Denitrification in a natural wetland receiving secondary treated effluent

The potential of a natural wetland as a site for nitrogen removal from secondary treated effluent was examined by investigating the distribution of denitrification rates and activity in soils and decaying plant material. Field measurements of soil Eh, pH and temperature showed that the effluent inflow favours denitrification by lowering Eh, maintaining pH 6.4–6.7, and raising soil temperature. Analysis of soil concentrations of nitrate plus nitrite and ammonium ions shows that the effluent inflow increased the concentrations of inorganic nitrogen in the soil, and encouraged higher rates of denitrification. Denitrification rates measured by an acetylene blockage technique were highest in soil samples from downstream of the effluent inflow, with the maximum rates being recorded in soils from 0 to 60 cm and in decaying plant material lying on the soil surface. Both nitrate plus nitrite concentration and denitrification activity declined rapidly below 6 cm in upstream and downstream soil samples. Denitrification rates in the natural wetland are increased by the addition of secondary treated effluent, and make a year-round contribution to the removal of nitrogen from the wastewater. Rates of nitrogen removal in the wetland could be increased by encouraging greater spatial and temporal interaction of the effluent amended water with the sites of highest denitrification activity.     

Simultaneous biological removal of nitrogen, carbon and sulfur by denitrification

Refinery wastewaters may contain aromatic compounds and high concentrations of sulfide and ammonium which must be removed before discharging into water bodies. In this work, biological denitrification was used to eliminate carbon, nitrogen and sulfur in an anaerobic continuous stirred tank reactor of 1.3 L and a hydraulic retention time of 2 d. Acetate and nitrate at a C/N ratio of 1.45 were fed at loading rates of 0.29 kg C/m3 d and 0.2 kg N/m3 d, respectively. Under steady-state denitrifying conditions, the carbon and nitrogen removal efficiencies were higher than 90%. Also, under these conditions, sulfide (S(2-)) was fed to the reactor at several sulfide loading rates (0.042-0.294 kg S(2-)/m3 d). The high nitrate removal efficiency of the denitrification process was maintained along the whole process, whereas the carbon removal was 65% even at sulfide loading rates of 0.294 kg S(2-)/m3 d. The sulfide removal increased up to approximately 99% via partial oxidation to insoluble elemental sulfur (S0) that accumulated inside the reactor. These results indicated that denitrification is a feasible process for the simultaneous removal of nitrogen, carbon and sulfur from effluents of the petroleum industry.     

Denitrification on poly-beta-hydroxybutyrate in microbial granular sludge sequencing batch reactor

Microbial granules were successfully cultivated in an alternating aerobic-anaerobic sequencing batch reactor (SBR) for removing organic carbon and nitrogen. It was found that almost all input ammonium was converted to nitrite and nitrate in the aerobic phase, while the efficiency of denitrification was highly related to the availability of external carbon source in the anaerobic phase. Complete denitrification was achieved with sufficient supply of external carbon, while only partial denitrification was observed with no addition of external carbon. Results showed that in the absence of external carbon source, pre-accumulated poly-beta-hydroxybutyric acid (PHB) in microbial granules could be utilized for cell maintenance and denitrification. With supply of external carbon but no addition of nitrate, PHB accumulation accounted for the main mechanism of the organic removal. Under balanced growth conditions (with organic carbon and nitrogen supply), external organic carbon was consumed simultaneously for denitrification, PHB storage as well as for cell functions. It was revealed that the potential role of PHB for denitrification by microbial granules was very limited, i.e. less than 28 mg nitrate-nitrogen l(-1) was found to be denitrified with internally accumulated PHB. This study for the first time shows the limiting capacity of PHB as reducing power for denitrification by microbial granules.     

