzu Co., Japan), a polarized Zeeman atomic absorption spectrometer (Z-6000; Hitachi Ltd. Tokyo), and a pH meter (F-13; Horiba Co., Ltd., Tokyo), respectively. 6. Results and discussion From the results for two experimental runs (Runs 2 and 3-2), shown in pig. 5 1561, it was found that the
ratio of the outlet concentration to the inlet one for values of TOC was kept at about 50% for a long period although some deviation occurs due to the changes in pH and the concentrations of other components [13-151. If all of the organic substances were removed only by adsorption, the capability of the carbon bed should saturate within 20 days. Removal of organics, however, still took place after this time. For example, in the case of Run 2, the sum of TOC removed was found to be about 7 x lo-” kg (3.50 x lo-’ kg/kg-A.C.) from graphical integration for 50 days, while the amount removed by simple adsorption was 1.85 x 10m3 kg (9.25 x lo-” kg/kg-A.C.). Therefore, it is clear that biological decomposition occurs in the system. Regarding the backwashing, it was not necessary for Runs 3-l-3-3 as the expanded bed was used. The washing was necessary, however, for other runs, because accumulation of surplus sludge occurred. Also, it was observed in the experiments that some kinds of heavy metal ions, especially cupric ion and chromium ion, were also removed, as shown in Fig. 6 [5,6]. For example, the amount of cupric ion which should be removed simply by adsorption was 2.49 x 10eh kg (1.66 X 10m5 kg/kg-A.C.) and this value was equal to that obtained for about 3 days from the beginning of the treatment in Run 3-2. The heavy metal species of higher concentration were extracted from biofilm with nitric acid or EDTA in order to examine whether they were uptaken by either the cell walls or the intra-cells of microorganisms. Each amount extracted with both solutions was almost the same as above described, however the uptake mechanism was not clear. It was found that the heavy metals were concentrated in the biofilm and removed from the water as sludge. Changes in the removal ratio of TOC and those of the two metal ions with the change of space velocity (SW are shown in Fig. 7 [5,61, where, SV is the ratio of the circulating flow rate to the volume of BAC column. For higher SV, the removal ratio of TOC and that of ionic species became lower, respectively, even though the types of activated carbon used and the condition of BAC formation were different from each
Table 4 Experimental conditions for contmuous treatment [5,6] Run No.
Kind of activated carbon
Particle diameter,
Weight of carbon,
Volume of aeration tank, [m3]
Circulating flow rate,
Feed rate to aeration tank,
[kg1
Cross secttonal area of column, [m’l
[ml
[m”/dayl
[m’/dayl
1
&-AC
1.19 x10-3
0.20
1.88 x lo-'
1.50x 10-3
0.144
7.30x 10-j
2
Br-AC
1.19 2: 10-j
0.20
1.88XlO~'
1.60x 10-j
0.216
2.16X10-' 1.14x10mJ
3-l
Cot-AC
1.19x10m"
0.15
1.88x 10 '
0.60~10
3
I.44
3-2
Br-AC
I.19x IOF'
0.15
1.88x IO i
0.60~10
3
1.44
1.14x IO_'
3-3
Cot-AC
1.19>: 10 3
0.15
1.88X10
0.60~10~'
1.44
7.88~10~'
4
Cot-AC
1.08>: lom"
4.5
1.06x 10'
2.00 x 10 z
2.88
I.14x 10-l
:
h
I
40
60
Time Fig. 5. Changes of C/C,,
other. It was clear that some types of ions were removed comparatively well by the BAC treatment. 7. Conclusion It was found that biological decomposition of organic substances occurred even in the wastewater that contained small amounts of heavy metals and high
20 Fig. 6. Changes of C/C,,
[days]
for TOC
(Runs 2 and i-2) [5,61
concentrations of sodium salts; about 50% of organic substances in the wastewater were removed. Cupric ion and chromic ion were also removed from the water by uptake to microorganisms, though the removal mechanism was not clear. It was also found that the removal ratios of these pollutants increased with the decreasing SV. Heavy metals can be removed by other methods,
40 Time [days ] for cupric ion and chromium
60 ion (Run 3-2) L5.61.
