底曝式氧化沟脱氮除磷的运行控制

结合工程实例,探讨了底曝式氧化沟系统的MLSS、泥龄、DO等运行参数的控制问题,通过对各参数进行分析和优化调整,使该工艺不但具有良好的脱氮效率,而且具有较好的除磷效果。     

DEAMOX--new biological nitrogen removal process based on anaerobic ammonia oxidation coupled to sulphide-driven conversion of nitrate into nitrite

This paper reports about the successful laboratory testing of a new nitrogen removal process called DEAMOX (DEnitrifying AMmonium OXidation) for treatment of typical strong nitrogenous wastewater such as baker's yeast effluent. The concept of this process combines the recently discovered anammox (anaerobic ammonium oxidation) reaction with autotrophic denitrifying conditions using sulphide as an electron donor for the production of nitrite from nitrate within an anaerobic biofilm. To generate sulphide and ammonia, a Upflow Anaerobic Sludge Bed (UASB) reactor was used as a pre-treatment step. The UASB effluent was split and partially fed to a nitrifying reactor (to generate nitrate) and the remaining part was directly fed to the DEAMOX reactor where this stream was mixed with the nitrified effluent. Stable process performance and volumetric nitrogen loading rates of the DEAMOX reactor well above 1000 mgN/l/d with total nitrogen removal efficiencies of around 90% were obtained after long-term (410 days) optimisation of the process. Important prerequisites for this performance are appropriate influent ratios of the key species fed to the DEAMOX reactor, namely influent N-NO(x)/N-NH(4) ratios >1.2 (stoichiometry of the anammox reaction) and influent S-H(2)S/N-NO(3) ratios >0.57 mgS/mgN (stoichiometry of the sulphide-driven denitrification of nitrate to nitrite). The paper further describes some characteristics of the DEAMOX sludge as well as the preliminary results of its microbiological characterisation.     

氧化沟系统除磷效果的提高途径

介绍了氧化沟技术的发展现状，通过分析生物除磷效果的影响制约因素以及氧化沟系统除磷效果差的症结，从加设厌氧池、减小硝态氮的影响等方面，提出了提高氧化沟系统除磷效果的有效途径。     

Achieving biofilm control in a membrane biofilm reactor removing total nitrogen

Membrane biofilm reactors (MBfR) utilize membrane fibers for bubble-less transfer of gas by diffusion and provide a surface for biofilm development. Nitrification and subsequent autotrophic denitrification were carried out in MBfR with pure oxygen and hydrogen supply, respectively, in order to remove nitrogen without the use of heterotrophic bacteria. Excessive biomass accumulation is typically the major cause of system failure of MBfR. No biomass accumulation was detected in the nitrification reactor as low-level discharge of solids from the system balanced out biomass generation. The average specific nitrification rate during 250 days of operation was 1.88 g N/m² d. The subsequent denitrification reactor, however, experienced decline of performance due to excessive biofilm growth, which prompted the implementation of periodic nitrogen sparging for biofilm control. The average specific denitrification rate increased from 1.50 g N/m² d to 1.92 g N/m² d with nitrogen sparging, over 190 days thus demonstrating the feasibility of stable long-term operation. Effluent suspended solids increased immediately following sparging: from an average of 2.5 mg/L to 12.7 mg/L. This periodic solids loss was found unavoidable, considering the theoretical biomass generation rates at the loadings used. A solids mass balance between the accumulating and scoured biomass was established based on the analysis of the effluent volatile solids data. Biofilm thickness was maintained at an average of 270 μm by the gas sparging biofilm control. It was concluded that biomass accumulation and scouring can be balanced in autotrophic denitrification and that long-term stable operation can be maintained.     

