INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCES Volume 5, No 4, 2015
© Copyright by the authors - Licensee IPA- Under Creative Commons license 3.0
Research article ISSN 0976 – 4402
Received on January 2015 Published on January 2015 709
Fouling characteristics of UF and RO membranes for reclamation of the
wastewater from Iron and Steel Industry Sang Kyo Choi1, Haakrho Yi1, Jeongki Moon2, Youlboong Sung2, Shin Gyung Kang2
1- Principal Researcher, Biodiesel TFT, Research Institute of Industrial Science and
Technology (RIST), 67, Cheongam-ro, Nam-gu, Pohang, Gyeongsangbuk-do, Korea
2- Principal Researcher, Environment Research Center, RIST, 67, Cheongam-ro, Nam-
gu, Pohang, Gyeongsangbuk-do, Korea
doi: 10.6088/ijes.2014050100066
ABSTRACT
Among the whole iron and steel-making processes, wastewaters from coke-making, blast
furnace and steel-making contain relatively high organic contaminants due to direct using of
raw materials like coal or iron ore. These wastewaters are pretreated by biological nutrients
removal processes. On the other hand, wastewater from rolling-mill processes contains
mainly inorganic contaminants. In this study, the fouling characteristics of membranes for
reclamation of wastewaters from the processes using raw materials were analyzed through the
pilot plant operation. The pilot plant was comprised of sand filter, activated carbon filter,
ultrafiltration (UF) and reverse osmosis (RO) processes. Through the fouling effect analysis,
algal and bacterial bio-foulings were dominant in the raw water tank and ultrafiltration
membrane modules. This serious microbial contamination problem was greatly improved by
using disinfectant and protection of sun-light by black painting. In the RO membranes, the
alginate type biopolymer originated from microbial metabolism in the biological wastewater
treatment process or contaminated membrane module was the main organic contaminant and
inorganic contaminants exhibited conventional compound of calcium, silicon or aluminum.
Keywords: Fouling, ultra filtration (UF), reverse osmosis (RO), wastewater, reclamation
1. Introduction
Iron and steel production requires a lot of water. Usually 3~10m3 of water is consumed to
produce the one tonnage of steel. Even for the companies showing the highest wastewater
recycling rates but those seem not so impressive as 3.84m3/ton steel (POSCO sustainability
report, 2013) and 4.11m3/ton steel (Huang et al., 2011). Therefore, many iron and steel
enterprises have been developing the wastewater recycle technologies to reduce the fresh
water consumption per ton steel (Huang et al, 2011, Jin et al. 2013, Zhang et al., 2010, 2011).
Though the various types of the industrial wastewater recycling technologies have been tried,
reverse osmosis (RO) is generally used nowadays due to the recent advancement of
membrane technologies. However, information of actual field application of wastewater
reclamation in the iron and steel industries is limited. Pilot plant study for coke wastewater
reclamation was reported by Jin et al. (2013). They have focused on the contaminants
removal efficiency for satisfying discharge standard in China. Though the removal efficiency
was confirmed in the report, the fouling problem on the RO membrane and concentrate
treatment should be further considered for the filed application.
Fouling characteristics of UF and RO membranes for reclamation of the wastewater from Iron and Steel Industry
S. K. Choi et al. International Journal of Environmental Sciences Volume 5 No.4, 2015
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Huang et al. (2011) pretreated iron production wastewater in constructed wet land then
recycled it through the UF and RO process. They reported that stable operation could be
possible for more than 60 days with 75% of recovery in RO without any chemical cleaning.
However, it requires large size of wet land therefore the application of this process may not
be possible if there is no feasible land. Zhang et al. (2011) suggested wastewater reusing
methods with distinct electrosorption technology and electrochemical catalytic oxidation
technology (2010), however, very few report on the iron and steel industry wastewater
reusing case with RO technology are available in the literature.
