PUB Singapore has been developing the membrane bioreactor (MBR) technology for water reclamation. The MBR technology has significant versatility and can be applied for production of industrial water or combined with reverse osmosis to produce NEWater. The MBR technology offers greater opportunity for process intensification and further enhancement to achieve water sustainability. Compared to conventional treatment, MBR is a 3-in-1 solution that combines bioreactor, secondary sedimentation tank and microfiltration/ultrafiltration in one single step. The advantages of MBR include process robustness, superior filtrate quality and compact footprint. Progressing from pilot studies and demonstration testing, the MBR technology is currently implemented at full-scale in Jurong and Changi Water Reclamation Plant. Moving forward, PUB continues to embark on R&D in developing innovative MBR systems for future application that includes the forthcoming Tuas Water Reclamation Plant as part of the Deep Tunnel Sewerage System Phase 2 project. This manuscript provides an overview of R&D initiatives for developing the MBR technology for water reclamation spanning more than a decade at PUB.

INTRODUCTION

Since 2003, PUB Singapore has been developing the membrane bioreactor (MBR) technology for water reclamation. The MBR technology has significant versatility and can be applied for production of industrial water or combined with reverse osmosis (RO) to produce NEWater. The NEWater is PUB's trade-marked high-grade reclaimed water that surpasses drinking water requirements, and a key pillar of Singapore's water sustainability.

The conventional treatment route for NEWater production begins at a water reclamation plant (WRP), where influent used water is treated using conventional activated sludge process (CASP) that comprises the main treatment units of primary sedimentation tank, bioreactor and secondary sedimentation tank (SST). The CASP-treated water, or secondary effluent, is then supplied as feedstock to a NEWater factory, where it is further purified with dual membrane processes comprising microfiltration (MF)/ultrafiltration (UF) and RO followed by ultraviolet disinfection to produce NEWater.

The conventional treatment processes for NEWater production are well established. However, with the MBR technology, there is greater opportunity for process intensification and further enhancement to achieve water sustainability. Fane et al. (2015) identified the MBR-RO process as the technology option for water reuse application involving indirect potable use or non-potable use that demands high water quality. Compared to conventional treatment, MBR is a 3-in-1 solution that combines bioreactor, SST and MF/UF in one single step (Figure 1). Advantages of MBR include process robustness, superior filtrate quality and compact footprint.
Figure 1

MBR is a 3-in-1 solution that combines bioreactor, SST and MF/UF to produce NEWater.

Figure 1

MBR is a 3-in-1 solution that combines bioreactor, SST and MF/UF to produce NEWater.

To date, PUB has more than a decade of experiences with the MBR technology. From pilot studies and demonstration testing, the MBR technology has now progressed to full-scale implementation. PUB continues to embark on R&D in developing innovative MBR systems for future application. This manuscript provides an overview of initiatives for developing the MBR technology for water reclamation at PUB from R&D to full-scale application.

PILOT STUDIES AND DEMONSTRATION TESTING

The beginning of PUB's R&D journey of MBR technology could be traced back to the pilot studies conducted at the now-decommissioned Bedok Water Reclamation Plant (Bedok WRP). Three MBR pilot plants with capacity of 300 m3/d each were commissioned in 2003 to test for different types of submerged membranes.

The pilot studies encompassed a range of investigations that included analysis of total organic carbon (TOC) for overall monitoring of organics, Gas Chromatography-Electron Capture Detector (GC-ECD) for scanning of homogenated organics, High Performance Liquid Chromatography (HPLC) for scanning of non-volatile organics, and Gas chromatography–mass spectrometry (GC-MS) for scanning of semi-volatile organics and various types of liquid and sludge analytical and monitoring methods. The pilot studies conclusively showed that the MBR product water quality is equivalent to or better than the UF product water quality in the NEWater process (Tao et al. 2005).

The pilot studies were subsequently expanded to include RO testing. It was found that the MBR-RO process achieved more stable and greater removal of organics as compared to the NEWater process of CASP-MF-RO. The RO-TOC values were in the range of 24–33 ppb for the MBR-RO process, while these were in the range of 33–53 ppb for the NEWater process. Furthermore, it was found that higher RO flux could be attained in the MBR-RO process as compared to the NEWater process (Qin et al. 2006).

