Directory UMM :Data Elmu:jurnal:E:Environmental Management and Health:Vol07.Issue3.1996:
Fate of heavy metals via chemical-biological
upgrading of sewage treatment plant
Hussein I. Abdel-Shafy Wate r Po llutio n Re se arc h De partme nt, Natio nal Re se arc h
Ce ntre , Cairo , Egypt, and
Werner Hegemann and Carola Güldner Te c hnisc he Unive rsität, Be rlin,
Ge rmany
Examines the fate of heavy
metals in sewage water and
the sludge produced. Investigates the level of metals
before and after the use of
chemical coagulants as well
as throughout every process
of the plant. Results reveal
that the present upgrading of
the plant has a remarkable
improvement in the performance of the sewage treatment. Concludes that such
upgrading of the plant
reduces sewage tax because
of the improvement in performance. In addition, the
hydrolysis of the pre-treated
sludge can improve the denitrifi ed process and therefore can save energy, while
the application of lime can be
a substitution for enlarging
the plant itself.
The authors wish to express
their deep gratitude and
appreciation to the
Deutscher Akademischer
Austauschdienst for the
fellowship that was granted
to Dr Abdel-Shafy throughout
this study. The authors also
are in great debt to the
scientifi c co-operation of
both Dipl.-Ing. N. Peschen
and Dipl.-Ing. K.S. Iter,
Forschungsinstitut der
Forschungsgemeinschaft
Kalk and Mörtel eV, Köln, the
fi nancial support of Arbeitsgemeinschaft Industrieller
Forschungsgemeinschaften
(AIF) eV and for the facilities
provided by the Sanitary
Engineering Department,
Technische Universität,
Berlin.
Enviro nme ntal Manage me nt
and He alth
7 / 3 [ 1996] 2 8 –3 6
© MCB Unive rsity Pre ss
[ ISSN 0956-6163]
[ 28 ]
Introduction
P r ocess u pgr a din g a n d optim iza tion is
br oa dly defin ed a s th e pr ocedu r e th a t is
im plem en ted to secu r e m a xim u m efficien cy.
Th is defin ition in clu des cr iter ia su ch a s oper a tin g costs, pr ocess per for m a n ce, m a n a gem en t of m a ter ia l a n d la bou r r esou r ces. Th ese
cr iter ia a r e focu sed on th e pr odu cts gen er a ted by th e a sset in th e over a ll con text of
en vir on m en ta l r e gu la tion s.
Th e pr esen t stu dy con cer n s th e Or a n ien bu r g sew a ge w a ter tr ea tm en t pla n t wh ich is
loca ted in th e Sta te of Br a n den bu r g, n or th of
Ber lin . Th is pla n t, lik e m a n y oth er tr ea tm en t
pla n ts in th e n ew Ger m a n sta te[1], w a s
r eceivin g in cr ea sin g a m ou n ts of sew a ge
w a ter over qu ite a lon g tim e per iod. In or der
to fu lfil th e str in gen t efflu en t cr iter ia wh ich
a r e n ow bein g im plem en ted a ll over E u r ope,
a n in te gr a ted n u tr ien t r em ova l pr ocess
sh ou ld be a dded to su ch pla n t. It is well
k n ow n th a t th e in tr odu ction of ch em ica ls a t
th e pr e-pr ecipita tion sta ge im pr oves a n d
h om ogen izes th e clea n in g per for m a n ce of
tr ea tm en t pla n ts[2,3]. Typica l efflu en t con cen tr a tion lim its a r e 1-2 g/ m 3 ph osph or u s
a n d 5-10 g/ m 3 n itr ogen a s N H 4+ a n d 10-18
g/ m 3 a s th e su m of N H 4+ –N, N O 2– a n d
N O 3–N. Ch em ica l-biologica l w a stew a ter
tr ea tm en t for n itr ogen a n d ph osph or u s
r em ova l a r e well k n ow n for im pr ovin g a n d
h om ogen izin g th e pla n t tr ea tm en t per for m a n ce w ith low in vestm en t costs[3,4].
Th e objective of th e pr esen t pr oject is th e
tech n ica l con str u ction of a m ech a n ica lbiologica l sew a ge tr ea tm en t pla n t w ith
pr esen tly in su fficien t tr ea tm en t per for m a n ce
by in sta lla tion of a pH-con tr olled qu ick lim e
dosin g device. Th e pu r pose of lim e a ddition
(a n d/ or m eta llic sa lts) a t pr e-pr ecipita tion
sta ge, is to ch a n ge th e sew a ge com position a s
well a s th e u n stea dy in flu x of sew a ge[5].
Th e pH-va lu e is con tr olled a t a bou t 9.0-9.2.
On th e oth er h a n d, it is well k n ow n th a t lim e
a n d fer r ic ch lor ide a t su ch pH-va lu e a r e ca pa ble of pr ecipita tin g th e h eavy m eta ls[6,7]. In
spite of th e fa ct th a t m eta ls in th e sew a ge
w a ter a r e va r ied fr om ver y low to low levels,
pr ecipita tion of su ch m eta ls wou ld cer ta in ly
in cr ea se th eir con cen tr a tion in th e slu dge.
Th er efor e, th e level of m eta ls in th e slu dge in
th is ca se, depen ds m a in ly on m a n y differ en t
va r ia bles in clu din g: th e in itia l m eta l con cen tr a tion in th e sew a ge w a ter, th e doses of
ch em ica l coa gu la n ts, th e pH a n d th e dr y
slu dge weigh t[6-9].
Th e a im of th e pr esen t stu dy is to in vestiga te th e fa te of h eavy m eta ls in th e Or a n ien bu r g sew a ge w a ter pla n t befor e a n d a fter th e
u se of ch em ica l coa gu la n ts. F a te of m eta ls in
th e pr ecipita tes a n d th e pr odu ced slu dge a r e
a lso in vestiga ted. Th e level of m eta ls in th e
sew a ge w a ter a s well a s th e slu dge th r ou gh ou t ever y pr ocess of th e pla n t (i.e. scr een in g,
gr it ch a m ber, pr im a r y sedim en ta tion , slu dge
h ydr olysis, a er a tion for n itr ifica tion , a n d
secon da r y sedim en ta tion ) is a lso stu died. In
a ddition , a sem i-tech n ica l sca le for th e a n a er obic r ea ctor of slu dge is ca r r ied ou t in th e
pla n t. Th e pu r pose of th is r ea ctor is to pr odu ce a sou r ce of ca r bon to be ava ila ble for th e
den itr ifi ca tion pr ocess (i.e. to im pr ove th e
C/ N r a tio wh ich is too low a t pr esen t). Th is
a n a er obic digestion is ca r r ied ou t a t a n a cidified pH-va lu e a r ou n d 6.0 - 6.5. Su ch decr ea ses
in pH wou ld cer ta in ly in cr ea se th e solu bilities of cer ta in m eta ls in th e sew a ge
w a ter [6,7,10]. Th er efor e, th e fa te of h eavy
m eta ls in th e slu dge befor e a n d a fter th e
a n a er obic digestion is a lso a n objective of
th e pr esen t stu dy.
Th e a r isin g qu estion s a r e: Wh a t is th e fa te
of h eavy m eta ls in th e slu dge befor e a n d a fter
th e a n a er obic pr ocess? Wh a t is th e level of
th ese m eta ls in th e fi n a l w a stew a ter efflu en t
a n d th e slu dge? Ca n su ch pr odu ced slu dge be
u sed for a gr icu ltu r e pu r poses?
Materials and methods
Th e dia gr a m of th e sew a ge w a ter tr ea tm en t
pla n t a t Or a n ien bu r g is sh ow n in F igu r e 1.
Th e tech n ica l da ta of th e Or a n ien bu r g
tr ea tm en t pla n t a r e a s follow s:
• Wa stew a ter tr ea tm en t ca pa city: a t 40,00050,000 P E ; fl ow r a te: a t 5,500 m 3/ d.
• F in e scr een w ith a ba r dista n ce of 20cm .
• Ta n gen tia l gr it ch a m ber : w ith tu r bu len t
zon es for m ixin g qu ick lim e a n d FeCl 3
w a stew a ter a t pH ~ 9.0.
• Two pr im a r y sedim en ta tion ta n k s: volu m e
2 × 510m 3 r eten tion tim e: 3h .
Husse in I. Abde l Shafy,
We rne r He ge mann and
Caro la Güldne r
Fate o f he avy me tals via
c he mic al-bio lo gic al upgrading
o f se wage tre atme nt plant
Figure 1
Se wage wate r tre atme nt plant with quic k-lime additio n de vic e at Oranie nburg
Enviro nme ntal Manage me nt
and He alth
7 / 3 [1 9 9 6 ] 2 8 –3 6
Lime -Fe Cl3
additio n
Sc re e n
Influe nt
Unc o ntro lle d
wild-nitrific atio n
COD/ BOD5 re mo val
P-re mo val
Partial
nitrific atio n
Efflue nt
Grit c hambe r
Primary
se dime ntatio n
Sludge
•
Sludge
Primary sludge tank
Two se ptic tanks
(Havel)
Ae ratio n tank
Primary sludge
Fo uling
wate r
•
Se c o ndary
se dime ntatio n
To the anae ro bic re ac to r
(hydro lysis)
Sludge po lde rs
(drying be ds)
Aer a tion ta n k : volu m e: 2,280m 3;
loa din g: a t 0.15k g BOD 5/ k g MLSSxd;
SVl: a t 250/ k g; slu dge a ge: 10d.
•
Two secon da r y sedim en ta tion ta n k s:
volu m e: 2 × 1,280m 3; r eten tion tim e: 3h .
•
•
Slu dge tr ea tm en t: two open ta n k s: volu m e:
2 × 4,200m 3; r eten tion tim e: 60d.
Slu dge polder : r eten tion tim e: sever a l
m on th s.
