Pugazhenthi of the Department of Chemical Engineering for his constant encouragement and nature's help in several ways during my PhD life. Kaustavmoni Deka (JTS) of the Department of Chemical Engineering for their timely assistance both technical and personal, without any hesitation have been invaluable.
RESULTS AND DISCUSSION 184
218 Table 6.1a Isotherm constants of Cr6+ adsorption on TBAC 243 Table 6.1b Langmuir separation factor (RL) for Cr6+ adsorption at. 244 Table 6.3a Isotherm constants of RB dye adsorption on TBAC 245 Table 6.3b Langmuir separation factor (RL) for RB dye adsorption.
C HAPTER 1
INTRODUCTION
- Sources of Heavy Metals
- Toxicological Aspects of Heavy Metals
- Effects of Heavy Metals on Human Health
- Effects of Heavy Metals on Aquatic Organisms
- Guidelines for Heavy Metals
- Need for the Removal of Heavy Metals
- Treatment Techniques for Heavy Metal Removal
Some heavy metals are found naturally in the body and are essential for human health. Over the past few decades, several methods have been devised for the treatment and removal of heavy metals.
DYE POLLUTION
- Sources of Dye Pollution
- Toxicological Aspects of Dyes
- Guidelines and Need of Dye Removal
- Treatment Techniques of Dye Removal
- Chemical Methods
- Physical Methods
- Biological Methods
Therefore, the removal of dyes from industrial effluents in an economical manner remains a major challenge (Figueiredo et al., 2000). The electrons react with the dye reducing the azo bonds, and eventually causing discoloration (Carliell et al., 1996).
PHENOLIC POLLUTION
- Sources of Phenolic Compounds
- Toxicological Aspects and Guidelines of Phenolic Compounds
- Treatment Techniques of Phenolic Wastewater
- Air Stripping
- Adsorption
- Electrochemical Oxidation
- Advanced Oxidation Processes (AOP)
- Ozonation/UV
- Ultrasonication
- Solar Photocatalytic Oxidation
- Biodegradation
Phenol and phenolic compounds have adverse effects on the aquatic microflora and fauna at a very low concentration of 5 mg/l (Santos et al., 2009). A limit of 0.5 µg/l has also been set by the European Council's directive for the regulation of phenol concentration in drinking water (Tziotzios et al., 2005).
REQUIRMENT OF ALTERNATIVE TREATMENT TECHNIQUE
Phenol and cresol can be degraded either aerobically or anaerobically depending on the specific growth conditions of the microorganisms. Some of the recently reported literature biosorbents for the removal of various heavy metals, dyes and phenols are listed in Tables 1.7-1.10.
IMPORTANCE AND OBJECTIVES OF THE PRESENT STUDY
Most of the literature reports that activated carbon and other biomass-based adsorbents have failed to adsorb/remove such mixed pollutants and highly concentrated pollutants. This information can then be used to rationally design and optimize adsorbents and adsorption conditions.
THESIS OUTLINE
In this chapter, the various kinetic and isotherm model fittings, thermodynamic studies and the adsorption mechanisms of the pollutants with adsorbent are described in detail. In this chapter, the various isotherm model fittings, thermodynamic studies and the adsorption mechanisms of the adsorbates with adsorbent are presented in detail.
SUMMARY
Slokar and Le Marechal, 1997 IrradiationEffective oxidation on a laboratory scale Requires a lot of dissolved O2Hosono et al., 1993 Electrokinetic coagulationEconomically feasibleHigh sludge productionGahret al., 1994 BiodegradationEfficient for specific dyes. Slow process, need to create an optimal favorable environment, maintenance and nutritional needs Banat et al., 1996; Kirby, 1999. Banana and orange peels Methyl orange, methylene blue, Rhodamine-B, Congo red, methyl violet, acid black 10BAnnaduraiet al., 2002.
Ahmaruzzaman and Sharma, 2005 Fresh coal, demineralized and oxidized coal o-crssol5.9, 9.0 & 5.6 Giirseset et al., 1992 M-bentonite Al-bentonite CTAB-bentonite T-bentonite.
C HAPTER 2
COLLECTION OF PRECURSOR
Two plant-based industrial waste materials such as Bael fruit (Botanical name: Aegle marmelos correa) shell (BS) and tannery residual biomass (TB) were used as precursors for the synthesis of different activated adsorbents for the removal of many industrial organics and inorganics. wastewater pollutants from aqueous solution. Bael fruit (Figure 2.1a) is an indigenous ayurvedic medicinal fruit used in India and many other South Asian countries. Bael fruit peel (Figure 2.1b) is a very hard peel (about 30% of the total weight of the fruit) and is considered a waste by-product after use in Ayurvedic medicinal industries across the country.