Plant carbohydrate limitation on nitrate reduction in wetland microcosms

Although nitrate limitation in most natural wetlands results in pseudo-first-order reductions, large site-to-site variations in apparent denitrification rates cannot be easily explained by water quality (e.g., pH, Temp, DOC) or plant productivity. Our microcosm results show increasing nitrate removal efficiencies at higher ratios of total applied plant carbon to nitrate reduced, suggesting that denitrification rates may be limited by the rates of supply of both electron donor or acceptor, described by an applied carbon to nitrate (C(App): N(Red)) ratio. However, the observed first-order rate constants varied more strongly (r2 = 0.77, p <0.0001) with the acid-soluble carbohydrates to nitrate (CH2O(App): N(Red)) ratio than the total C(App): N(Red) ratio. Although observed rate constants for bulrush (Scirpus sp.) were significantly lower (0.01 相似文献   

人工湿地的反硝化能力研究

利用人工湿地的反硝化作用进行去除硝态氮的试验,其反硝化碳源主要为植物根系的分泌物及湿地内腐败的死亡植株.结果表明,人工湿地内有着适宜反硝化的反应环境,反硝化茵能够很好地利用湿地内产生的碳源进行反硝化作用来去除硝态氮,且不会出现亚硝态氮的大量积累.在进水(NO3-)-N浓度为20-50 mg/L、水力停留时间为24 h的条件下,夏季运行时,湿地系统对硝态氮的去除率为20%～30%;冬季运行时,对硝态氮的去除率在10%左右.提供充足的反硝化碳源是硝态氮去除率进一步提高的瓶颈.     

Nutrient removal from effluents by an artificial wetland: Influence of rhizosphere aeration and preferential flow studied using bromide and dye tracers

Sewerage and effluents from rural industry can be treated by percolation through the root zones of emergent macrophytes growing in a gravel substratum. The hydrology of these systems is complex, being driven by both gravity and transpiration, and so measurements of nutrient transformations within the systems are complicated by incomplete mixing. Pulse addition of dye and bromide tracers concurrently with nutrients, has been used in one such experimental artificial wetland to investigate the rates and processes of nutrient removal. The tracer was used for comparison to compensate for incomplete mixing and concentration caused by evapotranspiration. Nitrogen removal efficiency is dependent on sequential mineralization of organic nitrogen to ammonium-nitrogen, followed by nitrification of the ammonium to nitrate or nitrite and denitrification of nitrate or nitrite to gaseous nitrogen products. The effluent from a rendering plant was dominated by organic and ammonium-nitrogen, and efficiency of nitrogen removal was probably impaired by inadequate rates of mineralization and nitrification. Aeration is required for the latter process. Apparently the macrophytes were not introducing sufficient oxygen into the effluent for nitrification to be complete. This may reflect an inadequate outward radial diffusion of oxygen into the rhizosphere, or the effects of channelling of the effluent in preferential flow paths around the aerating root masses, requiring changes in system design.     

Simultaneous carbon and nitrogen removal from high strength domestic wastewater in an aerobic RBC biofilm

High strength domestic wastewater discharges after no/partial treatment through sewage treatment plants or septic tank seepage field systems have resulted in a large build-up of groundwater nitrates in Rajasthan, India. The groundwater table is very deep and nitrate concentrations of 500-750 mg/l (113-169 as NO3(-)-N) are commonly found. A novel biofilm in a 3-stage lab-scale rotating biological contactor (RBC) was developed by the incorporation of a sulphur oxidising bacterium Thiosphaera pantotropha which exhibited high simultaneous removal of carbon and nitrogen in fully aerobic conditions. T. pantotropha has been shown to be capable of simultaneous heterotrophic nitrification and aerobic denitrification thereby helping the steps of carbon oxidation, nitrification and denitrification to be carried out concurrently. The first stage having T. pantotropha dominated biofilm showed high carbon and NH4(+)-N removal rates of 8.7-25.9 g COD/m2 d and 0.81-1.85 g N/m2 d for the corresponding loadings of 10.0-32.0 g COD/m2 d and 1.0-3.35 g N/m2 d. The ratio of carbon removed to nitrogen removed was close to 12.0. The nitrification rate increased from 0.81 to 1.8 g N/m2 d with the increasing nitrogen loading rates despite a high simultaneous organic loading rate. However, it fell to 1.53 g N/m2 d at a high load of 3.35 g N/m2 d and 32 g COD/m2 d showing a possible inhibition of the process. A simultaneous 44-63% removal of nitrogen was also achieved without any significant NO2(-)-N or NO3(-)-N build-up. The second and third stages, almost devoid of any organic carbon, acted only as autotrophic nitrification units, converting the NH4(+)-N from stage 1 to nitrite and nitrate. Such a system would not need a separate carbon oxidation step to increase nitrification rates and no external carbon source for denitrification. The alkalinity compensation during denitrification for that destroyed in nitrification may also result in a high economy.     

