Download Application of brass scrubber filter with copper hydroxide

Environ. Eng. Res. 2015
Research Article
http://dx.doi.org/10.4491/eer.2014.062
pISSN 1226-1025 eISSN 2005-968X
In Press, Uncorrected Proof
Application of brass scrubber filter with copper hydroxide
nanocomposite structure for phosphate removal
Ki-Ho Hong1, In-Sang Yoo2,3, Sae-Hoon Kim3, Duk Chang4, Young Sunwoo4, Dae-Gun Kim2†
1
Division of Interdisciplinary Studies, Konkuk University, Seoul 143-701, Korea
Green Energy and Environment Laboratory (GE2), Yeongwol-gun 230-884, Korea
3
Department
of Ceramic Engineering, Gangneung-Wonju National University, Gangneung 210-702, Korea
4
Department of Environmental Engineering, Konkuk University, Seoul 143-701, Korea
2
Abstract
In this study, a novel phosphorus removal filter made of brass scrubber with higher porosity of over
96% was fabricated and evaluated. The brass scrubber was surface-modified to form copper hydroxide
on the surface of the brass, which could be a phosphate removal filter for advanced wastewater
treatment because the phosphates could be removed by the ion exchange with hydroxyl ions of copper
hydroxide. The evaluation of phosphate removal was performed under the conditions of the batch type
in wastewater and continuous type through filters. Filter recycling was also evaluated with retreatment
of the surface modification process. The phosphate was rapidly removed within a very shorter contact
time by the surface-modified brass scrubber filter, and the phosphate mass of 1.57 mg was removed per
gram of the filter. The possibility of this surface-modified brass scrubber filter for phosphorus removal
was shown without undesirable sludge production of existing chemical phosphorus removal
techniques, and we feel that it would be very meaningful as a new wastewater treatment.
Keywords: Brass scrubber, Copper hydroxide, Nanocomposite, Phosphate removal, Surface modification
This is an Open Access article distributed under the terms
of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/)
which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Copyright © 2015 Korean Society of Environmental Engineers
Received September 13, 2014 Accepted May 19, 2015
†
Corresponding Author
E-mail: [email protected]
Tel: +82-10-9436-4292 Fax: +82-2-2201-6392
http://eeer.org
1. Introduction
Wastewater is relatively rich in phosphorus compounds, and the phosphorus is a nutrient used by
organisms for growth. Phosphates come from a variety of sources including agricultural fertilizers,
domestic wastewater, detergents, industrial process wastes and geological formations. Phosphates are
classified as orthophosphates, polyphosphates and organic phosphates [1, 2]. The discharge of
wastewater containing phosphorus may cause algae growth in quantities sufficient to cause taste and
odor problems in drinking water supplies [3-5]. Phosphorus can also interfere with coagulation and
with lime soda softening [6]. Dead and decaying algae can cause oxygen depletion problems which in
turn can kill fish and other aquatic organisms in streams. For this reason, phosphorus removal is an
essential role of wastewater treatment plants and testing for phosphorus in the plant effluent is critical
[7].
Biological nutrient removal and chemical precipitation are the most commonly used methods for
removal of phosphates in wastewater [8-10], whereas both methods have certain disadvantages. The
biological phosphorus removal process requires a highly efficient secondary clarifier and maintenance
of sufficient organics concentration. In addition, the main disadvantages in chemical precipitation are
higher maintenance cost, problems associated with the handling of chemicals, and the disposal of large
amounts of produced sludge. The common and inherent limitation of these two methods is that neither
of them can produce an effluent containing less than 0.5 mg/L as P [11, 12].
