Nanofiltration for Safe Drinking Water in Underdeveloped Regions – A Feasibility Study Sreenivasan Ramaswami, Zafar Navid Ahmad, Maximilian Slesina, Joachim Behrendt, Ralf Otterpohl Institute of Wastewater Management and Water Protection Hamburg University of Technology, Germany UNICEF & WHO (2015) 13th IWA Specialized Conference on Small Water and Wastewater Systems 1 15 September 2016 5th IWA Specialized Conference on Resources ‐ Oriented Sanitation
Is improved DW ‘safe’? Improved but not necessarily safe – Bain et al. 2012 www.un.org www.globalwaterforum.org • Improved DW as an indicator • Worldwide needs for safe drinking water are underestimated: billions of • Improved: Protected dugwell, people are impacted (Payen, 2011) public tap, borehole, piped supply, etc. • How safe are the global water coverage figures? Case study from Madhya • Unimproved sources: surface Pradesh, India (Godfrey et al., 2011) water, tanker truck, unprotected dugwell, bottled water, etc. • More than 1.8 billion worldwide! 13th IWA Specialized Conference on Small Water and Wastewater Systems 2 5th IWA Specialized Conference on Resources ‐ Oriented Sanitation
Other challenges 100% 3.6 1.1 1.8 0.71 47 80% 60% 40% 1,84 0,5 20% 0,45 0,09 0% 0,07 Papua New Madagascar Ghana Mozambique UK Guinea Typical low daily salary (in GBP) and the cost for 50L improved or safe water (in GBP) in some countries www.huffingtonpost.com [ based on WaterAid (2016) ] • High costs in developing countries • Challenges and risks for access • Chemical pollutants in water • Nearly 4 billion! (Payen, 2011) [ adapted from WaterAid (2016) ] 13th IWA Specialized Conference on Small Water and Wastewater Systems 3 5th IWA Specialized Conference on Resources ‐ Oriented Sanitation
Membrane processes for DW • Requirement for decentra- lised solution • Ultrafiltration cannot reject viruses, dissolved organics (insecticides, humics, etc.), heavy metals • Reverse osmosis requires high investment and opera- ting costs • Nanofiltration: better reject- ion than UF, 200 Da, lower Van der Bruggen et al. (2003) costs than RO • NF is used in industrialised countries for production of high quality DW 13th IWA Specialized Conference on Small Water and Wastewater Systems 4 5th IWA Specialized Conference on Resources ‐ Oriented Sanitation
NF for high quality DW Pollutant / [Sources] Findings Bacter-, fung-, herb- and pesticides Several NF membranes can remove many of these [Van der Bruggen et al., 2001; Košutić et compounds effectively. To pinpoint some, rejection al., 2005; Ogutverici et al., 2016; Pang et percentages up to 95, 94 and 92.5% have been reported for al., 2010; Saitúa et al., 2012; Sanches et triclosan, dichlorodiphenyl-trichloroethane and glyphosate by al., 2012] Ogutverici et al. (2016), Pang et al. (2010) and Saitúa et al. (2012) respectively. Emerging micro-pollutants (pharmac- Studies (including full scale in DWT plants) confirm that a eutical residues, hormones, endocrine wide spectrum of emerging pollutants can be retained by NF, disruptors, etc.) and pathogens better than conventional treatment powered with activated [Lopes et al., 2013; Radjenović, et al., carbon adsorption. Depending on the membrane properties 2008; Sanches et al., 2012; García- and the chemical characteristics of individual compounds, Vaquero et al., 2014; Yoon et al., 2007] the rejection capacities can range from about 30% to almost 100%. Harmful monovalent anions (nitrate, Some NF membranes can effectively reject nitrate as well as fluoride) fluoride ions. The main criteria for membrane selection [Van der Bruggen et al., 2001; Garcia et would be the pore diameter, besides the surface charge of the membrane. al., 2006; Shen and Schäfer, 2015] Heavy metal ions (As, Ni, Pb, U, etc.) Numerous studies (lab and pilot scale) report the ability of [Harisha et al., 2010; Košutić et al., 2005; NF to reject heavy metals from drinking water. Harisha et al. Maher et al., 2014; Favre-Réguillon et al., (2010) and Košutić et al. (2005) report rejection% of more 2008] than 85% for As using NF, which is not much different from the rejection capacity of RO. Natural organic matter Almost all NF membranes can remove humic substances [Costa and de Pinho, 2006; Ericsson et al., effectively without compromising on permeate flux unlike RO 1997] membranes. 13th IWA Specialized Conference on Small Water and Wastewater Systems 5 5th IWA Specialized Conference on Resources ‐ Oriented Sanitation