Y. Suxrki
et 01. / Separuriom
Technology
6 11996) l-17-15.3
121 Amakusa,
H. (1991)
wastewater
cu2+ 80 -
nol. Chem.
6. :TocJyp
,A .‘ _ “‘.&’ -._..,__ b I
0
0.2
Co. Ltd.
Fujikasui
Engineering,
Japan, pp. 1077108.
3-1 3-2
I.2
0.4
I
*
,
0.6
.
[5] Takeuchi.
Y..
Fukuda.
SV
heavy metal
-n 3-3
I
0.8
Asilomar,
*
1.2
1.0
[hr-‘1
of removal ratio for various SV [5,6].
[7] Kosaka,
Suzuki,
no
Wastewater).
Kaibundo,
[81 Kashiwaba. [9] Yagishita,
of industrial
wastewater
and sulfides of high concentrations. Eng. in Japanese),
Kagaku
Junkan-roka [IO] Committee (1987)
Y., acti-
of 5th Int. Conf.
on Adsorption,
Thesis. Meiji Univ.
Circulation
Haisui-syori-gijustu
(1991)
and reuse of water.
(Treatment
of
Plating
Japan, pp. 25-26. Status
of water
quality
Technologies). Examples
no Gaiyo (Outline
management,
Japan 4393,
of
apphcation
of Circulating
852-859. of
filters.
Filtration),
San-
of Total
Technology
Sec. 13-11 Cu electrolcss
Party on Plating edn., Tokyo plating. Guideb.
Plat. Technol.
Jpn. pp. 3988475. 1111 The Chemical
Society of Japan edn. (1992)
Technologies. 1121 Takeuchi, Fukuda.
Dai-Nippon-Tosyo,
Y..
Suzuki,
T.. Amakusa,
biodegradability Annual
Y..
activated
Y..
Mochidzuki, by chemical
Sot. Chem. Suzuki,
T., Amakusa,
114) Takeuchi,
Y.,
treatment
Plating and High
pp. 42. 56, 96, 190. K.,
H. and Abe. H. (1996)
of EDTA
Meeting,
tumn Meeting,
Yagishita,
Y.,
Improvement
of
oxidation.
Proc. 61st
Eng. Jpn. (in print).
Y..
Mochidzuki,
H. and Abe,
K.,
H. (1994)
of wastewater
Yagishita.
1). Proc. 27th Au-
Sot. Chem.
Eng. Jpn. p 204 of Part 3.
Suzuki,
Mochidzuki,
carbon
Y..
treatment
Y.,
Biological acti-
in which organic subs-
ions co-exist (Part
metals of low concentrations.
K. (1994)
of wastewater
Biological
containing
Proc. Kumamoto
heavy-
Meeting,
Sot.
Yagishita,
Y.,
Chem. Eng. Jpn. pp. 125-126.
tances
containing
sodium salts
Annual
Kemikaru
Enginiaringu 40, pp.
Yagishita, Biological
shin Mfg. Co.. Ltd., Japan, pp. 73.
Treatment
Kogyosya, Tokyo
K..
H. (1995)
Studies on the biological activated car-
(Surface
Y.
Y.,
Suzuki,
T., Amakusa,
vated carbon
316-321.
Handbook),
of waste water containmg organics and
K. (1994)
Hyomen-gijustu
Fukuda,
H. (1995)
Mochidzuki.
Sec. 2-4
Mekki-kojyo
[lS] Takeuchi.
References Y. and Amakusa,
Y..
ions co-exist, Master’s
vated carbon
The authors would like to express their deepest thanks to Messrs. Y. Ito, G. Nemoto, S. Watanabe, N. Shimura, S. Nishimura, and Miss. M. Okabe, for their assistance in the experimental work.