Scaling up from the pilot studies, an MBR demonstration plant with capacity of 5-MGD (=23,000 m3/d) was constructed at the Ulu Pandan WRP and began operations in 2006. The MBR demonstration plant was designed based on a retrofitting concept, where two existing aeration tanks in the North Works of Ulu Pandan WRP were modified into anoxic and oxic zones of the bioreactor. New membrane tanks and a MBR-dedicated process control building were constructed. The MBR demonstration plant is able to produce high quality filtrate (Table 1).

Table 1

Product water requirements for the 5-MGD MBR demonstration plant at Ulu Pandan WRP

ParameterRequirementMethod
Turbidity <0.2 NTU USEPA 180.1 
Ammonia (as N) <2 mg/L APHA 4500 
TOC <6 mg/L USEPA 415.1 
Nitrate (as N) <20 mg/L USEPA 300.0 
Total Phosphate (as P) <4 mg/L USEPA 300.0 
Total Coliform <100 CFU/100 mL APHA 9223 
ParameterRequirementMethod
Turbidity <0.2 NTU USEPA 180.1 
Ammonia (as N) <2 mg/L APHA 4500 
TOC <6 mg/L USEPA 415.1 
Nitrate (as N) <20 mg/L USEPA 300.0 
Total Phosphate (as P) <4 mg/L USEPA 300.0 
Total Coliform <100 CFU/100 mL APHA 9223 

Filtrate water from the MBR demonstration plant is supplied as industrial water. Industrial water is mainly supplied to chemical plants and petroleum refineries to be used for cooling applications. For industrial water supply, nitrate is not a pertinent parameter. Although the specified MBR product water requirement was 20 mg/L for nitrate, typical operational value for nitrate achieved by the MBR demonstration plant was approximately 6 mg/L and well within the specification.

As with any water infrastructure project, cost is a very important consideration. Historically, production for industrial water was based on an elaborate physical-chemical treatment process at the Jurong Industrial Water Works (JIWW), and was land-intensive (Section 3).

Using MBR technology to produce industrial water is therefore advantageous, as an MBR plant will entail lower capital costs in Singapore's context compared to conventional treatment process because of smaller footprint (it is done by retrofitting an existing activated sludge plant) and hence lower land cost. There are also operational advantages, as there is no longer the need to operate JIWW to produce industrial water.

However, existing MBR technology entails relatively high power consumption mainly due to additional energy requirement for permeate pumping as well as air scouring for the membrane. A key R&D objective therefore is to reduce power consumption to improve performance of the MBR technology through process optimisation measures (Figure 2).
Figure 2

Process optimisation of the MBR Process during pilot studies and demonstration testing.

Figure 2

Process optimisation of the MBR Process during pilot studies and demonstration testing.

When the MBR pilot studies were carried out on the three different types of membrane system in 2003, the specific power consumption of the three pilot plants ranged from 1.3 to 1.7 kWh/m3. The baseline operation was based on the recommendations of system suppliers, and the initial designs were found to be conservative. Process optimisation was then performed in two phases. The first phase involved increasing permeate flux while keeping the air supply rate constant. With this measure, the specific power consumption could be reduced to approximately 1 kWh/m3. The second phase involved reducing air supply rate without causing any significant change in product quality and membrane fouling rate. By the end of the second phase of pilot testing, it was established that the specific power consumption could be reduced to approximately 0.8 kWh/m3. Further information on the MBR pilot studies can be found in Tao et al. (2005).

Moving to demonstration plant testing, the guarantee figure for specific power consumption was 0.7 kWh/m3. A step by step approach was then applied to reduce specific power consumption at the 5-MGD MBR demonstration plant.

