Abstract:To solve the problem of backwashing interval shortness of water plants, several film peeling solvents including HCl, Na2SO3 and H2O2 were examined to peel off the overgrown filter film from filter sands surface. An optimized dosage and time were determined by batch tests. Subsequently, the optimized conditions were tested in the pilot-scale columns. The filter sands before and after treatment were characterized by scanning electron microscopy (SEM) and X-ray fluorescence spectroscopy (XRF). The results demonstrated that the optimized dosage and time by HCl peeling were found to be 14.6 mg/g film and 40 min, and they were 11.7 mg/g film and 40 min for both Na2SO3 and H2O2. After treatment by the film peeling solvents, the backwashing interval could be efficiently recovered. Especially for HCl, the bed voidage increased from 27.7% to 39.1%, and the backwashing interval increased from 33.7 h to 61.6 h. At the same time, the catalytic oxidation activity was not affected by the peeling, and the water quality of effluent was still lower than the permitted limit. From the results of SEM and XRF, the morphologies and elements of some films were rarely changed. Considering the recovery of the backwashing interval and economic factors, HCl is a suitable choice for peeling off the filter film.