## 3 Results
### Effect of Disinfectants  
Disinfectants are a significant element of water and wastewater treatment. To investigate the impact of disinfectant presence during heavy metal adsorption, a chlorine dose of 2 and 4 ppm and a monochloramine dose of 4 ppm were used during the adsorption of lead with DAC. The metal removal rates for these tests are shown in Figure 13. The results indicate that increasing the chlorine concentration generally led to lower lead removal efficiency for DAC across different doses. Specifically, at elevated chlorine concentrations, both adsorbents exhibited substantial deterioration, achieving lower levels of lead removal efficiency. This highlights the negative correlation between disinfectant concentration and the efficiency levels of DAC in removing lead from water. It was also observed that the addition of monochloramine resulted in 99% lead removal by DAC. The paired \(t\)-test analysis revealed a significant variation in Pb removal rates across different disinfectants (\(p\) = 4.80 \(\times\) 10\({}^{-6}\) to 0.002 \(<\) 0.05).  
At 2 ppm Cl\({}_{2}\), DAC shows a consistent and high lead removal efficiency, exceeding 90% across all adsorbent doses. The intense oxidative environment generated by chlorine is responsible for the superior performance, as it facilitates the breakdown of lead-containing complexes and increases the interaction of Pb\({}^{2+}\) ions with the active sites on the DAC surface. Additionally, a previous study corroborated the enhanced removal of lead from water through the use of activated carbon in oxidative environments [76]. At 4 ppm Cl\({}_{2}\), a slight decrease in removal efficiency can be observed in comparison to 2 ppm Cl\({}_{2}\), mainly in the case of lower adsorbent dosages. The explanation for this decline in efficiency may come from the changes brought about in surface chemistry as a result of chlorination. For instance, chlorination can change the functional groups existing on the DAC surface, such as -OH and -COOH groups [77], which is expected to decrease the number of active sites available for lead binding. Previous studies have indicated that chlorination enhances the surface acidity and changes the amount of surface oxide present [77], which means that the adsorption process can be modified. In addition, the attachment of Cl\({}^{-}\) to the carbon surface may result in altered structure of the adsorbent surface, which could affect the  
Figure 13: Lead removal efficiency (%) at 2 and 4 ppm of chlorine and 4 ppm monochloramine dose by DAC (blue bar: DAC+ 2 ppm Cl\({}_{2}\); orange bar: DAC+ 4 ppm Cl\({}_{2}\); grey bar: DAC + NH\({}_{2}\)C).  
surface interaction of the adsorbent with lead ions. These changes are known to reduce adsorption efficiency, particularly at higher levels of chlorine than were reported in previous studies [76].  
At a concentration of 4 ppm NH\({}_{2}\)Cl, the efficiency of lead removal was maintained at a level that was either comparable to or exceeded the outcomes achieved with 2 ppm Cl\({}_{2}\). Monochloramine appeared to operate as a milder oxidant compared to chlorine, preserving the integrity of the functional groups on the surface of DAC while still facilitating the adsorption of lead. The stability of NH\({}_{2}\)Cl in aqueous environments ensures that it does not undergo excessive oxidation, thereby preserving its adsorption efficiency even at elevated concentrations [78].