Nitrate reduction in a simulated free-water surface wetland system

The feasibility of using a constructed wetland for treatment of nitrate-contaminated groundwater resulting from the land application of biosolids was investigated for a site in the southeastern United States. Biosolids degradation led to the release of ammonia, which upon oxidation resulted in nitrate concentrations in the upper aquifer in the range of 65-400 mg N/L. A laboratory-scale system was constructed in support of a pilot-scale project to investigate the effect of temperature, hydraulic retention time (HRT) and nitrate and carbon loading on denitrification using soil and groundwater from the biosolids application site. The maximum specific reduction rates (MSRR), measured in batch assays conducted with an open to the atmosphere reactor at four initial nitrate concentrations from 70 to 400 mg N/L, showed that the nitrate reduction rate was not affected by the initial nitrate concentration. The MSRR values at 22 °C for nitrate and nitrite were 1.2 ± 0.2 and 0.7 ± 0.1 mg N/mg VSS_COD-day, respectively. MSRR values were also measured at 5, 10, 15 and 22 °C and the temperature coefficient for nitrate reduction was estimated at 1.13. Based on the performance of laboratory-scale continuous-flow reactors and model simulations, wetland performance can be maintained at high nitrogen removal efficiency (>90%) with an HRT of 3 days or higher and at temperature values as low as 5 °C, as long as there is sufficient biodegradable carbon available to achieve complete denitrification. The results of this study show that based on the climate in the southeastern United States, a constructed wetland can be used for the treatment of nitrate-contaminated groundwater to low, acceptable nitrate levels.     

无外加碳源SBBR脱氮工艺及其控制方法研究

为提高脱氮效果并实现利用内碳源进行反硝化,开展了SBBR（以好氧-缺氧方式运行）处理生活污水的脱氮研究.在好氧阶段,SBBR中的生物膜能创造缺氧微环境并吸收、储存碳,实现了同步硝化反硝化,降低了硝态氮的浓度;在缺氧阶段,可利用内碳源实现剩余硝态氮的反硝化.溶解氧浓度的大小对好氧时间、好氧剩余硝态氮浓度和缺氧反应时间有较大影响,因而可以利用在线检测的DO作为曝气量控制参数.DO、pH和ORP值的变化具有规律性,反映了生物脱氮过程中耗氧和供氧、产酸和产碱、氧化和还原过程的变化.为准确判断好氧和缺氧反应过程的终点,并减少控制的滞后时间,建议以pH值的＂氨谷＂和ORP的＂硝酸盐膝＂作为主控制特征点分别指示硝化和反硝化的终点,而以ORP的＂氨肘＂和pH值的＂硝酸盐峰＂作为参考或辅助控制特征点.     

Nitrification/denitrification in nitrogen high-strength liquid wastes

To evaluate the possibility of nitrogen removal from nitrogen high-strength wastewaters, nitrification rates, denitrification and related energy problems, emerging in nondiluted wastewater from a pig production plant, are studied on a laboratory level. Excess nitrogen can be removed by utilising a nitrification process first and a denitrification process afterwards, and so reduce the content of residual mineral nitrogen to less than 100 mg l⁻¹. Oxidation of ammonium, the most critical phase, is carried out with an inoculum of nitrifying bacteria adapted to the wastewater type under adequate aeration, and carefully controlled pH. The dilution of wastewater is not needed, nor external organic carbon to reduce nitrate.     

