Nanofiltration for Safe Drinking Water in Underdeveloped Regions A - - PowerPoint PPT Presentation

13th IWA Specialized Conference on Small Water and Wastewater Systems 5th IWA Specialized Conference on Resources‐Oriented Sanitation 1 15 September 2016

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 5th IWA Specialized Conference on Resources‐Oriented Sanitation 2

Is improved DW ‘safe’?

• Worldwide

needs for safe drinking water are underestimated: billions of people are impacted

(Payen, 2011)

• How safe are the global water coverage

figures? Case study from Madhya Pradesh, India

(Godfrey et al., 2011)

• More than 1.8 billion worldwide!

www.un.org www.globalwaterforum.org

Improved but not necessarily safe – Bain et al. 2012

• Improved DW as an indicator
• Improved:

Protected dugwell, public tap, borehole, piped supply, etc.

• Unimproved

sources: surface water, tanker truck, unprotected dugwell, bottled water, etc.

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Other challenges

• High costs in developing countries
• Challenges and risks for access
• Chemical pollutants in water
• Nearly 4 billion! (Payen, 2011)

www.huffingtonpost.com [ adapted from WaterAid (2016) ]

1,84 0,5 0,45 0,09 0,07 3.6 1.1 1.8 0.71 47 0% 20% 40% 60% 80% 100%

Papua New Guinea Madagascar Ghana Mozambique UK

Typical low daily salary (in GBP) and the cost for 50L improved or safe water (in GBP) in some countries

[ based on WaterAid (2016) ]

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Membrane processes for DW

Van der Bruggen et al. (2003)

• 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 costs than RO

• NF is used in industrialised

countries for production of high quality DW

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NF for high quality DW

Pollutant / [Sources] Findings Bacter-, fung-, herb- and pesticides [Van der Bruggen et al., 2001; Košutić et al., 2005; Ogutverici et al., 2016; Pang et al., 2010; Saitúa et al., 2012; Sanches et al., 2012] Several NF membranes can remove many

• f

these compounds effectively. To pinpoint some, rejection percentages up to 95, 94 and 92.5% have been reported for triclosan, dichlorodiphenyl-trichloroethane and glyphosate by Ogutverici et al. (2016), Pang et al. (2010) and Saitúa et al. (2012) respectively. Emerging micro-pollutants (pharmac- eutical residues, hormones, endocrine disruptors, etc.) and pathogens [Lopes et al., 2013; Radjenović, et al., 2008; Sanches et al., 2012; García- Vaquero et al., 2014; Yoon et al., 2007] Studies (including full scale in DWT plants) confirm that a wide spectrum of emerging pollutants can be retained by NF, better than conventional treatment powered with activated carbon adsorption. Depending on the membrane properties and the chemical characteristics of individual compounds, the rejection capacities can range from about 30% to almost 100%. Harmful monovalent anions (nitrate, fluoride) [Van der Bruggen et al., 2001; Garcia et al., 2006; Shen and Schäfer, 2015] Some NF membranes can effectively reject nitrate as well as fluoride ions. The main criteria for membrane selection would be the pore diameter, besides the surface charge of the membrane. Heavy metal ions (As, Ni, Pb, U, etc.) [Harisha et al., 2010; Košutić et al., 2005; Maher et al., 2014; Favre-Réguillon et al., 2008] Numerous studies (lab and pilot scale) report the ability of NF to reject heavy metals from drinking water. Harisha et al. (2010) and Košutić et al. (2005) report rejection% of more than 85% for As using NF, which is not much different from the rejection capacity of RO. Natural organic matter [Costa and de Pinho, 2006; Ericsson et al., 1997] Almost all NF membranes can remove humic substances effectively without compromising on permeate flux unlike RO membranes.

