Coagulation Lab Report

3. Results and discussion

3.1. Coagulation performance of CB[8] for HA removal

The effect of the CB[8] dosage on HA coagulation in the absence of added salts in the synthetic water (fresh water) was investigated at pH 7.5. When the CB[8] dosage was less than 0.2 mmol/L, flocculation was not observed during coagulation. The HA removal efficiency was less than 50% (Fig. 1a). When the CB[8] dosage was higher than 0.2 mmol/L, considerable amounts of flocs formed. At a CB[8] dosage of 0.3 mmol/L, the residual turbidity was approximately 1.5 NTU after sedimentation, corresponding to 89% of HA removal. The residual HA concentration of the settled water could be controlled within 1.50 mg/L. Meanwhile, the zeta potential of the coagulated HA generally increased with increasing CB[8] dosage, indicating that the negative charges on the HA molecules was neutralized by the positive charges on the CB[8] surface. This results are consistent with existing literature data for inorganic coagulants [4,25].

The number of charges on both HA and CB[8] surfaces varied with pH [26], which might affect HA removal by coagulation. It was determined that as the solution pH decreased

The positive charges on the CB[8] structure might be due to the protonation of nitrogen and oxygen to form =N-H+ and =O-H+ under neutral and acidic conditions (Fig. 4). Moreover, when the zeta potential of the HA solution was -33 mv, considerable amounts of flocs could be observed during coagulation (Fig. 1b). This result indicated that along with charge neutralization and electrical double-layer compression, other factors, such as adsorption-bridge building effect, might also contributed to the destabilization of the