Impact mechanism of cigarette butt leachate in runoff on the nutrient removal capacity of bioretention cells: metagenomic insights.

Discarded cigarette butts become soaked in surface runoff during rainfall, causing various pollutants within them to leach. The extent to which discarded cigarette butts impair bioretention cell nutrient removal efficiency remains understudied. In this study, three bioretention cells were constructed, exposed to simulated runoff containing non-cigarette-tip, low-concentration cigarette-tip, and high-concentration cigarette butt leachate. The effectiveness of nitrogen, phosphorus, and carbon purification was then determined; metagenomic sequencing was also performed to examine the microorganisms within the filler to propose a mechanism of how cigarette butt leachate input influences bioretention cell nutrient purification. The input of cigarette butt leachate limited filler adsorption capacity, but had little effect on the effluent NH4+-N concentration (1.08-1.14 mg/L). Cigarette butt leachate inhibited the nitrification potential in the upper layer of the cells as well as the denitrification potential in the lower layer; effluent NO3--N increased from 0.51 to 1.93 to 0.57-5.47 mg/L. The inflow of cigarette butt leachate had little effect on phosphorus removal, with efficiencies consistently ranging from 50.60% to 73.69%. Cigarette butt leachate enhanced the carbon release potential of slow-release carbon sources within the filler and impeded potential electron donor production. This study demonstrated that cigarette butt disposal significantly impaired the nitrogen removal capacity of bioretention cells.