Ammoniacal nitrogen removal from aqueous solution using activated carbon from papaya peel as adsorbent

Abstract

The presence of ammoniacal nitrogen (NH3-N) can be detected in industrial, domestic and even treated wastewater. High concentration of this pollutant can cause eutrophication which leads to the growth of excessive algae on the water surface and subsequently affecting the aquatic life due to the lack of oxygen. In recent years, researchers have begun to explore the potential of agro-waste as adsorbent to remove the pollutant from wastewater. Papaya peel has been used due to its abundant availability and cheap cost. There are several successful studies in the removal of dye and heavy metals by using papaya peel. However, no study has been conducted in removal of inorganic pollutant such as NH3-N. Understanding the capability of papaya peel to adsorb multiple pollutants can help in future studies in evaluating papaya peel adsorption capability in wastewater. In addition, utilization of peel waste also reduces the overall papaya peel waste. In this work, activated papaya peel capability to adsorb NH3-N was studied. The papaya peel was collected from local market, dried and heated up to 400 °C in the furnace and then activated by potassium hydroxide. The surface properties of adsorbents were characterised using Fourier transform infrared spectroscopy, field emission scanning electron microscope, x-ray diffraction, and Brunauer-Emmett-Teller techniques. The adsorption process was carried out in batch mode considering different control parameters of initial pH (4-9), dosage of adsorbent (0.01-0.3 g), contact time (5-120 min), initial ammonium ion (NH4+) concentration (10 -150 mg/L) and temperature (25-65 °C). The final concentrations of NH3-N were determined using the Nessler method. The best condition with highest removal (42%) was obtained at pH 7, 50 mg dosage of adsorbent, 100 mg/L NH4+ concentration at 30 min and 25 °C. Desorption and regeneration studies were additionally conducted to evaluate the reusability of the adsorbent. The experimental isotherm and kinetics data were evaluated using Langmuir, Freundlich, and Temkin isotherm models and pseudofirst- order and pseudo-second-order kinetic models to relate the mechanism o f adsorption ion and the activated carbon papaya peel powder. The data fitted well with the Freundlich model and the pseudo-second-order kinetic model. In addition, thermodynamic parameters such as enthalpy change (AH°= -9.627 kJ/mol), free energy changes (AG°= -0.851, -1.060, -1.385, -1.593, and -2.355 kJ/mol), and entropy change (AS°= 34.812 J/mol K) were also calculated. The result shows that the reaction occurred spontaneously with exothermic reaction under atmospheric condition. High percentage removal of NH3-N using Carica Papaya Activated Carbon compared to other agricultural waste confirmed that papaya peel potentially can be used as an alternative adsorbent for NH3-N removal.