Journ al of Scienti fic & Industri al Research Vol. 61. March 2002. pp 208-2 18

Removal of Phenol Pollutants from Aqueous Solutions Using Various Adsorbents D K Singh* and Bhavana Sri vasta va Department of Chemistry. Harcourt Butler Technological Ins titu te, Kanpur. 208 002. India Received: 19 September 200 I: accep ted: 03 December 200 I The review aims at providi ng stu dy concerned with the app lication of conve ntional and non-convent ional adsorbents fo r th e remova l of phenols. The data presented are mainly based on labo ratory studies and show potenti al ad"ant ages for treatment of phenol bearing was tewater by adsorpti on on non-conventi onal adsorbents.

Introduction Phenol and phenoli c compound s in wastewaters are haza rd ous pollutan ts whi ch ap pea r in almost all chem ica l and petrochemi cal effluents from industri es such as, iron -steel. coke, petroleum, pesti cides, in secticides , pharm aceuticals, wood preservin g chem icals, and paper and pul p industri es. Reported average phenolic concentrati ons for some of the ind ustri al wastewaters 1 are given in Table I . Phenolic compoun ds, especia ll y, chl orin ated, may be li fe threatenin g to hum ans even at low concentrati ons. The World Hea lth Organi zati on (WHO) includes nox ious substances fo r human health , some phenolic with a max imum admi ssible compound s concentrati on in dri nkin g water of 200 mg/L for 2,4,6- tri chl orophenol, 9 mg/L fo r pentachl orophenol, I 0 mg/L for 2- chl orophenol and 40 mg/L for 2,4dichl orophenol. The Envi ronment al Protecti on Agency (US-EPA) includes in th e Federal Register Lis t eleven substituted phenols kn own as hazard ous fo r hum an health and assign them a maximum admi ss ibl e concentrati on ran ge of 60 -400 mg/L in relati on to their toxi city degree 2 . The permi ss ible limit for phenolic concentrati ons in indu stri al effluents before di sc hargin g into muni cipal sewers and surface waters are 1-5 mg/eA _ Di sc harge of phenolic wastes may cau se seri ous probl em as they impart carboli c odour to the water course and can be tox ic to fi sh and hum an beings 5 . Some phenolic compound s have been found to acce lerate tum our formation ,cancer, and mutati on6 *Auth or for correspondence

Chl orin ated phenols are of greater environmental concern because of their hi gher tox ictt/ and wide di stributi on due to th e anthropoge nic in pu ts from industri al wastes , degradati on of chl orin ated pesti cides and use of pentachl orop henol (PCP) as a wood prese rvati ve 8 . Signifi ca nt PCP conta min at ion of soil s, lakes, ri vers, an d groun d waters has been reported9 . Because of their tox icity to hu man and marin e li fe, strin gent res tri cti ons have bee n im posed on the concentrat ion of these compoun ds in the wastewaters for safe di sc harge.Removal of phenoli c compound s from wastewater is therefo re of utmost importance to prevent polluti on of water in the receiving water course. Traditi onally, biological treatment, adsorpti on, sol vent extraction are widely used methods for remov in g from wastewaters 10- 14 . Phenol Removal through Adsorption The process of adsorpti on has an edge due to its sludge-free clean operati on and complete remova l of phenols from aqu eous soluti ons ha·vmg dilute or moderate concentrati ons. Activated carbon, m granul ar or powdered form is the most wid ely used adsorbentt 5- 17 . In spite of good capacity it suffers from several disadvantages . The cost of acti vated carbon is higher. Chemi cal as we ll as thermal regenerati on of spent carbon is expensive, imprac ti cal and produces additi onal efflu ent and res ults in a considerable loss of the ad sorbent 10· 12· ' 8· 19 • Thi s has led many workers to search for econom ic, practi cal and effici ent adsorbents. The ava il able literature on vari ous adsorbents and their adsorpti on characteri stics for di ffe rent phenols is summari zed in Tabl e 2. The adsorpti on

