Treatment of the actual landfill leachate in different constructed wetlands through intermittent and varied aeration mode.

This study focused on the removal of organic matter and nitrogen and explored the feasible operation strategies to achieve short-cut nitrification and denitrification in two constructed wetlands (CWs), which were designed to treat the actual landfill leachate from a small county in parallel. The two CWs were horizontal sub-surface flow constructed wetlands (HFCW) with partial-area aeration and vertical sub-surface flow constructed wetlands (VFCW) with full-area aeration. The experimental results showed that both CWs could achieve an excellent organic matter and nitrogen removal performance under the conditions of intermittent aeration with high frequency and medium intensity (2 h of aeration and 4 h of rest). The removal efficiencies of COD and total nitrogen by HFCW were 89.08% and 73.22%, and the corresponding values of VFCW were 84.51% and 71.44%, respectively. Meanwhile, the inhibition kinetics model indicated that HFCW with partial-area aeration could enhance the free ammonium (FA) tolerance of ammonium-oxidizing bacteria (AOB) and reduce the conversion percentage of ammonia nitrogen. In addition, the intermittent aeration mode with high frequency and medium intensity could keep the DO concentration below under 0.60 mg L-1 in HFCW, which helped to achieve stable short-cut nitrification and ensure the average nitrite accumulation rate (NAR) reach 50.96%. These results suggested that the intermittent aeration in partial-area could achieve successful short-cut nitrification in HFCW, thereby improving the removal efficiency of nitrogen in landfill leachate.

Effect of first-stage aeration on treatment of domestic sewage in different hybrid constructed wetlands.

Two sets of hybrid constructed wetlands (HCWs) with the first-stage aeration were used to treat actual domestic sewage in this paper, where the effects of three important factors of aeration mode, hydraulic loading rates (HLR), and aeration volume on the removal of pollutants in both HCWs were studied in contrasts. In addition, the pollutant removal efficiency, the contribution of plants, and the characteristics of biofilm in both HCWs were explored. The results of 250-day experiment showed that the TN removal capacity of HCW combining vertical flow CW with horizontal flow CW (VF-HF) was better than HCW's converse combination (HF-VF) in treatingsewage, while the removal efficiency of COD and NH4+-N were similar, and the concentrations of TN and COD in the effluent of VF-HF could successfully meet the National discharge requirements. Compared with the continuous aeration, the intermittent aeration only had a little effect on the removal of COD and NH4+-N, but could improve TN removal performance in both HCWs. Meanwhile, increasing the aeration volume was beneficial to remove NH4+-N but not TN in HCWs. In addition, although the pollutant removal performances in both HCWs were impacted, the removal capacity of TN in VF-HF was only affected a little, when HLR was increased by 50%. The contribution of plants' uptake accounted for about 10% to nitrogen removal and 20% to phosphorus removal in both HCWs. The biomass at the filler surface near the plant rhizosphere was greater than that in the non-rhizosphere zones, and the impact of plant rhizosphere on the nitrification activity of biofilm was significantly greater than that on denitrification activity in both HCWs.

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.

Effects and mechanisms of calcium peroxide on purification of severely eutrophic water.

In consideration of severe eutrophication of scenic water caused by pollutants released from sediments in summer, calcium peroxide (CaO2) was adopted as the slow release peroxide to improve the water quality in a field experiment of 600 m2. The effect of CaO2 on the overlying water, interstitial water, sediment, and sediment microorganisms of scenic water was studied. Results for two months indicated that the dissolved oxygen (DO) concentration of the overlying water in the test zone was 3.78 times that in the control zone; the oxidation-reduction potential (ORP) in the overlying water and sediment increased significantly (p = 0.002 and p = 0). Meanwhile, CaO2 could effectively inhibit the release of nitrogen (N) and phosphorus (P) from the sediment and could obviously reduce the concentrations of N and P in the overlying water by enhancing the microbiological action. Moreover, the average concentrations of total nitrogen and total phosphorus in the overlying water of the test zone were 46.27% and 50.51% of those in control zone, respectively, and the concentrations of N and P in the interstitial water decreased during the entire experiment. In addition, CaO2 decreased the relative abundance of anaerobic bacteria in the sediment, whereas it increased that of aerobic bacteria and promoted the appearance of the functional bacteria, such as Nitrospirae and Thermodesulfoba. In conclusion, CaO2 can improve the DO and ORP in the eutrophic water effectively and change the microbial community in the sediment to a certain extent, thereby controlling the pollutants released from the sediment and reducing the N and P concentrations in the overlying water. Thus, CaO2 can effectively realize the purification and restoration of the severely eutrophic scenic water.