Research and application status of ecological floating bed in eutrophic landscape water restoration.

Ecological floating bed (EFB) has become the preferred technology due to its reputation of green economy, convenience, and efficiency in treating eutrophic landscape water. Based on the statistical analysis of abundant literatures, this paper systematically summarizes the component elements, design parameters, purification mechanism, purification ability, strengthening methods and the correlations among various parameters of EFB, and points out some issues existing in the current research and applications. The results show that the coverage of 5% ~ 38% and water depth of 60 ~ 110 cm should be recommended for EFB design. The microbial transformation-sedimentation contributes mostly to the removal of pollutant, leading to the contribution rate of 51.9% ± 26.4% to nitrogen (N) removal and 50.8% ± 20.4% to phosphorus (P) removal in water respectively. Meanwhile, the average purification abilities of EFB for carbon (C), N and P in water are 4.59 ± 3.82, 0.43 ± 0.35 and 0.04 ± 0.04 g m-2 d-1 respectively. The purification effect is relatively superior when the initial concentration of C, N and P in water is close to C: N: P = 115: 11: 1. In order to enhance the EFB purification efficiency, the methods of artificial aeration, biological chain extension, functional filler introduction, and composite EFB construction can be used. Furthermore, the purification ability of EFB per unit area is correlated positively with water temperature and initial pollutant concentration (r ≥ 0.577, p < 0.01), and correlated negatively with EFB coverage (r ≤ -0.598, p < 0.01). The future research of EFB should focus on enhancing its purification efficiency and seasonal adaptability, studying the mechanism of algae inhibition by allelochemicals, and exploring the harvesting management and resource utilization of plants. This paper provides more reasonable design parameters, feasible management strategies and prospective research directions for environmental managers and researchers who would like to adopt EFB to purify eutrophic landscape water.

Impact of calcium peroxide dosage on the control of nutrients release from sediment in the anoxic landscape water.

The anoxic and reductive aquatic environment is formed easily in summer due to the global warming, which may accelerate endogenous release. In this experiment, four different dosages of calcium peroxide (CaO2) were adopted to study the control effects of nutrients release from the sediments in the simulated landscape waters. The results demonstrated that CaO2 addition could effectively improve the physicochemical properties and microbial composition in sediments, and an obvious improvement was achieved with a larger dosage. It was observed that the surface sediments of experiment groups were oxidized to form a capping barrier between the sediment and overlying water, which might cut off the pollutant diffusion in sediment. Meanwhile, CaO2 could decrease the nutrients concentration in water obviously, and the reduced effect was positively correlated with the CaO2 dosage. Compared with the nutrients release fluxes in CK (105.89 mg-TN m-2 day-1, 106.48 mg-NH4+-N m-2 day-1, 4.14 mg-TP m-2 day-1, and 4.30 mg-SRP m-2 day-1), the CaO2 dosages of 0.12 and 0.18 kg m-2 could entirely inhibit the nutrients release from sediment, and partially reduce the original pollutants in the overlying water. However, 0.18 kg m-2 CaO2 would cause a higher increase of pH value and NO2--N concentration, and bring potential risk to the aquatic ecosystem. Therefore, 0.12 kg-CaO2 m-2-sediment was selected as the optimal dosage by considering the control effect, economic cost, and potential risk comprehensively. In general, this study provided a quantitative usage method of CaO2, which is convenient and effective to prevent or control the nutrients release from sediment caused by anoxic and reductive condition in summer.

Dose effects of calcium peroxide on harmful gases emissions in the anoxic/anaerobic landscape water system.

