of 18
S1
Supporting Information for:
1
2
Toxic Byproduct Formation during Electrochemical Tr
eatment
3
of Latrine Wastewater
4
5
6
7
8
Justin T. Jasper, Yang Yang, and Michael R. Hoffman
n
*
9
10
18 pages
11
9 figures
12
4 tables
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
*Corresponding author: e#mail: mrh@caltech.edu; pho
ne (626) 395#4391
40
S2
Analytical Methods.
HAAs and THMs were quantified by GC/MS (HP 6890 GC/
HP
41
5973 MS). Disinfection by#products were separated
by a Phenomenex Zebron ZB#WAX column
42
(30 m x 0.25 mm x 0.25 <m df) using He at 1 mL min
#1
(6 psi). The injector was held at 200 °C
43
and a sample volume of 3 <L (splitless) was used.
For THMs, the oven was set at 30 °C (hold
44
for 2 min) and then ramped as follows: 5 °C min
#1
to 50 °C (hold 2 min); 35 °C min
#1
to 150 °C
45
(hold 5 min); 25 °C min
#1
to 185 °C (hold 5 min). For HAAs, the oven was se
t at 35 °C (hold for
46
10 min) and then ramped as follows: 5 °C min
#1
to 75 °C (hold 15 min); 40 °C min
#1
to 185 °C
47
(hold 5 min). Disinfection by#products were measur
ed in single ion monitoring (SIM) mode at
48
the following mass to charge ratios and dwell times
: chloroform (83; 100 ms);
49
bromodichloromethane (83; 100 ms); dibromochloromet
hane (129; 100 ms); bromoform (173;
50
100 ms); monochloroacetic acid (MCAA; 59; 250 ms),
dichloroacetic acid (DCAA; 59; 250 ms),
51
and trichloroacetic acid (TCAA; 59; 250 ms).
52
S3
Average Number of Treatment Cycles before Discharge
Calculation.
In off#the#grid
53
electrochemical wastewater treatment systems, treat
ed wastewater can be used as flushing water
54
to reduce or eliminate water requirements. This de
sign will result in parcels of water being
55
treated multiple times after flushing, potentially
increasing electrochemical byproduct
56
concentrations prior to discharge. The average num
ber of treatment cycles a parcel of water will
57
go through prior to discharge can be calculated acc
ording to:
58
cycles =

 


=


 



