Development of a mobile water maker, a sustainable way to
produce safe drinking water in developing countries
L. Groendijka�, H.E. de Vriesb
aDepartment of Environmental and Water Technology, Van Hall Larenstein, Part of Wageningen
University and Research, Post Box 1528, 8901 BV Leeuwarden, The Netherlands
Tel. þ31 58 2846215; Fax þ31 58 2846423
email: [email protected] Water management BV, Smidsstraat 7, 8601 WB Sneek, The Netherlands
Tel. þ31 515 482811; Fax þ31 515 424156
email: [email protected], www.mobilewatermaker.com
Received 31 January 2008; revised accepted 15 May 2008
Abstract
Moreover, there is a growing demand for a simple, low capacity drinking water treatment used by local people in developing
countries to reduce mortality caused by water born diseases. To solve this problem a small portable water treatment unit with a
production capacity of approximately 500 L/day was developed. The unit can operate without the use of external electricity/
pumps/generators in order to operate completely independent. The mobile water treatment unit uses tubular ceramic membranes
in combination with an anodic oxidation process, powered by a solar power panel. The membranes are cleaned by simple flushing
without the use of chemicals and this enables a sustainable production of safe drinking water on every location in the world without
replacing polluted filter cartridges. Laboratory tests with several kinds of surface water and effluent of a wastewater treatment
plant (WWTP) showed a very stable production and gave very good results in the removal of sediments, colloidal material, bacteria
and viruses.
Keywords: UF membrane filtration; Disinfection; Solar energy; Sustainable Mobile Water Maker
1. Introduction
Unsafe drinking water is the main contribution to
an estimated 4 billion cases of diarrhea each year, caus-
ing 1.8 million deaths mainly among children younger
than 5 years [1]. Even at locations where water is safe
at the source, it is often contaminated during tapping,
collection, storage and use unless it is protected by resi-
dual disinfection.
Safe drinking water is more and scarcer because of
the growing demand and diminishing resources in a lot
of developing countries. Also the growth of population
causes problems in the availability of clean and safe
drinking water.
Besides the amount of water, also the water quality
is a growing problem because the lack of good� Corresponding author.
Presented at the Water and Sanitation in International Development and Disaster Relief (WSIDDR) International
Workshop Edinburgh, Scotland, UK, 28–30 May 2008.
0011-9164/0x/$– See front matter # 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.desal.0000.00.000
Desalination 251 (2010) 106–113
sanitation. Contamination of water sources by feces
and other excrements is a very serious problem in
developing countries.
With the use of ultra filtration (UF) membranes,
combined with disinfection, bacteria and viruses are
removed from the water resulting in safe drinking
water free from water borne diseases.
Main research question is how to design a good
stand-alone membrane filtration system which oper-
ates without the use of pumps, electricity and chemical
cleaning agents for the membranes so that the system
can work independent from the delivery of spare parts
and electrical generators. A lot of systems are available
but most of times you are depending on disposable fil-
ters, cartridges or disinfecting or membrane cleaning
chemicals [6].
The main problem with membrane filtration sys-
tems is fouling of the membranes. Bio-fouling, cake
formation, pore blocking and adsorption of fouling
substances are serious problems which are generally
solved with the use of several techniques like mechan-
ical and chemical cleaning. For mechanical cleaning
periodical backwash combined with cross flow, air
flush and forward flush steps are generally used. Che-
micals for cleaning are often not available so this tech-
nique can cause problems because the lack of these
chemicals in the country. Also the costs of cleaning
agents are very high.
Beside this biological contamination which is fully
removed, there is also the possibility of chemical pol-
lution in the feed water. In this research this aspect is
not considered because this needs treatment with use
of, for example, activated carbon or high energy
demanding reverse osmosis filtration. If the water is
polluted with harmful toxic chemicals the unit will not
be producing safe water.
2. Experimental setup
In the laboratory of Van Hall Larenstein, a mem-
brane filter test unit including an anodic oxidation unit
was built up in sections. The feed water was supplied
via a tank a few meters above the module. The unit was
tested with polluted water from different sources.
Various UF membranes with a pore size between
10 and 100 nm were tested with respect to their fouling
behavior.
At the end a 40 nm tubular ceramic membrane
module (Hyflux Ceparation) was selected for further
research because of the easy way of cleaning this mem-
brane and her mechanical strength.
Hollow fibers, operated outside in appeared very
difficult to clean after only a few hours of production.
Flat sheet Kubota submerged membranes clogged very
quickly and were difficult to clean without continuous
air scouring or mechanical brushing.
