DEVELOPMENT OF LOW COST ADSORBENTS FOR WASTE WATER TREATMENT

Abstract

Fresh water is an important and essential component of this universe and plays a vital role in the proper functioning of the Earth's ecosystem. In spite of this, safe drinking water is not available in many parts of the world. Rapid industrialization, modern methods of agricultural, domestic activities and other geological, environmental and global changes has put undue pressure on the demand and quality of fresh water, and this has resulted in the generation of large amount of waste water containing diverse types of pollutants. According to United Nations World Water Development Report, some two million tonnes of waste are discharged to the water bodies per day including industrial wastes, dyes and chemicals, human waste and agricultural wastes (fertilizers, pesticides). The main sources of water contaminations are industrial, domestic and agricultural activities. More than one thousand pollutants are present in water and these include organic, inorganic and biological contaminants. Such pollutants in various forms are highly toxic, lethal and carcinogenic in nature due to their long environmental persistence and capability to control/affect the vital activities. Widespread concern over the toxicity and the environmental impact of the toxic pollutants has led to extensive research into developing effective technologies for the removal of these potentially damaging substances from effluents and industrial wastewater. The last decade has seen adsorption technology evolving as an efficient and universal method of water treatment as per the guidelines of WHO and EPA. Its wider applicability and greater momentum is due to its cost effectiveness and environmental-friendliness. The cost effectiveness of this technology is due to the use of effective adsorbents from solid industrial and agricultural wastes. Conversion of such negative—valued solid waste to value-added products finding use in environmental applications has further boosted its (i) demand. Research is ongoing in the search of more efficient adsorbent development from solid waste products. In this context, we have utilized two different waste products viz waste rubber tires and orange peel inorder to develop novel adsorbents for removal of various types of pollutants from waste water. It is worth mentioning that discarded tires comprise the biggest share amongst waste polymers in the world. Waste rubber tire does not decompose easily owing to its crosslinked structure and the presence of stabilizers and other additives and hence, traditionally they are being disposed by incineration or landfilling. However, this poses two problems: wasting of valuable rubber and environmental pollution. Literature study reveals that carbon black obtained by untreated rubber tire pyrolysis may be treated physically and/or chemically to develop its physico-chemical properties and hence to improve its adsorption behavior. As a means of reuse, we have developed various forms of novel activated carbon from waste tires for potential use in waste water treatment for adsorption of various types of toxic pollutants. This not only will provide a way for waste disposal and solid waste management but also their reuse will lower the cost of adsorbent production. My research activity will thereby-demonstrate a double benefit by utilizing waste tire as a feedstock for inexpensive, quality activated carbon production, enabling both material recovery and reuse and water pollution abatement. Novel adsorbents combining nanotechnology and magnetic separation technique have not only demonstrated high adsorption efficiency due to their large surface to volume ratio, but have shown additional benefits like ease of synthesis, easy usage, easy recovery and manipulation via subsequent coating and functionalization, absence of secondary pollutants, cost-effectiveness and environmental-friendliness. In this study, a novel magnetic nano- adsorbent (MNP-OPP) was developed by the surface modification of Fe304 nanoparticles (MNP) with orange peel powder (OPP) with the aim of exploring its feasibility as adsorbent for the removal of cadmium taken as a model toxic metal ion. The main objectives of this research work were: to develop novel adsorbents (i) RTAC, CTRTAC and RTACOX from waste rubber tire granules by various. physical and chemical activation methods for the removal of dyes, pesticides, metal ions and aromatic amines and (ii) magnetic nano-adsorbent (MNP-OPP) for metal ion removal from aqueous solutions. The physical and chemical properties of the adsorbents were evaluated with a view to incorporate a mechanistic approach to the adsorption phenomenon. The originality of this work was mainly based on the systematic investigations of adsorption over a wide range of pH, initial adsorbate concentration, contact time, adsorbent dosage, temperature and ionic strength. The experimental results were modeled by isotherm, kinetic and thermodynamic. equations. Column adsorption and desorption studies were also evaluated. The entire work is presented in seven chapters. Chapter 1 describes the background of the research work, the problem statement and objectives of the present study. A detailed description of the various pollutants present in the contaminated water bodies and the various waste water treatment technologies used is discussed. The chapter gives a short literature review emphasizing on the adsorption technology and various adsorbents widely used for the adsorption of various types of pollutants. Chapter 2 comprises the details of the experimental procedures adopted for the preparation of the adsorbents and the methods adopted for the adsorption and desorption studies. It also describes the various analytical and instrumental techniques used for the. characterization of the adsorbents and adsorbates. Various isotherm, kinetic and thermodynamic models are discussed