Abstract
The research is dedicated to studies of activated carbons performance in the wastewater treatment process of dye removal. The experiment was performed to assess the efficiency of the commercial activated carbons (F100, F600, F820, SGL 8×30, CAL, AP4-60, OLC12×30) in adsorption process for Dylon Burlesque Red removal. The effect of pH, type of activated carbon, dye, contact time, and salinity was studied. The experiments were performed by measuring the absorbances of the solutions before and after contact with the activated carbon. The absorbance was evaluated with UV-vis spectrometry. The adsorption of the dye took place on all the studied activated carbon samples, thus the dye concentration reduced comparing to the initial solutions.
The maximum efficiency for dye removal was observed with the minimal amount of carbon, which indicates the maximum use of the active adsorption centers. All the studied adsorbents showed moderate efficiency in the time sufficient for the industrial process. The data were fitted to the theoretical isotherm models, and the Langmuir model showed better fit. Therefore, the adsorption takes place as monolayer, and the adsorbents active sites are equal. The experiments with three activated carbons and three dyes, at various pH and salinity levels were performed by the software optimized experimental design. It was found that pH and salinity do not influence the adsorption efficiency.
I would like to express my gratitude to Sacred Heart University for the perfect time as an international student. These three years were of significance for me, both for scientific development and for personal maturity. I am glad to have such experience.
My deep and sincere thanks are for the scientific advisor Dr. Eid A. Alkhatib who encouraged and supported my growth not only as chemist, but also as a scientist and researcher. I thank my professor, Penny A. Snetsinger, for her guidance, patience, and understanding. Her valuable comments and discussion of scientific results advanced the research task. She encouraged me to persist and gain knowledge to reach the long-term career goals. It was a great joy for me to know such a supportive and positive person. I would like to thank my classmates, and particularly Sahar, for sharing the difficulties and successes of the international student’s life, providing entertainment and leisure time, as well as peer-assistance and support.
I thank my family, and especially my husband, Eng. Mahmood, for participating in my scientific life and supporting my career ambitions. My husband has always shared the challenges of my research work, and encouraged in stressful situations. I deeply value his patience and tolerance for my weaknesses. I cannot imagine the successful completion of the course without him.
Background
The life quality has significantly advanced for the last 50 years, which resulted in extensive consumption and formation of the significant quantities of waste. Nowadays, the research is often concentrated on covering the blunders and consequences of the ‘improved life’ strategy. Wastewater treatment is one of the areas that deals with the remedial actions of industrial progress.
The water polluted with dye originate from food and textile industry. The residual concentrations of dye remain in wastewater and are released to the natural water bodies. Dyes are complicated organic compounds, which are toxic to water biota. As dyes decompose, the numerous organic compounds, including hazardous, are generated (Lewinsky, 2007). Hence, dye removal is an important scientific task.
Adsorption is the most convenient method for dye removal. The main concern in applied adsorption science is the inexpensive, safe, and widely available adsorbent. The research activities are directed to development and studies of the adsorbents properties. The studies are realized by exposure of the adsorbent to the solution, which simulates real wastewater. The solution my include various compounds, including salts, and pH may vary from 3 to 12. Thus, the significant number of the experiments has to be conducted to predict adsorption performance in the real-world conditions.
The research paper is dedicated to theoretical and practical aspects of adsorptive wastewater treatment by various types of the activated carbons. Their efficiency is studied as a function of the initial dye concentration, time, in presence of salts, and at various pH values. The UV absorbance of the colored solutions is used to determine the dye concentrations. The experimental data are fitted to the theoretical models of adsorption, which are used to design industrial wastewater treatment methods.
Discussion
The primary procedure for adsorption assessment was calibration. The calibration indicated that the absorbance is very sensitive to concentration changes, and thus the calibration curves are well-fitted with the lines and perfectly described by the regression equations.
The studies of the carbon weights indicated gradual decrease. It should be noted, that the dye decay is observed in the sample that was not mixed with the sorbent. It indicates that dye degrades naturally. However, in the samples mixed with carbon, the degradation was significantly faster and more profound. Generally, the more carbon adsorbent was added, the lower the concentration was. The highest decrease rate was observed for the minimal dose. The increase of the carbon quantity intensified the dye adsorption, yet it was not proportional to the carbon weight. Therefore, the surface of the adsorbent is more efficiently used when less adsorbent is applied.
The comparison of the different types of carbons indicated that the maximal decrease of dye concentration was observed for F100, F820, and SGL 8*30. Summarizing, all the commercial activated carbons showed moderate efficiency for dye concentration.
The experimental data were fitted to Langmuir and Freundlich isotherms; the goodness-of-fit characteristics were 0.98 and 0.90, respectively. Therefore, the process follows the Langmuir adsorption mechanism, which is monolayer adsorption at the equal adsorption centers.
The multi-factors effect was studied using factor/level procedure. The factor analysis allowed to minimize the quantity of the experiments, and this reduces the cost and complicatedness. The results indicated that pH and salinity do not affect adsorption, and there is no need to perform the detailed experiments. The adsorption depends on the initial concentration of the dye and type of carbon. This also indicates that the adsorption on activated carbons is selective (Tascón, 2012), and its mechanism is not related to ionic interactions in the solution.
Conclusions
The research paper has contribution to the important environmental issue, namely wastewater treatment. The adsorptive removal of dye by activated carbons is presented in the paper. The adsorption process was studied using the UV-spectroscopy analytical technique. The adsorption characteristics of several activated carbons were assessed by the decrease of dye concentration in water samples. The analytical methods used provided high accuracy and replicability.
The dynamics of adsorption indicated that the adsorption rate is high on the first stages. Then, the rate significantly decreases and after 7 days the decrease is still observed, thus the equilibrium has not been reached. Thus, the experiments were performed at the times convenient for the industrial process, namely several hours. The moderate efficiency of the dye removal was observed, irrespective of the adsorbent quantity. This is explained by the limited number of the active centers available for dye adsorption.
Although the activated carbons showed various efficiencies, all of them were moderate. The experimental data fitted the theoretical models of Langmuir and Freundlich, with the perfect goodness-of-fit characteristics.
The wastewater may be polluted with the residual concentrations of several dyes, and the experiments with three types of dyes (procion blue, dylon yellow, procion red) and three activated carbons at different pH and salinity were performed. The experimental design was optimized with application of the software to reduce the number of the experiments. It was determined that pH and salinity do not influence the efficiency of the adsorptive removal. This indicates that the activated carbons are selective for dyes, which is a significant finding. Hence, the dye removal can be realized from the wastewater solutions, and pH adjustment is not necessary, which is a valuable finding for the industrial wastewater treatment.
Works Cited
Lewinsky, A. A. Hazardous materials and wastewater: Treatment, removal and analysis. Nova Science Publishers: New York, 2007.
Tascón, J. M. D. Novel carbon adsorbents. Elsevier: Amsterdam, 2012
