Abstract:

Biological activated carbon (BAC) filters that have been in service for an extended period (over 7 years) may encounter a decline or even a complete loss in the removal efficiency of organic compounds. To investigate the removal efficiency of organic compounds in long-serving BAC filters and propose targeted operational optimization strategies, we selected a 12-year-old BAC filter at the LC water treatment plant (WTP) in City Z as our research subject. We analyzed its operational performance by evaluating the total organic carbon (TOC) removal efficiency and explored optimization strategies from the aspects of ozone (O₃) dosage and backwashing methods. The results revealed that the LC WTP experienced significant fluctuations in the organic compound removal efficiency, with a high risk of ineffectiveness. Biodegradation is the primary mechanism for organic compound removal in long-serving BAC filters, accounting for approximately 67%, while adsorption only contributes 33%. When the specific O₃ dosage ranged from 0.36 to 0.52 mg O₃/mg TOC, the BAC filter at the LC WTP performed relatively well. Either too low or too high O₃ dosage was unfavorable for enhancing the performance of long-serving BAC filters. At the LC WTP, the TOC levels in the effluent from both the surface and upper layers of the BAC filter increased before backwashing. Backwashing with water containing 0.5 mg/L of effective chlorine can improve the performance of long-serving BAC filters.

Key words: BAC filter, long-term in-service, organic compounds, removal efficiency, total organic carbon, O₃ dosage, backwashing methods, operational performance, optimization scheme