Enhancing the availability of construction waste as substrate for constructed wetlands-through mixing substrates and...

Construction waste offers environmental and economic benefits as a substrate for constructed wetlands (CWs), but its adverse effects, particularly elevated pH reducing removal efficiencies (REs), remain poorly understood. This study investigated mitigating these effects by combining waste concrete with other substrates and adjusting influent carbon to nitrogen (C/N) ratios at 3:1 and 7:1. Vertical subsurface flow CW simulators with four treatments-volcanic rock (Vo), waste concrete (Co), a 1:1 volcanic rock/concrete mixture (Fm), and a 3:1 mixture (Tm)-were established, assessing pollutant RE, microbial community functions, and associated risks/potentials. Results showed substrate mixing significantly mitigated the pH of waste concrete, reducing effluent pH from 10.25 (Co) to 8.63 (Fm) and 8.61 (Tm). Nitrogen REs increased substantially when the influent C/N ratio was raised to 7:1. Waste concrete markedly inhibited methane and nitrous oxide emissions, with inhibition persisting despite substrate mixing and C/N adjustment. Mixed substrates alleviated concrete's negative impacts on microbial functionality. Combining waste concrete with suitable substrates while optimizing influent C/N ratio effectively counteracts its adverse effects, enhancing pollutant removal and reducing greenhouse gas emissions in CWs.