Potential Membrane Based Treatment of Triethylene Glycol ... JWS-CESE-14-0… · Potential Membrane...

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1 P. Jacob et al. / Journal of Water Sustainability 2 (2014) 123-136 *Corresponding to: [email protected] Potential Membrane Based Treatment of Triethylene Glycol Wastewater from Gas Separation Plant Paul Jacob 1 , Romchat Rattanaoudom 2* , Pimchanok Khachonbuna 1 , Nattawut Piyaprachakorn 2 , Gamgarn Thummadetsak 2 , Chettiyapan Visvanathan 1 1 Environmental Engineering and Management Program, School of Environment, Resources and Development, Asian Institute of Technology, P.O. Box 4, Klong Luang, Pathumthani 12120, Thailand 2 Environment and Management Research Department, PTT Research and Technology Institute, 71 M.2 Phaholyothin Rd., Sanubtub, Wangnoi Ayuttaya 13170, Thailand ABSTRACT In gas separation plant, triethylene glycol (TEG) is used in gas dehydration process. This in turn generates large volumes of two wastewater streams containing TEG in a range of 0.1-10% (by volume). TEG is a natural disinfectant, hence at higher concentrations it cannot be sent to a conventional effluent treatment. Thus this study was aimed to assess other alternative methods by utilizing two nanofiltration (NF) membranes (NF-TS40 and NF-TS80) and two reverse osmosis (RO) membranes (RO-ACM5 and RO-NTR759) for treating synthetic and real TEG wastewater. With the synthetic wastewater, RO-ACM5 and RO-NTR759 membranes presented highest TEG removal at 5% initial TEG concentration with 89.12% and 95.74% of TEG rejection and initial permeate flux of 2.57 L/m 2 · h· bar and 0.89 L/m 2 · h· bar, respectively. However, with real wastewaters, a pre-treatment using microfiltration and ultrafiltration was found to be a necessary step to remove contaminants, especially suspended solid (SS) and oil and grease (O&G) before NF and RO application. The pre-treatment system was able to remove 86-98% and 88-90% of SS and O&G, respectively. But a flux reduction of 10-70% in NF and RO systems was observed, as compared to synthetic wastewater. Hence, membrane based treatment was proven effective for low TEG wastewater concentrations of 0.1 to 5% only. Keywords: Triethylene glycol; reverse osmosis; nanofiltration; membrane; polarization; natural gas 1. INTRODUCTION Natural gas is widely used in many energy intensive sectors like automobile, electricity production and other day to day activities too. This gas in its crude form contains many impurities including water, which result in corrosion, pipe blockage and an overall loss in calorific value. Thus a need for gas dehydra- tion arises. This desiccation of natural gas is done by triethylene glycol. Triethylene glycol is also known as TEG, triglycol and trigen. TEG is hydrophilic, colourless, odourless and stable liquid with high viscosity and boiling point. The physical-chemical properties of TEG are summarized in Table 1. In the natural gas production plant (GSP), once TEG has been used for dehydration process, it generally ends up in two wastewater streams containing low and high concentrations of TEG. The stream termed Wastewater 1, produces wastewater with a COD concentration of 10 g/L or 0.1%-0.6% Journal of Water Sustainability, Volume 4, Issue 2, June 2014, 123-136 © University of Technology Sydney & Xi’an University of Architecture and Technology Presented at the International Conference on the Challenges in Environmental Science and Engineering (CESE-2013), Daegu, Korea, 29 Oct.-2 Nov. 2013

Transcript of Potential Membrane Based Treatment of Triethylene Glycol ... JWS-CESE-14-0… · Potential Membrane...

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1 P. Jacob et al. / Journal of Water Sustainability 2 (2014) 123-136

*Corresponding to: [email protected]

Potential Membrane Based Treatment of Triethylene Glycol

Wastewater from Gas Separation Plant

Paul Jacob1, Romchat Rattanaoudom2*, Pimchanok Khachonbuna1, Nattawut Piyaprachakorn2, Gamgarn Thummadetsak2, Chettiyapan Visvanathan1

1Environmental Engineering and Management Program, School of Environment, Resources and Development, Asian

Institute of Technology, P.O. Box 4, Klong Luang, Pathumthani 12120, Thailand 2Environment and Management Research Department, PTT Research and Technology Institute, 71 M.2 Phaholyothin

Rd., Sanubtub, Wangnoi Ayuttaya 13170, Thailand

ABSTRACT In gas separation plant, triethylene glycol (TEG) is used in gas dehydration process. This in turn generates large

volumes of two wastewater streams containing TEG in a range of 0.1-10% (by volume). TEG is a natural disinfectant,

hence at higher concentrations it cannot be sent to a conventional effluent treatment. Thus this study was aimed to

assess other alternative methods by utilizing two nanofiltration (NF) membranes (NF-TS40 and NF-TS80) and two

reverse osmosis (RO) membranes (RO-ACM5 and RO-NTR759) for treating synthetic and real TEG wastewater.