which enable for the theoretical aspect of the adsorption particularly at solid-liquid interface. In Chapter 3, a mesoporous carbon (RTAC) developed from physical activation (carbonization-activation) of the waste tire rubber, characterized by chemical analysis, FTIR, and SEM studies, was used as an adsorbent for the removal and recovery of a hazardous azo dye, Acid Blue 113. Surface area, porosity, and density were determined. The adsorption of the dye over the prepared adsorbent and a commercial activated carbon was achieved under different pH, adsorbate concentration, sieve size, adsorbent dosage, contact time and temperature conditions. Langmuir and Freundlich adsorption isotherm models were applied and thermodynamic parameters were calculated. Kinetic studies indicated that the adsorption process follow first order kinetics and particle diffusion mechanisms are operative. By percolating the dye solution through fixed-bed columns the bulk removal of the Acid Blue 113 was carried out and necessary parameters were determined to find out the percentage saturation of both the columns. Recovery of the dye was made by eluting 0.1M NaOH through the column. In Chapter 4, an inexpensive, mesoporous, carbonaceous adsorbent (CTRTAC) is prepared from a combined physical-chemical treatment (carbonization-chemical treatment-activation) of waste rubber tire and is used for the removal of toxic pesticides from waste water. SEM, porosity, FTIR studies reveal not only a well developed surface textural properties but also favorable surface chemistry. The developed characteristics were tantamount to admirable adsorption efficiency observed for the studied pesticides: methoxychlor, methyl parathion and atrazine. Batch adsorption studies revealed maximum adsorption of 112.Omgg 1, 104.9mgg 1 and 88.9mgg 1 for methoxychlor, atrazine and methyl parathion respectively occurring at a contact time of 60mins at pH 2 from an initial pesticide (iv) concentration of l2mg/L. These promising results were confirmed by column experiments; thereby establishing the practicality of the developed system. The adsorption process has a physisorption nature, follows Langmuir isotherm, first order kinetics and is pore diffusion controlled. Spontaneous, exothermic and random characteristics of the process are confirmed by thermodynamic studies. The developed sorbent has a far better efficiency for pesticide removal than most other adsorbents reported in literature. Chapter 5 has focused on utilizing the mesoporous adsorbent- RTAC to assess its adsorption efficiency for the removal of toxic lead and nickel ion from synthetic and real waste water. Effect of various operating parameters along with equilibrium, kinetic and thermodynamic studies reveal the efficacy of the RTAC for lead and nickel removal. The adsorption equilibrium data obeyed the Langmuir model and the kinetic data were well described by the pseudo-second-order model. A physical electrostatic adsorbate-adsorbent interaction is revealed from pHpz studies and from D-R model constants. The adsorption process is believed to proceed by an initial surface adsorption followed by intraparticle diffusion. Thermodynamic studies revealed the feasibility and endothermic nature of the system. Such promising results were confirmed by column experiments. Adequate desorption as well as reusability without significant loss of efficiency established the practicality of the developed system and demonstrated an important criterion of advanced adsorbent in RTAC for waste water treatment. In Chapter 6, a novel adsorbent RTACO,, developed by HNO3 treatment of thermally activated tire carbon (RTAC) (carbonization-activation-HNO3 treatment) revealed superior physico-chemical properties. The higher mesoporosity and excess oxygen enriched surface chemistry has played a significant role in enhancing the adsorption capacity and kinetics of RTACOX for liquid phase adsorption. Batch adsorption studies revealed the optimum levels of (v) various environmental parameters for maximizing efficiency. Langmuir and D-R model helped in indicating the underlying mechanism of the adsorption process. Kinetic modelling revealed the applicability of the pseudo-second-order model and intra particle diffusion to be more suitable to describe the adsorbate-adsorbent system for both RTAC and RTACO,,. Thermodynamic studies revealed the feasibility and exothermicity of the developed system. The regeneration and reuse without significant loss in efficiency showed an important criterion of advanced adsorbent in RTACOX for waste water treatment. The work demonstrates a cost-effective utilization of modified waste rubber tires for enhanced pollutant removal. Chapter 7 focused on assessing the adsorption efficiency of a novel N1NP-OPP adsorbent developed from a local agricultural waste-orange peel powder for a toxic cadmium metal ion. Characterization studies revealed the various physico chemical properties on MNP-OPP which are favorable for metal binding. Comparative preliminary batch studies demonstrated not only the optimal process parameters for maximizing metal sorption but also the principle underlying mechanism. Langmuir adsorption plot showed maximum Cd2+ removal by NINP-OPP at 76.92 mg/g at optimal conditions and thermodynamic studies revealed the feasibility of the process. Pseudo-second-order. model was determined as the best fit model. Column studies with a breakthrough capacity of 55.38 mg/g as well as 82% Cd2+ removals from an electroplating effluent simulated wastewater revealed the practical utility of the developed adsorbent. Finally, desorption and reusability studies indicate a fulfilling of important criteria for advanced adsorbents. The developed MNP-OPP has demonstrated not only high adsorption efficiency, faster kinetics but also have shown additional benefits like ease of synthesis, easy recovery, absence of secondary pollutants, and environmental-friendliness.