Model concept for nitrate and nitrite utilization during anoxic transformation in the bulk water phase of municipal wastewater under sewer conditions.

A two-stage anoxic transformation process, involving growth of biomass utilizing two types of different electron acceptors, namely nitrate and nitrite, has been observed. The present water quality modules established for sewer processes cannot account for the two-stage process. This paper outlines the development of a model concept that enables the two-stage anoxic transformation process to be simulated. The proposed model is formulated in a matrix form that is similar to the Activated Sludge Models and Sewer Process Model matrices. The model was successfully applied to simulate changes in nitrate and nitrite concentrations during anoxic transformations in the bulkwater phase of municipal wastewater.     

Long-term evaluation of a sequential batch reactor (SBR) treating dairy wastewater for carbon removal.

Many dairy industries have been using SBR wastewater treatment plants because they allow optimal working condition to be reached. However, to take advantage of SBR capabilities, strong process automation is needed. The aim of this work is to study the factors that influence SBR performance to improve modelling and control. To better understand the whole process we studied the kinetic modelling, the carbon removal mechanism and the relation between reactor performance, aerobic heterotrophic activity and bacterial population dynamics (by terminal restriction fragment length polymorphisms of 16S rDNA, T-RFLP). The heterotrophic activity values presented high variability during some periods; however, this was not reflected on the reactor performance. As sludge health indicator, the average activity in a period was better than individual values. Although all the carbon removal mechanisms are still unclear for this process, they seemed to be influenced by non-respirometric ways (storage, biosorption, accumulation, etc.). The variability of heterotrophic activity could be correlated with the bacterial population diversity over time. Despite the high variability of the activity, a simple kinetic model (pseudo ASM1) based on apparent constant parameters was developed and calibrated. Such modellisation provided a good tool for control purposes.     

Long-term nitrate trends in the river trent and four major tributaries

Nitrate levels which have been rising in many British rivers for at least thirty years have become of particular interest since Britain adopted the EC Drinking Water Directive. The literature examining nitrate trends in the rivers of the U.K. and Eire is reviewed. Long-term nitrate concentration trends are derived for eight sites in the River Trent drainage system. These include sites on two rural tributaries, two urbanized tributaries, and the main river. Currently, mean annual concentrations for these sites range from about 4.0 mg1^?1N in the rural catchments, to 12.4 mg 1^?1 N in the urbanized tributaries, and to between 8.7 mg 1^?1N and 11.0 mg 1^?1 N along the mainstream. Moreover rates of increase of nitrate concentration of approximately 0.06 mg 1^?1 N yr ^?1 in the rural catchments, contrast with values up to 0.20 mg 1^?1 N yr ^?1 in the two urbanized tributaries and River Trent. Long term nitrate loads have been calculated for the River Trent at Nottingham using a discharge weighted mean interval method. This method probably provides the best available estimate of nitrate loads calculable from irregular data of variable sampling frequency for lowland rivers. Annual nitrate loads varied between 10700t yr ^?1 and 29 800t yr ^?1 over the period of record. A rate of increase in nitrate load of 455 t yr ^?1 was obtained. The increases in nitrate concentrations and loads within the Trent basin are matched by similar rates of increase in other European catchments.     

关于测定水中亚硝酸盐氮、硝酸盐氮、总氮的方法探讨

含氮化合物是水体污染监测中的重要指标,因此需要可靠精确的检测方法作为支撑。本文采用气相分子吸收光谱法对亚硝酸盐氮、硝酸盐氮、总氮进行检测分析,结果表明:标准曲线相关系数均大于0.999,检出限、精密度、准确度、加标回收率均满足方法要求。表明气相分子吸收光谱法具有较高的灵敏度和准确度,稳定性好,可实现样品在线自动稀释和在线消解,简化样品前处理过程,更适用于大批量含氮化合物水质检测工作。     

Rate of nitrate production during a two-stage nitrification batch reaction.

The two steps of nitrification, namely the oxidation of ammonia to nitrite and nitrite to nitrate, often need to be considered separately in process studies. It has been assumed that these two reactions can be described by single Monod models. In this paper, the suitability of the single Monod model for describing nitrite oxidation to nitrate is discussed. The measured rate of nitrate production during a batch reaction is presented. For the system studied it was found that nitrate production actually increased after the completion of ammonia oxidation. It is suggested that the reason for the increase was a combination of: (i) likely competition for oxygen when both substrates were present, and (ii) a decrease in ammonia inhibition of nitrite oxidisers with the removal of ammonia. The result is that a single Monod expression (based on nitrite as the substrate) could not be used to describe nitrate production. In these types of systems the consequence of oxygen limitation and substrate inhibition should also be considered.     

