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International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of …

International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.

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  • 1. Sowmya T.P, Prof. G.K. Mahadevraju, A. Ramesh, V. Sreenivas / International Journal ofEngineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.817-820817 | P a g eOptimization Of Hexavalent And Trivalent Chromium Present InWaste Water By Chemical TreatmentSowmya T.P 1, Prof. G.K. Mahadevraju 1, A. Ramesh 2, V. Sreenivas 31Department of Chemical Engineering, Dayanandasagar College of Engineering, Bangalore2Senior Environmental Officer , Karnataka Pollution Control Board, Bangalore3Eco Green Solution Systems (P) LTD, KIADB Industrial Area, Veerapura Post, Doddaballapura , BengaluruABSTRACTChromium is one of the heavy metalcoming from various industries having hightoxicity. The main objective is to adoptappropriate methods and to develop suitabletechniques either to prevent metal pollution or toreduce it to very low levels. Initially, experimentswere conducted on Potassium dichromatesynthetic sample to find the optimum pH ofreduction, optimum dosage of reducing agentsand optimum reduction period for Ferroussulphate and Sodium metabisulphite .Thehexavalent chromium reduced synthetic sampleswere used to find optimum pH of precipitation,optimum dosage of precipitating agents forcalcium hydroxide, sodium hydroxide andcombination of these two chemicals .Experiments were carried out on industrial wastewater for the removal of Hexavalent andTrivalent chromium with optimum operatingconditions which were obtained from theexperiments on synthetic sample.Key Words: Reducing agents, Precipitatingagents, Hexavalent chromium Cr(VI) , Trivalentchromium Cr(III).1.0 INTRODUCTIONContamination of the environment byheavy metals has become a major area of concern.The most common heavy metals contaminants arearsenic, barium, mercury, lead, chromium, nickel,copper, cadmium and zinc are of considerableconcern because they are highly toxic andcarcinogenic [1]. Heavy metals negatively affect thehealth of humans, vegetation and aquatic life.Chromium is one of the heavy metal coming fromvarious industries having high toxicity. Chromiumcan occur at several different oxidation statesranging from –2 to 6. Out of which only Cr (III) andCr (VI) are the stable forms in the naturalenvironments. However Cr (VI) is rarely naturallyoccurring, relatively soluble in aqueous systems andis readily transformed in groundwater .Exposure toCr (VI) poses an acute health risk because it ishighly toxic and chronic exposure can lead tomutagenesis and carcinogenesis. On the contrary Cr(III) is naturally occurring, is much less toxic andeven essential to human glucidic metabolism,contributing to the glucose tolerance factornecessary for insulin-regulated metabolism [2].Chromium is used on a large scale in many differentindustries, including metallurgical, electroplating,production of paints and pigments, paper productiontanning and wood preservation. The chromiumcontents of waste water can be effectively removedto acceptable levels by precipitating the metals toinsoluble form Hexavalent chromium is present inthe effluents produced during the electroplating,leather tanning, cement, mining, dyeing andfertilizer and photography industries and causessevere environmental and public health problems[3]. Hexavalent chromium has been reported to betoxic to animals and humans and it is known to becarcinogenic. The tolerance limit for Cr(VI) fordischarge into inland surface waters is 0.1 mg·l-1and in potable water is 0.05 mg·l-1 . In order tocomply with this limit, it is essential that industriestreat their effluents to reduce the Cr(VI) toacceptable levels [4,5]..A number of treatment methods for theremoval of metal ions from aqueous solutions havebeen reported, mainly reduction, ion exchange,electrodialysis, electrochemical precipitation,evaporation, solvent extraction, reverse osmosis,chemical precipitation and adsorption [6,7] . Most ofthese methods suffer from drawbacks such as highcapital and operational costs or the disposal of theresidual metal sludge. In this study hexavalent andtrivalent chromium is removed by chemicaltreatment. When we need to remove hexavalentchromium out of solution we first need to reduce itfrom hexavalent to trivalent form by reducing agentslike ferrous sulphate and sodium metabisulphite.The reduced trivalent chromium is then precipitatedby addition of precipitating agents like calciumoxide and sodium hydroxide .Moreover Ferroussulphate requires pH =1 for complete reduction ascompared to sodium metabisulphite which requiresa pH of about 2 [8,9]2.0 MATERIALS AND METHODOLOGY2.1 Preparation of Synthetic hexavalentchromium sampleThe potassium dichromate solution (K2Cr2O7) isused as source of hexavalent chromium. A stock
