This research aims to evaluate the performance of PolyCera® Titan membrane for different wastewater treatment. Membrane filtration of several cycles was conducted in understanding the fouling mechanism, fouling propensity, and defouling potential of the PolyCera® Titan which had not been studied by any other researcher before. The PolyCera® Titan membrane is effective for the treatment of textile industry wastewater, palm oil mill effluent (POME), leachate, and semiconductor-industry wastewater. Rejection of methylene blue (MB) and Congo red (CR) was in the range of 78.76–86.04% and 88.89–93.71%, respectively; 94.72–96.50% NaCl, 96.07–97.62% kaolin, and 97.26–97.73% glucose were rejected from synthetic leachate indicating the removal of TDS, TSS, and COD from the leachate, respectively. Standard blocking and complete model were the best models used to explain the PolyCera® Titan membrane fouling mechanism in all types of wastewater treatment processes with a high R2 value. Physical cleaning with the use of distilled water was able to recover the permeate flux with the flux recovery ratio (FRR) value in the range of 79.2–95.22% in the first cycle, 81.20–98.16% in the second cycle, and 86.09–95.96% in the third cycle.

Graphical Abstract

Graphical Abstract
Graphical Abstract
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Graphical Abstract
Graphical Abstract
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  • Performance of PolyCera® Titan membrane for synthetic textile industry wastewater, POME, synthetic leachate, and semiconductor-industry wastewater treatment.

  • Understanding on fouling mechanism, fouling propensity, and defouling potential of the PolyCera® Titan membrane.

defouling, fouling, industrial wastewater, PolyCera® Titan membrane, rejection

The textile industry, palm oil industry, semiconductor industry, and leachate are the major contributors to water. Palm oil mill generates 65 million ton of palm oil mill effluent (POME), the palm oil industry's wastewater every year (Loh 2017). POME is a thick and viscous liquid with 25,000 mg/L BOD; 50,000 mg/L COD; 18,000 mg/L TSS; 4,000–6,000 mg/L oil and grease; 550–800 mg/L total nitrogen, and pH in the range of 4–5 (Saeed et al. 2016). Dye wastewater is widely generated from the textile industry where over 10,000 types of dyes are used in the textile industry. Over 7 × 105 tons of synthetic dye is produced annually worldwide (Ogugbue & Sawidis 2011) and about 10–15% of the dye gets lost in the effluent during the dyeing process (Kabra et al. 2012). A leachate is any liquid that, in the course of passing through matter, extracts soluble or suspended solids, or any other component of the material through which it has passed. Leachate from a landfill varies widely in composition depending on the age of the landfill and the type of waste that it contains (Bernat et al. 2021). Industries manufacturing semiconductor integrated circuits utilize highly sophisticated processes. These processes consume large quantities of water and generate a similar amount of wastewater (Tsai et al. 2007). Wastewater generated from the semiconductor industry is greatly different from other industrial wastewaters due to the distinct organic and inorganic chemicals used in the manufacturing process (Noor et al. 2020). Semiconductor-industry wastewater is characterized as highly turbid due to high solid content, high COD (3,000–5,000 mg/L), and major contaminants from organic and inorganic solvent particles ranging from nano to micro-sized (Fatehah et al. 2013).

Membrane technology has attracted the most attention as an advanced wastewater treatment method (Quist-Jensen et al. 2015). Ellouze et al. (2012) used NF membrane for textile wastewater treatment and successfully removed 57% COD, 100% colour, and 30% salinity. A study from Szlachta & Wójtowicz (2013) reported that 97% methylene blue (MB) rejection was achieved with the use of micellar-enhanced ultrafiltration at pH 2–11. On the other hand, our previous study obtained 47.80, 95.56, 90.91, 73.67, 96.25, 63.70, 99.96 and 73.64% reduction of BOD, COD, TSS, TDS, colour, phosphorus (P), turbidity, and conductivity in POME treatment using a commercial NF membrane (Teow et al. 2016). Though, membrane fouling is still a major obstacle to the wide use of membrane technology in wastewater treatment (Teow et al. 2021). Cleaning is usually conducted to remove the foulants attached to the membrane and to prolong the life span of the membrane.

This research aims to evaluate the performance of the PolyCera® Titan membrane in several industrial wastewater treatments. This includes synthetic textile industry wastewater, POME, synthetic leachate, and semiconductor-industry wastewater. There is not much research available for the PolyCera® Titan membrane. Previous research on the PolyCera® Titan membrane was studied using a single type of wastewater in a dead-end filtration system where no comparison could be done for the treatment of different types of wastewaters. On top of that, the dead-end filtration system could not reflect the actual operation of membrane filtration in industry. In this study, the experiment is conducted using a tubular membrane in a cross-flow filtration system which could give a better insight by imitating the industry's operation set-up. Additionally, membrane filtration of several cycles was conducted in understanding the fouling mechanism, fouling propensity, and defouling potential of the PolyCera® Titan which had not been studied by any other researcher before. Four membrane fouling models were used to identify the PolyCera® Titan membrane fouling mechanism, including standard blocking, complete blocking, intermediate blocking, and cake layer formation. The fouling propensity of the membrane was indicated by relative flux reduction (RFR) and the defouling potential of the membrane was evaluated through flux recovery ratio (FRR).