(Chem.
(Environmental
of waste water in which organic substances and
tances and heavy-metal
Technology
years of
of Japan edn. (1994) Sec. 7-D
H. and Abe,
K. (1995)
Y. (1988)
Fukuda.
Acknowledgement
Y., Takeuchi,
Thirty
USA.
[6] Mochidzuki,
1131 Takeuchi.
Suzuki,
of MIT1
ions. Preprint
heavy-metal
such as ion exchange and electrodialysis, however, these processes will be inefficient since such wastewater contains plenty of inorganic salts. Therefore, BAC treatment as described in this work may be used as a treatment process even in small-scale factories. On the basis of the results described in this paper, the feasibility of the BAC treatment for plating wastewaters is presently being studied in a pilot scale unit. Also, the species of microorganisms that contribute to the decomposition of organics and to the removal of small amount of some heavy metals from such wastewaters, are under investigation.
[I]
edn. (1986).
Kankyo-Soran
T.. Amakusa,
bon treatment
Fig. 7. Comparison
Proc.
Protect. Tech-
pp. l-13.
Engineering
vated carbon treatment
.-._
4
*
Factories,
Semin. Environ.
(31 Fujikasui
Plating Industries.
\\;a
I
technologies of
p. 690.
1 Run No. 1
Exchange
[4] Dept. for Environment
40 -Cr3+ e--------y
_
Present state of treatment
in plating industries and a view of the future.
of 8th Korea-Japan
&...
20 -
153
Y.,
Mochtdzuki,
H. and Abe.
H
treatment
of wastewater
and heavy-metal
ions co-exist
Mectmg,
Sot. Chem.
K., (1995)
Biological acti-
in which organic subs(Part
2). Proc. of 60th
Eng. Jpn p. 58 of Part 1.
Separations Technology 6 (1996) 147-153
Biological activated carbon treatment of effluent water from wastewater treatment processes of plating industries Yoshitake Suzuki”, Kazuhiro Mochidzuki”, Yasushi Takeuchi”, Yoshiteru Yagishitab, Tadashi Fukudab, Hideo Amakusab, Hiroshi Abeb “Department of Industrial Chemistry, Meiji University, l-l-l Higashi-Mita, Tama-Ku, Kawasaki 214, Japan ‘Sanshin Mfg. Co., Ltd., 2-22-2 Kamejima, Nakamura-Ku. Nagoya 453, Japan
Abstract Biological activated carbon treatment is applied to a type of wastewater collected from plating industries. The water contains small amounts of refractory organic pollutants, such as anionic surfactants, small amounts of heavy metals, such as cupric and chromic ions, and large amounts of sodium salts. It is found that the thickness of biofilm formed around activated carbon particles increases with time, even though the existence of heavy metals is unfavorable to the growth of microorganisms. As a result, about 50% of organic substances are removed from the water. Present removals for the ionic species of copper and chromium are about 80% and 30%, respectively. Heavy metals are removed from the wastewater by uptake in the bodies of microorganisms, while organic substances are removed by biological decomposition and partly by adsorption. Keywords:
Biological
activated
carbon,
Heavy metals, Plating
industries
wastewater,
Removal of organics, Wastewater
treatment
1. Introduction Plating processes including surface treatment of various metals are used widely, in the plating industry, the iron and steel manufacturing industry including metal processing, the motorcar manufacturing industry, and the electrical and electronics manufacturing industry. A special feature of wastewater discharged from these plating facilities is the presence of various harmful chemical substances [l]. Furthermore, these industries as well as need to consider their effect on the regional and global environment, to save source and energy [2]. Therefore, substances other than products and excess energy should be recovered as much as possible and reused. To meet with such requirements, various types of closed and semi-closed systems are being developed [3]. There are only a few industries, however, that adopted such systems mainly due to the incompatibility of these systems with small-scale industries [4]. Therefore, a novel treatment method, which requires lower construction and 0956-9618/96/$15.00
operating costs and can be adopted irrespectively of the size of the industry, should be developed. To meet this objective, it was found recently that the biological activated carbon (BAC) treatment, in which both adsorption and biological decomposition take place, has an advantage over conventional activated carbon treatment for the removal of organic substances [1,5,61. As the use of BAC treatment makes the whole facilities compact and the life of carbon longer, it has been attracting great attention as one of the most efficient advanced water treatment technologies, and is being applied to various treatment processes to remove pollutants. In general, the existence of heavy metals in the wastewater is very unfavorable to the growth of microorganisms. Actual industrial wastewater, such as that from the plating industry, often contains these ions. Even though heavy metal ions can be removed by physical-chemical treatment, e.g., coagulation and filtration, a part of them may remain in the water treated. When organic substances of lower concentra-
Q 1996 Elsevier Science Ireland Ltd. All rights reserved.