  • 2. Sowmya T.P, Prof. G.K. Mahadevraju, A. Ramesh, V. Sreenivas / International Journal ofEngineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.817-820818 | P a g esolution of potassium dichromate of concentration100 mg/l is prepared by dissolving 0.283 g ofpotassium dichromate in 1000 ml demineralisedwater in a standard volumetric flask. The solution isdiluted to obtain standard solutions containing 10mg/l of Cr (VI). Initial pH of the synthetic sample isdetermined by using pH meter.2.2 Analysis of Hexavalent ChromiumThe concentration of the hexavalentchromium ions in the sample is determinedspectrophotometrically by developing a red- violetcolour with 1,5-Diphenylcarbohydrazide in acidiccondition solution as a complexing agent.Hexavalent chromium is determined by the 1,5-Diphenylcarbohydrazide method. This 1,5-Diphenylcarbohydrazide, reacts to give a purplecolour when hexavalent chromium is present. Thehexavalent chromium then reacts with 1,5-diphenylcarbazide to form 1,5-diphenylcarbazone.Test results are measured at 540nm [10].2.2 Analysis Total ChromiumAtomic absorption spectrophotometer ofversion A-400 was used to measure the totalchromium concentration. In AAS fuel used wasacetylene C2H2 and the oxidant used was Nitrousoxide. Calibration of AAS was done according tothe equipment manual using certified standards andthe analysis of calibrated standards was attained toensure the accuracy of results.3. RESULT AND DISCUSSION3.1 Optimum time, Optimum pH and Optimumdosage for hexavalent chromium reductionCr(VI) from synthetic sampleExperiments were conducted to study the effect ofReduction time on the reduction of Chromiumagainst various doses of reducing agents likeFerrous Sulphate and Sodium metabisulphite.Fig. 1 : Effect of ferrous sulphate dose and pH onReduction of Cr(VI).Fig. 2 : Effect of sodium metabisulphite dose andpH on Reduction of Cr(VI).Jar test method has been used to determinethe effect of each parameter. 500 ml of syntheticsample is taken in four different beakers. Firstferrous sulphate was added to each beaker inincrements to determine optimum dosage , optimumpH and reduction time. After reduction process, thesample was analysed to know hexavalent chromiumconcentration .Similarly, reduction was carried forsodium metabisulphite. Ferrous Sulphate it was seenthat for a dose varying from 200 to 400 mg/l, thechange in % reduction Cr (VI) was rapid in first 30min and then it tapers towards the end. Same wasobserved for Sodium metabisulphite correspondingto the dose of 20 to 100 mg/1. In case of FerrousSulphate the reduction process is slow between 60to 75 min. Therefore 75 min was regarded as theOptimum Reduction period for comparison betweenvarious doses of Ferrous sulphate. Similarly forSodium metabisulphite 50 min should be regardedas the Optimum Reduction period.As from Fig .1, it can be seen that thereduction of 52.33 % can be obtained correspondingto a dose of 600 mg/1. When the dose was increasedto 800 and 1000 mg/l, % reduction of only 54.30and 55.50 % respectively were obtained. This showsthat % reduction depends upon the concentration ofhexavalent chromium Cr (VI) remaining in thesolution.Secondly Sodium metabisulphite dose wasvaried from 20 mg/1. From Fig. 2 we can make outthat as compared to Ferrous Sulphate, % reductionobtained by using sodium metabisulphite was more.It increased from 65.0 % , 70.36 % to 72.0 % asthe dose increased from 40 , 60 to 80 mg/1 resp.Moreover the reduction process of Sodiummetabisulphite completes within 50 mins while thatof Ferrous sulphate takes 75 mins for completion.Merely increasing the dose beyond a certain limit isof no use. Hence it is better to go for pH adjustment.So the pH was adjusted and its effect on %reduction was observed. In the case of Ferroussulphate % reduction increased from 55.5 % to 100% for the dose 1000 mg/l corresponding to pHvalue from 2.4 to 1.0 respectively. From Fig. 2 wecan see that using Sodium metabisulphite 100%reduction can be obtained at a dose of 100 mg/l forpH value 2.0 after only 50 mins of reduction time.