The first step was through improved design and selection of equipment, and specific power consumption of 0.6 kWh/m3 was achieved during baseline operation with mixed liquor suspended solids (MLSS) concentration of around 10,000 mg/L. The second step was to reduce the MLSS level in the aeration tank to around 6,000 mg/L by shortening the solids retention time (SRT). This optimisation measure of operating at lower SRT to save energy was feasible due to the warm climate condition in Singapore with the temperature here about 30°C. Lower MLSS leads to lower sludge viscosity and better aeration efficiency. The third step was to optimise the MLSS recirculation by recirculating the mixed liquor (2Q) from the membrane tank directly to the inlet of the anoxic tank and thereby relieving pumping for more recirculation. The fourth step was optimisation of process aeration with DO set point of 1.5 mg/L. The fifth step was optimisation of membrane scouring rate.

In the course of process optimisation, it was ensured that any power reduction was not achieved at the expense of water quality and cleaning frequency. These efforts were able to drive down the specific power consumption of MBR from the initial 1.3 kWh/m3 recorded during pilot studies to the guaranteed figure of 0.7 kWh/m3 and finally to an optimised specific power consumption of less than 0.5 kWh/m3 (Figure 2).

Operations’ experiences from the MBR demonstration plant confirm the advantages of the MBR technology that include robustness to take shock loadings, superior filtrate quality, small footprint and automation in operation. With successful pilot studies and demonstration testing, the MBR technology progressed from R&D to full-scale application at Jurong WRP (section 3), and Changi WRP (section 4).

FULL-SCALE IMPLEMENTATION AT JURONG WRP – MBR FOR INDUSTRIAL WATER PRODUCTION

The Jurong WRP, located in the western part of Singapore, treats used water of both industrial and domestic origin in the proportion of approximately 40% to 60%. The Plant currently has a configuration comprising 3 Phases with overall treatment capacity of 45 MGD (=205,000 m3/d).

Since 2013, Phase 1 treatment facilities at the Jurong WRP have been converted from CASP to an MBR Plant. The Jurong MBR Plant has a treatment capacity of 15-MGD (=68,000 m3/d) to treat domestic used water and produce high quality filtrate water suitable for reuse as industrial water. Together with the 5-MGD MBR Demonstration Plant at Ulu Pandan WRP (section 2), the two MBR Plants replaced the Jurong Industrial Water Works (JIWW) in supplying an alternative source of water to industries for non-potable use and thereby conserving potable water resource that is otherwise required for such purpose.

By leveraging on the MBR technology to produce industrial water, significant savings in process and land requirements could be achieved. The JIWW occupied a land area of some 5.2 hectares (=52,000 m2). It received secondary CASP-treated effluent from the Ulu Pandan WRP as feedstock, which was subjected to an elaborate tertiary treatment process comprising fine screen, pre-chlorination with sodium hypochlorite and pH correction with caustic soda, chemical clarification with alum, sand filtration, aeration, and finally, post-chlorination with sodium hypochlorite. The MBR Plants, on the other hand, avoid the need for such elaborate treatment process and require additional area of only some 2,050 m2 for the construction of membrane tanks that are spread out over 400 m2 at the Ulu Pandan MBR Plant and 1,650 m2 at the Jurong MBR Plant.

The 15-MGD Jurong MBR Plant is designed with a three-stage enhanced biological phosphorus removal (EBPR) process that is able to concomitantly treat for removal of organics, nitrogen and phosphorus. Screened primary effluent is fed into both the anoxic zone and the anaerobic zone of the bioreactor in the approximate proportion of 70% to 30%. The flow then passes through the oxic zone where it is aerobically treated, before filtration takes place in the membrane tank to produce MBR product water (Figure 3).
Figure 3

Schematics of the MBR system at Jurong WRP.

Figure 3

Schematics of the MBR system at Jurong WRP.