Materials and chemicals

A commercial tubular membrane, PolyCera® Titan was used in this study. The specifications and operating conditions of the membrane are summarized in Table 1.

Table 1

Specifications and operating conditions of the PolyCera® Titan membrane

Specifications/Operating conditionsRange
Membrane material/types Titan (polymer)/NF 
Nominal pore size/MWCO 500 Da 
Operating pH range 1–10.0 @ T < 70 °C 
1–13.5 @ T < 50 °C 
Operating temperature range 5–70 °C 
Maximum inlet pressure 20.7 bar 
Maximum pressure element 1.7 bar 
Maximum TSS ≤75 mg/L 
Continues total chlorine ≤2.0 mg/L 
Total operating flux 10–40 LMH 
Recommended pre-filter 75 μm 
Specifications/Operating conditionsRange
Membrane material/types Titan (polymer)/NF 
Nominal pore size/MWCO 500 Da 
Operating pH range 1–10.0 @ T < 70 °C 
1–13.5 @ T < 50 °C 
Operating temperature range 5–70 °C 
Maximum inlet pressure 20.7 bar 
Maximum pressure element 1.7 bar 
Maximum TSS ≤75 mg/L 
Continues total chlorine ≤2.0 mg/L 
Total operating flux 10–40 LMH 
Recommended pre-filter 75 μm 
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Chemicals are used to prepare synthetic wastewater as the feed solution for the membrane filtration process. MB and Congo red (CR) were purchased from Sigma Aldrich, USA. Kaolin, sodium chloride (NaCl), and sodium hydroxide were supplied by Sigma Aldrich, USA. High-range COD reagent, ammonia reagent, hardness solution pillow, phosphate buffer solution, magnesium solution, and calcium chloride solution used for water analysis were obtained from HACH, USA.

Four types of wastewater were used for membrane performance evaluation, namely POME, semiconductor-industry wastewater, synthetic dye wastewater, and synthetic leachate. Raw POME, anaerobic POME, and aerobic POME were collected from a palm oil mill in Tennamaram, Malaysia. The POME was stored in a cold storage room at a temperature below 4 °C to avoid microbial biodegradation (Ghani et al. 2017). The semiconductor-industry wastewater was collected from a semiconductor fabrication factory located in Kulim, Malaysia.

MB and CR were used for the preparation of synthetic dye wastewater. 10, 20, and 30 mg/L of MB solution and CR solution were prepared for this study. On the other hand, kaolin, NaCl, and glucose were used for the preparation of synthetic leachate in which kaolin, NaCl, and glucose responded to TSS, TDS, and COD in leachate, respectively.

Membrane performance study

Membrane permeability

The bench scale cross-flow membrane filtration system was used for the membrane performance study. The PolyCera® Titan membrane was placed at the membrane holder. Distilled water was used as the feed solution in the membrane permeability test. The distilled water was through the membrane at varied operating pressure, 0.1, 0.2, 0.3, 0.4, and 0.5 MPa. 50-mL permeate was collected while the retentate was recycled back to the feed.

Permeate flux is calculated as follows:
formula
(1)
where J is the permeate flux (L/m2 h), V is the volume of permeate flux (50 mL), A is membrane effective surface area (m2), Δt is the time taken to collect 50 mL of permeate volume (h). Membrane permeability is then determined from the gradient of permeate flux against operating pressure.

Membrane filtration system

POME, semiconductor-industry wastewater, synthetic dye wastewater, and synthetic leachate were used as the feed solution for the membrane filtration system. The operating pressure is set constant at 0.40 MPa.

Prior to the membrane filtration process, the feed solution was added to the feed tank. A filtration pump was used to pump the feed solution across the membrane matrix. Permeate passing through the membrane matrix was collected for water quality analysis while the retentate was recycled back to the feed tank. The water quality parameter involved in this study were pH, colour, TDS, TSS, AN, COD, BOD, and hardness. The percentage of rejection for each water quality parameter was calculated using Equation (2):
formula
(2)
where R is the membrane rejection (%), Cp is the concentration of the permeate (mg/L), and Cf is the concentration of the feed solution (mg/L):

Water quality analysis

TDS was measured by using HI-2550 multiparameter (Hanna Instrument, United Kingdom). The electrode was immersed into the water sample to get the reading. The initial concentration of the water sample was measured using DO probe (Hanna Instrument, United Kingdom). The water sample was then incubated in a BOD incubator at 20 °C for 5 days. The DO after 5 days of incubation was measured for the calculation of BOD5 using Equation (3):
formula
(3)
where P is the volume of the water sample.

COD was measured using the reaction digestion method. 2 mL of water sample was pipetted into the COD vial. The vial was inverted several times for good mixing of the content. The blank sample was prepared using deionized water. The water sample and blank sample were subsequently pre-heated in a COD reactor at 150 °C for 2 h. After 2 h, the samples were removed from the COD reactor and reduced to room temperature. Next, the COD was determined using the DR3900 spectrophotometer (HACH, USA).