.    
. 
= 11
(S1)
59
where V
treated
is the volume of water to be treated per use, whic
h is the input volume of urine per
60
use (V
input
) plus the volume of treated water used for flushin
g (V
flush
). Typical values of 0.3 L of
61
urine per user and 3 L of treated water per flush w
ere assumed.
62
S4
Table SI 1. Health guidelines for electrochemicall
y produced by-products in drinking
63
water measured in this study.
64
Contaminant
US EPA (μM) WHO (μM)
Chlorate
2.5
(
1
) a
8.4
(
2
) b
Perchlorate
0.15
(
3
) c
0.7
(
4
) d
Nitrate
700
(
5
) e
3500
(
6
) f
Bromate
0.08
(
5
) e
0.08
(
7
) b
Contaminant US EPA (mg L
-
1
) WHO (μM)
THMs
g
0.08
(
8
) e
no guideline
Chloroform
no guideline
3
(
9
)
f
Bromodichloromethane
no guideline
0.4
(
9
)
f
Dibromochloromethane
no guideline
0.5
(
9
)
f
Bromoform
no guideline
0.4
(
9
)
f
HAAs
h
0.06
(
8
) e
no guideline
MCAA
no guideline
0.2
(
10
) f
DCAA
no guideline
0.4
(
11
) d
TCAA
no guideline
1
(
12
) f
a
Health reference level.
b
Provisional guideline.
c
Health advisory.
d
Draft guideline.
e
Maximum
65
contaminant level.
f
Guideline.
g
Sum of chloroform, bromodichloromethane, dibromochl
oromethane,
66
and bromoform.
h
Sum of mono#, di#, and trichloroacetic acids and mo
no# and dibromoacetic acids.
67
S5
Table SI 2. Summary of Electrochemical Byproduct F
ormation in Previous Studies.
68
Water
Treated
Anode Current
Density
(mA cm
-2
)
Membrane [COD]
init
(mg L
-1
)
[Cl
-
]
init
(mM)
[NH
4
+
]
init
(mM)
[THM]
(mg L
-1
)
[HAA]
(mg L
-1
)
AOCl
(μM)
[ClO
3
-
]
(mM)
[ClO
4
-
]
(mM)
[NO
3
-
]
(mM)
Ref.
RO
a
BDD
b
12.5 cation exchange
140
40
0.4
1.3 (1.3)
c
3.8 (3.8)
c
800 (250)
c
##
d
##
##
13
RO
BDD
12.5 cation exchange
150
4
##
1.1
8.8
##
##
##
##
14
RO
BDD
12.5
cation exch., none
140
40
##
##
##
560 (200)
c
##
##
##
15
RO
BDD
2#20
none
130
20
8
0.2 (0.1)
c,e
##
##
3.6 (1.8)
c,e
##
2 (2)
c,e
16
RO
BDD
17
none
160
20
3
##
##
##
4 (4)
c
##
##
17
RO
BDD
10#30
none
180
20
3
##
##
##
4.2 (4.2)
c
##
##
18
RO
RuO
2
f
10#30
none
180
20
3
##
##
##
0.9
##
##
18
RO
Ir, SnO
2
g
12.5 cation exchange
150
4
##
0.7
3.9
##
##
##
##
14
RO
RuIrO
2
h
10
cation exchange
170
30
0.6
0.3 (0.1)
e
2.8 (0.8)
e
##
0.8 (0.2)
e
0
##
19
Domestic
i
BDD
10, 20 cation exchange
##
10
##
##
##
20 (8)
c
1.5 (0.1)
c
1 (0.4)
c
##
20
Domestic
BDD
2.5#120
none
##
3
##
##
##
30 (0.4)
j
0
0
##
21
Landfill
k
BDD
120#260
none
3400
70
90
2.1
##
##
##
##
4
22
Landfill
PbO
2
l
3.0
cation exchange
2800
130
2
##
##
560
##
##
##
23
Latrine
m
TiO
2
n
1.25
none
##
20
5
0.4
0.7
##
##
##
##
24
Latrine
SbSn
o
25
none
250
30#60
10
##
##
##
10 (3)
c,e
6 (6)
c,e
5 (1)
c,e
25
OO leach.
p
BDD
0.1, 0.3
none
1000
0.1
20
3.5 (2)
c
##
##
##
##
##
26
Drinking
q
BDD
10#30
none
##
1
##
##
##
##
##
1
##
27
Surface
r
IrO
2
s
0#8
none
10
3
##
0.05 (0.03)
j
0.1 (0.04)
j
##
0
0
##
28
GW
t
RuIrO
2
11
none
30
2
##
##
##
70
##
##
##
29
Urine
BDD
10#20
none
1710
35
133
3 (2)
c,u
##
280
20 (20)
c
30 (10)
c
##
30
Urine
TDIROF
v
10#20
none
1710
35
133
1.3
u
##
370
28
28
##
30
a
Reverse osmosis retentate.
b
Boron#doped diamond.
c
Max conc. (conc. upon COD removal).
d
Not measured.
e
Max conc. (conc. upon NH
4
+
69
removal).
f
RuO
2
/Ti.
g
Pt#IrO
2
/Ti or SnO
2
#Sb/Ti.
h
RuIrO
2
/Ti.
i
Domestic wastewater.
j
Max conc. (conc. upon disinfection).
k
Landfill leachate.
70
l
PbO
2
/Ti.
m
Latrine wastewater.
n
TiO
2
/IrO
2
/Ti.
o
Sb#SnO
2
/Co#TiO
2
/IrO
2
/Ti.
p
Olive oil leachate.
q
Drinking water.
r
Surface water.
s
IrO
2
/Ti.
71
t
Groundwater.
u
Only chloroform was measured.
v
Thermally decomposed iridium oxide film.
72
73
S6
Table SI 3. Chemical Oxygen Demand (COD), Total Or
ganic Carbon (TOC), and Total
74
Inorganic Carbon (TIC) Concentrations during Electr
olysis.
75
Conditions COD (mg O
2
L
-
1
)
TOC (mg C L
-
1
) TIC (mM)
TiO
2
/IrO
2
a
2.5 A L
#1
30 mM Cl
#
0 h: 510
6 h: 440
12.5 h: 370
0 h: 142
12.5 h: 112
0 h: 50
12.5 h: 6
TiO
2
/IrO
2
a
5.0 A L
#1
30 mM Cl
#
0 h: 510
3 h: 400
9 h: 360
0 h: 142
9 h: 82
0 h: 50
9 h: 3
TiO
2
/IrO
2
a
7.5 A L
#1
30 mM Cl
#
0 h: 610
6 h: 296
0 h: 142
6 h: 86
0 h: 51
6 h: 2
TiO
2
/IrO
2
b
7.5 A L
#1
65 mM Cl
#
0 h: 610
6 h: 164
0 h: 152
6 h: 83
0 h: 51
6 h: 4
TiO
2
/IrO
2
b
7.5 A L
#1
100 mM Cl
#
0 h: 432
4 h: 184
12 h: <LOD
c
0 h: 178
4 h: 128
12 h: 122
0 h: 52
4 h: 4
12 h: 4
BDD
d
4 A L
#1
30 mM Cl
#
0 h: 437
1 h: 120
2 h: <LOD
c
4 h: <LOD
c
6 h: <LOD
c
0 h: 149
6 h: 12
0 h: 55
6 h: 1
NaOCl addition
e
0 h: 510
2 h: 410
4 h: 270
6 h: 110
0 h: 147
6 h: 117
0 h: 54
6 h: 19
a
See Figure 2 of main manuscript and Figure SI 4 for
concentrations of other species.
c
See Figure 3 of
76
main manuscript and Figure SI 5 for concentrations
of other species.
c
Limit of detection (LOD) was 30
77
ppm O
2
.
d
See Figure 4 of main manuscript for concentrations
of other species.
e
See Figure 6 of main
78
manuscript for concentrations of other species.
79
80
S7
Table SI 4. Measured HAA Electrolysis Rates on BDD
Anodes.
a
81
HAA
k
borate
b
(
Ah L
-
1
)
k
latrine
c
(
Ah L
-
1
)
k
borate
b
(s
-
1
)
k
latrine
c
(s
-
1
)
MCAA 12.7 ± 0.4 × 10
#
2
26 ± 1 × 10
#
2
1.9 ± 0.1 × 10
#
4
2.0 ± 0.2 × 10
#
4
DCAA
8.2 ± 1.0 × 10
#
2
25 ± 1 × 10
#
2
2.2 ± 0.1 × 10
#
4
1.3 ± 0.1 × 10
#
4
TCAA
8.4 ± 2.5 ×10
#
2
35 ± 1 × 10
#
2
2.2 ± 0.1 × 10
#
4
1.4 ± 0.3 × 10
#
4
a
HAA concentrations are shown in Figure 5 of main ma
nuscript.
b
Borate buffer solution.
c
Latrine
82
wastewater.
83
S8
84
85
Figure SI 1. Oxidation reduction potential (ORP),
total chlorine concentration, cell voltage, and
86
ammonium concentration during electrolysis of latri
ne wastewater amended with sodium
87
chloride (TiO
2
/IrO
2
anodes; 7.5 A L
#1
; [Cl
#
]
initial
=100 mM). Near the breakpoint (complete
88
ammonium removal; ~3.2 h), total chlorine concentrat
ions and ORP spiked. At the same point,
89
cell voltage showed a distinct peak. Lines added f
or clarity.
90
91
S9
92
Figure SI 2. Concentrations of measured (symbols)
and modeled (dashed lines) chlorine species
93
following the breakpoint during electrolysis of lat
rine wastewater on TiO
2
/IrO
2
anodes at
94
7.5 A L
#1
. Reaction rate constants were obtained by fitting
reactions
95
(
2Cl