Estimation of nitrogen removal rate in aqueous phase based on delta15N in microorganisms in solid phase

Microbial nitrification and denitrification are important processes for removing nitrogenous compounds in aqueous systems. Nitrogen removal rate estimation is essential for controlling nitrogen removal processes and modeling the nitrogen cycle in ecosystems. The model described the relationship between ammonium removal rate (aqueous phase) and the nitrogen stable isotope ratio (delta15N) of microorganisms (solid phase) when a coupled nitrification-denitrification process occurs and assimilation and advections are maintained in a steady state. An oxidation ditch in a municipal wastewater treatment plant was evaluated for 3 years using the model. The ammonium removal rate was calculated from the data of delta15N of the activated sludge, it correlated significantly with the observed removal rate. The isotope fractionation factor (epsilon) was determined to be -5.5 per thousand by using a nonlinear method. The model and obtained factor value were applicable for standard activated-sludge processes performed in parallel in the oxidation ditch and a river watershed. The model may help illustrate nitrogen behavior in ecosystems.     

Comparison of control strategies for nitrogen removal in an activated sludge process in terms of operating costs: a simulation study

In this paper several control strategies for nitrogen removal are proposed and evaluated in a benchmark simulation model of an activated sludge process. The goal is to determine which control strategy delivers better performance with respect to plant operating costs. In the study, constant manipulated variables and various PI and feedforward control strategies are tested and compared with predictive control, which uses an ideal process model. The control strategies differ in the information used about the process (number of sensors and sensor location) and in the complexity of the control algorithms. To determine the set-points that yield optimal operating costs, an operational map is constructed for each control strategy. Results of the simulation show that with PI and feedforward controllers almost the same optimal operating costs can be achieved as with more advanced MPC algorithms under various plant operating conditions. More advanced control algorithms are advantageous only in cases where the plant is highly loaded and if stringent effluent fines are imposed by legislation.     

Study on two operating conditions of a full-scale oxidation ditch for optimization of energy consumption and effluent quality by using CFD model

The operating condition of an oxidation ditch (OD) has significant impact on energy consumption and effluent quality of wastewater treatment plants (WWTPs). An experimentally validated numerical tool, based on computational fluid dynamics (CFD) model, was proposed to optimize the operating condition by considering two important factors: flow field and dissolved oxygen (DO) concentration profiles. The model is capable of predicting flow pattern and oxygen mass transfer characteristics in ODs equipped with surface aerators and submerged impellers. Performance demonstration and comparison of two operating conditions (existing and improved) were carried out in two full-scale Carrousel ODs at the Ping Dingshan WWTP in Henan, China. A moving wall model and a fan model were designed to simulate surface aerators and submerged impellers, respectively. Oxygen mass transfer in the ditch was predicted by using a unit analysis method. In aeration zones, the mass inlets representing the surface aerators were set as one source of DO. In the whole straight channel, the oxygen consumption was modeled by using modified BOD-DO model. The following results were obtained: (1) the CFD model characterized flow pattern and DO concentration profiles in the full-scale OD. The predicted flow field values were within 1.98 ± 4.28% difference from the actual measured values while the predicted DO concentration values were within −4.71 ± 4.15% of the measured ones, (2) a surface aerator should be relocated to around 15 m from the curve bend entrance to reduce energy loss caused by fierce collisions at the wall of the curve bend, and (3) DO concentration gradients in the OD under the improved operating condition were more favorable for occurrence of simultaneous nitrification and denitrification (SND).     

Influence of operational parameters on nitrogen removal efficiency and microbial communities in a full-scale activated sludge process

To improve the efficiency of total nitrogen (TN) removal, solid retention time (SRT) and internal recycling ratio controls were selected as operating parameters in a full-scale activated sludge process treating high strength industrial wastewater. Increased biomass concentration via SRT control enhanced TN removal. Also, decreasing the internal recycling ratio restored the nitrification process, which had been inhibited by phenol shock loading. Therefore, physiological alteration of the bacterial populations by application of specific operational strategies may stabilize the activated sludge process. Additionally, two dominant ammonia oxidizing bacteria (AOB) populations, Nitrosomonas europaea and Nitrosomonas nitrosa, were observed in all samples with no change in the community composition of AOB. In a nitrification tank, it was observed that the Nitrobacter populations consistently exceeded those of the Nitrospira within the nitrite oxidizing bacteria (NOB) community. Through using quantitative real-time PCR (qPCR), nirS, the nitrite reducing functional gene, was observed to predominate in the activated sludge of an anoxic tank, whereas there was the least amount of the narG gene, the nitrate reducing functional gene.     

