A dynamic model of the high-rate algal-bacterial wastewater treatment pond

A mathematical model is presented to describe the symbiotic growth of algae and bacteria in a high-rate wastewater treatment pond. Good agreement with available experimental results is demonstrated. The variation of process parameters (pH, DO and substrate concentration) with channel length and time of day is illustrated for a recirculated pond of “race-track” design. The influence of operating conditions on the algal yield obtainable is evaluated.     

A Bayesian method to estimate proportional payments of users in a wastewater treatment plant

A simple Bayesian method to estimate proportional payments for using or constructing a wastewater treatment plant is presented. The method addresses the usually unknown individual participation in global pollution, of municipal and industrial wastewaters that are normally discharged into the same collecting pond. The individual contributions are calculated from the discharged volume of each source and its pollution percentage in the wastewater volume previous to the disposal. According to the method presented here, the costs in building and/or running the plant can be covered by proportional individual payments based on the individual contributions, in a more even way. The simplicity of the model allows to assess different strategies for the participants in a wastewater treatment system. A real case study in the Izta-Popo National Park, located in the Mexican States of Puebla, Mexico and Morelos, is analyzed.     

Effect of tapering on the performance of waste stabilization ponds

A model for wastewater degradation in a tapered waste stabilization pond was derived as a modified Bessel function by materials balance approach. Based on hypothetical data, the tapered model gave lower faecal bacteria removal than the conventional (rectangular) model for various values of dispersion number, die-off rate coefficient, average width and shape factors. The above results were corroborated by data collected from two laboratory ponds operated in parallel; one having a tapered and the other a rectangular surface area. The latter gave slightly higher hydraulic efficiency and BOD5 removal. Besides, faecal bacteria removal was significantly lower in the tapered pond than in the rectangular pond at 0.10 level of significance. Calculated faecal bacteria reduction using the tapered model was in good agreement with measured data with coefficient of correlation and standard error of 0.904 and 0.014, respectively. Effects of tapering on ponds with respect to construction cost, operational and maintenance ease and accuracy of estimated design parameters are also discussed.     

Algal wastewater treatment systems for seasonal climates: application of a simple modelling approach to generate local and regional design guidelines

Algal waste stabilisation ponds (WSP) provide a means of treating wastewater, and also a potential source of water for re-use in irrigation, aquaculture or algal biomass cultivation. The quantities of treated water available and the periods in which it is suitable for use or discharge are closely linked to climatic factors. This paper describes the application, at a continent-wide scale, of a modelling approach based on the use of readily available climate datasets to provide WSP design and performance guidelines linked to geographical location. Output is presented in regionally-based contour maps covering a wide area of Russia and central Asia and indicating pond area, earliest discharge date, discharge duration, wastewater inflow:outflow ratio and salinity under user-specified conditions. The results confirm that broad-brush discharge guidelines of the type commonly used in North America can safely be applied; but suggest that a more detailed approach is worthwhile to optimise operating regimes for local conditions. The use of long-series climate data can also permit tailoring of designs to specific sites. The work considers a simple 2-pond system, but other configurations and operating regimes should be investigated, especially for the wide range of locations across the world that are intermediate between the ‘one short discharge per year’ mode and year-round steady-state operation.     

Application of HDPE at a sewage treatment plant

A pair of aeration lagoons at a wastewater treatment facility were lined with 0.75-mm HDPE geomembrane in 1993. The ponds were placed in an area that previously contained an unlined sewage stabilization pond. This paper discusses activity at the east lagoon only. Prior to liner installation, a gas vent system was added in the design in the event that gases formed under the liner. That system employed approximately 30-cm-wide strips of geotextile/geonet geocomposite placed on 30-m centers in a grid pattern. Gas vents were cut in the liner around the top perimeter of the pond at 15-m centers. Thorough construction quality assurance practices were employed to insure that the geomembrane and seams were of a high quality. Seven months after installation, gas bubbles began to form under the liner, and large bubbles resulted. The bubbles were pierced to remove the gas. At that time, the lagoon was taken out of service and drained for inspection. Crescent moon-shaped cuts (about 300 mm in size) were then found at the location of some of the baffle curtain anchors. This damage was repaired in conjunction with the holes created by venting the gas bubbles. The lagoon was then partially filled, and more bubbles were formed under the liner. Analysis of the gas resulted in the opinion that it was the result of anaerobic digestion of organic matter under the liner. Also found were holes approximately 60 mm in size that were grouped in random locations throughout the lagoon. These holes were in pairs and spaced 3 to > 30 mm apart. The source of those holes remains unknown. In retrospect, a gas vent system capable of removing gases at a greater rate than it was generated from beneath the liner was required. It is suggested that when a previously existing pond is to be lined, extensive testing for organic matter be performed on subgrade material. Such testing is not currently well defined and should occur prior to design. Other investigations may include hydrological surveys that include several years' data on underlying water level activity. Also, a thicker geomembrane may have had enough resistance to mechanical damage to prevent the formation of the crescent moon and smaller holes.     