Aim of this work • Requirement for decentra- lised solution • Ultrafiltration cannot reject viruses, dissolved organics (insecticides, humics, etc.), heavy metals • Reverse osmosis requires high investment and opera- ting costs • Nanofiltration: better reject- ion than UF, 200 Da, lower Van der Bruggen et al. (2003) costs than RO Research question: • NF is used in industrialised Can a micro-enterprise using nanofiltration produce countries for production of safe drinking water at reasonable prices for a rural high quality DW area in a developing country? 13th IWA Specialized Conference on Small Water and Wastewater Systems 6 5th IWA Specialized Conference on Resources ‐ Oriented Sanitation
Ghana as reference country Ghana www.un.org • Several NGOs are working there already • Availability of literature 13th IWA Specialized Conference on Small Water and Wastewater Systems 7 5th IWA Specialized Conference on Resources ‐ Oriented Sanitation
Materials & Methods • Experiments with model groundwater • Feed – 15 mg TOC/L; 275 µS/cm • 750 W rotary vane pump – 800 L/h • Disc tube module with Dow NF270 with Experimental setup 1 m 2 membrane area • Temperature controlled at 14 o C • Seven concentration trials – at 7 bar – 120 L feed – water recovery ~88% • Cleaning: 0.1% NaOH and 0.2% HCl • Fouling experiment at 5 bar for 28 d RTS Rochem Technical Services GmbH ET-System 13th IWA Specialized Conference on Small Water and Wastewater Systems 8 5th IWA Specialized Conference on Resources ‐ Oriented Sanitation
Water flux - concentration trials 90 Flux at 25 o C (Lm -2 h -1 ) 75 Seven consecutive 60 concentration trials 45 without membrane 30 cleaning 15 0 0 3 6 9 12 15 18 21 Operation (h) 90 Temp. corrected flux (Lm -2 h -1 ) • Marginal difference in filtration trend 75 • Initial rapid decline – membrane compaction 60 • Low fouling – longer operation possible 45 • Concentration polarisation – insignificant 30 1 2 7 • 25% flux decline during the trial 15 • Average flux of about 52 Lm -2 h -1 at 7 bar 0 0 20 40 60 80 100 Water recovery (%) 13th IWA Specialized Conference on Small Water and Wastewater Systems 9 5th IWA Specialized Conference on Resources ‐ Oriented Sanitation
Rejections – concentration trials 105 105 Feed Retentate Permeate d 90 R 90 75 TOC (mg/L) P 75 60 TOC (mg/L) 45 60 30 45 15 30 0 1 2 3 4 5 6 7 15 Trial 0 0 20 40 60 80 100 1400 Feed Retentate Permeate d Water recovery (%) 1200 Conductivity (µS/cm) 1000 All permeate samples had 800 • < 2 mg TOC/L 600 • conductivities between 140-170 µS/cm 400 200 • pH between 7.2 and 8.2 0 1 2 3 4 5 6 7 Trial Poor rejection of nitrate ions by NF270 13th IWA Specialized Conference on Small Water and Wastewater Systems 10 5th IWA Specialized Conference on Resources ‐ Oriented Sanitation
Flux decline - fouling 60 Permeate flux at 25 o C (Lm -2 h -1 ) 50 40 30 20 10 0 0 3 6 9 12 15 18 21 24 27 30 Time (d) • Initially about 29% flux decline, thereafter about 40 Lm -2 h -1 at 5 bar • Water permeabilities of about 8 Lm -2 h -1 bar -1 possible for long durations • TOC in permeate samples were about 1.5 mg/L • Possibility to provide clean water during long continuous operation 13th IWA Specialized Conference on Small Water and Wastewater Systems 11 5th IWA Specialized Conference on Resources ‐ Oriented Sanitation
The micro-enterprise concept Micro-enterprise: <10 employees; annual turnover < €2 million 1. Water extraction 2. Pre-filtration (if needed) 3. Nanofiltration 4. (Re-)filling 5. Door-to-door delivery Ahmad (2015) Schematic of operations in a micro-enterprise 13th IWA Specialized Conference on Small Water and Wastewater Systems 12 5th IWA Specialized Conference on Resources ‐ Oriented Sanitation
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