The quality of the MBR product water surpasses that of the conventional effluent at Jurong WRP and is well within the typical industrial water quality (Table 2 and Figure 4). Even though the Plant is provided with alum dosing equipment to allow for chemical phosphorus removal, there is currently no need for this by achieving stable EBPR operation.
Table 2

Water quality comparison between conventional effluent, typical industrial water and typical MBR product water at Jurong WRP

ParameterConventional effluent qualityTypical industrial water qualityTypical MBR product water quality
Turbidity 6.8 NTU 0.5–2.0 NTU <0.2 NTU 
BOD5 17 mg/L 1.0–5.0 mg/L <2 mg/L 
Ammonia (as N) 25 mg/L <5.0 mg/L <2 mg/L 
Orthophosphate (as P) 3.7 mg/L 1.0–4.0 mg/L <3 mg/L 
ParameterConventional effluent qualityTypical industrial water qualityTypical MBR product water quality
Turbidity 6.8 NTU 0.5–2.0 NTU <0.2 NTU 
BOD5 17 mg/L 1.0–5.0 mg/L <2 mg/L 
Ammonia (as N) 25 mg/L <5.0 mg/L <2 mg/L 
Orthophosphate (as P) 3.7 mg/L 1.0–4.0 mg/L <3 mg/L 
Figure 4

Monitoring of MBR Product Water Quality at Jurong WRP.

Figure 4

Monitoring of MBR Product Water Quality at Jurong WRP.

FULL-SCALE IMPLEMENTATION AT CHANGI WRP – MBR FOR EXPANSION OF TREATMENT CAPACITY

The Changi WRP is currently the largest water reclamation facility located in the eastern part of Singapore. The influent used water to the Plant is predominantly domestic in nature. The Plant has a compact and covered design, and comprises two liquids modules. Each liquids module consists of two parallel treatment trains of step–feed activated sludge process with identical configuration and working volume. In order to meet increasing used water flow, the Plant is undergoing expansion with full-scale implementation of MBR technology over two phases. The first phase involves MBR-retrofit into the bioreactor basins 3.1 and 4.1 with combined treatment capacity of 13 MGD (60,000 m3/d), and the second phase involves MBR-retrofit into the bioreactor basins 1.1 and 2.1 with the same treatment capacity (Figure 5).
Figure 5

Expansion of treatment capacity with MBR retrofits at Changi WRP.

Figure 5

Expansion of treatment capacity with MBR retrofits at Changi WRP.

Currently, MBR 3.1 has been successfully commissioned, plant-proved and operating since May 2015. MBR 4.1 is on-track for completion within 2015, while MBR 1.1 and 1.2 are slated for completion in 2016. When the MBR-retrofits are completed, the total treatment capacity of Changi WRP will increase from the original 176 MGD (800,000 m3/d) to 202 MGD (920,000 m3/d).

By leveraging on the MBR-technology to retrofit the available bioreactor basins, Changi WRP is able to overcome the bottleneck of the existing SST and ensure adequate supply of feedstock for NEWater production.

Even though the original Plant already had a compact layout, the MBR facilities could still achieve approximately 25% further reduction in specific footprint compared to the conventional treatment comprising bioreactor and SST (Figure 6).
Figure 6

Specific footprint of MBR-retrofit compared to conventional treatment at Changi WRP.

Figure 6

Specific footprint of MBR-retrofit compared to conventional treatment at Changi WRP.

The daily specific power consumption of the MBR 3.1 was tracked against the daily permeate production throughout the 30-days plant-proving period from 18 April to 18 May 2015 (Figure 7). It was confirmed that the daily specific power consumption was consistently <0.5 kWh/m3. Towards the final two weeks of the plant-proving period, the daily specific power consumption could be further optimised to achieve below 0.4 kWh/m3 by reducing aeration supply. The Plant continues to monitor the long-term power consumption of the MBR. The MBR-plant has been operating with net average membrane flux of approximately 25 L/m2h and SRT of approximately 7 days. All product water quality requirements were met (Table 3).
Table 3

