Enviro nme ntal Manage me nt and He alth
8 / 2 [1997] 7 3 –7 9 © MCB Unive rs ity Pre s s [ISSN 0956-6163]
The elimination of chromium in the treatment of
tannery industrial wastewater
Hussein I. Abdel-Shafy
Wate r Re s e arc h and Po llutio n Co ntro l De partme nt, Natio nal Re s e arc h Ce ntre , Do kki, Cairo , Egypt
Werner Hegemann, Elke Genschow
Sanitary Engine e ring De partme nt, Te c hnis c he Unive rs ität Be rlin, Ge rmany
Hus s e in I. Abde l-Shafy, We rne r He ge mann and Elke Ge ns c ho w
The e liminatio n o f c hro mium in the tre atme nt o f tanne ry industrial waste wate r
Enviro nme ntal Manage me nt and He alth
8 / 2 [1 9 9 7 ] 7 3 –7 9
a n a er ob ic a n d a er ob ic p ilot p la n t s r esp ec-t ively.
Da ily sa m p les w er e collect ed fi ve d ay s a w eek a n d m ixed t oget h er a s a on e com p osit e sa m p le. T h ese sa m p les w er e:
• Raw w a st ew a t er a n d t h e slu d ge b efor e a cid ifi ca t ion .
• Raw w a st ew a t er a n d t h e slu d ge a ft er a cid i-fi ca t ion .
• Raw w a st ew a t er a n d t h e slu d ge a ft er st ir -r in g (in fl u en t t o t h e a n a e-r ob ic -r ea ct o-r ).
• T h e efflu en t w a st ew a t er a n d t h e slu d ge of t h e a n a er ob ic r ea ct or.
• T h e in fl u en t t o t h e a er ob ic r ea ct or a ft er st ir r in g.
• T h e fi n a l w a st ew a t er efflu en t a n d slu d ge a ft er a er ob ic t r ea t m en t .
T h e p h y sica l a n d ch em ica l ch a r a ct er ist ics of t h e t a n n er y r aw a n d t r ea t ed w a st ew a t er w er e d et er m in ed a ccor d in g t o DIN -n or m s[15].
For t h e h eav y m et a l a n a ly sis, t h e slu d ge sa m p les w er e oven d r ied a t 105°C for a p er iod of 24 h ou r s. All w a st ew a t er sa m p les a lon g w it h a k n ow n w eigh t of t h e slu d ge sa m p les w er e a cid d igest ed u sin g n it r ic a cid follow ed by h yd r ogen p er oxid e a ccor d in g t o US E PA[16]. Met a l con cen t r a t ion s w er e d et er -m in ed u sin g a Va r ia n a t o-m ic a b sor p t ion sp ect r om et er, m od el Sp ect r AA-400 eq u ip p ed w it h GTA-96 gr a p h it e t u b e a t om izer, a t t a ch ed t o a n IBM p er son a l com p u t er AT
(p r ogr a m m ed for Va r ia n -Sp ect r AA-300/ 400). T h e m et a ls st u d ied w er e Cr, N i, Cd , P b, Cu a n d Zn . E a ch r esu lt for ea ch sa m p le
p r esen t ed h er e is aver a ged fr om t en seq u en -t ia l r ea d in gs. As a n in s-t r u m en -t for p r oce-d u r e, oce-d ou ble-oce-d ist illeoce-d w a t er t h a t oce-d igest eoce-d u sin g t h e p r oced u r e p r ev iou sly d escr ib ed w a s em p loyed . T h e over a ll r esu lt s p r esen t ed h er e a r e t h e aver a ge of a ll t h e st u d ied sa m -p les.
Results and discussion
T h e ch em ica l ch a r a ct er ist ics of t h e t h r ee d iffer en t sa m p les of t a n n er y w a st ew a t er (A, B Figure 1
The c o mbine d anae ro bic -ae ro bic pilo t plant fo r the tre atme nt o f tanne ry indus trial was te wate r
Q Q
Q Q
Q
Surplus sludge Sludge recycle
Aeration el.