TSS was determined by using a gravity vacuum filtration unit. Membrane filter paper (Whatman, USA) of 0.45-μm pore size was dried in an oven at 103–105 °C for 1 h. The weight of the membrane filter paper after being oven dried was measured using an analytical balance. 100 mL of water sample was poured into the gravity vacuum filtration unit where TSS in the water sample was filtered by the membrane filter paper. After the filtration process, the membrane filter paper was removed from the filter holder and dried in an oven at 103–105 °C. The membrane filter paper was then weighed again using the analytical balance. TSS in the water sample was then calculated using Equation (4):
formula
(4)
where Wf and Wi are the weights of filter paper before and after the filtration (g), respectively.

AN, hardness, and colour were determined using a DR3900 spectrophotometer (HACH, USA). AN was determined by the salicylate method at the range of 0.4–50 mg/L. Blank and water samples were prepared and added with 0.1 mL of Amver dilute reagent, 5 mL of ammonia salicylate reagent powder, and an ammonia cyanurate reagent powder pillow. After 20 min of reaction, the AN concentration was measured using a DR3900 spectrophotometer. Colour was determined using the Platinum Colbat standard method, measured by a DR3900 spectrophotometer at the wavelength of 465 nm. Hardness was measured using a colourimetric method where Chlorophosphonazo solution pillow and ultra-low range hardness reagent were added in a vial and kept for 2–3 min before being measured by a DR3900 spectrophotometer.

Membrane fouling

Similar to the membrane filtration process, membrane fouling was conducted using POME, semiconductor-industry wastewater, synthetic dye wastewater, and synthetic leachate as the feed solution for the membrane filtration system. The operating pressure is set constant at 0.40 MPa, where the filtration process was carried out for 4 h.

Reflective flux reduction (RFR) was used to indicate the fouling propensity of the filtration process. RFR was calculated using Equation (5):
formula
(5)
where Jp is the instantaneous permeate flux at a specific time (L/m2 h), and Jpl is the initial permeate flux (L/m2 h).

Membrane cleaning

Membrane cleaning was conducted to recover the membrane's permeate flux. Distilled water was used for hydraulic cleaning. After filtering the feed solution at 0.4 MPa for 10 min, the membrane was cleaned by flushing it with distilled water at 35 °C. The FRR was calculated to evaluate the membrane defouling ability:
formula
(6)
where Jw1 is the initial permeate flux using distilled water as the feed solution (L/m2 h), and Jw2 is the permeate flux of distilled water after the hydraulic cleaning (L/m2 h).

Membrane fouling mechanism

Four membrane fouling models were proposed to identify the PolyCera® Titan membrane fouling mechanism. These models were standard blocking, complete blocking, intermediate blocking, and cake layer formation.

The standard blocking model involved the blocking occurring at the membrane matrix, where the size of the foulants is smaller than the membrane pore diameter. The foulants enter the membrane matrix and are deposited at the wall of the membrane pore channel, thus resulting in a decrease of membrane pore diameter and the reduction of permeate flux. The standard blocking model is presented by Equation (7):
formula
(7)
where J0 is the initial permeate flux (L/m2 h), t is the filtration time (s), and Ks is the standard blocking constant (m–1).
Complete blocking occurred when the foulants are relatively larger than the membrane pore diameter. The foulants will completely block the membrane pore and the available pores for permeation are decreased along the filtration period. Subsequently, the membrane permeate flux is decreased as the permeate can only pass through the unblocked pores. The complete blocking model is presented in Equation (8):
formula
(8)
where J0 is the initial permeate flux (L/m2 h), t is the filtration time (s), and Kb is the complete blocking constant (s–1).
The intermediate blocking model is similar to the complete blocking model, in addition, to account the possibility of foulants obstructing the membrane pore entrance without completely blocking it. This mechanism is represented by Equation (9):
formula
(9)
where J0 is the initial permeate flux (L/m2 h), t is the filtration time (s), and Ki is the complete blocking constant (m–1).
The cake layer is formed when large foulants are settled down on the membrane surface which had been covered by the foulants. With the aid of operating pressure exerted onto the membrane surface, a compact cake layer is formed. This mechanism is presented by Equation (10):
formula
(10)
where J0 is the initial permeate flux (L/m2 h), t is the filtration time (s), and Kc (s/m2) is the cake filtration constant.

Membrane performance

Membrane permeability

Figure 1 presents the permeate flux of the PolyCera® Titan membrane at varied operating pressure. As presented in Figure 1, the permeate flux was increased proportionally with an increase of operating pressure from 0.1 to 0.5 MPa. Therefore, it was proven that the PolyCera® Titan membrane is a pressure-driven membrane. Membrane permeability is then determined from the gradient of permeate flux against operating pressure. The membrane permeability was recorded as 61.525 L/m2 h bar. The high permeability of the PolyCera® Titan membrane was due to its high hydrophilicity and low surface roughness (Teow et al. 2020). Membrane surface hydrophilicity is a significant property of the membrane. The higher surface hydrophilicity of a membrane will have a higher affinity towards water molecules, which then contribute to higher permeate flux (Teow et al. 2018b) and lower fouling tendency that is attributed by the adsorption of hydrophobic foulants onto the membrane surface (Feng et al. 2012; Zhang et al. 2015). Water molecules can easily wet the PolyCera® Titan membrane’ surface and pass through the membrane matrix without much surface extension.
Figure 1
Permeate flux of the PolyCera® Titan membrane at varied operating pressures (feed solution: distilled water).
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Permeate flux of the PolyCera® Titan membrane at varied operating pressures (feed solution: distilled water).