The UF membrane unit was operated in a dead-end
configuration which means that all the water which
enters the module has to pass the membrane. Particles
bigger than the pore size of the membrane are retained
inside the membrane tubes in the module.
The study was carried out with a feed water storage
tank at a level of 3 m above the membrane filtration unit
which results in a constant Trans Membrane Pressure
(TMP) of 0.3 bar. In the lab experiments, feed water
was supplied from a 6 m3 underground storage tank out-
side the building. The level in the feed water tank was
kept constant by a level controller which could switch
on/off a centrifugal pump connected to the storage tank.
A drawing of the test unit is shown in Fig. 1.
All the valves, including the clean water tap, are
manually operated by hand. The bicycle pump is con-
nected by a quick fit connector to the air pressure con-
tainer. The pressure indicator on this container is not
drawn in the figure. The control box is controlling the
charging of the battery with the solar power panel and
also controls the disinfection level of the filtered water.
2.1. The feed water
The water used in the tests was surface water from
the Prinses Margriet channel near the city of Leeuwar-
den. Besides surface water, tests were also done with
effluent from the WWTP of the city of Leeuwarden.
Before the raw feed water was pumped from the
outdoor underground storage tank into the water supply
tank inside the laboratory it passed a raw filter nylon
screen of 0.13 mm to remove big particles from the
water such as leaves, frogs, fishes, snails and other
material which could clog the membrane inlet tubes.
The membrane unit was connected to the raw water
storage with use of Ø40 mm hoses.
The unit was provided with three valves in order to
be able to clean the membranes with a backwash and
forward flush (see Fig. 1).
L. Groendijk, H.E. de Vries / Desalination 251 (2010) 106–113 107
2.2. Membrane module
The membranes used in the test were Hyflux
Ceparation ceramic tubular UF membranes [2]. Pore
size is 40 nm and clean water permeability according
to the specification of the supplier 500 l/m2 h bar. The
inner tube diameter is 2.8 m. The membrane module
contained 210 tubes with an effective length of 43
cm resulting in a membrane area of 0.8 m2 [2]. The
membrane insert was built in a normal PVC housing,
built up from general available sewer PVC materials.
If the production tap is closed, the permeate vessel
besides the unit is filled by gravity and in this way
about 10 L of permeate becomes available for a back-
wash flush. A back flush is a high permeate water flow
through the pores of the membrane to the raw water
side in the tubes. Production is inside out and backwash
is outside in.
2.3. The disinfection unit
The permeate of the membrane unit flows to a
2Bsure disinfection unit, working as anodic oxidation
system. This 2Bsure unit was developed by Bright
Spark, Joure, The Netherlands. A couple of elec-
trodes are built in a PVC pipe and this reactor is
responsible for the disinfection of the water. The dis-
infection unit is powered by a 6 V battery. The
2Bsure unit is switched on when the water tap is
opened, so in case no water is produced, no electri-
city is used.
The permeate from the membrane filtration unit
was treated with use of anodic oxidation. During this
process an electrical field (low voltage) between two
electrodes, a cathode (�) and anode (þ) will generate
some chemical reactions. In the water also some chlor-
ide is present.
Membrane filter Tap with switch
Feed water storagebag/ tank 50 – 300 l
Valve
Forward flush valve
Disinfectionunit
Clean water
Pressure vessel air
Bicycle pump
Solar panel
Battery 6 V Control box
One way valve
Push valve
Fig. 1. Experimental laboratory test set up.
108 L. Groendijk, H.E. de Vries / Desalination 251 (2010) 106–113
At the anodic reaction chloride (Cl�) en hydroxide
(HO�) ions flow towards the anode where they will
oxidize.
At the anode chloride and hydroxyl radicals will be
formed which combine to the disinfectant hypochlor-
ous acid (HOCl), a strong and fast-acting oxidizer.
Microorganisms will be damaged by the HOCl.
The HOCl kills a variety of germs and is therefore
widely used to disinfect drinking water. A further
advantage is that the germs do not become resistant
to the sodium hypochlorite.
The disinfectant returns only to his original form
(NaCl) when the radical oxygen atom is exchanged.
Advantage of disinfection with HOCl is that there
is also a post-disinfection after the water will leave the
Mobile Water Maker. Storage tanks and bottles are dis-
infected with the produced water and recontamination
will be reduced [3,4].
2.4. Energy for disinfection
The energy, needed for the anodic oxidation is gen-
erated by a solar panel of 15 pW. This 12 V solar panel
charges a battery in the system which will store enough
energy for a few days of production. So the system is
self supporting with energy.