In the operation of RO processes, membrane fouling can be caused by inorganic salts (Jawor
and Hoek, 2009), micro-organisms (Vrouwenvelder et al., 2009), colloidal material (Chong et
al., 2009) and other pollutants. These pollutants depositing on the membrane surface will lead
to decline in the membrane flux and reduce the treatment efficiency. Therefore, the fouling
characteristics can be the most critical designing factor for proper selection of pretreatment
processes and chemical additives.
However, it is very limit that the fouling and improvement cases with real industrial waste
water from the iron and steel industries. Therefore, we would like to share the detailed
experiences through this publication.
Wastewater treatment system of P iron and steel-making company in Korea is quite different
from the other iron and steel works. Other firms collect all of the wastewater and then treat in
the final wastewater treatment process for discharge. But, P iron and steel-making company
split the area of iron and steel-making and rolling-mill. The wastewaters from these areas are
treated separately. In this study, pilot plant research was performed with raw wastewater from
the iron and steel-making area. Figure 1 shows the treatment processes of the wastewater
from this iron and steel-making area. Cokes wastewater is pretreated with biological
nitrification/denitrification, chemical coagulation and activated carbon filtration processes.
Blast furnace wastewater undergoes biological nitrification/denitrification and steelmaking
wastewater is treated only chemical coagulation. These three types of wastewaters are
collected to final wastewater treatment facility with secondary chemical coagulation,
filtration processes, and then discharged to sea water.
Figure 1: Schematic diagram of wastewater treatment processes in the Iron and Steel-making
area of the P company
2. Materials and methods
The pilot plant system operated continually at the flow rate of 48m3/day in the RO process as
shown in Figure 2. The raw wastewater for treatment was collected from mixed treated
wastewater from the discharge point shown in Figure 1. Collected raw water was pretreated
with the sand, carbon filter and UF before the RO process. The recovery ratio of RO was
Fouling characteristics of UF and RO membranes for reclamation of the wastewater from Iron and Steel Industry
S. K. Choi et al. International Journal of Environmental Sciences Volume 5 No.4, 2015
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controlled by adjusting the recycling and drain ratio of the concentrated water. The sand and
activated carbon filter beds were used ready-made products of Rotek (ACF 1465, Korea).
Three UF hollow fiber modules (DMF-8040, DM puretech, Korea) were used and two RO
modules having 8 inches diameter (FILMTECTM BW30-400i, Dow Chemical, USA) were
installed in Pressure Vessel. Figure 3 shows the real pictures of the pilot plant components.
NaOCl (8%, Samchun Chemicals, Korea) was used as disinfectant, SBS (IRO, China) as anti-
scalent and HCl, NaOH (Samchun Chemicals, Korea) were applied for pH adjustment.
Among the operational variables, pressure and conductivity data were collected through
programmable logic controller (Master-K series, LS Electronics, Korea) and HMI (Cimon,
KDT systems, Korea) connected to the on-line sensors (Georg Fisher, GF Signet, USA).
Figure 2: Schematic diagram of the wastewater reusing pilot plant.
Figure 3: Photographs of the main facilities of the wastewater reusing pilot plant.
Water quality was analyzed by the official test methods of water quality (2012, Korea), ion
analysis was done with Ion Chromatography (Dionex ICS-1600 Standard Integrated IC
System) and Inductively Coupled Plasma Spectrometry (Prism, USA)
After the pilot plant had operated for test period, a piece of fouled membrane were taken
from the UF and RO system, sliced, dried in the air and analyzed. Contaminants on the
membrane surface were confirmed with optical microscope (Carl Zeiss, Axio), scanning
electron microscope with EDX (JEOL, JSM-6480LV, Japan) and Fourier transform infrared
spectroscopy (Sens IR Technologies, IlluminatIR, USA).
3. Results and discussion
Quality of the raw water for the pilot plant operation was shown in Table 1. Each wastewater
showed high total dissolved solid (TDS) of Na, K, Ca, Cl, SO4 ions. Some organic
components such as COD, CN etc. (data not shown) are discharged with lower concentration
than the national discharge limit.
Fouling characteristics of UF and RO membranes for reclamation of the wastewater from Iron and Steel Industry
S. K. Choi et al. International Journal of Environmental Sciences Volume 5 No.4, 2015
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Table 1: Quality of the raw water for pilot plant operation.
