Application of Response Surface Methodology for Optimization of Ammonia Nitrogen Removal from Aqueous Solutions Using Powdered Activated Carbon

摘要

Background and Objective: High nitrogen compounds in natural water results from industrial and agricultural activities made the water ecological problems. Therefore, elimination or decrease of nitrogen compounds in the receiving environment must be considered. The objective of the present study was to compare the performance of commercial powdered activated carbon (CPAC) and modified commercial powdered activated carbon (MCPAC) with H₂SO₄, NaNO₃ and KMnO₄ for the ammonia removal from aqueous solution. Methodology: This experimental study was carried out at pilot scale. The effects of various operational variables such as adsorbent dosage (0.5-1.5 g L^–1), ammonia initial concentration (100-200 mg L^–1), pH (3-9) and contact time (2-120 min) on ammonia removal were examined for both MCPAC and CPAC. In this study, experiments were performed base on central composite design (CCD) and response surface methodology (RSM) to analyze and optimize the variables. The adsorption isotherm was evaluated using Freundlich and Langmuir models. Kinetics study was analyzed using pseudo-first order, pseudo-second order and penetration particle kinetics models. Data were analyzed by one way ANOVA. All the statistical tests were carried out using Design expert software. Results: The results showed that the removal rate increased by the increase of adsorbent dosage, pH and contact time. The maximum removal rate was seen at the pH 9, contact time 120 min, ammonia initial concentration 50 mg L^–1 and adsorbent dosage 1.5 g L^–1 (above 95%). The removal rate decreased as the ammonia initial concentration increased. According to CCD result, CPAC and MCPAC were fitted to linear and quadratic equation, respectively. Ammonia adsorption for CPAC and MCPAC followed the Langmuir (R² = 0.9831) and Freundlich (R² = 0.9745) isotherm model. The maximum adsorption capacity for MCPAC achieved 40.323 mg g^–1.The analysis of adsorption kinetic for both CPAC and MCPAC indicated that the ammonia adsorption was well-fitted by pseudo-second order kinetic model (R² = 0.997). Conclusion: Results confirmed that modified activated carbon can be uesd as an appropriate and cost effective adsorbent for water and wastewater treatment due to high adsorption capacity.