Water. desalination + reuse

TECHNOLOGY | 32 | Desalination & Water Reuse | May-June 2014 Deposition factors determined with MFI-UF using test membranes varying between 100 and 5 kDa for feedwater (pretreated with UF) to a seawater RO pilot plant in Jacobahaven (the Netherlands) showed Ω ranged between 0.20 to 0.45 (see table 1). References 1. ASTM, D4189 - 07(2014). 2014, ASTM International: West Conshohocken, PA. 2. JC Schippers, and J Verdouw, Desalination 1980. 32: p. 137-148. 3. A Nahrstedt and J Camargo Schmale, Water Sci Tech: Water Supply, 2008. 8(4): p. 401-412. 4. A Alhadidi et al. J Mem Sci, 2011. 381(1-2): p. 142-151. 5. A Alhadidi et al. J Mem Sci, 2011. 384(1-2): p. 205-218. 6. RM Rachman et al. Desalination Water Treat, 2013. 51(4-6): p. 1091-1103. 7. JC Schippers et al. Desalination, 1981. 38: p. 339-348. 8. JC Schippers, 1989, Rijswijk: Keuringinstituut voor waterleidingartikelen KIWA N.V. 179. 9. SFE Boerlage, et al. Desalination, 2004. 161: p. 103-113. 10. SG Salinas Rodríguez, 2011, Delft: CRC Press/Balkema. ISBN 978-0-415-62092-5 11. SG Salinas Rodríguez et al. Desalination Water Treat, 2012. 42: p. 155-162. 12. SFE Boerlage et al. J Mem Sci, 2002. 197(1-2): p. 1-21. 13. SFE Boerlage et al. J Mem Sci, 2003. 211: p. 271-289. 14. EMV. Hoek, and M Elimelech, Env Sci Tech, 2003. 37: p. 5581-5588. 15. LN Sim et al. Desalination, 2011. 273: p. 184-196. 16. LO Villacorte, 2014, Leiden: CRC Press/Balkema. ISBN 978-1-138-02626-1 with membranes having pores of 10 kDa at a constant flux of 60 L/m 2 h. The data shown in Figure 11 originate from 5 different plant locations including lake, river and seawater. CONCLusiONs aNd RECOmmENdaTiONs The presented results illustrate the benefit of the MFI-0.45 test to the industry to determine the particulate fouling potential of both high and low fouling feedwater. The MFI is corrected for temperature and pressure and has a linear relation with suspended/ colloidal matter. Semi- and fully automated equipment is available on the market to simultaneously measure MFI-0.45 and SDI on-line. The observed deficiencies in the SDI test and the demonstrated advantages of MFI have led the ASTM Committee charged with recertifying SDI to revisit the protocol for SDI and to start the approval process for a second standard based on the MFI test method. MFI-UF provides insight into the fouling potential of a feedwater due to particles smaller than 0.45 µm and enables one to measure the effect of different pretreatment processes on these particles. Three major aspects need to be addressed in further developing the MFI test: • MFI test membranes with even smaller pores, ideally close to the nanofiltration range, and preferably down to 5, 1, and 0.5 kDa. Unfortunately, membranes, in flat sheet form, and having sufficient permeability are not yet available on the market. Consequently, pencil capillary membranes modules need to be applied, complicating further research and application. • Measuring the deposition factor Ω in a multitude of full-scale plants to define the "safe MFI". This requires operational data on fouling rates in RO systems. Differentiation between particulate fouling and biofouling is also required. • Measuring the enhanced osmotic pressure effect due to fouling in full- scale plants. International collaboration of research organizations and the industry worldwide is proposed in order to establish a database of operational data and MFI-UF measurements for a wide range of RO feed water, pretreatment options and operational regimes. Such a database would be of considerable value to process engineers and plant operators in designing and operating desalination plants. l The performance of pretreatment processes at the Jacobahaven SWRO demonstration plant was assessed using MFI-UF measured with 100, 50 and 10 kDa test membranes as shown in Figure 10. The Amiad strainer showed only a small reduction in MFI-UF, as expected, with a relatively large aperture size of 50 µm. Whereas, the reduction in MFI- UF (and fouling) observed following UF (nominal MWCO of 150 kDa) was much larger, ie, of 94%, 93% and 88% reduction for 100 kDa, 50 kDa and 10 kDa MFI-UF test membranes, respectively. These results clearly illustrate that the MFI-UF can be used (at any temperature) to measure low and high fouling feedwater and for UF permeates. FOuLiNG POTENTiaL iN uF aNd mF sYsTEms Predicting the rate of fouling in MF and UF systems, ie, development of pressure during operation at constant flux, seems to be less complicated than in RO systems, since filtration is conducted in dead-end mode. Hence, the deposition factor Ω is 1.0, completely eliminating the need to measure Ω. Moreover, the MFI can be measured using the same membrane as applied in the full scale plant, so that Equation 2 can be applied to predict the development of the pressure during one cycle. Recently transparent exopolymer particles (TEP) have been identified as potential foulants in MF, UF and RO. These foulants, originating from algal activities and other aquatic life, have been overlooked by the industry for many decades. Villacorte 16 recently developed a method to semi-quantatively measure the concentrations of TEP down to a size of 10 kDa. A good correlation was observed between TEP10 kDa and MFI-UF measured Table 1: Deposi on factor measured with various MFI test membranes (PES) at a SWRO pilot plant, determined 11 May 2010. 10 Deposi on factor Ω Membrane, MWCO 100 kDa 0.23 50 kDa 0.29 10 kDa 5 kDa 0.20 0.45

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