Accordingly, we have collected sufficient quantity of this waste Bael fruit shells as a precursor from the nearby industrial area in Guwahati near Assam, India.
SYNTHESIS OF ADSORBENTS
- Thermal Activation
- Chemical Activation
- Thermochemical Activation
Thermal activation was a one-step process involving calcination of the precursor (BS and TB) at various desired temperatures and residence times in the absence of an inert gas atmosphere in a closed digital muffle furnace. The activation temperatures and time were chosen only in the range of 200 °C to 600 °C and 0.5 to 2.0 h to avoid major oxidation and weight loss of the precursor material in the absence of an inert gas atmosphere. Initially, chemical activation of the precursor (BS and TB) with different acid concentrations was performed, followed by thermal activation (calcination) at different desired temperatures and activation times in the absence of an inert gas atmosphere in a closed muffle furnace.
Activation temperatures and calcination time after chemical treatment with HCl, H2SO4 and KOH were chosen in the range of 200oC to 400oC and 1 hour, respectively, to avoid large weight loss.
SURFACE AREA OPTIMIZATION OF ADSORBENTS
- Optimization of thermal activated BS and TB
- Optimization of chemical activated BS and TB
- Optimization of thermochemical activated BS and TB
Due to the high surface area, H3PO4 followed by thermally activated BS and TB were optimized using Beckman Coulter surface area analyzer and rest of the thermochemically activated adsorbents such as (H2SO4 + thermal), (HCl + thermal) and (KOH + thermal) activated BS and TB were analyzed using Chemisorb analyzer. After chemical treatment of BS and TB with HCl, H2SO4 and KOH, activation temperature and time were selected in the range of 200oC to 400oC and 1 hour respectively to avoid the large weight loss. The BET surface area of HCl, H2SO4 and KOH treated followed by thermally activated BS and TB adsorbents are presented in Tables 2.7 to 2.12.
The high BET surface area adsorbents of thermochemically activated BS and TB were selected for the removal of wastewater pollutants.
PRELIMINARY PERFORMANCE EVALUATION TEST (PPET)
The PPET results of each synthesized BS and TB adsorbents with target pollutants such as heavy metals (Cr6+, Pb2+, Ni2+ and Sr2+), phenolics (phenol and okresol) and cationic dyes (rhodamine B and methylene blue) are tabulated and 2.17. PPET result reveals that thermally activated BS and TB, H3PO4, KOH, (HCl + Thermal) and (KOH + Thermal) have less adsorption capacity with target metals and phenols. H2SO4 treated bael shell (SBS) and TB (STB) has higher adsorption capacity with Pb2+, Ni2+, Sr2+, rhodamine B and methylene blue dye when compared to its thermochemically treated BS and TB adsorbent (H2SO4 + thermal) .
Other optimized high surface area adsorbents have significant adsorption capacity with only cationic dyes, not with targeted metals and phenols.
C HAPTER 3
INTRODUCTION
- Experimental Protocol
- Adsorbent Characterization
Samples at predetermined time intervals were withdrawn and the supernatant of Cr6+ and Sr2+ solution was separated by filtration using Whatman filter paper no. Similarly, the supernatant of RB dye, MB dye, phenol and o-cresol solutions were separated by centrifugation (5000 rpm) and the dye filtrate was analyzed for residual dye concentrations using UV-Visible spectrophotometer (Perkin-Elmer , model: Lambdas 45) at the maximum wavelength (λmax = 555 nm for RB and 667 nm for MB) of the colors. The percentage of absorption/desorption and absorption capacity/adsorption capacity of the adsorbent was calculated using the calculations given in Appendix 2.
The pore size distribution was obtained through the Barrett, Joyner and Halenda (BJH) model using desorption isotherms and the total pore volume was estimated at a relative pressure of 0.98, assuming complete surface saturation with nitrogen.