Slu dge h ydr olysis: volu m e: 80; r eten tion
tim e: 0.7-2d; pH a r ou n d 6.0-6.5.
Table I
Le ve l o f he avy me tals in the waste wate r o f the se wage via diffe re nt tre atme nt pro c e sse s using
c he mic al c o agulants (mg/ l)
Different treatment steps
Wastewater (average)
After grit chamber and after chemical addition
After primary sedimentation
Biodegradation (nitrification)
Final effluent (after secondary sedimentation)
Cr
Ni
Cd
Pb
Cu
Zn
0.823
0.074
0.035
0.043
0.172
0.188
a
0.813
0.068
0.032
0.041
0.165
0.162
b
0.721
0.061
0.025
0.039
0.15
0.143
c
0.613
0.052
0.022
0.03
0.12
0.129
d
0.522
0.041
0.019
0.025
0.113
0.118
a
0.76
0.062
0.028
0.038
0.149
0.151
b
0.673
0.055
0.021
0.03
0.128
0.146
c
0.598
0.044
0.018
0.023
0.107
0.138
d
0.489
0.039
0.017
0.022
0.103
0.13
a
0.645
0.063
0.03
0.04
0.139
0.148
b
0.622
0.054
0.023
0.031
0.13
0.143
c
0.541
0.046
0.018
0.023
0.105
0.14
d
0.493
0.038
0.018
0.02
0.106
0.132
a
0.61
0.059
0.025
0.032
0.12
0.14
b
0.602
0.05
0.02
0.028
0.114
0.126
c
0.532
0.039
0.018
0.02
0.099
0.12
d
0.498
0.037
0.015
0.017
0.095
0.117
Notes:
Results presented here are the average of 12 weekly suc c essive samples
a: No c hemic als were added (c ontrol)
b: Addition of FeCl3 only (8.4 g/ m3 )
c : Addition of lime only (120 g/ m3 )
d: Addition of FeCl3 and lime
[ 29 ]
Husse in I. Abde l Shafy,
We rne r He ge mann and
Caro la Güldne r
Fate o f he avy me tals via
c he mic al-bio lo gic al upgrading
o f se wage tre atme nt plant
Enviro nme ntal Manage me nt
and He alth
7 / 3 [1 9 9 6 ] 2 8 –3 6
Dose of lim e = 120 g/ m 3 (20 per cen t); dose
of FeCl 3 = 8.4g Fe + 3/ m 3[3.4gla s FeCl 3/ m 3] a t
14/ d.
•
Week ly sa m ples of th e w a stew a ter a n d/ or
slu dge wer e collected for a per iod of 12 su ccessive week s. Th e w a stew a ter sa m ples wer e
fr esh ly filter ed th r ou gh Wh a tm a n N o. 4
equ iva len t filter pa per, a cidified to below pH
2.0 u sin g a n a lytica l r ea gen t (AR) of n itr ic
a cid. Th e slu dge sa m ples wer e oven dr ied a t
105°C for 24 h ou r s. A k n ow n weigh t of ea ch
slu dge sa m ple w a s a cid digested u sin g AR
n itr ic a cid followed by AR h ydr ogen per oxide,
a ccor din g to US E n vir on m en ta l P r otection
Agen cy[11].
Meta l con cen tr a tion s in th ese w a stew a ter
a n d slu dge sa m ples wer e deter m in ed u sin g
Va r ia n a tom ic a bsor ption spectr om eter,
m odel Spectr AA-400 equ ipped w ith GA 1-96
gr a ph ite tu be a tom izer, a tta ch ed by IBM
per son a l com pu ter AT (pr ogr a m m ed for
Va r ia n -Spectr AA-300/ 400). Th e stu died
m eta ls a r e Cr, N i, Cd, P b, Cu a n d Zn .
E a ch r esu lt of ea ch sa m ple is th e aver a ge of
ten sequ en tia l r ea din gs. As a n in str u m en t
a n d pr ocedu r e: bla n k of dou ble distilled
w a ter th a t digested u sin g th e pr ocedu r e pr eviou sly descr ibed w a s em ployed. Th e a ll-over
r esu lts pr esen ted h er e a r e th e aver a ge of a ll
th e stu died sa m ples.
Results and discussion
Th e level of h eavy m eta ls in th e r aw w a stew a ter of th e sew a ge befor e tr ea tm en t a n d
a fter gr it-ch a m ber (ch em ica l a ddition ), pr im a r y sedim en ta tion , a er a tion a s n itr ifica tion
a n d fin a lly a fter th e secon da r y sedim en ta tion
su ccessively a r e sh ow n in Ta ble I. Th e ch em ica ls wer e a dded a s 8.4g/ m 3 FeCl 3 or 120g/ m 3
Figure 2
The pe rc e ntage o f me tals e liminatio n in the waste wate r se wage via diffe re nt tre atme nt pro c e sse s
using c he mic al c o agulants
To tal re mo val (pe r c e nt)
60
To tal re mo val (pe r c e nt)
50
50
40
40
30
30
20
20
10
10
0
0
Cr
Ni
Cd
Pb
Cu
Zn
(a) Afte r grit-c hambe r (afte r c he mic al additio n)
Cr
Ni
Cd
Pb
(c ) Biodegradation (nitrific ation)
Cu
Zn
Cu
Zn
To tal re mo val (pe r c e nt)
To tal re mo val (pe r c e nt)
60
70
60
50
50
40
40
30
30
20
20
10
10
0
Cr
Ni
Cd
Pb
(b) After primary sedimentation
Cu
Zn
0
Cr
Ni
Cd
Pb
(d) Afte r se c o ndary se dime ntatio n
(sludge o f the final e fflue nt)
Key
No c he mic als we re adde d (c o ntro l)
Additio n o f Fe Cl3
Additio n o f lime o nly (1 2 0 g/ m3 )
Additio n o f lime and Fe Cl3
[ 30 ]
Husse in I. Abde l Shafy,
We rne r He ge mann and
Caro la Güldne r
Fate o f he avy me tals via
c he mic al-bio lo gic al upgrading
o f se wage tre atme nt plant
Enviro nme ntal Manage me nt
and He alth
7 / 3 [1 9 9 6 ] 2 8 –3 6
a dded to th e w a stew a ter in cor r ela tion w ith
th e con tr olled on e. Mea n wh ile, th e u se of th e
com bin ed coa gu la n ts, n a m ely FeCl 3 a n d lim e,
w a s m or e effective in r edu cin g th e level of
lim e a n d/ or com bin a tion of both FeCl 3 a n d
lim e togeth er. Resu lts obta in ed sh ow th a t a
n oticea ble decr ea se in th e level of m eta ls w a s
r ecor ded wh en th e ch em ica l coa gu la n ts wer e
Table II
Ave rage tre atme nt pe rfo rmanc e be fo re and during the lime phase to the se wage wate r at
Oranie nburg
Jan
Unit
BOD5 – precipitation after sedimentation
Total BOD5-degradation
COD-precipitation after sedimentationa
Total COD-degradationa
NH4-N in effluent
Inorganic N in effluent
Total P in effluent
%
%
%
%
(mg/ I)
(mg/ I)
(mg/ I)
Feb
M ar
Apr
Without lime addition
23
94
26
87
–
–
–
28
93
30
84
34
36
7.1
11
96
26
85
–
–
–
14
93
29
84
32
33
3.4
M ay
Jun
Jul
Lime addition
21
94
32
85
36
37
3
48
98
49
85
17
27
1.7
49
94
50
85
17
29
1.6
Note:
a COD-measurement
with potassium permanganate
Source:[5]
Table III
Le ve l o f he avy me tals in the pre tre atme nt sludge via the suc c e ssive tre atme nt pro c e ss (mg/ kg
dry we ight)
Successive treatment processes
Cr
Ni
M etals (mg/ kg dry weight)
Cd
Pb
Cu
Zn
Sludge of the raw sewage
Average
305
33
7.21
40
131
837
(before chemical addition)
Maximum
319
46
10.33
61
176
866
Minimum
301
22
1.04
18
64
791
After grit chamber
a
195
22
2.73
30
111
719
(after chemical addition)
b
215
32
3.11
42
123
790
c
240
41
4.82
55
131
803
d
282
58
5.13
68
133
827
a
92
31
1.32
38
108
866
b
48
29
1.14
37
97
754
c
34
25
1.07
34
82
683
After primary sedimentation
Aeration as biodegradation (nitrification)
d
31
20
0.51
33
80
662
a
302
32
7.01
38
125
871
b
214
31
2.24
37
113
852
c
153
24
1.33
31
104
730
d
102
20
0.71
29
100
694
After secondary sedimentation
a
137
30
1.96
42
108
854
(sludge of the final effluent)
b
118
27
1.05
33
92
843
c
91
23
0.74
29
83
669
d
Guideline
88
21
0.58
28
77
594
900
200
10.00
900
800
2,500
Notes:
Results presented here are the average of 12 weekly suc c essive samples
a: No c hemic als were added (c ontrol)
b: Addition of FeCl3 only (8.4g/ m3 )
c : Addition of lime only (120g/ m3 )
d: Addition of FeCl3 and lime
[ 31 ]
Husse in I. Abde l Shafy,
We rne r He ge mann and
Caro la Güldne r
Fate o f he avy me tals via
c he mic al-bio lo gic al upgrading
o f se wage tre atme nt plant
Enviro nme ntal Manage me nt
and He alth
7 / 3 [1 9 9 6 ] 2 8 –3 6
m eta ls followed by th e u se of lim e th a n FeCl 3.
