Bibadsorptive Removal ofChromium and Lead by AquaticMacrophyte

Rupa ChakrabortyResearch Scholar*Environmental Engineering divisionCivil Engineering DepartmentJadavpur University, Kolkata- 700032rupachakra@yahoo.co.in

Somnath Mukherjee "..ProfessorEnvironmental Engineering divisionCivil Engineering Department,Jadavpur University, Kolkata- 700032snmJu@yahoo.co.in

ABSTRACT

The accumulation of heavy metals in the waterenvironment receives increasing attention becauseof the indiscriminate adverse public health effect bythe respective elements. For removal of such toxicmetals from the aqueous phase in a more innocuousway, biosorption is emerged as a potential optionfor heavy metal removal as reported in variousliteratures. The accumulation of heavy metals usingliving photosynthetic species such as aquatic weedsand plants are applied for the purpose to establishan alternative method to different existing physico-chemical method for such purposes. Thebioremediation as utilizing some aquatic plants forremoval of toxic metals from water environmentunveils to be a plausible alternative. The present

- paper discusses on laboratory investigation ascarried out in Environmental Engineering division,Civil Engineering Department, Jadavpur Universityto explore chromium and lead uptake capacity of oneof the common aquatic macrophytes normally grownabundantly in Indian subcontinent such as waterlettuce (Pistia stratiotes). The plants were collectedfrom a nearby pond and hydroponically cultured inthe laboratory condition using Hoagland solution.The sample water was prepared with Cr (VI) and Pb(II) -spiked synthetic solution with varied initialconcentrations as single substrate respectively inseveral test cases. The plants of different quantities(biomass) were exposed to spiked solutions inseparate containers batch wise for a specific periods.it was observed that for an initial concentrationrange of 1-5mg / L of Cr (VI), about 99-72%corresponding removal took place after a contactperiod of9 days. In case of lead, about 82% removalwas achieved after 9 days contact period for an initial

*Corresponding Author

concentration range 2mg / L for same biomass (60g /L ) concentration.

Key words: Bioremediation, Chromium, Lead,water lettuce, hydroponic culture

INTRODUCTION

Management of water quality in thehydrosphere is a big challenge throughout the worldbecause of different anthropogel.ic pollution. Theremoval of heavy metals from contaminated wateris of great importance in terms of protection of theenvironment and human health. Heavy metals maybuild up various physiological effects in biologicalsystems and cause serious health hazards like skindiseases, lung cancer, liver dysfunction, kidneydamage, permanent damage in nervous system etc.The conventional removal methods like chemicalJecipitation, coagulation, lime-softening etc. aregenerally expensive and require frequentmonitoring apart from high chemical cost anddisposal problem of chemical sludge, though suchprocess are attenuative. . Biosorption is one of themost important biological methods which has beenrecommended as cheaper, eco-friendly and effectivetechniques for removal of heavy metals fromaqueous environment (Miretzky et aI, 20041;Odjegba and Fasidi, 20042). Aquatic macrophytessuch as water lettuce, duckweeds etc. are one ofthe biological components as being used in recentyears as functional intent to prevent the hazards oftoxic metal pollution successfully (Suhag et al.,201P,Maine et al.,2006,4). The treatment responses in anaquatic macrophyte treatment system are due todirect uptake of material by plants' root underfavorable environmental conditions. This uptakecapacity of aquatic plants along with otherinfluencing factors has also been reported asphytoremediation technology (Pilon-Smiths, 20055).This technology involves several sub-mechanisticprocesses like rhizofiltration, phytostimulation,phytostabilization, phytoextraction, phytodegra-dation, phytomining and phytovolatilization. Thephytoremediation process involves the introductionof plants into an ecosystem and allowing them toassimilate rather hyperaccumulate thecontaminants in their roots and associated parts.Some earlier studies have shown thehyperaccumulation potential for metals like Pb, Hg,Cd,.etc. (Alam et al., 19946; Baharudin et al., 20087).In certain cases the rate of metal uptake has beenreported to go up to even 90-95% depending on theplant species concerned, its biomass, metalconcentration and environmental factors like pH,temperature, etc. (Baharudin et al., 20087, Mishraand Tripathi, 20088).

Volume 2012-13 e Number 2 eJuly2012 43

(Rupa UhakralJOny, i:>OrrUtUtl£"'"""H'<-'J~~ '1.

