The optimization of volume ratio (VAn/VA/VO) and nitrate recycling ratio (R) in a two-sludge denitrifying phosphorus removal (DPR) process of Anaerobic Anoxic Oxic-Moving Bed Biofilm Reactor (A2/O-MBBR) was investigated. The results showed that prolonged anaerobic retention time (HRTAn: 1.25→3.75 hr) exerted favorable effect on chemical oxygen demand (COD) removal (57.26%→73.54%), poly-β-hydroxyalkanoates (PHA) synthesis (105.70→138.12 mgCOD/L) and PO43? release (22.3→38.9 mg/L). However, anoxic retention time (HRTA) and R exhibited positive correlation with PHA utilization (43.87%-81.34%) and denitrifying phosphorus removal (DPR) potential (ΔNO3?/ΔPO43?: 0.57-1.34 mg/mg), leading to dramatical TN removal variations from 68.86% to 81.28%. Under the VAn/VA/VO ratio of 2:6:0, sludge loss deteriorated nutrient removals but the sludge bioactivity quickly recovered when the oxic zone was recovered. The sludge characteristic and microstructure gradually transformed under the dissolved oxygen (DO) control (1.0-1.5→1.5-2.0 mg/L), in terms of sludge volume index (SVI: 194→57 mL/gVSS), median-particle-size (D50: 99.6→300.5 μm), extracellular polymeric substances (EPS) (105.62→226.18 mg/g VSS) and proteins/polysaccharides (PN/PS) ratio (1.52→3.46). Fluorescence in situ hybridization (FISH) results showed that phosphorus accumulation organisms (PAOs) (mainly Cluster I of Accumulibacter, contribution ratio: 91.79%-94.10%) dominated the superior DPR performance, while glycogen accumulating organisms (GAOs) (mainly Competibacter, contribution ratio: 82.61%-86.89%) was responsible for deteriorative TN and PO43? removals. The optimal HRTA and R assembled around 5-6.5 hr and 300%-400% based on the PHA utilization and DRP performance, and the oxic zones also contributed to PO43? removal although it showed low dependence on DO concentration and oxic retention time (HRTO). 相似文献
Acid deposition causes carbonate dissolution in watersheds and leads to profound impacts on water chemistry of lakes. Here, we presented a detailed study on the seasonal, spatial, and vertical variations of calcium and magnesium species in the overlying water, interstitial water, and sediment profiles in eutrophic Taihu Lake under the circumstance of regional acid deposition. The result showed that both the acid deposition and biomineralization in Taihu Lake had effects on Ca and Mg species. In the lake water, calcium carbonate was saturated or over-saturated based on long-term statistical calculation of the saturation index (SI). On the sediment profiles, significant difference in Ca and Mg species existed between the surface sediment (0–10 cm) and deeper sediments (>10 cm). The interstitial water Ca2+ and Mg2+, ion-exchangeable Ca and Mg in the surface sediment were higher than those in the deeper sediment. In the spring, when the acid deposition is more intensive, the acid-extracted Ca and Mg in the surface sediment were lower than that in the deeper sediment in the northwest lake, due to carbonate dissolution caused by the regional acid deposition. Spatially, the higher concentration of acid-extracted Ca and Mg in the northwest surface sediment than that in the east lake was observed, indicating the pronounced carbonate biomineralization by algae bloom in the northwest lake. Statistical analysis showed that acid deposition exerted a stronger impact on the variation of acid-extracted Ca and Mg in the surface sediment than the biomineralization in Taihu Lake. For the total Ca and Mg concentration in the spring, however, no significant change between the surface and deeper sediment in the northwest lake was observed, indicating that the carbonate precipitation via biomineralization and the carbonate dissolution due to acidic deposition were in a dynamic balance. These features are of major importance for the understanding of combined effects of acid deposition and eutrophication on freshwater lakes.