A2O工艺中N2O的产生与逸散特征简

目前污水处理过程中产生温室气体的问题已经引起普遍关注。本文通过实验室小试,研究了不同污水水质条件下A²O工艺中N₂O的产生特征,以及氧化亚氮还原酶编码基因nosZ含量对N₂O产生量的影响。结果表明,在A²O工艺中的各单元均有N₂O产生,其中厌氧池产生量最大,约占总产生量的32%~85%;A²O工艺产生的N₂O主要通过逸散进入大气,少量随二沉池出水进入到环境中。N₂O的产生量与污泥中nosZ的含量成负相关,而碳源和DO对含有nosZ基因的反硝化细菌有明显的影响,低DO环境和充足的碳源能够极大的促进其含量的提高,从而显著减少N₂O的产生量。     

A2/O工艺中的反硝化除磷

A2/O工艺是一种最简单的同步脱氮除磷工艺,但由于其系统中固有的基质竞争和污泥龄等矛盾,在实际应用中特别是处理低C/N比污水时脱氮除磷效率较低.反硝化除磷工艺作为近年来颇受关注的污水生物处理新技术.由于在脱氮除磷过程中可以在碳源利用上耦合,可从一定程度上缓解A2/O工艺中的基质竞争矛盾,使得其在处理低C/N比污水时也能实现较高的脱氮除磷效率.就反硝化除磷的技术原理,结合其在A2/O工艺中的最新研究成果及其控制策略,对A2/O工艺中的反硝化除磷的实现、维持及影响因素进行了分析和探讨,并对其发展方向进行了展望.     

Enhanced deodorization and sludge reduction in situ by a humus soil cooperated anaerobic/anoxic/oxic (A2O) wastewater treatment system

Simultaneous sludge reduction and malodor abatement in humus soil cooperated an anaerobic/anoxic/oxic (A2O) wastewater treatment were investigated in this study. The HSR-A2O was composed of a humus soil reactor (HSR) and a conventional A2O (designated as C-A2O).The results showed that adding HSR did not deteriorate the chemical oxygen demand (COD) removal, while total phosphorus (TP) removal efficiency in HSR-A2O was improved by 18 % in comparison with that in the C-A2O. Both processes had good performance on total nitrogen (TN) removal, and there was no significant difference between them (76.8 and 77.1 %, respectively). However, NH₄ ⁺–N and NO₃ ^?–N were reduced to 0.3 and 6.7 mg/L in HSR-A2O compared to 1.5 and 4.5 mg/L. Moreover, adding HSR induced the sludge reduction, and the sludge production rate was lower than that in the C-A2O. The observed sludge yield was estimated to be 0.32 kg MLSS/day in HSR-A2O, which represent a 33.5 % reduction compared to a C-A2O process. Activated sludge underwent humification and produced more humic acid in HSR-A2O, which is beneficial to sludge reduction. Odor abatement was achieved in HSR-A2O, ammonium (NH₃), and sulfuretted hydrogen (H₂S) emission decreased from 1.34 and 1.33 to 0.06 mg/m³, 0.025 mg/m³ in anaerobic area, with the corresponding reduction efficiency of 95.5 and 98.1 %. Microbial community analysis revealed that the relevant microorganism enrichment explained the reduction effect of humus soil on NH₃ and H₂S emission. The whole study demonstrated that humus soil enhanced odor abatement and sludge reduction in situ.     

