Biofilm in the sediment phase of a sanitary gravity sewer

Microbial activity of the sediment phase in a 1.5-km-long concrete sewer section with a cement pipe in a 540-mm diameter was investigated in this paper. SEM examinations and elementary composition analyses of the sediment samples have identified the presence of a biofilm layer at the sediment surface. Bacterial counting results with a DNA-staining technique have revealed that the amount of bacteria in this layer was 2.1 x 10(11)cellg(-1) dry wt, which is close to that of activated sludge. ATP content in the sewer biofilm was found relatively high, demonstrating that the sewer biofilm is active. Throughout the entire 1.5-km sewer section, the biofilm activity was maintained at almost the same level. Lab-scale sediment oxygen uptake flux (SOUF) tests showed that the shear flow velocity above the sediment phase linearly increases the SOUF, which of the potential value was determined to be 32gO(2)m(-2) day(-1) at an estimated shear flow velocity of 0.055ms(-1) at 25 degrees C in the sewer line, provided that the mean flow velocity was 1.5ms(-1), and the mean water depth was 220mm. Such a high SOUF value further endorsed the existence of the active sewer biofilm.     

An economic loss model for failure of sewer pipelines

Estimating the costs of failure for sewer pipelines is usually accompanied with uncertainties because of the difficulty in capturing the relationship between the physical and economical characteristics of failed pipelines. To reduce such uncertainties economic loss models are usually used to evaluate the consequences of failure. This paper presents a methodology to estimate economic loss as a result of sewer pipelines’ failure using cost benefit analysis approach. Costs of sewer pipelines’ failure in addition to costs resulting from avoiding such failures are identified and analysed. To validate the proposed methodology, actual costs from a real failure incident were compared with the proposed model outputs. The model could estimate the direct and indirect costs with a deviation ranging between 10–12% and 22–30%, respectively. By implementing the proposed methodology on two case studies, it was found that the indirect costs as a result of sewer pipelines’ failure represent a significant portion ranging between 89 and 94% of the total costs of failure. Also, it was found that costs related to environment, delays to work and traffic disruptions contribute by 12–35% to the indirect costs.     

Possibilities of sewer model simplifications

With increased computer performance and data-processing functionalities, there has been a tendency in the last few years to apply detailed hydrodynamic sewer modelling for long-term simulations, with long time series of rainfall. Although this is now fairly realistic for small networks, there is still a clear limit as to what can be done in the case of running bigger models for a long time, which need a lot more computational effort. Therefore, the idea has grown to investigate the possibilities of hybrid sewer modelling, a combination of conceptual and mechanistic modelling approaches to combine the advantages of both models, the speed of conceptual models and the accuracy of mechanistic models. Suggestions for hybrid model simplifications are presented in this paper within their application for two case studies.     

An assessment of the accuracy of a home energy analysis system based on a modified TWOZONE computer model

Recently, a number of computer models have been utilized in the analysis of the energy performance of residences. In many cases, input to the computer model is provided by the homeowner. This may introduce significant error into the data inasmuch as the homeowner may not be aware of the sensitivity of the program to the accuracy of the data. This research was directed toward the validation of the class B energy audit program for the State of New Mexico and deals with the accuracy of the TWOZONE computer auditing program when used as a class B auditing tool, i.e. when used with homeowner supplied data. This study reveals a number of significant factors which are not properly dealt with in the TWOZONE model. It also presents a methodology which can be used generally to evaluate the overall accuracy of similar auditing tools.     

