Urine concentration by forward
osmosis process
Takeru Maeda, Benedicte Carolle Nikiema, Guizani
Mokhtar, Ryusei Ito, Naoyuki Funamizu
Laboratory on Engineering for Sustainable Sanitation, Graduate
school of Engineering, Hokkaido University, Japan
The 13th IWA specialized conference on small
water and wastewater systems
The 5th IWA specialized conference on resources-
oriented sanitation
September 14th~16th, 2016
Nutrients in human urine 2)
N:12 g/L
P:1.0 g/L
K:2.0 g/L
Introduction 2
The demands of the major nutrients
(N, P, K) for fertilizers are increasing.
The nutrients are produced from
mining minerals and fossil fuels
which are limited resources.
Global consumption of nutrients (N+P2O5+K2O)1)
1) FAO, 2015 2) Wilsenach et al., 2007
Annual nutrients discharge
N:32 Mtons (27%)
P2O5:6.1 Mtons (13%)
K2O:6.4 Mtons (19%)
7.3 billions
Human urine can contribute to the nutrient resources.
Urine excretion
1.0 L/person/day
27 34
39 47
104
119
0
50
100
150
200
N+
P2O
5+
K2O
[M
ton
s]
N
P2O5
K2O
Human urine has a potential to saving the natural resources.
Farmlands
Introduction 3
Urine volume reduction is important
for reducing collection and transportation cost.
Urine collection system Urban area
Urine storage
Collection Transportation
Peri-urban area
Collection and transportation cost of urine is
huge owing to its volume.
Evaporative concentration (Masoom., 2008)
Electro dialysis (Pronk et al., 2006)
Reverse osmosis (RO)
Forward osmosis (FO)
Introduction
Seawater desalination
Wastewater treatment
Food processing
4) Cath et al., 2006
4
Simple system for urine concentration
A low energy consumption
A low fouling tendency
Applications in FO process 4)
Advantage
Concentration systems of urine
Introduction
Concentration level Osmotic pressure (POsm)
[MPa]
Fresh urine
(pH5.3 – 5.5)
1 1.9
2 3.6
5 8.2
Urea hydrolyzed
urine
(pH9.5 – 9.6)
1 3.1
2 6.0
5 12
5) Oishi., 2013
A draw solution requires high solute
concentration for urine volume reduction.
The osmotic pressure of concentrated fresh
urine has higher than that of seawater*.
* Osmotic pressure of seawater is 2.5 [MPa].
5
Osmotic pressure and concentration level 5)
Introduction 6
Sucrose is a candidate for a draw
solution.
0
100
200
300
400
500
0 1 2 3
Vis
co
sity
[m
Pa・s]
Concentration [mol/L]
Sucrose solution has a very high
viscosity at the high concentration.
The high viscosity gives a thick
boundary layer.
It is easy to obtain and a food additive.
To study
Feasibility of urine concentration with sucrose draw
solution in FO process
Effect of concentration of sucrose on overall water
permeability
Objectives
Draw solution
2.1 3.6 5.2
Osmotic pressure [MPa] 0
Theory 7
𝐽𝑤 = 𝑃∆𝜋 = 𝑃𝑅𝑇 𝑎𝑖,𝑑𝑟𝑎𝑤 − 𝑎𝑖,𝑓𝑒𝑒𝑑𝑖𝑖
Water flux
𝐽𝑤 = −𝐷𝑑𝐶
𝑑𝑥= −𝑘∆𝑥
𝑑𝐶
𝑑𝑥
Diffusion and convection as equation
where
𝐽𝑤 is water flux [m/s], 𝑃 is a water permeability coefficient [m/s/Pa], ∆𝜋 is a difference of osmotic pressure [Pa], 𝑅 is
the gas constant [J/K/mol], 𝑇 is a temperature [K], 𝑎𝑖 is an activity of component 𝑖 in the draw or feed solution [mol/m3], 𝐶 is a concentration in the draw or feed solution [mol/m3], 𝐷 is a diffusion coefficient [m2/s], 𝑘 is an
overall mass transfer coefficient [m/s], and ∆𝑥 is a thickness of the membrane and the boundary layer.
Profile of concentration in membrane
∆𝑥
Theory 8
𝑆ℎ =𝑘𝐿
𝐷
The Sherwood number
𝑆𝑐 =𝜇
𝜌𝐷
The Schmidt number
The Reynolds number
𝑅𝑒 =𝜌𝜈𝐿
𝜇
𝑆ℎ = 0.664𝑆𝑐1/3𝑅𝑒1/2
The equation for Sh calculation
where
𝐶 is a concentration in the draw or feed solution [mol/m3], 𝑘 is an overall mass transfer coefficient in boundary
layer [m/s], 𝐿 is a characteristic length [m], 𝐷 is a diffusion coefficient [m2/s], 𝑆𝑐 is the Schmidt number [-], 𝑅𝑒 is
the Reynolds number [-], 𝜇 is a viscosity coefficient [Pa・s], 𝜌 is a density of solution [kg/m3], and 𝑣 is a flow
velocity of solution at the membrane surface [m/s].
