THE REMOVAL OF PHENOLS FROM WASTEWATER.pdf | Adsorption

Please download to get full document.

View again

of 6
All materials on our website are shared by users. If you have any questions about copyright issues, please report us to resolve them. We are always happy to assist you.
Information Report
Category:

Documents

Published:

Views: 4 | Pages: 6

Extension: PDF | Download: 0

Share
Related documents
Description
A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T T h e S i l e s i a n U n i v e r s i t y o f Te c h n o l o g y N o. 2 / 2 0 1 2 THE REMOVAL OF PHENOLS FROM WASTEWATER THROUGH SORPTION ON ACTIVATED CARBON Jolanta BOHDZIEWICZ a, Gabriela KAMIŃSKA b*, Malwina TYTŁA c a Prof. ;
Transcript
  1. INTRODUCTION The growing population, industrial development andurbanization contributes to the deterioration of theenvironment. In recent years, due to the poor condi-tion of surface waters particular attention is paid tothe quality of the aquatic environment. Serious threatto the quality and purity of water constitute micropol-lutants (anthropogenic srcin) which include phenolsand its derivatives. These substances and the productsof incomplete oxidation, already at low concentrationsdischarged along with the purified wastewater into THE REMOVAL OF PHENOLS FROM WASTEWATERTHROUGH SORPTION ON ACTIVATED CARBON Jolanta BOHDZIEWICZ  a , Gabriela KAMIŃSKA   b *, Malwina TYTŁA   ca Prof. ; Faculty of Energy and Environmental Engineering, The Silesian University of Technology, Konarskiego 18,44-100 Gliwice, Poland b MSc; Faculty of Energy and Environmental Engineering, The Silesian University of Technology, Konarskiego 18,44-100 Gliwice, PolandE-mail address:  gabriela.liszczyk@pols.pl b MSc; Faculty of Energy and Environmental Engineering, The Silesian University of Technology, Akademicka 2A,44-100 Gliwice, PolandReceived: 01.03.2012; Revised: 12.03.2012; Accepted: 14.03.2012 Abstract In the presented study sorption potential of activated carbon to removal of phenolic compounds from municipal wastewater was investigated. The structural property of carbon was characterized by nitrogen adsorption – desorption isotherms. Thesorption experiments were carried out in batch system for raw and biologically treated wastewater, namely influent andeffluent respectively. The effectiveness of phenols removal was determined by measurement of phenolic index and was in therange 20.7-60.5%; 49.6-94% for influent and effluent respectively. Lower removal of phenols from influent resulted fromhigher competition with another pollutants for the sorption sites than in effluent. The experimental data fitted slightly bet-ter Freundlich model than Langmuir which indicates favorable adsorption and heterogeneity of the sorbent adsorptionsites. Streszczenie Celem naukowym prezentowanych badań było określenie możliwości sorpcyjnych węgla aktywnego w stosunku do związków fenolowych zawartych w ściekach komunalnych. W pracy scharakteryzowano również właściwości strukturalne badanego węgla za pomocą izoterm sorpcji – desorpcji azotu.Badania sorpcji przeprowadzono w układzie statycznym dla surowych i oczyszczonych ścieków komunalnych. Efektywnośćusuwania fenoli została określona na podstawie pomiaru indeksu fenolowego i była w zakresie 20.7-60.5% i 49.6-94%odpowiednio dla dopływu i odpływu. Niższy stopień usunięcia fenoli ze ścieków surowych wynikał z większej konkurencjio centra adsorpcyjne na powierzchni sorbentu spowodowanej większą liczbą zanieczyszczeń w ściekach surowych niżoczyszczonych. Dane eksperymentalne lepiej opisywał model Freundlicha niż Langmuira, co wskazuje na heterogenicznośćenergetyczną powierzchni sorbentu. Keywords:  Adsorption; Activated Carbon; Wastewater; Phenols. 2/2012 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T  89 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T The Silesian University of Technology No. 2/2012  J . B o h d z i e w i c z , G . K a m i ń s k a , M . T y t ł a90  A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T 2/2012 surface waters impair their quality. This creates aserious threat to aquatic ecosystems. The mainsources of phenols in environment are production of drugs and several pesticides in particular: phenoxy-herbicides and phenolic biocides like pen-tachlorophenol, dinoseb or diaryl-ether pesti-cides [2]. Phenols and their derivatives are releasedinto the environment through municipal/industrialsewage, and landfill leachate [1]. The presence of phenolic compounds have been documented in dif-ferent mediums such as sewage sludge, influent andeffluent of wastewater, river water and soil [3-6].Pocurull et al. showed concentrations of nitrophenols(2-nitrophenol, 4-nitro -phenol and 2.4-dinitrophe-nol) in Ebro river (Spain) ranging from 0.1 to5.0  󰂵 g/l [6]. The other results indicated concentrationof phenol over 40mg/l in river water, which wasreceiver of wastewater from petrol