Characteristics of particle formation in O3-UBAC filter and effects of operational parameter on particles

Abstract

The ozone oxidation and up-flow biological activated carbon (O3-UBAC) process has been recognized for its ability to extend the operating cycle of biological activated carbon (BAC) filters by expanding the carbon layer and maintaining a dynamic balance of the carbon biofilm. However, the primary focus of O3-UBAC is the removal of organic pollutants, often overlooking the treatment of particles. To address this gap, a pilot-scale study was conducted using sedimentation basin effluent samples from a drinking water treatment plant (DWTP), which were added into BAC columns. The study aimed to investigate the seasonal variation of effluent particles during the UBAC operating cycle, including particle counts, size distribution, and mass composition. Based on particle characteristics and the combined effects of adsorption and biodegradation, the UBAC operation cycle was divided into three periods. Results revealed that hydraulic impacts and biofilm desorption on carbon could increase the proportion of particles >5 μm in effluent. Pre-ozonation demonstrated significant effects on particle counts and Heterotrophic Plate Count (HPC) levels (p < 0.05), with the addition of 1 mg/L O3 resulting in a reduction in particle counts in the effluent. Moreover, particle removal could be achieved by adjusting the upward flow velocity, necessitating comprehensive consideration of pollutants. Furthermore, microbial community analysis under optimal operating conditions unveiled significant changes in the microbial diversity of UBAC-treated water particles. Although the influent and effluent exhibited similarities at different phylum levels, the dominant bacteria differed significantly at various levels.