Journal of Polymer Research 9: 69–73, 2002.© 2002 Kluwer Academic Publishers. Printed in the Netherlands.

69

Synthesis of Plantago Psyllium Mucilage Grafted Polyacrylamideand its Flocculation Efficiency in Tannery and Domestic Wastewater

Monika Agarwal, Rajani Srinivasan and Anuradha Mishra∗Department of Chemistry, Institute of Engineering and Technology, CSJM University, 208 024 Kanpur, India(∗Author for correspondence; Tel.: +91-512-218330; E-mail: anuradha_mishra@rediffmail.com)

Received 12 March 2001; accepted in revised form 14 October 2001

Key words: flocculant, Jar test, P.psyllium-g-Polyacrylamide (Psy-g-PAM), Tannery and Domestic waste water, X-ray

Abstract

A graft copolymer of P.psyllium mucilage and polyacrylamide has been synthesized in the presence of nitrogen using cericion-nitric acid redox initiator. This grafted copolymer was tested for its flocculation efficiency in Tannery and Domesticwastewater by the standard Jar Test method. The effects of polymer concentration, contact time and pH on percent removalof solid wastes from Tannery and Domestic effluents have been reported. The optimal dose was found to be 60 ppm, atwhich maximum solid removal from both the effluents took place. The maximum solid removal was seen after one hour atacidic pH in the case of the Domestic effluent and at alkaline pH in the case of Tannery effluent. X-ray analysis of the solidwaste from effluents, grafted copolymer and flocs obtained after treatment of the effluents with the mucilage showed theinteraction of the suspended solid wastes with the P. psyllium grafted polyacrylamide (Psy-g-PAM) copolymer. Psy-g-PAMhas been proved to be a better flocculant than pure psyllium mucilage.

Introduction

The use of polyelectrolytes for the removal of suspended anddissolved solids is the most significant development in watertechnology in recent years. The destabilization of suspen-sions by organic polyelectrolytes has become increasinglypractical in light of their effectiveness in extremely lowconcentrations. The characteristics of the use of cationic,anionic and non-ionic grafted and ungrafted polysaccharidesas flocculants have been extensively studied [1].

Grafted and ungrafted natural water soluble polysaccha-rides have the capability of flocculating small particles [1]and of causing turbulent drag reduction. These propertieshave led to their novel applications in agriculture, in efflu-ent treatment and in mineral beneficiation. Natural polymerssuch as starch [1, 2], sodium alginate [3, 4], amylopectin,guar gum, xanthan gum [1], kendu gum [5], and chitosan [6]have found extensive application as flocculants. Many starchbased products have been used for the removal of toxicwastes like hexavalent chromium [7], cadmium [8] andgallium [9], which are usually present in most industrialwaste water, such as that from the textile, leather tanning,electroplating and metal finishing industries [10].

Homopolymers have various drawbacks, such as theirshear instability, uncontrolled biodegradability and varyinginefficiency. On the other hand, synthetic flocculants aregood flocculating agents but are non biodegradable and ex-pensive. Many attempts have been made to combine thedesired properties of both by grafting synthetic polymersonto the backbone of natural polymers [1, 11].

In the present study, the synthesis of Psy-g-PAM and itsuse as a flocculant for suspended solid removal from Tanneryand Domestic wastewater are reported.

Experimental

P.psyllium mucilage was obtained from an Indian groceryshop. It was purified by precipitation from aqueous solutionwith alcohol and finally washed with acetone. Acrylamide,ceric ammonium nitrate (Merk chemical Co. extra pure)and nitric acid, analar, grade, from BDH, India were usedas received. The FTIR spectrum of purified okra gum wasrecorded on a Brucker-Vector-22 spectrophotometer. Theviscosity of the polymer solution was measured by an Ost-wald viscometer. The intrinsic viscosity was obtained (frompoint of intersection) after the extrapolation of two plots,i.e. ηsp/C vs C and ln ηrel/C vs C to zero concentration.Here C is the concentration of polymer in g/dL and ηsp/C =ηrel − 1/C, where ηrel = η/η0 = t/t0; t being time of flowof polymer solution (of viscosity η), t0 the time of flow ofsolvents (of viscosity η0) at the time of measurements.

Tannery wastewater was collected from a Tannery situ-ated at Jajmau, Kanpur (India) where vegetable and chrometanning processes are used. Domestic wastewater was col-lected from its source (main sewage collection point). ThepH of the wastewater samples and grafted copolymer solu-tion in water were measured by a Microprocessor pH meterCP 931. The conductivity of the wastewater samples wasmeasured by a Century Microprocessor conductivity meter

70 M. Agarwal et al.

CC 631 and the COD was measured by the usual standardmethod.

The (Psy-g-PAM) was synthesized by following themethod as given by Singh et al. [4, 12, 13].

