A B S T R A C T
B R A D B E N N E T T
:C H A R A C T E R I Z A T I O N O F Z I N C A S A P O T E N T I A L A L T E R N A T I V E F O R
T H E R E D U C T I O N O F N I T R A T E I N
W
A T E R S U P P L I E S
(
U
nd
e rt
h
ed ir e
ct
i
o n of D
rO
rl
a nd
oC
o r o nel l
)
G
r o u nd w
at
e r c ont
am i
nat
i
onb y
nit
r at
e(
N 0
3 ~)
i
s c a u sed m
ai
nl
y
b
y
a nt
h
rop
og
eni
c sou r c esi
n cl
ud i
ng
nit
r og
e nf
e rt
i l i
z ers, a ni m
al w
a ste s
, s ep
t
ic s
y
ste
m
s a nd in
d
u str
i
al p
r o c e s s e s.D
u et
oth
ep
ot
ent
i
al
to x
i
ci
t y
of
ni
t
r ate
and
nitr
i
te
,t
h
eU
ni
te
d St
at
e sE
nvi
r o nm
e nta
l P
r ot
e cti
o nA g
e n cy
(
U S E P A
)
h
a s e st
ab l i
sh
ed m
a xi m
um
c o nt
am i
n a nt
l
e v el
s(
M
C L
s)
of 1 0 m g
-N /
L
and I m g
-N / L
, r e s
p
e ct
i
vel y
,f
ort
he
t
w
op
ol lu
t
ants
i
ndr
i
nk i
ng w
at
e rT h
e si g
ni f i
cant
dr
aw b
a ck
s as s o cia
t
ed w it
h
c ur re nt t
re atm
ent
a
l
t
er n at
i
ve sf
or ni
tr
ate
-co n
t
am i
n at
ed w
at
erh
av e r e sul
te
d i
n al
a rg
e r e s e arch
t
h
r u st
b
ei
ng d
e v el
op
ed
t
ow
a rd
th
e ap p l i
c at
io n o
f
r ed
u cin
g
nit
r at
eto
le s s
to x
i
cfo r
m
s(
ie
.N
2(g
)
o rN H
4 ^)
w ith
z e r o-v al
e nt
i
r o n(
F
e°)
.W
ith
t
h
em
oti
v at
i
o nto
e xp
a nd
th
e s c op
e of
ch
em i
c al
r ed
u ct
a nt
s of
nit
r at
e, zi
n c(
Z
n ' ')
,w h i
ch i
se
l
ectr o
che
m i
cal l
y
si m i l
art
oi
r on ,br
a s s, a zi
n c-c o
p
p
er al l
oy
, a nd
c op p
e r(
C
u °)
w
er et
e ste
d
, usi
ng
b
at
ch
r e a cti
o n s,t
o ch
a r a ct
e ri
zeth
ei
r ef f
e ct
i
v e n e s si
n r ed
u ci
ng
ni
tr a
t
eS in c e z
in c
p
r o v ed
t
ob
e v e ry
e
f f
e ct
i
vei
n red
u ci
ng
ni
t
r at
e, an em p i
ri
c al
r ate
l
aw w
a sd
ev el
op
ed
t
od
et
erm i
n et
h
ed
ep
end
e n cy
of
t
h
er e a c
t
i
o n sb
et
w
ee n zi
n c a nd
o xid i
zed
nit
r og
e n sp
e ci
e s ont
he
i
nit
i
al
ni
tr a
t
e c on ce nt
rat
i
on, zin c
d
o se,a n
d i
ni
t
i
al p H
T h
e r ate
l
aw w
a s ap p
r o xi m
ate
l y f
i r st
o rd
e rw i
t
h
r e sp
e ct to
t
h
ei
ni
t
i
al
nit
r ate
c o n c e n
t
rat
i
o n and
zi
n cd
o s e, a nd
af
r a ct
i
o n al
o rd
erw i
t
h
r e sp
e ct to
t
h
ei
nit
i
al p H w
a s ob
s e r v ed
A
d ir e c
t
ele
ctr o n
tr a
nsf
e rm
ech
a ni
sm b
etw
e e nt
h
e zi
n c and
o xid i
zed
nit
rog
en sp
e ci
esi
s s ug g
e ste
d
a nd
f
utu
r ew
ork i
nv ol
vi
ng p
ot
ent
ia
l b
e n ch
-sA C
K
N O
W
L E D G E
M
E N T S
I w
oul d li k
et
ot
h
a nk m
y
w i f
e,H
ol l
y
,f
o ry
o u r u nw
a v e ri
ng
s up p
ort
a nd
e n c o u r ag
em
e nt
al l
t
h
r o ug h
o ut
t
h i
s e xp
e ri
e n c e.D
r .O
rla n
do
C
or on el l
,
th
a nk
y
o uf
orta
k i
ng
m
e o n a s a stu
d
e nt
a nd
,i
n s od
oin
g
,p
r ovi d i
ng m
ew i
t
h
a no
p p
ort
u nit
y
to
g
rad
uat
efr
om U N C
-C h
ap
el H i l l
I
coul d
n ot
h
av e ea rn ed
t
h i
sd
eg
re ew ith
o ut
y
ourt
i
r el
e s sh
el p
a nd d ir e c
ti
o n .I w
o ul d l ik
et
ot
h
a nk D
rP h i l S i
ng
e rf
o rh i
si
np
ut
i
nt
ot
h
ep
r oj
e ct
