The document summarizes a meta-analysis that compared the nitrate removal performance of different substrates used in denitrifying bioreactors. It found that wood media had the highest nitrate removal rate (NRR) and percentage (NRE), followed by mulch media, nutshell-based media, and inorganic media. However, when considering cost-effectiveness, woodchip and corn cob were the most economical natural organic carbon substrates. Overall, the analysis suggests that mulch media is the optimal material for nitrate removal due to its low cost and potential to overcome deficiencies in other media types.