Grey-box modelling of pollutant loads from a sewer system

Using a compact measuring unit with on-line meters for UV absorption and turbidity, it is possible to determine concentrations of organic load (chemical oxygen demand (COD) and suspended solids (SS)) anywhere in a sewer system. When measurements of the flow are available as well, the pollutant mass flow at the measuring point can be calculated.The measured data are used to estimate different models describing the load of pollutants in the sewer. A comparison of the models shows that a grey-box model is most informative and best in terms measured by the multiple correlation coefficient. The grey-box model is a state-space model, where the state represents the actual amount of deposition in the sewer, and the output from the model is the pollutant mass flow to the wastewater treatment plant (WWTP). The model is formulated by means of stochastic differential equations. Harmonic functions are used to describe the dry weather diurnal load profiles. It is found that the accumulation of deposits in the sewer depends on previous rain events and flows.By means of on-line use of the grey-box models, it is possible to predict the amount of pollutants in a first flush at any time, and hence from the capacity of the plant to decide if and when the available detention basin is to be used for storage of wastewater. The mass flow models comprise an important improvement of the integrated control of sewer and WWTP including control of equalisation basins in the sewer system. Further improvements are expected by the introduction of an additive model where dry weather situations and storm situations are modelled separately before addition to the resulting model.     

Constrained Ant Colony Optimisation Algorithm for the layout and size optimisation of sanitary sewer networks

The incremental solution building capability of Ant Colony Optimisation Algorithm (ACOA) is used in this paper for the efficient layout and pipe size optimisation of sanitary sewer network. Layout and pipe size optimisation of sanitary sewer networks requires optimal determination of pipe locations, pipe diameters and pipe slopes leading to a highly constrained mixed-integer nonlinear programming (MINLP) problem presenting a challenge even to the modern heuristic search methods. A constrained version of ACOA equipped with a Tree Growing Algorithm (TGA) is proposed in this paper for the simultaneous layout and pipe size determination of sewer networks. The method is based on the assumption that a base layout including all possible links of the network is available. The TGA algorithm is used in an incremental manner to construct feasible tree-like layouts out of the base layout, while the constrained ACOA is used to optimally determine the cover depths of the constructed layout. Proposed formulation is used to solve three hypothetical test examples of different scales and the results are presented and compared with those produced by a conventional application of ACOA in which an ad-hoc engineering concept is used for layout determination. The results indicate the effectiveness and efficiency of the proposed method to optimally solve the problem of layout and size determination of sewer networks.     

工程勘察与地基评价计算机专家系统(EIFEES)

分析了在工程勘察领域开发计算机专家系统的必要性，论证了专业特点对系统的要求，介绍了在上述工作基础上研制成功并已投入使用的“工程勘察与地基评价计算机专家系统（ＥＩＦＥＥＳ）”的主要功能与特点。该系统的开发成功对勘察行业计算机应用水平的提高和技术进步将起到很大的推动作用。     

An evaluation exercise of a wind pressure distribution model

The wind pressure distribution (WPD) around a building is an important parameter for multi-zone airflow simulation. The input is usually in the form of pressure coefficients (C_p). The values of C_p are traditionally derived based on wind tunnel studies. However, since it is not possible to always conduct wind tunnel tests to obtain the C_p values, alternative approaches have been suggested. One approach involves the use of statistical regression analysis of data obtained from wind tunnel studies. In this paper, C_p values of a shophouse building under investigation are generated using wind tunnel, a WPD model, which is based on the regression analysis of wind tunnel data as well as based on wall averaged values from published data. Using the C_p values obtained from the wind tunnel as the reference, the accuracy of the C_p values generated by the WPD model and the wall averaged values are analysed and discussed. The effects of such accuracy on the computed air flow rates and age of air for the building using a multi-zone network airflow model are also considered.     

An evaluation exercise of a multizone air flow model

In the IEA-ECBCS Annex 23 `Multizone Air Flow Modelling,' a sensitivity analysis procedure, that included both the Monte Carlo and Fractional Factorial analyses, was defined to evaluate COMVEN, a multizone air flow code. This procedure is here applied to evaluate COMVEN, when the simulation of the ventilation of a detached house is performed for the case of ventilation driven mainly by stack effect. The simulated values are compared to the measured values using the uncertainty range for each value; the confidence interval for the simulated values are obtained using the Monte Carlo method while the fractional factorial analysis has been used to identify the relative effects of the input parameters on the output accuracy. It is an interesting case which makes it possible to demonstrate the application of both sensitivity techniques.     