Study of different methods for enhancing the nitrate removal efficiency of a zero-valent metal process.

This study explores the effect of several enhancing methods, namely acid wash pretreatment, ultrasound treatment and addition of nickel catalyst on the nitrate removal efficiency of three zero-valent metals--iron, aluminium and zinc. It is hoped that by learning about the major reaction pathways of nitrate removal with zero-valent metals and the main factors influencing the reactivity of those zero-valent metals, optimum process conditions may be identified. The study results show that direct transfer of electrons is the major reaction pathway. Thus increasing a clean, fresh metal surface and decreasing the thickness of the diffusion layer to accelerate mass transfer are the main determinants of reaction rate. In the absence of a clean, fresh metal surface, the catalytic reaction of nickel becomes the primary removal pathway.     

Sensitivity analysis of a biofilm model describing mixed growth of nitrite oxidisers in a CSTR.

A simple kinetic model has been developed for describing nitrite oxidation by autotrophic aerobic nitrifiers in a CSTR reactor, in which mixed (suspended and attached) growth conditions are prevailing. In this work, a critical dimensionless parameter is identified containing both biofilm characteristics and microbial kinetic parameters, as well as the specific (per volume) surface of the reactor configuration used. Evaluation of this dimensionless parameter can easily provide information on whether or not wall attachment is critical, and should be taken into account either in kinetic studies or in reactor design, when specific pollutants are to be removed from the waste influent stream. The effect of bulk dissolved oxygen (DO) concentration on the validity of this model is addressed and minimum non-limiting DO concentrations are proposed depending on the reactor configuration.     

Modelling nitrate losses from agricultural activities on a national scale.

The Nitrogen Risk Assessment Model for Scotland (NIRAMS) has been developed as a screening tool for prediction of streamwater N concentrations draining from agricultural land in Scotland. The objective of the model is to be able to predict N concentrations for ungauged catchments, to fill gaps in monitoring data and provide guidance in relation to policy development. The model uses national land use, soils and meteorology data sets and has been developed within an ArcView GIS user interface. The model includes modules to calculate N inputs to the land, residual N remaining at the end of the growing season, weekly time-series of leached N and transport of N at the catchment scale. The N leaching and transport are. controlled by hydrological modules, including a national water balance model and a catchment scale transport model. Preliminary testing of NIRAMS has been carried out on eight Scottish catchments, diverse in terms of geographic location as well as land use. The model is capable of predicting the correct mean level of stream N concentrations, as well as the basic characteristics of seasonal variation. As such the model can be of value for providing estimates of N concentrations in ungauged areas.     

Integrated soft sensor model for flow control.

Tighter discharge permits often require wastewater treatment plants to maximize utilization of available facilities in order to cost-effectively reach these goals. Important aspects are minimizing internal disturbances and using available information in a smart way to improve plant performance. In this study, flow control throughout a large highly automated wastewater treatment plant (WWTP) was implemented in order to reduce internal disturbances and to provide a firm foundation for more advanced process control. A modular flow control system was constructed based on existing instrumentation and soft sensor flow models. Modules were constructed for every unit process in water treatment and integrated into a plant-wide model. The flow control system is used to automatically control recirculation flows and bypass flows at the plant. The system was also successful in making accurate flow estimations at points in the plant where it is not possible to have conventional flow meter instrumentation. The system provides fault detection for physical flow measuring devices. The module construction allows easy adaptation for new unit processes added to the treatment plant.     

考虑残留氮对非稳定流场硝态氮淋失贡献的传递函数模型Ⅰ.地中渗透计验证

本文通过引入溶质迁移距离的概率密度函数的修正系数，将Jury等提出的模拟非稳定流条件下土壤保守溶质运移的传递函数模型理论扩展到考虑土壤剖面存在残留氮分布的土壤中，构造了一个能估算表施和残留氮对土壤硝态氮淋失动态贡献的传递函数模型。通过与野外地中渗透计实验资料的对比，表明该模型具有一定的仿真精度，模拟的土壤硝态氮累积淋失量的相对误差小于15％。     

Long-term monitoring and proposed diffuse pollution control of a tropical reservoir.