al
o ng
th
ew
ay
.I f
e el f
o rtu
nat
et
oha v
ew
o rk
ed
a nd
stu
d i
ed
u nd
e ry
o u rd i
r ect
i
o n.I w
o ul d li k
et
og
en ui
n el y
t
h
a nk D
r.A itk
en a nd D
r.S
te
w
a rt
f
o r of f
eri
ng
to
s e r ve o nm
y
c om m i
t t
e e a sr ea
d
er s,d
esp i
te
t
h
ei
n c onv e ni
e n c et
h
at
it
i m p
o s ed
o n e a ch
of y
o uI w
o ul d l ik
et
ot
h
a nk
M
r.Ja c
k
W
ha
le
y
and
M
s.M
el
od y L
e vy f
ort
h
ei
rf
ri
e nd l y
, e x cel l
e nt
h
elp
t
h
r o ug h
o ut
m y
t
e n u r eh
e r e.I w
oul d li k
et
ot
ha n
k
M
r.A l
e x a nd
erG
o r z al
sk i
v e ry m
u ch f
o rt
ak i
ng p h
ot
o s of
t
h
eb
r a s sm
ed i
aw it
h
t
h
eS E
M
.T A B L E O F C O N T E N T S
L I S T O
F
T A
B L
E S
vi
L I S T O F F I G U R E S
vi i
L O I N T R O D U C T I O N
1
1
.1 I
n o rg
ani
c ni
t
rog
e np
ol lu
ti
o n a nd p
ub l i
ch
e al
t
h i m p
act
s1
1 2 R
ed
uct
i
o n of
nit
r at
e(
N O
3 ")
w it
h
ze r o-va
l
e nt
i
ro n(
F
e°)
2
1
.3 P
ot
enti
al
red
u ct
i
o n of
ni
tr a
t
ew i
t
h
oth
e r z e r o-v a
l
e nt
m
ed i
a4
1 4 O b
j
e ct
i
v e s7
2
.0
M
A
T
E R I A
L
S A N D
M
E T H O D S
8
2
.1.
R
e ag
e nt
s a nd
ch
em i
c al
s8
2
.2 S
ol
ut
i
o n s9
2
.3 Z
e r o-v a
le
nt
m
ed i
a9
2 4 D
et
erm
i
n at
i
o n of
t
h
eB
ru na ue rE m m
et
T
el l
er(
B E T
)
m
ul
t
i
-p
oi
nt
s urf
a c e a r e a1 0
2
.5 D
et
erm i
n at
i
on of
t
h
ep
a rt
ic
le s
i
z e of
t
he
b
ra s s-
fi
n em
ed i
a1 0
2 6
M
e a s urem
e nt
of i
n o rg
ani
c nit
r og
en sp
e cie s
1 1
2
.7 B
at
ch
e xp
e rim
e nt
s1 7
2
.7 1 R
e act
o rT
y
p
e1 7
2
.7
.2 N i
tr
ate r e
d
u ct
i
o nb y
zero-v a
l
e nt
zi
n c(
Z
n")
1 7
2
.7
.3 N i
tr a
te r e
d
u ct
i
onb y
z e r o-v a
l
e nt
i
r o n(
F
e°)
2 2
2 7
.4 N i
tr
ate
r ed
u ct
i
o nb y d i f f
ere nt
z e r o-v a
l
e nt
m
e
d i
a2 4
3
.0 R E SU L T S A N D D I S C U S S I O N
2 6
3
.1 R
ed
u ct
i
o n of
ni
tr a
t
e(
N O
s"
)
w i
t
h
z e r o-v al
e nt
i
ro n(
F
e°)
t
ova
l id
at
e e xp
eri m
e nt
al m
et
h
od
s2 6
3
.2 C
om p
a ri
ng
t
h
e ef f
e ct
i
v e n e s s of
ni
t
r at
e r ed
u ct
i
o nb y i
r o n, z
i
n c, c op p
e r a nd b
r a s s2 8
3 3 D
ete r
m i
n at
i
o n of
exp
eri
m
e nta
l
c o nd i
t
i
o n sf
o rk i
n et
i
c s e xp
eri m
ent
sw i
t
h
zero-v al
e nt
zi
n c(
Z
n°)
3 4
3
.3 1 O
v e r vi
ew
3 4
3
.3
.2 D
et
erm i
n at
i
on of
zer o-v a
l
ent
zi
n c(
Z
n)
d
o s ag
ef
ork i
n et
i
c s e xp
e rim
ent
s3 4
3 4 E
v al
u at
i
o n of
t
h
ef
e a si b i l i
t
y
of
u si
ng p h
o sp h
at
e(
H
3P O
4)
b
uf f
e rf
o rp H
c o nt
r ol d
u ri
ng
ni
t
r at
e r ed
u ct
i
o n e xp
e ri m
e nts
w i
t
h
z e r o-v al
e nt
zi
n c(
Z
n °)
3 7
3
.5 K i
n et
i
cs of
ni
tr
at
e r ed
u ct
i
onb y
z e r o-va
l
ent
zi
nc(
Z
n ")
4 1
3
.5
.1 O
v e r vi
ew
4 1
3
.5
.2 E f f
e ct
of i
ni
t
i
al
ni
t
r at
e c o n c e ntr a
t
i
o n([
N O
s'
j
o)
o n
t
h
e r ed
u ct
i
o n of
ni
t
r at
eb y
zi
n c4 1
3
.5
.3 E f f
e ct
of
zi
n cd
o s e(
C
zno)
o nt
h
e r ed
u ct
i
o n of
ni
t
rat
eb y
zi
n c4 5
3 5
.4 E f f
ect
of h y d
rog
e n c o n c e nt
rat
i
o n o nt
h
e r ed
u ct
i