Effect of influent C/N ratio on N2O emissions from anaerobic/anoxic/oxic biological nitrogen removal processes

The problem of producing strong greenhouse gas of nitrous oxide (N₂O) from biological nitrogen removal (BNR) process in wastewater treatment plants (WWTP) has elicited great concern from various sectors. In this study, three laboratory-scale wastewater treatment systems, with influent C/N ratios of 3.4, 5.4, and 7.5, were set up to study the effect of influent C/N ratio on N₂O generation in anaerobic/anoxic/oxic (A²O) process. Results showed, with the increased influent C/N ratio, N₂O generation from both nitrification and denitrification process was decreased, and the N₂O-N conversion ratio of the process was obviously reduced from 2.23 to 0.05%. Nitrification rate in oxic section was reduced, while denitrification rate in anaerobic and anoxic section was elevated and the removal efficiency of COD, NH₄ ⁺-N, TN, and TP was enhanced in different extent. As the C/N ratio increased from 3.4 to 7.5, activities of three key denitrifying enzymes of nitrate reductase, nitrite reductase, and nitrous oxide reductase were increased. Moreover, microorganism analysis indicated that the relative abundance of ammonium-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) were positively correlated with N₂O generation, which was reduced from (8.42 ± 3.65) to (3.61 ± 1.66)% and (10.38 ± 4.12) to (4.67 ± 1.62)%, respectively. NosZ gene copy numbers of the A²O system were increased from (1.19 ± 0.49) × 10⁷ to (2.84 ± 0.54) × 10⁸ copies/g MLSS with the influent C/N ratio elevated from 3.4 to 7.5. Hence, appropriate influent C/N condition of A²O process could optimize the microbial community structure that simultaneously improve treatment efficiency and decrease the N₂O generation.

     

Impact of carbon source on nitrous oxide emission from anoxic/oxic biological nitrogen removal process and identification of its emission sources

Wastewater treatment is an important source of nitrous oxide (N₂O), which is a strong greenhouse gas and dominate ozone-depleting substance. The purpose of this study was to evaluate the effect of carbon source on N₂O emission from anoxic/oxic biological nitrogen removal process. The mechanisms of N₂O emission were also studied. Long-term experiments were operated to evaluate the effect of three different carbon sources (i.e., glucose, sodium acetate, and soluble starch) on N₂O emission characteristics. And batch experiments, in the presence or absence of specific inhibitors, were carried out to identify the sources of N₂O emission. The ammonia-oxidizing bacteria (AOB) and denitrifiers community compositions under different circumstances were also analyzed based on which the underlying mechanisms of N₂O emission were elucidated. The conversion ratios of N₂O in reactors with glucose, sodium acetate, and soluble starch were 5.3 %, 8.8 %, and 2.8 %, respectively. The primary process responsible for N₂O emission was nitrifier denitrification by Nitrosomonas-like AOB, while denitrification by heterotrophic denitrifiers acted as the sink. Reactor with sodium acetate showed the highest N₂O emission, together with the highest nitrogen and phosphate removal ratios. Carbon source has a significant impact on N₂O emission quantity and relatively minor effect on its production mechanism.     

Influence of environmental factors on net N2 and N2O production in sediment of freshwater rivers

Denitrification is an important N removal process in aquatic systems but is also implicated as a potential source of global N₂O emissions. However, the key factors controlling this process as well as N₂O emissions remain unclear. In this study, we identified the main factors that regulate the production of net N₂ and N₂O in sediments collected from rivers with a large amount of sewage input in the Taihu Lake region. Net N₂ and N₂O production were strongly associated with the addition of NO₃ ^?-N and NH₄ ⁺-N. Specifically, NO₃ ^?-N controlled net N₂ production following Michaelis–Menten kinetics. The maximum rate of net N₂ production (V _max) was 116.3 μmol N₂-N m^?2 h^?1, and the apparent half-saturation concentration (k _m) was 0.65 mg N L^?1. N₂O to N₂ ratios increased from 0.18?±?0.03 to 0.68?±?0.16 with the addition of NO₃ ^?-N, suggesting that increasing NO₃ ^?-N concentrations favored the production of N₂O more than N₂. The addition of acetate enhanced net N₂ production and N₂O to N₂ ratios, but the ratios decreased by about 59.5 % when acetate concentrations increased from 50 to 100 mg C L^?1, suggesting that the increase of N₂O to N₂ ratios had more to do with the net N₂ production rate rather than acetate addition in this experiment. The addition of Cl^? did not affect the net N₂ production rates, but significantly enhanced N₂O to N₂ ratios (the ratios increased from 0.02?±?0.00 to 0.10?±?0.00), demonstrating that the high salinity effect might have a significant regional effect on N₂O production. Our results suggest that the presence of N-enriching sewage discharges appear to stimulate N removal but also increase N₂O to N₂ ratios.     

