外文原文-高级氧化工艺和生物处理：在组合处理工业废水中的作用.pdf

Advanced oxidation process and biotreatment Their roles in combined industrial wastewater treatment Tamal Mandal a Sudakshina Maitya Dalia Dasguptab Siddhartha Dattac a Department of Chemical Engineering NIT Durgapur India b Department of Biotechnology BCET Durgapur 12 India c Department of Chemical Engineering Jadavpur University Kolkata 32 India a b s t r a c ta r t i c l ei n f o Article history Accepted 21 April 2009 Available online 14 October 2009 Keywords Wastewater Fenton s reagents Fenton s oxidation and coagulation H2O2 FeSo4ratio Biochemical treatment T ferrooxidans Combined treatment process Synergistic effect The use of Fenton s reagents in destruction of waste material present in Tambla Tributory Durgapur India industrialwastewaterhasbeeninvestigated Signifi cantdropinCODremovalhasbeenobserved Optimisation of process parameters like pH temperature H2O2and FeSO4has been done Temperature and pH played a key roleinthistreatmentprocess inadditiontheprocessinitiallyliberatedheatduetoreactionbetweenFeSO4and H2O2 From the experimental results it has been observed that with increasing FeSO4and H2O2concentration the degradation of waste increases At an optimum concentration of FeSO4 6 gm l and H2O244 40 gm l reduced 60 COD whereas 220gm l H2O2was required for 95 COD removal To reduce cost and the H2O2 concentrationformaximumwastedegradation Fenton soxidationprocessfollowedbybiochemicaltreatment wastriedatsameexperimentalcondition Thetreatmentenhancedtheoverallremovaleffi ciencyofCOD BOD salinity and colour signifi cantly The microbial treatment by Thiobacillus ferrooxidans following Fenton s reagents treatment showed that the COD reduction has reached to about 97 compared to 60 with Fenton s reagents and 17 with T ferrooxidans alone in 24 h showing the synergistic effect Thus the combined treatment results indicate the possibility to minimize the Fenton s reagents without compromising the effi ciency of the process but ultimately reducing the overall treatment cost This study seems to be very much important and economical by reducing the required H2O2 amount to about fi ve times using a suitable micro organism This hybrid treatment system showed 97 COD reduction can be achieved within two days 2009 Published by Elsevier B V 1 Introduction Theeffl uentshavingcontaminantssuchassyntheticchemicals dyes organic matters refractory organic waste heavy metals etc are dischargedtothenearestwaterbodieswithorwithoutany preliminary treatments This causes serious damage to the DO level and ecological balance of the ecosystem of the nearby receiving water bodies 1 2 Thusnumerous studies are goingonfor fi ndinga suitable technologyto the wastewater treatment Within that advanced oxidation processes AOPs have ledthewayinthe treatment of aqueouswaste It israpidly becoming the chosen technology for its many applications such as organic pollutant destruction in the form of toxicity reduction Bio degradability improvement BOD COD removal as well as odour and colour removal Literature reveals that a lot of effl uents like carpet dyeing wastewater 3 trihalomethanes 4 cork cooking wastewater 5 synthetic dye Orange II 6 Acid dyebath effl uent 7 textile secondaryeffl uents 8 dyewastewater 9 areeffectivelybeingtreated by Fenton s reagents Fenton s treatment also improves the biodegrad ability of the wastewater 10 The major drawback of Fenton s treatment appears to be the requirement of large concentrations of H2O2and FeSO4in the treatment process It is also supported by several studies thatthe H2O2 Fe2 ratio are the keytoimprove theeffi ciencyof the Fenton s treatment Tang and Tassos Kochany and Lugowski 4 11 have pointed out that optimal H2O2 Fe2 ratio has to be maintained to achieve the maximal degradation effi ciency The optimum reaction conditions like temperature pH H2O2and FeSO4have to be optimized to achieve maximum waste degradation by Fenton s reagents Though most of the literature reported 6 8 that 30 C is the optimum temperature for Fenton s oxidation there are studies suggesting that this may vary with the type of effl uents 6 7 Nowadays bioremedia tion biotreatment has also proved to be a new technology for wastewater treatment and people are fi nding the signifi cant role of micro organismsinreducingtheCODlevelofdifferenttypesofwastein industrial effl uents 12 15 Among the various micro organisms studied for wastewater treatment process chemolithotropic bacteria Desalination 250 2010 87 94 