Figure 1
Permeate flux of the PolyCera® Titan membrane at varied operating pressures (feed solution: distilled water).
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Permeate flux of the PolyCera® Titan membrane at varied operating pressures (feed solution: distilled water).

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Membrane permeate flux

Table 2 summarizes the permeate flux of different wastewater under the PolyCera® Titan membrane filtration process at the operating pressure of 0.4 MPa. The permeate flux at 0.4 MPa using distilled water as feed solution was recorded at 196.64 L/m2 h. Comparatively, the permeate flux was decreased with the use of wastewater as the feed solution. On top of that, the permeate flux further decreases at a higher concentration of the wastewater. This is mainly due to the higher number of solutes in the wastewater at higher concentrations. Concentration polarization will occur at a faster rate when the high number of solutes close to the membrane surface boundary layer, and create resistance for selective transport through the membrane. Although there is no change in operating pressure, the driving force was reduced, and thus resulting in a decrease in permeate flux.

Table 2

Permeate flux of different wastewater under the PolyCera® Titan membrane filtration process (operating pressure: 0.4 MPa)

FeedPermeate flux (L/m2 h)
a. Synthetic textile industry wastewater 
 10 mg/LMB 89.74 
 20 mg/LMB 80.10 
 10 mg/LCR 99.95 
 20 mg/LCR 90.26 
b. Synthetic leachate 
 2.192 g/L NaCl 136.81 
 4.384 g/L NaCl 120.40 
 8.768 g/L NaCl 113.91 
 89 g/L Kaolin 129.14 
 178 g/L Kaolin 122.28 
 356 g/L Kaolin 118.39 
 1,469.8 mg/L glucose 143.86 
 2,938.0 mg/L glucose 132.80 
 4,407.8 mg/L glucose 116.13 
c. POME 
 Fresh POME 63.93 
 Aerobic POME 65.76 
 Anaerobic POME 65.24 
d. Semiconductor-industry wastewater 90.89 
FeedPermeate flux (L/m2 h)
a. Synthetic textile industry wastewater 
 10 mg/LMB 89.74 
 20 mg/LMB 80.10 
 10 mg/LCR 99.95 
 20 mg/LCR 90.26 
b. Synthetic leachate 
 2.192 g/L NaCl 136.81 
 4.384 g/L NaCl 120.40 
 8.768 g/L NaCl 113.91 
 89 g/L Kaolin 129.14 
 178 g/L Kaolin 122.28 
 356 g/L Kaolin 118.39 
 1,469.8 mg/L glucose 143.86 
 2,938.0 mg/L glucose 132.80 
 4,407.8 mg/L glucose 116.13 
c. POME 
 Fresh POME 63.93 
 Aerobic POME 65.76 
 Anaerobic POME 65.24 
d. Semiconductor-industry wastewater 90.89 
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On the other hand, it was also noticed that the permeate flux varied with the use of different wastewater as feed solutions in the membrane filtration process. This is because the solutes contain in each wastewater has different hydrodynamic particle size. Wastewater solutes at larger hydrodynamic particle sizes such as POME (7.5–15 nm) will easily block the pores on the membrane surface and therefore leading to lower permeate flux.

Membrane rejection

Synthetic textile industry wastewater
The ability of the PolyCera® Titan membrane for the treatment of textile industry wastewater was assessed with the use of MB solution and CR solution as the synthetic textile industry wastewater. Figure 2 depicts the rejection of MB solution and CR solution at different concentrations. In general, the PolyCera® Titan membrane was having a high performance for synthetic textile industry wastewater treatment with the rejection of 78.76–86.04% for MB solution and 88.89–93.71% for CR solution.
Figure 2
Rejection of the MB solution and CR solution at different concentrations (operating pressure: 0.4 MPa).
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Rejection of the MB solution and CR solution at different concentrations (operating pressure: 0.4 MPa).

Figure 2
Rejection of the MB solution and CR solution at different concentrations (operating pressure: 0.4 MPa).
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Rejection of the MB solution and CR solution at different concentrations (operating pressure: 0.4 MPa).

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Comparatively, the PolyCera® Titan membrane was having higher rejection towards CR ions than MB ions. This can be explained by the membrane size exclusion mechanism. MB ion's hydrodynamic particle size was 1.38 nm as reported by Jia et al. (2018), whereas CR ions have larger hydrodynamic particle sizes and are reported at 2.56 nm (Dapson 2018). In this case, CR ions were easier to reject by the PolyCera® Titan membrane and resulted in a higher rejection.