MBR product water requirements at Changi WRP

ParameterRequirementMethod
Turbidity <0.2 NTU 95% of the time
<0.5 NTU 100% of the time 
Continuous online measurement 
Ammonia <2.0 mg/L NH4-N daily average
<6.0 mg/L NH4-N 100% of the time 
Online measurement at hourly interval 
pH 6.5 to 7.2 (3-hour average) Continuous online measurement 
Alkalinity >50 mg/L as CaCO3 at all times Daily grab sample (method APHA 23208) 
Total Coliform <100 CFU/100 mL monthly geometric average Daily grab sample (method APHA 92228) 
ParameterRequirementMethod
Turbidity <0.2 NTU 95% of the time
<0.5 NTU 100% of the time 
Continuous online measurement 
Ammonia <2.0 mg/L NH4-N daily average
<6.0 mg/L NH4-N 100% of the time 
Online measurement at hourly interval 
pH 6.5 to 7.2 (3-hour average) Continuous online measurement 
Alkalinity >50 mg/L as CaCO3 at all times Daily grab sample (method APHA 23208) 
Total Coliform <100 CFU/100 mL monthly geometric average Daily grab sample (method APHA 92228) 
Figure 7

Daily specific power consumption and daily permeate production of MBR 3.1.

Figure 7

Daily specific power consumption and daily permeate production of MBR 3.1.

Various water quality parameters were also closely monitored at the Changi WRP. As the MBR is able to produce filtrate water that is free of suspended solids, traditional parameter such as total suspended solids is not applicable. Rather, a concern is on the removal of organics. Water quality parameters that are relevant include the 5-day biochemical oxygen demand (BOD5) and the chemical oxygen demand (COD). Based on regular monitoring, the MBR has proven to achieve distinctly better removal efficiency compared to conventional treatment for both BOD5 and COD (Figure 8).
Figure 8

Monitoring of the parameters BOD5 and COD for effluent from conventional treatment compared to MBR-filtrate at the Changi WRP.

Figure 8

Monitoring of the parameters BOD5 and COD for effluent from conventional treatment compared to MBR-filtrate at the Changi WRP.

Liquid chromatography-organic carbon detection (LC-OCD) analysis is a useful research method that is used in MBR studies (Rosenberger et al. 2006; Lyko et al. 2008). The LC-OCD analysis provides quantitative as well as qualitative result in the form of chromatogram on the classes of dissolved organic carbon (DOC) compounds present in water. The LC-OCD can characterise DOC based on molecular weight (MW), and is able to differentiate between biopolymers, humic substances (humics), building blocks, low molecular weight (LMW) neutrals and LMW organic acids.

The LC-OCD analysis was performed by researchers from the National University of Singapore. Analysis was carried out on three different water samples at Changi WRP: (a) Effluent from conventional treatment for the liquids Train 3, (b) Filtrate from MBR 3.1, and (c): Combined product water sampled from Train 3′s plant effluent wet well where MBR filtrate is mixed with effluent from conventional treatment.

Qualitatively (Figure 9), it can be observed from the LC-OCD chromatograms that sample (b) MBR filtrate exhibited a different profile compared to the other two samples (a) and (c). The sample (c) combined product water indicated a profile that is more similar to that of sample (a) conventional treatment effluent due to mixing effect in the plant effluent wet well, and served as a control sample.
Figure 9

LC-OCD chromatograms. (a): Effluent from conventional treatment, (b): MBR Filtrate, and (c): Combined Product Water.

Figure 9

LC-OCD chromatograms. (a): Effluent from conventional treatment, (b): MBR Filtrate, and (c): Combined Product Water.

Quantitatively (Table 4), sample (b) MBR filtrate has the lowest total DOC among the 3 samples with a measured value of 6773.60 ppb (=6.77360 mg/L). This total DOC is composed of 1940.05 ppb of hydrophobic-DOC fraction and 4833.56 ppb of hydrophilic-DOC fraction. The hydrophilic-DOC fraction, in turn, can be further categorised into the different classes: biopolymers (1.38 ppb), humics (3082.18 ppb), building blocks (865.36 ppb), LMW neutrals (884.64 ppb) and LMW organic acids (n.q.).