Abbreviations SAIL Steel authority of India DPL Durgapur projects Limited DCL Durgapur Chemicals Limited Corresponding authors Mandal is to be contacted at Department of Chemical Engi neering NIT Durgapur Mahatma Gandhi Avenue Durgapur West Bengal 713209 India Tel 91 9474533097 Mobile fax 91 343 2547375 Datta Department of Chemical Engineering Jadavpur University Raja S C Mallik Road Kolkata 32 India Tel 91 9830108902 Mobile 91 33 2335 9345 fax 91 33 2413 7121 E mail addresses tamal mandal T Mandal provc admin jdvu ac in S Datta 0011 9164 see front matter 2009 Published by Elsevier B V doi 10 1016 j desal 2009 04 012 Contents lists available at ScienceDirect Desalination journal homepage have shown to have potential role in wastewater treatment under aerobic condition 16 20 Thiobaccilus ferrooxidans is a member of chemolithotropic group and it grows in a FeSO4containing inorganic media 9 K at pH 2 5 3 5 Advanced oxidation process reduces the toxicity level of the wastewater and allows the micro organisms to grows Thus enhances the biodegradability 10 The present study is therefore designed to see the effect of combination of Fenton s reagents and suitable micro organisms in wastewater treatment so that an economical time saving tools can be designed for effective wastewater treatment system 2 Materials and methods 2 1 Wastewater Durgapur is called the rurh of Bengal W B India A number of giant manufacturing units like Durgapur steel plant DSP Alloy steel plant ASP Durgapur Chemicals DCL Durgapur projects LTD DPL and East India pharmaceuticals are located surrounding the city In addition a number of power plants are there to cater the power demand of various industries and localities The wastewater gener ated are normally disposed off to the nearby channel Tamla tributary from these industries either with minor treatment or without treatment Table 1 This channel fi nally fi nds its way into the river Damodar the only potable source of water Day by day the quality of water is being degraded which is ultimately affecting the health of human beings and the entire ecosystem of the aquatic life Wastewater samples were collected from the different points of Tamla tributary see Pic 1 which is not the waste of any specifi c Table 1 The effl uent wastewater characteristics in Tamla nalah in general Temp C 30 40 pH6 5 11 5 ColourSlight Brownish dark Brownish TDS mg L at 105 C200 440 TSS mg L at 105 C320 450 BOD mg L 900 1100 COD mg L 2700 4000 Phenol mg L 4 12 Cyanide mg L 0 4 2 5 Free Ammonia mg L 45 65 Fixed Ammonia mg L 1100 1800 Oil k 70M 1s 1 1 OH RH H2O R k 109 1010M 1s 1 2 R Fe3 R Fe2 3 R H2O ROH H 4 The other side reactions are also important for the fate of con centration of total H2O2and FeSO4in Fenton s treatment 24 OH OH H2O2 5 OH H2O2 H2O HO 2 k 3 3 107M 1s 1 6 The peroxide radicals HO2 produced from reaction 6 are capable to further oxidize other species including Fe2 present in the reaction medium 25 HO 2 Fe2 O2 Fe3 H k 1 26 106M 1s 1 7 There is a possibility to be auto regenerated of Fe 2in this system and act as catalyst Fe 3 H2O2 HO 2 Fe2 H 8 In addition it was observed that with time temperature was increased in both experimental and control set if the experiments are conducted in ambient temperature around 30 C The reaction between FeSO4and H2O2for the generation of the OH radical the effective component for the waste degradation appears to be exothermic It was observed from experimental results presented in the Fig 1 that the temperature was increased to about 40 C from 30 C 10 C rise after 10 15 min of reaction time when 44 40 gm L H2O2and 1 5gm L FeSO4were used and it increased with increasing the amount of H2O2and FeSO4 Fig 1 The magnitude of temperature rise was same in both the experimental and control set This signifi es that heat is generated due to the reaction between H2O2and FeSO4 only Eq 1 and this heat may help to gear up the reaction between OH and the waste material present in the water The temperature rise was also found to be dependent on the pH of the reaction At the optimum pH of 3 5 the rise of temperature maximum up to 57 C within 15 min Whereas temperature rise was 42 C and 40 C for the reaction pH of 2 0 and 8 0 in 45 min and 55 min respectively This also indicates that the reaction rate is very much pH dependent Rise of temperature is directly proportional to the reaction rate i e OH generation from H2O2to FeSO4 Eq 1 It may also conclude that reaction between H2O2and FeSO4 Eq 1 is slower below and