COD reduction of municipal wastewater using mesoporous walnut shell-activated carbon: One step synthesis-modification via chemical activation with FeCl3

Urban effluents are one of the important sources of the pollution of surface and groundwater. Therefore, it is inevitable to treat and reduce their pollution load before discharging it into the environment. In this paper, modified activated carbon (MAC) synthesized from walnut shells has been used as an adsorbent to reduce the COD of municipal wastewater in Yasouj city. MAC was synthesized using iron chloride as an activator and modifier by chemical activation method. The characterization of synthesized MAC was determined using FTIR, BET, XRF, and SEM techniques. The prepared adsorbent has a meso porosity structure and a BET-specific surface area of 1150.37 m 2 g −1 . The effect of 4 adsorption parameters including initial concentration, adsorbent amount, contact time, and temperature were analyzed in a batch adsorption process. According to the results, it was found that the Freundlich isotherm is well compatible with the equilibrium data, and the adsorption efficiency increases with decreasing temperature. Also, the information obtained from the kinetic experiments showed that the kinetic data are highly compatible with the pseudo-first-order and second-order kinetics models. It was also found that the film diffusion step is very effective in reducing COD in adsorption by the synthesized adsorbent. It was found that the prepared adsorbent can reduce about 63.1% of the COD of municipal wastewater using 1 g L −1 adsorbent after 100 min. The results obtained from the continuous process show an increase in the amount of adsorbed pollutant (q tot ) and the breakthrough time (t 0.05 ) with a decrease in the flow rate of the inlet flow and an increase in the height of the adsorption bed. Physical adsorption, electrostatic interaction, ion exchange, π-π interaction, and hydrogen bonding are the possible mechanisms for COD reduction. Batch and continuous adsorption experiments show that the modified AC (MAC) can be an excellent option for reducing the COD of municipal sewage.