With the synthetic wastewater, RO-ACM5 and RO-NTR759 membranes presented highest TEG removal at 5% initial

TEG concentration with 89.12% and 95.74% of TEG rejection and initial permeate flux of 2.57 L/m2·h·bar and 0.89

L/m2·h·bar, respectively. However, with real wastewaters, a pre-treatment using microfiltration and ultrafiltration

was found to be a necessary step to remove contaminants, especially suspended solid (SS) and oil and grease (O&G)

before NF and RO application. The pre-treatment system was able to remove 86-98% and 88-90% of SS and O&G,

respectively. But a flux reduction of 10-70% in NF and RO systems was observed, as compared to synthetic

wastewater. Hence, membrane based treatment was proven effective for low TEG wastewater concentrations of 0.1 to

5% only.

Keywords: Triethylene glycol; reverse osmosis; nanofiltration; membrane; polarization; natural gas

1. INTRODUCTION

Natural gas is widely used in many energy intensive sectors like automobile, electricity production and other day to day activities too. This gas in its crude form contains many impurities including water, which result in corrosion, pipe blockage and an overall loss in calorific value. Thus a need for gas dehydra-tion arises. This desiccation of natural gas is

done by triethylene glycol. Triethylene glycol is also known as TEG, triglycol and trigen. TEG is hydrophilic, colourless, odourless and stable liquid with high viscosity and boiling point. The physical-chemical properties of TEG are summarized in Table 1.

In the natural gas production plant (GSP), once TEG has been used for dehydration process, it generally ends up in two wastewater streams containing low and high concentrations of TEG. The stream termed Wastewater 1, produces wastewater with a COD concentration of 10 g/L or 0.1%-0.6%

Journal of Water Sustainability, Volume 4, Issue 2, June 2014, 123-136

© University of Technology Sydney & Xi’an University of Architecture and Technology

Presented at the International Conference on the Challenges in Environmental Science and Engineering (CESE-2013), Daegu, Korea, 29 Oct.-2 Nov. 2013

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124 P. Jacob et al. / Journal of Water Sustainability 2 (2014) 123-136

TEG by volume (PTT-GSP., 2012). Total generation of this stream per day is 19 m3. This wastewater had low TEG and high BOD content. Comparatively, wastewater 2 of 1 m3/day is generated after gas dehydration process. This wastewater contained high TEG concentrations and low BOD. This wastewater streams COD content was reported to be ~200 g/L or 10% TEG by volume (PTT-GSP., 2012).

The conventional effluent treatment plant currently in use treats wastewater 1 and wastewater generated from human facilities. Similar treatment of synthetic TEG wastewater with 98% removal efficiency was observed in literature (Alberta-Environment, 2010). Wastewater 2 with higher TEG concentration (8-10% TEG) is being disposed by a licensed company using incineration.

Current research on TEG wastewater treatment is very limited in the literature. But few researchers have studied wastewater treatment or concentration process for ethylene glycol, a molecule very similar to TEG. Jehle et al. (1995) reported that evaporation was an effective way to concentrate ethylene glycol from 25% up to 70%. But due to high energy consumption and relatively slow process, this process is not favourable. Orecki et al. (2006) used different nanofiltration (NF) membranes for concentrating varying ethylene glycol concentrations (1-20% by volume). But high percentage of ethylene glycol passage was found in effluent from all tests.

In light of this research gap, a study was conducted which was aimed to investigate the potential of NF and Reverse Osmosis (RO) for treatment of TEG wastewater from gas separation plant (GSP). The research was conducted in two stages. Firstly, two NF and two RO membranes were tested for their flux and removal efficiencies, respectively with synthetic TEG wastewater. The better performing NF and RO membranes were selected for the second stage of the research

and then used for treating wastewater 1 and 2. Both wastewater 1 and 2 were pre-treated using MF and UF membranes to remove total suspended solids (TSS), oil and grease (O&G) and assessed for their removal efficiencies.