Effects of different quinoid redox mediators on the removal of sulphide and nitrate via denitrification

The impact of different quinoid redox mediators on the simultaneous conversion of sulphide and nitrate in a denitrifying culture was evaluated. All quinones evaluated, including anthraquinone-2,6-disulphonate (AQDS), 2-hydroxy-1,4-naphthoquinone and 1,2-naphthoquinone-4-sulphonate (NQS) were reduced by sulphide under abiotic conditions. NQS showed the highest reduction rate by sulphide (132 μmol h⁻¹) and promoted the maximum rate of sulphide oxidation (87 μmol h⁻¹) by denitrifying sludge, which represents an increase of 44% compared to the control lacking quinones. The reduced form of AQDS (AH₂QDS) served as an electron donor for the microbial reduction of nitrite and N₂O, which represents the first demonstration of hydroquinones supporting the microbial reduction of denitrifying intermediates. The results taken as a whole suggest that some quinones may significantly increase the rate of removal of S and N under denitrifying conditions.     

Phosphorus removal in a sulfur–limestone autotrophic denitrification (SLAD) biofilter

The sulfur–limestone autotrophic denitrification (SLAD) biofilter was able to remove phosphorous from wastewater during autotrophic denitrification. Parameters influencing autotrophic denitrification in the SLAD biofilter, such as hydraulic retention time (HRT), influent nitrate (NO₃ ^?), and influent PO₄ ^3? concentrations, had significant effects on P removal. P removal was well correlated with total oxidized nitrogen (TON) removed in the SLAD biofilter; the more TON removed, the more efficient P removal was achieved. When treating the synthetic wastewater containing NO₃ ^?-N of 30 mg L^?1 and PO₄ ^3?-P of 15 mg L^?1, the SLAD biofilter removed phosphorus of 45 % when the HRT was 6 h, in addition with TN removal of nearly 100 %. The optimal phosphorus removal in the SLAD biofilter was around 60 %. For the synthetic wastewater containing a PO₄ ^3?-P concentration of 15 mg L^?1, the main mechanism of phosphorus removal was the formation of calcium phosphate precipitates.     

Measuring and modeling nitrous oxide and methane emissions from beef cattle feedlot manure management: First assessments under Brazilian condition

Intensive beef production has increased during recent decades in Brazil and may substantially increase both methane (CH₄) and nitrous oxide (N₂O) emissions from manure management. However, the quantification of these gases and methods for extrapolating them are scarce in Brazil. A case study examines CH₄ and N₂O emissions from one typical beef cattle feedlot manure management continuum in Brazil and the applicability of Manure-DNDC model in predicting these emissions for better understand fluxes and mitigation options. Measurements track CH₄ and N₂O emissions from manure excreted in one housing floor holding 21 animals for 78 days, stockpiled for 73 days and field spread (360 kg N ha^?1). We found total emissions (CH₄ + N₂O) of 0.19 ± 0.10 kg CO₂eq per kg of animal live weight gain; mostly coming from field application (73%), followed housing (25%) and storage (2%). The Manure-DNDC simulations were generally within the statistical deviation ranges of the field data, differing in ?28% in total emission. Large uncertainties in measurements showed the model was more accurate estimating the magnitude of gases emissions than replicate results at daily basis. Modeled results suggested increasing the frequency of manure removal from housing, splitting the field application and adopting no-tillage system is the most efficient management for reducing emissions from manure (up to about 75%). Since this work consists in the first assessment under Brazilian conditions, more and continuous field measurements are required for decreasing uncertainties and improving model validations. However, this paper reports promising results and scientific perceptions for the design of further integrated work on farm-scale measurements and Manure-DNDC model development for Brazilian conditions.     