Therefore, ion exchange and adsorption methods can be a good candidate for phosphorus removal,
which is defined as the displacement of one ion by another. To overcome the disadvantages of
biological nutrient removal and chemical precipitation methods, an ion exchange and adsorption
techniques which are cost effective, easily performed, offers limited sludge production, and has the
1
potential for retained phosphate recycling are needed to remove the phosphate effectively. Concerning
phosphate removal through an ion exchange and adsorption method, the use of a filter is more desirable
than is an adsorbent. If one is able to selectively remove the phosphorus and to repeatedly use a recycle
treatment, it can be a very effective method for advanced wastewater treatment because chemical
sludges will not occur and the removed phosphorus can be a useful element as a resource. In addition,
there will be no requirement for a large area to set-up a wastewater treatment system. There are other
major advantages: low energy consumption, easy upgrading of existing facilities, continuous separation,
better effluent quality, and avoidance of any chemical addition. Although there are many kinds of
adsorbents for phosphate removal such as activated alumina treated with aluminium sulfate, boehmite,
goethite, akaganeite, yttrium carbonate, and polymeric ligand exchanger [13-18], an additional
collection process after the phosphate adsorption should be considered. The recycling requirements for
these adsorbents should also be addressed.
In our previous research [19], a sintered porous aluminium filter covered by Al(OH)3 through surface
modification by alkali treatment and stabilization process was designed for phosphorus removal.
Phosphorus in artificial wastewater was removed by ion exchange mechanism from aluminium
hydroxide to aluminium phosphate (AlPO4). However, the filter had limitations such as low porosity
resulting in severely lower permeability and application of very small amount of artificial wastewater.
In this research, thus, a phosphorus removal filter was fabricated by using a brass scrubber with
higher porosity. The brass scrubber was surface-modified to form copper hydroxide (Cu(OH)2) on the
surface of the brass, which acts as a phosphate removal filter for advanced wastewater treatment
because phosphate ions may be removed by the ion exchange with hydroxyl ions of copper hydroxide.
The evaluation of phosphate removal was performed under conditions of an immersion state of the
filters in wastewater and a flowing state through filters. Filter recycling was also evaluated with
2
retreatment of the surface modification process.
2. Materials and Methods
2.1. Material
The brass scrubber filter with an average weight of 35 g for each has a flexible porous structure
entangled by the coil with a thickness of 40 μm and width of 1 mm, as shown in Fig. 1. This is
chemically surface-modified to form a functional surface for the preparation of a phosphorus removal
filter. The surface modification process composed of three step, surface oxidation, alkali-treatment, and
stabilization, was applied to form the micro-porous surface [20].
The oxidation of the copper surface was performed by boiling in hydrogen peroxide solution of 34%
for 30 minutes. The alkali-treatment was subsequently performed by boiling in sodium hydroxide
solution of 10mM for 2 hours. The alkali-treated body was then immersed in boiling distilled water for
30 minutes to stabilize the surface layer after the alkali-treatment. For the recycle of brass scrubber
filter, it was re-treated by alkali solution by the same method. The microstructure of the brass scrubber
filter was evaluated by scanning electron microscopy (SEM) and transmission electron microscopy
(TEM).
Three types of experiments were performed for the evaluation of phosphorus removal performance.
The measurement of phosphate was conducted using the ascorbic acid method in the American public
health association (APHA) standard methods [21].
3
Fig. 1. Brass scrubber filter with flexible porous structure.
2.2. Methods
2.2.1. Batch type experiments using synthetic wastewater
For the evaluation of phosphorus removal by batch type experiments under conditions of various
concentrations, synthetic wastewaters with phosphate concentrations of 5 mg/L and 50 mg/L were used.
The surface-modified brass scrubber filters, with a weight of 35 g, were immersed in each batch reactor
filled with synthetic wastewater of 2 L, and the phosphate concentration in the wastewater was
measured at an interval of 10 minutes for 1 hour.
2.2.2. Continuous flow type experiments using synthetic wastewater
Samples with lower phosphate concentrations of 5 mg/L and 10 mg/L, similar to that of typical
wastewater, were used in the continuous flow type experiments. The surface-modified brass scrubber
filters were stacked in an acryl tube with a diameter of 30 mm, and the wastewater was consecutively
sent through the filter stack in the tube. After filtering the wastewater, the brass scrubbers were re4
treated by alkali solution using the same method and then filtering was performed once again.