If 220 V AC is available the unit can be charged and
operated without solar energy. Also an external 12 V
car battery can be used.
3. The tests
3.1. Laboratory tests
The filtration unit is operated during 10 h a day to
simulate the operation in practice (see Table 1). In the
morning the module is first backwashed with a little
amount of permeate from the housing of the membrane
module. The driving force for this backwash is gener-
ated by an air pulse from a compressed air container in
the unit. The compressed air container is pumped up to
a pressure of about 4–6 bar with use of a hand powered
bicycle pump. During the forward flush with feed
water a few pulses compressed air are released to the
permeate side of the membrane. During this backwash
the water tap is closed so the permeate will be pumped
backwards to the feed side of the membrane. After
this hydraulic cleaning step, the unit is switched on for
production. During the day some interruptions in the
production are simulated by closing the tap valve.
The permeate flow out of the unit is measured and
registered automatically with a magnetic flow meter.
This meter is calibrated by hand with a flask and a stop-
watch. The signal of the magnetic flow meter is
recorded in a data logger and stored in an excel file.
Samples of the feed water and the permeate were
analyzed by the Dutch Water Company Vitens. Samples
of the permeate were taken before and after disinfection.
The running time is limited to 10 h a day and the
filtration tests went on for about 52 weeks.
The course of the permeate flow during the filtra-
tion runs gives an indication for the fouling behavior
of the membranes.
The concentrate or brine was drained into the sewer.
3.2. Field tests
In October 2006, a first prototype of the unit was
used for a short field test for 2 weeks at
Restaura&ion, a village at the Dominican Republic
(Fig. 2). A group of field workers of World Servants
Europe, young people in the age of 20–30 years, tested
the unit under field conditions. During this field test a
lot of practical problems were encountered and the
results were used to improve the prototype.
The feed water came from the river beside the camp
and the quality of the feed water was varying a lot
because of heavy rain weather from time to time.
Table 1
Procedure of operating the unit
08.00 am
Pulsed backwash with permeate combined with a feed
water forward flush
08.03 am
Start production of permeate during the day with
continuous filtration or sometimes with an start stop
program that simulates the use by a person several times
a day
17.00 pm
Stop production, closure of the tap water valve
17.00 pm–8.00 am
Relaxation during the night till pulsed backwash at 8.00 in
the morning
L. Groendijk, H.E. de Vries / Desalination 251 (2010) 106–113 109
In the first water maker, the solar panel was inte-
grated in the housing of the unit. This meant that the
unit must be placed in the sunshine during the day.
Now the panel is separated from the water maker; it
is connected with a 20 m long cable to the unit so the
unit can be installed inside a building.
The electrical unit in the housing caused also pro-
blems because of the inflow of rainwater during stormy
weather and heavy rainfall that was not foreseen. So the
electrical circuit was better insulated in the next
prototype.
Also the transport of a few hundred liters of water to
the vessel at 3 m height appeared a hard job. For that
reason a simple hand pump with a capacity of 30 L/min
is incorporated in the unit.
4. Results
4.1. Filtration tests with effluent water
The membrane and disinfection units were tested in
the laboratory during 4 months with effluent water as
feed water. This effluent was stored in 6 m3 under-
ground storage tank and pumped up to the feed vessel
at 3 m height above the filtration unit.
As can be seen in Figs. 3–5 there is a slow decrease
in permeate production rate during the day. At the end
of the day the unit was stopped and after relaxation dur-
ing the night the production was started again in the
morning with a pulsed backwash and forward flush.
This relaxation and cleaning operation appeared suffi-
cient to increase the production rate again to the initial
0
1
2
3
4
5
6
0
1.5 3
4.5 6
7.5 9
10.5 12
13.5 15
16.5 18
19.5 21
22.5 24
Time (h)
Pro
du
ctio
n (L
/min
)
Fig. 4. The production rate in case the filtration is started
at 8 am without a pulsed backwash on 22/04/2006 and
without a forward flush. Production rate is lower without
the backwash.
Fig. 2. On the left picture the first Mobile Water Maker prototype during the field test in Restaura&ion in the Dominican
Republic in October 2006. On the right picture the second prototype in November 2007 [5].
0
1
2
3
4
5
6
0
1.5 3
4.5 6
7.5 9
10.5 12
13.5 15
16.5 18
19.5 21
22.5 24
Time (h)
Pro
du
ctio
n (L
/min
)
Fig. 3. The production rate during a standard day, 21/11/
2006. Filtration starts at 8 am is started with a pulsed
backwash combined with forward flush.