2. MATERIALS AND METHODS

2.1 Synthetic wastewater and membranes

Synthetic TEG wastewater of 0.1, 5, 10 and 20% were prepared using stock solution containing 99.5% TEG by volume provided by the GSP. The characteristics of these four membranes used in this study included two NF membranes (NF-TS40 and NF-TS80) and two RO (RO-ACM5 and RO-NTR759HR) membranes are presented in Table 2.

As real wastewater contained TSS and O&G which pose a potential threat in high pressure membranes applications, a ceramic microfil-tration (MF) and PTFE hollow fiber ultrafil-tration (UF) were used for the pretreatment. The properties of these membranes are also presented in Table 2.

2.2 Membrane units

Two membranes systems were used in this research, a high pressure membrane filtration unit and pretreatment unit for filtering real wastewater. The high pressure membrane unit used NF and RO membranes. As seen in Fig. 1, a double wall stainless steel feed tank with a water jacket to maintain feed temperature at 25±1°C was used. A high pressure pump connected with inverter delivered TEG wastewater from the feed tank to the mem-brane module at a flow rate of 2 L/min. The stainless steel membrane module had an effective surface area of 0.032 m2. Pressure gauges were installed at feed and concentrate sides to maintain 15 bar pressure for NF membranes and 20 bar pressure for RO membranes, respectively. This membrane unit

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was operated in cross flow mode, thus the concentrate was sent back to the feed tank. Permeate flux was measured by an electronic balance. The schematic of the experimental setup is presented in Fig. 1.

For real TEG wastewater, a pretreatment was carried out to remove TSS and O&G. Commercially available cartridge ceramic MF membrane and hollow fiber UF membranes

were used in the pretreatment unit. Fig. 2 presents the experimental set up of the unit. Real wastewater from GSP was fed into Tank 1. Pump and level controller transferred the wastewater first to MF membrane and then to the UF membranes, respectively, before being stored in Tank 3 for further use. The system was fully automated.

Table 1 Triethylene glycol physical and chemical properties

Parameter Unit Properties Empirical formula - C6H14O4 Molecular weight g/mol 150.17 pKa - 14.5 Log Kow - minus Boiling point at 760 mm Hg °C 287.8 Density mg/mL 1.1 Surface tension at 20°C dyne/cm 45.2 Solubility - Highly miscible in water Viscosity mPa·s 49 pH - 7

Source: Alberta-Environment, 2010; ScienceLab, 2013

Table 2 Properties of membranes used in this study

Type Model number

Manufacture MWCO/

Pore size PWF (LMH/bar) @25±1°C

Membrane Materials a

Zeta Po-tential (mv) pH 7a

pH

Rejection b

(%) NaCl

NF TS40 Trisep 200 Da 4.48 Polypiperazine amide

-14±3 2-11 40-60

TS80 150 Da 7.84 Polyamide -14±3 2-11 80-90

RO ACM5 - 5.75 Polyamide NA 2-11 98.5

NTR759HR Nitto Denko - 1.70 Aromatic Polyamide

NA 2-11 99.5

MF OBE Cartridge

Mazuma Company

0.3 µm 2,500 Ceramic - 4.5-9.5 -

UF UFH-PST -90

Shanghai Megavision

50-60 Da 17.2 PTFE - 2-13 -

afrom Manufacturer, b1,000 mg L-1NaCl

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Figure 1 Experimental set up for high pressure membrane unit

Figure 2 Experimental setup of pre-treatment process

2.3 Experimental runs and parameter analysis

The study was divided into two stages. In stage 1, the synthetic TEG wastewater was prepared by diluting the 99.5% stock TEG solution received from the industry with Milli-Q water to get 0.1, 5, 10 and 20% TEG synthetic wastewater. Each experimental runs for all four membranes were done in 8 hours (in triplicates), with prior pre-compaction with Milli-Q water for 10 hours to get stable pure water flux (PWF). TEG rejection and permeate flux were determined by equations 1 and 2.

The TEG rejection (R, %) by membrane was calculated as follows:

% 1 100p

f

CR

C

= − ×

(1)

Where Cp = TEG concentration in permeate, mg/L

Cf = TEG concentration in feed, mg/L

The permeate flux (J, unit is L/m2·h·bar) of compound was calculate as follows:

.