基于Matlab的GUI绘制给水管网等压线和三维水压面

为了解供水管网的工作状况并控制管网运行，需进行管网等压线和三维水压面的绘制。为此利用Matlab软件的矩阵计算和绘图功能，通过管网平差计算结果即管网中各节点的水压值绘制了等压线和三维水压面；并对GUI（Graphical User Interface，图形用户界面）的界面程序进行了二次开发，实现了给水管网水力计算图的绘制。将该方法用于某多水源管网的水力计算及管网等压线和三维水压面的绘制，结果表明该算法具有简单可靠、易于实现、直观易懂的优点。     

长春城市绿地植物群落生态脆弱度分析

以北方寒地城市长春市为例,提出城市绿地植物群落生态脆弱度计算方法,对长春城市各类绿地进行了详细的植物群落生态脆弱度分析,分别论述了景观效果、绿地结构、绿地养护及人工干扰与生态脆弱度的关系,指出建立科学合理的复合群落绿地是从根本上降低城市绿地生态脆弱度的唯一出路。     

高效藻类塘处理农村生活污水研究

对高效藻类塘处理太湖地区农村生活污水的效果进行了研究。结果表明，太湖地区农村生活污水的水质受季节影响变化较大，秋、冬季的有机物浓度较夏季高3～4倍；高效藻类塘内存在的菌藻共生体系使塘内溶解氧浓度较高（保持好氧状态），而pH值则存在周期性变化；对COD的平均去除率可达70％，氨氮主要通过硝化作用去除，去除率〉90％，磷酸盐主要通过沉淀作用去除，去除率为50％。系统运行效果受季节性光照和温度变化影响很大，夏季停留时间需4d，冬季需8d。较高流速可强化系统的传质效果，提高了对污染物的去除能力。塘深较浅时，塘深对处理效果影响不大。高效藻类塘系统能较好地净化太湖地区的农村生活污水。     

Dynamic modelling of nitrification in an aerated facultative lagoon

Faced with the need to improve ammonia removal from lagoon wastewater treatment plants (WWTPs) operated in Quebec, Canada, mechanistic modelling has been proposed as a tool for explaining the seasonal nitrification phenomenon and to evaluate optimization and upgrade scenarios. A lagoon model that includes a modified activated sludge biokinetic model and that assumes completely mixed conditions in the water column and sediments has been applied to simulate 3 years of consecutive effluent data for a lagoon from the Drummondville WWTP. Successful prediction of results from this plant indicates that the seasonal nitrification is determined by temperature, dissolved oxygen (DO) concentrations, hydraulic retention time (HRT) of the water column and washout driven by a well-mixed water column. Results also indicate that sediments contribute to the ammonia load in the lagoon effluent, particularly in spring and early summer. Sensitivity analyses performed with the model indicate that the nitrification period could be prolonged by increasing DO concentrations in the lagoon and that bioaugmentation would be particularly effective in spring and early summer. Limitations of the model are discussed, as well as ways to improve the hydraulic model.     

生态塘技术特点及应用实例

用生态塘系统工艺处理石化废水,分析青肯泡石化废水生态处理系统和山东省东营市污水处理与利用生态系统的工程实例.工程运行结果显示:生态塘系统处理石化废水效果显著,出水分别达到GB 18918-2002《城镇污水处理厂污染物排放标准》二级和1A标准,生态塘系统处理石化废水具有投资少、维护和运行费用低、可改善和恢复生态环境等优点,是一种低成本高效益的生态工程技术.     