Profile of concentration in membrane
∆𝑥
Material & methods: Run 1 9
Schematic diagram of FO test
Run 1
− Feed solution: Synthetic urine* (pH5.8)
− POsm: 1.6 MPa, 500 mL
− Draw solution: Sucrose
− 2.5 mol/L (POsm: 4.8 MPa), 200 mL
Salt Concentration
[mol/L]
MgCl2・6H2O 0.0032
NaCl 0.079
Na2SO4 0.016
KCl 0.022
CaCl2・H2O 0.0044
KH2PO4 0.031
NH4Cl 0.019
(NH2)2CO (urea) 0.42
*Composition of synthetic urine
Flow direction Co-current
Cross flow rate 14 L/hr
Membrane
surface area 98 cm2
FO test
Measurement
− Ions by an ion chromatograph analyzer
− Urea by a LC/MS system
− Sucrose by a TOC analyzer
Results & discussion: Run 1 10
0
0.5
1
1.5
2
2.5
3
0 2 4 6 8 10
Time [hr]
0
0.1
0.2
0.3
0.4
0.5
0 2 4 6 8 10
Time [hr]
Concentrations of solutes in feed and draw solutions
0
0.1
0.2
0.3
0.4
0.5
0 2 4 6 8 10
The concentrations of the ions in feed solution were
increasing, while that of the sucrose in draw was diluted.
The concentration of urea was slightly decreased in feed
solution and increased in draw solution.
◆Urea □Sucrose ▲Na+ ×Cl- *K+ ○NH4+ +PO4
3- Ca2+ ‐Mg2+ ◇SO4
2-
Co
nc
en
tra
tio
ns
in
fe
ed
[m
ol/
L]
Co
ncen
trati
on
s in
dra
w [
mo
l/L]
Urea Urea
Ions
Ions Sucrose
Results & discussion: Run 1 11
Mass balances of urea and ammonium ion
Urea permeated from feed solution to draw solution.
Ammonium ion did not pass through the membrane.
0
0.05
0.1
0.15
0.2
0.25
0 1 2 3 5 8
Ure
a [
mo
l]
Time [hr]
Draw Feed
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0 1 2 3 5 8
NH
4+ [
mo
l]
Time [hr]
Urea hydrolysis can contribute to concentration of nitrogen.
Results & discussion: Run 1 12
Effect of osmotic pressure difference on water flux
Water flux is proportional to the
difference of osmotic pressure.
A diffusion in a boundary layer should be considered for
the water permeability.
𝐽𝑤 = 𝑃∆𝜋
Water flux
But the water flux did not follow the liner correlation at the large
osmotic pressure difference.
0
0.2
0.4
0.6
0.8
1
1.2
0 0.5 1 1.5 2 2.5 3 3.5
Wate
r fl
ux
[1
0-6
m/s
]
Δπ [MPa]
y = 0.465 x
R2 = 0.965
The water flux was a linear correlation for the small osmotic pressure
difference.
But the water flux did not follow the linear correlation at the large
osmotic pressure difference.
Material & methods: Run 2 13
Schematic diagram of FO test
FO test
Run 2
− Feed solution: Deionized water
− 500 mL
− Draw solution: Sucrose
− 0.4, 0.5, 1.0, 2.0, and 2.6 mol/L, 250 mL
𝑃 =𝐽𝑤∆𝜋
𝐽𝑤 = 𝑃∆𝜋
To calculate water permeability
Calculation
Cross flow rate 14 L/h
Flow direction Co-current
Membrane
surface area 98 cm2
0
0.2
0.4
0.6
0.8
1
0 0.5 1 1.5
Wate
r fl
ux
[1
0-6
m/s
]
Concentration [mol/L]
Results & discussion: Run 2 14
Effect of sucrose concentration on water permeability
The high concentration of sucrose in draw solution gave a
low water permeability.
0
2
4
6
8
10
12
0 0.5 1 1.5 2 2.5 3Wate
r p
erm
eab
ilit
y [
10
-13m
/s/P
a]
Concentration [mol/L]
Water permeability
Results & discussion: Run 2 15
Effect of sucrose concentration on water permeability and
overall mass transfer coefficient
The overall mass transfer coefficient had a similar trend to
the water permeability.
The results suggested the relationship between the overall
mass transfer coefficient and the water permeability.
0
1
2
3
4
5
6
7
0
2
4
6
8
10
12
0 0.5 1 1.5 2 2.5 3
Overa
ll m
ass
tra
nsf
er
co
eff
icie
nt
[10
-5m
/s]
Wate
r p
erm
eab
ilit
y [
10
-13m
/s/P
a]
Concentration [mol/L]
Water permeability
Mass transfer coefficient
Conclusions 16
Urine volume reduction was achieved by FO
process.
Ammonia did not pass through the membrane
although urea permeated from feed to draw
solution,.
→ Urea hydrolysis can contribute to concentration of
nitrogen.
The overall mass transfer coefficient had a similar
trend to the water permeability.
→ This results suggested the relation between the
overall mass transfer coefficient and the water
permeability.