QJ

A P= (2)

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Where Q = flow rate of the permeate, L/h

A = Active surface area, m2

P = Applied pressure, bar

In stage 2, wastewater 1 and 2 were pre-treated by a pretreatment unit. After the pretreatment process was complete, the wastewater was sent to the high pressure membrane filtration unit and further testing were done as described in stage 1.

TEG concentrations were analyzed with GC Agilent HP 6890 after the samples were diluted with methanol. The Restex Rxi 624 sil MS 30 m × 0.25 m × 1.4 m column was used at a flow rate of 1.2 ml/min. The Inlet was set in splitless mode at 250°C. The TEG concentration in standard curve was in range of 0.1-2.0% v/v and R2 value was 0.9993. The general wastewater characteristics such as carbonate alkalinity as CaCO3, BOD, COD, ammonia nitrogen, oil and grease (O&G), pH, total dissolved solids (TDS), total phosphorus (TP), total suspended solids (TSS) were analyzed according to the standard methods (APHA, 2005). As the wastewater originates from an industrial stream metal concentration were also analyzed according to standard methods (APHA, 2005; USEPA, 1994). The specific metals tested were mercury, cadmium, calcium, chromium, copper, iron, lead, sodium, zinc and arsenic. But due to non-detection of various metals only results for iron and zinc are presented in Table 3.

3. RESULTS AND DISCUSSION

3.1 Wastewater characteristics

Stock solution used for preparation of synthetic wastewater, real wastewater 1 and 2 were collected and analysed for their characteristics. The results are presented in Table 3.

Staples et al. (2001) reported that biodeg-radation for ethylene glycol (EG) in water either under aerobic or anaerobic condition

could be achieved but it was dependant on the concentration levels. McGahey et al. (1992) tested the biodegradability of 0.1 g/L EG in the ground water. They found that the half-life of EG was less than 1 days. But McGahey et al. (1992) also reported that at 10 g/L (10% EG) initial concentration of EG, minimal degrada-tion was observed. In the case of wastewater concentrations greater than 10 g/L (10% TEG) the degradation fluctuated between 30-90% over a period of 30 days (Alberta-Environment, 2010). As can be seen in Table 3, both wastewater samples (1 & 2) contained low BOD to COD ratio, thus indi-cating potential difficulty in biodegradation through biological processes.

Overall the wastewater did not contain much organic matter as seen from Table 3, but it is important to note that TDS concentrations were abnormally high. This is due to the fact that boiling point of TEG (refer Table 1) was interfering with the standard method for evaluation (APHA, 2005), 2530 C, similar interferences from TEG were also observed in other wastewater parameters but were limited. Metal concentrations in the wastewater were done to better understand the potential of environmental toxicity of the wastewater streams. But analysis showed that other than iron at 3.58 mg/L for wastewater 1 and 0.14 mg/L for wastewater 2, most heavy metals were not detected in both streams.

Stock TEG solution was virtually free of any contamination but pH was acidic (4.61) in nature. It indicates that minor contaminants from the distillation process were not removed completely as pH for pure TEG is neutral (Table 1). Similar acidic nature for wastewater 1 and 2 with pH 4.97 and 5.82 were also observed. This reduced pH might be due to the organics that were present in all three streams after gas separation process. The compounds causing the pH drop could not be verified in this study.

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Table 3 Characteristics of wastewater collected from GSP

Parameters Unit WW 1 WW 2 Stock References

TEG % vol. 0.51 8.35 99.5 Refer section 2.3

Metals Iron mg/L 3.58 0.14 ND APHA (2005), 3111B

Zinc mg/L 0.08 0.13 ND APHA (2005), 3111B

Wastewater (WW) Alkalinity mg/L <1 <1 <1 APHA (2005), 2320B

BOD5 mg/L 1,843 974.51 <2 APHA (2005), 5210B

COD g/L 8.5 114 1,660 APHA (2005), 5220D

TN mg/L 0.56 10.5 0 APHA (2005), 4500-NH3(B), (C)

O&G mg/L 453.2 975 30 APHA (2005), 5520B

pH 4.97 5.82 4.61 APHA (2005), 4500-H(B)

TDS g/L 6.96 115.8 ND APHA (2005), 2530C

TP mg/L <1 <1 <1 US EPA, Method 365.4

TSS mg/L 257 546 8.78 APHA (2005), 2130B

ND = Not Detected

For high pressure membrane applications SS and O&G could pose a threat in both short and long term application. Thus wastewater 1 and 2 with 453.2 and mg/L 975 mg/L of O&G, respectively were treated with a pre-treatment units before testing with NF and RO membranes. The details of the experiments are presented section 3.3.1. Apart from the stock TEG containing 30 mg/L O&G, all synthetic wastewater in this study were observed to have O&G concentrations < 1 mg/L.