F u r th er m or e, th e pr im a r y a n d secon da r y
sedim en ta tion wer e a lso sligh tly effective in
m eta ls elim in a tion . Th e per cen ta ges of
m eta ls elim in a tion in th e w a stew a ter via
th ese su ccessive tr ea tm en t pr ocesses u sin g
ch em ica l coa gu la n ts a r e pr esen ted in F igu r e
2. Su ch decr ea se in th e level of m eta ls is
a ttr ibu ted m a in ly to th e in cr ea se of pH-va lu e
to 9.0-9.2 wh ich in du ces th e decr ea se of m eta ls
solu bility[6,7,10,12]. As th e pH in cr ea se, th e
co-pr ecipita tion of m eta l h ydr oxide
in cr ea ses[6], bu t cer ta in a m ph oter ic m eta ls
w ill r e-dissolve a t h igh er pH-va lu es[6,7]. Th e
pr eviou s stu dy on th e sa m e pla n t pr oved th a t
lim e pr ecipita tion a t pH between 9.0-9.2 h a s
a lso im pr oved th e pr e-tr ea tm en t per for m a n ce
by @20 per cen t com pa r ed to th e zer o-ph a se
(Ta ble II)[5].
F u r th er stu dy w a s ca r r ied ou t on th e level
of m eta ls in th e sew a ge slu dge via th e sa m e
su ccessive tr ea tm en t pr ocesses u sin g lim e
a n d/ or FeCl 3 (Ta ble III). Th e given r esu lts
sh ow th a t th e ch em ica l coa gu la n t in cr ea sed
th e level of m eta ls in th e slu dge a s a r esu lt of
th e co-pr ecipita tion effect, i.e. con ver tin g th e
solu ble for m s of m eta l to th e in solu ble for m
in th e slu dge. Aga in th e u se of th e com bin ed
coa gu la n t in cr ea sed th e co-pr ecipita tion r a te.
However, th e u se of lim e w a s m or e effective
Figure 3
The pe rc e ntage o f me tals e liminatio n in the pe rme ate d sludge via diffe re nt tre atme nt pro c e sse s in
c o rre latio n to the le ve ls o f me tals in the raw se wage sludge
Me tals e liminatio n (pe r c e nt)
Me tals e liminatio n (pe r c e nt)
100
70
60
80
50
40
60
30
40
20
20
10
0
Cr
Ni
Cd
Pb
Cu
Zn
(a) Afte r grit-c hambe r (afte r c he mic al additio n)
Me tals e liminatio n (pe r c e nt)
100
0
Cr
Ni
Cd
Pb
(c ) Biodegradation (nitrific ation)
80
60
60
40
40
20
20
0
Cr
Ni
Cd
Pb
(b) After primary sedimentation
Zn
Cu
Zn
Me tals e liminatio n (pe r c e nt)
100
80
0
Cu
Cu
Zn
Cr
Ni
Cd
Pb
(d) Afte r se c o ndary se dime ntatio n
(sludge o f the final e fflue nt)
Key
No c he mic als we re adde d (c o ntro l)
Additio n o f lime o nly (1 2 0 g/ m3 )
Additio n o f Fe Cl3
Additio n o f lime and Fe Cl3
Table IV
Ge rman guide line re gulatio n fo r the le ve l o f he avy me tals in the sludge (mg/ kg dry we ight)
[ 32 ]
M etal
Ag
Cr
Ni
Cd
Pb
Cu
Zn
Guideline level
Source:[13]
8
900
200
10
900
800
2,500
Husse in I. Abde l Shafy,
We rne r He ge mann and
Caro la Güldne r
Fate o f he avy me tals via
c he mic al-bio lo gic al upgrading
o f se wage tre atme nt plant
Enviro nme ntal Manage me nt
and He alth
7 / 3 [1 9 9 6 ] 2 8 –3 6
th a n FeCl 3. Th e per cen ta ge of m eta ls elim in a tion in th e slu dge in cor r ela tion to th e or igin a l con cen tr a tion in th e r aw w a stew a ter is
illu str a ted in F igu r e 3. Th e pr im a r y a n d secon da r y sedim en ta tion ta n k s w ith th e th r ee
h ou r s’ r eten tion tim e sh owed h igh efficien cy
in tr a ppin g th e pr ecipita ted m eta ls. Th e level
of m eta ls in th e pr im a r y slu dge wer e fa r
below th e Ger m a n per m issible level (Ta ble
IV)[13]. In a ddition , th e for m er stu dies
Figure 4
Co rre latio n be twe e n the c apillary suc tio n time and the so lids c o nte nt
Capillary suc tio n time (se c o nds)
700
Key
Be fo re c he mic al additio n
Lime additio n
Lime and Fe Cl3 additio n
600
500
400
Faste r
filte ring
300
200
100
0
1
2
3
Solids c ontent (per c ent)
4
5
6
7
8
Source: [5 ]
Table V
Le ve l o f he avy me tals in the sludge be fo re and afte r the anae ro bic re ac to r pro c e ss (mg/ kg dry
we ight)(pH 6 .0 -6 .5 )
Type of treatment
Cr
Ni
M etals (mg/ kg dry weight)
Cd
Pb
Cu
Zn
After primary sedimentation
a
96
31
1.32
38
108
866
(influent to the anaerobic reactor)
b
48
29
1.14
37
97
760
c
34
25
1.07
34
82
683
d
31
20
0.51
33
80
662
Average
46
25
0.95
31
92
757
After secondary sedimentation
a
137
30
1.96
42
108
854
(influent to the anaerobic reactor)
b
118
27
1.05
33
92
943
Final effluent of the anaerobic reactor
Guideline
c
10
23
0.74
29
83
669
d
88
21
0.58
28
77
594
Average
103
28
1.07
30
91
845
Average
99
39
1.92
49
157
876
Maximum
117
36
2.11
54
187
951
Minimum
81
24
0.38
22
70
472
900
200
10.00
900
800
2,500
Notes:
Results presented here are the average of 12 weekly suc c essive samples
Average = average metal c onc entration of the four different sewage sludges
a: No c hemic als were added (c ontrol)
b: Addition of FeCl3 only (8,4g/ m3 )
c : Addition of lime only (120g/ m3 )
d: Addition of FeCl3 and lime
[ 33 ]
Husse in I. Abde l Shafy,
We rne r He ge mann and
Caro la Güldne r
Fate o f he avy me tals via
c he mic al-bio lo gic al upgrading
o f se wage tre atme nt plant
Enviro nme ntal Manage me nt
and He alth
7 / 3 [1 9 9 6 ] 2 8 –3 6
[ 34 ]
sh owed th a t th e ch a r a cter istics of th is slu dge
wer e sign ifica n tly im pr oved by th e a ddition
of lim e. Du r in g th e lim e ph a se th e solids
con ten t in cr ea sed fr om between 1 a n d 3 per
cen t to between 3 a n d 8 per cen t a s sh ow n in
F igu r e 4, i.e. in cr ea sin g th e slu dge weigh t
wh ile th e slu dge volu m e r em a in s th e sa m e[5].
Th e loss a t VSS decr ea ses fr om @ 75 per cen t
to @ 50 per cen t.
Rea son a ble por tion s of th e liqu id slu dge
obta in ed fr om both pr im a r y a n d secon da r y
sedim en ta tion ta n k s wer e su bjected to a cidifica tion a n d h ydr olysis u sin g a sem i-tech n ica l
sca le a n a er obic r ea ctor (F igu r e 1). Th is biologica l h ydr olysis a n d a cidifi ca tion ta k e pla ce
a t pH-va lu es between 6.0-6.5 w ith a r eten tion
tim e of on e to two days. Th e level of m eta ls in
th e slu dge befor e a n d a fter th e a n a er obic
h ydr olysis is pr esen ted in Ta ble V. Th e level
of m eta ls in th e fin a l efflu en t of th e a n a er obic
r ea ctor is sligh tly h igh er th a n th a t of th e
in flu en t to th e r ea ctor. Su ch sligh t in cr ea se of
m eta ls r efer r ed m a in ly to th e decr ea se of pH
fr om 9.0-9.2 to th e sligh t a cidic va lu e of 6.0-6.5
wh ich in du ce th e pa r tia l dessolu tion of cer ta in m eta ls in to th e system [6,7,12]. Th e level
of m eta ls in th e fin a l h ydr olized slu dge w a s
still below th e per m issible level (Ta ble
IV)[13]. Cor r ela tion between th e level of
m eta ls in th e h ydr olyzed slu dge efflu en t of
th e a n a er obic r ea ctor a n d th e level of m eta ls
in ea ch of th e slu dge in flu en t to th e a n a er obic
r ea ctor is r epr esen ted in F igu r e 5. Th e pr odu ced vola tile or ga n ic a cids (C2-C6) for m ed
du r in g th is pr ocess wer e exa m in ed pr eviou sly[5], a n d it w a s pr oved th a t th ey ca n be
u sed a s a sou r ce of ca r bon for th e den itr ifica tion [14-16]. F igu r e 6 pr esen ts th e cor r ela tion
between th e level of m eta ls in th e fi n a l w a stew a ter of th e u pgr a ded pla n t a n d th e level of
m eta ls in th e fi n a l w a stew a ter of th e a n a er obic r ea ctor.
Th e pr esen t stu dy w a s expa n ded to in clu de
th e level of m eta ls in tr ea ted slu dge, n a m ely
two septic ta n k s a n d fou r (dr yin g beds)
slu dge polder s (Ta ble VI). Th is ta ble in clu des
a lso th e slu dge ch a r a cter istics, n a m ely th e
per cen ta ge of th e dr y r esidu e a n d per cen ta ge
of vola tile or ga n ic m a tter. Th e r esu lts
obta in ed sh ow th a t th e level of m eta ls in th e
two septic ta n k s is h igh er th a n th a t of th e
pr im a r y slu dge befor e tr ea tm en t. F u r th er
in cr ea se in th e level of m eta ls w a s exh ibited
in th e slu dge polder s (dr yin g beds). Cor r ela tion between th e level of m eta ls in th e fi n a l
slu dge polder a n d th e Ger m a n gu ide lin e[13]
sh ow th a t th e level of N i (aver a ge 317 m g/ k g
dr y weigh t) is h igh er th a n th e per m issible
level (Ta ble IV). Cor r ela tion between th e level
of m eta ls in th e w a stew a ter of th e u pgr a ded
pr ocess a n d th e w a stew a ter of th e a n a er obic
r ea ctor is given in F igu r e 6.