Anaerobic pretreatment Aerobic treatment
Biogas
Influent Stirring tank
Fixed film bed reactor Influent Activated sludge cascade
Sedimentation tank
Effluent
Table I
Che mic al c harac te ris tic s o f the thre e diffe re nt s ample s o f c hro mium tanne ry was te wate r
No. of Standard- M ean
Parameter (mg/ l) samples M inimum M aximum deviation value
COD
A 1 3 0 2 ,0 7 0 3 0 ,5 0 0 6 ,1 9 0 8 ,2 0 0
B 2 8 0 8 6 1 1 6 ,8 0 0 3 ,0 8 0 5 ,0 7 0
C 5 7 1 ,6 9 0 1 4 ,7 0 0 2 ,8 7 0 2 ,9 9 0
Sulphide
A 1 1 5 1 1 1 ,6 0 0 2 0 6 2 8 0
B 2 5 0 0 6 5 2 1 5 5 1 3 9
C 4 8 5 3 7 0 5 1 7 8 2 8 2
Sulphate
A 5 2 6 7 3 ,4 0 0 5 4 7 9 9 6
B 2 7 9 1 6 2 3 ,5 9 0 8 4 6 1 ,2 5 0
C 2 4 3 2 3 1 ,2 6 0 2 8 7 7 5 0
Chloride
A 3 9 4 ,1 0 0 7 ,4 0 0 8 4 0 5 ,2 0 0
B 1 6 5 0 1 1 ,8 0 0 3 ,1 0 0 4 ,0 0 0
Hus s e in I. Abde l-Shafy, We rne r He ge mann and Elke Ge ns c ho w
The e liminatio n o f c hro mium in the tre atme nt o f tanne ry industrial waste wate r
Enviro nme ntal Manage me nt and He alth
8 / 2 [1 9 9 7 ] 7 3 –7 9
a n d C) a r e given in Ta ble I. T h e aver a ge va lu es of a m ixt lu r e of t h e t h r ee sa m p les of t a n -n er y w a st ew a t er a r e p r ese-n t ed i-n Ta ble II. It ca n b e seen t h a t su ch w a st ew a t er s a r e ch a r a c-t er ized by a h igh or ga n ic loa d a s w ell a s a h igh con t en t of su lp h id e, su lp h a t e, ch lor id e, TKN a n d a m m on ia n it r ogen . F u r t h er m or e, gr ea t fl u ct u a t ion in t h e given va lu es is a p p a r -en t fr om t h e st a n d a r d d ev ia t ion s. E v-en w it h t h e r e p r esen t a t ive sa m p les t a k en ever y t wo h ou r s, t h er e w a s a gr ea t fl u ct u a t ion in t h e con cen t r a t ion of su ch w a st ew a t er. T h e w eek ly fl u ct u a t ion of t h e COD va lu es is p r e-sen t ed in F igu r e 2.
T h e levels of ch r om iu m a n d t h e ot h er a sso-cia t ed m et a ls in t h e t h r ee d iffer en t sa m p les a n d t h e t ot a l m ixed slu d ge a r e given in Ta ble III. T h ese r esu lt s sh ow t h a t t h e r aw w a st e-w a t er con t a in s a h igh level of Cr e-w h ile t h e ot h er a ssocia t ed m et a ls sh ow ed ver y low
con cen t r a t ion s. T h e h igh est Cr level w a s fou n d in t a n n er y w a st ew a t er (A). On t h e ot h er h a n d , t h e r aw m ixed slu d ge sh ow ed r ea son a ble a ccu m u la t ion of t h e st u d ied m et a ls a s in d ica t ed by t h e va lu e SLG: TMWW (i.e. t h e level of m et a l in t h e slu d ge in cor r ela -t ion -t o i-t s p r esen ce in -t h e m ixed -t a n n er y w a st ew a t er ). T h e low est SLG : T.M.WW w a s exh ib it ed by Cr, w h ich exp la in s t h e h igh p r esen ce of Cr in t h e w a st ew a t er a n d v ice ver sa for t h e ot h er a ssocia t ed m et a ls.