o no
f
ni
t
r ate
b y
zi
n c4 9
3
.5
5
C
al
cul
at
i
o n of
r e a ct
i
o n r at
e c onst
ant
k
(
i
nE q
uat
i
o n2
)
5 3
3
.5
.6 C
om p
a ri
s o nb
et
w
een ob
s er ved
a nd
c al
c ul
at
ed
ch
ang
ei
np H
5 4
3
.6 C h
ara ct
e ri
zi
ng
t
h
ei
nt
e r a ct
i
o nb
et
w
e e n zi
n c(
Z
n°
)
a nd p
r oto
n s(
E
T)
5 7
3
.7 A
n aly
zi
ng
t
h
ed i
s s ol
v ed
zi
n c[
Z
n^^
]
c o n c e nt
r at
i
o n s6 3
4
.0 C O N C L U S I O N S
6 8
5
.0 F U T U R E
W
O R K
7 0
A P P E N
D
I X A
7 4
A P P E N D I X B
7 8
L I
S T O
F T
A
B L
E S
T
ab l
e1
P
rop
e rt
i
e s of
t
h
e red
u ct
i
v em
ed i
a10
2
.[
Z
n^^
]
a s af
u n ct
i
o n of p H
19
3
.E
xp
e ri m
e nt
s um m
a ry f
o rt
h
e c om p
a ri
s on of d i f f
er e nt
m
ed i
a2 8
L I S T
O
F F I
G U
R
E S
F ig
u re1
.F ig
u re1
6
2
.F ig
ure2
13
3
.F i g
u r e3
14
4
.F i g
u r e4
1 7
5
.F i g
u r es
1 9
6
.F i g
u r e6
2 7
7
.F i g
u r e7
3 3
8
.F i g
u r es
3 6
9
.F ig
u r e9
3 9
10
.F i g
u re10
4 0
1 1
.F i g
u r e1 1
4 3
12
.F i g
u r e12
4 5
1 3
F i g
u r e13
4 7
14
.F i g
u r e14
4 9
1 5
.F ig
u r e1 5
5 1
1 6
.F ig
u r e16
5 3
1 7
.F ig
u r e1 7
5 4
1 8
.F ig
u r e1 8
5 6
19
.F
i
g
u r e19
5 8
2 0
.F i g
u r e2 0
5 8
2 1
.F
i g
u r e2 1
6 0
2 3
.F i g
u r e2 3
.2 4
.F i g
u r e2 4
.2 5
.F i g
u r e2 5
.2
6
.F
i
g
u r e2 6
.,
6 4
.
6 7
.
7 8
.
7 9
1
.0
I
N T R
O
D U C T I
O
N
1
.1 I
norg
a ni
c ni
t
r og
e np
ol l
ut
i
o n a nd p
ub l i
ch
e al
t
h i
m
p
a ct
sN it
r at
e(
N O
a"
)
c ont
am i
nat
i
on of g
ro u nd
a nd
s urf
a cew
ate
r s up p l i
e sl
ia s em
e rg
ed
as aw
orl d w id
e en vi
r onm
ent
al p
r ob l
em
[
1
]
;
and g
r o und w
at
er cont
am i
nati
oni
s caused m
ai
nly b
y
a n
th
rop
og
eni
c s ou r c e si
n cl
ud i
ng
ni
t
r og
e nf
e rt
i l i
z e r s, a nim
al w
a st
e s, s ep
t
i
c sy
st
em
s and i
ndu s
t
ri
al
p
r o c e s s e s[
1
-3
]
.S
t
o rm w
at
er r u n of f
a nd i
r rig
ati
on a r e oft
e n re sp
o n si b l
ef
ort
r a nsp
ort
i
ng
nitr a
t
et
og
r o u nd w
at
e r sup p l i
e s[
3
]
.N i
t
r at
ei
s r el
ati
v ely
n o n-
t
o xi
ct
oh
um
a n sw ith
o ut
ag l
u c o s e-p h
o sp h
at
ed
eh y d
r og
e n a s ed
efi
ci
e n cy
[
4
]
a si
t
i
s e x c r et
ed b y
t
h
ek i d
n ey
s[
5
]
.H
ow
e v e r, c o n c e nt
r at
i
o n sg
r e at
e rth
a n10 m g N O
j-N / L
c a nb
el
et
h
al
t
ob
ab i
e sl
e s st
h
a n si
xm
o nth
s ol d
[
5
]
.O
n c eit
i
si
ng
e st
ed i
t
i
sr e
d
u c ed
t
o nit
rit
e(
N O
a ")
i
nt
h
eg
a st
ro-i
nt
e st
i
n al
tr a
ct
[
3
,
4
]
.N i
tr
i
te
o xi d i
ze sth
ef
errou si
ro n(
F
e *)
i
nhe
m
og l
ob i
nt
om
eth
em
og l
ob i
n,w h i
ch i
s u n ab l
et
otr a
n sp
o rt
o xy g
e nt
h
r o ug h
o ut t
h
eb
od y
[
3
]
.T h i
sp h
e n om
e n o ni
s r ef
er red
t
om
eth
em
og l
ob i
na em ia
, or "b l
ueb
ab y
sy
ndr
om
e"[
4
,5
]
T h i
s c ond i
t
i
oni
sl ik
ely
t
o o c c u ri
nd
e v el
op i
ng
c o u nt
ri
e s, s u ch
a sw h
e r ed
ri
nk i
ng w
at
e ri
s ob
t
ai
n ed fr
om
sh
al l
ow w
el l
si
n ag
ri
c ul
t
u r al
a r e a s[
6
]
.T h
eW
orl d H
e al
t
h O
rg
ani
z at
i
o n(W