industry [7].Moreover, in the area fertilized by municipal sewagesludge, the concentration of 4-nonylphenol was 2.7mg/kg of soil [8]. Phenols are also included in TheList of Priority Pollutants by the US EnvironmentalProtection Agency (EPA) [2]. They are also highlytoxic which is very important due to ecologicalaspects [9]. Chronic toxicity of phenols in humansresults in: headache, vomiting, difficulty in swallow-ing, liver injury, fainting and etc. [10]. Therefore, dueto the environmental and ecological safety it is advis-able to clean municipal and industrial wastewater of toxic organic micropollutants, to the level excludingtheir negative impact on the natural environment andsurroundings. Among the methods used to phenols removal,adsorption is one of the simplest and widely appliedmethod. Examination of wastewater treatment con-taining phenolic compounds, have shown thatadsorption on activated carbon is considered as amost potential treatment technique [9,10,11]. USEPA also considers adsorption on activated carbon asone of the best available environmental control tech-nologies.The aim of the study was: (1) determination of struc-tural property of studied activated carbon, (2) toassess the effectiveness of phenols removal from rawand biologically treated wastewater using activatedcarbon, (3) fit adsorption models to the experimentaldata. 2. METHODS 2.1. Characterization of wastewater The wastewater used in this work was influent andeffluent from Wastewater Treatment Plant located inurban and industrial zone of Silesia. The characteris-tic of wastewater is presented in Tab. 1. After sam-pling, wastewater was filtered instantly in the labo-ratory with paper filter then with glass fibre filters. All samples were stored at 4°C and utilized for thebatch experiments within 2 days. 2.2. Characteristics of carbon The activated carbon AKPA-22 was purchased fromGRYFSKAND (Poland). The particle size was lessthan 0.12 mm. The carbon was characterized byN 2  /77 K adsorption-desorption isotherms using ASAP 2010 analyzer (Micrometrics, USA). Thestudied carbon did not undergo any extra treatmentin order to repeat its application in commercial watertreatment processes. 2.3. Batch adsorption studies Sorption experiments were carried out by means of shaking out various mass of activated carbon with 100ml of wastewater with initial phenol concentration inambient conditions. The time required to reach Table 1.Characteristics of wastewater Parameter Influent Effluent COD (mgO 2  /l)  886 46 BOD5 (mgO 2  /l)  399 9.3 Chlorides (mgCl -  /l)  347 294 Sulfates (mgSO 4-2  /l)  185 155 N-NH 4  (mgN-NH 4  /l)  57.3 1.86 N-NO 2  (mgN-NO 2  /l)  0.11 0.13 N-NO 3  (mgN-NO 3  /l)  0.64 2.80 N TOT  (mgN/l)  97.70 8.10 P-PO 4  (mgP-PO 4  /l)  35.50 1.21 Phenolic index (mg/l)  0.54 0.27COD - Chemical Oxygen Demand,BOD 5  – Biochemical Oxygen Demand,N TOT  – Total Nitrogen  THE REMOVAL OF PHENOLS FROM WASTEWATER THROUGH SORPTION ON ACTIVATED CARBON       E      N      V      I      R      O      N      M      E      N      T 2/2012 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T  91 adsorption equilibrium was determined in earlierkinetics studies and equalled 4 hours. The pH of influent and effluent samples was adjusted to the value 7.5 by means of NaOH and HCl solutions. After reaching equilibrium, carbon was separatedfrom wastewater and filtrates were analyzed. Theconcentration of phenols in all samples was deter-mined using phenol test (photometric method).Simultaneously blank determination was performedaccording to the same instruction, excluding dosageof carbon. Above operation was carried out to verifyphenols potential accumulation on the glass or fil-ters, which could provide erroneous experimentaldata. The amount of phenols absorbed onto activat-ed carbon was calculated according to the equation 1: where  q  e (mg/g) is the equilibrium amount of phenolsabsorbed onto AKPA-22,  C 0  (mg/l) is the initial con-centration of phenols in wastewater and  C e  (mg/l)equilibrium concentration of phenols,  ν  (l) is the vol-ume of wastewater,  m  (g) is the mass of sorbent. 3. RESULT AND DISCUSSION 3.1. Textural characteristics of carbon Carbon AKPA-22 showed type I isotherm accordingto the IUPAC (International Union of Pure and Applied Chemistry) categorization what indicatedoccurrence of micropores (Fig. 1). The lack of signif-icant increase of adsorption at higher values of rela-tive pressure resulted from presence of very narrowpores, that it could not contain more adsorbate thansingle monolayer. Type I isotherm is characterizedfor chemisorption although several cases of physis-sorption such as, for very microporus activated car-bon could also belong to type I isotherm. The nitro-gen adsorption mensuration was used to calculateseveral parameters such as: the specific surface area,total area in pores, total pore volume and pore