13th IWA Specialized Conference on Small Water and Wastewater Systems 5th IWA Specialized Conference on Resources‐Oriented Sanitation 6

Aim of this work

Van der Bruggen et al. (2003)

• 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 costs than RO

• NF is used in industrialised

countries for production of high quality DW Research question: Can a micro-enterprise using nanofiltration produce safe drinking water at reasonable prices for a rural area in a developing country?

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Ghana as reference country

• Several NGOs are working there already
• Availability of literature

Ghana

www.un.org

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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

1 m2 membrane area

• Temperature controlled at 14oC
• 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

Experimental setup ET-System

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Water flux - concentration trials

• Marginal difference in filtration trend
• Initial rapid decline – membrane compaction
• Low fouling – longer operation possible
• Concentration polarisation – insignificant
• 25% flux decline during the trial
• Average flux of about 52 Lm-2h-1 at 7 bar

15 30 45 60 75 90 3 6 9 12 15 18 21

Flux at 25oC (Lm-2h-1) Operation (h)

15 30 45 60 75 90 20 40 60 80 100

• Temp. corrected flux (Lm-2h-1)

Water recovery (%)

1 2 7

Seven consecutive concentration trials without membrane cleaning

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Rejections – concentration trials

All permeate samples had

• < 2 mg TOC/L
• conductivities between 140-170 µS/cm
• pH between 7.2 and 8.2

Poor rejection of nitrate ions by NF270

15 30 45 60 75 90 105 1 2 3 4 5 6 7

TOC (mg/L) Trial

Feed Retentate Permeate d 200 400 600 800 1000 1200 1400 1 2 3 4 5 6 7

Conductivity (µS/cm) Trial

Feed Retentate Permeate d 15 30 45 60 75 90 105 20 40 60 80 100

TOC (mg/L) Water recovery (%)

R P

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Flux decline - fouling

• Initially about 29% flux decline, thereafter about 40 Lm-2h-1 at 5 bar
• Water permeabilities of about 8 Lm-2h-1bar-1 possible for long durations
• TOC in permeate samples were about 1.5 mg/L
• Possibility to provide clean water during long continuous operation

10 20 30 40 50 60 3 6 9 12 15 18 21 24 27 30

Permeate flux at 25oC (Lm-2h-1) Time (d)

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Schematic of operations in a micro-enterprise

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)

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Economic evaluation

1 - personal communication, 2 - www.alibaba.com, 3 - www.ecgonline.info, 4 - Ghana Statistical Service (2014)

• Existence of a well or bore-hole
• Life of ET-System: 4 years (27000 hours)
• 20 hours of operation per day and CIP once in two weeks
• 6720 operating hours per year
• Water flux of 60 Lm-2h-1 at 8 bar – about 403 m3 clean water per year
• Investments for land, mechanical, electrical, etc. / Misc. expenses & taxes

Fixed costs - for first 4 years Variable costs One-time investment Cost (in €) For 4 yrs. (in €) ET-System (trade discount possible) 3000-45001 For electricity (€0.3 per kWh) 60503 20 L water containers (250 nos.) 5002 For chemicals (€2.6 per month) 125 Delivery vehicle (tricycle cart) 5002 Personnel cost (one employee) 30004 Initial investment for 4 yrs. (total) 4000 Total variable costs 9175 Fixed costs (for every 4 yrs.) after first 4 yrs. Revenue for 4 yrs. (in €) Motor plus pump (aft-shop.de) 500 Water cost (€0.01 per L) 16,125 Membrane (replacement, RTS) 1501 Total fixed cost after first 4 yrs. 650

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Conclusion

• Nanofiltration can produce safe drinking water at low prices ( < €0.01 per litre )
• With a 1m2 unit, production capacities of 1200 litres clean water per day
• NF permeate for drinking and cooking needs
• Micro-enterprise employing NF can be a solution for economic water scarcity

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Sreenivasan Ramaswami, M.Sc.

Doctoral researcher Hamburg University of Technology Institute of Wastewater Management and Water Protection Hamburg, Germany Email: sreeni@tuhh.de Website: www.tuhh.de/aww