Figure 5
Co rre latio n be twe e n the le ve l o f me tals in the
hydro lyze d sludge e fflue nt and the two diffe re nt
influe nts (name ly afte r primary se dime ntatio n
and afte r the se c o ndary se dime ntatio n) to the
anae ro bic re ac to r
mg/ kg dry we ight
1 ,0 0 0
100
10
0
Cr
Ni
Cd
Pb
Cu
Zn
Key
Afte r primary se dime ntatio n
(influe nt to re ac to r)
Afte r se c o ndary se dime ntatio n
(influe nt to re ac to r)
Hydro lyze d sludge
(e fflue nt o f re ac to r)
Note: The re sults pre se nte d he re are the ave rage
o f the fo ur diffe re nt sludge s fo r the 1 2 suc c e ssive
we e kly sample s
Figure 6
Co rre latio n be twe e n the le ve l o f he avy me tals
in the final waste wate r o f the upgrade d plant
and the le ve l o f me tals in the final waste wate r
o f the anae ro bic re ac to r
Me tals (mg/ litre )
0 .8
0 .6
0 .4
0 .2
0
Cr
Key
Ni
Cd
Pb
Cu
Zn
Final upgraded wastewater
Effluent of the anaerobic reac tor
Th e over a ll r esu lts of th e pr esen t stu dy
r evea led th a t th e u pgr a din g of th e sew a ge
tr ea tm en t pla n t by th e a pplica tion of lim e in
th e pr e-pr ecipita tion sta ges h a s a r em a r k a ble
im pr ovem en t in per for m a n ce of sew a ge tr ea tm en ts. Su ch im pr ovem en t w a s expr essed n ot
on ly in decr ea sin g th e level of m eta ls in th e
w a stew a ter (Ta bles I a n d II), bu t a lso in th e
sta biliza tion of th e clea n in g per for m a n ce of
Husse in I. Abde l Shafy,
We rne r He ge mann and
Caro la Güldne r
Fate o f he avy me tals via
c he mic al-bio lo gic al upgrading
o f se wage tre atme nt plant
Enviro nme ntal Manage me nt
and He alth
7 / 3 [1 9 9 6 ] 2 8 –3 6
Table VI
Charac te ristic s and the le ve l o f me tals in the primary and the tre ate d sludge (se ptic tanks and
sludge po lde r)
Type of sludge
Before the sludge treatment
(primary sludge)
Septic tank (No. 1)
Septic tank (No. 2)
Sludge polder (drying beds)
M etals (mg/ kg dry weight)
Cd
Pb
Cu
Cr
Ni
Zn
Average
104
25
0.93
33.6
111
730
Maximum
151
37
2.01
43.5
178
997
Minimum
78
19
0.3
25.4
69
496
Average
217
187
2.21
118.2
214
1,993
Maximum
295
219
7.92
218.4
351
2,501
Minimum
187
76
0.79
97.3
179
705
Average
196
308
2.54
125.8
204
2,013
Maximum
257
395
5.93
216.8
312
2,704
Maximum
134
112
0.51
90.8
163
812
Dry
residue %
%
ovm
6.39
38.46
4.18
57.83
3.44
59.86
Average
322
317
3.19
126.8
239
2,451
9.22
61.08
Maximum
517
386
6.98
247.3
352
2,985
12.56
62.87
5.98
59.65
Maximum
Guideline
239
175
0.79
97.8
193
2,175
900
200
10.10
900.0
800
2,500
Note:
ovm: perc entage of the volatile organic matter
th e over loa ded pla n t[5]. Th e decr ea se of
m eta ls con cen tr a tion in th e w a stew a ter w a s
du e to th e in cr ea se of pH-va lu es a s a r esu lt of
lim e a ddition . As th e pH-in cr ea se, th e for m a tion of m eta l h ydr oxide in cr ea ses[6,7,12]. Th is
r ela tion sh ip is expr essed by th e follow in g
sta bility pr odu ct equ a tion :
(M + 2)(OM)2 = K sp (solu bility con sta n t)
Th e solu bility pr odu ct con sta n ts for a n u m ber of m eta ls a r e well docu m en ted a n d
a lr ea dy pu blish ed[13]. However, beca u se of
pr ecipita tion a gein g, in com plete solid sepa r a tion or th e co-pr ecipita tion a n d a dsor ption
effects in w a stew a ter solu bility pr odu cts
pr ovide on ly a gen er a l gu ide to r esidu a l m eta l
con cen tr a tion to be expected in pr a ctice[10].
Th e level of m eta ls in th e pr e-tr ea tm en t
slu dge is fa r below th e Ger m a n r estr iction
lim its[13]. It h a s been r epor ted th a t th is pr etr ea tm en t slu dge is im pr oved con sider a bly in
ter m s of th ick en in g a n d dr a in in g qu a lities[5].
Despite th e in cr ea se in th e solid con ten t, on ly
sligh t in cr ea se in th e slu dge volu m e w a s
r epor ted[5].
Th e h ydr olysis a n d a cidifi ca tion of th e
pr im a r y slu dge exh ibited con sider a ble
in cr ea se in th e level of m eta ls du e to th e
decr ea se of pH-va lu e fr om 9.0-9.2 to 6.0-6.5.
However, th e vola tile or ga n ic a cids (C2-C6)
for m ed du r in g th e pr ocess ca n be u sed a s a
sou r ce of ca r bon for th e den itr ifica tion [14-16].
Th e level of N i in th e tr ea ted slu dge of th e
dr yin g bed r ea ch ed 317m g/ k g. Th is h igh level
of N i is du e to th e disch a r ge of cer ta in in du str ia l w a stew a ter to th e sewer system .
Tr ea tm en t of th is in du str ia l w a stew a ter
sh ou ld be ca r r ied ou t befor e disch a r gin g to
th e sewer system . Accor din g to th e Ger m a n
r e gu la tion N i sh ou ld n ot exceed 200m g/ k g a s
dr y weigh t. Th er efor e, su ch slu dge ca n n ot be
u sed a s a m a n u r e in a gr icu ltu r e[17]. On th e
oth er h a n d, su ch u pgr a din g of th e sew a ge
pla n t im pr oved th e per for m a n ce of tr ea tm en t
a n d th is r edu ces sew a ge ta x. Mea n wh ile, th e
h ydr olysis of th e pr e-tr ea tm en t slu dge ca n
im pr ove th e per for m a n ce of th e den itr ifica tion pr ocess a n d th er efor e it ca n save en er gy.
F u r th er m or e, th e lim e a pplica tion for th e
u pgr a din g of th e sew a ge pla n t ca n be a su bstitu tion for en la r gin g th e pla n t itself.
It is wor th n oticin g h er e th a t th e level of Zn
in th e dr yin g bed slu dges r a n ges fr om 2,175 to
2,985 w ith th e aver a ge of 2,451m g/ k g dr y
weigh t (Ta ble VI). Th e gu idelin e[5] is
2,500m g/ k g.
Th e pr esen t gu idelin e lim its for th e level
of m eta l in slu dge is su fficien t for th e en vir on m en ta l pr otection . Th e settin g of lim its
a t levels lower th a n n ecessa r y ca n be cou n ter pr odu ctive a n d lea d to ille ga l discon tin u ou s
disch a r ges a n d la ck of co-oper a tion between
th e en for cem en t body a n d th e fir m s. Th is
ca n lea d to excessive costs in con tr ol a n d
m or e fr equ en t fa ilu r e to m eet th e r equ ir ed
sta n da r d.
References
1
Ru dolph , D., “Rech tsgr u n dla gen der
Abw a sser ein leitu n g in den n eu en
[ 35 ]
Husse in I. Abde l Shafy,
We rne r He ge mann and
Caro la Güldne r
Fate o f he avy me tals via
c he mic al-bio lo gic al upgrading
o f se wage tre atme nt plant
Enviro nme ntal Manage me nt
and He alth
7 / 3 [1 9 9 6 ] 2 8 –3 6
2
3
4
5
6
7
8
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[ 36 ]
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con cept”, in Ha h n , H.H. a n d Klu te, R. (E ds),
Ch em ica l Wa ter a n d Wa stew a ter T rea tm en t,
Spr in ger -Ver la g, Heidelber g, Ber lin , 1990,
pp. 499-509.
Pesch en , N. a n d Sch u ster, G., “Steiger u n g der
Rein igu n gsleistu n g u n d Sta bilisier u n g des
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He gem a n n , W., “An wen du n g von F ä llu n gsver fa h r en zu r Ver besser u n g der Leistu n gsfä h igk eit biologisch er An la gen a u s
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existin g w a stew a ter tr ea tm en t system ”, 2n d
in ter n a tion a l specia lized con fer en ce: u pgr a din g of w a stew a ter tr ea tm en t pla n ts, Ber lin ,
21-24 Septem ber 1993.
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a n d Mn fr om in du str ia l w a stew a ter ”, B u lletin
N a tion a l R esea rch Cen tre, Vol. 17 N o. 3, 1992,
pp. 153-60.
Abu -E l-Wa fa , O., Abdel-Sh a fy, H.I. a n d
E l-Ga m a l, I.M., “Stu dies on h eavy m eta ls
r em ova l via ch em ica l tr ea tm en t”, T h e 1st
n a tion a l con feren ce – In stitu te of En viron m en ta l S tu d ies a n d R esea rch , Ca ir o, 31 J a n u a r y4 Febr u a r y 1988, pp. 757-65.
Leon h a r d, K. a n d He gem a n n , W., “Th e effect of
copper a n d zin c in sew a ge slu dge”, B er ich te
a u s Wa ssergü tew ir tsch a ft u n d Gesü n d h eitsin gen ieu r w esen , T U M ü n ch en , N o. 62, 1985, pp. 1-55.