3.2 Stage I: Synthetic wastewater treat-ment using NF and RO membranes

After membrane pre-compaction with Milli-Q water, the synthetic wastewater was used as feed with NF membranes (NF-TS40 and NF-TS80) and RO (RO-ACM5 and RO- NTR759HR) to determine the membrane flux and rejection efficiency. The result of permeate flux and TEG removal efficiency is presented in the following subsections.

3.2.1 Permeate Flux

Flux reductions with time were observed for all 4 membranes. As seen in Fig. 3, it was also detected that at higher TEG concentrations (10 and 20% vol.) low permeate flux was predominant in all 4 membranes. At higher TEG concentration, flux reduction might be a direct result from progressive fouling due to pore blocking and TEG sorption on and inside the membrane pore. The flux decline with time with increasing concentrations of organic compound, which was similar with finding from other researches using organic membranes (UF and NF) to remove high concentration of natural organic matter (Cho et al., 2000; Lee et al., 2007) or micro-pollutants (Rattanaoudom et al., 2011) in the water.

The predominant presence of low permeate flux at high concentrations might have resulted from concentration polarization and membrane fouling, which normally present more effect with high concentration feed. Another major

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parameter that influences flux is viscosity of the substance being separated. In this study, TEG viscosity (µ) of 49 m Pa·s (about 55 times of water) might be a possible cause of flux reduction. It should be noted that as the experiments ran for 8 hours, the feed viscosity keeps increasing with time thus contributing to a flux decline. Hence, high feed viscousity could have a negative effect on permeate flux at a constant applied pressure. The relation of

permeate flux, viscosity, pressure and resistance (RTotal = Rmembrane + Rpore-blocking, Rad-

sorption, Rgel layer and Rconcentration polarization) as de-scribed in Mulder (1996).

This study found that at 0.1% and 10% TEG, the comparable concentration with real wastewaters, NF-TS80 and RO-ACM5 showed highest permeate flux of 0.69 L/m2·h·bar and 0.20 L/m2·h·bar respectively.

(a) NF-TS40

(b) NF-TS80

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(c) RO-ACM5

(d) RO-NTR 759 HR

Figure 3 Permeate flux of NF and RO treating synthetic wastewater 3.2.2 TEG rejection by membranes

RO membranes were more effective than NF for all test runs. Highest TEG removal was observed at low TEG concentrations of 0.1 and 5% TEG. At these low concentrations, RO-ACM5 had a rejection efficiency of 83-89% TEG removal, while 87-96% rejection was observed by RO-NTR759 as seen in Fig. 4. But at highest concentration of 20% TEG, the removal efficiency for all 4 was observed to be

very low. All membranes exhibited a rejection efficiency of 20% with limited flux as seen in Fig. 3.

Generally, removal efficiency for NF and RO membranes is dependent on many factors which includes membrane properties (surface roughness, surface charge, hydrophobicity etc.), compound properties (molecular weight, polarity and structure), water matrices etc. In this study, NF-membranes had a negative

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P. Jacob et al. / Journal of Water Sustainability 2 (2014) 123-136 131

surface charge while TEG was protonated (pH 4.5-5.7, pKa of TEG = 14.5). Membrane could electrostatically sorb TEG until its surface reached saturation point. Hence, low rejection was observed at high concentration. However, Plakas et al. (2012) reported that there was no observable effect of solute concentration on compound rejection in various NF based applications. The feed concentration used in those studies was less than 1 mg/L, which might not be enough to result in membrane surface saturation.