Parameter (Unit)
Final
Wastewater
Treatment
Plant
Coke Making
Plant
Blast
Furnace
Steel Making
Plant
pH 7.77 7.88 7.58 7.45
Conductivity (mS/cm) 6.040 6.790 5.060 6.440
TDS (g/L) 3.240 3.390 2.530 3.220
NH3-N (mg/L) 0.271 1.548 0.000 1.276
NO2-N (mg/L) 0.00 0.00 0.00 0.00
NO3-N (mg/L) 5.803 0.939 4.471 3.793
PO4-P (mg/L) 0.00 0.00 0.00 0.00
SO4 (mg/L) 755.0 1876.0 494.0 170.0
Cl (mg/L) 1140.0 940.0 1076.0 1948
Fe (mg/L) 0.168 0.483 0.391 0.036
Zn (mg/L) 0.133 0.279 0.651 2.55
Ba (mg/L) 0.121 0.011 0.233 0.192
Mn (mg/L) 0.185 0.062 0.356 0.151
Na (mg/L) 634.0 1356.0 450.0 961
K (mg/L) 416.00 7.78 596.00 88.1
Al (mg/L) 0.344 0.230 0.040 0.05
Ca (mg/L) 136.3 125.0 110.0 172.0
Mg (mg/L) 25.4 7.8 43.2 50.1
Si (mg/L) 3.570 1.040 5.360 1.92
Figure 4 demonstrates the result from the initial continuous operation of the pilot plant after
the test period. There was no change in RO permeate flux, but the plugging phenomenon was
occurred on the UF membrane from the very initial phase of operation. It strongly suggests
that the fouling was progressed with very fast rate in spite of the regular air backwash and
chemical cleaning in UF process.
Figure 4: Result of initial operation without any modification of pilot plant for 10 days.
The cause of this initial plugging in UF membrane was algal blooming in raw water storage
tank as shown in Figure 5 (c). The microbial metabolites such as soluble microbial products
(SMP) from the biological wastewater treatment process and the direct sun light support good
condition of algal growth in the raw water tank. The photosynthetic algae have affected the
plugging of the UF hollow fiber membrane module.
Fouling characteristics of UF and RO membranes for reclamation of the wastewater from Iron and Steel Industry
S. K. Choi et al. International Journal of Environmental Sciences Volume 5 No.4, 2015
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In Figure 5 (a) shows the initial stage storage tank. Sunlight can pass through the tank wall at
this condition. Black painting was done for block the sunlight as shown in Figure 5 (b).
Figure 5 (c) is the picture of the water with algal booming and (d) is inner part of the raw
water storage tank after painting and cleaning.
Figure 5: Photographs of the raw water tank: (a) Semi-transparent raw water tank, (b) black
painted raw water tank, (c) algal bloom in raw water tank, (d) clean tank after black painting.
In addition to painting, 1 ppm level of NaOCl was maintained in the influent storage tank for
the sterilization purpose. After that, improved stable operation was achieved for more than 2
weeks despite of large variation of raw water conductivity as shown in Figure 6. However,
gradual increase of UF inlet pressure was observed and a stable operation for several months
was hard to achieve. In the RO process, there was also gradual decrease of permeate flowrate.
This phenomenon suggested that fouling was progressed to RO membrane from the quite
early stage. Therefore autopsy test of the UF and RO membrane modules was done after 3
months operation.
Figure 6: The result of tank painting and disinfectant application
Figure 7 (a) is the disassembled pictures for the confirmation of the contamination on the UF
and RO membrane surface. UF hollow fiber membrane was severely contaminated with
microorganisms and RO membrane was coated with some contaminants showing brown
Fouling characteristics of UF and RO membranes for reclamation of the wastewater from Iron and Steel Industry
S. K. Choi et al. International Journal of Environmental Sciences Volume 5 No.4, 2015
714
color. Figure 7 (b) is the optical microscopic pictures. A lot of microbes and protozoa were
observed in the samples from the UF membrane modules. In this study, the application of the
NaOCl as a disinfectant to the raw water tank and activated carbon filtrated water tank was
critical to maintain this system without serious microbial contamination. Hence, protection of
microbial propagation should be considered when organic material containing wastewater
treated with membrane such as UF or microfiltration (MF) in the RO pretreatment system.
