fouling characteristics of uf and ro membranes for ... · parameter (unit) final wastewater...

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

[email protected]

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

710

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



711

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.



712

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.



713

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



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



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.



716

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).

5. References

1. Chong, T.H., Wong, F.S., Fane, A.G., (2008), Implications of critical flux and cake

enhanced osmotic pressure (CEOP) on colloidal fouling in reverse osmosis:

experimental observations, Journal of Membrane Science, 314, pp 101–111.

2. Jin, X., Li, E, Lu, S., Qiu, Z., Sui, Q., (2013), Coking wastewater treatment for

industrial reuse purpose: Combining biological processes with ultrafiltration,

nanofiltration and reverse osmosis, Journal of Environmental Sciences, 25(8), pp

1565-1574.

3. Huang, X.F., Ling, J., Xu, J.C., Feng, Y., Li, G.M., (2011), Advanced treatment of

wastewater from an iron and steel enterprise by a constructed

wetland/ultrafiltration/reverse osmosis process, Desalination 269, pp 41-49.

4. Huajuan, M., (2009), A study on organic fouling of reverse osmosis membrane, Ph.D.

Thesis, Department of Civil Engineering, National University of Singapore.

5. Jawor, A., Hoek, E.M.V., (2009), Effects of feed water temperature on inorganic

fouling of brackish water RO membranes, Desalination, 235, pp 44–57.

6. Lee, S., Ang, W.S., Elimelech, M., (2005), Fouling of Reverse Osmosis Membranes

by Hydrophilic organic matter: Implications for water reuse, Integrated Concepts in

Water Recycling - S.J. Khan, A.I. Schäfer, M.H. Muston (Eds) – ISBN 1 74128 082 6,

pp 374-383.

7. Vrouwenvelder, J.S., Graf von der Schulenburg, D.A., Kruithof, J.C., Johns, M.L.,

van Loosdrecht, M.C.M., (2009), Biofouling of spiral-wound nanofiltration and

reverse osmosis membranes: a feed spacer problem, Water Research, 43, pp 583–594.

8. Zhang, Y.H., Gan, F.X., Li, M., Li, J., Li, S.Q., Wu, S.H, (2010), New integrated

processes for treating cold-rolling mill emulsion wastewater, Journal of Iron and Steel

Research, 17(6), pp 32-35.

9. Zhang, Y.H., Gan, F.X., Li, M., Wang, D.H., Huang, Z.M., Gao, Y.P., (2011),

Treatment of reused comprehensive wastewater in iron and steel industry with

electrosorption technology, Journal of Iron and Steel Research, 18(6), pp37-42.

fouling characteristics of uf and ro membranes for ... · parameter (unit) final wastewater...

Documents