Spectrofluorometric properties of dissolved organic matter from Central and Southern Ontario streams and the influence of iron and irradiation

Fluorescence measurements were used to compare characteristics of dissolved organic matter (DOM) from distinctly different origins: boreal, agricultural and urban streams as well as a storm runoff pond and the outlet of a tertiary wastewater treatment plant. The primary goal was to determine if differences among stream types could be detected using DOM fluorescence in lieu of isolated fulvic acids (FA). Differences in peak excitation and peak emission wavelengths, fluorescence integrated over the 3-D matrix volume integrated fluorescence (VIF), and in a fluorescence index (FI) were examined. In general, peak fluorescence excitation and emission wavelengths as well as FI best distinguished DOM from the various origins. Results suggested that DOM from the boreal streams was of a higher molecular weight and more complex than that of agricultural and urban streams. The effects of irradiation as well as Fe on fluorescence of natural stream waters were also investigated, both of which decreased the ability of optical properties to distinguish DOM source.     

Municipal-treated wastewater reuse for plant nurseries irrigation

Results of an experiment aimed at assessing the possibility of reusing reclaimed wastewater for nursery ornamental plants are presented. Tests were carried out in Pistoia (Italy). A pilot plant for tertiary treatment (filtration and peracetic acid + UV disinfection) of the local wastewater treatment plant (WWTP) effluent was set up. An experimental plot with six containerized ornamental species was irrigated with the tertiary effluent and growth and physiological parameters were monitored. A control plot irrigated with fertigated water (nutrient-enriched groundwater) was also set up in order to compare the plants response to different kinds of irrigation water. The refinery treatment by filtration and disinfection with Peracetic Acid (PAA) and UV together was very effective in bacteria removal. The value of 2 MPN of Total Coliforms in 100 ml set by Italian law (until June 2003) for unrestricted irrigation was constantly satisfied. Agronomic results indicate no major limitations to the use of a tertiary effluent as an irrigation source in an ornamental plant nursery. The nutrient content of the tertiary effluent was able to maintain good plant growth as well as fertigated water for most of the tested species.     

边坡人工湿地/水生植物塘集成技术处理水产养殖排水

针对上海松江五厍农业园区水产养殖污染问题,提出以边坡人工湿地/水生植物塘集成技术进行处理。集成技术示范工程的实际运行结果表明:该技术对水产养殖污染物的削减行之有效,每年COD、TN、TP的减排强度分别达到896、35.21、0.9 kg/hm2,初步解决了园区水产养殖排水污染问题。同时,水生植物塘中生长的浮萍可以用作水产养殖饲料,符合现代水产养殖的发展趋势。     

A time series model for influent temperature estimation: application to dynamic temperature modelling of an aerated lagoon

Thirty-nine linear regression and time series models were built and calibrated for influent temperature (Ti) estimation at the primary aerated facultative lagoon in a municipal wastewater treatment plant. The models were based on mean daily ambient air temperature (Ta) and/or daily rainfall (P), and-optionally-wastewater temperature autoregression. The best fits were achieved with some time series models involving Ta and P, and Ti autoregression. The best-fit model was able to estimate influent temperature with a root-mean-square-error of 0.5 degrees C, and an R2 of 0.925, for the calibration period of 10.5 months. In addition, a dynamic lagoon-temperature (Tw) model from the literature was modified in its terms of solar radiation and aeration latent heat, and applied to the primary lagoon. The model was fed with the estimated influent temperature, and five model parameters were identified by calibration against 10.5-month Tw data. Dynamic lagoon-temperature estimation results were comparable to or better than other results of long-term simulations found in the literature. Sensitivity analyses were run on both models. Further validation with independent sets of data is needed for verification of the predictive capability of the models.     

Stockholm builds a “snake” tunnel to avoid flooding and improve water quality

Rainwater that falls on the city of Stockholm is led to the wastewater treatment facility at Henriksdal. The water is transported through a network of pipelines where domestic wastewater is mixed with rainwater. The existing network does not have sufficient capacity during heavy precipitation. To avoid flooding, the mixture of rainwater/wastewater is allowed to overflow into the nearest stretch of water. To reduce this overflow, a wastewater tunnel is being built where the “surplus” water can be temporarily stored until the pressure on the pipelines and the wastewater treatment works is reduced. This new tunnel, called “The Snake” because of its winding course, will have a capacity of approximately 35.000 m³. This will be sufficient to reduce the risk of flooding considerably, while simultaneously stopping the undesirable discharge into Brunnsviken completely. To achieve the best interaction between the tunnel and the system of water mains, the water level will be regulated and monitored with the help of computers.     

