Performance and mechanisms of biochar for promoting the removal efficiency of organic solids in the vermi-wetland during the recycling of excess sludge

Abstract

Although the vermi-wetland associated with earthworms and plants can recycle the excess sludge, the efficiency of organic solids decomposition needs to be improved. This study aimed at investigating the effects and mechanisms of biochar added to a vermi-wetland by promoting the removal efficiency of organic solids during excess sludge treatment. Two vermi-wetland systems were built, with the wetland plant Acorus calamus and the earthworm Eisenia fetida inoculated. The corncob biochar was blended into the top and bottom layers of one of the vermi-reactors. The results revealed that the removal rates of chemical oxygen demand and total solids separately accounted for 86.2%–94.3% and 64.93%–82.40% of the vermi-wetland with biochar. They were significantly (P < 0.01) higher by 8.1% and 15.7% than those of the vermi-wetland without biochar, respectively. Compared to the counterpart, the interception loading of organic matter significantly decreased (P < 0.05) by 1.6 times in the vermi-wetland with biochar. In addition, an intense and broad carbonyl group substance was adsorbed in the vertical profile of the vermi-wetland with biochar. Biochar enhanced members of Luteimonas, Sphingomonas, and Paracoccus that enable the decomposition of organic solids in the vermi-wetland. This study suggests that the addition of biochar in the vermi-wetland can promote the treatment performance of excess sludge via enhancing the organic interception and bacterial community diversity.