Five years of nitrate removal, denitrification and carbon dynamics in a denitrification wall

Denitrification walls are a useful approach for removing nitrate from shallow groundwater, but little is known about the sustainability of nitrate removal, which is dependent on the continued supply of organic carbon to denitrifying bacteria. To address this question, we monitored nitrate removal, denitrification and carbon dynamics in a pilot-scale denitrification wall for 5 yr. The wall continuously removed more than 95% of the incoming nitrate in groundwater, which ranged from 5 to 15 mg N L(-1). We did not detect decreases in total carbon during the 5-yr study. Available carbon declined for the first 200 days after the wall was constructed but has since remained relatively constant. While microbial biomass has varied between 350 and 550 microg C g(-1) there was no downward trend, suggesting that carbon availability was not limiting the size of the microbial population. However, there was a large decrease in denitrifying population, as indicated by declines in denitrifying enzyme activity. Despite this decrease, denitrification rates have remained high enough to remove nitrate from groundwater and denitrification was limited by nitrate rather than by carbon. Our data demonstrates that there was sufficient available carbon in this denitrification wall to support denitrification and nitrate removal for at least 5 yr.     

Denitrification rates in relation to stream sediment characteristics

Potential rates of nitrate removal were studied in sediments from three Ontario rivers that differed in texture, organic carbon contents and other characteristics. Intact 0–5 cm depth sediment cores from 22 sites on each river were overlain with aerated 5 mg 1⁻¹ NO₃⁻-N solution and incubated in the laboratory at 21°C for 48 h. Rates of nitrate-N loss from the overlying solutions varied from 37 to 412 mg m⁻² day⁻¹ for a 24 h incubation period. The acetylene blockage technique was used with nitrate amended sediments to evaluate the relative importance of denitrification and nitrate reduction to ammonium. Denitrification accounted for 80–100% of the nitrate loss in the majority of sediment samples tested. Rates of nitrate loss for the 24 h period exhibited a highly significant positive correlation (r = 0.82–0.89) with the water-soluble carbon content of the sediments in each river. Significant relationships were also observed between nitrate loss and organic carbon, total nitrogen and sediment ammonium. A decline in nitrate loss via denitrification and increased nitrate reduction to ammonium was correlated with the organic carbon and water-soluble carbon content of the stream sediments.     

Denitrification and dissimilatory nitrate reduction to ammonium (DNRA) in a temperate re-connected floodplain

The relative magnitudes of, and factors controlling, denitrification and dissimilatory nitrate reduction to ammonium (DNRA) were measured in the soil of a re-connected temperate floodplain divided into four different land management zones (grazing grassland, hay meadow, fritillary meadow and a buffer zone). Soil samples were collected from each zone to measure their respective potentials for nitrate attenuation using ¹⁵N both at the surface and at depth in the soil column and additional samples were collected to measure the lability of the organic carbon. Denitrification capacity ranged between 0.4 and 4.2 (μmol N g⁻¹ dry soil d⁻¹) across the floodplain topsoil and DNRA capacity was an order of magnitude lower (0.01-0.71 μmol N g⁻¹ d⁻¹). Land management practice had a significant effect on denitrification but no significant effects were apparent for DNRA. In this nitrogen-rich landscape, spatial heterogeneity in denitrification was explained by differences in lability and the magnitude of organic carbon associated with different management practices (mowing and grazing). The lability of organic carbon was significantly higher in grazing grassland in comparison to other ungrazed areas of the floodplain, and consequently denitrification capacity was also highest in this area. Our results indicate that bacteria capable of DNRA do survive in frequently flooded riparian zones, and to a limited extent, compete with denitrification for nitrate, acting to retain and recycle nitrogen in the floodplain. Exponential declines in both denitrification and DNRA capacity with depth in the floodplain soils of a hay meadow and buffer zone were controlled primarily by the organic carbon content of the soils. Furthermore, grazing could be employed in re-connected, temperate floodplains to enhance the potential for nitrate removal from floodwaters via denitrification.     