2.2.3. Batch type experiments with typical wastewater
For the performance evaluation of phosphorus removal in typical wastewater, samples with phosphate
concentration of 7.3 mg/L were collected from the end of a grit chamber in a small sized wastewater
treatment plant in Korea. The BOD, total nitrogen (TN) and total phosphorus (TP) of the raw municipal
wastewater ranged 110-190 mg/L (average 155 mg/L), 28.0-39.5 mg/L (average 35.5 mg/L), and 2.78.2 mg/L (average 7.3 mg/L), respectively. Experimental procedure was performed in the same manner
with the batch type experiments using synthetic wastewater as mentioned above.
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3. Results and Discussion
Ion exchange, which is defined as the displacement of one ion by another, can be a good candidate for
phosphorus removal in wastewater. The displaced ion is originally a part of the insoluble material and
the displacing ion is originally in the soluble material. The ion exchange reactions are governed by
equilibrium, so that effluents from ion exchange processes never yield pure water. In case of anions,
the displacement preferential order for ion exchange can be arranged as follows: SO4-2, CrO4-2, NO3-,
AsO4-3, PO4-3, MoO4-2, I-, Br-, Cl-, F-, and OH- [22]. That is, former anions in this sequence can displace
the ions coming after them. Thus, the phosphate ion can replace the hydroxide ion which can be formed
on the surface of filter. As discussed in a previous study [19], a phosphate removal filter was suggested
using porous aluminum, surface-modified to form aluminum hydroxide on the surface. The chemical
surface modification treatment gave a unique structure on the surface inducing metal hydroxide.
In this study, the brass scrubber with extremely higher porosity of over 96% was employed for
higher permeability. Generally, a highly permeable filter does not guarantee higher filtration efficiency.
However, a nanoporous structure on the filter surface revised in this study increases specific surface
area which leads to enhanced filtration efficiency.
Fig. 2. Scanning electron micrographs of the surfaces of brass (a), that treated by H2O2 (b), and the
phosphate removal filter (c).
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Fig. 2 shows the surface morphologies of brass (a), oxidized brass (b) and surface-modified brass (c).
The surface of brass is very smooth. Then, the brass surface was oxidized and became rough by H2O2
treatment as depicted in Fig. 2(b), in which it looks like irregular particulates of several nanometers
covered the surface with nanoporous morphology. When the brass was treated in boiling H2O2,
oxidation of Cu (Cu+H2O2→CuO+H2O) took place, and then alkali treatment resulted in the reaction of
CuO with NaOH as CuO+2NaOH→Na2[Cu(OH)2]. Soluble Na2[Cu(OH)2] salt on the surface is
transformed into Cu(OH)2 in the boiling water; Na2[Cu(OH)2]+H2O→Cu(OH)2+2NaOH+H2O. At this
point, Cu2+ prefers a square planar coordination with OH-, and this leads to an extended chain that can
be connected with each other forming a two-dimensional (2D) structure. Finally, the 2D layers are
stacked through the relatively weak hydrogen bond interactions, become a three-dimensional (3D)
crystal [23]. This self-assembly can give Cu(OH)2 nanowhiskers. Fig. 2(c) presents the surface
morphology of completely treated brass. The copper hydroxide nanowhiskers are grown with a very
narrow width of around 20 nm to 100 nm. The nanowhiskers are shaped like corals. This surface
structure of the nanowhiskers distribution typically increases the specific surface area by several times.
Fig. 3. Transmission electron micrographs for the cross-sectioned surface of the phosphate filter; high
magnification (a), low magnification (b) and (c).