T h e levels of h eav y m et a ls in t h e efflu en t of t h e a n a er ob ic r ea ct or a r e given in Ta ble IV. T h e r esu lt s ob t a in ed sh ow ed a m a r k ed d ecr ea se in t h e level of Cr in t h e fi lt er a ble w a st ew a t er, w h ile t h e levels of t h e ot h er a sso-cia t ed m et a ls on ly d ecr ea sed sligh t ly. T h e r a t e of elim in a t ion r a n ged fr om 98.7 t o 99.8 p er cen t for Cr a n d 31 t o 80 p er cen t for N i. T h e n on -fi lt er a ble t ot a l solid s exh ib it ed a n ot icea ble u p t a k e of Cr a s w ell a s t h e ot h er a ssocia t ed m et a ls. T h e levels of m et a ls in t h e slu d ge of t h e a n a er ob ic efflu en t (Ta ble IV) w er e con sid er a bly h igh er t h a n t h e slu d ge of in fl u en t t o t h e a n a er ob ic r ea ct or (Ta ble III), p a r t icu la r ly in t er m s of Cr a n d N i. T h is m ay b e d u e t o t h e lon g r et en t ion t im e of t h e slu d ge in t h e a n a er ob ic r ea ct or (F igu r e 1) w h ich a llow ed t h e slu d ge t o a b sor b t h e d issolved m et a ls a s a con seq u en ce of lon ger p er iod s of con t a ct . A r em a r k a ble a ch ievem en t in t h e levels of COD a n d or ga n ic N in t h e efflu en t of t h e a n a er ob ic r ea ct or w a s ob t a in ed (Ta ble V). H ow ever, a m m on ia in cr ea sed fr om 318 t o 353 m g/ l w h ich is d u e t o t h e d issolu t ion of Table II
Charac te ris tic s o f a mixture o f the thre e s ample s o f tanne ry raw was te wate r
No. of Standard- M ean
Parameter (mg/ l) samples M inimum M aximum deviation value
COD 4 6 7 8 6 1 3 0 ,5 0 0 4 ,5 1 0 5 ,7 1 0
Sulphide 4 1 3 0 1 ,6 0 0 1 8 7 1 9 6
Sulphate 3 5 5 6 7 3 ,5 9 0 7 9 4 1 ,1 8 0
Chloride 2 5 5 0 1 1 ,8 0 0 3 ,1 4 0 5 ,0 6 0
Chromium 3 1 9 0 .4 8 3 7 8 8 3 6
TKN 4 0 3 0 0 8 2 0 1 3 2 4 0 6
NH4+–N 4 0 2 9 0 6 3 0 5 9 3 1 8
Figure 2
Hus s e in I. Abde l-Shafy, We rne r He ge mann and Elke Ge ns c ho w
The e liminatio n o f c hro mium in the tre atme nt o f tanne ry industrial waste wate r
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Table IV
Le ve l o f me tals in the e fflue nt o f the anae ro bic re ac to r (as filte rable was te wate r and no n-filte rable to tal s o lids ) and the to tal mixe d s ludge
No. of
Sample samples Cr Ni Cd Pb Cu Zn
Tannery A Filterable wastewater (mg/ l) 3 0 max. 0 .3 3 5 0 .0 4 2 0 .0 1 2 0 .0 4 2 0 .1 6 2 0 .0 3 3
min. 0 .1 4 2 0 .0 0 1 0 .0 0 1 0 .0 0 3 0 .0 0 1 0 .0 0 4 average 0 .2 2 1 0 .0 1 1 0 .0 0 4 0 .0 1 2 0 .0 4 2 0 .0 1 8
%E 9 9 .8 3 1 .3 – 4 7 .8 – –
Non-filterable total solids as 3 0 max. 1 7 ,5 8 3 .7 6 .9 4 .2 1 7 8 .6 2 4 3 .5 1 ,0 3 3 .2
dry weight (mg/ kg) min. 8 ,6 9 3 .9 4 .4 0 .2 1 2 4 .9 1 3 .5 1 3 6 .8