Large-area hypoxia of urban landscape water often causes the emissions of harmful gases in summer, which not only reduces its sensory effects, but also brings a potential threat to aquatic ecosystem and human health. This study explored the dose effects of calcium peroxide (CaO2) on inhibiting harmful gases emissions and restoring the scenic effect (including visual sense and olfactory sense) of anoxic/anaerobic landscape water system. The results indicated that the emissions of H2S, CO2 and CH4 from the anoxic/anaerobic water system were obviously inhibited in the reactors with CaO2 additions and the effect was positively correlated with the CaO2 dose. Meanwhile, the concentrations of total chemical oxygen demand (TCOD) and soluble sulfide (S2-), and turbidity in the overlying water (the water-layer above the sediment-water interface) were also decreased in the reactors dosed with CaO2. The reason was ascribed to the improvement of the anoxic/anaerobic condition in the water system and the increase of the species richness, bacteria count and aerobic microorganism abundance in sediment. Furthermore, 0.12 kg-CaO2 m-2-sediment was selected as the optimal dose, which was based on considering the inhibiting effect of the harmful gases emissions, comprehensive influence and costs. Compared with control check (CK, the reactor without adding CaO2), the optimal dose of CaO2 could reduce 75.10% CH4, 81.02% CO2 and 100% H2S in gases, and decrease 81.52% S2-, 42.85% TCOD and 84.01% turbidity in the overlying water. In conclusion, all the dosages of CaO2 could improve the anoxic condition of water system and 0.12 kg-CaO2 m-2-sediment was the optimal dose in inhibiting harmful gases emissions, which could keep an excellent water quality in this simulation experiment. Therefore, this study may provide a feasible method and the optimal dose for inhibiting the emissions of harmful gases and restoring the scenic effect in the similar anoxic/anaerobic landscape water.

Effect of calcium peroxide on the water quality and bacterium community of sediment in black-odor water.

This study investigated how efficiently CaO2 could treat black-odor landscape water caused by low dissolved oxygen (DO) in a field experiment of 600 m2. The study demonstrated that CaO2 could significantly elevate the DO concentration in waters and the oxidation-reduction potential (ORP) level in sediments (p = 0.003 and p = 0), which is conducive to improving the anoxic environment of landscape water. The concentrations of total chemical oxygen demand (TCOD) and S2- in overlying and interstitial waters were considerably decreased. The average concentrations of TCOD in the overlying and interstitial waters of the test zone (TZ) were 52.98% and 66.05% of those of the control zone (CZ), and the average concentrations of S2- in the overlying and interstitial waters of TZ were 29.63% and 39.79% of those of CZ. Meanwhile, CaO2 could obviously reduce turbidity but increase the transparency in the overlying water. The mean value of turbidity in the overlying water of TZ was 39.46% of that of CZ, whereas the transparency in the overlying water of TZ was 2.07 times that of CZ. Furthermore, CaO2 changed the microbial community structure in the sediments, where the relative abundance of anaerobic bacteria was decreased but that of the aerobic bacteria was increased with some functional bacteria. In summary, CaO2 could significantly increase the DO and ORP in black-odor landscape water, obviously inhibit the release of pollutants from sediment, and increase the diversity of microbial strains. Consequently, the black-odor phenomenon of landscape water could be alleviated effectively by adding CaO2.

Effect of a strengthened ecological floating bed on the purification of urban landscape water supplied with reclaimed water.

A floating bed (FB) system vegetated with calamus, iris, lythrum, and Hydrocotyle vulgaris, and a strengthened FB (SFB) system with zeolite and sponge iron as fillers were simultaneously applied to purify urban landscape water in different zones. The urban landscape water, an artificial lake of approximately 326m2, was supplied with reclaimed water during a six-month experiment. Results indicated that the concentrations of nitrogen (N) and phosphorus (P) in the SFB zone (SFBZ) were significantly lower than those in the control zone (CZ) and the FB zone (FBZ) after six months of operation. The average removal efficiencies (AREs) in the SFBZ, FBZ and CZ were 89.98%, 77.39% and 56.37%, respectively, for ammonia nitrogen (NH4+-N); 92.49%, 79.55% and 47.85%, respectively, for phosphate (PO43--P). Meanwhile, the average concentration of Chlorophyll a and the algae density in SFBZ during the experiment were 12.54µg/L and 1.31×104cells/mL, which were lower, obviously, than those in the FBZ and CZ. Moreover, the contribution rates analysis of nutrient removal exhibited that the plant absorption in the removal of N and P occupied 27.85% and 26.36%, whereas the filler adsorption occupied 7.93% and 11.93%, respectively, in the SFB. Thus, the water quality of the artificial lake was improved greatly by the SFB which hybridized fillers and FB together. Finally, it was found that the AREs of NH4+-N and PO43--P in the SFBZ could reach 73.93% and 84.56%, approximately 1.39 and 1.41 times that of the FBZ during the winter. Therefore, the application of an SFB can keep a stable water quality in urban landscape water and avoid the lower removal rate of an FB at low-temperature. In summary, the SFB could effectively improve the water quality of urban landscape water supplied with reclaimed water even in winter.