PII:SO956-9618(96)0015~~-6
Fig. 1. Flow diagram of physical-chemical
treatment
for a plating wastewater
tion coexist with such ions, conventional biological removal processes may not be effective. Therefore, as an alternative, the BAC treatment may be adopted to clean up the wastewater. In this paper, our results on BAC treatment of plating wastewater containing both heavy metals and organics are presented [5,6].
Main generating sources of wastewater in plating industries are washing processes from which the washing water is thrown away. On the other hand, plating solutions and other solutions used in acid treatment processes need to be discharged. These solutions, even though their quantities are small, may contain various harmful chemicals, such as concentrated cyanides and acids. Therefore, the water quality must be carefully monitored as serious accidents may occur under poor control of wastewater treatment. Treatment of plating wastewater is usually difficult. It is generally divided into three kinds of treatments, 1
Water
quality of an effluent
discharged from a wastewater
[1.3.7i
as shown in Fig. 1 [1,2,71. The first one discharged from a plating bath that contains high concentration cyanides and washing processes of the plating object. Consequently, these cyanides are decomposed by adding NaClO, NaOH and H,SO,. The second one contains Crh+ generated from plating processes in the case of chromium plating. Therefore, Ca(OH&, H,SO, and NaHSO, are added to reduce Crhi. The last one contains acids and alkalis added to neutralize a worn-out concentrated acid as well as solutions generated in the washing process after acid treatment. Therefore, sodium salts and sulfides of high concentrations remain in the wastewater, even though the quality meets with national and regional regulations
2. Water quality of plating wastewater
Table
and addition of BAC treatment
Dl. Plating wastewater also differs depending on the type of plating process used in the industry. In the following, we summarize two types of wastewater discharged from electroplating and electroless plating processes, respectively. Electroplating processes are divided into (a) pre-
treatment
facility of electroplating
process and that of a sample water used in this
work [5, 61 Component
Concentration
Component
[ppml
Concentration
Component
Concentration Lppml
[ppml
____~
_____.-.__
4 -
N.i) N.D.
SS
29.1
TOC
10.6
Zn’+
0.357
Pb’
COD
14.3
cu? +
0.275
Cl
662
NH,+
13.2
Nip’
0.21 I
so;--
6546
Cal’
32.4
Cd2
K’
55.5
Cr.1 +
0.00s
NO,
2.73
Na’
3455
Fe”‘
N.D.
NO,
72.4
Mg’+
7.04
co’+
N.D.
