title: CWIV 2
design: Carbon limited wastewater with carbon to nitrogen (C/N) ratio less than 6, such as marginally contaminated river water, agriculture drainage and secondary effluents from the wastewater treatment plant (Wang et al., 2022), has the potential to induce water environment eutrophication. Typically, the removal of nitrate (NO3-N) poses a significant challenge in purifying these wastewater (Wang et al., 2022). Constructed wetlands (CWs), especially vertical ow CWs (VFCWs), due to their low construction cost and environmental friendliness, are a promising eco-technology for NO3-N removal with the combined process of plant assimilation, substrate adsorption, and microbial degradation (Zhuang et al., 2019). Nevertheless, the primary bottleneck for achieving effective denitrification in CWs remains the availability of electron donors.