110 L. Groendijk, H.E. de Vries / Desalination 251 (2010) 106–113
value of the day before. This indicates that the fouling
which is build up on top and/or inside of the mem-
branes during the continuous filtration is reversible and
easy to remove.
Obviously, a flux of 60 L/m2 h (permeability 250 L/
m2 h bar) is easy to handle for ceramic membranes with
this kind of feed solution. A permeability of 250 L/m2 h
bar on effluent is only a factor 2 lower than the clean
water permeability of the membrane. This is also an
indication of the low fouling behavior under these
process conditions.
Figs. 3–5 show the influence of the relaxation per-
iod during the night and the hydraulic backwash and
forward flush on the production rates. The measure-
ments show the filtration behavior for three subsequent
days with a constant influent water quality.
After the initial start up on the day, the production
rate gradually decreases from 1.5 to 1 L/min.
Comparing Figs. 3 and 4 it is shown that the initial
backwash and forward flushes give raise to higher
production rates during the day.
Intermediate pulsed backwash flushes do not give
rise to higher production rates (see Fig. 5).
Relaxation over a prolonged period of time fol-
lowed by a combined forward and backwash flush seem
the best procedure for long-term sustainable operation.
Optimum time for relaxation and hydraulic clean-
ing are not yet investigated.
Fig. 6 shows the initial (morning) and final (after-
noon) flow rates during 2 months of operation with
surface water.
It can be seen that the initial flow rates are stable
over this period (flow at 30/11/2006: 72 L/h; flow at
30/01/2008: 72 L/h).
At some days lower values are obtained. This is
caused by skipping the pulsed backwash but only doing
a forward flush in the morning. Later this procedure
was improved by adding the pulsed back flush again
and the original initial flow rates were established
again. If a backwash after relaxation is not carried out
the production rate stays low. This is visible in the end
of Fig. 6.
0,00
10,00
20,00
30,00
40,00
50,00
60,00
70,00
80,00
90,00
100,00
30−11
−2007
1−12
−2007
2−12
−2007
03/12
/"07
04/12
/"07
05/12
/"07
06/12
/"07
07/12
/"07
11/12
/"07
12/12
/"07
17/12
/"07
18/12
/"07
14/01
/"08
16/01
/"08
21/01
/"08
28/01
/"08
30/01
/"08 2
Date
Pro
du
ct fl
owra
te in
L/h
Initial flow rate Final flow rate
No backwash
No backwash
Fig. 6. Initial (blue) and final (purple) daily flow rates during two months of production with surface water of the Prinses
Margriet channel.
0
1
2
3
4
5
6
0
1.5 3
4.5 6
7.5 9
10.5 12
13.5 15
16.5 18
19.5 21
22.5 24
Time (h)
Pro
du
ctio
n (L
/min
)
Fig. 5. Filtration is started on 23/04/2006 with a combined
pulsed backwash and forward flush. During the day at
14.00 pm an extra pulsed backwash and forward flush was
carried out but did not have the right effect.
L. Groendijk, H.E. de Vries / Desalination 251 (2010) 106–113 111
4.2. Chemical and biological analyses of the
laboratory tests
The influent water and purified water is analyzed
periodically by the Vitens water company laboratory.
All samples are taken with a disinfection rate which
resulted in a 0.2 mg/L free chlorine in the produced
water. In Table 2 the results of the test with surface
water are presented.
5. Conclusions
The Mobile Water Maker can be used to produce
drinking water from biological polluted surface water.
Besides membrane filtration a disinfection step with
using in line anodic oxidation for the production of
hypochlorite is used in the treatment process. This dis-
infection also results in a post-disinfection of the water
collection containers.
Rejections of all kind of bacteria are high (>99%).
More accurate removal efficiencies can not be pre-
sented because the initial influent values for the content
microorganisms are not counted exactly. Only results
as >1000 are presented by the laboratory. The turbidity
of the permeate is very low, indicating that the perme-
ate is a clear solution without particles. The CFU of the
permeate sample is <100/mL. The WHO standard is
<100/mL [1]. The mean indicator for faecal pollution
E. coli says that there is a total removal of these bac-
teria. In the permeate the amount of Adsorbed Organic
Halogenated Compounds (AOX) increased through
the use of anodic oxidation. The free chlorine concen-
tration in the permeate is 0.2 mg/L so it will indicate
that the bacteria will be killed [5].
A sufficient relaxation period and a pulsed hydrau-
lic backwash and forward flush are sufficient to
prevent the ceramic membranes against fouling. A
hydraulic cleaning combined with a backwash is not
sufficient if a relaxation time of several hours is left.