The graft copolymers were synthesized by grafting acry-lamide onto purified P.psyllium mucilage by radical poly-merization method in aqueous system using ceric ion-nitricacid redox initiator. The following procedure was adopted incarrying out the reactions. One gram of P.psyllium mucilagewas dissolved in distilled water (200 mL) in an Erlenmeyerflask. 0.14 mole of acrylamide monomer was dissolved indistilled water (100 mL) in another flask and the solutionwas added to the P.psyllium mucilage solution in the Er-lenmeyer flask. This mixture was stirred with a magneticstirrer. The flask was then sealed with a septum stopperand nitrogen gas was flushed into the solution through ahypodermic needle. The solution was stirred for 30 minwhile being bubbled with nitrogen. 0.40 × 10−3 moles ofceric ion solution (ceric ammonium nitrate dissolved in 1MHNO3 solution) was then injected through the stopper byhypodermic syringe. The nitrogen flushing was continuedfor another 20 min; then the needles were taken out andflasks were further sealed with Teflon tape. The reactiontemperature was maintained at 30 ◦C by immersing the flaskin a constant temperature bath. The reaction mixture wasstirred occasionally. The reaction was continued for 24 hoursand then terminated by adding 0.5 mL of saturated aqueoushydroquinone solution.

The reaction product was precipitated in an excess ofisopropanol and filtered through a scintered glass filter. Theprecipitate was again slurried in acetone followed by filtra-tion and finally the precipitate was dried in a vacuum ovenat 40 ◦C.

There is always the possibility of the formation of ho-mopolymers in grafting. But Oven and Shen [14] showedthat if the monomer (here polyacrylamide) concentration isless than 2.0 moles and the CAN concentration is less than0.1 mole, the chances of a homopolymer forming are greatlyreduced. In the present study, these concentrations were keptwithin the critical values. It was thus assumed that no ho-mopolymerisation took place. IR spectroscopy of the graftedproducts supported the claim that grafting indeed had takenplace [15, 16]. The total monomer conversion was calculatedby the equation

Conversion = W0 − W1

W2,

where W0 = weight of resulting polymer, W1 = weight ofadded P.psyllium mucilage, W2 = weight of total addedmonomer. The conversion of the total monomer in thepresent system is 85%.

Measurement of the flocculation efficiency of Psy-g-PAM was conducted by the Standard Jar Test methoddescribed by Huck et al. [17].

Beakers of 1000 mL capacity each equipped with vari-able speed (0–100 rpm) agitators were used. 500 mL waste-water (Tannery and Domestic) was added to the beaker andthen the polymer solution was added into it by means of asyringe (capacity 1–2 mL). The agitator was first adjusted to

100 rpm for 1 min and then continued for a total of 10 minat 50 rpm. The agitator was subsequently stopped and thewastewater was allowed to settle for 1 h.

A measured volume of 20 mL of samples was taken todetermine the solid content of the effluents before and af-ter treatment with the polysaccharide. The suspended solidcontents were calculated by the equation [18]

Solids (mg/L) = A − B × 1000

volume of the sample (mL),

where A = weight of the dried residue + crucible, B =weight of the crucible.

To determine the total dissolved solids, known volumesof samples were filtered and the solids so obtained weredried and weighed; for total solids unfiltered samples weretaken. The amount of suspended solids in wastewater wasdetermined by subtracting the total dissolved solids from thetotal solids.

Flocculation efficiency was seen at three pH values –4.0, 7.0 and 9.2. The pH of the solution was maintained bythe addition of 450 mL of buffer solution of required pH to50 mL of wastewater.

X-ray powder diffraction patterns of grafted copoly-mer, solid waste and flocs after treatment of effluent withgrafted copolymer were obtained on X-ray diffractometermodel Iso-Debyflux-2002 (Rich and Scifert) using Cu K∝radiations.

Results and Discussions

Characterization

The FTIR spectrum of the prepared Psy-g-PAM givescharacteristics peaks of –OH between 3609–3288 cm−1,–COOH between 1600–1557 cm−1, lactone at 1734 cm−1

and amide at 1665 cm−1. The intrinsic viscosity of thecopolymer was found to be 5.73 dL/g.

Tannery effluent has a pH of 7.35, a conductivityof 2.90 mS, a turbidity of 70.7 NTU, a COD value of2800 mg/L, with 3000 mg/L suspended solids (S.S) and6555 mg/L total dissolved solids (TDS). The pH of thetannery effluent after the addition of the grafted copolymer(60 ppm) was found to be 7.80.

Domestic wastewater has a pH of 7.84, a conductiv-ity of 5.69 mS, a turbidity of 26.8 NTU, a COD value of525 mg/L, with 400 mg/L suspended solids and 2314 mg/Ltotal dissolved solids. The pH of the domestic wastewaterafter the addition of Psy-G-PAM (60 ppm) was found tobe 7.25.