E l Ga m a l, I.M. a n d Abdel-Sh a fy, H.I., “Role of
la n d ir r iga tion by liqu id sew a ge on th e u pta k e
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11
12
13
14
15
16
17
of m eta ls a n d n u tr ien t elem en ts by pla n ts”,
B iom a ss a n d B ioen erg y – A n In ter n a tion a l
J ou r n a l, Vol. 1 N o. 5, 1991, pp. 275-80.
E l-Goh a r y, F.A., La sh een , M.R. a n d AbdelSh a fy, H.I., “Tr a ce m eta ls r em ova l fr om w a stew a ter via ch em ica l tr ea tm en t”, Heavy Meta ls
in th e E n vir on m en t – Th e In ter n a tion a l Con fer en ce, Lon don , Septem ber 1979.
US E n vir on m en ta l P r otection Agen cy, M eth od s
for Ch em ica l A n a lysis of Wa ter a n d
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Wa sh in gton , DC, 1974.
Feitk n ech t, W. a n d Sch in dler, P., “Solu bility
con sta n ts of m eta l oxides, m eta l h ydr oxides
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den itr ifi ca tion poten tia l in biologica l w a stew a ter tr ea tm en t by dosin g ca r bon fr om slu dge
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Ch em ica l Wa ter a n d Wa stew a ter T rea tm en t,
Spr in ger -Ver la g, Ber lin -Heidelber g, 1990.
Ka r lsson , I., Gör a n sson , J . a n d Rin del, K.,
“Use of in ter n a l ca r bon fr om slu dge h ydr olysis
in biologica l w a stew a ter tr ea tm en t”, in Ha h n ,
H.H. a n d Klu te, R. (E ds), Ch em ica l Wa ter a n d
Wa stew a ter T rea tm en t, Spr in ger -Ver la g,
Ber lin -Heidelber g, 1990.
Kofoed, A.D., Willia m s, J .H. a n d L’Her m ite, P.,
Efficien t L a n d Use of S lu d ge a n d M a n u re, E lsevier Applied Scien ce P u blish er s, Lon don a n d
N ew Yor k , N Y, 1985, p. 245.
upgrading of sewage treatment plant
Hussein I. Abdel-Shafy Wate r Po llutio n Re se arc h De partme nt, Natio nal Re se arc h
Ce ntre , Cairo , Egypt, and
Werner Hegemann and Carola Güldner Te c hnisc he Unive rsität, Be rlin,
Ge rmany
Examines the fate of heavy
metals in sewage water and
the sludge produced. Investigates the level of metals
before and after the use of
chemical coagulants as well
as throughout every process
of the plant. Results reveal
that the present upgrading of
the plant has a remarkable
improvement in the performance of the sewage treatment. Concludes that such
upgrading of the plant
reduces sewage tax because
of the improvement in performance. In addition, the
hydrolysis of the pre-treated
sludge can improve the denitrifi ed process and therefore can save energy, while
the application of lime can be
a substitution for enlarging
the plant itself.
The authors wish to express
their deep gratitude and
appreciation to the
Deutscher Akademischer
Austauschdienst for the
fellowship that was granted
to Dr Abdel-Shafy throughout
this study. The authors also
are in great debt to the
scientifi c co-operation of
both Dipl.-Ing. N. Peschen
and Dipl.-Ing. K.S. Iter,
Forschungsinstitut der
Forschungsgemeinschaft
Kalk and Mörtel eV, Köln, the
fi nancial support of Arbeitsgemeinschaft Industrieller
Forschungsgemeinschaften
(AIF) eV and for the facilities
provided by the Sanitary
Engineering Department,
Technische Universität,
Berlin.
Enviro nme ntal Manage me nt
and He alth
7 / 3 [ 1996] 2 8 –3 6
© MCB Unive rsity Pre ss
[ ISSN 0956-6163]
[ 28 ]
Introduction
P r ocess u pgr a din g a n d optim iza tion is
br oa dly defin ed a s th e pr ocedu r e th a t is
im plem en ted to secu r e m a xim u m efficien cy.
Th is defin ition in clu des cr iter ia su ch a s oper a tin g costs, pr ocess per for m a n ce, m a n a gem en t of m a ter ia l a n d la bou r r esou r ces. Th ese
cr iter ia a r e focu sed on th e pr odu cts gen er a ted by th e a sset in th e over a ll con text of
en vir on m en ta l r e gu la tion s.
Th e pr esen t stu dy con cer n s th e Or a n ien bu r g sew a ge w a ter tr ea tm en t pla n t wh ich is
loca ted in th e Sta te of Br a n den bu r g, n or th of
Ber lin . Th is pla n t, lik e m a n y oth er tr ea tm en t
pla n ts in th e n ew Ger m a n sta te[1], w a s
r eceivin g in cr ea sin g a m ou n ts of sew a ge
w a ter over qu ite a lon g tim e per iod. In or der
to fu lfil th e str in gen t efflu en t cr iter ia wh ich
a r e n ow bein g im plem en ted a ll over E u r ope,
a n in te gr a ted n u tr ien t r em ova l pr ocess
sh ou ld be a dded to su ch pla n t. It is well
k n ow n th a t th e in tr odu ction of ch em ica ls a t
th e pr e-pr ecipita tion sta ge im pr oves a n d
h om ogen izes th e clea n in g per for m a n ce of
tr ea tm en t pla n ts[2,3]. Typica l efflu en t con cen tr a tion lim its a r e 1-2 g/ m 3 ph osph or u s
a n d 5-10 g/ m 3 n itr ogen a s N H 4+ a n d 10-18
g/ m 3 a s th e su m of N H 4+ –N, N O 2– a n d
N O 3–N. Ch em ica l-biologica l w a stew a ter
tr ea tm en t for n itr ogen a n d ph osph or u s
r em ova l a r e well k n ow n for im pr ovin g a n d
h om ogen izin g th e pla n t tr ea tm en t per for m a n ce w ith low in vestm en t costs[3,4].
Th e objective of th e pr esen t pr oject is th e
tech n ica l con str u ction of a m ech a n ica lbiologica l sew a ge tr ea tm en t pla n t w ith
pr esen tly in su fficien t tr ea tm en t per for m a n ce
by in sta lla tion of a pH-con tr olled qu ick lim e
dosin g device. Th e pu r pose of lim e a ddition
(a n d/ or m eta llic sa lts) a t pr e-pr ecipita tion
sta ge, is to ch a n ge th e sew a ge com position a s
well a s th e u n stea dy in flu x of sew a ge[5].
Th e pH-va lu e is con tr olled a t a bou t 9.0-9.2.
On th e oth er h a n d, it is well k n ow n th a t lim e
a n d fer r ic ch lor ide a t su ch pH-va lu e a r e ca pa ble of pr ecipita tin g th e h eavy m eta ls[6,7]. In
spite of th e fa ct th a t m eta ls in th e sew a ge
w a ter a r e va r ied fr om ver y low to low levels,
pr ecipita tion of su ch m eta ls wou ld cer ta in ly
in cr ea se th eir con cen tr a tion in th e slu dge.
Th er efor e, th e level of m eta ls in th e slu dge in
th is ca se, depen ds m a in ly on m a n y differ en t
va r ia bles in clu din g: th e in itia l m eta l con cen tr a tion in th e sew a ge w a ter, th e doses of
ch em ica l coa gu la n ts, th e pH a n d th e dr y
slu dge weigh t[6-9].
Th e a im of th e pr esen t stu dy is to in vestiga te th e fa te of h eavy m eta ls in th e Or a n ien bu r g sew a ge w a ter pla n t befor e a n d a fter th e
u se of ch em ica l coa gu la n ts. F a te of m eta ls in
th e pr ecipita tes a n d th e pr odu ced slu dge a r e
a lso in vestiga ted. Th e level of m eta ls in th e
sew a ge w a ter a s well a s th e slu dge th r ou gh ou t ever y pr ocess of th e pla n t (i.e. scr een in g,
gr it ch a m ber, pr im a r y sedim en ta tion , slu dge
h ydr olysis, a er a tion for n itr ifica tion , a n d
secon da r y sedim en ta tion ) is a lso stu died. In
a ddition , a sem i-tech n ica l sca le for th e a n a er obic r ea ctor of slu dge is ca r r ied ou t in th e
pla n t. Th e pu r pose of th is r ea ctor is to pr odu ce a sou r ce of ca r bon to be ava ila ble for th e
den itr ifi ca tion pr ocess (i.e. to im pr ove th e
C/ N r a tio wh ich is too low a t pr esen t). Th is
a n a er obic digestion is ca r r ied ou t a t a n a cidified pH-va lu e a r ou n d 6.0 - 6.5. Su ch decr ea ses
in pH wou ld cer ta in ly in cr ea se th e solu bilities of cer ta in m eta ls in th e sew a ge
w a ter [6,7,10]. Th er efor e, th e fa te of h eavy
m eta ls in th e slu dge befor e a n d a fter th e
a n a er obic digestion is a lso a n objective of
th e pr esen t stu dy.
Th e a r isin g qu estion s a r e: Wh a t is th e fa te
of h eavy m eta ls in th e slu dge befor e a n d a fter
th e a n a er obic pr ocess? Wh a t is th e level of
th ese m eta ls in th e fi n a l w a stew a ter efflu en t
a n d th e slu dge? Ca n su ch pr odu ced slu dge be
u sed for a gr icu ltu r e pu r poses?
Materials and methods
Th e dia gr a m of th e sew a ge w a ter tr ea tm en t
pla n t a t Or a n ien bu r g is sh ow n in F igu r e 1.
Th e tech n ica l da ta of th e Or a n ien bu r g
tr ea tm en t pla n t a r e a s follow s:
• Wa stew a ter tr ea tm en t ca pa city: a t 40,00050,000 P E ; fl ow r a te: a t 5,500 m 3/ d.
• F in e scr een w ith a ba r dista n ce of 20cm .