A comparison of stochastic process models for definition of design contours

So-called design contour methods are frequently applied for large and complex structures in order to minimize the number of time-consuming structural analyses. These methods are based on first identifying extreme environmental conditions with a given probability of exceedance based on the relevant joint distribution function. These conditions are located along a level surface (i.e. “contour”) in the space of load parameters. As the second step, response analyses are performed for a selection of extreme conditions which are located along this contour. The highest response level which is obtained as a result of these analyses is then applied for design purposes.This approach is based on a representation of the underlying stochastic processes in terms of a sequence of piecewise constant levels. In the present paper, the extreme environmental conditions which are obtained based on such a model are compared to those obtained by instead applying a continuous process model. Furthermore, various alternative and relevant definitions of design contours are compared for the two-component case.In the present analysis, mainly stochastic processes which represent load parameters are considered. However, the approach for identification of level surfaces is of a general nature and can be applied to any types of random vector processes.     

A data‐driven approach to determining freeway incident impact areas with fuzzy and graph theory‐based clustering

Determining spatiotemporal impact areas of incidents plays a significant role in incident impact analysis. Although existing empirical methods have proven to be promising, they suffer from the drawbacks that limit their wide applications in automated freeway safety management. This study presents a data‐driven approach to automatically determining the spatiotemporal impact areas of freeway incidents. The spatiotemporal contour plots were first constructed using three representative traffic measures. Next, a nonrecurrent congestion area identification method based on fuzzy clustering was developed. To distinguish possible multiple independent blocks in the nonrecurrent congestion area, a clustering algorithm based on graph theory was adopted. The incident impact areas were then determined by conducting a postprocessing strategy. The incident records and the associated traffic flow data, collected on I‐5 freeway segments in San Diego Region, CA, were used to evaluate the proposed approach. Experimental results show the proposed approach can automatically and properly determine incident impact areas while accounting for the uncertainty resulting from traffic variations.     

Optimalization of coagulant dose in coagulation-flocculation of sewage

This article describes how the optimal coagulant dose in chemical treatment can be calculated from a limited number of raw sewage characteristics. Ferric chloride and aluminium sulphate were used as coagulants. In jar tests ten characteristics were determined in the sewage and for each separate sample of wastewater “optimal” coagulant doses were determined. There was a very high correlation between the “optimal” coagulant dose of aluminium sulphate and ferric chloride and one or two quality parameters of the influent. A comparison was made between aluminium sulphate and ferric chloride as coagulant. The findings were verified in two pilot plants. In one a constant coagulant dose m⁻³ influent was set; in the other plant the coagulant dose was also related to the orthophosphate content of the sewage. By this means a reduction of the coagulant dose was obtained of 35%, while on average the removal percentage of TOC was the same.     

Methods for measuring the degree of stability of aerobic stabilized sludges

This study was conducted to find one or several parameters that can be used as a measure of the degree of stability of wastewater sludges and to define in terms of the measured parameters what is meant by a fully stabilized sludge.Based on the data from this study, the following requirements regarding odour should be met before an aerobically stabilized sludge can be considered as a fully stabilized sludge:The Odour Intensity Index (ASTM D1292) should not exceed 11 at any time during 14 days of storage at 20°C, unless the odour can clearly be classified as a typical “soil” odour.Oxygen uptake rate was found to be a reliable indicator of sludge stability if the temperature effect is taken into consideration. It was also experienced that short aeration period (2–8 days during batch operation) would make the sludge less suitable for storage since they would give a higher rise in odour intensity than raw sludges. This would probably not be true for biological sludges.The reduction of BOD and COD in the sludge liquor could not be used to measure sludge stability.     

Cost models for small wastewater treatment plants

The cost models of small wastewater treatment plants serving to population sizes of 2000 to 25,000 were prepared for Turkey with intermediate degree of accuracy. In the first phase, kinetic models of aerated lagoon, stabilization pond, trickling filter, oxidation ditch and rotating biological contactor (RBC) were derived in terms of area and flow rates at various treatment efficiencies considering different temperature ranges. Secondly the construction, mechanical, electrical equipment, operation and maintenance costs were computed as function of flow rates for each biological treatment process in the development of cost models. These models will be employed in the selection of the appropriate biological treatment process before investment of limited funds.