H O
)
i
s c ur r ent
ly
c ol l
e cti
ng d
at
at
oq
u ant
i
fy
t
h
ew
o rl d w i d
e ext
e nt
of
t
h i
s co nd it
i
on si
nc e n o e st
i m
at
e s c u r r ent
ly
e xi
st
[
6
]
.h
i ad d i
ti
o n,n
i
t
rit
e c a n r e a ct
w it
h
ot
h
e r c om p
o u nd
si
nt
h
eb
od y
t
of
o rm
ni
t
r o s am i
n e s,w h i
ch
a r ep
ot
e nt
i
al
c a r c
i
n og
e n st
h
at
c a n al
s op
o s si b ly d
am
ag
e vit
al
o rg
ans[
3
]
.D
u et
oth
et
o xi
ci
t
y
of
nit
rat
e a nd
ni
t
ri
t
e,t
h
eU
nit
ed
S
t
at
e sE
nvi
ronm
e nt
al P
r ot
e ct
i
onA g
ency
(
U S E P A
)
h
a s e st
ab l i
sh
ed m
a xi m
um
c o nt
am i
na nt
l
evel
s(M
C L
s)
of 10 m g
-N / L
a nd I m g
-N / L
, r e s
p
e cti
v ely
[
7
]
.N i
t
r at
ei
sd i f fi
c ul
t t
o r em
o v ew i
th
c op
r e ci p i
t
ati
o n o r ad
s o rp
t
i
o nb
e c a u s e of i
t
sh i g h
s ol
ub i l i
t
y
a n
d
st
ab i l i
ty
i
n sol
ut
i
o n[
5
]
.T h
e c ur r ent
alt
er n at
i
v e st
ot
r e at
d
ri
nk i
ng w
at
erw i
t
h
ni
t
rat
e a nd
nitr
i
t
ec o nce n
t
rat
i
o ns ab
o v eth
ei
r r e sp
e ct
i
veM
C L
val
u e si
n cl
ude
i
o n e x ch
ang
e, rev e rse o sm
o si
s,b i
ol
og i
c al
d
eni
t
ri fi
c at
i
o n(
t
h
e ana e r ob i
c r ed
u ct
i
o n of
nit
r at
et
o ni
t
r og
e ng
a s vi
am i
c r ob
e s)
, a nd
ch
em i
c al
r e
d
u ct
i
o n[
5
]
T h
efi
r st th
r e et
e ch
n ol
og i
e s al l h
a v e si g
ni
f
i c a nt
d
r aw b
a ck
s[
3
]
.I
o n e x ch
a ng
ei
sa
f f
e cte
d b y
s ul f
at
e(
S 0
4 ^")
, o rg
a ni
cm
at t
e r(
O
M )
, a nd
ch l
orid
e(
C F
)
conc ent
r at
i
o n si
nth
e r aw w
at
e r;
b
e c au s e of i
t
s c o r r o si
vi
t y
[
5
]
.R
e v ers e osm
o si
si
s af f
e ct
ed b
y t
h
ep
r e s e n c e of O
M
a nd
to
t
al
d i
s s ol
v ed
so
l id
s(
T
D S
)
i
nt
h
e r aw w
at
er, and
req
ui
rest
h
ed i
sp
os al
of
a c onc e nt
r at
ew i
t
h
ve ry h i g h T D S
c o n c e n
t
r at
i
o n s[
5
]
.I
n ad d i
t
i
o n,b
ot
h i
o n e x ch
a ng
e a nd
r e v e r s e o sm
o si
s a r e n ot
s el
ect
i
v ef
o rt
h
er e
m
o v al
of
ni
tr a
t
e a nd d
o n ot
c onv e rt
i
t to a n o
t
h
er c om p
ou nd
,t
h
er eb y m
ak i
ng
t
h
e r e sp
e ct
i
v ew
a st
ep
r od
uct
s u nd
e si
r ab l
e[
3
]
.B i
ol
og i
c al d
e ni
t
ri f i
c at
i
o n,b
ei
ng
an a n a erob i
cp
r o c es s,i
s se n si
t
i
v eto
t
h
ed i
s s ol
v ed
o xy g
en(
D O
)
c o n cent
rat
i
o n si
nt
h
e r aw w
at
e r; t
h
ep
r o c e s si
s c om p
a r at
i
v ely i
n c om p l
et
e and
s
l
ow
; t
h
et
r eat
m
ent
sy
ste
m m
u st
b
eh i g h l y m
o ni
to
r ed
;
and
t
h
efi
ni
sh
ed w
at
er r eq
ui
re st
reat
m
ent
b
e c a u s ei
t
c o nt
ai
n sm i
cr ob
e s a nd
,i
nm
o st
c a s e s, an org
a ni
c el
e ctr o
nd
on or[
3
,5
]
.D
uet
ot
h
ea
f
or em
e nt
i
o ned d
raw b
a ck
s a s s o ci
at
ed w i
t
h
ot
h
e r al
te r n a
t
i
v e sf
o rt
r e at
i
ng
ni
tr a
te c o n
t
am i
n at
ed w
at
e r,a
l
a rg
e r e s e a r ch
t
h
r u sth
a sb
e e nd
e v el
op
ed
t
ow
a rd
t
h
ep
ot
e nt
i
al
of
t
r e at
i
ng
ni
t
r at
e-c o nt
am i
n at
ed w
at
e r sw i
t
h
ze r o-v al
ent
i
r o n(
F
e°) [
3
]
.