  • 3. Sowmya T.P, Prof. G.K. Mahadevraju, A. Ramesh, V. Sreenivas / International Journal ofEngineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.817-820819 | P a g eThis % reduction was faster than that obtained usingFerrous sulphate. One more point to be noted is thatthe reduction process is over after 50 minscompared to 75 mins for Ferrous sulphate. Thus 50min as the Optimum Reduction time for Sodiummetabisulphite.3.1.1 Precipitation of Cr (III)After the complete reduction of hexavalentchromium the precipitating agents viz., calciumhydroxide Ca(OH)2, Sodium hydroxide (NaOH) andcombination of Calcium hydroxide and Sodiumhydroxide were added to each sample separately ofvarying dosage. In order to mix the solution, samplewere taken to jar apparatus and samples were mixedfor 20 mins with speed of 60 rpm. The precipitateformed was allowed to settle completely.Supernatant was withdrawn from the beaker andanalysed for hexavalent chromium and totalchromium. The mathematical subtraction of totalchromium and hexavalent chromium gives trivalentchromium value. The experimental results fortrivalent chromium removal using combination ofCa(OH)2 and NaOH are shown in Fig 3 and Fig 4Fig. 3: Volume of sludge produced per litreunder various pH conditions for Ca(OH)2 +NaOH ( Synthetic sample reduced by FeSO4 )Fig. 4 : Volume of sludge produced per litreunder various pH conditions for Ca(OH)2+NaOH( Synthetic sample reduced by Na2S2O5 )From the results of synthetic sample, the bestoptimum operating conditions for differentprecipitating agents are shown in Table 1 and Table2Table. 1 : Results of various precipitating agentsin removal of Cr(III) in synthetic sample, (FeSO4is used as a reducing agent , Cr(III) afterreduction = 10 mg/l)Precip-itatingagentsofoptimumdosageOptim-izedpH ofprecip-itationVolumeofsludgegenerated,ml/lAfterprecip-itationprocess,Cr(III)mg/l% removalofCr(III)Ca(OH)2,30 mg/l11.5 16.6 0.515 94.8NaOH,40 mg/l9.6 25.6 0.254 97.5Ca(OH)2+NaOH, 30mg/l10.2 5.8 0.016 99.8Table. 2 : Results of various precipitating agentsin removal of Cr(III) in synthetic sample,(Na2S2O5 is used as a reducing agent , Cr(III)after reduction = 10 mg/l)Precip-itatingagents ofoptimumdosageOptim-izedpH ofprecip-itationVolumeofsludgegenerated,ml/lAfterprecip-itationprocess,Cr(III)mg/l% removal ofCr(III)Ca(OH)2,40 mg/l11.2 10.1 0.64 93.6NaOH,30 mg/l9.2 18.4 0.05 95Ca(OH)2+NaOH, 30mg/l9.8 3.0 0.00 100From Table 1, NaOH produces large volume ofsludge because sludge produced by NaOH isgelatinous in nature whereas sludge produced byCa(OH)2 is dense in nature. Combination ofCa(OH)2+NaOH of dosage 30 mg/l shows 99.8 %removal efficiency. From Table 2 , combination ofCa(OH)2+NaOH produced less volume of sludgewith higher 100 % removal of Cr(III) . Theoptimum pH for ( Ca(OH)2+NaOH) is lesser thanthat obtained from using Ca(OH)2 and NaOH .Hence the combination ( Ca(OH)2+NaOH) isconsidered the best precipitating agent inprecipitation Cr(III).The industrial waste water showedhexavalent chromium concentration of 26 mg/l, itwas diluted to obtain concentration of Cr(VI) in therange of 10 mg/l. The diluted industrial waste wateris treated with optimum dosage Ferrous sulphate andSodium metabisulphite individually to convertCr(VI) to Cr(III) and resulted partially treated wastewater is subjected to precipitation process usingpreviously used chemicals.