The TEG removal due to hydrophobic sorption was expected to be low as TEG has a negative log Kow and high water solubility (Alberta-Environment, 2010). Comerton et al. (2008) reported that endocrine disrupting and pharmaceutically active compounds (1 µg/L of feed concentration) having low molecular weight (150-236 Da), low log Kow (minus-0.46) as well as high water solubility (14,000-21600 mg/L) presented low mem-brane rejection, whereas other compounds tend to sorb on membrane presented higher removal in all RO and most of NF applications. Researchers (Kiso et al., 2000, 2001) tested the rejection efficiency of membrane with a various type of chemicals such as pesticides, alcohols, saccharides, aromatic compounds etc. with initial concentration of each compound within the range of 0.5-1.5 mg/L. They observed that NF’s removal efficiency for compounds having high water solubility such as alcohol were less than others. As TEG was highly hygroscopic, these researches finding complement low TEG removal efficiency in the current study. It can be concluded that low TEG rejection was due to electrostatic sorption in the studied membranes.

3.2.3 Membrane selection for real wastewater application

Based on higher permeate flux and TEG

rejection at comparable concentration with the synthetic wastewater, NF-TS80 and RO-ACM5 were selected to test with real wastewater. In the following sections, results for their rejection efficiency were investigated and compared with synthetic wastewater results. The results for wastewater 1 are compared with synthetic wastewater with 0.1% TEG while wastewater 2 was compared with synthetic wastewater containing 10% TEG.

3.3 Stage II: Treatment of real TEG wastewater

The effective membranes selected from section 3.2 (stage I) were further tested with real TEG wastewaters in stage II. The characteristics of real wastewater can be seen in Table 3. However, both wastewaters need to be pre-treated first by MF, followed by UF to remove TSS and O&G. 3.3.1 Effectiveness of pretreatment process

for real wastewater

A summary of the pre-treatment unit’s efficiency is presented in Fig. 5. The mem-brane based pre-treatment process was an effective way to remove TSS and O&G. About 86% and 95% of TSS and 88% and 90% of O&G for low and high TEG wastewaters were removed, respectively. Additionally, 95% of the initial BOD was removed for low TEG wastewater. This was due to the biodegradable organic matter at low TEG concentration was separated by the pre-treatment process. As observed in literature, both MF and UF were capable to deal with a variable feed character-istics with stable permeate quality and flux (Lee et al., 2007; Ordóñez et al., 2011). Thus the membrane based pretreatment was concluded to be an effective step prior to real wastewater application of RO or NF. The characteristics of pre-treated wastewater 1 & 2 and the overall pretreatment units efficiencies

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are presented in Table 4. It should also be noted that some TSS and O&G still remained in the treated samples and could pose a problem in NF and RO application.

3.3.2 NF and RO treatment of real wastewater with synthetic wastewater comparison

The permeate flux for real wastewater in all tests continuously decreased with the filtration period as seen in Fig. 6, similar observation were made for synthetic wastewater. The permeate flux for wastewater 1 and 2 streams after pretreatment were lower than those of synthetic wastewater, especially with wastewater 1. This was due to the residual pollutants (such as O&G, SS, and organic compounds). These pollutants generated more fouling (compound sorption on mem-brane/inside membrane pore, cake layer formation) as compared to the synthetic wastewater (0.1% TEG).

Water matrices and TEG formed complex flocs resulting in lower permeate flux in real wastewater. Similar flux reduction due to water matrices were observed by Lee et al. (2007). In addition to the matrices in the real wastewater, marginally higher TEG concentration in

wastewater 1 as compared to synthetic wastewater with low TEG (0.1%) could have potentially lower observable permeate flux. The permeate flux of real wastewaters 1 and 2 at the 8th hour of filtration period were lower than those observed for synthetic solution by 70% and 10% for wastewater 1 and 2, respectively.

TEG rejection for both membranes with real wastewater treatment was higher than those of synthetic ones as seen in Fig. 7. The contami-nants in real wastewater enhanced the effi-ciency of NF and RO membranes, especially for wastewater 1 containing 0.51% of TEG by volume. The improved efficiency potentially resulted from foulants formed on the mem-brane. This observation corresponds to the low permeate flux observed in real wastewater. Interaction between TEG and water matrices might also enhance TEG rejection. Similar results for higher compound rejection by NF and RO membranes in the real water samples as compare synthetic solution were also re-ported by Comerton et al. (2008). They con-cluded that the enhanced rejection was resulted from the membrane fouling on compound in-teractions with water matrices.

Figure 4 TEG rejection by NF and RO treating synthetic wastewater

80

71

36

12

60

67

51

12

84

89

76

15

87

96

60

19

0

20

40

60

80

100

0.1% TEG 5% TEG 10% TEG 20% TEG

% R

emov

al

Triethylene glycol concentrations

NF-TS40 NF-TS80 RO-ACM5 RO-NTR 759 HR

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55

12

6

1

1

43

20

84

31

22

0 10 20 30 40 50 60 70 80 90 100

TSS

TDS

O&G

COD

BOD

% Removal

MF UF

(a) Wastewater 1 (0.51 % by vol.)