Long-term test show no decrease of flow rate caused
by any fouling during 1 year of operation, even with
some breaks without production in summer holiday
(4 weeks) and Christmas holiday (3 weeks). No chemi-
cals and electricity from generators have to be used. A
15 peak Watt solar panel used at 1 day sunshine is big
enough to provide enough back up energy for 3 days
water production. With a 0.8 m2 ceramic tubular UF
module, a water column of 3.5 m is sufficient to
produce continuously 60 L/h. In more than 2 years
no parts have been replaced or repaired so the system
seems to be very reliable. A prototype of the complete
system is produced. The technical features are pre-
sented in Table 3 [5].
The produced water has an excellent quality and, if
no chemical pollutants are present, the water meets the
WHO standard for drinking water [1].
In combination with a built in activated carbon
filter stage the chemical pollutants can be removed
from the produced permeate. To avoid necessary
Table 2
The analytical results of the influent (surface water) and
produced water
Sample Influent
surface
water
Permeate
after
disinfection
Rejection
(%)
pH 8.5 8.5 –
Temperature 17 18 –
HCO3� (mg/L) 213 223 –
Turbidity (FTE) 100 <0.2 >99.8
Color
(mg Pt/Co/L)
51 49 4
Dissolved
oxygen
(mg/L)
9.5 10.1 –
Sulfate (mg/L) 59 64
Coli forms 37�C(#/100 mL)
>275 <1 >99.7
Escherichia coli
(#/100 mL)
>600 <1 >99.8
Clostridia
(#/100 mL)
>300 <1 >99.7
Aeromonas
30�C(#/100 mL)
>600 <1 >99.8
CFU 22�C(#/mL)
>1000 23 >97.7
Bacteriophages
(pve)
<1 <1 –
Na (mg/L) 73 71.2 2.5
Fe (mg/L) 2.96 <0.02 >99.3
Mn (mg/L) 0.148 <0.01 >99.3
AOX (mg/L) 49 77 �57
TOC (mg/L) 19 13 31.5
DOC (mg/L) 26 13 50
Free Cl2 (mg/l) 0 0.2 –
112 L. Groendijk, H.E. de Vries / Desalination 251 (2010) 106–113
replacement of any carbon filters during operation this
technique is not applied because most water born dis-
eases are caused with using biological polluted water.
Acknowledgements
This research was funded by Technology Centre
North Netherlands in 2006–2008.
The author wishes to thank Prof. Dr. Walter van der
Meer from Vitens Water Company (analyses), Harry
van Dalfsen from Hyflux – Ceparations Liquid (cera-
mic module) Tjerk Kaastra from Bijl en de Jong (mem-
brane housing) and Maurice Tax from Bright Spark
(2Bsure disinfection unit) for the support during this
feasibility research.
Dr. Arie Zwijnenburg from Wetsus Technological
Top Institute Water is thanked for the stimulating dis-
cussions about membrane filtration and his contribu-
tion to this paper.
References
[1] http://www.who.int, March 2008.
[2] http://www.ceparation.com, February 2008.
[3] http://www.gallep.nl/ppt/2B_Sure_UK.ppt, February
2008.
[4] http://www.brightspark.nl, February 2008.
[5] http://www.mobilewatermaker.com, February 2008.
[6] Water purifier essential for hurricane preparedness, J.
Membr. Technol., September 2006.
Table 3
Features of the prototype Mobile Water Maker
Technical specifications:
Production capacity 300–600 L/day (10 h)
Power consumption 2 W
Solar panel capacity 20 pW
Battery capacity 7 Ah
Electrical connectors: Additional external 220 V AC
Additional external 12 V DC
(XLR 3 pin connector male)
Solar panel connector (XLR 3
pin connector male)
Premium filter Ceramic Tubular Filter HC08
Disinfection module Bright Spark Module 2BSafe 1
L/min
Regeneration time Once at every 24 h
Recovery 98%Tube fittings GEKA fast fit connectors
Body of the case Polymer Foamed Hood
Flight case material Alumina and stainless steel
Dimensions H � D � W (75 � 40 � 40) cm
Color case Blue, grey, red, black
Weight 22 kg
Wheels 2 rubber wheels 100 mm
Accessories 40 mm rubber coated flexible
tubes
Water source Surface water, biologically
polluted
Treatment efficiency:
E. coli 37 >99.999%E. coli >99.999%Enterococs >99.99%Total count 22�C >99.99%Total count 37�C >99.99%Chlorine in treated water <0.2 ppm
Turbidity <1 NTU
L. Groendijk, H.E. de Vries / Desalination 251 (2010) 106–113 113