209

SINGH & SRIVASTAVA: REMOVAL OF PHENOL POLLUTANTS

Table !-Industri al source and concentrati on of phenol Indu stry Concentrati on, (mg/L) Cok ing plant 580 10.000 Weak ammonia liquor wit hout dcphen oli zation 4-332 Weak ammonia liqu or after dephcnolizati on 30-150 Was h oil still was tes Oi l refi neries 80- 185 Sour water 10-100 General wastewater 0.3-6.8 APF separator effluent Petrochemical 2 10 Benzene refinery 300 Tar di stillati on 250 Nitroge n works 100- 150 Orean manufacturin g 600-2000 Plastic factory 1600 Phenoli c resin production 150 Fiberboard factory 40-400 Fiberglass manufacturin g 200-400 Aircraft maintenance

capacity data reveal that non-conventional adsorbents possess remarkable capacity for the removal of phenols from aqueous solution s. The review documents variou s adsorbents available for removal of phenols form wastewater systems. Many factors influence the rate of adsorption and extent to which a particular adsorbate can be adsorbed . The parameters which have been investigated for optimizing the use of nonconventional adsorbents in wastewater treatment in c lude nature of adsorbate and adsorbent, adsorbate concentration , adsorbent dose, contact time, pH of so l uti on , particle size of adsorbent, etc.

Nature of Adsorbate - The characteristics of ions, molecul es (s ize, shape, charge, etc.) present in wastewater and their concentration have profound influence on the extent of adsorption. Phenols are dissociated in aqueous medium to form anionic species at pH > 6. These anionic species adsorbs at positive ly c harged surface centers on adsorbent. Streat et al. 20 have reported a c lear difference in the ad sorption beh av iour of phenol and p-chlorophenol on acti vated carbon and explained this by difference in molecular size, so lubility, dissociation equi librium , and ben zene ring reactivity. The sorption capacity for p-chlorophenol is greater than for phenol on each of 21 the sample tested . Mattson eta!. have suggested that phenol adsorption on carbon occurs by a donor-

acceptor complex mechani sm involving carbon yl oxygen groups on the carbon surface acting as th e electron donor and the aromatic rin g of phenol as the acceptor. 22

Coughlin et at. have argu ed that phen o l adsorption on carbon involves dispersive forces between rt-electrons in the phenol and the rt-el ectron in the carbon . This effect is more in p-chlorophen o l, since the electronegative chlorine atom attracts electrons towards the ben zene rin g, thu s enhancin g the activation of the molecule. Since p-chlorophen o l is less soluble in water than phenol the sorption of the former is increased . 23

Daifullah and Girgis have studi ed th e effect of six physical properties of phenols on th e amou nt adsorbed. These are: molecular weight, so lubility , pKa, cross-sectional area of adsorbed phenol s, molecular volume and effective molec ular diameter. They have reported that adsorption is direct functi on of these parameters. It has been seen th at substituted phenol with hindered group is less adsorbed th an 24 phenol on fly ash and impregnated fly as h and adsorption follows the order :m- nitrophenol > onitrophenol > phenol > m-cresol > a -cresol .

Nature of Adsorbents- Though every so lid is an adsorbent, the physicochemical nature of adsorbent can have profound effect on both, the rate and 24 capacity for adsorption . Singh et a!. have reported that impregnated fly ash has shown better efficiency of phenol removal than fly ash. The sorption of phenol, 2,4,5- trichlorophenol and tannic acid onto montmorillonite based sorbents was studied by 25 Dente! et al. The sorbents used were homoioni c Naor Ca-montmorillonite, montmorillonite compl etely exchanged with the cationic organic surfactant dimethyl distearyl ammonium choride (or DDA-M) and DDA-M partially re-exchanged with Ca++ (CaDDA-M). It has been noted that sorption capacity significantly enhanced by surfactant treatment of the homoionic clay. Iron (III) hydroxide loaded marbl e has been reported as a potentia l adsorbent for th e 26 removal of phenols . The iron (ill) marble ex hibited much higher adsorptivity compared to unloaded marble. The sorption capacity values of phenol and pyrocatechol on nonimpregnated and impregnated saw dust 27 are 2.10, 5.70;15 . 14, 28.01 mg/5 g, respectively. Higher sorption capacity of impregnated saw dust has been explained on the bas is of iron (ill)phenol complex formation. The adsorption capacities

