DEVELOPMENT OF NOVEL ADSORBENTS FOR REMOVAL OF NOXIOUS IMPURITIES FROM WASTEWATER

Abstract

Over the past few years, the quality of water is of very important concern for living beings as well prevailing flora and fauna since it has direct connection with the human welfare and ecosystem. Numerous unwanted and noxious impurities are discharged in to the aquatic ecosystem, which directly affects the aquatic food chain. The major sources of water pollution are domestic waste from urban, rural areas and industries wastes which discharged directly into the nearby aquatic streams. The large number of water pollutants includes organic and inorganic pollutants, sediments, radioactive materials and thermal pollutants. Once they come into our body, they perturb our biochemical processes leading to deadly consequences. Several techniques like electrochemical oxidation and sensors, sorption, chemical coagulation, solvent extraction, bioremediation, photo catalytic degradation and adsorption were reported for the removal of noxious impurities from polluted aquatic source, but among all the adsorption was proved to be the most economical and efficient method for the removal of noxious inorganic and organic impurities from aqueous solution, it has been extensively applied because it is a simple and cost effective technique and low cost adsorbents, these adsorbents are particularly attractive to current researchers due to its potential applications in the wastewater treatment, wastewater management and environmental research areas. The research and development (R&D) in the field of wastewater treatment and wastewater management has expanded exponentially in terms of financial investment, numbers of paper published, and the number of active researchers worldwide. Hence for the remediation of aquatic sources we designed efficient and excellent adsorbents, which lead to rapid removal and fast adsorption of these noxious inorganic and organic impurities. The main objective of the present work is to convert waste products, nanoparticles and surface hydrogels in to novel adsorbents for the removal of noxious inorganic contaminants i.e. Ni2+, As(III) and As(V) and organic contaminants i.e. Phenols and its derivatives and noxious dyes like Acid Blue 129 (AB 129), Congo Red (CR) and Malachite green (MG) from the solvent phase. The results of these investigations are incorporated in the present thesis; a chapter wise summary of the thesis content is discussed below: In Chapter 1, a general introduction and a survey of novel, low cost and potential adsorbents reported in the literature, various types of water pollutants i.e. heavy metals, dyes, pesticides, biological agents and dissolved and non-dissolved solids are well investigated and vi reported in this chapter. This chapter also summarised the different sources of the adsorbents i.e. Silica gel, Zeolites and ion exchange resins and activated carbon prepared from various sources i.e. rubber tire, lignin, fly ash, bagasse ash etc are well elucidated and presented. The chapter finally concludes with the scope and objective of the research work undertaken. In Chapter 2, the theory which involve during the adsorption phenomenon of various noxious impurities is described. Details related to the adsorption isotherms and kinetics will be discussed in the different subsections. Several adsorption isotherm models i.e. Langmuir and its types such as Type 1, 2, 3, and 4, Fruendlich, Temkin and Dubinin-Raduskevich etc, additionally various kinetics model such as Pseudo-first-order, Pseudo-second order and Intraparticle-diffusion etc are well investigated and discussed in this chapter. Various analytical characterization techniques and adsorbent preparation methods have also been discussed in this chapter. In Chapter 3, the potential of scrap tire as adsorbent for the rapid removal of Ni2+ from the aqueous source is presented. The developed adsorbent is well characterized using SEM, EDAX and FT-IR. The activated carbon prepared showed porous morphology and favorable surface chemistry for binding to Ni2+. Batch adsorption method is used for the optimization of influential parameters such as adsorbent dose, pH, contact time and temperature, the obtained optimized data reveals that a 0.5 g/L adsorbent dose was found to be optimum at a pH of 7, contact time of 50 min and temperature of 55 °C for achieving ≥95% Ni2+ removal from synthetic solution containing 0.1 ppm Ni2+ concentration. Thermodynamic studies revealed the feasibility and endothermic nature of the system. The results of the present study suggest that scrap tire can be used beneficially for Ni2+ removal from aqueous solution. In Chapter 4, waste tire rubber derived activated carbon-alumina composites (ACALs) and Tire rubber alumina composite (TRAL) were used as efficient adsorbent for the rapid removal of As (III) and As (V). The developed adsorbents i.e. activated carbon-alumina composites were synthesized through two-steps pyrolytic technique at 700ºC in the presence of N2 gas along with steam and characterized using FE-SEM, EDX and FT-IR. Ratio metric preparation of the activated carbon-alumina composites was carried out using activated carbon and aluminium hydroxide in 1:1 ratio by weight i.e. activated carbon-alumina composites (ACAL) 11, and 1:2 ratio by weight i.e. activated carbon-alumina composites (ACAL) 12 and vii 2:1 ratio by weight i.e. activated carbon-alumina composites (ACAL) 21. Though TRAL has greater BET surface area, its adsorptive capacity towards arsenic in aqueous solution is lower than that of ACAL11. Further, TRAL contains sulphur derived from tire rubber but ACAL11 is free of sulphur as it is prepared from AC-HCl which is free from sulphur as well as other acid soluble impurities. Adsorption of As(III) as well as As(V) on ACAL11 and TRAL are best fitted to Langmuir adsorption isotherm with pseudo-second order kinetics. In Chapter 5, the Rubber tire activated carbon modification (RTACMC) and rubber tire activated carbon (RTAC) were prepared from waste rubber tire by microwave assisted chemical treatment and physical heating respectively. A greater improvement in porosity and total pore volume was achieved in RTACMC as compared to that of RTAC. But both have a predominantly mesoporous structure. Under identical operating conditions, an irradiation time of 10 min, chemical impregnation ratio of 1.50 and a microwave power of 600W resulted in maximizing the efficiency of RTACMC for p-cresol (250 mg/g) at a contact time of 90 min while RTAC showed a 71.43 mg/g adsorption capacity at 150 min. Phenol, due to its higher solubility was adsorbed to a lesser extent by both adsorbents. Physical nature of interactions, pore diffusion mechanism and exothermic nature of the adsorption process was operative in both adsorbents. The outcomes support the feasibility of preparing high quality activated carbon from waste rubber tire by microwave assisted chemical activation. In Chapter 6, a novel adsorbent, copper oxide nanoparticle loaded on activated carbon (CuO-NP-AC) was synthesized by a simple, low cost and efficient procedure. Subsequently, this novel sorbent was characterized and identified using different techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), and laser light scattering (LLS). The effects of some variables including pH, adsorbent dosage, initial dye concentration, contact time and temperature were examined and optimized. The adsorption kinetic data were modelled using the pseudo-first-order, pseudo-second order, intraparticle diffusion and Elovich models, respectively. In Chapter 7, applications of compounds like 2-Hydroxyethylmethacrylate (HEMA), 2-Hydroxyethyl methacrylate–ethoxy ethyl methacrylate–methacrylic acid (HEMA–EEMA– MA), and Polyvinyl alcohol (PVA) as an adsorbent for the removal of two hazardous toxic azo dyes i.e. Malachite green (MG) and Congo red (CR) from aqueous solutions were well viii explained and elucidated. The adsorbents under consideration were synthesized and characterized by using SEM, and ATR-FTIR. The dye removal depends on the pH of the solution, the optimum pH for this experimentation was found to be 9. The adsorption affinity of MG onto HEMA–EEMA–MA was increased from 245 to 330 mg/g > CR onto PVA 169–236 mg/g > MG onto HEMA 130–205 mg/g > CR onto HEMA–EEMA–MA 90–155mg/g > MG onto PVA 35–140mg/g > CR onto HEMA 17–57 mg/g, respectively.