Silica removal in industrial effluents with high silica content and low hardness

High silica content of de-inked paper mill effluents is limiting their regeneration and reuse after membrane treatments such as reverse osmosis (RO). Silica removal during softening processes is a common treatment; however, the effluent from the paper mill studied has a low hardness content, which makes the addition of magnesium compounds necessary to increase silica removal. Two soluble magnesium compounds (MgCl₂?6H₂O and MgSO₄?7H₂O) were tested at five dosages (250–1,500 mg/L) and different initial pH values. High removal rates (80–90 %) were obtained with both products at the highest pH tested (11.5). With these removal efficiencies, it is possible to work at high RO recoveries (75–85 %) without silica scaling. Although pH regulation significantly increased the conductivity of the waters (at pH 11.5 from 2.1 to 3.7–4.0 mS/cm), this could be partially solved by using Ca(OH)₂ instead of NaOH as pH regulator (final conductivity around 3.0 mS/cm). Maximum chemical oxygen demand (COD) removal obtained with caustic soda was lower than with lime (15 vs. 30 %). Additionally, the combined use of a polyaluminum coagulant during the softening process was studied; the coagulant, however, did not significantly improve silica removal, obtaining a maximum increase of only 10 %.     

Spatial and temporal variations of nitrous oxide flux between coastal marsh and the atmosphere in the Yellow River estuary of China

To investigate the spatial and seasonal variations of nitrous oxide (N₂O) fluxes and understand the key controlling factors, we explored N₂O fluxes and environmental variables in high marsh (HM), middle marsh (MM), low marsh (LM), and mudflat (MF) in the Yellow River estuary throughout a year. Fluxes of N₂O differed significantly between sampling periods as well as between sampling positions. During all times of day and the seasons measured, N₂O fluxes ranged from ?0.0051 to 0.0805 mg N₂O m^?2 h^?1, and high N₂O emissions occurred during spring (0.0278 mg N₂O m^?2 h^?1) and winter (0.0139 mg N₂O m^?2 h^?1) while low fluxes were observed during summer (0.0065 mg N₂O m^?2 h^?1) and autumn (0.0060 mg N₂O m^?2 h^?1). The annual average N₂O flux from the intertidal zone was 0.0117 mg N₂O m^?2 h^?1, and the cumulative N₂O emission throughout a year was 113.03 mg N₂O m^?2, indicating that coastal marsh acted as N₂O source. Over all seasons, N₂O fluxes from the four marshes were significantly different (p?<?0.05), in the order of HM (0.0256?±?0.0040 mg N₂O m^?2 h^?1)?>?MF (0.0107?±?0.0027 mg N₂O m^?2 h^?1)?>?LM (0.0073?±?0.0020 mg N₂O m^?2 h^?1)?>?MM (0.0026?±?0.0011 mg N₂O m^?2 h^?1). Temporal variations of N₂O emissions were related to the vegetations (Suaeda salsa, Phragmites australis, and Tamarix chinensis) and the limited C and mineral N in soils during summer and autumn and the frequent freeze/thaw cycles in soils during spring and winter, while spatial variations were mainly affected by tidal fluctuation and plant composition at spatial scale. This study indicated the importance of seasonal N₂O contributions (particularly during non-growing season) to the estimation of local N₂O inventory, and highlighted both the large spatial variation of N₂O fluxes across the coastal marsh (CV?=?158.31 %) and the potential effect of exogenous nitrogen loading to the Yellow River estuary on N₂O emission should be considered before the annual or local N₂O inventory was evaluated accurately.     