above the pH 3 5 which may also effect on overall COD reduction 3 1 1 Effect of pH on waste degradation by Fenton s reagents From the initial study it is understood that role of pH on the reaction system is very important since pH plays an important role in OH production 10 11 26 So the wastewater was treated with Fenton s reagents at different pH ranging from 2 6 keeping all other experimentalconditionsconstant Thedegradationpatternatdifferent pH from 2 0 to 6 0 is shown in Fig 2 It has been observed that the optimum pH is 3 5 at which maximum COD reduction has been achieved It has been also observed that for pH greater than 4 0 the degradation is reduced The reasons could be the reduced rate of generation of hydroxyl radical OH because of the formation of the ferric hydroxo complexes which subsequently form Fe OH 4 at higher pH 11 The results also indicate that at pH below 3 0 the degradation of the waste is also less This may be due to the formation of complex species Fe H2O 6 2 which reacts more slowly with peroxide compared to that of Fe OH H2O 5 2 In addition the peroxide gets solvated in presence of high concentration of H ion to form stable oxonium ion H3O2 An oxonium ion makes peroxide electrophilic to enhance its stability and presumably reduces substan tially the reactivity with Fe2 ion 27 This trend also satisfi es the trendofheatgenerationandoverallCODreductionpresentedinFig 1 Thus pH 3 5 was considered as optimum pH for further studies 3 2 The effect of temperature on COD removal by Fenton s treatments The effect of temperature on COD removal of wastewater treatment has been investigated for the temperature range of about 30 C to 60 C with two different dose of Fenton s reagents The results presented in Fig 3 show that the degradation of waste increases gradually with the temperature and at around 50 C the degradation is nearly maximum Above 50 C rate of degradation is not increased insignifi cantly In this study it was also observed that there is about 2 5 times increase in Fig 2 Removal of COD with changing initial pH by Fenton s treatment of Tamla wastewater Conditions Temp 50 C H2O2concentration 44 40 and 111 gm l FeSO4 6 0 gm l initial COD 2740 mg l and time of reaction 24 h Fig 3 Removal of COD with changing reaction temperature by Fenton s treatment of Tamla wastewater Conditions pH 3 5 H2O2concentration 111 gm l FeSO4 6 0 gm l initial COD 2740 mg l and time of reaction 24 h 90T Mandal et al Desalination 250 2010 87 94 percentagereductionofCODwhentemperatureisincreased from30 C to 50 C and then it remains same Previous studies have indicated the role of temperature on waste degradation 6 7 10 The results obtained in this study have been found to follow the same trend as that of previous researchers though some literatures 5 6 28 reported that 30 C is the optimum temperature for Fenton s treatment But the present study shows that 50 C is optimum and which correlates with the work of Alaton and Teksoy 7 where the 50 C is the optimum for the treatment of acid dye bath effl uent Ramirez et al 6 reported that thetemperatureof29and50 CasoptimumforcolourandTOCremoval for the degradation of the synthetic dye orange II Few studies 6 28 indicatedthathydrogenperoxidedecomposesintooxygenandwaterat above50 CandcaneffectgreatlyinoverallCODreduction whichisnot observed in the present study as there is no decrease in COD reduction above 50 C 3 3 Effect of FeSO4Concentration The effect of FeSO4concentration in Fenton s reagents on COD removal was investigated by changing the FeSO4concentration between 1 5 to 9 0 g l while keeping the concentration of H2O2 pH and temperature constant at 44 44 mg l 3 5 and 50 C respectively The results Fig 4 depict that COD reduction effi ciency has been increased from 25 to65 withincreasingFeSO4from1 5gm lto6gm l So thereis about2 8timesenhancedCODreductionwith4times increaseinFeSO4 concentration Hence it may bestatedthat higherferrousconcentration causes generation of more OH radicals and accelerate the redox reaction Another important thing is that Fe2 converts into Fe3 as shown in Eqs 1 and 7 whichact ascoagulant resultingin improved COD reduction But more than 6 0gm L FeSO4did not enhanced COD reduction signifi cantly rather slightly reduced COD reduction with higher concentration of FeSO4 which indicate that OH generation is hindered in the presence of extra FeSO4concentration In addition the Fe3 formed can react with H2O2 Eq 8 to generate Fe2 and hydroperoxyl radicals HO2 in the reaction