• Ta n gen tia l gr it ch a m ber : w ith tu r bu len t
zon es for m ixin g qu ick lim e a n d FeCl 3
w a stew a ter a t pH ~ 9.0.
• Two pr im a r y sedim en ta tion ta n k s: volu m e
2 × 510m 3 r eten tion tim e: 3h .
Husse in I. Abde l Shafy,
We rne r He ge mann and
Caro la Güldne r
Fate o f he avy me tals via
c he mic al-bio lo gic al upgrading
o f se wage tre atme nt plant
Figure 1
Se wage wate r tre atme nt plant with quic k-lime additio n de vic e at Oranie nburg
Enviro nme ntal Manage me nt
and He alth
7 / 3 [1 9 9 6 ] 2 8 –3 6
Lime -Fe Cl3
additio n
Sc re e n
Influe nt
Unc o ntro lle d
wild-nitrific atio n
COD/ BOD5 re mo val
P-re mo val
Partial
nitrific atio n
Efflue nt
Grit c hambe r
Primary
se dime ntatio n
Sludge
•
Sludge
Primary sludge tank
Two se ptic tanks
(Havel)
Ae ratio n tank
Primary sludge
Fo uling
wate r
•
Se c o ndary
se dime ntatio n
To the anae ro bic re ac to r
(hydro lysis)
Sludge po lde rs
(drying be ds)
Aer a tion ta n k : volu m e: 2,280m 3;
loa din g: a t 0.15k g BOD 5/ k g MLSSxd;
SVl: a t 250/ k g; slu dge a ge: 10d.
•
Two secon da r y sedim en ta tion ta n k s:
volu m e: 2 × 1,280m 3; r eten tion tim e: 3h .
•
•
Slu dge tr ea tm en t: two open ta n k s: volu m e:
2 × 4,200m 3; r eten tion tim e: 60d.
Slu dge polder : r eten tion tim e: sever a l
m on th s.
Slu dge h ydr olysis: volu m e: 80; r eten tion
tim e: 0.7-2d; pH a r ou n d 6.0-6.5.
Table I
Le ve l o f he avy me tals in the waste wate r o f the se wage via diffe re nt tre atme nt pro c e sse s using
c he mic al c o agulants (mg/ l)
Different treatment steps
Wastewater (average)
After grit chamber and after chemical addition
After primary sedimentation
Biodegradation (nitrification)
Final effluent (after secondary sedimentation)
Cr
Ni
Cd
Pb
Cu
Zn
0.823
0.074
0.035
0.043
0.172
0.188
a
0.813
0.068
0.032
0.041
0.165
0.162
b
0.721
0.061
0.025
0.039
0.15
0.143
c
0.613
0.052
0.022
0.03
0.12
0.129
d
0.522
0.041
0.019
0.025
0.113
0.118
a
0.76
0.062
0.028
0.038
0.149
0.151
b
0.673
0.055
0.021
0.03
0.128
0.146
c
0.598
0.044
0.018
0.023
0.107
0.138
d
0.489
0.039
0.017
0.022
0.103
0.13
a
0.645
0.063
0.03
0.04
0.139
0.148
b
0.622
0.054
0.023
0.031
0.13
0.143
c
0.541
0.046
0.018
0.023
0.105
0.14
d
0.493
0.038
0.018
0.02
0.106
0.132
a
0.61
0.059
0.025
0.032
0.12
0.14
b
0.602
0.05
0.02
0.028
0.114
0.126
c
0.532
0.039
0.018
0.02
0.099
0.12
d
0.498
0.037
0.015
0.017
0.095
0.117
Notes:
Results presented here are the average of 12 weekly suc c essive samples
a: No c hemic als were added (c ontrol)
b: Addition of FeCl3 only (8.4 g/ m3 )
c : Addition of lime only (120 g/ m3 )
d: Addition of FeCl3 and lime
[ 29 ]
Husse in I. Abde l Shafy,
We rne r He ge mann and
Caro la Güldne r
Fate o f he avy me tals via
c he mic al-bio lo gic al upgrading
o f se wage tre atme nt plant
Enviro nme ntal Manage me nt
and He alth
7 / 3 [1 9 9 6 ] 2 8 –3 6
Dose of lim e = 120 g/ m 3 (20 per cen t); dose
of FeCl 3 = 8.4g Fe + 3/ m 3[3.4gla s FeCl 3/ m 3] a t
14/ d.
•
Week ly sa m ples of th e w a stew a ter a n d/ or
slu dge wer e collected for a per iod of 12 su ccessive week s. Th e w a stew a ter sa m ples wer e
fr esh ly filter ed th r ou gh Wh a tm a n N o. 4
equ iva len t filter pa per, a cidified to below pH
2.0 u sin g a n a lytica l r ea gen t (AR) of n itr ic
a cid. Th e slu dge sa m ples wer e oven dr ied a t
105°C for 24 h ou r s. A k n ow n weigh t of ea ch
slu dge sa m ple w a s a cid digested u sin g AR
n itr ic a cid followed by AR h ydr ogen per oxide,
a ccor din g to US E n vir on m en ta l P r otection
Agen cy[11].
Meta l con cen tr a tion s in th ese w a stew a ter
a n d slu dge sa m ples wer e deter m in ed u sin g
Va r ia n a tom ic a bsor ption spectr om eter,
m odel Spectr AA-400 equ ipped w ith GA 1-96
gr a ph ite tu be a tom izer, a tta ch ed by IBM
per son a l com pu ter AT (pr ogr a m m ed for
Va r ia n -Spectr AA-300/ 400). Th e stu died
m eta ls a r e Cr, N i, Cd, P b, Cu a n d Zn .
E a ch r esu lt of ea ch sa m ple is th e aver a ge of
ten sequ en tia l r ea din gs. As a n in str u m en t
a n d pr ocedu r e: bla n k of dou ble distilled
w a ter th a t digested u sin g th e pr ocedu r e pr eviou sly descr ibed w a s em ployed. Th e a ll-over
r esu lts pr esen ted h er e a r e th e aver a ge of a ll
th e stu died sa m ples.
Results and discussion
Th e level of h eavy m eta ls in th e r aw w a stew a ter of th e sew a ge befor e tr ea tm en t a n d
a fter gr it-ch a m ber (ch em ica l a ddition ), pr im a r y sedim en ta tion , a er a tion a s n itr ifica tion
a n d fin a lly a fter th e secon da r y sedim en ta tion
su ccessively a r e sh ow n in Ta ble I. Th e ch em ica ls wer e a dded a s 8.4g/ m 3 FeCl 3 or 120g/ m 3
Figure 2
The pe rc e ntage o f me tals e liminatio n in the waste wate r se wage via diffe re nt tre atme nt pro c e sse s
using c he mic al c o agulants
To tal re mo val (pe r c e nt)
60
To tal re mo val (pe r c e nt)
50
50
40
40
30
30
20
20
10
10
0
0
Cr
Ni
Cd
Pb
Cu
Zn
(a) Afte r grit-c hambe r (afte r c he mic al additio n)
Cr
Ni
Cd
Pb
(c ) Biodegradation (nitrific ation)
Cu
Zn
Cu
Zn
To tal re mo val (pe r c e nt)
To tal re mo val (pe r c e nt)
60
70
60
50
50
40
40
30
30
20
20
10
10
0
Cr
Ni
Cd
Pb
(b) After primary sedimentation
Cu
Zn
0
Cr
Ni
Cd
Pb
(d) Afte r se c o ndary se dime ntatio n
(sludge o f the final e fflue nt)
Key
No c he mic als we re adde d (c o ntro l)
Additio n o f Fe Cl3
Additio n o f lime o nly (1 2 0 g/ m3 )
Additio n o f lime and Fe Cl3
[ 30 ]
Husse in I. Abde l Shafy,
We rne r He ge mann and
Caro la Güldne r
Fate o f he avy me tals via
c he mic al-bio lo gic al upgrading
o f se wage tre atme nt plant
Enviro nme ntal Manage me nt
and He alth
7 / 3 [1 9 9 6 ] 2 8 –3 6
a dded to th e w a stew a ter in cor r ela tion w ith
th e con tr olled on e. Mea n wh ile, th e u se of th e
com bin ed coa gu la n ts, n a m ely FeCl 3 a n d lim e,
w a s m or e effective in r edu cin g th e level of
lim e a n d/ or com bin a tion of both FeCl 3 a n d
lim e togeth er. Resu lts obta in ed sh ow th a t a
n oticea ble decr ea se in th e level of m eta ls w a s
r ecor ded wh en th e ch em ica l coa gu la n ts wer e
Table II
Ave rage tre atme nt pe rfo rmanc e be fo re and during the lime phase to the se wage wate r at
Oranie nburg
Jan
Unit
BOD5 – precipitation after sedimentation
Total BOD5-degradation
COD-precipitation after sedimentationa
Total COD-degradationa
NH4-N in effluent
Inorganic N in effluent
Total P in effluent
%
%
%
%
(mg/ I)
(mg/ I)
(mg/ I)
Feb
M ar
Apr
Without lime addition
23
94
26
87
–
–
–
28
93
30
84
34
36
7.1
11
96
26
85
–
–
–
14
93
29
84
32
33
3.4
M ay
Jun
Jul
Lime addition
21
94
32
85
36
37
3
48
98
49
85
17
27
1.7
49
94
50
85
17
29
1.6
Note:
a COD-measurement
with potassium permanganate
Source:[5]
Table III
Le ve l o f he avy me tals in the pre tre atme nt sludge via the suc c e ssive tre atme nt pro c e ss (mg/ kg
dry we ight)
Successive treatment processes
Cr
Ni
M etals (mg/ kg dry weight)
Cd
Pb
Cu
Zn
Sludge of the raw sewage
Average
305
33
7.21
40
131
837
(before chemical addition)
Maximum
319
46
10.33
61
176
866
Minimum
301
22
1.04
18
64
791
After grit chamber
a
195
22
2.73
30
111
719
(after chemical addition)
b
215
32
3.11
42
123
790
c
240
41
4.82
55
131
803
d
282
58
5.13
68
133
827
a
92
31
1.32
38
108
866
b
48
29
1.14
37
97
754
c
34
25
1.07
34
82
683
After primary sedimentation
Aeration as biodegradation (nitrification)
d
31
20
0.51
33
80
662
a
302
32
7.01
38
125
871
b
214
31
2.24
37
113
852
c
153
24
1.33
31
104
730
d
102
20
0.71
29
100
694
After secondary sedimentation
a
137
30
1.96
42
108
854
(sludge of the final effluent)
b
118
27
1.05
33
92
843
c
91
23
0.74
29
83
669
d
Guideline
88
21
0.58
28
77
594
900
200
10.00
900
800
2,500
Notes:
Results presented here are the average of 12 weekly suc c essive samples
a: No c hemic als were added (c ontrol)
b: Addition of FeCl3 only (8.4g/ m3 )
c : Addition of lime only (120g/ m3 )
d: Addition of FeCl3 and lime
[ 31 ]
Husse in I. Abde l Shafy,
We rne r He ge mann and
Caro la Güldne r
Fate o f he avy me tals via
c he mic al-bio lo gic al upgrading
o f se wage tre atme nt plant
Enviro nme ntal Manage me nt
and He alth
7 / 3 [1 9 9 6 ] 2 8 –3 6
m eta ls followed by th e u se of lim e th a n FeCl 3.
