Natural pyrite improves nitrate removal in constructed wetlands and makes wetland a sink for phosphorus in cold climates

Pyrite, a natural ore was introduced into constructed wetlands (CWs) to intensify the denitrification and phosphorus deposition in cold climate conditions. Here, CWs with matrices of pyrite/volcanic rock ratios (m/m) of 0:1(CW-V), 1:10 (CW-P1), 1:5 (CW-P2), 1:1 (CW-P3) and 2:1 (CW-P4) were set up. Compared with the control group (CW-V), CW-P1-4 produced a gradual increase of nitrate-nitrogen (NO3--N) and total nitrogen (TN) removal by 6.4-19.9% and 6.2-17.5%, respectively, under a 24 h-hydraulic retention time (HRT). Accordingly, the pyrite based autotrophic denitrification (PAD) contributed to 6.7-24.7% of the TN removal in CW-P1-4. For phosphate-phosphorus (PO43--P) and total phosphorus (TP) removal, CW-P3 and CW-P4 shared the highest efficiency, which was approximately 60% higher than that in CW-V. The main deposition form of phosphorus in CW-P1-4 was iron and aluminium bound phosphorus (Fe/Al-P), which accounted for 43.2-74.2%. By contrast, calcium and magnesium bound phosphorus (Ca/Mg-P) was the major form in CW-V. In addition, sequencing data implied that Simplicispira was the most abundant heterotrophic denitriflers in CWs in cold climate. Thiobacillus, which is involved in PAD, was highly enriched only in the rhizosphere (6.9%) and matrix (7.3%) of CW with pyrite. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

The study demonstrated that introducing pyrite into constructed wetlands can enhance denitrification and phosphorus deposition in cold climate conditions. Pyrite-based autotrophic denitrification was found to contribute to nitrogen and phosphorus removal, especially in CW-P3 and CW-P4. Furthermore, Thiobacillus was highly enriched in the rhizosphere and matrix of CW with pyrite, indicating its involvement in pyrite-based autotrophic denitrification.