Synthetic leachate
The rejection of NaCl solution, kaolin solution, and glucose solution at different concentrations is depicted in Figure 3. As presented in Figure 3, the PolyCera® Titan membrane demonstrated good rejection for synthetic leachate with 94.72–96.50% removal of NaCl, 96.07–97.62% removal of kaolin, and 97.26–97.73% removal of glucose that indicate the TDS, TSS, and COD in leachate, respectively. The size of NaCl, kaolin, and glucose were reported as less than 2 μm (Madsen et al. 2018), 25–35 μm (Yahaya et al. 2017), and 83–523 μm (Ansari et al. 2018) respectively. Larger hydrodynamic particle size of ions in synthetic leachate compared to the PolyCera® Titan membrane makes it easily rejected by the membrane filtration through the size exclusion mechanism.
Figure 3
Rejection of the NaCl solution, kaolin solution, and glucose solution at different concentrations (operating pressure: 0.4 MPa).
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Rejection of the NaCl solution, kaolin solution, and glucose solution at different concentrations (operating pressure: 0.4 MPa).

Figure 3
Rejection of the NaCl solution, kaolin solution, and glucose solution at different concentrations (operating pressure: 0.4 MPa).
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Rejection of the NaCl solution, kaolin solution, and glucose solution at different concentrations (operating pressure: 0.4 MPa).

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POME
The performance of the PolyCera® Titan membrane in POME treatment was evaluated based on its rejection towards TSS, TDS, COD, BOD, AN, hardness, and colour. Figure 4 presents the PolyCera® Titan membrane performance for the treatment of POME, aerobic POME, and anaerobic POME. The PolyCera® Titan membrane demonstrated good removal of TSS (93–95%), TDS (93–95%), COD (83–96%), BOD (88–94%), AN (81–86%), hardness (96–97%), and colour (71–72%) regardless the type of POME. This is because the components present in POME, aerobic POME, and anaerobic POME are the same. Since the mechanism of the membrane filtration process is size exclusion, the same content in the feed solution is expected to achieve a similar percentage of rejection. In addition, organic matters in POME are negative in charge (Mi et al. 2021). Therefore, the rejection performance of the PolyCera® Titan membrane was enhanced with the repulsion between organic matters in POME and the negatively charged membrane surface. Though, the repulsive effect of the membrane surface towards the organic matter in POME was reduced attributed to the high fouling propensity of POME at high viscosity. Foulants fouled onto the membrane surface will act as the barrier for the direct contact between the membrane and the organic matters, and reduced the repulsive force of both. In this spectrum, the rejection performance of the PolyCera® Titan membrane for POME was slightly lower as compared to aerobic POME and anaerobic POME.
Figure 4
The PolyCera® Titan membrane performance for the treatment of POME, aerobic POME, and anaerobic POME (operating pressure: 0.4 MPa).
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The PolyCera® Titan membrane performance for the treatment of POME, aerobic POME, and anaerobic POME (operating pressure: 0.4 MPa).

Figure 4
The PolyCera® Titan membrane performance for the treatment of POME, aerobic POME, and anaerobic POME (operating pressure: 0.4 MPa).
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The PolyCera® Titan membrane performance for the treatment of POME, aerobic POME, and anaerobic POME (operating pressure: 0.4 MPa).

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Semiconductor-industry wastewater
The performance of the PolyCera® Titan membrane in semiconductor-industry wastewater treatment was evaluated based on its rejection towards TDS, TSS, COD, AN, hardness, and colour. Figure 5 presents the PolyCera® Titan membrane performance for the treatment of semiconductor-industry wastewater. High rejection was obtained by the PolyCera® Titan membrane for the treatment of semiconductor-industry wastewater in which the rejection was recorded at 91.7% TDS, 95.6% TSS, 96.1% COD, 83% AN, 98% hardness, and 99% colour. Semiconductor-industry wastewater contained a large amount of nano-size and micro-size particles (Huang et al. 2011). These particles with a particle size larger than the membrane pore diameter will retain on the membrane surface from passing through the membrane matrix.
Figure 5
Rejection of semiconductor-industry wastewater (operating pressure: 0.4 MPa).
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Rejection of semiconductor-industry wastewater (operating pressure: 0.4 MPa).

Figure 5
Rejection of semiconductor-industry wastewater (operating pressure: 0.4 MPa).
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Rejection of semiconductor-industry wastewater (operating pressure: 0.4 MPa).

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Table 3 summarizes the comparison of the PolyCera® Titan membrane with other types of NF membranes. Generally, the PolyCera® Titan membrane presented higher rejection as compared to other types of NF membranes (both polymeric membrane and ceramic membrane) for different wastewater treatments. High rejection the PolyCera® Titan membrane is thus widely applicable as an advanced wastewater treatment method for various types of wastewaters.