1
.2 R
ed
u ct
i
on of
ni
t
r at
e(
N O
a ")
w i
t
h
zero-va
l
e nt
i
ro n(
F
e ")
M
a ny
st
ud i
e sh
av ed
em
o n str ate
d
t
h
e su cc e ssf
ul
r ed
u ct
i
o n of
ni
tr a
t
eb
y
zero-v a
l
ent
i
r o n(
el
em
e nta
l i
r o n o rF
e°) [
1
-4
,8
-
19
]
,
w i
t
h
am m
o ni
um
(
N H
4 ^)
b
ei
ng
t
h
em
aj
o rp
rod
u ct
[
2
-4
,8
-
14
,1 6
,1 7
,19
]
S
t
ud i
e sh
a v ed
em
o n st
r at
ed
t
h
at t
h
e r ed
u ct
i
o n of
ni
t
r at
eto a
m m
o ni
ab y
z e r o-v a
l
e nt
i
r o ni
sen
h
an c ed
at
l
ow p H
c o nd i
t
i
o n s[
2
,3
,8
-10
,
12
,13
,1 8
,1 9
]
.A l
so, re c e nt
stu
d i
e sh
a v e sh
ow
nt
h
at
a u
g m
ent
i
ng
t
h
e s ol
ut
i
o nw i
t
h
aq
u e ou sf
e r r ousi
ro n(
F
e ^^(
aq)
)
im p
r o v ed
t
h
e r ed
u ct
i
on of
ni
t
rat
e at
e n v
i
r o nm
e nt
al ly
r el
e v a nt,
o rm
ore n e ut
ral p H
c o nd i
t
i
ons[
1 3
,14
,19
]
T w
o r ea ct
i
o nm
ech
ani
sm
s of
n
i
t
r at
e red
uct
i
o nh
a veb
e enp
rop
o sed
,t
h
oug h
a c on sen sush
a s n ot
b
ee n reach
ed
[
1
,4
,9
,1 0
,12
,1 8
]
T h
ef i
r st
p
r op
o sed m
e ch
a ni
sm i
s a ni
nd i
r e ct
m
et
h
od
, a c c o rd i
ng
t
ot
h
e r e a ct
i
o n sb
el
ow
:(
R
c.2
)
N
O
,'
+
4
H
,(^) +2
H
^-^
N
H ^
+3
H
^O E
' =0
.8 8 0 F
T h
ei
nd i
r e ct
m
e ch
a ni
sm
sta
te s
t
h
at
h y d
rog
e ng
a s,f
o rm
ed
a s a c orr o si
o np
r od
u ct
of
t
h
e r e a ct
i
o nw i
t
h
zero
-va
l
ent
i
r on a nd p
r ot
o n s,d
on ate s
t
h
e el
e ct
r on sf
ort
h
e r ed
uct
i
o n of
ni
tr
ate
t
o am m
o ni
a[
10
,1 7
]
.T h
e s e c o nd p
r op
o s ed m
e ch
a ni
sm i
s ad i
r e ct
m
et
h
od
,i
nw h i
ch
el
e ct
ro n sf
rom
t
h
eF
e °p
art
i
cl
e sa r e
t
r a n sf
e r r ed d i
r e ct
l y
t
ot
h
eN O
a "m
ol
e c ul
e si
n s ol
ut
i
o nT h
ep
r op
o sed m
od
el
u nd
e rly i
ng
t
h i
sm
e ch
a ni
sm i
sI
c now
n ast
h
et
w
ol
ay
e r s em i
-c o nd
u ct
o rm
od
el
[
1
3
,1 4
]
.T h
i
sm
od
el
st
at
e st
h
at
a st
h
eF
e°p
a rt
ic
l
e s a r e o xi d iz e
d
a r el
at
i
v el y
t
h i
ck b l
a ck
c o at
i
ng
, of
rel
at
iv e
ly h i g h
c o nd
uct
i
vi
t
y k
n ow
n a sm
ag
net
i
t
e(
F
e 30
4)
,f
orm
s a r ound
t
h
eF
e°
c or e
T h
em
ag
net
i
t
e c o at
in
g f
a ci li
t
at
e st
h
e el
e ct
r o nt
r a n sf
e rf
r om
t
h
ei
n n erF
e" c o r et
ot
h
e ni
tr
at
e.H
ow
e v e r,d
urin
g
t
h i
s r e a ct
io n
, a very
t
h i
n , n o n-co n
d
uct
i
v el
ay
er c om p
o sed
of i
ro n oxi d
e s, su ch
a sl
ep i d
o croci
t
e(y
-
F
eO O H
)
and m
ag h
em i
te
(
y
-F
e2
0
3)
,f
orm
s o nt
h
e o ut
si d
e of
t
h
et
h i
ck
erm
ag
net
i
t
el
ay
e r.S i
n cet
h
et
h i
n o ute
rl
ay
e ri
s non-con
d
u ct
i
v e,i
t
si g
ni f
i c a nt
l
y
o
b
st
r u ct
st
h
et
r a n sf
e r of
el
ect
r o ns, and
c o n seq
u ent
ly
t
h
e r ed
u ct
i
o n of
ni
t
r at
e[
1 7
]
.H
ow
e v e r,in
t
he
p
r e s e n c e of
aq
u e o u sf
e r r o u si
r o n(
F
e^ '(
aq)
)
,t
h
et
h i
n,p
a s si
v eir o n
o xi d
el
ay
e ri
s c o n v e rt
ed i
nt
om
ag
n et
i
t
e at t
h
ep
oin
t
w he
r et
h
eF
e^^
a
ds o r
b
st
ot
he
p
a s si
v ela
y
er,t
h
u s al l
ow in
g f
or el
e ct
ro nt
r a n sf
e rac co r
d i
ng
t
ot
he
f
ol l
