Preparation and evaluation of wetland plant-based biochar for nitrogen removal enhancement in surface flow constructed wetlands

In the present study, biochar was prepared from scrap wetland macrophyte Arundo donax at different temperatures and then was evaluated for its feasibility as substrate to enhance nitrogen removal performance of surface flow constructed wetlands (SFCWs). Three groups of SFCW systems with different addition of biochar (0, 10, 20%, v/v) were constructed to investigate the effect of dissolved organic matter (DOM) released from biochar on nitrogen transformation. Results showed that the concentration of DOM released from biochar widely ranged from 6.01 to 125.67 mg L-1, and the DOM amount decreased with increasing pyrolysis temperature. Five humic acid-like components of DOM were identified by the parallel factor analysis (PARAFAC) model. The release capacity of DOM from biochar is observed to be closely related to microbial nitrogen removal efficiency. Enhanced removal efficiencies of NO3 (-)-N (81.16%) and total nitrogen (85.62%) were achieved in SFCWs with 20% biochar, which was higher than SFCWs with 10% biochar (62.74 and 73.83%) and the control groups with no biochar (36.16 and 57.90%), respectively. Increased plant height in SFCWs with more biochar addition confirmed the positive effect of biochar on plant growth. Results from the present study suggested that the application of wetland plant-derived biochar was a promising strategy to enhance treatment performance and utilization of waste biomass resource in SFCWs.