This paper presents the results of 30 years of water quality monitoring in a tropical water supply reservoir (Vargem das Flores, Brazil). This water body is subjected to eutrophication problems caused by point sources (discharge of untreated sewage) and diffuse pollution (agricultural use in the drainage basin). Emphasis is given here on the estimation of nutrient loads and on the study of the N/P ratio in the water body. In spite of the prevalence of high N/P values, there is a clear trend in the dominance of cyanobacteria in the phytoplankton, which contradicts results from research in temperate aquatic environments. Some restoration measures for Vargem das Flores Reservoir are currently being implemented: construction of wastewater treatment plants, control of recreational activities, erosion control by hydroseeding and use of natural wetlands. Finally some management strategies in order to prevent algae input in the water abstraction system are discussed. Examples of these techniques are the installation of plastic barriers and the construction of an air curtain device.     

Characterisation of high-rate acidogenesis processes using a titration and off-gas analysis sensor.

The characteristics of the glucose degradation by acidogenesis processes were investigated both in a long-term operating laboratory-scale continuously stirred tank reactor and in short-term experiments utilising a titration and off-gas analysis (TOGA) sensor. The results obtained from continuous-flow experiments in both reactors demonstrated that the TOGA sensor can be applied as a useful tool for the study of acidogenesis processes under steady-state and dynamic conditions. No significant effect from the culture transfer could be detected in the study with the TOGA sensor. Furthermore, the variation of gas production rate could be monitored at real time by the TOGA sensor. The experiments showed that the distribution of acidogenic products in the liquid and the gas phase was significantly influenced by the hydraulic retention time at least in the short term.     

Towards a common benchmark for long-term process control and monitoring performance evaluation.

The COST/IWA benchmark simulation model has been available for seven years. Its primary purpose has been to create a platform for control strategy benchmarking of biological wastewater treatment processes. The fact that the benchmark has resulted in more than 100 publications, not only in Europe but also worldwide, demonstrates the interest for such a tool in the research community. In this paper, an extension of the benchmark simulation model no. 1 (BSM1) is proposed. It aims at facilitating evaluation of two closely related operational tasks: long-term control strategy performance and process monitoring performance. The motivation for the extension is that these two tasks typically act on longer time scales. The extension proposed here consists of 1) prolonging the evaluation period to one year (including influent files), 2) specifying time varying process parameters and 3) including sensor and actuator failures. The prolonged evaluation period is necessary to obtain a relevant and realistic assessment of the effects of such disturbances. Also, a prolonged evaluation period allows for a number of long-term control actions/handles that cannot be evaluated in a realistic fashion in the one week BSM1 evaluation period. In the paper, models for influent file design, parameter changes and sensor failures, initialization procedure and evaluation criteria are discussed. Important remaining topics, for which consensus is required, are identified. The potential of a long-term benchmark is illustrated with an example of process monitoring algorithm benchmarking.     

Effect of solid hold-up on nitrite accumulation in a biofilm reactor--molecular characterization of nitrifying communities.

Biological ammonium oxidation was carried out in two inverse turbulent bed reactors fed with synthetic mineral wastewater containing a high ammonium concentration (100 mg N-NH4+/L). Both reactors were started-up and operated in the same conditions except for the solid carrier concentration: the solid hold-up ratios applied, defined as the ratios of static to expanded bed height, were 0.1 and 0.3 in reactors R10 and R30 respectively. These two solid hold-up ratios generate different particle-to-particle collision frequencies and, therefore, detachment forces. The influence of solid hold-up on biofilm growth and nitrifying performance was studied from a macroscopic (i.e. nitrate and/or nitrite production) and microbiological point of view. After 60 days of operation, both reactors contained the same amount of biomass. However, R10 produced only nitrate while nitrite accumulated in R30. A comparison of microbial populations in the reactors showed that R10 contained both ammonium and nitrite oxidizing populations such as Nitrosomonas and Nitrospira, whereas in R30, ammonium oxidizing populations were much greater than those of nitrite oxidizers. The major ammonium-oxidizing organism was not the same in both reactors.     

On the effect of pharmaceuticals on bacterial nitrite oxidation.