ow i
ng
rea ct
i
o n[
17
,2 0
]
:{
R
x.3
)
2r
-
F
eO O
H
+
F
e^^^
F
e^
O
,+
2
H
^
A
r e a ct
io n
t
h
at
de s c r
i b
e st
h
e sp
e ci fi
c r e a ct
i
o nm
e ch
a ni
sm
sf
o rt
h
et
w
ol
ay
er s em ic o n
d
u ct
o rm
od
el h
as not
b
e end
e v elo
p
ed
[
1 4
,17
]
.In
t
h
ep
r e s en c e of d i
s s ol
ved
o xy g
e n,t
h
e n o n-c o n
d
u ct
i
v ep
a s si
v ela
y
e r c om p
o s ed
of ir o
n o xi d
e si
st
h i
ck
e rt
h
a n und
e r a n a e r ob ic c o n
d i
t
i
o n s.H
ow
e v e r ,t
h i
st
h i
ck
er n o n-c o nd
u ct
i
v el
ay
e ri
s n ot
a ni
nt
e rf
e r e n c et
ot
h
e rap i d
r edu c
t
i
o n of
ni
t
r at
e a sl
o ng
a st
he
so
l
ut
i
on c ont
ain s
F
e^^
(
aq)
[
1 4
]
T w
o r e act
i
o n sha
veb
eend
ev el
op
ed
t
ha
t
de s c
ri b
et
h
e n et
s
t
oic
h i
om
et
ri
c r e a ct
i
o nf
o r ni
t
r at
e r ed
u ct
i
o nb y
z e r o-v al
e nt
i
r o ni
nt
h
ep
r e s e n c e of F
e^ ^(
aq)
[
13
,1 7
]
:(
Rx
A
)
N
O
, ~ +2
.S2 F
e°
+
0
.7 5
F
e ^*+
2
2 5
H
^O
-
^
N H
^ ^
+
\
.\ 9 F
e^O
^ +0
.5
QO
H
-(
P
x .5
)
N
O
~+
2
.8 0
F
e °+
O
.S O
F
e ^ *+
I
I
OH
^O
-
>N
H
^^
+
l
.2 0
F
e^
O
^ +OA OO
H
'R
eact
io n
4 w
a sd
e v el
op
ed
u si
ng d
e-o x
i d i
z ed w
at
e r a nd F
e^ c o at
ed w i
t
h F
e30
4i
nt
h
e s up p
o rt
in
g
e x
p
e ri m
e nt
s[
13
]
.R
e a ct
io n
5 w
a sd
e v elo
p
ed
u sin
g
o xy g
e n s at
urat
ed w
at
e r a nd
u nco at
ed F
e"
.
h
it
h
ee x
p
erim
e nt
s s up p
o rt
i
ng
t
h
ede v
el
op m
e nt
of
re act
i
o n5,
t
he
d i
s s olv
ed
o xy g
en(
D O
)
w
a sq
uic
k l y
d
ep l
et
ed w h i
ch
re s ul
t
ed in
t
h
ef
o rm
at
i
o n of
t
h
eb l
a ck F
e30
4 c o at t
h
at
s u r r o u nde
d
t
he
F
e "p
a rt
i
cl
e s[
17
]
F
u rt
he r
m
o r e, r e c e nt
w
o rk h
a sd
em
o n st
r at
ed
t
ha
t
at
n e a r n e ut
r al p H
c o nd i
t
i
o n s,w h
e n ni
t
r at
ei
ns
t
oi
ch i
om
et
ri
c al l
y
c orr e ct
d
o se of F
e^ ^(aq), v
i
rt
u al l
y
al l
of
t
h
e ni
t
r at
e a nd
aq
u e ousf
e r r ousi
r o n a r econ s u
m
ed
a c c o rd i
ng
t
o r e a ct
io n
5
[
1 7
]
.1
.3 P
ot
e nt
i
al
r ed
u ct
i
o n of
ni
t
r at
ew i
t
h
ot
h
e r z e r o-v a
l
e nt
m
ed i
aT h
e ap p l i
cat
i
on of
zer o-va
l
e nt
i
r o nf
o rt
h
e rem
ov al
of
ni
t
rat
eh
asd i f f
e r e nt
d
r aw b
a ck
s, s u ch
a st
he
l
ow p H
r eq
ui
r em
ent
s a nd
t
h
e e x c e s siv
ep
rod
uct
i
o n of f
e r r o u si
r o n(
F
e^ ^)
,w h ic
h
c a u s e st
a st
e a nd
o
d
o rp
r ob l
em
sw h
en e xp
o s ed
t
o o xy g
en[
2 1
]
, and
am m
o ni
um
(
N H
'^^) [
3
]
.C
o n s eq
ue nt
ly
,t
h
er ei
s st
i l l
an
i
n c e nt
i
v et
o e xp
a nd
t
he s c o
p
e of
ch
em i
c al
red
u ct
a nt
s of
ni
t
r at
e.Z
e ro-v a
l
ent
zi
n c(
Z
n °)
i
s el
ect
roch
em i
cal l y
sim
i l
a rt
o ze r o-v al
e nt
i
r o n(
F
e")
a c c o rd i
ng
t
ot
h
ef
ol l
ow i
ng h
al f
r e a ct
i
o n s[
2 1
]
:{
R
x(
))
F
e '*+
2
e ~-^
F
e^^^
E
"
= -
0 44 0 F
(
R
x .7
)
Z
n "'+
l
e--^
Z m
.E
"= -
0
.7 6 3 F
Sp
e ci f ic a
l l y
,t
h
e r ed
u ct
i
o nha
l f
-r e a c
t
i
on sf
orb
ot
h m
et
al
sh
a ve st
a nda r
d
el
e ct
rod
ep
ot
ent
i
al
sw h i
ch
in
d i
c at
et
ha
t t
h
et
end
e ncy f