F u r th er m or e, th e pr im a r y a n d secon da r y
sedim en ta tion wer e a lso sligh tly effective in
m eta ls elim in a tion . Th e per cen ta ges of
m eta ls elim in a tion in th e w a stew a ter via
th ese su ccessive tr ea tm en t pr ocesses u sin g
ch em ica l coa gu la n ts a r e pr esen ted in F igu r e
2. Su ch decr ea se in th e level of m eta ls is
a ttr ibu ted m a in ly to th e in cr ea se of pH-va lu e
to 9.0-9.2 wh ich in du ces th e decr ea se of m eta ls
solu bility[6,7,10,12]. As th e pH in cr ea se, th e
co-pr ecipita tion of m eta l h ydr oxide
in cr ea ses[6], bu t cer ta in a m ph oter ic m eta ls
w ill r e-dissolve a t h igh er pH-va lu es[6,7]. Th e
pr eviou s stu dy on th e sa m e pla n t pr oved th a t
lim e pr ecipita tion a t pH between 9.0-9.2 h a s
a lso im pr oved th e pr e-tr ea tm en t per for m a n ce
by @20 per cen t com pa r ed to th e zer o-ph a se
(Ta ble II)[5].
F u r th er stu dy w a s ca r r ied ou t on th e level
of m eta ls in th e sew a ge slu dge via th e sa m e
su ccessive tr ea tm en t pr ocesses u sin g lim e
a n d/ or FeCl 3 (Ta ble III). Th e given r esu lts
sh ow th a t th e ch em ica l coa gu la n t in cr ea sed
th e level of m eta ls in th e slu dge a s a r esu lt of
th e co-pr ecipita tion effect, i.e. con ver tin g th e
solu ble for m s of m eta l to th e in solu ble for m
in th e slu dge. Aga in th e u se of th e com bin ed
coa gu la n t in cr ea sed th e co-pr ecipita tion r a te.
However, th e u se of lim e w a s m or e effective
Figure 3
The pe rc e ntage o f me tals e liminatio n in the pe rme ate d sludge via diffe re nt tre atme nt pro c e sse s in
c o rre latio n to the le ve ls o f me tals in the raw se wage sludge
Me tals e liminatio n (pe r c e nt)
Me tals e liminatio n (pe r c e nt)
100
70
60
80
50
40
60
30
40
20
20
10
0
Cr
Ni
Cd
Pb
Cu
Zn
(a) Afte r grit-c hambe r (afte r c he mic al additio n)
Me tals e liminatio n (pe r c e nt)
100
0
Cr
Ni
Cd
Pb
(c ) Biodegradation (nitrific ation)
80
60
60
40
40
20
20
0
Cr
Ni
Cd
Pb
(b) After primary sedimentation
Zn
Cu
Zn
Me tals e liminatio n (pe r c e nt)
100
80
0
Cu
Cu
Zn
Cr
Ni
Cd
Pb
(d) Afte r se c o ndary se dime ntatio n
(sludge o f the final e fflue nt)
Key
No c he mic als we re adde d (c o ntro l)
Additio n o f lime o nly (1 2 0 g/ m3 )
Additio n o f Fe Cl3
Additio n o f lime and Fe Cl3
Table IV
Ge rman guide line re gulatio n fo r the le ve l o f he avy me tals in the sludge (mg/ kg dry we ight)
[ 32 ]
M etal
Ag
Cr
Ni
Cd
Pb
Cu
Zn
Guideline level
Source:[13]
8
900
200
10
900
800
2,500
Husse in I. Abde l Shafy,
We rne r He ge mann and
Caro la Güldne r
Fate o f he avy me tals via
c he mic al-bio lo gic al upgrading
o f se wage tre atme nt plant
Enviro nme ntal Manage me nt
and He alth
7 / 3 [1 9 9 6 ] 2 8 –3 6
th a n FeCl 3. Th e per cen ta ge of m eta ls elim in a tion in th e slu dge in cor r ela tion to th e or igin a l con cen tr a tion in th e r aw w a stew a ter is
illu str a ted in F igu r e 3. Th e pr im a r y a n d secon da r y sedim en ta tion ta n k s w ith th e th r ee
h ou r s’ r eten tion tim e sh owed h igh efficien cy
in tr a ppin g th e pr ecipita ted m eta ls. Th e level
of m eta ls in th e pr im a r y slu dge wer e fa r
below th e Ger m a n per m issible level (Ta ble
IV)[13]. In a ddition , th e for m er stu dies
Figure 4
Co rre latio n be twe e n the c apillary suc tio n time and the so lids c o nte nt
Capillary suc tio n time (se c o nds)
700
Key
Be fo re c he mic al additio n
Lime additio n
Lime and Fe Cl3 additio n
600
500
400
Faste r
filte ring
300
200
100
0
1
2
3
Solids c ontent (per c ent)
4
5
6
7
8
Source: [5 ]
Table V
Le ve l o f he avy me tals in the sludge be fo re and afte r the anae ro bic re ac to r pro c e ss (mg/ kg dry
we ight)(pH 6 .0 -6 .5 )
Type of treatment
Cr
Ni
M etals (mg/ kg dry weight)
Cd
Pb
Cu
Zn
After primary sedimentation
a
96
31
1.32
38
108
866
(influent to the anaerobic reactor)
b
48
29
1.14
37
97
760
c
34
25
1.07
34
82
683
d
31
20
0.51
33
80
662
Average
46
25
0.95
31
92
757
After secondary sedimentation
a
137
30
1.96
42
108
854
(influent to the anaerobic reactor)
b
118
27
1.05
33
92
943
Final effluent of the anaerobic reactor
Guideline
c
10
23
0.74
29
83
669
d
88
21
0.58
28
77
594
Average
103
28
1.07
30
91
845
Average
99
39
1.92
49
157
876
Maximum
117
36
2.11
54
187
951
Minimum
81
24
0.38
22
70
472
900
200
10.00
900
800
2,500
Notes:
Results presented here are the average of 12 weekly suc c essive samples
Average = average metal c onc entration of the four different sewage sludges
a: No c hemic als were added (c ontrol)
b: Addition of FeCl3 only (8,4g/ m3 )
c : Addition of lime only (120g/ m3 )
d: Addition of FeCl3 and lime
[ 33 ]
Husse in I. Abde l Shafy,
We rne r He ge mann and
Caro la Güldne r
Fate o f he avy me tals via
c he mic al-bio lo gic al upgrading
o f se wage tre atme nt plant
Enviro nme ntal Manage me nt
and He alth
7 / 3 [1 9 9 6 ] 2 8 –3 6
[ 34 ]
sh owed th a t th e ch a r a cter istics of th is slu dge
wer e sign ifica n tly im pr oved by th e a ddition
of lim e. Du r in g th e lim e ph a se th e solids
con ten t in cr ea sed fr om between 1 a n d 3 per
cen t to between 3 a n d 8 per cen t a s sh ow n in
F igu r e 4, i.e. in cr ea sin g th e slu dge weigh t
wh ile th e slu dge volu m e r em a in s th e sa m e[5].
Th e loss a t VSS decr ea ses fr om @ 75 per cen t
to @ 50 per cen t.
Rea son a ble por tion s of th e liqu id slu dge
obta in ed fr om both pr im a r y a n d secon da r y
sedim en ta tion ta n k s wer e su bjected to a cidifica tion a n d h ydr olysis u sin g a sem i-tech n ica l
sca le a n a er obic r ea ctor (F igu r e 1). Th is biologica l h ydr olysis a n d a cidifi ca tion ta k e pla ce
a t pH-va lu es between 6.0-6.5 w ith a r eten tion
tim e of on e to two days. Th e level of m eta ls in
th e slu dge befor e a n d a fter th e a n a er obic
h ydr olysis is pr esen ted in Ta ble V. Th e level
of m eta ls in th e fin a l efflu en t of th e a n a er obic
r ea ctor is sligh tly h igh er th a n th a t of th e
in flu en t to th e r ea ctor. Su ch sligh t in cr ea se of
m eta ls r efer r ed m a in ly to th e decr ea se of pH
fr om 9.0-9.2 to th e sligh t a cidic va lu e of 6.0-6.5
wh ich in du ce th e pa r tia l dessolu tion of cer ta in m eta ls in to th e system [6,7,12]. Th e level
of m eta ls in th e fin a l h ydr olized slu dge w a s
still below th e per m issible level (Ta ble
IV)[13]. Cor r ela tion between th e level of
m eta ls in th e h ydr olyzed slu dge efflu en t of
th e a n a er obic r ea ctor a n d th e level of m eta ls
in ea ch of th e slu dge in flu en t to th e a n a er obic
r ea ctor is r epr esen ted in F igu r e 5. Th e pr odu ced vola tile or ga n ic a cids (C2-C6) for m ed
du r in g th is pr ocess wer e exa m in ed pr eviou sly[5], a n d it w a s pr oved th a t th ey ca n be
u sed a s a sou r ce of ca r bon for th e den itr ifica tion [14-16]. F igu r e 6 pr esen ts th e cor r ela tion
between th e level of m eta ls in th e fi n a l w a stew a ter of th e u pgr a ded pla n t a n d th e level of
m eta ls in th e fi n a l w a stew a ter of th e a n a er obic r ea ctor.
