Abstract
The present study is to explore the possibility of utilizing granular activated charcoal (GAC) for the removal of total phosphorous (T-P) and total nitrogen (T-N) in aqueous solution. Batch adsorption studies were carried out to determine the influences of various factors like initial concentration, contact time and temperature. The adsorption data showed that GAC has a similar adsorption capacity for both T-N and T-P. The adsorption degree of T-N and T-P on GAC was highly concentration dependent. It was found that the adsorption capacity of GAC is quite favorable at a low concentration. At concentrations of 1.0 mg L-1 of T-P and 2.0 mg L-1 of T-N, approximately 97 % of adsorption was achieved by GAC. The equilibrium data were fitted well to the Langmuir isotherm model. The pseudo-second-order kinetic model appeared to be the better-fitting model because it has higher R2 compared with the pseudo-first-order and intra-particle kinetic model. The theoretical adsorption equilibrium qe,cal from pseudo-second-order kinetic model were relatively similar to the experimental adsorption equilibrium qe,exp. To evaluate the effect of thermodynamic parameters at different temperatures, the change in free energy ΔG, the enthalpy ΔH and the entropy ΔS were estimated. Except for adsorption of T-P at 278 K, the ΔG values obtained were all negative at the investigated temperatures. It indicates that the present adsorption system occurs spontaneously. The adsorption process of T-N by GAC was exothermic in nature, whereas T-P showed endothermic behavior. In addition, the positive values of ΔS imply that there was the increase in the randomness of adsorption of T-N and T-P at GAC-solution interface.
Highlights
Nitrogen and phosphorous are essential nutrients necessary for all living cells as components of cell membrane
Based on the initial concentrations, roughly 14-97 and 20-97 % of adsorption for total nitrogen (T-N) and total phosphorous (T-P) at equilibrium was accomplished by granular activated charcoal (GAC), respectively
These results suggest that the adsorption process of T-N and T-P on GAC may be controlled by both film and intra-particle diffusion, rather than only film or intra-particle diffusion
Summary
Nitrogen and phosphorous are essential nutrients necessary for all living cells as components of cell membrane. There have been a lot of studies on the removal of nitrogen and/or phosphorous from wastewater using biological and chemical methods [1,2,3,4,5,6]. Chemical methods have been widely used as a viable alternative to biological methods Their applicability of wastewater treatment has been limited in terms of the high cost of chemical additives and the production of chemical sludge. Even though the high cost of activated carbon makes its use limited, it may be still a favorite choice as an adsorbent for removal of nitrogen and phosphorous from wastewater because of its high surface area and pore volume, along with convenient regeneration of spent carbon. Thermodynamic parameters such as the change in Gibbs free energy ΔG, the enthalpy ΔH and the entropy ΔS were estimated to study the feasibility of the adsorption process
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