H
"
O
$
%
→OCl

Cl

2H

2e

; OCl

2H
"
O
$
(
→ClO


4H

4 e

)
25
to the
96
experimental data (k
1
= 0.35
M
#1
(Ah L
#1
)
#1
; k
2
= 0.030 (Ah L
#1
)
#1
). See Figure 1 of main
97
manuscript for concentrations of other species.
98
99
S10
100
Figure SI 3. Trihalomethane concentrations during
electrolysis (TiO
2
/IrO
2
anodes; 7.5 A L
#1
;
101
3.8 V) of latrine wastewater amended with sodium ch
loride ([Cl
#
]=100 mM). Bromoform was
102
not detected. Dotted lines indicate where the chlo
rination breakpoint was reached (i.e., complete
103
ammonium removal).
104
105
S11
106
Figure SI 4. Ion and inorganic byproduct concentra
tions during electrolysis of latrine wastewater
107
at various current densities with TiO
2
/IrO
2
anodes. Average cell voltages: 2.5 A L
#1
: 3.6 V;
108
5.0 A L
#1
: 4.0 V; 7.5 A L
#1
: 4.4 V. Dotted lines indicate where the chlorinat
ion breakpoint was
109
reached (i.e., complete ammonium removal).
110
S12
111
112
Figure SI 5. Ion and inorganic byproduct concentra
tions during electrolysis of latrine wastewater
113
at various chloride concentrations with TiO
2
/IrO
2
anodes at 7.5 A L
#1
. Average cell voltages:
114
30 mM Cl
#
: 4.4 V; 65 mM Cl
#
: 4.0 V; 100 mM Cl
#
: 3.9 V. Dotted lines indicate when the
115
chlorination break point was reached (i.e., complet
e ammonium removal).
116
117
S13
118
Figure SI 6. Concentrations of measured (symbols)
and modeled (dashed lines) chlorine species
119
during electrolysis of latrine wastewater on BDD an
odes at 4.0 A L
#1
. First#order reaction rate
120
constants were obtained by fitting the model
121
(
Cl

3H
"
O
$
+
→ClO


6H

6e

; ClO


H
"
O
$
-
→ ClO
.

2H

2e

) to the experimental
122
data (k
3
= 0.17 (Ah L
#1
)
#1
; k
4
= 0.087 (Ah L
#1
)
#1
). See Figure 4 of main manuscript for
123
concentrations of other species.
124
S14
125
126
Figure SI 7. Natural log of normalized TCAA and pC
BA concentrations during electrolysis in
127
borate buffer on BDD anodes (30 mM; pH 8.7).
128