I

II

Chromium (VI) rarely occurs naturally, but isusually produced from anthropogenic sources. It isused in various industries such as chrometanneries, plating, cooling tower water treatmentetc. The hexavalent form of chromium is of

particuLar concern because of its great toxicityresulting from its powerful oxidation properties. Itis classified as a group A carcinogen and poses otherhealth risks such as liver damage, dermatitis andgastrointestinal ulcers (Dokken et al.,19999).Reduction of hexavalent chromium to trivalent with

subsequent immobililation as the hydroxide isconsidered as one of the main strategies forchromium removal from waster water (Lazardis andAsouhidou, 200310). In a separate study Lytle et al.,199811found that water hyacinth could accumulatehexavalent chromium from contaminated water.Under X-ray spectroscopy, the plants had convertedhexavalent chromium to trivalent chromium in the

lateral roots of the plant, thus detoxifying the watersignificantly. Keith et al., 200612 also showed thatthe water hyacinth can hyper accumulate chromiumin the tune of72.3, 21, and 19% chromium( Cr VI)removal for 7,14 and 28 mg/L respectively. EspinozaQuinones et al., 200613 observed that for a range of2-3 mg / L initial Cr (VI) concentration, Salviniaauriculata could remove 90 percent of Cr(VI) , muchhigher than Pistia stratiotes (70 percent) andEichhornia crassipes (50 percent) after 35 days ofuptake experiment. Aquatic fern (Azolla) has beendemonstrated as an important candidate forpolishing wastewateT containing Cr (VI). Arora etal., 200614 detected the high tolerance of Azolla spfor a wide range ofCr(VI) [up to 10 mg / L] as wellas to bioconcentrate [BCF i.e. Bio concentrationfactor ( ratio of metal concentration in the drybiomass to the initial concentration of metal ion infeed solution) ranged between 243 -4617 for threesp of Azolla] them. Toxicity in treated tanneryeffluent has been reduced using alga Nostocmuscorum and bacterium Photobacteriumphosphorium [Chandra et al., 200415]

Lead [Pb (II)] contamination of the environmenthas resulted from mining and smelting activities,leads based paints, gasoline, storage batterymanufacturing plants and explosives as well as frommunicipal sewage sludges enriched in Pb (II) inwater environment (Chaney and Ryan, 199416).Leadattributes to its toxic ability to interfere with severalenzymes like CAT, POD, SOD (Odjegba andFasidi,200717). As lead causes a large variety oftoxiceffects, including gastrointestinal, muscular,reproductive, neurological, behavioral and geneticmalfunctions [Johnson ,199818], the fate oflead inthe aquatic environment is of great concern.Moodley et al., 200719 found that Alternanthera

sessilis (grown on settling ponds of a sewagetreatment works) can accumulate Pb in leaves inhigher amount than in the roots and stemscombined. In contrary to the above, Sharma andDubey ,200520 reported lead accumulation in rootjn hjgher as compared to other parts of plants.

Verma et al., 200521 detected that water hyacinthcould remove lead to a higher percentage 80.3%from industrial wastewater with Pb 1.39 mg / L.).Shao-Wei Liao, 200422 exhibited water hyacinth canbe an useful macrophytes for absorption of leadand storing it in root tissue along with other heavymetals.

The present investigation was carried out toexplore the potential use of water-lettuce (Pistiasp.), a floating aquatic plant to remove toxic heavymetals like chromium (VI) and lead (II) from alaboratory prepared spiked solution in presence ofhydroponic solution.

MATERIALS AND METHODS

Designing of the Experiment: The presentexperiments were carried out in multicells aquariummade of Perspex sheet in the laboratory inEnvironmental Engineering division, J adavpurUniversity, Kolkata, West Bengal, India. The youngplants were collected from a nearby pond andacclimatized hydroponically in flat bottom HDPEtray. Plants harvested from this tray weresubsequently washed in single distilled water,O.OlM NH4-EDTA solutions respectively and finallyin deionised distilled water. They were grownhydroponically in Hoagland solution (1950)23 as anutritional supplement at pH 7 :t 0.2 inapproximately 10000 lux/m2 light intensity. Theexperiment was carried out at ambient temperature(250 :t 50 C). For treatment purpose, culture mediumwas prepared with Cr (VI) and Pb (II) -spikedsynthetic solutions separately. The differentsynthetic solutions of varied concentration levelswere prepared by diluting stock solution withnutrient solution in required quantity to get thedesired concentration of metallic solutions. Stockpotassium dichromate solution of the strength of1000mg of Cr (VI)/L was prepared by dissolving 2.82gK Cr 0 (oven dried) in lL of double distilled water.A2set2of intermediate stock chromium of differentdiluted strength solution were made by addingdeionised distilled water plus nutrient solution tostock in such quantity that finally solution volumein each container became lL. Approximate 60g ofbiomass were placed in the aquarium withpredetermined volume (lL) and allowed to retainin the solutions with supplement of Hoaglandsolution. Volume of solution was adjusted after

