Application of Biochar on the runoff purification performance of porous asphalt pavement

Biochar is currently applied in many low-impact development measures, such as biofilters and filter strips. However, its application in permeable pavement is limited. Due to the wide range of raw material sources, biochar may also contain nutrients and heavy metals. Whether its leachate will cause contamination during application remains unknown. Based on the static leachate contamination test, this study first evaluated the leachate contamination risks of three types of biochar and porous asphalt mixture(PA) with three biochar fillers. Through the pavement infiltration test, the purification performance of PA with biochar fillers and filter layers was further analysed. The results show that biochar contains nitrogen and phosphorus, and the leaching contamination of coconut shell is the most obvious; when the biochar is applied as a filler in PA, the leaching contamination decreases, while the pollutant purification performance is not obvious; when 3-5 mm rice straw biochar is used as a filter layer, the removal rate of total suspended solids can be 100%, but it is accompanied by more serious nitrogen and phosphorus leaching, and the greater the thickness, the more serious the degree of leaching. Deionized water cleaning can remove the phosphates contained in biochar, but have little effect on nitrogen.Therefore, before the application of biochar, cleaning measures should be taken to minimize its leaching contamination.