Table 4

Results of LC-OCD analysis for characterisation of organic compounds in the water samples

  
 Approximate Molecular Weight in g/mol
 Total  > 20,000∼ 1,000300–500< 350< 350
 DOCHOCCDOC     
 DissolvedHydrophobicHydrophilicBiopolymersHumic substancesBuilding BlocksLMW NeutralsLWM Acids
Sample[ppb-C] / [%DOC][ppb-C] / [%DOC][ppb-C] / [%DOC][ppb-C] / [%DOC][ppb-C] / [%DOC][ppb-C] / [%DOC][ppb-C] / [%DOC][ppb-C] / [%DOC]
(a) Effluent from conventional treatment 9819.59 3450.37 6369.22 765.97 3045.74 1093.06 1463.11 1.34 
100.00% 35.14% 64.86% 7.80% 31.02% 11.13% 14.90% 0.01% 
(b) MBR Filtrate 6773.60 1940.05 4833.56 1.38 3082.18 865.36 884.64 n.q. 
100.00% 28.64% 71.36% 0.02% 45.50% 12.78% 13.06% – 
(c) Combined Product Water 9160.04 3067.83 6092.21 690.80 3034.39 937.22 1429.79 n.q. 
100.00% 33.49% 66.51% 7.54% 33.13% 10.23% 15.61% – 
  
 Approximate Molecular Weight in g/mol
 Total  > 20,000∼ 1,000300–500< 350< 350
 DOCHOCCDOC     
 DissolvedHydrophobicHydrophilicBiopolymersHumic substancesBuilding BlocksLMW NeutralsLWM Acids
Sample[ppb-C] / [%DOC][ppb-C] / [%DOC][ppb-C] / [%DOC][ppb-C] / [%DOC][ppb-C] / [%DOC][ppb-C] / [%DOC][ppb-C] / [%DOC][ppb-C] / [%DOC]
(a) Effluent from conventional treatment 9819.59 3450.37 6369.22 765.97 3045.74 1093.06 1463.11 1.34 
100.00% 35.14% 64.86% 7.80% 31.02% 11.13% 14.90% 0.01% 
(b) MBR Filtrate 6773.60 1940.05 4833.56 1.38 3082.18 865.36 884.64 n.q. 
100.00% 28.64% 71.36% 0.02% 45.50% 12.78% 13.06% – 
(c) Combined Product Water 9160.04 3067.83 6092.21 690.80 3034.39 937.22 1429.79 n.q. 
100.00% 33.49% 66.51% 7.54% 33.13% 10.23% 15.61% – 

DOC, dissolved organic carbon; HOC, hydrophobic organic carbon; CDOC, hydrophilic organic carbon; LMW, low molecular weight; n.q., not quantifiable.

Analysing in more detail between sample (a) conventional treatment effluent, and sample (b) MBR filtrate, the following points can be made:

  • i) The superiority of the MBR filtrate in total DOC is attributed to both reduced hydrophobic-DOC fraction and hydrophilic-DOC fraction.

  • ii) There is significant difference in DOC value for the fraction biopolymers, indicating that this class of organics has been effectively removed by the MBR but not by the conventional treatment.

  • iii) There is no significant difference in DOC value for the fraction humics for both MBR and conventional treatment, indicating that this class of organics is neither effectively removed by the MBR nor by the conventional treatment.

  • iv) There is significant difference in DOC value for the fractions building blocks and LMW neutrals, indicating that these classes of organics have been effectively removed by the MBR but not by the conventional treatment.

  • v) The DOC value for the fraction LMW acids for both MBR and conventional treatment is either not quantifiable or in negligibly small amount, indicating that this class of organics is not significantly present in all water samples and therefore needs no further discussion.

The above points (i) and (ii) can be well understood as colloidal and macromolecular compounds (e.g. biopolymers) could be effectively retained by the MBR3.1, which uses UF-membrane with nominal pore size of 0.04 μm that may correspond to molecular-weight-cut-off in the range >10,000 g/mol (Judd 2006; Le-Clech et al. 2006). The same colloidal and macromolecular compounds, however, would be carried over into the effluent in the SST of conventional treatment and hence detected in that sample. It should be noted that the total DOC values were separately checked and validated by TOC-analysis carried out by another independent laboratory.