210

J SC IIND RES VOL 6 1 MARCH 2002

Table 2 - Adsorbents and their performance for wastewater treatment Sl No

Adsorbent

Selecti vity

Conventional (A) Orga nic Ion exchangers Dowex 50 W- X8

Phenol. p- cresol

2

Amberlite- XAD

Phenol. p-ni trophenol , ch lorophenol

Operating conditions

Adsorption /Removal

Column

References

41 42-44

3

Polymeric Adsorbent

Phenols

4

Dowex I X 4

Phenol

5

Porous polymer based on acry lic martix

Phenol, p- nitropheno l. m-aminophenol

6

Macroreticular resin

Phenols

48

7

Weakly bas ic anion exchanger

Phenols

49

R

Anion exchange resin

Phenols

50-55

9

Vinyl pyridine diviny l benzene copolymer

Phenols

56

10

Crossli nked polyvinyl pyrrol idone

Sali cyli c acid. 2,4dihydroxy benzoic acid, catechol. resorcinol, p-hyd roxy benzoic acid

II

Chelatin g Ion exchange in iron (I ll ) form

45 Column Batch, cone: I00 mg/L

46. 60-186 mg/g

47

Batch, cone: Io·4- l o· 2 M, pH 6.5 , equi l time: 2h

18-93 per cent

57

Ch lorophenols, nitrophenols

Column cone: I00 mg/L

28-100 per cent

58

Column ,conc: I mg/mL, equ il time: 20 min

36-1 33 mg/g

28

B. Inorganic ion exchangers 12

Zinc silicate in iron (Ill ) form

Pyrogall ol. catechol, ocresol. phenol

13

Stan ni c mol ybdate

Phenols

14

Zinc si licate

m-, p-cresol, 4-chlorophenol , onitrophenol.

15

Stannic tungstate

Phenols

16

Ion - exchange resins

Phenols

17

Iron (Ill) dieth anol amine

Pyrogallol catechol , resorcinol . quinol

18

Alu mina in Fe (Il l) fo rm

Phenol, resorcinol, o-chlorophenol, catechol, pyrogallol

Column

59

Impregnated paper

60

TLC

61 62,63

Column, cone: l mg/mL

24-83 mg/g

64

Column, cone: I mg/mL

3-29 mg/g

65

-Contd

2 11

SINGH & SRIVASTAVA: REMOVAL OF PHENOL POLLUTANTS

Table 2 - Adsorbents and thei r performance for wastewater treatment -

Co111d

Sl. No.

Adsorbent

Selecti vi ty

Operating conditions

19

Hydrous ZnS

Substituted phenols

Batch

20

Nickel, cobalt and cadmium ferrocyanides

o-Nitrophenol, o-ami nophenol

Batch

9.8-27. 1 mg/g

67

21

Iro n (Ill ) hexamine

Resorci nol. quninol.phlorog-lucinol , salicyli c acid , pyrocatechol pyrogallol

Column, impregnated paper

21-92 mg/g

68

22.

Iron (Ill) morpholinc

Phenol , m-aminophenol , a:naphthol pyrocatechol. pyrogallol

Column , cone: I mg/mL

24.8-1 18.9 mg/g

69

23

Ac ti vated carbons Acti vated carbon from stra w and used rubber tyrcs

Phenol, p- chlorophenol

Batch , cone: 6.03 mmoi/L, equil time:2h

2.08 mmol /g

20

24

Activated carbon from ap ri cot ston e shell

2,4- Dinitro- and 2.4- di-chlorophenol s

Batch , cone: I0 mg/L, eq uil time: 20h

63-65 %

23

25

Activated carbon

Phenols and substituted phenols

Batch

26

Burnt wood charcoal

Phenol

Batch, conc:25-400 mg/L, pH 7, equil time lh

1-7 mg/g

33

27

Activated carbon Fi Itrasorb- 400

Phenols, p-chlorophenol

Batch, equil time: 48h,

2 10,400 mg/g

37

28

Activated carbon from agricultural raw materi al and spani sh lignite

chlorophenols

29

Activated carbon from fertilizer waste slurry

4-Nitrophenol 2,4,6trinitrophenol, 4cholorophenol, resorcinol

Batch

30

Activated carbon from Jute fib er

Phenol

Batch , cone: I00 mg/L, equil time: 5h

31

Granul ar activated carbon

Phenol

32

Biological activated carbon

Phenol , 2,4- dichlorophenol

Batch. cone: I00 and 116 mg/L, pH 7 equil time: 25 h,

33

Surface modified carbon bl ack

Phenol

Batch

100

34

Surface treated activated carbon

Phenol

Batch

101

Phenols, o- and m-cresols, o- and m-nitrophenol

Batch , cone: 500 mg/L, pH 6.5, equil time: 2 h

Phenol. 2.4.5trichlorophenol , tannic acid

Batch

35

36

Non-conventional Impregnated fl y ash

Montmorill onite based sorbents

Adsorption/Removal

Referen ces 66

32,35.70-89

90

91.