Effect of heat recovery from raw wastewater on nitrification and nitrogen removal in activated sludge plants

By recovery of heat from the raw wastewater in the sewer system, the influent temperature of a wastewater treatment plant (WWTP) is reduced. This can have a negative effect on nitrification in the WWTP, since this process strongly depends on temperature. The analysis of the temperature regime in the WWTP of Zurich, Switzerland, revealed that in the cold season, the effluent temperature is about 0.7 degrees C higher than the influent temperature and that nitrification is not affected by a decrease of the influent wastewater temperature lasting for a couple of hours only, but is significantly affected by a longer lasting temperature decrease. Three diagrams were developed with a steady-state model, from which the consequences of a permanent temperature decrease on the nitrification safety factor, aerobic sludge retention time and total nitrogen removal can be evaluated. Using simulations with a dynamic model, calibrated for the Zurich WWTP, a quantitative relationship between the wastewater temperature and the ammonium effluent concentration was established. This relationship can, in combination with measured effluent concentrations of an existing WWTP, be used to predict the increase of the ammonium effluent concentration in this plant resulting from a permanent decrease of the wastewater influent temperature.     

Dynamics of phosphorus, nitrogen and carbon removal in a horizontal subsurface flow constructed wetland

The dynamics of nitrogen (N), phosphorus (P) and carbon (C) accumulation in the filter material of a horizontal subsurface constructed wetland (HSSF CW; established in 1997) and in a specially designed oil-shale ash filter (2002) for P retention have been studied. Concentrations of N, P and C in filter media (coarse sand) in the HSSF beds show an increasing trend. Both the annual accumulation of P and increasing outflow concentrations of P in the HSSF CW reflect the possible saturation of filter media with P after 8 years working. Tested ash material derived from oil-shale combustion demonstrated very high P removal efficiency in laboratory batch experiments. However, during the first 4 months of the in situ ash filter experiment, the efficiency of P removal was about 71% (an average outflow concentration of 1.9 mg L(-1) was achieved). Subsequently, the efficiency decreased to 10-20%, which might be a sign of saturation or clogging due to quick biofilm development on the ash particles. The increasing of hydraulic retention time and the improvement of design for maximal contact between material and wastewater are considered to be key factors that can provide optimal pH for the removal processes.     

Annual cycle of nitrogen removal by a pilot-scale subsurface horizontal flow in a constructed wetland under moderate climate

The annual course of nitrogen removal in a stable operating subsurface horizontal flow constructed wetland (SSF) in a moderate climate was evaluated using a large pool of data from 4 years of operation. In spring and autumn removal efficiencies were found to depend on the nitrogen load in a linear mode. The efficiencies in winter and summer differed extremely (mean removal rates of 0.15/0.7 g m(-2) d(-1) (11%/53%) in January/August) and were independent of the nitrogen load (0.7-1.7 g m(-2) d(-1)) in principle. Oscillations of the removal rates in spring, forming several maxima, suggest seasonal specific effects caused by the dynamics of the plant-physiology finally determining the nitrification efficiency, i.e. via O(2)-supply. Nitrification is limited by temperature during all seasons and surprisingly in midsummer additionally restricted by other seasonal aspects forming a clear-cut relative nitrification minimum (mean rate of 0.43 g m(-2) d(-1) (32%)) in July. The importance and the effect of the plants' gas exchange and oxygen input into the rhizosphere are discussed. Denitrification was nearly complete in midsummer and was clearly restricted at seasonal temperatures below 15 degrees C.     