(a) (b)
Figure 7: The pictures of autopsy testing of UF and RO separation membrane: (a)
Disassembled parts of UF and RO membrane, (b) optical microscopic pictures of sludge from
the UF membrane module.
Figure 8 is the surface pictures of the RO separation membrane. The upper pictures represent
contaminated membrane surface and the lower pictures after cleaning with citric acid for a
long time. It shows a lot of extraneous materials accumulated on the surface and some
scratches implying the physical damage from the contamination or the washing process. Also
slippery and sticky materials were observed on the separation membrane. FT-IR analysis was
performed for the identification for this sticky organic material.
Figure 9 shows the FT-IR result. Alginic acid sodium salt or sodium alginate, the typical
SMP secreted by microbes, was detected as a most probable matching material from the IR
library. This alginate effect on the membrane fouling was well documented by Lee et al.
(2005), Huajuan M. (2009). It is well known material that causes the most serious organic
fouling in the RO membrane process.
Figure 8: Optical microscopic pictures of the surface of RO membrane: (top) contaminated
membrane surface, (bottom) surface after acid washing.
Therefore, considerations for these kinds of the biopolymers will be required for the RO
recycling of biological treated wastewater. It was not clear that the alginate source introduced
from newly growth microorganism in the UF membrane modules or originated from
Fouling characteristics of UF and RO membranes for reclamation of the wastewater from Iron and Steel Industry
S. K. Choi et al. International Journal of Environmental Sciences Volume 5 No.4, 2015
715
biological wastewater treatment pretreatment systems. Considering the raw water underwent
the activated carbon process, the alginate can be synthesized in the UF modules.
Figure 9: FT-IR result of organic contaminant Figure 10: SEM EDX analysis result of the
on the RO membrane surface. inorganics on the RO membrane surface
Inorganic fouling materials were analyzed by SEM EDX as shown in Figure 10. The Ca, Al,
Si components were main contaminants on the surface. These materials are generally found
the alum ingredient used in coagulating sedimentation process and the scale ingredient
accumulation. The inorganic contamination problem can be solved through the antiscalant
application and periodic acid/alkali chemical cleaning in place (CIP) process. The most
critical problem in recycling of the iron and steel-making wastewater can be defined the
organic contamination induced by microbes.
Figure 11 shows the operation result with newly replaced UF and RO membranes. Little bit
more stable operation than previous runs was possible for test period.
Figure 11: Continuous operation after the separation membrane replacement
Although the total operating period was up to a year, long term stable operation was not
achieved. However considering the severe operating environment such as RO concentrate
recycling and small capacity, the wastewater from the iron and steel-making process could be
reused by RO membrane system when microbial contamination is treated properly.
This study can be a help to the engineering on the wastewater recycling system from the iron
and steel-making process or a trouble-shooting inspiration for the process improvement.
Related report is preparing with totally mixed wastewater from another iron and steel works.
Fouling characteristics of UF and RO membranes for reclamation of the wastewater from Iron and Steel Industry
S. K. Choi et al. International Journal of Environmental Sciences Volume 5 No.4, 2015
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4. Conclusion
Based on the pilot plant operations for the wastewater reclamation at the iron and steel works,
it was elucidated that the response to the algal booming and microbial propagation in the
influent was critically important. The disinfectant spray and shading were applied against the
serious microbial contamination occurred in UF process as the pretreatment process for RO.
Alginate biopolymer was the main causes for the flux reduction on the RO membrane as a
major organic contamination. However, inorganic contaminants exhibited well known
components like in many other processes.
Acknowledgment
This subject is supported by Korea Ministry of Environment as "Global Top Project" (Project
No.:GT-11-B-02-003-2).
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