RESULTS AND DISCUSSION
- Characterization of Activated Carbon
- SEM Analysis
- Energy Dispersive X-ray Spectroscopy (EDX) Analysis
- BET Surface Area Analysis
- Point of Zero Charge (pH pzc ) Analysis
- Effect of Other Co-ions in Test Solution
- Adsorption Kinetics
- Desorption Effect
- Adsorption Mechanism
- Adsorption Mechanism of Cr 6+ and Sr 2+
- Adsorption Mechanism of Phenol and O-cresol
The zeta potential results in Figure 3.5 reveal that the positive charge of BSAC decreases with increasing solution pH. Adsorption of Cr6+ at pH 2.0 shows that the binding of the negatively charged chromium species (HCrO4-. ) occurred through electrostatic attraction to the positively charged (due to more H+ ions) surface functional groups of the adsorbent (Uysal and Ar, 2007; Barrera et al. al., 2006). At low pH, the adsorption capacity of Sr 2+ decreased due to the protonated surface of BSAC (Dakiky and Khamis, 2002).
However, at pH above 8.0, dye removal occurred due to dissociation of the dye molecules.
SUMMARY
The probable mechanism of RB dye binding to BSAC can be described as follows: at acidic pH, the highly protonated (excess H+ ions) positive sites (–OH2+. ) of BSAC are not favorable to the cationic adsorption of RB dye due to its electrostatic repulsion (Chuah et al., 2005). The existence of the monomeric form of RB molecules at pH 3.5 increases pore diffusion and surface adsorption (Figure 3.19). At pH more than 3.5, the zwitterionic form of RB dye (Figure 3.19) in solution can increase the aggregation of the RB dye molecule to form larger molecules (dimer and trimer) and thus cannot enter the BSAC micropores.
The aggregation of zwitterions is due to the electrostatic attraction between the carboxyl and xanthene groups (Figure 3.19) of RB dye.
C HAPTER 4
C HEMICALLY A CTIVATED B AEL S HELL
INTRODUCTION
- Experimental Protocol
- Adsorption Experiment
- Desorption Experiment
- Adsorbent Characterization
Before mixing the adsorbent, the pH of the solution was adjusted using 0.1 N HCl or 0.1 N NaOH. Samples at different time intervals were taken, and the supernatant of metal and dye solution was separated by filtration using Whatman filter paper No. After desorption, the supernatant of desorbed metal and dye eluent solutions were collected for the desorbed metal and dye analysis.
The detailed procedure for calculating the amount of metal and color desorbed is presented in Appendix-2. i) Scanning electron microscope (SEM) characterization (Leo, 1430 vp, Carl Zeiss, German) was performed to observe the surface structure and porosity for two states of BS such as BS without activation and BS with H2SO4 activation (SBS). ii).
RESULTS AND DISCUSSION
- Effect of Acid Activation
- Surface Characterization of Adsorbent
- SEM Analysis
- ChemiSorb Surface Area Analysis
- Fourier Transform-Infrared (FT-IR) Spectra Analysis
- Point of Zero Charge (pH pzc ) Analysis
- Energy Dispersive X-ray Spectroscopy (EDX) Analysis
- Effect of pH
- Effect of Other Ions in Test Solution
- Isotherm Studies
- Sorption Kinetics
- Sorption Thermodynamics
- Desorption Studies
- Adsorption Mechanism
- Adsorption Mechanism of Metals
- Adsorption Mechanism of Dyes
However, the sorption capacity of Pb2+, Ni2+, and Sr2+ decreased as the concentration of other ions such as K+, Na+, and NH4+ increased. However, there is no significant reduction in the adsorption capacity of dyes with metal combinations. The decrease in adsorption capacity of Pb2+ and Sr2+ with increase in temperature may be due to desorption caused by an increase in thermal energy.
The adsorption of RB and MB dye on the SBS adsorbent can be attributed to (i) electrostatic interaction between the dye molecules and the carboxylations on the biomass surface, (ii) weak physical forces such as hydrogen bonding between the nitrogen atom of RB and MB with hydroxyl groups on the SBS surface, and (3) van der Waals interactions between the hydrophobic parts of the dye molecules (eg, the aromatic rings) and the polysaccharides of SBS.
SUMMARY
Moreover, Figure 4.3b could be seen that the peak of C-O stretching and stretching vibrations of C-O-C around 1610 cm-1 and hydroxyl functional groups (O–H) were also significantly shifted after dye adsorption. These changes showed that carboxyl and hydroxyl groups were involved in the adsorption of RB and MB dye. A schematic diagram of RB and MB dye molecule absorbed on the SBS surface is presented in Figures 4.21a and 4.21b, respectively.