28 .50 mg/g, 77.9 per cent

92 93-98

25.04 and 43.75 mg/g

9-46 per cent

99

24

25

-Contd

212

J SCIIND RES VOL 61 MARCH 2002

Table 2 - Adsorbe nts and their performance for was tewater treatmen t -

Conte/

Sl. No_

Adsorbent

Select ivity

Operating conditions

Adsorpt ion/Removal

37

Iron ( Il l) hydroxide loaded marble

Pyrogallo. pyrocatechol

Batch

9, 10 mg/g

26

38

Chemicall y treated saw dust

Pyrogallo. pyrocatec hol

Batch, cone: 100 mg/L, pH 6

28-52 mg/g

27

39

Peat. Fly as h and ben toni te

Phenol

Batch. cone: lmg/L, pH: 4-5 . eq uil time: 16,5and 16h

42-4 per cent

29

40

Activa ted carbons from used tea leaves

Phenol. o-.m -cresol, 4- chlorophenol . 4- nitro phenol 2,4 -d ichI orophenols. 2,4- dinitrophenol

Batch. Column . cone: 500 mg/g

80.2- 438.4 mg/g

31

41

Organobenton ite

Phenol. m- ch lorophenol

Batch, cone: I00 mg/L. eq uiltime: 12 h

80 per cent

102

42

Organoclays

p-ch Jorophenol. tannic acid

103.104

43

Soil

Sustituted phenols

105, 106

44

Dol amite

Phenols

References

107

45

Sediment fractions

Phenol s

108

46

Silt stone

Phenols

109

47

Aquifer material and natural sediments

Chlorinated phenols

11 0

48

Na and Kmontmorillonite

Phenol , 111-cresol. nitrophenol p-bromophenol

Batch , pH : 5.4-6.5, eq uil time:24h

29.48- I09.4 mg/g

Ill

111-

Batch. eq uil time: 2h

3.4-34.4 mg/g.

112

49

Dual cati on organobentonites

Phenol , p- nit rophenol

50

Modified bentonites

Phenols

51

Lake sed iments

Phenols

Batch , pH 7, equil time: 40 h

52

Bagasse fly ash

2.4- Trinitrophenol

Batch

53

Acti va ted sludge

Phenolic waste

54

Hcxadecyl trimethylammonium montmorrilonite clay

Pentachlorophenol

Batch

117

55

Coal. fly ash and acti vated carbon

Phenol

Batch

118

56

Fly ash

Phenols

Batch

119-126

57

Activated sludge and fly ash

Phenol

Batch

58

Biopolymers

Phenol

Batch

59

Pulped wood fiber

2.4- Dichlorophenol 2.4,5- trichloro-phenol

60

Polyurethane foams

Phenols

61

Fertilizer waste slurry

2.4 Dinitrophenol

113 28-67 mg/g

114 11 5 116

91 .0, 27.9 mg/g

127 128 129

Batch

130 13 1 Conte/

Sl GH & SRIVASTAVA: REMOVAL OF PH ENOL POLL UTA TS

213

Table 2- Adsorbents and their performance for was tewater treatment- Conte/ Sl. No.

Adsorbent

Selecti vit y

62

Low cos! carbonaceous adsorbents

2,4,6 Trinitrophenol , 4-nitrophenol. 4-chlorophenol . resorcinol

63 64

Ac tivated carbon from bamboo

Phenol

Batch

Marine sediments

2.4-Dichlorophenol

Batch. cone: 5-20 mg/L

Bacillu s subtili s

2,4 ,6-Trichloro -phenol

Batch

65

of phenol , a-naphthol, a-creso l, catecho l and pyrogallol on untreated zin c sili cate were found to be 11.28. 30.28 , 21.63. 28.62, 42.87 mg/g, respectively. whereas the capacity va lu es of zinc si li cate in Fe (III) form 28 were 35.72, 72 .09, 60.56, 96.89, 133 .67 mg/g, respectively. The hi g her capacity in the latter case occu rs by vi rtu e of the ab ility to form compl exes of varying stabi lit y wit h Fe (IJI) boun d to the zi nc sili cate matri x.

