Effect of biochar particles applied in bedding course of the innovative permeable pavement on enhancing nitrogen removal

Abstract

Coconut shell biochar and bamboo biochar were added to the bedding courses of permeable pavements to improve nitrogen removal efficiency. This was expected to be particularly effective for innovative permeable pavements that increase evaporation of stored rainwater. The effects of the rainfall intensity and ambient temperature on nitrogen removal were assessed. The NO3−-N removal rate for the pavements with biochar added and the blank controls were 48.6%–54.0% and 10.8%, respectively, at a rainfall intensity of 10 mm/h and temperatures of 22–28 °C. The total nitrogen removal rates for the pavements with biochar added and the blank controls were 52.6%–57.7% and 20%, respectively. Adding coconut shell and bamboo biochar improved denitrification without causing organic matter to be leached. Increasing the rainfall intensity and decreasing the temperature caused less nitrogen to be removed. The total nitrogen balance indicated that the innovative pavements and conventional pavements with the same biochar amendments removed 781.58 and 733.30 mg of nitrogen, respectively, suggesting that adding biochar improved the performances of the innovative pavements more than the conventional pavements. Quantitative polymerase chain reaction assays of bedding course samples indicated that adding biochar markedly increased the abundances of denitrifying microorganisms. HIGHLIGHTS Adding biochar (3%–6% w/w) to a permeable pavement (PP) bedding course can increase the amount of nitrogen removed obviously.; The innovative PP units with capillary columns performed better than the conventional PP units with the same amounts of biochar added.; Denitrification in the units with biochar added was markedly weakened during heavy rain and at ambient temperatures <10 °C.;

Keywords

• biochar
• capillary column
• denitrification
• nitrogen removal
• permeable pavement