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Hydrolysed urine concentration by forward osmosis: Numerical modelling of water flux and nutrients concentration

Graduate School of Engineering, HOKKAIDO UNIVERSITY Bénédicte Carolle NIKIEMA Ryusei ITO Mokhtar GUIZANI Naoyuki FUNAMIZU

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CRISIS OF CHEMICAL FERTILIZER DEMAND

The global nitrogen, phosphorous and potassium (NPK) fertilizer demand is increasing and is affected by the population growth (FAO, 2015) Chemical fertilizer production problem

Sustainable alternatives for nutrients management are needed

Phosphorous is a limited ressource Nitrogen price is linked to the fluctuating price of energy

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URINE AS AN ALTERNATIVE TO CHEMICAL FERTILIZER Nutrients generation in wastewater

Urine fraction represents 80% of N, 55% of P and 60% of K [1]

Stored Water Urine

Farmland (rural area) Household level (urban or peri-urban area)

Urine reuse (system configuration)

Urine diverting systems

80% volume reduction required for efficiency

Urine transportation

[1]Kirshman and Petterson, 1995

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FORWARD OSMOSIS (FO) FOR URINE CONCENTRATION

 Water flux (Jw = K. ∆π )  FO models developed focus

• Reverse draw solution diffusion
• Concentration polarizations
• Single solute in the system

Additional considerations required

• Feed solutes diffusion
• Multiple solute diffusion in the system

Membrane Osmotic pressure (∆π)

A new model is required for estimation of water flux in hydrolyzed urine

Hydrolyzed urine ( Na, Cl, K , PO4, NH3, IC, TOC) Sodium chloride ( Na, CL)

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 To prepare a new numerical model considering the bidirectional diffusion of multiple components through the FO membrane  To estimate the membrane permeability and solutes (Na, K, Cl, PO4, NH3 ) diffusivities through a FO membrane by fitting  To simulate hydrolyzed urine concentration by FO

RESEARCH OBJECTIVE To develop a numerical FO model for hydrolyzed urine concentration

FO EXPERIMENTAL SET UP

Diffusion

Water flux

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 FS and DS volumes : 500 ml  Flow rate FS and DS : 14L/h  Sampling of FS and DS every hour

Using the mass transport across an asymmetric FO membrane

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Feed solution Draw solution AL SL

 The equations were solved with Crank Nicholson scheme  The solutions were obtained by Newton Raphson method

MODEL EQUATIONS

Run1: Water permeability estimation EXPERIMENTAL PROCEDURE

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y = 0,3279x R² = 0,9919 0,5 1 1,5 2 2,5 3 3,5 5 10 water flux(L/m2.h)) Δπ (105 Pa)

Feed solution Draw solution Deionized water NaCl (0.02, 0.05, 0.1, 0.2, 0.5 mol/L )

EXPERIMENTAL PROCEDURE

Feed solution Draw solutions Deionized water NaCl , 0.5 M NH4Cl (pH 9.4) , 1.4 M Na2HPO4, 0.5M KCl , 0.5M

Run2: Fitting for diffusivities estimation

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Feed solution Draw solutions Hydrolysed urine NaCl (4M)

Run 3 : Simulation of Hydrolyzed urine concentration

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2 4 6 1 2 3 Water flux (l/m2.h) Time (h) Jw_Exp Jw_Sim 0,0 0,2 0,4 0,6 1 2 3 Concentration (mol/L) Time (h)

0,000 0,002 0,004 1 2 3 Concentration (mol/L) Time (h)

2 4 6 8 1 2 3 Water flux (L/m2.H) Time(h) Jw_Exp Jw_Sim 0,0 0,2 0,4 0,6 1 2 3 Concentration (mol/L) Time (h)

0,000 0,001 0,002 0,003 0,004 1 2 3 Concentration (mol/L) Time (h)

ESTIMATION OF THE DIFFUSIVITIES BY FITTING

Sodium Chloride (Na,Cl) Potassium (K) SL : 5.5 x 10-10 m2/s AL: 2.85 x 10-12 m2/s SL : 2.5 x 10-10 m2/s Al :2.75 x 10-12 m2/s

Sim Exp

Water flux DS FS

Cl Na

Water flux

DS FS

Sim Exp Cl K

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2 4 6 1 2 3 Water flux(l/m2.H) Time (h) Sim 0,0 0,2 0,4 0,6 1 2 3 Concentration (mol/L) Time (h) 0,000 0,001 0,002 0,003 0,004 1 2 3 Concentration (mol/L) Time (h) 4 8 12 1 2 3 4 5 Water flux (L/m2.H) Time (h)

Sim Exp

0,0 0,4 0,8 1,2 1,6 1 2 3 4 5 Concentration (mol/L) Time (h) 0,00 0,01 0,02 0,03 0,04 1 2 3 4 5 Concentration (mol/L) Time (h)

Phosphate (PO4) Ammonia (NH3)

Exp

SL : 1.5 x 10-10 m2/s AL: 1.85 x 10-12 m2/s SL: 1.5 x 10-9 m2/s AL: 5.75 x 10-12 m2/s

Water flux

DS FS

NH3 Cl

FS

DS

Water flux

PO4 Na

ESTIMATION OF THE DIFFUSIVITIES BY FITTING

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10 20 2 4 6 8 Water flux (L/m2.H) Time(h)

Exp Sim

2 4 6 2 4 6 8 Concentration Na (mol/L) Time (h)

2 4 6 2 4 6 8 Concentration Cl (mol/L) Time (h)

Cl FS The simulation results agreed to the water flux and NaCl concentrations except NH3 concentration which was estimated above.

HYDROLYZED URINE SIMULATION

Na DS DS DS FS NH3 Water flux

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SUMMARY A new numerical model was developed The permeability was experimentally estimated The diffusivities of solutes were estimated but NH3 concentration had a deviation Good simulation of water flux and draw solute concentration were obtained however feed solute simulation should be improved. Further considerations should be included in the model such as NH3 and NH4 species concentrations variation in the feed and draw solution.

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Supporting information Composition of human synthetic urine

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Membrane thickness (m) Membran e division ∆x (m) Time step ∆t(s) Number of division n Al ( 20 x 10-6 ) Sl ( 60 x 10-6 ) 4 X 10-6 0.1 20

SEM picture of the cross section of a CTA membrane AL SL

Supporting information