Nitrogen transformation in a denitrification layer irrigated with dairy factory effluent

Adoption of land-based effluent treatment systems can be constrained by the costs and availability of land. Sufficient land area is needed to ensure nitrate leaching from applied effluent is minimised. One approach to decrease required land area is to enhance N removal by denitrification. Layers of organic matter (100 mm thick) were installed below topsoil of a site irrigated with dairy factory effluent. These "denitrification" layers were tested to determine whether they could decrease nitrate leaching by increasing denitrification. Four plots (10x10 m2 each) were constructed with a denitrification layer installed at 300 mm below the surface, and N losses were measured in leachate using suction cups every 3 weeks for 19 months. N in leachate was compared with 4 control plots. Denitrifying enzyme activity, nitrate concentrations, and carbon availability were measured in samples collected from the denitrification layers. These measurements demonstrated that denitrification occurred in the layer; however, denitrification rates were not sufficiently high to significantly decrease nitrate leaching. Total N leaching was 296 kg N ha(-1) from control plots and 238 kg N ha(-1) from plots with denitrification layers; a total of 798 kg N ha(-1) was applied in effluent. More than 50% of the leached N to 40 cm was as organic N, presumably due to bypass flow. Other studies have demonstrated that thicker denitrification layers (more than 300 mm) can reduce nitrate leaching from small-scale septic tank drainage fields but this study suggests that it is probably not practical to use denitrification layers at larger scales.     

补充生物质强化水平潜流湿地去除硝酸盐氮研究

针对垂直流-水平流组合人工湿地的水平流段反硝化碳源不足的问题,研究了投加香蒲枯叶对去除硝酸盐氮及出水水质的影响.结果表明,投加经过碱处理和未处理的香蒲枯叶均可以提高水平潜流人工湿地系统对硝酸盐氮的去除速率.在进水硝酸盐氮为50 mg/L时,投加经碱处理的香蒲枯叶后,运行初期的出水硝酸盐氮<7 mg/L,去除速率可达12.18 S/(m~3·d);投加未处理的香蒲枯叶后,运行初期的出水硝酸盐氮<15 mg/L,去除速率为9.21 g/(m~3·d).投加香蒲枯叶后,系统出水总氮的变化趋势与硝酸盐氮的一致.     

进水N/S值对同步脱硫反硝化特性的影响

研究了不同进水N/S值条件下,不同接种物的厌氧体系的同步脱硫反硝化特性。结果表明:在N/S为0.6或0.4的条件下,3个体系对硫化物的去除率均达到90%以上,其中以进水N/S为0.4时产生的悬浮态硫最多;硝态氮的去除特性与硫化物不同,3个体系对硝态氮的去除率均在进水N/S为1.0时达到100%,且此时N2的产量也最大。可见,尽管同步脱硫反硝化工艺具备同时脱氮及除硫的能力,但其进水N/S的控制值却不相同。对于脱硫而言,最佳的进水N/S为0.4;对于脱氮而言,最佳的进水N/S为1.0。此外,研究发现3个不同接种物的厌氧体系对硫化物及硝态氮的去除途径不同,进水N/S值的影响也有差异。对于接种了厌氧污泥的体系,存在自养反硝化和异养反硝化的竞争,改变进水N/S值可调节二者的竞争,高N/S值会抑制硫化物自养反硝化过程,降低对硫化物的去除率;对于接种脱氮硫杆菌的纯菌体系,多硫自催化反应会与硫化物自养反硝化反应竞争硫化物,降低对硝态氮的去除率,高N/S值会导致出水硝态氮浓度较高;对于添加脱氮硫杆菌的强化厌氧污泥体系,以硫化物自养反硝化过程为主,最佳的N/S为0.4。     

Control of denitrification in a septage-treating artificial wetland: the dual role of particulate organic carbon

