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.