Point (iii) can be explained as humics are non-readily biodegradable substances that are small enough to pass through the UF-membrane in the MBR, and therefore are present in all water samples (Rosenberger et al. 2006; Lyko et al. 2008).

Point (iv), however, is noteworthy. In terms of MW, building blocks (300–500 g/mol) and LMW neutrals (<350 g/mol) could not be retained by the UF-membrane of the MBR, and should be detected in similar concentration in the conventional treatment effluent as well as in the MBR filtrate as is the case for humics. However, result conclusively shows that there is enhanced removal efficiency of lower molecular weight organic compounds by the MBR over the conventional treatment. The conclusion is that there is enhanced removal efficiency of lower molecular weight organic compounds including organic micro-pollutants by the MBR as a system that is not due to physical separation of the membrane alone. Similar observations and conclusions are also well documented in the literature. This is a distinctive advantage of MBR system that utilises the synergistic interaction between membrane and biological process. Current theory is that the enhanced removal efficiency of lower molecular weight organic compounds can be attributed to the formation of a gel/biofilm layer on the membrane surface that improves the separation performance of MBR system (Tao et al. 2005; Qin et al. 2006; Melin et al. 2006; Sahar et al. 2011).

CONTINUAL R&D IN DEVELOPING MBR TECHNOLOGY

Moving forward, PUB continues the efforts in developing the MBR technology. The R&D approach is to progressively advance innovative technology up the value chain from fundamental research to pilot and validation studies, demonstration testing and finally full-scale implementation. Key objectives are to increase water recovery, maintain water quality and security and reduce production and distribution cost by minimising footprint of resources including energy, land area, chemicals and manpower while coping with the warm climate condition in Singapore.

Ongoing R&D efforts include the 1-MGD (=4,550 m3/d) demonstration testing of ceramic MBR system to treat industrial used water at the Jurong WRP and the 0.22-MGD (=1,000 m3/d) integrated validation plant (IVP) to treat domestic used water at the Ulu Pandan WRP. Integral in the IVP is a process combination of enhanced primary treatment and low-energy MBR technology that was conceptualised based on extensive review of potential technologies and study on global trends in municipal used water treatment (Lee et al. 2013).

The IVP has been able to produce high quality MBR filtrate with nutrient removal at short SRT of 5 days. Further optimisation studies at the IVP are ongoing. Based on studies carried out at the IVP, a tender for the construction for of a demonstration plant with capacity of 2.75-MGD (=12,500 m3/d) has recently been awarded to gain operational experiences with the technology. The IVP and the demonstration plant serve as part of a greater effort in developing innovative technology that may be applied at the upcoming Tuas WRP under the Phase 2 of the Singapore's Deep Tunnel Sewerage System (DTSS) project targeted for completion by 2024. The DTSS is an integral part of PUB's strategy to meet Singapore's long-term needs for water reclamation. The Tuas WRP is planned to tie in with the phasing out of Jurong WRP and Ulu Pandan WRP, and to consist of both domestic module and industrial module in the approximate proportion of 80% to 20%. The Tuas WRP is conceptualised to leverage on energy- and space-efficient MBR-RO process for NEWater production.

After more than a decade of developing the MBR technology for water reclamation at PUB, the installed MBR capacity has grown from the 3 × 300 m3/d pilot-scale R&D in 2003 to multiple full-scale applications with total projected installed MBR capacity of nearly 48 MGD (=218,000 m3/d) by 2016. On the horizon are forthcoming projects that include the demonstration plant (Demo-Plant) for Tuas WRP, the Phase-II expansion of Changi WRP and the Tuas WRP itself (Figure 10). The R&D journey continues.
Figure 10

Development of MBR technology for water reclamation at PUB.

Figure 10

Development of MBR technology for water reclamation at PUB.

ACKNOWLEDGEMENTS

The authors acknowledge and thank research groups of Associate Professor Hu Jiang Yong and Associate Professor Ng How Yong from the National University of Singapore for the performance the LC-OCD analyses and Bernard Lim for the assistance in preparing some of the figures in this manuscript as part of his internship at PUB.

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