  • 4. Sowmya T.P, Prof. G.K. Mahadevraju, A. Ramesh, V. Sreenivas / International Journal ofEngineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.comVol. 3, Issue 3, May-Jun 2013, pp.817-820820 | P a g eTable. 3: Results of various precipitating agentsin removal of Cr(III) in effluent sample, (FeSO4is used as a reducing agent , Cr(III) afterreduction = 10 mg/lPrecip-itatingagentsofoptimumdosageOptim-izedpH ofprecip-itationVolum-e ofsludgegenera-ted,ml/lAfterprecip-itationprocess,Cr(III)mg/l%removalofCr(III)Ca(OH)2,40 mg/l11.8 85.9 0.99 90.1NaOH,30 mg/l9.8 15.4 0.28 97.2Ca(OH)2+NaOH,30 mg/l10.5 36.0 0.03 99.0Table. 4: Results of various precipitating agentsin removal of Cr(III) in effluent sample, (Na2S2O5is used as a reducing agent , Cr(III) afterreduction = 10 mg/l)Precip-itatingagents ofoptimumdosageOptim-ized pHofprecip-itationVolumeofsludgegenerate-d, ml/lAfterprecip-itationprocess,Cr(III) mg/l%removal ofCr(III)Ca(OH)2,40 mg/l11.6 14.7 0.98 90.2NaOH,30 mg/l9.5 22.6 0.59 94.1Ca(OH)2+NaOH,30 mg/l10.2 10.5 0.04 99.6From Table. 3 and Table. 4, almost 100 % removalof Cr (III) is achieved for combination ofCa(OH)2+NaOH with minimum volume of sludge4.0 CONCLUSIONAs compared to Ferrous Sulphate, Sodiummetabisulphite is more efficient in Reducing Cr (VI)to Cr (III). Optimum Dose requirement of FerrousSulphate is more 1000 mg/l ,while that of Sodiummetabisulphite is only 100 mg/l. Ferrous Sulphaterequires pH =1.0 for complete reduction ascompared to Sodium metabisulphite which requiresa pH of about 2.0. Reduction time required forSodium metabisulphite is only 50 mins whereas forFerrous Sulphate at least 75 mins reduction time isrequired. Combination of Ca(OH)2 and NaOH ofoptimum dose 30 mg/l is the most efficient forprecipitation of Cr(III) to Cr(OH)3 at pH 10.5 and10.2 with Cr(III) removal efficiency of and withminimum volume of sludge produced 36.0 ml/l and10.5 ml/l. From results it can be concluded thatcombination of Calcium hydroxide and Sodiumhydroxide is the best precipitating agent forchromium removal.REFERENCES[1]. Hossain M.A, Alam M. and Yonge D.R.,Estimating the dual-enzyme kineticparameters for Cr (VI) reduction byShewanella oneidensis MR-1 from soilcolumn experiments., Water Research, 39,3342–3348, (2005).[2]. Viamajala S., Peyton B.M., Apel W.A.andPetersen J.N., Chromate reduction inShewanella oneidensis MR-1, Is aninducible process associated with anaerobicgrowth., Biotechnology. Prog.,18, 290–295, (2002)[3]. Arumugam V., Recovery of chromiumfrom spent chrome tan liquor by chemicalprecipitation, Indian J.of EnvironmentalHealth, 39(2), 192-198, (1976).[4]. MINAS, Pollution control acts, rules, andnotification there under Central PollutionControl Board, Ministry of Environmentand Forests, Government of India, NewDelhi, 2011.[5]. Water discharge standard of CentralPollution Control Board . ISI, 1991.Methods of sampling and test (Physical andchemical) for water and waste water: 3025:IS 105005. Indian Standard, Drinkingwater-specification (first revision). 1991.IS 10500.[6]. B.H. Hintermeyer, N.A. Lacour,A.Perezpadilla, and E.L.Tavani,,2008,”Separation of the chromium(III)present in a tanning waste water by meansof precipitation, reverse osmosis andadsorption” Latin American AppliedResearch, vol.38, pp.63- 71, 2008[7]. J. Kotai. Z. Stasicka. ChromiumOccurrence in the Environment andMethods of its Speciation. ELSEVIER.Amsterdam.107, 2000 (263- 283)[8]. Tiwari D.P. et.all., Removal of toxic metalsfrom electroplating industries, Indian J.ofEnvironmental Health, 31(2), 122-126,(1989).[9]. R.S. Karale, D.V.Wadkar andP.B.Nangare, Removal and Recovery ofHexavalent Chromium from IndustrialWastewater by precipitation with dueconsideration to cost optimization, Journalof Environmental Research andDevelopment, Volume 2(2), pp 209-216,2007.[10]. Standard Methods for the Examination ofWater and Wastewater, American PublicHealth Association (APHA), the AmericanWater Works Association (AWWA), andthe Water Environment Federation (WEF)Publication, 2006