Flocculation Studies

Effect of Polymer DoseThe Flocculation efficiency of P.psyllium-g-Polyacrylamidewith Tannery and Domestic effluent is given in Figure 1. Itshows the plot between the polymer dose and the percentof removal of the suspended solid in Tannery and Domestic

Synthesis of Plantago Psyllium Mucilage Grafted Polyacrylamide 71

Figure 1. Plots of percent removal of suspended solid vs copolymer dose:tannery ("), domestic (!) wastewater, temperature = 32 ◦C.

wastewater. From the plots it is apparent that with an in-crease in polymer dose, the percent removal of solid wasteincreases, but above a certain dose of polymer, a decreasingtrend in percent solid removal is seen in both cases.

The above behavior could be explained by the factthat the optimal dose of flocculant in suspension causeslarger amounts of suspended solid to aggregate and set-tle. However, an overoptimal amount of flocculant insuspension would cause the aggregated particles to redis-perse in the suspension and would also disturb particlesettling.

It is clear from Figure 1 that the most effective dose is60 ppm. At this concentration, a maximum removal of solidwaste is seen in both the cases.

The pure P.psyllium mucilage was also found to bea good flocculant, but the dose needed for almost thesame percent removal of solid from waste was doublethat of Psy-g-PAM. Among the various flocculation mech-anisms for long chain polymers, a bridging mechanismis predominant. For a polymeric system in which bridg-ing is predominant, an increase in chain length improvesflocculation. In grafted P.psyllium mucilage, the danglingpolyacrylamide chains have a better approachability to sus-pended particles and hence an increased flocculation ca-pability [1] as compared to that of pure P.psyllium mu-cilage.

Effect of Contact TimeThe flocculation efficiency of the Psy-g-PAM is shown withvarying contact times in Figures 2 and 3. Figures 2 and 3show percent removal of the solid waste from Tannery andDomestic effluent respectively with contact time at differentpolymer doses.

The maximum solid removal was seen after one hour ofcontact time in the case of domestic wastewater and afterfive hours in the case of tannery effluent. The time taken forsolid removal from tannery effluent was much longer thanthat taken by domestic wastewater. This may be becauseof the higher COD values of the tannery effluent comparedwith those of domestic wastewater. In addition, there isproteinaceous matter in tannery effluent, which surroundsthe colloidal particles, thus slowing down the neutralizationprocess of the zeta potential.

Figure 2. Plots of percent removal of suspended solids vs contacttime of tannery effluent with varying copolymer dose: (") 20 ppm;(!) 40 ppm; (a) 60 ppm; (e) 80 ppm.

Figure 3. Plots of percent removal of suspended solids vs contact timeof domestic wastewater with varying copolymer dose: (") 20 ppm; (!)40 ppm; (a) 60 ppm; (e) 80 ppm.

Effect of pHThe flocculation efficiency of the optimal dose of graftedmucilage (60 ppm) is shown with varying contact time andpH in Figures 4 and 5 for tannery and domestic wastewaterrespectively. From the plots, it is apparent that maximumsolid removal was found after one hour at alkaline pH (9.2)in the case of tannery effluent and at acidic pH (4.0) in thecase of domestic wastewater.

Mechanism

X-ray powder diffraction patterns of solid waste, polymerand flocs obtained after treatment are shown in Figure 6(a–c)and Figure 7(a–c). Figures 6(a) and 7(a) show the crystallinenature of waste material in tannery and domestic wastewaterrespectively, whereas the pattern for (b) shows the completeamorphous nature of Psy-g-PAM copolymer. Figure 6(c),the XRD pattern for flocs for tannery wastewater, is quitedifferent from Figures 6(a) and (b). Similar results are shownin Figures 7(a), (b) and (c) for domestic wastewater. The 2θ

values and d-values observed in (a) are changed altogetherin (c) in both the cases and this constitutes primary evidencethat different crystal types were found [19–21] in the flocs.

72 M. Agarwal et al.

Figure 4. Plots of percent removal of suspended solids vs contact timeof tannery wastewater at polymer dose 60 ppm, with varying pH:(") 4.0; (a) 7.0; (!) 9.2.

Figure 5. Plots of percent removal of suspended solids vs. contact time ofdomestic waste water at polymer dose 60 ppm, with varying pH: (!) 4.0;(") 7.0; (a) 9.2.

Figure 6. XRD patterns of solid waste (a), Psy-g-PAM copolymer (b) andflocs after treatment of tannery wastewater (c).

Figure 7. XRD patterns of solid waste (a), Psy-g-PAM Copolymer (b) andFlocs after treatment of domestic wastewater (c).