o rb
ot
h m
et
al
st
o o xi d i
zei
st
he r
m
od y
n am i
c al l
y
f
a v o r ab l
e.T h
eref
o r e, zi
n csho u
l d
als o
be
ab l
et
o ef f
ect
iv
el y
r edu
ce ni
t
rat
eb
y
a ct
i
ng
a s a n ef f
e ct
i
v e r ed
u ci
ng
ag
e nt
.I
np
aral l
el
t
ot
h
ep
r op
o s ed m
e ch
a ni
sm
s of
ni
t
r at
e r ed
u ct
i
o nb y F
e°, zi
n cw
o ul d p
r ob
ab l y
t
r a n sf
e r el
e ct
r o n s ei
t
h
e ri
nd i
rect
l
y t
o ni
t
r at
eb y h
y
d
r og
e ng
a s, a c or ro si
o np
r od
uct
of
zi
nc,(
R
x8
a nd 2
)
:{
R
x.^
)
Z
n^
^)
+2
H
*-
^ Z
n ^ *+ '
^
2
{
g)
^
°
=
0
.76 3 K
(
R
x.2
)
N O
,~
+
4
H
^^g^+2
H
^-^
N H
4
^ +3
H
^
0
£
"
=
0
.88 0 F
o r
d i
r e ct
l y
t
o ni
t
rat
e(
R
x .9
)
:(
R
x.9
)
n
o
;
+\ Q
H
*+
4 Z
^
^)
- »4 Z
« '"+
NH
^
+3
,H
fi
E
f
=1
M
3 V
I
n ad d i
t
i
o n,b
r a s s,w h i
ch i
s a zi
n c a nd
c op p
er al l
oy
,i
s c om m
erci
al l y
a v ai l
ab l
e, ab
unda n
t
,r e
la
t
iv
el y i
n e xp
en siv
e, a nd ha
sd
em
onst
r at
ed
s uc ce s si
n r ed
u ci
ng m
et
al i
ons[
2 2
]
,f
re e ch l
o ri
n e, a nd
c
h l
or am i
n es[
2 3
]
F
orb
r a s s,i
t
i
s sp
e c ula
t
ed
t
h
at
in
st
e ad
of
t
h
e zi
n ci
nt
h
ebr a s s
g
r a n ul
et
r a n sf
e r rin
g
e
l
ect
ro nsd i
r e ct
ly
t
o ni
t
r at
e,t
h
e zi
n c and
c op p
e r a ct
as ag
al
va ni
c c el l
[
2 4
]
.I
nt
h i
sm
od
el
,t
h
ef
r e e el
e ct
r o n sw
o ul d m i
g
r at
et
ot h
e c op p
e r c at h
od
e.C
o n seq
u e ntl
y
, th
e c op p
e r cath
od
ew
o uld b
ew h
e r et
h
e a ct
u al
r ed
u ct
i
o n o c c u r sw it
h b
r a s sm
ed i
a[
2 4
]
.A
s e ri
es of
exp
e ri m
e nt
sw it
h b
ra s sm
ed i
ai
nt
h
e5
t
o1 6 5 g / L
co n cent
r at
i
o n r a ng
e,i
n a ni
ni
t
i
al
p
H
r a ng
e of 2
.0 0
t
o7
.0 0
,
w
e r ep
e rf
o rm
ed i
nw h i
ch b
r as sw
as al l
ow
ed
t
o r ea ct
w ith
ni
t
r at
eI
na
d d it
i
o nto
e xp
e ri m
e nts
w i
t
h b
ra s s,t
h
e ef f
ect
i
v e nes s of
t
h
e zi
n cg
ra n ul
e s a nd
c op p
e rp
ow d
e r at
r e
d
uci
ng
nit
rat
ew
ast
e st
ed
[
1
1
]
.T
h
e zi
n c e xp
e ri m
ent
sw
er e c o nd
u ct
ed i
n a c o n c ent
r ati
o n rang
e of
10 0
t
o1 6 5 g / L
a nd i
n a ni
nit
ia
l p H
r a ng
e of 2 0 0
to
7
.0 0
T h
e c op p
e r e xp
e ri m
e nt
sw
e r e c o nd
u ct
ed i
na c o n c en
t
rat
io n
r a ng
e of 5
t
o16 5 g / L
at
a ni
nit
i
al p H
of 2 0 0
[
1 1
]
.T h
e r e s ult
sf
r om
th
eb
r a s s, c op p
e r,a n
d
zi
n c exp
eri m
e nts
d
em
on st
rat
ed
th
at
w h i l
et
h
eb
r a s sm
ed i
a a nd
c op p
e rp
ow d
e rw
e r ei
n ef f
e cti
vei
nr e
d
u ci
ng
nit
r at
e, a zi
n c c o n c e ntr a
ti
o n of 10 0 g / L
(
s e eF i g
ur e1
)
, ac r o ss ani
ni
t
i
al p H
r a ng
e of 2
.0 0
t
o7
.0 0
,
f
ul ly
r ed
uc ed
ani
nit
i
al
nit
r at
e co n c ent
r at
i
o n of 3 0 m g
-
N / L
A
s
w i
th
t
h
e z e r o-v al
e nt
i
r o n , a ni
ni
t
i
al l
ow p H
enha n c e
d
th
e r at
e of
ni
tr a
t
e rem
oval
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ow
ev e r,
th
e zi
n cm
ed i
a al
s o r ed
u ced p
ract
i
c all y
T
i
m
e
(
h
)
T
i
m
e
(
h
)
I
n
i t i
a
l p H
=
2
.0 0
I
n
i t i
a
l p H
=
4
.0 0
I
n
i t i
a
l p H
=7
.