average 1 3 ,6 3 8 .8 6 .7 1 .5 1 7 6 .7 1 2 9 .4 5 9 5 .6
Tannery B Filterable wastewater (mg/ l) 3 0 max. 0 .3 5 2 0 .0 1 4 0 .0 1 1 0 .0 3 2 0 .2 1 1 0 .0 3 5
min. 0 .1 1 1 0 .0 0 1 0 .0 0 2 0 .0 0 7 0 .0 0 2 0 .0 1 0 average 0 .2 1 5 0 .0 0 3 0 .0 0 2 0 .0 1 3 0 .0 4 2 0 .0 2 2 % E 9 8 .7 7 0 .0 7 5 .0 – 4 .5 2 9 .0
Non-filterable total solids 3 0 max. 9 ,2 2 1 .4 1 5 7 .1 3 .0 1 8 8 .3 8 1 .5 3 0 9 .9
as dry weight (mg/ kg) min. 3 ,1 6 6 .1 1 9 .4 0 .1 1 7 .3 0 .8 1 2 1 .3
average 5 ,2 1 0 .4 1 0 3 .8 0 .9 1 6 3 .4 1 1 .8 1 6 5 .8
Tannery C Filterable wastewater (mg/ l) 3 0 max. 0 .3 1 0 .0 4 2 0 .0 1 0 0 .0 3 8 0 .1 6 6 0 .0 4 8
min. 0 .1 5 0 .0 0 1 0 .0 0 2 0 .0 0 4 0 .0 0 9 0 .0 1 2 average 0 .2 2 0 .0 0 2 0 .0 0 4 0 .0 2 3 0 .0 4 3 0 .0 2 3 % E 9 9 .6 8 0 .0 4 2 .9 – 1 0 .4 1 7 .9
Non-filterable total solids 3 0 max. 1 4 ,8 1 1 .5 7 .2 3 .8 2 8 2 .6 2 7 4 .6 5 8 2 .0
as dry weight (mg/ kg) min. 7 ,4 1 2 .4 2 .6 0 .1 1 2 8 .5 1 5 .2 1 7 9 .1
average 1 0 ,7 8 1 .4 4 .4 1 .0 1 8 9 .5 1 9 7 .9 4 0 8 .4
Total mixed 3 0 max. 1 0 ,6 7 6 .0 4 1 .2 1 .9 2 1 8 0 .3 2 0 5 .7 4 4 3 .6
sludge as dry min. 5 ,0 5 1 .2 2 0 .6 0 .0 2 1 0 1 .6 1 8 .7 1 9 9 .5
weight (mg/ kg) average 8 ,4 8 5 .7 2 9 .4 0 .8 5 1 3 5 .0 1 3 9 .0 3 0 6 .4
Note:
% E = perc entage of elimination
Table III
Le ve l o f me tals in the influe nt was te wate r and the s ludge to the anae ro bic re ac to r
No. of
Sample samples Cr Ni Cd Pb Cu Zn
Tannery A (mg/ l) 3 0 max. 8 2 3 .9 0 .0 4 2 0 .0 1 1 0 .0 4 4 0 .0 5 2 0 .0 4 4
min. 1 2 .7 0 .0 0 2 BDL BDL 0 .0 0 1 BDL average 8 9 .9 0 .0 1 6 0 .0 0 3 0 .0 2 3 0 .0 1 8 0 .0 2 0
Tannery B (mg/ l) 3 0 max. 2 7 1 .5 0 .0 1 2 0 .0 1 1 0 .0 3 5 0 .1 9 4 0 .0 7 4
min. 0 .9 BDL BDL 0 .0 0 2 0 .0 0 2 0 .0 0 5 average 1 6 .8 0 .0 0 4 0 .0 0 5 0 .0 1 2 0 .0 5 4 0 .0 3 1
Tannery C (mb/ l) 3 0 max. 4 8 5 .8 0 .0 2 2 0 .0 2 1 0 .0 2 5 0 .1 2 4 0 .0 3 0
min. 5 .1 0 .0 0 1 0 .0 0 4 0 .0 0 1 0 .0 1 0 0 .0 0 1 average 5 8 .6 0 .0 1 0 0 .0 0 8 0 .0 0 5 0 .0 4 4 0 .0 1 5
Total mixed tannery 3 0 max. 5 3 0 .6 0 .0 2 6 0 .0 1 8 0 .0 3 7 0 .1 7 5 0 .0 6 6
wastewater (mg/ l) min. 7 .2 0 .0 0 1 0 .0 0 4 0 .0 0 2 0 .0 0 8 0 .0 0 4
average 5 6 .5 0 .0 1 0 0 .0 0 7 0 .0 2 1 0 .0 4 8 0 .0 2 8
Total mixed sludge as 3 0 max. 8 ,6 3 0 .9 1 3 .1 1 .5 1 8 4 .3 1 5 5 .6 4 6 9 .7
dry weight (mg/ kg) min. 1 ,2 1 4 .4 0 .8 0 .2 6 0 .2 1 3 .0 1 1 4 .9
average 5 ,2 3 5 .4 6 .3 0 .8 1 0 3 .6 1 0 4 .1 2 7 1 .9
SLG: M TWW 3 0 9 2 .7 6 3 0 .0 1 1 4 .3 4 ,9 3 3 .3 2 ,1 6 8 .8 9 ,7 1 0 .7
Note:
BDL = below minimum detec tion limits (0 .0 0 1 mg/ l)
p a r t icu la t e a m m on ia fr om t h e slu d ge of t h e r ea ct or t o t h e w a st ew a t er.