Effect of Adsorbate Con centration - Th e increase in concentrat ion of the adsorbate results in increase in the magnitud e of adsorption at a g iven temperature. Thi s parameter has been studi ed by several in vesti gators and th e resu lts are generall y expressed by a lin ea r form of Freundlich and Langmuir adsorpti on isotherm s26 ' 29 ·30 . Figure I a and b show the lin ear adsorption mode ls of 4- c hl orophenol (4-CP) and 4- nitrop heno l (4-NP) on acti vated carbon prepared from used tea leaves 3 1. Adsorbate Dose - It is import ant to determine the dose of adsorbent req uired to achi eve a des ired 0 leve l of treatment. Swamy et al? have studied the effect of adsorbent dose on the removal of a-creso l by bagasse and fl y ash. It is observed that the per cent re mova l of a -c reso l in creases with increase in adsorbent dose, while remova l per unit we ight of adsorben t increases with decrease in adsorbent dose. The reported optimum dose is 12 g/L fo r about 90 per cent removal of a -creso l (I 00 mg/L), The variation of adsorption density and fraction adsorbed again st adsorbent dose for catec hol remova l on indu strial grade granular activated carbon and laboratory grade granul ar activated carbon has been studied 32 . It is observed that fraction adsorbed increases with in crease in adsorbent dose. Effect of adsorbent dose studied for used tea leaves activated carbon reveals

Operatin g conditions

Adsorpti on / Removal

References 132

133 1.5-4 mg/g

134 135

that 120 and 140 mg/L carbon is sufficie nt for I 00 per cent remova l of 4-chlorophenol and 4-nitrophenol ( I 00 mg/L), respectively 31 . Effect of adsorbent dose on removal of phenol has a lso been stud ied by several other investi gators 33 .

Effect of Co ntact Tim e- Adsorption of adsorbate spec ies is faster in the initi a l stages of contact period and becomes slow near · 24 ·26 ·29 ··3 t · Contact ttme . . . eq ut.11.b num req utred to attatn eq uilibrium is a function of particle size, pH, rate of ag itat ion, temperature, etc. Pretreatment of adsorbent a lso influ ences the eq uilibrium time . The eq uilibriu m time for adsorption of phenols on impregnated fly 24 26 as h , iron loaded marbl e , peat 29 , bagasse-fly ash 30 • used tea leaves activated ca rbon 3 1 and iron oxide 34 coated sand are 2, 1.5, 16, 1.5 , 3 and 2 h, respectivel y. Effect of pH- The re mova l of phen ol from water by adsorption is hi ghl y de pende nt on pH of the solution , which affects the surface c harge of the adsorbent, degree of ionization , and spec iati on of phenol. It is reported that per cent adsorption of 31 phenol on activated carbon increases up to pH 6 and then decreases with further increase in pH. Effect of pH on batch adsorption studi es of ph enol by peat, fly ash and bentonite 29 indi cated th at ph enol was better adsorbed at pH 4.0, 5.0, and 4.0, respect ively (Figure 2) . The re mova l of a-creso l from wa stewa ter by adsorption onto activated carbon (laboratory grade), bagasse-fl y as h and act ivated carbon (comme rcial grad e) was found to be hi ghl y dependent on pH of the so lution , which affects the surface charge of adsorbent and degree of ioni zation 30 , 35 Mahesh et a/. have reported the favourable adsorption of phenol at low pH on activated carbon. The dec rease in adsorpti on with in crease in pH has

2 14

JSCI!NDRES VOL61 MARCH2002

2.5

60

*"

'" 2.0

50

--

F

~

40

"'o ~

-I J'

0

.:c

t

30

0

0.0 0

3

lfl

~

....l...x 10 2(l•g-1)

~

Ct

20

10

2.6

0~~~~~~~----------~

2 2.5 3 3 . 5 4 4.5 5 5.5 6 6.5 7 7.5 8 pH

Figure 2- Effect of pH on the adsorption of phenol by peat(x),tly ash(+) , bentonite(O)

10~--~----~--~--~~--~--~--~

0.0

Ill

lA

1.2

2.0

2. ~

2J

Lt9 Ct

20

Figure !-Linear absorption models of 4-CP and 4-NP on activated carbon prepared from used tea leaves (a) Langmuir eq uation and (b) Freudlich eq uati on · - J'M1ide

di3I!IO!