Enhancement of Biological Activated Carbon (BAC) Process to Improve Removal Efficiency of Micropollutants

Abstract

Objectives : In this study, the removal efficiency of micropollutants in the biological activated carbon (BAC) process was investigated, and a method for improving the removal efficiency of micropollutants in the BAC process of water treatment plants was proposed.Methods : Dibromo-methylparaben (Br<sub>2</sub>-MP) was selected as the target micropollutant. Batch and lab-scale column experiments were conducted to evaluate the removal efficiencies of Br<sub>2</sub>-MP in the conventional BAC process and the BAC with enhanced biofilm properties by the addition of phosphorus (P) and hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>). Biodegradation kinetics were evaluated using results from batch and lab scale column experiments.Results and Discussion : As a result of comparing the removal efficiency of Br<sub>2</sub>-MP in a batch experiment with the same biomass concentrations (2.0±0.2×10<sup>7</sup> cells), the biodegradation rate constant (<i>k</i><sub>bio</sub>) of the enhanced BAC process was found to be 1.2 times higher than that of the conventional BAC process due to its higher biological activity (enhanced BAC: 3.4±0.3 mg·C/g·hr, conventional BAC: 2.9±0.4 mg·C/g·hr). Comparison of removal efficiencies of Br<sub>2</sub>-MP in batch experiments with the same wet weight of BAC (1 g) showed that the biodegradation rate constant (<i>k</i><sub>bio</sub>) of the enhanced BAC process was 1.9 times higher than that of conventional BAC process due to higher biomass (enhanced BAC: 3.5±0.4 µg·ATP/g·GAC, conventional BAC: 2.3±0.2 µg·ATP/g·GAC). Through the batch experiments, the enhanced BAC process was efficient in removing Br<sub>2</sub>-MP via increasing both biomass concentrations and activity of attached microorganisms. Lab-scale column experiments conducted under different water temperatures (5 and 25℃) and empty bed contact time (EBCT: 5-40 min) conditions showed higher removal efficiency of Br<sub>2</sub>-MP in the enhanced BAC process than the conventional BAC process throughout the entire period of operation. In particular, the removal efficiency of Br<sub>2</sub>-MP between the enhanced and conventional BAC processes showed significant differences at low temperature (5℃) and short EBCT (5 min). At 5℃ and 25℃, the kbio of the conventional BAC process was 0.0229 min<sup>-1</sup> and 0.0612 min<sup>-1</sup>, respectively, and the <i>k</i><sub>bio</sub> of the enhanced BAC process was 0.0470 min<sup>-1</sup> and 0.1421 min<sup>-1</sup>, respectively, These results showed that the enhanced BAC process had two times higher biodegradability of Br<sub>2</sub>-MP than the conventional BAC process. These results showed a similar trend to the results from the batch experiment. In an experiments simulating the impact of frequent EBCT changes during summer, the enhanced BAC process maintained a relatively stable removal efficiency of Br<sub>2</sub>-MP compared to the conventional BAC process.Conclusion : The enhanced BAC process showed superior biodegradation of micropollutant compared to the conventional BAC process. Considering economic costs (e.g., costs of adding phosphate and hydrogen peroxide) and water quality, it appears to be an efficient alternative to operate the enhanced BAC process intermittently, limited to cases where EBCT is shortened, such as summer, or when water temperature is low, such as in winter.