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Fig. 3(a) shows the cross-sectional TEM micrograph of the surface of phosphate filter covered by
copper hydroxide. The nanowhiskers of copper hydroxide were grown on the flat surface of brass with
a porous structure of which thickness was over 1μm. Near the surface, large nanowhiskers of 200 nm
length were grown in a vertical direction to the brass surface, while the small whisker particles
aggregated forming a network on the large nanowhiskers which were observed from an overhead view
of the filter surface as presented in Fig. 2(c). Fig. 3(b) shows several large nanowhiskers near the brass
surface. Their shape looks like a single crystal but several grains are observed in the large whiskers.
However, the small whiskers on the large ones were single crystal grains and they were mutually
coagulated. Fig. 3(c) presents a high magnification micrograph of the end of a nanowhisker in which
the lattice fringe is observed in the vertical direction to the longitudinal direction of the nanowhisker.
Such a lattice fringe is revealed to be with 0.2616 nm distance and the longitudinal direction of the
nanowhisker is the z direction of orthorhombic copper hydroxide.
The copper hydroxide nanowhiskers formed on the brass surface have many pores so that the
surface area is extremely increased. These nanoporous surfaces of Cu(OH)2 supplies a large number of
sites for ion exchange with phosphates. The brass coil macroporous structure has a higher permeability,
and such nanoporous surfaces of Cu(OH)2 should have advanced filtration efficiency.
40
30
30
20
20
10
10
0
0
0
10
20
30
40
Time (min)
50
60
Phosphate
Concentration (mg/L)
Phosphate
Concentration (mg/L)
50
40
(b)
5
8
4
6
3
4
2
2
1
0
0
0
10
20
30
40
50
Removed Phosphate Mass (mg)
60
50
Removed Phosphate Mass (mg)
(a)
60
Time (min)
Fig. 4. Change of phosphate concentration and removed phosphate mass when the phosphate filter is
immersed in the synthetic wastewaters with concentrations of 50 mg/L (a) and 5 mg/L (b).
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Fig. 4 shows the phosphate removal characteristics of the filter for when it was immersed in the
synthetic wastewaters with phosphate concentrations of 50 mg/L and 5 mg/L, as mentioned regarding
the first batch type experimental procedure. The phosphate concentration of 50 mg/L dramatically
decreased to around 23 mg/L during the first 10 minutes, and then instantly saturated, as shown in Fig.
4(a). The phosphate concentration decreased to around 2 mg/L during the first 10 minutes when the
filter was immersed in wastewater with the lower concentrations of 5 mg/L, and it decreased very
slowly to about 1 mg/L at 60 minutes as illustrated in Fig. 4(b). The ion exchange site of Cu(OH)2 on
the filter surface can easily meet the phosphate ions in wastewater with higher concentrations so that
the surface of the filter can change almost completely from Cu(OH)2 to Cu3(PO4)2. Whereas, the
phosphate in wastewater with lower concentrations is pressed to find ‘vacant’ Cu(OH)2 sites between
previously ion-exchanged Cu3(PO4)2 parts for absorption onto the filter surface. This means that the
filtration of wastewater with lower phosphate concentration should require more sufficient contact time
for higher removal of phosphate in wastewater.
(a)
(b)
5.0
45
40
4.0
3.5
1
2
3
4
5
6
7
8
9
10
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0
2
4
6
8
10 12 14 16 18 20
Influent (L)
Removed
Phosphate Mass (mg)
Phosphate
Concentration (mg/L)
4.5
35
30
1
2
3
4
5
6
7
8
9
10
25
20
15
10
5
0
0
2
4
6
8
10 12 14 16 18 20
Influent (L)
Fig. 5. Change of phosphate concentration (a) and removed phosphate mass (b) when the synthetic
wastewater with concentrations of 5 mg/L is passed through the phosphate removal filters.
9
Fig. 5 and Fig. 6 show the results of the continuous flow type experiments, as mentioned regarding
the second experimental procedure. The synthetic wastewaters with phosphate concentrations of 5
mg/L and 10 mg/L were passed through the acryl tube stacked with surface-modified brass scrubber
filters for only several seconds. After the first flowing experiments, filters retreated by alkali solution
were used for the saturation evaluation of the filter.