Volume2012-13. Number 2. July 2012 44

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Rupa Chakraborty, Somnath Mukherjee

aliquots of solution were taken for analysis and tomake up the loss due to evaporation with deionisedw:ater. The total retention period for each set ofexperiment was nine days. In each case 'control'set was kept without any metal solution.

Estimation of Cr(VI) and Pb(II): The sample wasdigested with a sui ph uric-nitric acid mixture andfollowed by oxidation with potassium permanganate[for total conversion of all chromium species to Cr(VI) ]. Dissolved hexawalent chromium wasestimated colorimetrically by reaction withdiphenylcarbazide in acid solution to form a red-purple chromium 1, 5-diphenyl-carbohydrazinecomplex that is measured at 540 nm in accordancewith Standard Methods (APHA 1985)24 in UV-VISSpectrophotometer (Varian, USA make, model Cary50).

For lead treatment, a stock (lOOmg/L) leadsolution was prepared by dissolving lead nitrate saltin double distilled water. Spike sample solution of2mg/L was prepared by diluting the stock 50 timeswith double distilled water. Lead concentration wasdetermined using Flame Atomic AbsorptionSpectrophotometer (Perkin Elmer Analyst 200model)

All reagents were used of AR grade ofE-Merck,India make.

All the tests were conducted with threereplicates. The experiment was performed as batchmode kinetic. Sixty gm ofihitial biomass (laboratorycultured samples) was next placed equally in thedifferent cells of the multicells aquarium containingthe mixture of chromium and nutrient solution. Thesolution was buffered to a pH of 6.8:!::O.2.Sampleswere pipetted out from each cell after 1,2,3,4,5,6,7,8and 9 days from the start of the experiment andanalysed for residual chromium and leadconcentration as described above.

For each initial concentration set, the sameprocedure was repeated three times with freshlaboratory cultured samples. All the above testshave been carried out as batch kinetic studies.

RESULTS AND DISCUSSIONThe residual Cr (VI) concentrations in the

solutions were determined from the culture solution

after every 24h interval up to 9 days contact periodcontinuously for different initial Cr (VI)concentrations. From the residual Cr (VI)concentration left in the culture media aftertreatment with the test plant, the removalpercentage was calculated at specified time intervals.The results are shown in the Table 1. It revealsthat the uptake took place in two phases with rapidinitial uptake up to 4 days which gradually reached

to an equilibrium concentration level after a periodof 9 days. It is also revealed that the sorption bythe plants was maximum at lower initialconcentration (1 mg/L) and started declining athigher initial concentrations which could be due toimposition of toxic effects to the plant metabolism.

Lead is not an essential element for the plantsbut it gets easily absorbed and accumulated indifferent parts of the plant unless it reaches athreshold inhibitory limit. This uptake is controlledby pH, particle size and other physico-chemicalparameters. The uptake oflead at pH (7.0) for theremoval percentage with time, the different initiallead concentrations are shown in Table 2. It isevident from the data set that like Cr (VI) uptakeinitially the adsorption rates are faster and thenfound to be decreased gradually to reach anequilibrium level between the time period after7days. It is noted that about 82% removal took placeafter same retention period (9 days) for an initiallead concentration range 2mg/L for same biomassconcentration (60g/L ). However, in the fieldcondition it can be achieved more by adoptingcontinuous harvesting technique with moreexposure to sunlight or better photosynthesis sinceit is expected that cells may be vibrant within theplant regime by photosynthetic action. The increasein initial rate of removal with subsequent increaseof initial lead concentration may be due to thedifference in concentration potential between thesolution and root system. The rapid uptake perhapsdue to an initial phase of exchange phenomenonfollowed by a slow phase due to metabolic regulationand more flux intrusion through root system.