(pH[-I)
6.83
N.D.:
Not detected
Y. Suxki et al. /Separations
treatment, such as degreasing and washing, (b) plating, and (c) post-treatment. The degreasing solution is reused after purification [9]. An example of the quality data of a certain wastewater, discharged from the physical-chemical treatment facility shown in Fig. 1, is tabulated in Table 1 [5,6]. Metal ions, related directly to the electroplating process were removed well, while K+, Na+, and anionic ions were originated from reagents added to decompose some harmful substances or to neutralize the solution, remained. Part of the residual substances can be used as nutrients for microorganisms in the following biological treatment, but the presence of heavy metals may prohibit their growth. Electroless plating processes are often applied to the treatment of wastewater from high technology industries and the main procedure [lo] is as follows: (a) solvent extraction and removal of the solvent, (b) etching, (c) neutralization, id) catalyst application, (e) promotion of the catalytic activity, and (f) plating, respectively. In these sequential processes, various chemical reagents are used [l,ll]. Especially, EDTA (Ethylene-Diamine-Tetraacetic Acid) is used widely in the electroless plating of copper and palladium. Though treatment is applied to the wastewater, EDTA remains at higher concentrations 11,121, and the effluent water is at present discharged into the sea. This disposal method will not be possible from the beginning of 1996, therefore various ways are being investigated presently for the decomposition and removal of EDTA from such wastewater [ 121.
3. Raw water to be treated and activated carbons used
Raw water, which was used as a sample in this study, was already treated by a series of physicalchemical treatment as shown in Fig. 1 after collecting it from plating factories. Its quality is also shown in Table 1 and satisfies local regulations. Two kinds of commercial granular activated carbons were used. One was brown coal based, and the other was coconut shell based (referred here as Br-AC and Cot-AC, respectively). Physical properties of the two samples are shown in Table 2 [5,6].
Table 2 Physical properties cjf activated carbon used [5,6] .___. Process or plating bath
Br-AC
Raw material True density [kg/m’] B.E.T. specific surface area [m’/kg] Total pore volume [m’/kg] ______-
Brown 2.08 x 1.04 x 2.67 x
Cot-AC coal 101 10h lo-’
Coconuts shell 1.98x IO’ 1.34 x 10h 3.95 x 10-j
Trchndo~
6 (1996) I-I7--1.53
Raw Water Tank
I49
Aeration Tank
Fig. 2. Experimental
-Carbon
Bed
setup [5.h].
4. Feasibility of BAC treatment for a plating wastewater
To study if BAC treatment is applicable to the wastewater from plating factories, the formation of biofilm onto activated carbon particles’ surfaces was investigated. The experimental set-up is shown in Fig. 2 [5,61. A synthetic wastewater containing cupric ion, A, whose components are listed in Table 3 [5,6], was used instead of the actual plating wastewater, and Br-AC was selected. 1.0 X lo-’ kg of the activated carbon particles were inoculated with floe, in which microorganisms acclimatized to the other synthetic wastewater of cupric ion free (designated as B) existed, and were packed in a glass column (2.5 x lo-’ m in internal diameter). The synthetic water, A, was fed to an aeration tank (6.0 X 10m4 m”) at a feed rate of 6.0 x lo-” m”/h and was aerated. Then, the water was fed to the activated carbon bed of 4.7 x lo-’ m in height at 6.0 X 10d3 m3/h, and a part of the effluent water from the bed was recycled to the aeration tank while allowing overflow. This experiment was performed at 303 K. Similarly, a synthetic wastewater B was, also, used as a control. As a result, biofilm formed around particles’ surfaces as shown in Fig. 3 [1,6]. The removal ratio of phenol under existence of cupric ion was smaller than the case of cupric ion free. The thickness of the film was 1 x 10-j m after about 20 h and it increased gradually, however it was only about 30% of the value achieved under the cupric ion free solution. This shows that microorganisms can grow even under the presence of metal ions indicating the ability of decomposing organics. Fig. 4 [1,5,6] shows changes in the concentrations of TC (total carbon), IC (inorganic carbon) and TOC (total organic carbon) with time, respectively. In this case, the actual plating wastewater, as shown in Table 1, and an activated carbon, Br-AC, were used and the experiment was performed by using a batch system,
Water
quality
of two kinds of synthetic
Mg’+
wastewater
0.6
[5.6]
(pH[ ~ I)
0.6