Pharmaceuticals or their metabolites are partially excreted with urine or faeces ending up in raw sewage. Many of these substances are not biodegradable and their presence in influents of municipal wastewater treatment plants may cause adverse effects to sensitive biological processes such as nitrification, while on the other hand, they may go through the activated sludge process unreacted. The second step of nitrification, i.e. oxidation of nitrite to nitrate is particularly sensitive. Inhibition of this step under uncontrolled conditions may lead to accumulation of nitrite nitrogen in the plant effluent, a form of nitrogen which is particularly toxic. The effects caused by the presence of seven different pharmaceuticals to a culture of nitrite-oxidizing bacteria isolated from activated sludge are presented. These pharmaceuticals were ofloxacin, propranolol, clofibrate, triclosan, carbamazepine, diclofenac and sulfamethoxazole. Different effects were observed for each of the pharmaceuticals tested in this study. In the cases of ofloxacin and sulfamethoxazole significant inhibition was observed. Triclosan presented a substantial inhibitory effect on the substrate (nitrite) reduction rate. The long-term effect of triclosan on nitrite oxidizers was also examined in a CSTR reactor and conclusions were drawn regarding the reversibility of the inhibition caused by this compound.     

A nitrate biosensor based methodology for monitoring anoxic activated sludge activity.

An improved methodology based on a nitrate biosensor is developed and applied successfully for in-depth monitoring and study of anoxic activated sludge activities. The major advantages of the methodology are its simplicity, reliability and high data quality. The resulting data allowed for the first time to monitor anoxic respiration rate of activated sludge (nitrate uptake rate (NUR)) at a high time resolution making it clearly comparable with high frequency oxygen uptake rate (OUR) measurements obtained under aerobic conditions. Further, the anoxic respiration data resulting from a pulse addition of carbon source to endogenously respiring anoxic activated sludge shows a clear start-up phenomenon and storage tail that is usually also observed in high-frequency OUR measurements. Finally, the improved methodology can be expected to serve as an anoxic respirometer for activated sludge treatment plants where denitrification process occurs in single-step. Further, it can be used for a variety of purposes e.g. for toxicity and activity monitoring, process control and parameter estimation of the activated sludge process, similar to the aerobic respirometers.     

Long-term and seasonal nitrate trends illustrate potential prevention of large cyanobacterial biomass by sediment oxidation in Hamilton Harbour,Lake Ontario

Several studies have shown that large, experimental additions of nitrate (NO₃) to eutrophic systems can mitigate large populations of nuisance cyanobacteria and that high NO₃ concentrations can oxidize anoxic sediments. These studies are consistent with observations from numerous aquatic systems across a broad trophic range showing development of reduced surficial sediments precedes the formation of large cyanobacteria populations. We use 50+ years of data to explore whether high NO₃ concentrations may have been instrumental both in the absence of large populations of cyanobacteria in eutrophic Hamilton Harbour, Lake Ontario in the 1970s when total phosphorus (TP) and total nitrogen (TN) concentrations were high, and in delaying large populations until August and September in recent decades despite much lower TP and TN. Our results indicate that large cyanobacteria population events do not occur at the central station in July-September when epilimnetic NO₃ > 2.2 mg N L^?1. The results further suggest that remedial improvements to wastewater treatment plant oxidation capacity may have been inadvertently responsible for high NO₃ concentrations > 2.2 mg N L^?1 and thus for mitigating large cyanobacteria populations. This also implies that large cyanobacteria populations may form earlier in the summer if NO₃ concentrations are lowered.     

Treatment of spent brine from a nitrate exchange process using combined biological denitrification and sulfate precipitation.

A combined biological denitrification and sulfate precipitation process was developed to treat and reuse the spent brine produced by a nitrate exchange system. Although the spent brine contained a relatively high salt concentration, more than 80% of NO3(-)-N fed into the denitrification reactors was removed at a nitrate-N loading rate of 2.2 g NO3(-)-N/l x day, regardless of the presence or absence of sulfate up to 8,000 mg/l. Sulfate present in the spent brine was successfully removed by the addition of BaCl2 and the settling velocity of BaSO4 suspension was remarkably enhanced by FeCl3 coagulation. Since most of the chloride consumed in regenerating the exhausted resins was replaced during chemical treatment with BaCl2 and FeCl3, it was possible to reuse the treated spent brine as a regenerant after compensating for the small amount of unreplaced NaCl.     

Study of the biological N removal over nitrite in a physico-chemical-biological treatment of digested pig manure in a SBR.

SBR technology is used to treat the supernatant from mesophilic anaerobic digestion of piggery wastewater. The novelty of the treatment consists in the use of a final coagulation/flocculation step inside the SBR cycle to reach the legal COD effluent standard. The pH changes introduced by the use of FeCl(3) do not affect the nitrifying activity. The SBR treatment includes a strategy to the control of oxygen supply and ammonia concentrations inside the digester to favor the biological nitrogen removal over nitrite, which makes the process more economical. The influence of several of these parameters on the AOB biomass activity is studied in this paper.