The observed adsorption behavior shown in Fig. 3a can be attributed to a Combination of surface charg characteristics of adsorbent and pH-dependent speciation of CIP and NOR. The positively charged adsorbent becomes progressively negatively charged with increasing pH. When pH is above 9 or 5 for CIP or NOR, respectively, the electrostatic repulsion between adsorbent and adsorbate prevailed so that the adsorbed amounts begin to decrease. This has been explained by Sun et al. [9] for CIP removal by activated carbon from cyperus alternifolius precursor. They reported 8.7 as a best pH value, where adsorption initially increased with increasing pH and reached a plateau when solution pH was approaching its pKa2 (8.7) and then decreased at higher pH. Liu et al. [10] showed that maximum adsorption was achieved at pH 5.5 and decreased significantly when pH was higher or lower than this range for NOR removal by adsorption on activated carbon from lotus stalk (LAC). Although both antibiotics have two similar proton-binding sites (carboxyland piperazinyl group) with reported pKa values of 6.22 and 8.51, respectively, there is a difference in pH values which give best adsorbed amounts. This may be confirmed by the fact that the solution pH increased after NOR sorption at pH 4.5–5.5, causing repulsion between adsorbent and adsorbate and the sorption greatly depressed. Accordingly, cation exchange is proposed to be an important mechanism participating in the adsorption of FQs compounds. Fig. 3a also shows that the removal efficiency decreased with increasing initial CIP or NOR concentration. This is probably because at lower initial concentration the ratio of surface active sites to the total adsorbate molecules in the solution is high and hence all adsorbate molecules may interact with the adsorbent and be removed from the solution.