which was accomplished by stopping the feed to the aeration tank, and allowing overflow from the tank as shown in Fig. 2. It was thought that most of organic substances were removed by adsorption on the activated carbon until 50 h elapsed, because the change of TOC was similar to that of TC. After that, while the concentration of TC was kept constant, the concentration of TOC decreased and IC concentration increased. A large concentration change in terms of TOC that occurred after 50 h seems to be caused by the biological decomposition and, consequently, the organic substances decompose to inorganic carbon. From these results, it is concluded that BAC treatment may be applied to clean actual plating wastewater that contains organic pollutants, small amounts of heavy metals, and sodium salts of high concentration. 5. Continuous
treatment
of the plating waste water
5.1. Experimental
Continuous treatment of an actual plating wastewater was performed using the experimental apparatus
6.6
8.0
shown in Fig. 2. The wastewater (hereafter, described simply as raw water), already subjected to various kinds of physical-chemical treatment as shown in Fig. 2, was aerated in the aeration tank, then fed to a BAC column and a part of the effluent water was fed back to the tank while allowing overflow. Experimental conditions are shown in Table 4 [5,6]. In Runs 1 and 4, BAC, whose surface had been covered with biofilm acclimatized to the raw water, was used. On the other hand, in Runs 2, 3-l and 3-2, an original activated carbon was simply packed in the column, and biofilm was allowed to form onto the particles’ surfaces. In Run 3-3, BAC column after used in Run 3-l was reused. In Runs 3-l-3-3, the circulation of up-flow with higher flow rates was employed to expand carbon bed, while the circulation was done using down-flow in other runs. At certain time intervals, water samples of 1.0 X lo-’ m3 each were collected from the aeration tank and the same volume of raw water was added afterwards. Changes in TOC, metal ions, pH, etc. with time were measured by a TOC analyzer (TOC-500;
a) With the presence of cupric ion
b) Without the presence of cupric ion Fig. 3. Influence
of the cupric
ion on changes
0 in biofilm
thickness
with time II.61.
1
2mm
0
50
100 Time [hrs]
150
200
0
50
100 Time [hrs]
150
200
Fig. 4. Biological decomposition of organ& in the actual plating wastewater by a batch method [1,5,6]. (a) Changes of C/C,, for TC and TOC (b) Changes of concentration for TC, IC and TOC.
Shimadzu Co., Japan), a polarized Zeeman atomic absorption spectrometer (Z-6000; Hitachi Ltd. Tokyo), and a pH meter (F-13; Horiba Co., Ltd., Tokyo), respectively. 6. Results and discussion From the results for two experimental runs (Runs 2 and 3-2), shown in pig. 5 1561, it was found that the
ratio of the outlet concentration to the inlet one for values of TOC was kept at about 50% for a long period although some deviation occurs due to the changes in pH and the concentrations of other components [13-151. If all of the organic substances were removed only by adsorption, the capability of the carbon bed should saturate within 20 days. Removal of organics, however, still took place after this time. For example, in the case of Run 2, the sum of TOC removed was found to be about 7 x lo-” kg (3.50 x lo-’ kg/kg-A.C.) from graphical integration for 50 days, while the amount removed by simple adsorption was 1.85 x 10m3 kg (9.25 x lo-” kg/kg-A.C.). Therefore, it is clear that biological decomposition occurs in the system. Regarding the backwashing, it was not necessary for Runs 3-l-3-3 as the expanded bed was used. The washing was necessary, however, for other runs, because accumulation of surplus sludge occurred. Also, it was observed in the experiments that some kinds of heavy metal ions, especially cupric ion and chromium ion, were also removed, as shown in Fig. 6 [5,6]. For example, the amount of cupric ion which should be removed simply by adsorption was 2.49 x 10eh kg (1.66 X 10m5 kg/kg-A.C.) and this value was equal to that obtained for about 3 days from the beginning of the treatment in Run 3-2. The heavy metal species of higher concentration were extracted from biofilm with nitric acid or EDTA in order to examine whether they were uptaken by either the cell walls or the intra-cells of microorganisms. Each amount extracted with both solutions was almost the same as above described, however the uptake mechanism was not clear. It was found that the heavy metals were concentrated in the biofilm and removed from the water as sludge. Changes in the removal ratio of TOC and those of the two metal ions with the change of space velocity (SW are shown in Fig. 7 [5,61, where, SV is the ratio of the circulating flow rate to the volume of BAC column. For higher SV, the removal ratio of TOC and that of ionic species became lower, respectively, even though the types of activated carbon used and the condition of BAC formation were different from each
Table 4 Experimental conditions for contmuous treatment [5,6] Run No.
