Stability and purification efficiency of composite ecological floating bed with suspended inorganic functional filler in a field study

Planting macrophytes can increase the contribution of plant uptake to pollutant removal in ecological floating bed (EFB). However, the low system stability of traditional EFB often causes large-area plant lodging during the rainy season. This phenomenon not only reduces the ornamental value of EFB but also causes the problem of secondary pollution. Furthermore, the reduction of removal rate under low temperature condition is also an inevitable defect in the application of EFB. Therefore, a composite EFB (CEFB) was built by suspending inorganic functional filler below the traditional EFB to remedy these defects. Results of a two-year field test showed that the suspension of inorganic functional filler not only enhanced the system stability, plant lodging resistance and removal efficiency of CEFB but also fundamentally resolved the problem of low purification efficiency of the traditional EFB during the low-temperature season. Compared with EFB, CEFB could increase the average removal rates of total nitrogen (TN), ammonia nitrogen (NH4+-N), total phosphorus (TP), phosphate (PO43--P), turbidity, algae density and chlorophyll-a (Chl-a) by 46.85 %, 53.97 %, 44.45 %, 54.55 %, 53.63 %, 42.16 % and 29.79 %, respectively. In addition, CEFB effectively avoided the great increase in organic matter concentration and the decline in sensory effects of the scenic water caused by plant lodging and plant tissue decomposition. In general, the suspension of inorganic functional filler could enhance the plant lodging resistance and purification efficiency of CEFB evidently, which is expected to become a feasible approach for eutrophic water restoration.