Nutrient removal effect and characteristics of integrated floating beds at low temperature

To investigate the effect of combined floating beds on nutrient removal under low temperature, an integrated floating bed with corn flakes (IFB-CF) and an integrated floating bed with light ceramsite (IFB-LC) were constructed in parallel. IFB-LC was used as control group under water temperatures of 9.3-14 °C and a water exchange time of 168 h. Nitrogen and phosphorus removal efficiency, the nutrient level of a hydrophyte (Oenanthe javanica), and the microbial population characteristics of the combined floating bed were investigated. For IFB-CF removal efficiencies, the degradation quantities of total nitrogen (TN), NO₃^--N, and NH₄⁺-N for IFB-CF were 13.58 ± 0.67 mg/L, 4.40 ± 0.61 mg/L, and 9.21 ± 0.38 mg/L, respectively; in contrast, degradation quantities for IFB-LC were lower (6.41 ± 1.47 mg/L, 2.15 ± 0.40 mg/L, and 5.95 ± 0.46 mg/L, respectively). The reductions in COD (Chemical Oxygen Demand, using K₂Cr₂O₇ as oxidizer) for IFB-LC and IFB-CF were 86.89% and 66.06%, respectively. Using the MiSeq high throughput sequencing method, we analysed microbial community structure and diversity on the base material surface of the IFB-CF and IFB-LC. The results showed 15 phyla, 165 genera, and 78 families on the surface of the IFB-CF. The phylum, genus, and family with the highest abundances were Proteobacteria (48.29%), Trichococcus (10.39%), and Comamonadaceae (12.45%), respectively. We identified 15 phyla, 144 genera, and 93 families on the surface of the IFB-LC. The phylum, genus, and family with the highest abundances were Proteobacteria (46.10%), Dyadobacter (22.67%), and Cytophagaceae (28.75%), respectively. The Chao, ACE, and Shannon & Simpson indices for the IFB-LC were 4081, 6295, and 5.10, and 0.05, respectively; for the IFB-CF they were 4938, 7461, 5.77, and 0.02, respectively. Catalase (CAT) and Peroxidase (POD) concentrations in Oenanthe javanica for IFB-LC were 35.48 u/gFW/min and 1.03 u/gFW/min, respectively; for IFB-CF they were 32.33 u/gFW/min and 1.25 u/gFW/min, respectively. The nutritional energies of IFB-CF and IFB-LC were 107 kJ/100g and 84 kJ/100g. Using the Mondal model of TN removal, k (half-saturation constant) values for IFB-LC and IFB-CF were 35.67 mg/L and 39.23 mg/L, respectively, with a correlation coefficient (R²) of 0.97.