Kind of activated carbon
Particle diameter,
Weight of carbon,
Volume of aeration tank, [m3]
Circulating flow rate,
Feed rate to aeration tank,
[kg1
Cross secttonal area of column, [m’l
[ml
[m”/dayl
[m’/dayl
1
&-AC
1.19 x10-3
0.20
1.88 x lo-'
1.50x 10-3
0.144
7.30x 10-j
2
Br-AC
1.19 2: 10-j
0.20
1.88XlO~'
1.60x 10-j
0.216
2.16X10-' 1.14x10mJ
3-l
Cot-AC
1.19x10m"
0.15
1.88x 10 '
0.60~10
3
I.44
3-2
Br-AC
I.19x IOF'
0.15
1.88x IO i
0.60~10
3
1.44
1.14x IO_'
3-3
Cot-AC
1.19>: 10 3
0.15
1.88X10
0.60~10~'
1.44
7.88~10~'
4
Cot-AC
1.08>: lom"
4.5
1.06x 10'
2.00 x 10 z
2.88
I.14x 10-l
:
h
I
40
60
Time Fig. 5. Changes of C/C,,
other. It was clear that some types of ions were removed comparatively well by the BAC treatment. 7. Conclusion It was found that biological decomposition of organic substances occurred even in the wastewater that contained small amounts of heavy metals and high
20 Fig. 6. Changes of C/C,,
[days]
for TOC
(Runs 2 and i-2) [5,61
concentrations of sodium salts; about 50% of organic substances in the wastewater were removed. Cupric ion and chromic ion were also removed from the water by uptake to microorganisms, though the removal mechanism was not clear. It was also found that the removal ratios of these pollutants increased with the decreasing SV. Heavy metals can be removed by other methods,
40 Time [days ] for cupric ion and chromium
60 ion (Run 3-2) L5.61.
Y. Suxrki
et 01. / Separuriom
Technology
6 11996) l-17-15.3
121 Amakusa,
H. (1991)
wastewater
cu2+ 80 -
nol. Chem.
6. :TocJyp
,A .‘ _ “‘.&’ -._..,__ b I
0
0.2
Co. Ltd.
Fujikasui
Engineering,
Japan, pp. 1077108.
3-1 3-2
I.2
0.4
I
*
,
0.6
.
[5] Takeuchi.
Y..
Fukuda.
SV
heavy metal
-n 3-3
I
0.8
Asilomar,
*
1.2
1.0
[hr-‘1
of removal ratio for various SV [5,6].
[7] Kosaka,
Suzuki,
no
Wastewater).
Kaibundo,
[81 Kashiwaba. [9] Yagishita,
of industrial
wastewater
and sulfides of high concentrations. Eng. in Japanese),
Kagaku
Junkan-roka [IO] Committee (1987)
Y., acti-
of 5th Int. Conf.
on Adsorption,
Thesis. Meiji Univ.
Circulation
Haisui-syori-gijustu
(1991)
and reuse of water.
(Treatment
of
Plating
Japan, pp. 25-26. Status
of water
quality
Technologies). Examples
no Gaiyo (Outline
management,
Japan 4393,
of
apphcation
of Circulating
852-859. of
filters.
Filtration),
San-
of Total
Technology
Sec. 13-11 Cu electrolcss
Party on Plating edn., Tokyo plating. Guideb.
Plat. Technol.
