Experimental study on the water purification performance of biochar-modified pervious concrete

•A kind of biochar-modified water purifying pervious concrete was analyzed.•The purification effects of different biochar contents were compared.•The water purification mechanism of pervious concrete was investigated.•The optimized content of biochar was recommended. Pervious concrete, a kind of porous material, is commonly used in permeable pavement and ecological slope protection. Biochar has the characteristics of absorbing pollutants and improving the performance of concrete. Therefore, the purification performance of different contents of biochar-modified pervious concrete on sewage was studied in this work. The experimental results show that the pervious concrete has obvious purification performance on sewage and adding biochar to the pervious concrete can further improve the removal capacity of total nitrogen (TN) and total phosphorus (TP). The removal efficiency of TN and TP increased by 34.1% and 47.3%, respectively, compared with the specimen without biochar. The water purification mechanism of pervious concrete is mainly mechanical retention adsorption and microbial degradation. With increasing biochar content, the adsorption increased, whereas the porosity of the specimen decreased, which was not conducive to microorganism growth. Therefore, the pervious concrete block with moderate biochar content had the best water purification performance. It is recommended to use pervious concrete with a biochar content range of 15 kg/m3-20 kg/m3.