Photocatalytic Degradation Of Humic Acids By TiO₂/MF Systems

Photodegradation of humic acids (HAs) in aqueous solution was investigated using combined photocatalysis/microfiltration systems. The effects of initial HAs concentration, and UV irradiation intensity on HAs removal were assessed in the batch operation. The desorption of HAs from TiO₂ surfaces was observed at the initial stage, which could be attributed to the breakage of the coordinative binding between HAs and TiO₂ surfaces resulting from the irradiation of UV photons. However, further oxidative photodegradation of HAs intermediates caused the breakdown of aromatic structures in HAs leading to a continuous decrease in UV254 and TOC. Also, the mechanisms of adsorption and desorption of HA to the TiO₂ surfaces were elucidated by adsorption isotherms of feedwater and permeate, which verified the conversion of original HAs into some intermediates and their desorption from the TiO₂. The photodegradation efficiency increased by the addition of iron oxide particles (IOPs) together with TiO₂. During the longtime, continuous operation, the kinetics of photodegradation was investigated to estimate the Microfiltration (MF) system performance. It was discovered that membrane fouling became significant along with lower natural organic matter (NOM) removal as a result of deposition of HAs combining with TiO₂ particles onto the membrane surfaces. Therefore, strengthening aeration intensity, increasing TiO₂ dosage, and decreasing operation flux could reduce the membrane fouling as well as improve its performance. For illumination of membrane fouling mechanisms, it was proposed that the rate of degree of fouling disproportional to the fouling resistance based on the Random-Walk Theory. The model indicated that the photocatalytic MF system should be operated at a flux below the criteria to prevent serious membrane fouling.