Global Significance of Substrates for Nitrate Removal in Denitrifying Bioreactors Revealed by Meta-analysis

Yuchuan Fan, Jie Zhuang, Michael Essington, Sindhu Jagadamma, John Schwartz, and Jaehoon Lee

Abstract: Denitrifying bioreactors (DNBR) are widely used to reduce excess nitrate from agricultural drainage. Their performance depends on the physical and chemical properties of the substrate. Substrates' types have been partly reviewed in previous studies. However, few studies have been conducted in an attempt to get a generalized pattern on the role of substrate for nitrate removal. In this study, 41 types of substrates were summarized, and the dataset was collected from 63 refereed articles, which include 219 independent DNBR units. The substrate was classified into four groups: a) natural carbon (NC) such as woodchip; b) non-natural carbon (NNC) such as biodegradable polymers (e.g., polycaprolactone) and waste products (e.g., cardboard); c) inorganic material (IM) such as non-carbon materials (e.g., iron oxide); and d) multi-materials (MM) such as a mixture of the above materials. These materials were compared and evaluated using the meta-analysis regarding nitrate removal rate (NRR, g N m-3 d-1) and nitrate removal efficiency (NRE, %). This study reviewed substrate performance (NRR & NRE), potential mechanisms, pollution swapping, and cost analysis. Our analysis indicated that woodchip and corncob were the most cost-effective substrates for NCs. Comparing all substrates, MM is recommended as the optimal substrate, especially woodchip-based and corncob-based substrate, which have great potential for improvement. This analysis can help optimize the design of DNBR to meet the practical requirements of users both environmentally and economically.