Development and evaluation of a decision-supporting model for identifying the source location of microbial intrusions in real gravity sewer systems

Assuming a scenario of a hypothetical pathogenic outbreak, we aimed this study at developing a decision-support model for identifying the location of the pathogenic intrusion as a means of facilitating rapid detection and efficient containment. The developed model was applied to a real sewer system (the Campbell wash basin in Tucson, AZ) in order to validate its feasibility. The basin under investigation was divided into 14 sub-basins. The geometric information associated with the sewer network was digitized using GIS (Geological Information System) and imported into an urban sewer network simulation model to generate microbial breakthrough curves at the outlet. A pre-defined amount of Escherichia coli (E. coli), which is an indicator of fecal coliform bacteria, was hypothetically introduced into 56 manholes (four in each sub-basin, chosen at random), and a total of 56 breakthrough curves of E. coli were generated using the simulation model at the outlet. Transport patterns were classified depending upon the location of the injection site (manhole), various known characteristics (peak concentration and time, pipe length, travel time, etc.) extracted from each E. coli breakthrough curve and the layout of sewer network. Using this information, we back-predicted the injection location once an E. coli intrusion was detected at a monitoring site using Artificial Neural Networks (ANNs). The results showed that ANNs identified the location of the injection sites with 57% accuracy; ANNs correctly recognized eight out of fourteen expressions with relying on data from a single detection sensor. Increasing the available sensors within the basin significantly improved the accuracy of the simulation results (from 57% to 100%).     

Cosmoss: conceptual simplified model for sewer system simulation: A new model for urban runoff quality

In order to minimise storm water impact on receiving waters, mathematical models to simulate processes occurring in sewer systems are needed. The aim of this study is to propose a simple and reliable conceptual model for simulating suspended solids discharge during storm events. The model has been tested using experimental data acquired in Parco d'Orleans catchment, Palermo, in Fossolo catchment, Bologna, and in Milijakovac catchment, Belgrade. Results obtained show the need to extend the experimental investigations in order to obtain more reliable information about the washoff rate.     

Prototype expert system for site selection of a sanitary landfill

It is desirable to incorporate heuristic and empirical knowledge including hydrological and bio-geochemical considerations into the selection process of a potential landfill site. In this article, a prototype expert system for the selection of a landfill site, with hybrid knowledge representation approach under object-oriented design environment in a blackboard architecture, is described. It incorporates an artificial neural network for training of partial hazardous scores and a fuzzy rule base for the representation of heuristic knowledge. The evaluation is based on the hazardous waste site ranking system recommended by the US Environmental Protection Agency, adapted to Hong Kong conditions by incorporating the stipulation of some local regulations. It is shown to be a useful aid in assisting novice engineers in the selection process of a potential landfill site during preliminary investigation.     

Characterization of the settling process for wastewater from a combined sewer system

Among the methods used for determining the parameters necessary for design of wastewater settling tanks, settling column tests are used most commonly, because of their simplicity and low costs. These tests partly mimic the actual settling processes and allow the evaluation of total suspended solids (TSS) removal by settling. Wastewater samples collected from the Liguori Channel (LC) catchment in Cosenza (Italy) were subject to settling column tests, which yielded iso-removal curves for both dry and wet-weather flow conditions. Such curves were approximated well by the newly proposed power law function containing two empirical parameters, a and b, the first of which is the particle settling velocity and the second one is a flocculation factor accounting for deviations from discrete particle settling. This power law function was tested for both the LC catchment and literature data and yielded a very good fit, with correlation coefficient values (R(2)) ranging from 0.93 to 0.99. Finally, variations in the settling tank TSS removal efficiencies with parameters a and b were also analyzed and provided insight for settling tank design.     

