Effects of plant species on reverse osmosis concentrate treatment in constructed wetlands: Performance, plant growth, and microbial community structure

The efficient treatment of reverse osmosis concentrate (ROC) is crucial for the widespread application of reverse osmosis technology. This study investigated the ROC removal performance of constructed wetlands (CWs) planted with five different plant species. The results showed that plants can improve the efficiency of pollutant removal in CWs. Among the species tested, I. wilsonii showed superior pollutant removal performance, achieving average removal rates of 91.66 % for nitrate, 87.95 % for total nitrogen (TN), 72.40 % for total phosphorus, and 52.30 % for dissolved organic carbon (DOC). After 30 days of CWs operation, the biomass growth, nitrogen uptake, and phosphorus uptake of I. wilsonii were 2.42 g, 27.76 mg, and 14.23 mg per plant, respectively. However, those of the other species ranged from 0.32 to 0.78 g, 3.46-17.23 mg, and 1.05-5.55 mg per plant, respectively. The predominant functional microbial phylum in all CW substrate samples was Proteobacteria, accounting for 42.56 % to 64.44 % of the total microbial community. At the genus level, the dominant genera in unplanted CWs were two heterotrophic denitrifiers: Pseudomonas and Thauera, representing 12.88 % and 8.57 % of the total microbial community, respectively. In I. wilsonii CW, the dominant genera shifted to two autotrophic denitrifiers: Thiobacillus and Sulfurimonas, representing 17.45 % and 7.74 % of the total microbial community, respectively. Redundancy analysis indicated that plant biomass exhibited a positive correlation with pollutant removal, and the abundance of Thiobacillus and Sulfurimonas had a significant positive correlation with DOC and TN removal.