Nitrogen transformations and balance in constructed wetlands for slightly polluted river water treatment using different macrophytes

Nitrogen removal processing in different constructed wetlands treating different kinds of wastewater often varies, and the contribution to nitrogen removal by various pathways remains unclear. In this study, the seasonal nitrogen removal and transformations as well as nitrogen balance in wetland microcosms treating slightly polluted river water was investigated. The results showed that the average total nitrogen removal rates varied in different seasons. According to the mass balance approach, plant uptake removed 8.4–34.3 % of the total nitrogen input, while sediment storage and N₂O emission contributed 20.5–34.4 % and 0.6–1.9 % of nitrogen removal, respectively. However, the percentage of other nitrogen loss such as N₂ emission due to nitrification and denitrification was estimated to be 2.0–23.5 %. The results indicated that plant uptake and sediment storage were the key factors limiting nitrogen removal besides microbial processes in surface constructed wetland for treating slightly polluted river water.     

Effects of biofilter media depth and moisture content on removal of gases from a swine barn

Media depth (MD) and moisture content (MC) are two important factors that greatly influence biofilter performance. The purpose of this study was to investigate the combined effect of MC and MD on removing ammonia (NH₃), hydrogen sulfide (H₂S), and nitrous oxide (N₂O) from swine barns. Biofiltration performance of different MDs and MCs in combination based on a mixed medium of wood chips and compost was monitored. A 3 × 3 factorial design was adopted, which included three levels of the two factors (MC: 45%, 55%, and 67% [wet basis]; MD: 0.17, 0.33, and 0.50 m). Results indicated that high MC and MD could improve NH₃ removal efficiency, but increase outlet N₂O concentration. When MC was 67%, the average NH₃ removal efficiency of three MDs (0.17, 0.33, and, 0.50 m) ranged from 77.4% to 78.7%; the range of average H₂S removal efficiency dropped from 68.1–90.0% (1–34 days of the test period) to 36.8–63.7% (35–58 days of the test period); and the average outlet N₂O concentration increased by 25.5–60.1%. When MC was 55%, the average removal efficiency of NH₃, H₂S, and N₂O for treatment with 0.33 m MD was 72.8 ± 5.9%, 70.9 ± 13.3%, and –18.9 ± 8.1%, respectively; and the average removal efficiency of NH₃, H₂S, and N₂O for treatment with 0.50 m MD was 77.7 ± 4.2%, 65.8 ± 13.7%, and –24.5 ±12.1%, respectively. When MC was 45%, the highest average NH₃ reduction efficiency among three MDs was 60.7% for 0.5 m MD, and the average N₂O removal efficiency for three MDs ranged from –18.8% to –12.7%. In addition, the pressure drop of 0.33 m MD was significantly lower than that of 0.50 m MD (p < 0.05). To obtain high mitigation of NH₃ and H₂S and avoid elevated emission of N₂O and large pressure drop, 0.33 m MD at 55% MC is recommended.

Implications: The performances of biofilters with three different media depths (0.17, 0.33, and 0.50 m) and three different media moisture contents (45%, 55%, and 67% [wet basis]) were compared to remove gases from a swine barn. Using wood chips and compost mixture as the biofilters media, the combination of 0.33 m media depth and 55% media moisture content is recommended to obtain good reduction of NH₃ and H₂S, and to simultaneously prevent elevated emission of N₂O and large pressure drop across the media.     

Electrochemical treatment of domestic wastewater using boron-doped diamond and nanostructured amorphous carbon electrodes

The performance of the electrochemical oxidation process for efficient treatment of domestic wastewater loaded with organic matter was studied. The process was firstly evaluated in terms of its capability of producing an oxidant agent (H₂O₂) using amorphous carbon (or carbon felt) as cathode, whereas Ti/BDD electrode was used as anode. Relatively high concentrations of H₂O₂ (0.064 mM) was produced after 90 min of electrolysis time, at 4.0 A of current intensity and using amorphous carbon at the cathode. Factorial design and central composite design methodologies were successively used to define the optimal operating conditions to reach maximum removal of chemical oxygen demand (COD) and color. Current intensity and electrolysis time were found to influence the removal of COD and color. The contribution of current intensity on the removal of COD and color was around 59.1 and 58.8 %, respectively, whereas the contribution of treatment time on the removal of COD and color was around 23.2 and 22.9 %, respectively. The electrochemical treatment applied under 3.0 A of current intensity, during 120 min of electrolysis time and using Ti/BDD as anode, was found to be the optimal operating condition in terms of cost/effectiveness. Under these optimal conditions, the average removal rates of COD and color were 78.9?±?2 and 85.5?±?2 %, whereas 70 % of total organic carbon removal was achieved.     