Jpn. pp. 3988475. 1111 The Chemical
Society of Japan edn. (1992)
Technologies. 1121 Takeuchi, Fukuda.
Dai-Nippon-Tosyo,
Y..
Suzuki,
T.. Amakusa,
biodegradability Annual
Y..
activated
Y..
Mochidzuki, by chemical
Sot. Chem. Suzuki,
T., Amakusa,
114) Takeuchi,
Y.,
treatment
Plating and High
pp. 42. 56, 96, 190. K.,
H. and Abe. H. (1996)
of EDTA
Meeting,
tumn Meeting,
Yagishita,
Y.,
Improvement
of
oxidation.
Proc. 61st
Eng. Jpn. (in print).
Y..
Mochidzuki,
H. and Abe,
K.,
H. (1994)
of wastewater
Yagishita.
1). Proc. 27th Au-
Sot. Chem.
Eng. Jpn. p 204 of Part 3.
Suzuki,
Mochidzuki,
carbon
Y..
treatment
Y.,
Biological acti-
in which organic subs-
ions co-exist (Part
metals of low concentrations.
K. (1994)
of wastewater
Biological
containing
Proc. Kumamoto
heavy-
Meeting,
Sot.
Yagishita,
Y.,
Chem. Eng. Jpn. pp. 125-126.
tances
containing
sodium salts
Annual
Kemikaru
Enginiaringu 40, pp.
Yagishita, Biological
shin Mfg. Co.. Ltd., Japan, pp. 73.
Treatment
Kogyosya, Tokyo
K..
H. (1995)
Studies on the biological activated car-
(Surface
Y.
Y.,
Suzuki,
T., Amakusa,
vated carbon
316-321.
Handbook),
of waste water containmg organics and
K. (1994)
Hyomen-gijustu
Fukuda,
H. (1995)
Mochidzuki.
Sec. 2-4
Mekki-kojyo
[lS] Takeuchi.
References Y. and Amakusa,
Y..
ions co-exist, Master’s
vated carbon
The authors would like to express their deepest thanks to Messrs. Y. Ito, G. Nemoto, S. Watanabe, N. Shimura, S. Nishimura, and Miss. M. Okabe, for their assistance in the experimental work.
(Chem.
(Environmental
of waste water in which organic substances and
tances and heavy-metal
Technology
years of
of Japan edn. (1994) Sec. 7-D
H. and Abe,
K. (1995)
Y. (1988)
Fukuda.
Acknowledgement
Y., Takeuchi,
Thirty
USA.
[6] Mochidzuki,
1131 Takeuchi.
Suzuki,
of MIT1
ions. Preprint
heavy-metal
such as ion exchange and electrodialysis, however, these processes will be inefficient since such wastewater contains plenty of inorganic salts. Therefore, BAC treatment as described in this work may be used as a treatment process even in small-scale factories. On the basis of the results described in this paper, the feasibility of the BAC treatment for plating wastewaters is presently being studied in a pilot scale unit. Also, the species of microorganisms that contribute to the decomposition of organics and to the removal of small amount of some heavy metals from such wastewaters, are under investigation.
[I]
edn. (1986).
Kankyo-Soran
T.. Amakusa,
bon treatment
Fig. 7. Comparison
Proc.
Protect. Tech-
pp. l-13.
Engineering
vated carbon treatment
.-._
4
*
Factories,
Semin. Environ.
(31 Fujikasui
Plating Industries.
\\;a
I
technologies of
p. 690.
1 Run No. 1
Exchange
[4] Dept. for Environment
40 -Cr3+ e--------y
_
Present state of treatment
in plating industries and a view of the future.
of 8th Korea-Japan
&...
20 -
153
Y.,
Mochtdzuki,
H. and Abe.
H
treatment
of wastewater
and heavy-metal
ions co-exist
Mectmg,
Sot. Chem.
K., (1995)
Biological acti-
in which organic subs(Part
2). Proc. of 60th
Eng. Jpn p. 58 of Part 1.