The use of hybrid constructed wetlands for wastewater treatment with special attention to nitrogen removal: A review of a recent development

The hybrid systems were developed in the 1960s but their use increased only during the late 1990s and in the 2000s mostly because of more stringent discharge limits for nitrogen and also more complex wastewaters treated in constructed wetlands (CWs). The early hybrid CWs consisted of several stages of vertical flow (VF) followed by several stages of horizontal flow (HF) beds. During the 1990s, HF–VF and VF–HF hybrid systems were introduced. However, to achieve higher removal of total nitrogen or to treat more complex industrial and agricultural wastewaters other types of hybrid constructed wetlands including free water surface (FWS) CWs and multistage CWs have recently been used as well. The survey of 60 hybrid constructed wetlands from 24 countries reported after 2003 revealed that hybrid constructed wetlands are primarily used on Europe and in Asia while in other continents their use is limited. The most commonly used hybrid system is a VF–HF constructed wetland which has been used for treatment of both sewage and industrial wastewaters. On the other hand, the use of a HF–VF system has been reported only for treatment of municipal sewage. Out of 60 surveyed hybrid systems, 38 have been designed to treat municipal sewage while 22 hybrid systems were designed to treat various industrial and agricultural wastewaters. The more detailed analysis revealed that VF–HF hybrid constructed wetlands are slightly more efficient in ammonia removal than hybrid systems with FWS CWs, HF–VF systems or multistage VF and HF hybrid CWs. All types of hybrid CWs are comparable with single VF CWs in terms of NH₄-N removal rates. On the other hand, CWs with FWS units remove substantially more total nitrogen as compared to other types of hybrid constructed wetlands. However, all types of hybrid constructed wetlands are more efficient in total nitrogen removal than single HF or VF constructed wetlands.     

Simultaneous microbial removal of carbon,nitrogen, and phosphorus in a modified anaerobic/aerobic (A/O) bioreactor with no phosphorus release

A modified anaerobic/aerobic (A/O) bioreactor that simultaneously removed carbon, nitrogen ( ‐N) and phosphorus ( ‐P) was continuously run and debugged. After 34 days of reactor operation, the removal efficiencies of ‐N, carbon (glucose) and ‐P reached 99.26, 95.81 and 94.35%, respectively. Notably, the ammonium removal with no accumulation of nitrite ( ‐N) and nitrate ( ‐N) in the anaerobic part supported the occurrence of simultaneous nitrification and denitrification and no ‐P was released during the removal process of phosphorus. Moreover, the principal component analysis and response surface methodology based on the Box–Behnken design were applied to determine the optimal removal conditions for volatile suspended solids (VSS) (335 mg/L), ‐N (60 mg/L), glucose (900 mg/L) and pH (7). Finally, phylogenetic analysis of the bacterial consortium was conducted by denaturing gradient gel electrophoresis, which demonstrated that Clostridium and Proteobacteria were the potential functional groups in the anaerobic tank of the A/O bioreactor.     

溶解氧对含氨氮地下水生物除铁除锰效果的影响

采用生物滤柱进行了地下水除铁除锰效果的研究,通过检测滤柱不同滤层深度Mn^2＋、Fe^2＋、NH4^＋-N与DO浓度的变化,研究了各离子的去除效果与DO的关系,并对比了不同DO水平和不同滤速时离子的去除情况。结果表明,铁比锰和氨氮更优先被去除,滤速越低,溶解氧消耗越多。     

动冰力模型参数对墩柱结构非线性地震反应影响研究

结冰水域墩柱结构往往被大片的海冰包围,地震作用下,把冰与墩柱结构的相互作用以动冰力模型的形式考虑将大大简化结构地震反应的工作量,但合理的动冰力模型参数仍有待于进一步研究。本文对已有冰力模型进行分析,在适用于地震动力反应分析的Croteau冰力模型的基础上,建立冰水域墩柱结构地震反应计算模型,并以一桥墩为研究对象,研究该冰力模型参数对墩柱结构地震非线性反应的影响。结果表明:地震作用下海冰对桥墩的影响随着冰力模型中加载位移的增大而减小,且加载位移对墩底的剪力影响较小而对弯矩影响较大;动冰力模型中的位移比小于1.5时,结构的地震响应偏小,为了冰水域墩柱结构的抗震设计更安全,建议动冰力模型中位移比取2.0～2.5。     