We examined the factors controlling organic carbon (C) cycling and its control of nitrogen (N) removal via denitrification in an aerated artificial wetland treating highly concentrated wastewater to nutrient-removal standards. Processing of organic material by the septage-treating wetland affected the biological reactivity (half-life, or t1/2) of organic C pools through microbial degradation and gravity fractionation of the influent septage. Primary sedimentation fractionated the initial septage material (t1/2 = 8.4d) into recalcitrant waste solids (t1/2 = 16.7d) and highly labile supernatant (t1/2 = 5.0d), allowing this reactive fraction to be further degraded during treatment in aerobic wetland tanks until a less labile material (t1/2 = 7.3d) remained. Organic C contributions from in situ fixation by nitrifying bacteria or algae in these tanks were small, about 1% of the C degradation rate. In the aerated tanks, denitrification was correlated with particulate organic C loading rates, although the average C required (0.35 mg C L(-1)h(-1)) to support denitrification was only 12% of the total C respiration rate (2.9 mg C L(-1)h(-1)). Additions of plant litter (2.5g C L(-1)) to the aerated tanks under normal operating conditions doubled denitrification rates to 0.58 mg N L(-1)h(-1), and reduced effluent nitrate levels by half, from 12.7 to 6.4 mg N L(-1). However, C degradation within the plant litter (0.15mg C L(-1)h(-1)) was sufficient to have accounted for only 35% of the additional denitrification. Evidence from laboratory and full-scale plant litter additions as well as process monitoring indicates that the stimulation of denitrification is due to the respiration-driven formation of anaerobic microsites within particulate organic C. In this aerated highly C-loaded septage-treating wetland, anaerobic microsite, rather than C substrate availability limits denitrification.     

Microbial fuel cells for simultaneous carbon and nitrogen removal

The recent demonstration of cathodic nitrate reduction in a microbial fuel cell (MFC) creates opportunities for a new technology for nitrogen removal from wastewater. A novel process configuration that achieves both carbon and nitrogen removal using MFC is designed and demonstrated. The process involves feeding the ammonium-containing effluent from the carbon-utilising anode to an external biofilm-based aerobic reactor for nitrification, and then feeding the nitrified liquor to the MFC cathode for nitrate reduction. Removal rates up to 2 kg COD m(-3)NCC d(-1) (chemical oxygen demand: COD, net cathodic compartment: NCC) and 0.41 kg NO(3)(-)-Nm(-3)NCC d(-1) were continuously achieved in the anodic and cathodic compartment, respectively, while the MFC was producing a maximum power output of 34.6+/-1.1 Wm(-3)NCC and a maximum current of 133.3+/-1.0 Am(-3)NCC. In comparison to conventional activated sludge systems, this MFC-based process achieves nitrogen removal with a decreased carbon requirement. A COD/N ratio of approximately 4.5 g COD g(-1) N was achieved, compared to the conventionally required ratio of above 7. We have demonstrated that also nitrite can be used as cathodic electron acceptor. Hence, upon creating a loop concept based on nitrite, a further reduction of the COD/N ratio would be possible. The process is also more energy effective not only due to the energy production coupled with denitrification, but also because of the reduced aeration costs due to minimised aerobic consumption of organic carbon.     

深床反硝化生物滤池碳源优选研究

借助深床反硝化生物滤池对葡萄糖和乙酸钠两种碳源的挂膜及硝态氮去除性能进行了对比研究。试验结果表明,当碳氮比为3时,连续投加葡萄糖36 h以上,滤池内部开始进入缺氧环境,此时出水硝态氮浓度开始降低;而乙酸钠在碳氮比为3. 2时,需连续投加碳源26 h,出水DO才开始降低到0. 5 mg/L以下,此时滤池出水硝态氮浓度开始降低。当碳源均按照葡萄糖和乙酸钠的最佳碳氮比进行投加时,硝态氮最大去除率分别为82%和85%;此外,当以葡萄糖作为碳源时,反洗排水中MLSS约为乙酸钠的3倍。     

天然水中硝酸盐氮氧同位素测试技术研究进展

水环境的硝酸盐污染是一个全球性环境问题。识别水环境中硝酸盐的来源及其转化,对更好地管理水质是十分重要的。硝酸盐的稳定氮氧同位素组成可有效识别水环境中NO 3-来源及其转化。本文总结了典型的测定硝酸盐中稳定氮氧同位素组成的方法:石墨燃烧法、AgNO3-离子交换法、细菌反硝化法、亚硝酸盐去除联合细菌反硝化法、两步化学还原法、连续选择性细菌还原法,同时对这些方法的优缺点进行了评述。最后分析了检测技术中存在的共同问题及其发展方向:δ18O精确度仍有提高的潜力;把NO 3-从水中独立提取出来进行三氧同位素的测试方法还需改进和提高;水样的采集、保存有待进一步改进。