Table 3

Comparison of the PolyCera® Titan membrane with other types of NF membranes

Membrane materialType of wastewater
Reference
Textile industryLeachatePOMESemiconductor industry
Polyetherimide PEI15/65/20 rejection = 15.33–57.76%
PEI16/64/20 rejection = 74.76–81.42% 		– – – Karisma et al. (2017)  
Polyester – MPT-20 rejection:
COD = 74%
BOD = 85%
TKN = 22%
N-NH4+ = 12%
Na+ = 15%
Ca2+ = 36%
Cl− = 19%
Fe = > 99%
Ni = > 99% 		– – Trebouet et al. (2001)  
MPT-31 rejection:
COD = 80%
BOD = 98%
TKN = 30%
N-NH4+ = 21%
Na+ = 16%
Ca2+ = 56%
Cl− = 11%
Fe = > 99%
Ni = > 99% 
Polyamide – – BW30–4040 rejection:
BOD = 42.42%
COD = 99.90%
TSS = 20.00%
TDS = 92.88%
Colour = 100%
Phosphorus = 99.91%
Turbidity = 99.88%
Conductivity = 92.66% 		– Teow et al. (2016)  
NF270–4040 rejection:
BOD = 96.23%
COD = 99.20%
TSS = 90.78%
TDS = 29.87%
Colour = 99.95%
Phosphorus = 98.72%
Turbidity = 99.15%
Conductivity = 37.77% 
Ceramic – – – Rejection:
TOC = ∼ 100%
TN = ∼36–37%
Ammonium = ∼38–39%
Calcium = ∼41–42%
Sulfate = ∼58–60% 		Cha et al. (2022)  
PolyCera® Titan Rejection:
10 mg/L MB = 86.04%
20 mg/L MB = 80.38%
30 mg/L MB = 78.76%
10 mg/L CR = 93.70%
20 mg/L CR = 92.70%
30 mg/L CR = 88.90% 		Rejection:
2.192 g NaCl = 96.50%
4.384 g NaCl = 95.08%
8.768 g NaCl = 94.72%
89 g kaolin = 97.62%
178 g kaolin = 97.57%
356 g kaolin = 96.07%
1.46 g glucose = 97.73%
2.9 g glucose = 97.58%
4.4 g glucose = 97.26% 		Rejection:
TSS = 93.5–94.2%
TDS = 93.9–94.8%
COD = 83.6–99.0%
BOD = 88.6–96.4%
AN = 81.2–86.4%
Hardness = 96.3–97.6%
Colour = 71.6–72.4% 		Rejection:
TSS = 95.6%
TDS = 91.7%
COD = 96.1%
AN = 83.0%
Hardness = 98.0%
Colour = 99% 		This study 
Membrane materialType of wastewater
Reference
Textile industryLeachatePOMESemiconductor industry
Polyetherimide PEI15/65/20 rejection = 15.33–57.76%
PEI16/64/20 rejection = 74.76–81.42% 		– – – Karisma et al. (2017)  
Polyester – MPT-20 rejection:
COD = 74%
BOD = 85%
TKN = 22%
N-NH4+ = 12%
Na+ = 15%
Ca2+ = 36%
Cl− = 19%
Fe = > 99%
Ni = > 99% 		– – Trebouet et al. (2001)  
MPT-31 rejection:
COD = 80%
BOD = 98%
TKN = 30%
N-NH4+ = 21%
Na+ = 16%
Ca2+ = 56%
Cl− = 11%
Fe = > 99%
Ni = > 99% 
Polyamide – – BW30–4040 rejection:
BOD = 42.42%
COD = 99.90%
TSS = 20.00%
TDS = 92.88%
Colour = 100%
Phosphorus = 99.91%
Turbidity = 99.88%
Conductivity = 92.66% 		– Teow et al. (2016)  
NF270–4040 rejection:
BOD = 96.23%
COD = 99.20%
TSS = 90.78%
TDS = 29.87%
Colour = 99.95%
Phosphorus = 98.72%
Turbidity = 99.15%
Conductivity = 37.77% 
Ceramic – – – Rejection:
TOC = ∼ 100%
TN = ∼36–37%
Ammonium = ∼38–39%
Calcium = ∼41–42%
Sulfate = ∼58–60% 		Cha et al. (2022)  
PolyCera® Titan Rejection:
10 mg/L MB = 86.04%
20 mg/L MB = 80.38%
30 mg/L MB = 78.76%
10 mg/L CR = 93.70%
20 mg/L CR = 92.70%
30 mg/L CR = 88.90% 		Rejection:
2.192 g NaCl = 96.50%
4.384 g NaCl = 95.08%
8.768 g NaCl = 94.72%
89 g kaolin = 97.62%
178 g kaolin = 97.57%
356 g kaolin = 96.07%
1.46 g glucose = 97.73%
2.9 g glucose = 97.58%
4.4 g glucose = 97.26% 		Rejection:
TSS = 93.5–94.2%
TDS = 93.9–94.8%
COD = 83.6–99.0%
BOD = 88.6–96.4%
AN = 81.2–86.4%
Hardness = 96.3–97.6%
Colour = 71.6–72.4% 		Rejection:
TSS = 95.6%
TDS = 91.7%
COD = 96.1%
AN = 83.0%
Hardness = 98.0%
Colour = 99% 		This study 
View Large

Membrane fouling

Membrane fouling membrane happened due to the deposition of foulants onto the membrane surface and/or into the membrane pores. Membrane fouling is seen as the major obstacle for the development of membrane technology in many applications due to the reduction of permeate flux and the need for membrane replacement. Figure 6 presents the membrane permeate flux profile for the filtration of different feed solutions.
Figure 6
Permeate flux profile of the PolyCera® Titan membrane for the filtration of different wastewaters (operating pressure: 0.4 MPa).
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Permeate flux profile of the PolyCera® Titan membrane for the filtration of different wastewaters (operating pressure: 0.4 MPa).