0 0
w
i t h
2 m M N
a
H C 0 3 B
u
f f
e r
F i
g
ure1
.R
e s ul
t
sf
rom H
ol
c om
b
et
al
.(
u np
ub l i
sh
ed
)
t
e st
i
ng p
ot
e nt
i
al
of
zi
n ci
n r ed
u ci
ng
ni
t
r at
e.I
ni
t
i
al
[
N O
3]
=3 0 m g N O
3-N /
L
,
l OOg
Z
n"
/
L
,i
ni
t
i
al p H
v al
u e s of
2
.0 0
,4
.0 0
a nd
7
.0 0
(
w i
t
h
a2 m
M
N
aH
C O
j)
b
uf f
e r.C
o nt
a ct t
i m
e s of 2 4
h
f
o ri
ni
t
i
al
p
H
of 2
.0 0
a nd 4 8 h f
o ri
ni
ti
al
p
H
s of 4
.0 0
a n
d 7
.0 0
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a n el F i g
u r e s :(
a) [
N O
3 "] (
m g
-N / L
)
v s.
T i
m
e(
h
)
,(
b
)
p
H
v s.t
i
m
e(
h
)
,(
c)
l
eg
e nd
T h
e c om p l
et
e sy
st
em
of
eq
u at
i
o n si
n v ol
v ed i
nth
e r ed
u ct
i
o n of
nit
r at
ew it
h
el
em
e nt
al
zi
n cw
a sd
evel
op
ed
a sf
ol l
ow
s[
2 1
]
:(
i t
c.8
)
Z
n^
^)
+2
H
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Z
n'' +H
,,
^)
{
Rx
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)
n o
;
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H
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M
r\
^
^
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rf
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N H
^
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H
p
(
E
x.10
)
n
o
;
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Z
n^
^)
^
Z
n'' +
N
O
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H
,0
{
Rx
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)
2
^
0
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12 / /
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«(
,)
^
5Z
«'" +
#
2,^,+
6 / /
2O
(
/ 6c
.12
)
n
o
;
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"+
3 Z
n^
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n^*
+
N H
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fl
{
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H
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(
R
x.H
)
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3 Z
W(,)-^
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2
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;
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"E
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0
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1 6 4 3K
E
° =l 0 6 3 V
E
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£
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£
° =2
.
2 7 2 K
A ft
e r stud y i
ng
th
e sy
stem
of
eq
u atio
ns ab
o v e,i
tw
as ap p
are n tfr
om
vie
^vi
ng
th
e sta nd
a rd
el
e ctr od
ep
ot
e nt
i
al f
or e ach
r e act
i
o nt
h
at
ele
m
e nt
al
zi
n cw
a sp
ot
e nt
i
al ly
v e ry
ef f
e ct
i
v e at
r ed
u ci
ng
ni
t
r at
e si
n c ea
l l
of
t
h
e r e a ct
i
o n sl i
st
ed
ab
o v ew
eret
h
erm
od y
nam i
cal ly f
av or ab l
eT
o ourk
n ow l
ed g
e,
t
h i
sb
od y
of
w
ork
a nd
t
h
at
f
r om H
ol
com b i
sth
efi
rst
w
ork i
nw h i
ch
zi
n cw
as used
t
o r ed
u c e nit
r at
ew i
t
h
ap
ot
e nt
i
al
ap p l i
cat
i
onf
ord
ri
nk i
ng w
at
e rt
r eat
m
ent
.A
s a r e sult
of
t
h
e a n al y
si
s a nd
e xp
e ri m
e nt
al
resul
t
s[
1 1
]
,t
h
e ob
j
ect
i
v e of
th i
sw
o rk w
a sto
p
erf
o rm
at
h
oroug h
a nal
y
si
sof
ni
t
r at
e r ed
u ct
i
onb y
zi
n c.1
.4 O b
j
e ct
i
ve sG i
v e nt
h
e ap p
a r e nt
s u c c e s s of
el
em
e nt
al
zi
n ci
n r ed
u ci
ng
ni
t
r at
e,it
w
a sd
e ci d
ed
t
op
u r s u et
h
ec
h
ar acte
ri
zat
i
on of
zi
n c as ap
ote
nt
i
al
sur rog
at
ete
ch
n ol
og y f
o r ze r o-v al
e nt
i
r o ni
nt
h
e r ed
u ct
i
o n of
n
i
t
r at
ef
r om d
ri
nk i
ng w
at
e r.T h
e ob
j
e ct
i
v e s of
th
e st
ud y w
e r e:•
T
o a n al y
z e rel
at
i
v e ef f
e ct
i
v en e s s of
el
em
e nt
al
zi
n c(
Z
n")
c om p
a red
t
o el
em
e nt
al i
ro n(
F
e")
,b
ra ss, a nd
cop p
er(
C
u °)
b
y
s ub
j
e ct
i
ng
e ach m
ed i
at
o a c om m
o n e xp
e ri m
e nt
•
T
o ch
a r act
eri
z eth
e ef f
e ct
of
ab
uf f
er,i
ni
t
i
al p H
, zi
n cd
o s e, a nd i
ni
t
i
al
nit
r at
e[
N O
3 "]
c o n c e n
t
r at
i
o n onth
e re act
i
o nk i
n et
i
c s of
ni
t
rat
e r ed
uct
i
o nb y
zi
n c•
T
od
e v el
op
a n em p i
ri
c al m
od
el fr
om
th
e e xp
eri m
e nt
al d
at
at
h
at
d
e s cri b
ed
th
ek i
n et
i
c so
f
t
h
e red
uct
i
o n of
nit
rat
ew i
th
el
em
e nt
al
zi
n c•
T
od
et
e rm i
n et
h
e el
e ct
r o nt
r a n sf
e rm
e ch
a ni
sm b
et
w
e e n zi
n c a nd
o xi d i
z ed
ni
t
r og
e ns
