Removal of Anitbiotics from Wastewater by Nanocomposites and Membrane Hybrid Technology

Abstract

Magnetic Carbon Nanocomposites (MCN) was prepared from pineapple and mango biomass precursors and then characterized by mean of SEM, XRD, FT-IR, TG/DTA, EDX, surface area analyzer and pH (PZC). XRD patterns show the presence of Fe3O4 deposited on the surface of carbon materials with cubic crystalline structure at different 2θ values which corresponds to indices planes. SEM images show the mean diameter of both MCN are around 50-70 nm with equal distribution of white areas in the images of both MCN show the crystallization of nano-particles of Fe3O4, while black spots represent the carbon contents. The BET surface area of pineapple and mango MCN are 43 and 51 m2g-1 respectively and BJH pore size distribution are 17.50 and 21.65 m2g-1 respectively, whereas, the total pore volume and pore diameter of both MCN are 0.015 and 0.019 cm3g-1 and 15.05 and 15.03 Ao respectively. The low surface area is due to impregnation of magnetic particles (Fe3O4), which resulted into pore blockage. The FTIR spectra of MCN shows peaks at 3470 and 3200 cm-1 which may be due to the presence of surface groups such as phenol, carboxylic acids, carboxylic acid derivatives along with physically adsorbed water and surface moisture. The two narrow peaks in the region of 3000-2800 cm-1 correspond to C-H alkanes, peaks at 1450-1600 cm-1 corresponds to C=C aromatic, peaks at 1300-1000 cm-1 corresponds to -OH alcoholic and ether, while the peak at 575-580 cm-1 corresponds to Fe-O of magnetite and maghemite. The pHpzc of pineapple and mango MCN were found to be 7.2 and 7.3 respectively. The removal of antibiotics such as ciprofloxacin (CIP), levofloxacin (LEV) and enrofloxacin (ENR) from the water system was carried out by adsorption (adsorption kinetics and isotherm studies) and MCN-membrane hybrid technology. The adsorption data shows that the equilibrium was established within 220 min. The adsorption kinetics data were applied to both 1st, 2nd order pseudo kinetics and intraparticle diffusion models. Pseudo 2nd order kinetics and intraparticle diffusion models were found best fits to the adsorption kinetics data. Thermodynamic parameters like rate constant (K), ∆𝐻°, ∆𝑆° and ∆𝐺° were determined using the Van’t Hoff equation. It was found that the rate constant increases with rise in temperature. The rate constant (K) trend for the adsorption of antibiotics was found as: LEV>ENR>CIP. Entropy of activation (ΔSo) was found to be positive which shows an increase in randomness at the solid-liquid interface during the adsorption. Enthalpy of activation (∆𝐻°) decreases in the following order LEV>ENR>>CIP for PAMCN, and ENR>LEV>CIP for MAMCN. ΔSo decreased in the sequence of, CIP>LEV=ENR for pineapple nanocomposites and ENR>LEV>CIP for mango nanocomposites respectively. The negative values of ΔG˚ at various temperatures specify the spontaneous nature of the adsorption process and have a high affinity of antibiotics molecules for both nanocomposites. The intraparticle diffusion model shows that the adsorption of antibiotics is a diffusion controlled process. For adsorption isotherm studies the mathematical models like Freundlich, Langmuir, Jovanovich and Tempkin isotherms were used for the determination of adsorption parameters. The isotherm data fitted well to Langmuir model for the adsorption data. The effects of pH, temperature, time, concentration, adsorbent dosage, humic acid and ionic strength on adsorption process were evaluated. The adsorbent after use was regenerated using NaOH, methanol and distilled water. The equilibrium time for both adsorbents at pH 7 was reached in 60-80 min. Improved permeate fluxes and percent retentions of antibiotics by membranes were observed for adsorption/membrane hybrid process MCN/UF (magnetic carbon nanocomposite/Ultrafiltration), MCN/NF (magnetic carbon nanocomposite/ Nanofiltration) and MCN/RO (magnetic carbon nanocomposite/Reverse osmosis filtration). The percent retention of antibiotics molecules in NF was 96% which increased to 100% when membrane was used in hybrid manner with MCN. Which is a great achievement in the present study.