T h e a n a er ob ic efflu en t w a s su b ject ed t o t h e a er ob ic r ea ct or w h er e a fu r t h er im p r ovem en t in t h e ch a r a ct er ist ics of t h e t a n n er y w a st e-w a t er e-w a s exh ib it ed (Ta ble V) a s in d ica t ed fr om t h e p er cen t a ge of elim in a t ion for COD, or ga n ic N a n d a m m on ia . T h e level of h eav y m et a ls in t h e efflu en t of t h e a er ob ic r ea ct or is given in Ta ble VI. T h ese r esu lt s d em on st r a t e a sligh t in cr ea se in t h e level of m et a ls in t h e efflu en t com p a r ed w it h in fl u en t w a st ew a t er. Mea n w h ile, t h e level of m et a ls in t h e efflu en t slu d ge w a s con sid er a b ly low er t h a n t h a t of t h e in fl u en t slu d ge, w h ich exp la in s t h e in cr ea se of m et a ls in t h e efflu en t w a st ew a t er (a cce p t ed levels of h eav y m et a ls in t h e slu d ge
a r e given in Ta ble VII). It is wor t h n ot in g t h a t t h e a er ob ica lly p r od u ced slu d ge a ccu m u la t ed Cr m u ch m or e t h a n t h e r aw slu d ge a s in d i-ca t ed fr om t h e va lu e SLG/ WW for a er ob ic slu d ge (2,824) a n d for t h e r aw slu d ge (92.7) a s sh ow n in F igu r e 3. T h is exp la in s t h e sign ifi -ca n t d ecr ea se of Cr in t h e fi n a l efflu en t of t h e a er ob ic r ea ct or com p a r ed t o t h e r aw w a st e-w a t er (Ta bles III a n d VI).
In con clu sion , t h e a n a er ob ic t r ea t m en t p r ocess h a s cer t a in ly im p r oved t h e ch a r a ct er -ist ics of t h e d iffer en t sa m p les of t a n n er y w a st ew a t er. In t er m s of h eav y m et a ls, t h e m a in p r oblem w a s t h e h igh level of Cr in t h e t h r ee d iffer en t sa m p les of w a st ew a t er. T h e a n a er ob ic p r ocess d ecr ea sed t h e level of Cr a s w ell a s t h e ot h er a ssocia t ed m et a ls. T h e r esu l-t a n l-t slu d ge, l-t h er efor e, con l-t a in ed a h igh er level of Cr u p t o 8,486 m g/ k g a s d r y w eigh t w h ich is fa r in excess of t h e a cce p t a ble gu id e-lin e r e gu la t ion for t h e level of m et a ls in t h e slu d ge (Ta ble VII). F u r t h er t r ea t m en t of t h e w a st ew a t er t h r ou gh t h e a er ob ic p r ocess a ch ieved a r em a r k a ble im p r ovem en t in t h e w a st ew a t er ch a r a ct er ist ics. Mea n w h ile, a con sid er a ble d ecr ea se in t h e level of m et a ls in t h e p r od u ced slu d ge w a s ob t a in ed (F igu r e 4). Hus s e in I. Abde l-Shafy,
