Véronique Amstutz, Alexandros Katsaounis, Agnieszkakapalka, Christos Comninellis, Kai M. Udert

Effects of carbonate on the electrolytic removal of ammonia and urea from urine with thermally prepared IrO2 electrodes

Véronique Amstutz, Alexandros Katsaounis, AgnieszkaKapalka, Christos Comninellis, Kai M. Udert

Supplementary information

1)Calculation of the total charge passed, Q

Q is the charge passed through both electrolyte-electrode interfaces [AhL-1], I is the current [A], τ is the electrolysis time [h] and V is the volume of the solution [L].

2)Recipes for synthetic fresh and stored urine

The compounds have to be added in the order they are presented in the table, and every salt has to be well dissolved before the addition of the next one.

Table 1Synthetic fresh urine. Ac: acetate.

Compound / Concentration [gL-1]
Urea / 16.0
NaAc anhydrous / 10.25
Na2SO4anhydrous / 2.30
NH4Cl / 1.80
NaH2PO4anhydrous / 2.90
KCl / 4.20
MgCl2 / 0.370
CaCl2 / 0.510
NaOH / 0.120

Table 2Synthetic stored urine. Ac: acetate.

Compounds / Concentration [gL-1]
Na2SO4anhydrous / 2.30
NaH2PO4 anhydrous / 2.10
NaCl / 3.60
KCl / 4.20
NH4Ac / 9.60
25% NH4OH solution[mL·L-1] / 13.0
NH4HCO3 / 21.40

3)Calculation of the initial and the overall current efficiencies, and of the conversion ratio of species i

The initial current efficiency for a reaction j is defined as

The overall current efficiency for a reaction j is defined as:

The term [molC-1] is the change of the amount of species i (ni in [mol]) as function of the charge passedQ [C], when Q approaches time t=0.We used the slope between the measurement points at 0h and 6h to calculate this term.z is the number of exchanged electrons per mole of degraded species [molmol-1], F is the Faraday constant [F = 96,485 Cmol-1], ∆n is the amountof product that has reacted [mol] during the complete electrolysis experiment, I is the imposed current [A] and t is the total electrolysis time [s].

The conversion ratio of species i is defined aswhere is the amount of species i that has reacted [mol], and is the initial amount of species i present in the solution at the beginning of the electrolysis experiment [mol].

4)Fit equations

Some of the curves shown in Figures 1 and 2 were fitted with the empirical curves given below using Igor Pro software. The types of curves were chosen based on experiences with previous studies:

Figure 1c – CNtot curve:

withA = 7327.3, B = 959.15 and C = 0.29951

Figure 1d – Cactive chlorine curve:

with A= 0, B = 35.45, C = 10.17 andD = 1

Figure 2a – CNtot and CNH4 curves:

withA = 8680.1,B = -491.46,C = 0.012771, D = -481.69 and E = 0.0092258

with A = 8298.1,B = -514.44,C = 0.012741, D = -504.64 and E = 0.009203

Figure 2b – Cactive chlorine curve:

withA = 1.5775,B = -1.6188 and C = 0.19654

Figure 2c – CNtotand CNH4curves:

with A = 4591.1, B = 2486.9 and C = 0.16502

withA = 3753.7, B = 2818.7 and C = 0.12226

Figure 2d – Cactive chlorine curve:

withA = 0, B = 106.35, C = 36.27 and D = 1

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