(b) Wastewater 2 (8.35 % by vol.)

Figure 5 Pretreatment efficiency for wastewater 1 and wastewater 2

3.4 Assessment of treated wastewater af-

ter NF and RO application

The characteristics of treated wastewaters by both membranes were still higher than industrial effluent standard in Thailand. Hence, a further treatment process is required to improve water quality. As found in the literature, 3 g/L of diethylene glycol was able to be biodegraded within 28 days (Gotvajn et al., 2003). An activated sludge process (AS), currently used for central wastewater treatment

in industry, could be applied as a further treatment for permeate, which contained around 0.03% by volume and 0.14% by volume of TEG after NF and RO treatment, respectively. With the combination of wastewater generated from other sources containing more nutrients, no toxic metals, AS could to operate effectively. For high TEG wastewater stream, the effluent from each membrane contained significantly high TEG concentration. Thus further research in this direction to increase the rejection of TEG is needed.

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Table 4 Characteristics of treated wastewater by pre-treatment process

Parameter Unit Wastewater 1 Wastewater 2 Value % Removal Value % Removal

BOD5 mg/L 95 94.8 750 23

COD g/L 5.66 33.4 66 42.1

O&G mg/L 57.8 87.2 78.9 92

TDS g/L 3.46 50.3 78.8 31

TSS mg/L 36 85.9 14 97.4

(a) NF-TS80

(b) RO-ACM5

Figure 6 Comparison of permeate fluxes between real and synthetic TEG wastewaters

0

1

2

3

4

5

6

7

8

0 1 2 3 4 5 6 7 8

Per

mea

te F

lux

(L/m

2.h

.bar

)

Time (hr)

0.1%TEG 10% TEG 0.5% TEG WW 8.3% TEG WW

0

1

2

3

4

5

6

7

8

0 1 2 3 4 5 6 7 8

Pe

rme

ate

Flu

x (

L/m

2.h

.ba

r)

Time (hr)

0.1%TEG 10% TEG 0.5% TEG WW 8.3% TEG WW

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P. Jacob et al. / Journal of Water Sustainability 2 (2014) 123-136 135

60

51

84

76

73

47

95

78

0

20

40

60

80

100

120

Low TEG WW High TEG WW Low TEG WW High TEG WW

NF TS80 RO ACM5

% T

EG

re

mo

va

l

Synthetic WW Real WW

Wastewater1 Wastewater2 Wastewater1 Wastewater2

Figure 7 Comparison of TEG removal efficiency between real and synthetic wastewaters

Table 5 Characteristics of treated wastewater by NF and RO membranes

Parameter Unit NF-TS80 RO-ACM5

Wastewater 1 Wastewater 2 Wastewater 1 Wastewater 2

Value %Removal Value %Removal Value %Removal Value %Removal TEG %vol. 0.14 72.98 4.39 47.15 0.03 94.79 1.86 77.56

BOD5 mg/L 65 31.58 300 60.00 40 57.89 100 86.67

COD g/L 1.5 72.95 12.3 81.36 1.3 75.52 6.9 89.49

O&G mg/L 4.12 92.87 4.35 94.49 3.44 94.05 3.46 95.61

TDS g/L 5.16 84.54 10.2 87.06 4.27 87.19 9.88 87.43

TSS mg/L 6 83.33 4 71.43 3.33 90.75 3.56 74.57

CONCLUSIONS

Application of high pressure membrane filtration (NF and RO) for treatment of synthetic and real TEG wastewater was limited to lower TEG concentrations of 0.1 to 0.5% TEG. Flux decline at higher TEG concentration were potentially due to fouling caused by concentration polarization and residual organic matter in the feed. This study found that RO-ACM5 presented highest TEG removal efficiency (>80%) with synthetic wastewater containing 5% initial TEG concentration. For both NF and RO membranes, TEG concentrations <5% TEG showed decline in both flux and removal efficiency, significantly. Pre-treatment was

found to remove ~90% SS and O&G from wastewater 1 & 2. Further research is required in this direction by potentially combining NF and RO or 2 stages RO for effective high concentration TEG wastewater treatment.

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