This change in angle and d-values may be due to stronginteractions between the free hydroxyl groups and car-boxylic groups and the contents of the tannery and domesticwastes. Although the XRD patterns do not provide any spe-cific evidence for the mechanism of flocculation, anionicpolymers are known to make larger flocs by the bridg-ing mechanism but, in these cases, the extent of changeobserved in the patterns suggests that, apart from sec-ondary bonding between flocculant and solid waste, theremay also be involvement of primary bonding like chela-tion between the crystalline matter of the waste and thepolymer.

Conclusion

Water-soluble Plantago psyllium mucilage grafted polyacry-lamide, synthesized using ceric ions as the initiator, has beenused to flocculate suspended solids in Tannery and Domesticwastewater. The optimal concentration of the copolymer asflocculant was found to be 60 ppm, at which >95% and>89% solid removal were seen in tannery and domesticwastewater respectively. The time required for maximumremoval was only one hour in both cases. The optimal pHwas 9.2 and 4.0 for tannery and domestic wastewater re-spectively. X-ray diffraction patterns show the unambiguousinteractions of the polymer with the suspended solids ofeffluents. Psy-g-PAM copolymer was found to be a moreeffective flocculant for tannery effluent treatment than fordomestic wastewater. The flocculation efficiency of puremucilage was also tested and was found to be a little inferiorto the grafted copolymer.

Synthesis of Plantago Psyllium Mucilage Grafted Polyacrylamide 73

Acknowledgements

The authors are grateful to Dr. Tapan Raoth, Incharge, ZonalLaboratory Kanpur, National Environmental EngineeringResearch Institute, Dr. Padma S. Vankar, Incharge, Facil-ity for Ecological and Analytical Testing, Indian Institute ofTechnology and Dr. R. P. Mishra, Scientist, Central PollutionControl Board, Kanpur for their valuable help during thisstudy by providing some of the research facilities.

References

1. R. P. Singh, G. P. Karmakar, S. K. Rath, S. R. Pandey, T. Tripathy,J. Panda, K. Kanan, S. K. Jain and N. T. Lan, Polymer Eng. and Sci.,40(1), 46 (2000).

2. M. I. Khalil and S. Farag, J. Appl. Polym. Sci., 69, 45 (1998).3. S. Rajani, M. Agarwal and A. Mishra, In Proceedings of National

Symposium of Indian Society of Agricultural Biochemists, 2000.4. T. Triphati, S. R. Pandey, R. P. Bhagat and R. P. Singh, Eur. Polym. J.,

37, 125 (2001).5. S. Samantaroy, A. K. Mohanty and M. Misra, J. Appl. Polym. Sci., 66,

1585 (1997).6. P. Udaybhaskar, L. Iyengar and R. A. V. S. Prabhakar, J. Appl. Polym.

Sci., 39, 739 (1990).

7. V. Tare and S. Choudhary, Water Res., 22, 1109 (1987).8. M. Jawed and V. Tare, J. Appl. Polym. Sci., 42, 317 (1991).9. V. C. Chan, J. Appl. Polym. Sci., 50, 1733 (1993).

10. R. W. C. Peters, K. Young and D. Bhattacharya, Aiche Symp. Ser.No. 243, 83, 165 (1995).

11. W. C. Chan and C. Y. Chiang, J. Appl. Polym. Sci., 58, 1721 (1995).12. S. R. Deshmukh and R. P. Singh, J. Appl. Polym. Sci., 32, 6163 (1986).13. S. K. Rath and R. P. Singh, J. Appl. Polym. Sci., 66, 1721 (1997).14. D. R. Owen and T. C. Shen, The Effect of Acrylamide Graft Copoly-

merisation on Solubility and Viscosity of Several Polysaccharides inStucture Solubility Relationship in Polymers, F. W. Harris and R. W.Seymour (eds), Academic Press, New York.

15. N. C. Karmakar, S. K. Rath, B. S. Sastry and R. P. Singh, J. Appl.Polym. Sci., 70, 2619 (1998).

16. S. K. Rath and R. P. Singh, J. Appl. Polym. Sci., 70, 1795 (1998).17. P. M. Huck, Scavenging and Flocculation of Metal Bearing Waste Wa-

ter Using Polyelectrolyte Environment Protection Service, Burlington,Canada, 1997.

18. A. E. Greenberg, R. R. Tussel and L. S. Clesceri, Standard Methodsfor Examination of Water and Waste Water, 16th Edit., Amer. PublicHealth Assoc., Washington, 1985.

19. L. Huang, E. Allen and A. E. Tonelli, Polymer, 39, 4857 (1998).20. A. Harada, M. Li, J. Kamachi, Y. Kitagawa and Y. Katsube, Polymer

Prep., 38, 533 (1997).21. L. Huang, A. Emily and A. E. Tonelli, Polymer, 40, 3211 (1999).