改良型A2/O-MBR工艺的反硝化除磷性能研究简

重点考察了一种改良型膜生物反应器（A²/O-MBR）的脱氮除磷性能。该工艺主要特点在于对膜池硝化回流液进行了固液分离,并将上清液和浓缩污泥分别回流至缺氧池和厌氧池,这种改进提高了系统对氮、磷的同步去除效率。实验结果表明,在水力停留时间（HRT）为12 h,污泥龄（SRT）为30 d,混合液回流比为200%的运行条件下,进水COD、NH₄⁺-N、TN和TP平均浓度分别为（225±38）、（24.8±3.9）、（26.7±2.9）和（2.90±0.53）mg/L时,增加膜池硝化回流液固液分离装置前后,系统对COD和NH₄⁺-N的去除都维持在较高水平,而系统对TN和TP的去除效果显著提高,出水TN和TP平均浓度分别由（14.9±3.3）mg/L和（1.95±0.72）mg/L下降到（9.4± 1.9）mg/L和（0.91±0.38）mg/L,表明增加膜池硝化回流液固液分离装置显著改善了A²/O-MBR系统的脱氮除磷效果。反硝化除磷活性实验结果进一步表明,改进后系统中反硝化除磷活性占总除磷活性的比例由51.5%上升至61.7%,说明增加膜池硝化回流液固液分离装置强化了系统的反硝化除磷性能。     

循环比对氧化沟脱氮除磷效果及磷转化途径的影响

在改良型氧化沟工艺的循环廊道内增设缓流板,以此改变循环廊道过流断面面积,进而调控循环比(循环廊道断面通过的循环流量和进水流量的比值)。利用胞内、胞外聚合物的分析及物料平衡的方法,研究了增设缓流板、调控循环比前后系统同步脱氮除磷效果和磷转化途径的变化及聚磷菌种含量的差别。结果表明,增设缓流板,循环比为27时,COD、NH+4、TN和TP的平均去除率分别为93.3%、87.1%、78.1%和96.0%,反硝化聚磷菌占总聚磷菌的比例为46.1%;而不设缓流板,循环比为241时,COD、NH+4、TN和TP的平均去除率分别为91.2%、82.7%、67.2%和86.4%,反硝化聚磷菌占总聚磷菌的比例为17.54%。综上可知,增设缓流板控制循环比,有助于提高反硝化聚磷菌的富集,有助于提高反硝化吸磷量,同时有助于提高氧化沟工艺的同步脱氮除磷效果。     

Mitigating Global Warming Potentials of Methane and Nitrous Oxide Gases from Rice Paddies under different irrigation regimes

A field experiment was conducted in Bangladesh Agricultural University Farm to investigate the mitigating effects of soil amendments such as calcium carbide, calcium silicate, phosphogypsum, and biochar with urea fertilizer on global warming potentials (GWPs) of methane (CH₄) and nitrous oxide (N₂O) gases during rice cultivation under continuous and intermittent irrigations. Among the amendments phosphogypsum and silicate fertilizer, being potential source of electron acceptors, decreased maximum level of seasonal CH₄ flux by 25–27 % and 32–38 % in continuous and intermittent irrigations, respectively. Biochar and calcium carbide amendments, acting as nitrification inhibitors, decreased N₂O emissions by 36–40 % and 26–30 % under continuous and intermittent irrigations, respectively. The total GWP of CH₄ and N₂O gases were decreased by 7–27 % and 6–34 % with calcium carbide, phosphogypsum, and silicate fertilizer amendments under continuous and intermittent irrigations, respectively. However, biochar amendments increased overall GWP of CH₄ and N₂O gases.     