We rne r He ge mann and Elke Ge ns c ho w
The e liminatio n o f c hro mium in the tre atme nt o f tanne ry industrial waste wate r
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Table VI
Le ve ls o f me tals in the influe nt, e fflue nt and the s ludge o f the ae ro bic re ac to r
No. of
Sample samples Cr Ni Cd Pb Cu Zn
Influent wastewater (mg/ l) 3 0 max. 0 .2 2 6 .0 3 0 .0 1 0 .0 2 0 .1 8 0 .0 5
min. 0 .1 0 BDL <0 .0 1 <0 .0 1 0 .0 1 0 .0 1 average 0 .1 8 <0 .0 1 0 .0 1 0 .0 1 0 .0 6 0 .0 2
Effluent wastewater (mg/ l) 3 0 max. 0 .3 7 0 .0 5 0 0 .0 1 8 0 .0 4 0 .2 2 0 .2 1
min. 0 .1 3 0 .0 2 1 0 .0 0 7 0 .0 1 0 .0 1 0 .0 2 average 0 .2 2 0 .0 3 7 0 .0 1 1 0 .0 2 0 .0 8 0 .0 9
Effluent sludge as dry weight (mg/ kg) 3 0 max. 3 ,1 9 0 .6 2 2 .6 1 .7 6 1 8 0 .7 3 2 4 .7 6 4 0 .6
min. 2 ,1 8 8 .7 1 6 .6 0 .0 2 1 1 5 .1 1 6 .5 2 8 7 .6 average 2 ,8 2 4 .3 1 8 .6 0 .5 0 1 4 1 .3 1 1 1 .8 4 3 5 .1
SLF: Effl. WW 1 2 ,8 3 7 .7 5 0 2 .7 4 5 .5 7 ,0 6 5 1 ,3 9 7 .5 4 ,8 3 4 .4
Note:
SLG: Effl. WW = the level of metal in the sludge c orrelated to its presenc e in the effluent BDL = below minimum detec tion limits (0 .0 0 1 mg/ l)
Table VII
Ge rman guide line re gulatio ns fo r the le ve ls o f he avy me tals in the s ludge (mg/ kg dry we ight)
M etal Guideline level
Pb 9 0 0
Cd 1 0
Cr 9 0 0
Cu 8 0 0
Ni 2 0 0
Ag 8
Zn 2 ,5 0 0
Table V
Charac te ris tic s o f the tanne ry was te wate r influe nt and e fflue nt o f bo th anae ro bic and ae ro bic re ac to rs
No. of Standard M ean %
Parameter weeks M inimum M aximum deviation value TE
COD (mg/ l)
Influent anaerobic 1 0 1 ,9 5 0 1 3 ,2 0 0 3 ,1 2 0 4 ,4 8 0
Effluent anaerobic 1 1 8 0 0 1 ,5 3 0 2 2 2 1 ,1 1 0 7 5 .2
Influent aerobic 1 0 3 3 2 1 ,5 0 0 4 5 2 7 0 0 8 4 .4
Effluent aerobic 1 1 1 2 1 2 7 8 4 7 .1 1 7 1 9 6 .2
Organic N
Influent anaerobic 1 0 <1 0 1 8 0 5 6 .8 6 4 .3
Influent aerobic 6 <1 0 6 9 1 9 .5 3 3 .7 4 7 .6
Effluent aerobic 9 <2 6 0 1 9 .8 2 3 .9 6 2 .8
Ammonia
Influent anaerobic 1 1 1 3 0 4 5 3 6 5 .5 3 1 8
Influent aerobic 7 2 5 2 3 4 0 2 8 .0 3 5 3 –
Effluent aerobic 1 0 1 3 1 2 8 2 4 9 .4 2 2 4 3 6 .5
Note:
Hus s e in I. Abde l-Shafy, We rne r He ge mann and Elke Ge ns c ho w
The e liminatio n o f c hro mium in the tre atme nt o f tanne ry industrial waste wate r
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Figure 3
The le ve l o f me tals in the s ludge in c o rre latio n to its pre s e nc e in the was te wate r, i.e . raw was te -wate r and/ o r the final e fflue nt o f the ae ro bic re ac to r
Figure 4