sizedistribution (PSD), listed in Tab 2. The specific sur-face area of carbon was determined by the standardBET method. The PSD of carbon (Fig. 2) was calcu-lated according to method of Density FunctionalTheory (DFT), which is based on a molecular modelfor adsorption of nitrogen in porous solids. Porousstructure of AKPA-22 is bidispersion, in majority con-sists of micropores and average fraction of meso-pores, macropores do not occur. Figure 1.Nitrogen adsorption-desorption isotherms of AKPA-22               (1) Table 2.Structural property of AKPA-22 Structure parameter BET Surface Area [m 2  /g] Total Area in Pores [m 2  /g] Total Pore Volume [cm 2  /g] AKPA-22 900.4 693.7 0.3652 e   Figure 2.Pore size distributions of AKPA-22  J . B o h d z i e w i c z , G . K a m i ń s k a , M . T y t ł a92  A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T 2/2012 3.2. Removal efficiency of phenols Figure 3 illustrates relation between dose of carbonand effectiveness of phenols removal from influentand effluent. This is obvious that dose of carbon hadan important role on treatment effects. The applica-tion of increasing carbon doses to constant phenolinitial amount in wastewater resulted in obtainingadditional adsorption sites for phenols, thereforetheir reduction was improved. It was also found thatthe efficiency of phenols reduction was higher foreffluent than influent and ranged 20.7-60.6% and49.6-94% respectively for influent and effluent.Observed effect could be explained by presence of more kinds and amount of pollutants in influent thaneffluent. Probably these pollutants competed withphenols on the adsorption sites, therefore smalleramount of phenols uptake. Sufficient carbon concen-tration to remove most of phenols from effluentequaled 10 mg/l. Obtained results indicated that acti- vated carbon AKPA-22 has ideal performance forremoval of phenols from wastewater even in lowdose. 3.3. Adsorption isotherms The equilibrium adsorption isotherms were shownfor both influent and effluent in Fig. 4. The experi-mental data were fitted to Freundlich and Langmuirmodels, according to equation 2, 3 respectively.Where  q  e  is the equilibrium amount absorbed in mgper gram of sorbent (mg/g),  K   f   is the Freundlichadsorption coefficient ((mg/g)(L/mg) n ),  C  e  is theequilibrium concentration (mg/L),  n  is the number which describes surface heterogeneity and sorptionintensity,  a  is the maximum adsorption capacity(mg/g), and  b  is the Langmuir fitting parameter(L/mg). A trial and error procedure was used for the non-lin-ear method using the solver add-in with spreadsheet,Microsoft Excel. The equation parameters wereobtained by means of minimization of the sum of squared errors (SSE) and listed in Tab. 3. Fittingexperimental data to sorption models provides infor-mation about type of sorption (chemisorption,physissorption). The Langmuir theory is based on theassumption of monolayer adsorption, where mole-cules interact only with the surface of sorbent.Moreover, it is assumed that the surface is complete-ly smooth and homogeneous, and there is no interac-tion between adsorbate molecules on adjacent sites.However, Freundlich theory is empirical anddescribes heterogeneous surface energy system. Onthe basis of R 2  value it was found that Freundlichmodel slightly better describes adsorption of phenolsonto AKPA-22 both for influent and effluent, whichindicates multilayer coverage. This result in connec-tion with earlier outcomes concerning I-type of nitro-gen adsorption-desorption isotherms indicates caseof physissorption on microporous carbon. Moreover,in this case, I-type of isotherm did not fit to Langmuirequation due to false assumption, that the surfacecontaining the absorbing sites is perfectly flat planeand energetic homogenous are rare and difficult toobtain [12]. Based on the n value smaller than 10 it was found that adsorption process is favorable andheterogenity of the sorbent adsorption sites.Batch studies indicated that phenols were betteradsorbed onto AKPA-22 from effluent than influ-ent. This is because of the fact that, in influent phe-nols were in more competition with another pollu-tants for the sorption sites than in effluent. A com-parison of the maximum phenols uptake (a)between influent and effluent also confirmed thesisabout competition. Moreover as shown in Tab. 3. the values of   K   f  , and  b  are lower for influent than efflu-ent which also indicate for more phenols uptake foreffluent than influent. Figure 3.The removal efficiency of phenols depending on dose of carbon         (2)          (3)
Recommended
View more...
We Need Your Support
Thank you for visiting our website and your interest in our free products and services. We are nonprofit website to share and download documents. To the running of this website, we need your help to support us.

Thanks to everyone for your continued support.

No, Thanks