Figure 6
Permeate flux profile of the PolyCera® Titan membrane for the filtration of different wastewaters (operating pressure: 0.4 MPa).
View largeDownload slide

Permeate flux profile of the PolyCera® Titan membrane for the filtration of different wastewaters (operating pressure: 0.4 MPa).

Close modal

As presented in Figure 6, permeate flux was decreased drastically at the beginning of filtration process regardless of the type of wastewater uses as the feed. At the beginning of filtration process, quick deposition of foulants happened on the membrane surface and into the membrane pores due to the high availability of adsorption sites. Foulants from wastewater have a high tendency to introduce to the membrane through convection, thus sharp declination of permeate flux was observed. After sometime, the rate of membrane fouling was reduced where the gradient of permeate flux profile has reduced. With the increasing filtration time, foulants gradually built up at the membrane surface. The available membrane surface for the adsorption of foulants was lesser and thus then was less uptake of foulants onto the membrane surface. The rate of membrane fouling is low in this spectrum.

Membrane fouling mechanism

Standard blocking, complete blocking, intermediate blocking, and cake layer formation were used for membrane filtration data fitting to identify the membrane fouling mechanism. Table 4 summarizes the R2 value of four membrane fouling models applied to explain the PolyCera® Titan membrane fouling mechanism in different wastewater treatments.

Table 4

R2 value of membrane fouling models

WastewaterR2
Standard blockingComplete blockingIntermediate blockingCake formation
MB 0.9994 0.9720 0.8556 0.8564 
CR 0.9982 0.9845 0.8749 0.8431 
Synthetic leachate (NaCl) 0.9999 0.9496 0.8673 0.7591 
Synthetic leachate (kaolin) 1.0000 0.9573 0.8673 0.7669 
Synthetic leachate (glucose) 0.9939 0.8831 0.8673 0.7092 
Anaerobic POME 0.9965 0.9589 0.8410 0.7764 
Aerobic POME 0.9995 0.9375 0.8641 0.8466 
Semiconductor-industry wastewater 0.9993 0.9543 0.8594 0.8340 
WastewaterR2
Standard blockingComplete blockingIntermediate blockingCake formation
MB 0.9994 0.9720 0.8556 0.8564 
CR 0.9982 0.9845 0.8749 0.8431 
Synthetic leachate (NaCl) 0.9999 0.9496 0.8673 0.7591 
Synthetic leachate (kaolin) 1.0000 0.9573 0.8673 0.7669 
Synthetic leachate (glucose) 0.9939 0.8831 0.8673 0.7092 
Anaerobic POME 0.9965 0.9589 0.8410 0.7764 
Aerobic POME 0.9995 0.9375 0.8641 0.8466 
Semiconductor-industry wastewater 0.9993 0.9543 0.8594 0.8340 
View Large

As summarized in Table 4, the standard blocking and complete model were the best model used to explain the PolyCera® Titan membrane fouling mechanism in all types of wastewater treatment processes with high R2 value compared to other models. The standard blocking theory is specified to the accumulation of particles smaller than membrane pore diameter, which are deposited inside the pores on the cylindrical walls of the membrane and therefore resulting constrictions of pores, reducing the membrane's permeability (Hou et al. 2021). Whereas, according to the complete blocking model, the particle seal off the pores without superimposition upon each another (Kazemimoghadam & Amiri-Rigi 2017). This is true as membrane fouling is a complex phenomenon caused by a combination of varied particle-size foulants. Foulants with particle sizes smaller than the membrane pore diameter fouled onto the membrane through the standard blocking mechanism and reduced the membrane pore diameter; while foulants at larger particle sizes deposited onto the membrane surface through the complete blocking model.

Membrane cleaning

Membrane cleaning was carried out when permeate flux was reduced 10–20% in each filtration cycle to recover the membrane's permeate flux (Teow et al. 2018a). Since the PolyCera® Titan membrane is a thermos-responsive membrane, membrane cleaning was conducted at 35 °C, the optimum cleansing temperature reported in our previous study (Teow et al. 2020). Figure 7 depicts the multiple filtration cycles of the PolyCera® Titan membrane. On the other hand, Table 5 summarizes the RFR and FRR values of PolyCera® Titan membrane for the filtration of different wastewater.
Table 5

RFR and FRR values of the PolyCera® Titan membrane for the filtration of different wastewaters