As shown in Fig. 5(a), the phosphate concentration rapidly decreased during the first filtering of 1 L,
whereas the concentration gradually increased due to saturation of the filter later. When the wastewater
of 20 L with a concentration of 5 mg/L was filtered, about 40 mg of phosphate mass was removed, and
the removed amount of phosphate was about 40%. The removal also showed similar tendency for the
wastewater with a concentration of 10 mg/L. However, rapid saturation was observed and the removed
amount of phosphate decreased to about 25% due to the relatively higher phosphate concentration. For
both cases, the filtering characteristics were maintained after recycling of used filters.
10
(b)
Phosphate
Concentration (mg/L)
9
8
7
1
2
3
4
5
6
7
8
9
10
6
5
4
3
2
1
0
0
2
4
6
8
10 12 14 16 18 20
Influent (L)
Removed
Phosphate Mass (mg)
(a)
60
55
50
45
40
35
30
25
20
15
10
5
0
1
2
3
4
5
6
7
8
9
10
0
2
4
6
8
10 12 14 16 18 20
Influent (L)
Fig. 6. Change of phosphate concentration (a) and removed phosphate (b) when the synthetic
wastewater with concentrations of 10 mg/L is passed through the phosphate removal filters.
10
Fig. 7 shows the phosphate removal characteristics of the filter on a typical wastewater of 10 L with
a concentration of about 7 mg/L. For this experiment, wastewater was collected from the end of a grit
chamber in a small sized wastewater treatment plant. At the initial filtering, the phosphate
concentration decreased to about 2.5 mg/L and gradually increased due to saturation of the filter as
with the case of the synthetic wastewater. After filtration, the phosphate concentration was about 4
mg/L and the removal amount of phosphate was over 50%.
Therefore, this filter was very effective in removing phosphate ions from typical wastewater as well
as from the synthetic ones, which is a meaningful result, having done so without additional phosphate
treatments. The phosphate has various states in typical wastewater, different from synthetic wastewater.
The phosphate filtering by ion exchange can be an applicable method for phosphorus removal process
because small wastewater treatment facilities generally do not have counter measures for that. The
phosphate filtering system can be easily added to a small wastewater treatment facility without change
to the original set-up. Also, recycling of used filters was very simple and the extracted phosphate ions
8
40
7
35
6
30
5
25
4
20
3
15
2
10
1
5
0
0
0
1
2
3
4
5
6
7
8
9
Removed Phosphate Mass (mg)
Phosphate Concentration
(mg/L)
could be applied as an industrial resource for synthesis of phosphate compounds.
10
Influent (L)
Fig. 7. Change of phosphate concentration and removed phosphate when typical wastewater of about
7 mg/L concentration is passed through the phosphate removal filters.
11
4. Conclusion
In this study, the possibility of fabricating and recycling a brass scrubber filter through surface
modification for phosphate removal was evaluated. The brass scrubber filter was surface-modified to
form copper hydroxide on the surface of the brass, which acted as a phosphate removal filter for
advanced wastewater treatment because phosphate ions could be removed by the ion exchange with
hydroxyl ions of copper hydroxide. The phosphate was rapidly removed within a very shorter contact
time by the surface-modified brass scrubber filter, and the phosphate mass of about 1.6 mg was
removed per gram of the filter.
The results showed the possibility of this phosphorus removal without undesirable sludge
production of existing chemical phosphorus removal techniques. This surface-modified silica filter
could be an alternative option for phosphorus removal in small-scale wastewater treatments facilities
suffering from unbalanced influent with relatively higher concentration of phosphorus than other
components.
Acknowledgements
This subject is supported by the Korea Research Foundation Grant funded by the Korean Government
(MOEHRD)"(KRF-2006-511-D00181).
12
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