Th e pr esen t stu dy w a s expa n ded to in clu de
th e level of m eta ls in tr ea ted slu dge, n a m ely
two septic ta n k s a n d fou r (dr yin g beds)
slu dge polder s (Ta ble VI). Th is ta ble in clu des
a lso th e slu dge ch a r a cter istics, n a m ely th e
per cen ta ge of th e dr y r esidu e a n d per cen ta ge
of vola tile or ga n ic m a tter. Th e r esu lts
obta in ed sh ow th a t th e level of m eta ls in th e
two septic ta n k s is h igh er th a n th a t of th e
pr im a r y slu dge befor e tr ea tm en t. F u r th er
in cr ea se in th e level of m eta ls w a s exh ibited
in th e slu dge polder s (dr yin g beds). Cor r ela tion between th e level of m eta ls in th e fi n a l
slu dge polder a n d th e Ger m a n gu ide lin e[13]
sh ow th a t th e level of N i (aver a ge 317 m g/ k g
dr y weigh t) is h igh er th a n th e per m issible
level (Ta ble IV). Cor r ela tion between th e level
of m eta ls in th e w a stew a ter of th e u pgr a ded
pr ocess a n d th e w a stew a ter of th e a n a er obic
r ea ctor is given in F igu r e 6.
Figure 5
Co rre latio n be twe e n the le ve l o f me tals in the
hydro lyze d sludge e fflue nt and the two diffe re nt
influe nts (name ly afte r primary se dime ntatio n
and afte r the se c o ndary se dime ntatio n) to the
anae ro bic re ac to r
mg/ kg dry we ight
1 ,0 0 0
100
10
0
Cr
Ni
Cd
Pb
Cu
Zn
Key
Afte r primary se dime ntatio n
(influe nt to re ac to r)
Afte r se c o ndary se dime ntatio n
(influe nt to re ac to r)
Hydro lyze d sludge
(e fflue nt o f re ac to r)
Note: The re sults pre se nte d he re are the ave rage
o f the fo ur diffe re nt sludge s fo r the 1 2 suc c e ssive
we e kly sample s
Figure 6
Co rre latio n be twe e n the le ve l o f he avy me tals
in the final waste wate r o f the upgrade d plant
and the le ve l o f me tals in the final waste wate r
o f the anae ro bic re ac to r
Me tals (mg/ litre )
0 .8
0 .6
0 .4
0 .2
0
Cr
Key
Ni
Cd
Pb
Cu
Zn
Final upgraded wastewater
Effluent of the anaerobic reac tor
Th e over a ll r esu lts of th e pr esen t stu dy
r evea led th a t th e u pgr a din g of th e sew a ge
tr ea tm en t pla n t by th e a pplica tion of lim e in
th e pr e-pr ecipita tion sta ges h a s a r em a r k a ble
im pr ovem en t in per for m a n ce of sew a ge tr ea tm en ts. Su ch im pr ovem en t w a s expr essed n ot
on ly in decr ea sin g th e level of m eta ls in th e
w a stew a ter (Ta bles I a n d II), bu t a lso in th e
sta biliza tion of th e clea n in g per for m a n ce of
Husse in I. Abde l Shafy,
We rne r He ge mann and
Caro la Güldne r
Fate o f he avy me tals via
c he mic al-bio lo gic al upgrading
o f se wage tre atme nt plant
Enviro nme ntal Manage me nt
and He alth
7 / 3 [1 9 9 6 ] 2 8 –3 6
Table VI
Charac te ristic s and the le ve l o f me tals in the primary and the tre ate d sludge (se ptic tanks and
sludge po lde r)
Type of sludge
Before the sludge treatment
(primary sludge)
Septic tank (No. 1)
Septic tank (No. 2)
Sludge polder (drying beds)
M etals (mg/ kg dry weight)
Cd
Pb
Cu
Cr
Ni
Zn
Average
104
25
0.93
33.6
111
730
Maximum
151
37
2.01
43.5
178
997
Minimum
78
19
0.3
25.4
69
496
Average
217
187
2.21
118.2
214
1,993
Maximum
295
219
7.92
218.4
351
2,501
Minimum
187
76
0.79
97.3
179
705
Average
196
308
2.54
125.8
204
2,013
Maximum
257
395
5.93
216.8
312
2,704
Maximum
134
112
0.51
90.8
163
812
Dry
residue %
%
ovm
6.39
38.46
4.18
57.83
3.44
59.86
Average
322
317
3.19
126.8
239
2,451
9.22
61.08
Maximum
517
386
6.98
247.3
352
2,985
12.56
62.87
5.98
59.65
Maximum
Guideline
239
175
0.79
97.8
193
2,175
900
200
10.10
900.0
800
2,500
Note:
ovm: perc entage of the volatile organic matter
th e over loa ded pla n t[5]. Th e decr ea se of
m eta ls con cen tr a tion in th e w a stew a ter w a s
du e to th e in cr ea se of pH-va lu es a s a r esu lt of
lim e a ddition . As th e pH-in cr ea se, th e for m a tion of m eta l h ydr oxide in cr ea ses[6,7,12]. Th is
r ela tion sh ip is expr essed by th e follow in g
sta bility pr odu ct equ a tion :
(M + 2)(OM)2 = K sp (solu bility con sta n t)
Th e solu bility pr odu ct con sta n ts for a n u m ber of m eta ls a r e well docu m en ted a n d
a lr ea dy pu blish ed[13]. However, beca u se of
pr ecipita tion a gein g, in com plete solid sepa r a tion or th e co-pr ecipita tion a n d a dsor ption
effects in w a stew a ter solu bility pr odu cts
pr ovide on ly a gen er a l gu ide to r esidu a l m eta l
con cen tr a tion to be expected in pr a ctice[10].
Th e level of m eta ls in th e pr e-tr ea tm en t
slu dge is fa r below th e Ger m a n r estr iction
lim its[13]. It h a s been r epor ted th a t th is pr etr ea tm en t slu dge is im pr oved con sider a bly in
ter m s of th ick en in g a n d dr a in in g qu a lities[5].
Despite th e in cr ea se in th e solid con ten t, on ly
sligh t in cr ea se in th e slu dge volu m e w a s
r epor ted[5].
Th e h ydr olysis a n d a cidifi ca tion of th e
pr im a r y slu dge exh ibited con sider a ble
in cr ea se in th e level of m eta ls du e to th e
decr ea se of pH-va lu e fr om 9.0-9.2 to 6.0-6.5.
However, th e vola tile or ga n ic a cids (C2-C6)
for m ed du r in g th e pr ocess ca n be u sed a s a
sou r ce of ca r bon for th e den itr ifica tion [14-16].
Th e level of N i in th e tr ea ted slu dge of th e
dr yin g bed r ea ch ed 317m g/ k g. Th is h igh level
of N i is du e to th e disch a r ge of cer ta in in du str ia l w a stew a ter to th e sewer system .
Tr ea tm en t of th is in du str ia l w a stew a ter
sh ou ld be ca r r ied ou t befor e disch a r gin g to
th e sewer system . Accor din g to th e Ger m a n
r e gu la tion N i sh ou ld n ot exceed 200m g/ k g a s
dr y weigh t. Th er efor e, su ch slu dge ca n n ot be
u sed a s a m a n u r e in a gr icu ltu r e[17]. On th e
oth er h a n d, su ch u pgr a din g of th e sew a ge
pla n t im pr oved th e per for m a n ce of tr ea tm en t
a n d th is r edu ces sew a ge ta x. Mea n wh ile, th e
h ydr olysis of th e pr e-tr ea tm en t slu dge ca n
im pr ove th e per for m a n ce of th e den itr ifica tion pr ocess a n d th er efor e it ca n save en er gy.
F u r th er m or e, th e lim e a pplica tion for th e
u pgr a din g of th e sew a ge pla n t ca n be a su bstitu tion for en la r gin g th e pla n t itself.
It is wor th n oticin g h er e th a t th e level of Zn
in th e dr yin g bed slu dges r a n ges fr om 2,175 to
2,985 w ith th e aver a ge of 2,451m g/ k g dr y
weigh t (Ta ble VI). Th e gu idelin e[5] is
2,500m g/ k g.
Th e pr esen t gu idelin e lim its for th e level
of m eta l in slu dge is su fficien t for th e en vir on m en ta l pr otection . Th e settin g of lim its
a t levels lower th a n n ecessa r y ca n be cou n ter pr odu ctive a n d lea d to ille ga l discon tin u ou s
disch a r ges a n d la ck of co-oper a tion between
th e en for cem en t body a n d th e fir m s. Th is
ca n lea d to excessive costs in con tr ol a n d
m or e fr equ en t fa ilu r e to m eet th e r equ ir ed
sta n da r d.
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[ 35 ]
Husse in I. Abde l Shafy,
We rne r He ge mann and
Caro la Güldne r
Fate o f he avy me tals via
c he mic al-bio lo gic al upgrading
o f se wage tre atme nt plant
Enviro nme ntal Manage me nt
and He alth
7 / 3 [1 9 9 6 ] 2 8 –3 6
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