Impact of raw pig slurry and pig farming practices on physicochemical parameters and on atmospheric N2O and CH4 emissions of tropical soils,Uvéa Island (South Pacific)

Emissions of CH₄ and N₂O related to private pig farming under a tropical climate in Uvéa Island were studied in this paper. Physicochemical soil parameters such as nitrate, nitrite, ammonium, Kjeldahl nitrogen, total organic carbon, pH and moisture were measured. Gaseous soil emissions as well as physicochemical parameters were compared in two private pig farming strategies encountered on this island on two different soils (calcareous and ferralitic) in order to determine the best pig farming management: in small concrete pens or in large land pens. Ammonium levels were higher in control areas while nitrate and nitrite levels were higher in soils with pig slurry inputs, indicating that nitrification was the predominant process related to N₂O emissions. Nitrate contents in soils near concrete pens were important (≥55 μg N/g) and can thus be a threat for the groundwater. For both pig farming strategies, N₂O and CH₄ fluxes can reach high levels up to 1 mg N/m²/h and 1 mg C/m²/h, respectively. CH₄ emissions near concrete pens were very high (≥10.4 mg C/m²/h). Former land pens converted into agricultural land recover low N₂O emission rates (≤0.03 mg N/m²/h), and methane uptake dominates. N₂O emissions were related to nitrate content whereas CH₄ emissions were found to be moisture dependent. As a result relating to the physicochemical parameters as well as to the gaseous emissions, we demonstrate that pig farming in large land pens is the best strategy for sustainable family pig breeding in Uvéa Islands and therefore in similar small tropical islands.     

Salt marsh plants as key mediators on the level of cadmium impact on microbial denitrification

The fate of excess nitrogen in estuaries is determined by the microbial-driven nitrogen cycle, being denitrification a key process since it definitely removes fixed nitrogen as N₂. However, estuaries receive and retain metals, which may negatively affect this process efficiency. In this study, we evaluated the role of salt marsh plants in mediating cadmium (Cd) impact on microbial denitrification process. Juncus maritimus and Phragmites australis from an estuary were collected together with the sediment involving their roots, each placed in vessels and maintained in a greenhouse, exposed to natural light, with tides simulation. Similar non-vegetated sediment vessels were prepared. After 3 weeks of accommodation, nine vessels (three per plant species plus three non-vegetated) were doped with 20 mg/L Cd²⁺ saline solution, nine vessels were doped with 2 mg/L Cd²⁺ saline solution and nine vessels were left undoped. After 10 weeks, vessels were dissembled and denitrification potential was measured in sediment slurries. Results revealed that the addition of Cd did not cause an effect on the denitrification process in non-vegetated sediment but had a clear stimulation in colonized ones (39 % for P. australis and 36 % for J. maritimus). In addition, this increase on denitrification rates was followed by a decrease on N₂O emissions and on N₂O/N₂ ratios in both J. maritimus and P. australis sediments, increasing the efficiency of the N₂O step of denitrification pathway. Therefore, our results suggested that the presence of salt marsh plants functioned as key mediators on the degree of Cd impact on microbial denitrification.     

缺氧池填料投配比对A~2/O-MBR工艺反硝化除磷的影响

按20%的投配比往好氧1,2池中加入相同数量的悬浮式填料,将传统A2/O工艺转变为A2/O-MBR复合工艺。通过处理实际市政污水,重点考察了在缺氧池中不同填料投配比条件下,复合工艺的去除效果以及反硝化除磷效果。实验结果表明,当缺氧池中填料投配比为20%时,装置总体的处理效果最好。COD、总氮、氨氮和总磷的去除率分别达到了81.1%、80.3%、100%和85.2%。当投配比为10%时,反硝化除磷效果最明显,占总除磷量的48.3%。从经济角度出发,10%的投配比为最佳投配比。