Optimization of filter media parameters and backwashing scheme for carbon-sand filter in treating micro-polluted water

The carbon-sand filter has attracted extensive interest due to its advantages such as minimal space occupation, low operating costs, and effective removal of organic matter and ammonia nitrogen from water sources. This study investigates the impact of filter media parameters and backwashing scheme on the operational performance of the carbon-sand filter, with the aim for optimizing its operating conditions. The results show that the carbon-sand filter using granular coconut shell activated carbon can effectively remove 2-MIB, GSM, and other micro-pollutants in water. The filter achieves optimal performance when the upper layer consists of 5–10 mesh granular coconut shell activated carbon with a thickness of 130 cm (K₈₀<1.6), and the lower layer is composed of quartz sand with d₁₀= 0.9 mm–2.0 mm and a thickness of 60 cm (K₈₀<2.0). Under these conditions, the removal rates of ammonia nitrogen, permanganate index, and turbidity pollutants can reach 59 %, 57 %, and 87 %, respectively. The optimal backwashing scheme involves initial air scouring (at an intensity of 15.00 L/s·m² for 2 min), followed by water scouring (at an intensity of 3.0 L/s·m² for 10 min) after a 2-min standing period. This study provides experimental evidence and theoretical guidance for the design and practical operation of carbon-sand filters.