计算机网络安全分层防护评价体系研究

随着计算机网络技术的不断发展,网络安全系统已经在全球范围内得到广泛应用。虽然网络安全系统的防护工作越来越缜密,但是病毒攻击也变得日益复杂化和全球化。新型的二代防护技术被发明并应用到计算机网络安全防护当中,其与一代相比较来看安全防护体系更加完善。但是,当计算机受到病毒侵害之后仍然不能够进行全面的查杀和系统恢复,因此对于网络防护体系的建设仍然属于时代所关注的重要话题。文章将对安全分层防护系统开发的技术、设计以及功能进行分析。     

Development and performance of a parsimonious model to estimate temperature in sewer networks

This paper presents a model (inspired by another model) to calculate water temperature in free-surface flow with two main innovations: the convective heat transfer occurs only at the wetted perimeter of pipes, and the model was integrated to commercial software used for hydraulic calculations in drainage systems. Given these innovations, we could reduce the number of modeling input data to calculate the temperature of water and soil in the radial and tangential directions along the pipes, with the advantages of using industry-standard software. To test the performance of the model, it was firstly calibrated in two sets of experiments (to calibrate the hydraulic and the thermal parameters separately), and benchmarked with a third controlled discharge against the case model. The results indicate that in unsteady-state situations the parsimonious model can be twice as accurate as the underlying model because the parsimonious model considers the hydraulic influence of sewer infrastructure.     

An investigation of the factors influencing sewer structural deterioration

In this paper, the influence of sewer physical properties on the structural deterioration of the Leuven (Belgium) sewers was investigated using logistic regression. The analysis revealed that out of the 10 variables considered, only three significantly affected the deterioration process, namely, age, material and length. Comparing the results of this study with similar studies revealed that no single set of factors can explain sewer deterioration, i.e. the process is a localised phenomenon. This study contributes to the widening and ascertaining of the limited – and often conflicting – knowledge with regard to the relationship between sewer properties and sewer deterioration.     

Optimization of sewer networks using the mixed-integer linear programming

This paper introduces a method for optimizing sewer networks using the mixed-integer linear programming (MILP) for a given layout. The objective function is defined as the sum of the costs for pipe purchase, pipe-laying, and manhole construction expressed in linear terms and subject to minimum and maximum allowable slopes, velocities, and relative depths for both minimum and maximum sewage discharge rates in each pipe. Additionally, provisions are made as constraints or conditions to ensure that a minimum pipe cover is required, that pipe diameters do not decrease in the flow direction, and that pipes maintain a steady elevation at each manhole. All the non-linear constraints are transformed into the linear format. Pipe slope, binary variables accounting for commercial pipe diameters and average implemented depths have also been considered as decision variables. Finally, the performance of the proposed optimization method is evaluated in a benchmark sewer network from the literature.     

Evaluation of oxygen injection as a means of controlling sulfide production in a sewer system

Oxygen injection is often used to control biogenic production of hydrogen sulfide in sewers. Experiments were carried out on a laboratory system mimicking a rising main to investigate the impact of oxygen injection on anaerobic sewer biofilm activities. Oxygen injection (15-25 mg O₂/L per pump event) to the inlet of the system decreased the overall sulfide discharge levels by 65%. Oxygen was an effective chemical and biological oxidant of sulfide but did not cause a cessation in sulfide production, which continued in the deeper layers of the biofilm irrespective of the oxygen concentration in the bulk. Sulfide accumulation resumed instantaneously on depletion of the oxygen. Oxygen did not exhibit any toxic effect on sulfate reducing bacteria (SRB) in the biofilm. It further stimulated SRB growth and increased SRB activity in downstream biofilms due to increased availability of sulfate at these locations as the result of oxic conditions upstream. The oxygen uptake rate of the system increased with repeated exposure to oxygen, with concomitant consumption of organic carbon in the wastewater. These results suggest that optimization of oxygen injection is necessary for maximum effectiveness in controlling sulfide concentrations in sewers.     

利用管沟污泥配制水泥砂浆体安全性能的研究

分别采用GB 5086.2—1997和EPA SW-846(TCLP)2种方法对掺管沟污泥水泥砂浆中的重金属离子毒性进行了测定;同时测定了掺管沟污泥水泥砂浆中有机质和细菌的含量。并与GB 5085.3—1996《危险废物鉴别标准浸出毒性鉴别》进行比较,试验结果表明将管沟污泥用于混凝土和砂浆中替代部分细集料不会对生态环境造成不良的影响。