Intensified nutrients removal in constructed wetlands by integrated Tubifex tubifex and mussels: Performance and mechanisms

The synergy of Tubifex tubifex (T. tubifex) and mussels on SFCWs (named SFCW-MT) performance was well studied in laboratory throughout a year. The SFCW-MT were steady operated with high TN and TP treatment, with the removal efficiencies of 37.85 +/- 5.22% and 39.26 +/- 5.20% even in winter. The mussels had excellent NH4-N removal efficiency, and avoid the shortage of NH4-N removal with T. tubifex in winter. Simultaneously, the SFCW-MT improved the NO3-N treatment by 51% than that in control group. The plant growth was improved in SFCW-MT, which reflected in the improvement of total chlorophyll contents and plant heights. The N and P absorbed by wetland plants and adsorbed by substrate were both increased with mussels. Microbial analysis results revealed that, the mussels could keep the abundance of nitrifiers despite the negative effect of T. tubifex. On that basis, the improved proportions of denitrifiers (Firmicutes) have a significantly recognized role in NO3-N transformation in SFCW-MT. The gut and membrane sections of mussels, as well as T. tubifex, also has proportions of denitrifiers and part of nitrifiers, and thus changed the microbial community in substrate. This evidence indicated that the co-existence of T. tubifex and mussels have potential application for simultaneous removal of NH4-N and NO3-N in CWs.