Percent removal data of Cr (VI) and Pb (II) bywater lettuce (Pistia) from 0 to 9 days of culturehas been plotted in Figure 1. In each treatment,the results showed a rapid removal at initial phasewhich ultimately reached at equilibrium after 6 to7 days. Among two metals tested, highest removal(82%) was observed in case ofPb (II) followed by Cr(VI) (79.5%) at an initial concentration of 2 mg/Lafter 9 days of culture as shown in Table 3.

CONCLUSIONPhytoremediation technology is gaining the

status of a major scientific progress in ecologicaland environmental engineering application and hasimmense contemporary relevance for potential useto decontaminate or to render harm lessenvironmental ecosystem. Plant species such aswater lettuce (Pistia sp,) has been successfullyexplored to examine the sorption potential forchromium and lead separation from the spikedsolution. So this plant can be used as low costtreatment material for scavenging heavy metal from

Volume 2012-13 - Number 2- July 2012 45

(i.

Rupa Chakraborty, Somnath Mukherjee

Table: 1 Batch Kinetic Results of Cr (VI) Removal by Water lettuce Biomass cone. 60gIL

Volume2012-13. Number 2. July 2012 46

81 No. InHial cone. of Time (Days) Residual cone. of Percent

Cr (mg/L) Cr (mg/L) removal

0 1.0 01 0.75 25.02 0.55 45.03 0.45 55.0

1. 1 4 0.30 70.0".. 5 0.26 74.0

6 0.08 92.07 0.04 96.08 0.02 98.09 0.01 99.0

0 2.0 01 1.65 17.52 1.31 34.53 1.05 47.5

2. 2 4 0.71 64.55 0.62 69.06 0.51 74.57 0.46 77.08 0.43 78.59 0.41 79.5

0 30.0 01 2.50 16.72 2.06 31.33 1.84 38.7

3. . 3 4 1.45 51.75 1.21 59.76 1.08 64.07 0.88 70.78 0.79 73.79 0.76 74.67

0 4.0 01 3.15 21.32 2.59 35.33 2.31 42.3

4. 4 4 1.82 54.55 i.70 57.56 1.45 63.87 1.25 68.88 1.18 70.59 1.13 71.70 5.0 01 3.95 21.0

. 2 3.25 35.03 2.87 42.6

1. 1 4 2.38 52.45 2.05 59.06 1.70 66.07 1.53 69.48 1.44 71.2-9 1.40 72.0

(' .

Table 2. Batch kinetic Results of Pb(lI)Removal by Water lettuce

Table 3. Comparative Results of Cr (VI) andPb (II) Removal (%) by Water Lettuce after 9

Days of Culture

Biomall concentration - 60g/L

90

80

~-~

70

- 60..~ 50E~ 40~0 30

Biomass conc.- 60g/LSoiution \Olume-1 L

Initial conc.2mg/L

20

10

1--.

CreVI)

J

I

~ --"'111!L

0

0 2 4 6

Time (days)

8 10

Figure 1: Percent removal of Cr (VI) andPb (II) by Water lettuce

waste water. For chromium (VI) treatment, 99-72%removal was obtained at 1-5mg/L initial Cr (VI)concentration after a contact period of 9 days. Incase of lead, about 82% removal was obtained foran initial concentration of 2mg/L for same biomassconcentration (60g/L).

The present study is a prospective one,however, it also suggests that in future somemetabolic factors on growth parameters of the plantand associated plant physiological stress should beinvestigated in details to explain the metals hyperaccumulation behavior by the plants and also toassess the stress response to various heavy metalconcentration level in the solution so that this

Rupa Chakraborty, Somnath Mukherjee

technology can be used in real life technology innear future.In connection with this, it must be mentioned thatthere are certain hazards associated with the useof water lettuce as a means for bioremediation.Sometimes this plant produces a nuisance when itfinds entry in natural water bodies and decreasedissolved oxygen level in water. After harvesting,proper disposal will also pose a problem toenvironment. Dissociation of soluble matters inwater bodies from the plant will increase thepollutant levels. This is a serious limitation forusing plants for heavy metal and metalloid removalfrom wastewater.

A list showing the common names of aquaticplants against their scientific names is enclosed.

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Volume2012-13. Number 2. July 2012 47

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