WastewaterFirst cycle
Second cycle
Third cycle
RFR (%)FRR (%)RFR (%)FRR (%)RFR (%)FRR (%)
MB 8.95 91.05 14.02 85.08 11.03 88.97 
CR 9.94 90.06 10.78 89.22 9.74 90.26 
Synthetic leachate (NaCl) 5.78 94.22 4.63 95.37 7.58 92.42 
Synthetic leachate (kaolin) 4.78 95.22 4.08 95.92 4.21 95.79 
Synthetic leachate (glucose) 8.70 91.30 1.84 98.16 4.04 95.96 
Anaerobic POME 18.37 81.63 10.91 89.09 12.61 87.39 
Aerobic POME 20.80 79.20 18.80 81.20 13.91 86.09 
Semiconductor-industry wastewater 10.00 90.00 10.83 89.17 9.84 90.16 
WastewaterFirst cycle
Second cycle
Third cycle
RFR (%)FRR (%)RFR (%)FRR (%)RFR (%)FRR (%)
MB 8.95 91.05 14.02 85.08 11.03 88.97 
CR 9.94 90.06 10.78 89.22 9.74 90.26 
Synthetic leachate (NaCl) 5.78 94.22 4.63 95.37 7.58 92.42 
Synthetic leachate (kaolin) 4.78 95.22 4.08 95.92 4.21 95.79 
Synthetic leachate (glucose) 8.70 91.30 1.84 98.16 4.04 95.96 
Anaerobic POME 18.37 81.63 10.91 89.09 12.61 87.39 
Aerobic POME 20.80 79.20 18.80 81.20 13.91 86.09 
Semiconductor-industry wastewater 10.00 90.00 10.83 89.17 9.84 90.16 
View Large
Figure 7
Multiple filtration cycles of the PolyCera® Titan membrane (operating pressure: 0.4 MPa, cleaning agent: distilled water at 35 °C).
View largeDownload slide

Multiple filtration cycles of the PolyCera® Titan membrane (operating pressure: 0.4 MPa, cleaning agent: distilled water at 35 °C).

Figure 7
Multiple filtration cycles of the PolyCera® Titan membrane (operating pressure: 0.4 MPa, cleaning agent: distilled water at 35 °C).
View largeDownload slide

Multiple filtration cycles of the PolyCera® Titan membrane (operating pressure: 0.4 MPa, cleaning agent: distilled water at 35 °C).

Close modal

As presented in Table 5, physical cleaning with the use of distilled water was able to recover the permeate flux with the FRR value in the range of 79.2–95.22% at first cycle, 81.20–98.16% at second cycle, and 86.09–95.96% at third cycle. At 35 °C, PolyCera® Titan membrane pores were stretched and enlarged. The enlargement of membrane pores made the foulants attached to the PolyCera® Titan membrane easily flush out from the membrane. The high FRR value of the PolyCera® Titan membrane signifies great potential of the PolyCera® Titan membrane for the application of textile industry wastewater, leachate, POME, and semiconductor-industry wastewater treatment with low frequency of membrane replacement and without the use of chemicals for membrane cleaning.

The PolyCera® Titan membrane is effective for the treatment of textile industry wastewater, POME, leachate, and semiconductor-industry wastewater with high TDS, TSS, COD, AN, hardness, and colour. Rejection of MB and CR was in the range of 78.76–86.04% and 88.89–93.71%, respectively. 94.72–96.50% NaCl, 96.07–97.62% kaolin, and 97.26–97.73% glucose were rejected from synthetic leachate indicating the removal of TDS, TSS, and COD from leachate, respectively. Good removal of TSS (93–95%), TDS (93–95%), COD (83–96%), BOD (88–94%), AN (81–86%), hardness (96–97%), and colour (71–72%) was also demonstrated by the PolyCera® Titan membrane for the treatment of POME. High rejection was obtained by the PolyCera® Titan membrane for the treatment of semiconductor-industry wastewater in which the rejection was recorded at 91.7% TDS, 95.6% TSS, 96.1% COD, 83% AN, 98% hardness, and 99% colour.

Standard blocking and complete model were the best models used to explain the PolyCera® Titan membrane fouling mechanism in all types of the wastewater treatment process with high R2 values compared to other models. Foulants with particle sizes smaller than the membrane pore diameter fouled onto the membrane through the standard blocking mechanism and reduced the membrane pore diameter, while foulants at larger particle sizes deposited onto the membrane surface through the complete blocking model.

Physical cleaning with the use of distilled water was able to recover the permeate flux with the FRR value in the range of 79.2–95.22% in first cycle, 81.20–98.16% at second cycle, and 86.09–95.96% at third cycle. High FRR value of the PolyCera® Titan membrane signifies great potential of the PolyCera® Titan membrane for the application in textile industry wastewater, leachate, POME, and semiconductor-industry wastewater treatment with a low frequency of membrane replacement and without the use of chemicals for membrane cleaning.

We would like to express our appreciation towards the funding for this research by Geran Translational UKM (UKM-TR-009) and Hydrofil (M) Sdn. Bhd. This research collaboration between Hydrofil (M) Sdn. Bhd. and UKM is derived from Hydrofil (M) Sdn. Bhd.’s initiative towards achieving 2030 Sustainable Development Goals and the company's focus on Environmental Sustainability & Climate Protection.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.

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