Biochar has gained global recognition as an effective tool for environmental remediation, and is increasingly being used as an alternative substrate in constructed wetlands (CWs). While, most studies have focused on the positive effects of
biochar for the
pollutant removal in CWs, less is known about aging and longevity of the embedded
biochar. This study investigated the aging and stability of
biochar embedded in CWs post-treating the effluent of a municipal and an industrial wastewater treatment plant. Litter bags containing
biochar were inserted into two aerated horizontal subsurface flow CWs (350 m2 each), and retrieved on several dates (8-775 days after burial) for assessment of
weight loss/gain and changes in
biochar characteristics. Additionally, a 525-day laboratory incubation test was conducted to analyze
biochar mineralization. The results showed that there was no significant
biochar weight loss over time, but a slight increase in weight (2.3-3.0%) was observed at the end, likely due to
mineral sorption.
Biochar pH remained stable except for a sudden drop at the beginning (8.6-8.1), while the electrical conductivity continued to increase (96-256 μS cm-1) throughout the experiment. The sorption capacity of the aged
biochar for
methylene blue significantly increased (1.0-1.7 mg g-1), and a change in the
biochar's elemental composition was also noted, with O-content increasing by 13-61% and C content decreasing by 4-7%. Despite these changes, the
biochar remained stable according to the criteria of the European
Biochar Foundation and International
Biochar Initiative. The incubation test also showed negligible
biochar mass loss (<0.02%), further validating the stability of the
biochar. This study provides important insights into the evolution of
biochar characteristics in CWs.