地面沉降与地下水位动态监测数据模型的研究

针对西安市大量的地面沉降与地下水位长期观测数据，采用数值模拟方法建立地面沉降监测点沉降过程曲线模型和地下水位监测井水位升降曲线模型并编制程序，并对地面沉降与地下水位监测数据进行内插外推计算、分析和研究，进而对地面沉降和地下水动态进行预测预报。     

基于代理模型的无砟轨道模拟方法及其在车-线-桥分析中的应用

为解决轨道结构有限元建模的复杂性和计算效率低等问题,针对桥上双块式无砟轨道结构,该文提出一种新型的无砟轨道简化方法：K-G离散点支承梁模型。利用自适应Kriging代理模型,建立了无砟轨道简化模型与精细化模型响应间的对应关系,采用遗传算法(GA)确定了简化模型的结构参数,并与精细化模型进行对比,验证了简化模型的准确性。最后,将该无砟轨道简化模拟方法应用于某大跨铁路拱桥,进行车-线-桥耦合分析,结果表明：K-G离散点支承梁模型的竖向位移响应计算结果与精细化有限元模型结果比较吻合,最大相对误差不超过5%,可以进一步应用于车-线-桥耦合振动分析。     

A Bayesian changepoint-threshold model to examine the effect of TMDL implementation on the flow-nitrogen concentration relationship in the Neuse River basin

In-stream nutrient concentrations are well known to exhibit a strong relationship with river flow. The use of flow measurements to predict nutrient concentrations and subsequently nutrient loads is common in water quality modeling. Nevertheless, most adopted models assume that the relationship between flow and concentration is fixed across time as well as across different flow regimes. In this study, we developed a Bayesian changepoint-threshold model that relaxes these constraints and allows for the identification and quantification of any changes in the underlying flow-concentration relationship across time. The results from our study support the occurrence of a changepoint in time around the year 1999, which coincided with the period of implementing nitrogen control measures as part of the TMDL program developed for the Neuse Estuary in North Carolina. The occurrence of the changepoint challenges the underlying assumption of temporal invariance in the flow-concentrations relationship. The model results also point towards a transition in the river nitrogen delivery system from a point source dominated loading system towards a more complicated nonlinear system, where non-point source nutrient delivery plays a major role. Moreover, we use the developed model to assess the effectiveness of the nitrogen reduction measures in achieving a 30% drop in loading. The results indicate that while there is a strong evidence of a load reduction, there still remains a high level of uncertainty associated with the mean nitrogen load reduction. We show that the level of uncertainty around the estimated load reduction is not random but is flow related.     

热力盾构隧道先盾后井施工衬砌接头变形机理与控制

先盾后井是热力盾构隧道建设中一种高效经济的施工工法。结合中国首例大断面热力盾构隧道工程,基于纵向等效连续化模型和弹性地基梁理论,对施工过程中衬砌接头受力特征和变形机理进行了分析,并提出控制措施;然后建立了衬砌接头全断面接触面单元数值模型,对控制效果进行分析和评价;最后通过现场监测,得到了不同施工阶段管片纵向轴力及接缝变形规律。研究结果表明:先盾后井工法施工中,衬砌接头变形分为两个阶段:基坑开挖及管片拆除,其中管片拆除为接头变形的主因,基坑施工中,基底卸荷产生的负弯矩作用于隧道上,导致邻近竖井管片底部轴力减小、环缝张开,拆除基坑内管片时,作用于端头管片的残余盾构推力和螺栓预紧力消失,导致管片纵向轴力进一步衰减,环缝二次张开;根据现场监测结果,提出的对邻近竖井的管片纵向拉紧并复紧连接螺栓,进行混凝土铺底及衬砌背后二次注浆的控制措施能够有效控制轴力损失,减小接头变形,施工中环向接缝最大张开量3.51 mm,满足隧道防水要求;采用全断面接触面单元建立的数值模型可以较为精确地模拟施工中管片接头力学行为,其结果可作为控制效果评价参考依据。     

关于框架结构填充墙裂缝成因及控制

对框架结构填充墙裂缝的特点及出现部位进行了阐述,分析了框架填充墙裂缝产生的原因,在此基础上提出了裂缝的预防和控制措施,以期减少框架结构填充墙的裂缝,确保工程质量。