medium The oxidation capacity of HO2 is less compare to OH which effect the overall COD reduction Thus the optimum Fe2 concentration with maximum COD reduction in this experiment is 6 0 3 4 Role of H2O2and reaction time in waste treatment The effects of H2O2doses were checked in COD reduction For this differentamountofH2O2intherangeof44 40 277 50gm lwereused at 6 0gm l of FeSO4concentration To treat the wastewater it was kept at pH 3 5 and temperature 50 C for 30 min and 24h The results are shown in Fig 5 It reveals from the results shown in Fig 3 that COD reduction increases with increasing H2O2concentration for each time point 4 11 At 44 40gm l H2O2 COD removal was 60 32 and it increased to 95 37 when H2O2was used 277 50gm l for 24 h This increase in COD removal is similar to the fi ndings presented by Gulkaya et al and Kang and Hwang 3 29 This may be due to the fact that increased amount of H2O2reacts with more FeSO4and produces more amount of hydroxyl radical leading to more waste degradation Another point could be the production of Ferric sulphate which act as coagulant and help in enhanced COD reduction Bae et al 25 have reported that maximum COD was reduced by ferric coagulation rather than Fenton oxidation in their textile wastewater The results are correlated with the observation of Rameej et al and Tang and Tassos and Kochany and Lugowski 4 6 11 In the present study when the treatmenttimewasextendedto24 hfrom30 minthe CODreduction reached to 95 37 which is not very much signifi cant when compared with the 30 min treatment time 90 at the highest H2O2 concentration of 277 50gm l which follow the equilibrium time is reported in the range of 10 30 min for Fenton s oxidation reaction 9 26 30 31 In this study it was observed that for 48 COD reduction the amount of H2O2used is 44 40gm L whereas for 95 COD reduction the amount of H2O2required is 277 50gm L indicating that about six times more H2O2is required to achieve just double COD reduction which makes this process very costly 3 5 Analysis of removal of organic compounds by Fenton s reagent using UV spectophotometer The degradation of organic compound was monitored by the study of the absorbance of the untreated and treated after oxidation and coagulation sample of wastewater in UV absorbance range from 190 600 nm The original wastewater shows fi ve peaks at 266 270 350 400 and470 nm Amongthese theabsorbance is maximumat 350 nm After Fenton s oxidation the peaks have been found to disappear and a continuous decrease in absorbance has been observed it signifi es that the Fenton s oxidation can remove the organics present in the wastewater samples When Fenton s treated wastewater were further passed through coagulation stage it is observed that the absorbance at those wavelength is less compared to the absorbance after oxidation stage which signify that the remaining organics are also being removed by coagulation Fig 5 Removal of COD with changing treatment time and H2O2concentration by Fenton s treatment of Tamla wastewater Conditions pH 3 5 Temp 50 C initial COD 2740 mg l and FeSO4 6 0 gm l Fig 4 Removal of COD with changing FeSO4by Fenton s treatment of Tamla wastewater Conditions H2O2concentration 44 40 g l pH 3 5 Temp 30 C initial COD 2740 mg l and time of reaction 24 h 91T Mandal et al Desalination 250 2010 87 94 3 6 Effect of H2O2 Fe2 ratio The molar ratio of H2O2 Fe2 plays an important role in COD removal fromwastewatersample Gulkayaetal showedthattheratioeffectivefor 95 COD removal from carpet dyeing wastewater is 95 to 296 Below and above this ratio the treatment is ineffi cient Some other researcher alsoshowedthedifferentratioforthetreatmentofspecifi c wastewater Like Casero et al 42 reported that the required molar ratio for the oxidation of amine around 5 40 For the removal of azo dye active yellow lightfast 2KT required a wide range of molar ratio 5 8 340 9 26 Tang and Huang shows that the effective ratio 5 11 w w for treatmentofchlorinatedaliphaticorganicswhereasTangandTossos 4 suggested molar ratio 2 1 5 1 for bromoform oxidation So H2O2 Fe2 molar ratio in wide variation plays a key role in waste degradation depending on the types of waste as well as their loads Keeping thecostof H2O2inmind theoptimum H2O2 Fe2 ratiowas tried to evaluate in the present study which can minimize the required amount of Fenton s reagents H2O2and Fe2 Inthe presentstudy ratio wt wt of H2O2 Fe2was used keeping H2O2concentrations at a constant value of 111gm L for the treatment