1. Materials and Methods1.1 Chemicals: All reagents used wereAR grade.
PAHs stock solutions of 250 mg/1 containing 8 compounds (Naphthalene,Flourene, Anthracene, Pyrene, indeo (1,2,3,c,d)pyrene, Benzo(a)pyrene, dibenzo(a,h)anthracene, and Benzo (a)anthracene) were preparedby dilution with n-Hexane (HPLC grade) of corresponding PAHs solution purchasedas certified standard from Accustandard. All spikes used in this paper wereprepared using Milli-Q water spiked with PAHs stock solutions. Other necessarymaterials, anhydrous sodium sulfate extra pure and glass wool were purchasedfrom Fisher chemicals. 1.2 Adsorbent:Agricultural waste (corncob) was collected fromEgyptian agriculture places. These wastematerial was washed with deionizedwater, and dried then crushed and grinded into small pieces then treated with phosphoric acid, ignited at 400°Cfinally it was washed until reached pH 7 and used as adsorbent.
Physical properties of activated carbon weremeasured Table 1. (Gamal et al., 2014).1.3 Extraction method of PAHs:The amount of PAHs in the solution beforeand after the adsorption test was determined by liquid–liquid extractionsreferred to the US-EPA 3510 C method.
PAHs aqueous solutions were extractedwith n-Hexane three times in a separating funnel before and after the treatmentwith activated carbon. The organic phase containing the PAHs was separated anddried with Na2SO4 anhydrous. The final extract was prepared throughconcentration using the rotary evaporator apparatusto a volume of 5 ml and then to 1 ml under flow of clean nitrogen.
1.4 Sample Analysis using GC-FIDAnalysisPAHs was carried out using Agilent gas chromatography model 7980 equipped withFlame Ionization Detector (FID). The column used was a HP5 (30 m x 0.
25 mm i.d x 0.25 µm film thickness); carriergas is Helium at a flow rate of 1.6 mL/min. Injections were made in the splitless mode at an injector temperature of 25 oC. The FID workingcondition was: temperature 300 oC Hydrogen flaw (30 ml min-1),Air flaw (400 ml min-1) and Make up N2 (25 ml min-1).The temperature program employed was: initial oven temperature at 60 oC(holding time 1 min) to 175 °Cat 6 °C min-1 (holding time 4 min) to 235 °C at 3 °C min-1 and finally to 300 °C at 8 °C min-1, keeping the finaltemperature constant for 5 min.
1 µl injections of thefinal extracts were auto-injected into the GC system.(Jahin et al., 2015).2.5 Adsorption studies Batchexperiments were implemented by spiking known concentrations of standardssolutions of PAHs in deionized water.
, the adsorption studies were carried out toillustrate the effect of pH, contact time, activated carbon dose and theinitial concentration of PAHs on the efficiency of adsorption processes .Ablank sample was prepared by adding 0.5 g of activated carbon to 500 ml oforganic free water and carried out through the same analytical procedure alongwith each batch to identify any contamination from reagents, glassware,equipment’s, etc.
2.5.1.pH effect studyThe adsorption of PAHs on corncob activated carbon wasstudied at pH 1.5, 3, 4, 5 and 7 to determine the optimum pH for the adsorptionof these PAHs. In a conical flask 0.5 g of activated carbon was added to 500 mlorganic free water spiked with PAHs standard solution at concentration of 100 µg/1.The PAHs solutions were adjusted to the needed pH with concentrated HNO3or NaOH.
The solutions were shaken at 12 rpm for 6 h in a rotary mixer(Heidolph Reax 20) at room temperature. The samples were then centrifuged (MedtronicBL-S) and the supernatant were separated by decantation. Finally, thesupernatants were extracted and analyzed using the force mentioned method.
2.5.2.Effect of contact time studyBatch experiment was conducted to estimate the timeneeded to reach equilibrium. In a conical flask 0.5 g of activated carbon wasadded to 500 ml organic free water spiked with PAHs standard solution atconcentration of 100 µg/1. The solutions were shaken at 12 rpm for various times:10, 30, 60, 120, 180 min at room temperature, The PAHs residues in the solutionwere extracted and analyzed using the previously mentioned procedure.
2.5.3.Effect of activated carbon dose.Theeffect of adsorbent amount was studied on PAHs removal from aqueous solutionsby varying the amount of activated carbon from 0.
1 to 1 g while keeping other conditionsconstant pH?7, temperature ? 25 oC, initial concentrations of PAHs =100ug/l for each PAHs individual and 1 h as contact time) The adsorption capacitieswere calculated based on the differences between the concentrations of solutesbefore and after the experiment according to the following Equation (1): (1) Where qe is the concentration of the adsorbed solute (µg/g); Co and Ce are the initial and final concentrations ofthe solute in solution (µg/l); V(ml) is the volume of the solution and W(g) is the amount of the adsorbent. Adsorption isotherms (relationship between the adsorption capacities and the concentrations of PAHs) were investigated using the linear form of both Langmuir and Freundlich sorption isotherms equations.2.5.
4.Effect of Initial concentration of PAHs Different PAHs/activated carbon mass ratios wereprepared in glass flasks to determine the adsorption capacity of the adsorbentmaterial. These experiments were performed on solutions with PAHs individual concentrationsof 5, 25, 50, 100, 150 and 200 µg/ l and a constant dose of activated carbon (0.5g) at 1 hour contact time. The PAHs residues in the solutions were then extractedand analyzed using the same procedure as previously described.2. Results and Discussions: