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.     

The use of long-term on-line turbidity measurements for the calculation of urban stormwater pollutant concentrations,loads, pollutographs and intra-event fluxes

This paper presents one of the largest databases on the quality of urban wet weather discharges measured since the development of continuous in-sewer water quality sensors in the late 1990s. Five years of continuous turbidity measurements enabled the validation of 263 and 239 rainfall events, respectively on two experimental catchments in Lyon (France), Chassieu (185 ha separate sewer) and Ecully (245 ha combined sewer). Except for high rainfall events of summer and second half of winter, analysis of database representativeness showed that all seasons were relatively well represented. As a first analysis of the database, traditional tools used in the urban drainage field were applied to assess: i) statistics and analysis of distributions of TSS and COD events loads and event mean concentrations (EMCs) and ii) the correlations between these statistics and events characteristics and iii) M(V) curves describing the intra-event mass distribution. Results showed that: i) EMCs and loads were approximately log-normally distributed, with a clear impact from wastewater contribution in Ecully, ii) EMCs are not correlated with storm event characteristics, whereas loads have shown significant correlation with key storm event variables such as total event volume, rainfall depth, maximum rainfall intensity and discharge and iii) M(V) curves dynamic could be classified in three categories, however with no clear correlation with storm event characteristics. The visual analysis of continuous time series of TSS and COD pollutographs, derived from turbidity time series showed that event pollutographs were highly variable, due to complex interacting processes during and between events, and suggests that further progress in knowledge and modelling of urban wet weather pollutant loads and pollutographs should be based on more detailed analyses of continuous time series rather, than on the traditional single event approach.     

Production and transport of urban wet weather pollution in combined sewer systems: the “Marais” experimental urban catchment in Paris

An experimental catchment area was set up in the centre of Paris (France) so as to follow up the quality of wet weather flows from the entry to the exit of a combined sewer network. The distinctive characteristic of this site is its location in a town centre and the extent of the equipment used to monitor the water pollution over the whole length of its course through the catchment area. The results obtained show a change in quality between the runoff entering the sewer network and the combined storm water flow at the sewer's outlet, which cannot be explained only by the mixture with domestic wastewater. In particular, an increase was observed in the concentrations of suspended solids (SS), VSS, COD, BOD and Cu, in the proportion of pollutants linked to particles and in the characteristics of the particles. A calculation of the total masses going in and out of the sewer network during a rainfall event shows that the erosion of in-sewer pollution stocks is the main source of particles and of organic matter in wet weather flows, whereas heavy metals loads originated from roof runoff, due to the corrosion of metallic roofs. Particles eroded from the sewer sediments during rain events were found to be quite different from the particles of type A deposits and organic biofilms. Nevertheless, they have mean organic and metallic loads that are of the same order of magnitude as the particles of the organic layer at water sediment interface. A change in the chemical form of heavy metals was noticed during the transport in the sewer and it is suspected that a fraction of the dissolved metals from the runoff is adsorbed on sewer sediments.     

Potential of tipping flush gate for sedimentation management in open stormwater sewer

This paper presents the design of a tipping flush gate and its potential use in servicing open storm sewers in terms of sedimentation management. The tipping flush gate was installed in a section of open concrete storm sewer located in a commercial area in Taman Pekaka, Nibong Tebal, Penang, Malaysia. Monitoring of the gate operation and performance was done from 14^th November 2012 to 15^th March 2013 covering the beginning and end of the wet season. The sediment profile inside the sewer was measured after each operation of the gate or rainfall event. Results showed that the gate was effective in reducing naturally accumulated sediment in the chosen sewer section. However, proper litter management is needed if the gate is to be implemented in open storm sewer systems. A design guideline for the usage of a tipping flush gate for open storm sewers is also presented in this paper.     

COD fractionation of tannery wastewaters--particle size distribution, biodegradability and modeling

This study aims to establish the scientific link between particle size distribution (PSD) and biodegradability of different COD fractions of tannery wastewater, by means of sequential filtration/ultrafiltration, respirometric analysis and model evaluation. PSD profiles were determined in physical segregation experiments, using eight membrane discs, each with different pore sizes between 2 and 1600 nm. Biodegradability-related COD fractionation was determined at each size interval by model simulation and calibration of the corresponding oxygen uptake rate (OUR) profiles. Activated Sludge Model No. 3 (ASM3), modified for direct growth on hydrolysis products, was adopted for evaluation. PSD analyses defined a COD fingerprint with two significant portions at the two ends of size distribution, with 60% of the total COD at the particulate range, 25% at the soluble range and the remaining 15% well distributed among the colloidal range. Comparative evaluation of the sequence of OUR profiles yielded values of applicable model coefficients. It also enabled the assessment of size distribution for each major COD fraction, as an original tool for better interpretation of specific biodegradation characteristics of the selected tannery wastewater. Results also revealed a very slowly biodegradable/residual particulate COD component with a significant inhibitory effect. Model-based evaluation of the OUR profiles enabled quantifying the impact of inhibition in terms of changes in rate coefficients for growth, hydrolysis of soluble COD and endogenous decay.     

Temperature effect on aerobic biodegradation of feces using sawdust as a matrix

Temperature is one of the most important factors affecting microbial growth and biological reactions. In this study, the effect of temperature on aerobic biodegradation of feces is described through the comparison and analysis of experimental oxygen utilization rates (OUR) profiles obtained from batch tests conducted at several temperatures covering mainly mesophilic and thermophilic ranges. Additionally, the temperature effect was incorporated into the bio-kinetic model introduced by Lopez Zavala et al. (Water Res 38(5) (2004) 1327) and simulation of experimental OUR profiles was conducted. Results show that mesophilic and thermophilic microorganisms behaved differently to temperature; additionally, results suggest that the optimum temperature from the viewpoint of feces biodegradability is within the thermophilic range, nearly 60 degrees C. The enzymatic activity of microorganisms at 70 degrees C was remarkably diminished. For better predictions in the mesophilic range, two fractions of slowly biodegradable organic matter were identified, easily hydrolyzable organic matter (X(Se)) and slowly hydrolyzable organic matter (X(Ss)).     

上海中心城区合流制排水系统雨天溢流水质研究

合流制排水系统雨天溢流已成为上海中心城区河道的主要污染源.为此,重点研究了上海中心城区某合流制排水区域JXB系统雨天污染物溢流的出流过程和污染物的事件平均浓度,并探讨了溢流污染物的初期效应.结果表明,降雨特性对污染物溢流过程的水质影响较大;该区域雨天溢流COD、BOD5、SS、NH3-N的事件平均浓度分别为268、101、110、9.5 mg/L,SS浓度明显低于相关研究的结果;分析溢流污染物的初期效应表明,JXB系统排江污染物的初期效应较为显著,其中COD和BOD5的初期效应比SS的显著.     

Quantification of oxygen fluxes in a long gravity sewer

Quantification of the oxygen fluxes in the sewer system is at present the optimal methodology to obtain information about the influence of sewers on transformations and mass balances in the urban drainage system. However, the relative and absolute values of these fluxes are practically unknown. In this work, the oxygen fluxes were quantified experimentally in a full-scale aerobic main sewer. The sewer biofilm respiration was determined with an in situ flow cell, a method that has not been used before in the sewer. The surface reaeration was determined with a gas tracer method based on the inert, non-radio-active and non-toxic gas tracer sulphur hexafluoride. In addition, the wastewater biomass respiration rate was measured. The validity of the applied methods was verified with redundant oxygen balances over a 2-km-long section. Measurement campaigns under different hydrodynamic conditions showed that the relative contribution of the biofilm, the wastewater, the reaeration and the in- and outflow with the water, all contributed significantly. However, the absolute contributions varied extensively and depended especially on the discharge. The COD conversion in the sewer could be estimated from the aerobic activity. The aerobic total degradation in the study reach was 3%. However, when extrapolated to the entire sewer net of the catchment area with 5000 PE, the COD conversion was estimated as high as 30% of the dissolved COD during the night. This indicates that the wastewater composition at the treatment plant will be strongly affected by the sewer system.     

Size distribution of wastewater COD fractions as an index for biodegradability

The study proposes direct particle size measurement by sequential filtration and ultrafiltration as a convenient method for wastewater characterization for appropriate treatment technology. It also explores the correlation between particle size distribution (PSD) and chemical oxygen demand (COD) fractionation, as an index for biological treatability. Profiles obtained through PSD-based COD fractionation serve as the fingerprints for wastewaters, and as demonstrated in this study, reflect different pictures for textile wastewater and domestic sewage. PSD-based COD fractionation profiles identify the soluble range below 2 nm as the size interval housing both the soluble inert COD initially present in the wastewater and soluble inert microbial products generated during biological treatment, as also supported by the metabolic fractionation attained through respirometric analyses. Moreover, PSD-based color profiling offers a good index for the fate of biologically resistant chemicals passing through biological treatment. Compatible results obtained from comparative evaluation of PSD-based COD and color profiles provide useful information on the biodegradability of the textile wastewater studied.     

Aerobic transformations of organic matters in sewer wastewater,a case study of Milan,Italy

Today, we know that not only the sewers carry urban wastewater, but also act as chemical and biological reactors, in which both organic and inorganic substances undergo significant transformations. This article describes a study on the western part of the sewer system of the city of Milan. The hydraulic model of the sewer system was coupled with the chemical and dynamic biological model to assess the extent of the degradation of organic matter in the network. The hydraulic and biological models were calibrated with real data obtained at the entrance of the wastewater treatment plant (WWTP) ‘Milan South’ and assuming standard values of daily per capita loads of COD and BOD₅.     

A simple biological method to estimate the readily biodegradable organic matter in wastewater

A simple method was proposed to measure the readily biodegradable COD in wastewater. The method, denoted as the single-OUR method, is based on monitoring the oxygen concentration decrease in a single oxygen utilization measurement. The oxygen consumption related to readily biodegradable COD can be estimated from the oxygen concentration profile. In order to transfer this oxygen consumption to the readily biodegradable COD a calibration curve is needed. For the evaluation of the method a batch OUR test was performed in parallel. A good agreement between the two methods was obtained.     

Source characterisation and loads of metals and pesticides in urban wet weather discharges

Contaminants in urban wet weather discharges originate from a number of sources such as materials from wet and dry atmospheric deposition, wastewaters, urban surface erosion, traffic-related activities, in-sewer deposits, etc. In the current study, four contributions (rainwater, dry atmospheric deposition, dry weather discharge and catchment surface + possible erosion of in-sewer deposits) to the total concentrations of priority substances have been assessed at the outlet of two urban catchments (one residential catchment with a combined system and one industrial area with a separate stormwater system) for 12 storm events (six for each catchment). Mass balances were calculated for seven metals and four pesticides, as well as for total suspended solids and chemical oxygen demand. The respective contributions of dry and wet atmospheric deposition, wastewater and catchment surface differ for each pollutant type, corresponding to different land use, activities, environments and sewer systems. For most of the pollutants, the catchment surface appears to be the main contribution, with significant storm event variability, excepted for atrazine in one catchment.     

城市排水系统的集成化模拟研究

城市排水系统的集成化模拟是国际上推行的一种研究方法，但在我国尚没有相关的实例报道。将美国环保局提供的城市暴雨径流管理模型（SWMM）与清华大学环境系自行研制开发的河流水质模型相结合，构成城市排水系统集成化模拟工具，它可以动态模拟暴雨径流（生活污水）→排水管网→污水处理厂→受纳水体的全过程。以深圳河湾地区为例，针对深圳市提出的排水系统规划布局方案运用该模拟工具进行模拟计算，评估该方案对深圳河湾地区水环境的影响。模拟结果表明，规划方案实施后对深圳河干流水质的改善效果突出，对支流水体水质的改善效果略差，需要进一步优化雨水管网布置和污水厂选址；规划方案可大大提高河水的COD达标率，但TN和TP的达标率仍相对较低，需要加强源头控制并提高污水处理厂的脱氮除磷效果。     

ABR-BAF工艺处理采油废水的中试研究

进行了利用折流板厌氧反应器（ABR）-曝气生物滤池（BAF）工艺处理江汉油田马-25污水处理站采油废水的中试研究，主要考察了ABR的除油效果、提高废水可生化性的作用以及BAF的运行参数、处理效果等。研究结果表明：当废水流量为0．3m^3／h时，ABR反应器对油的去除率平均为83．5％，对COD的去除率平均为40．8％，出水BOD，／COD值提高了24．8％。ABR一方面去除了采油废水中的大部分油，另一方面提高了采油废水的可生化性。当BAF的水力负荷为0．6m／h、进水COD平均为203．5mg／L时，出水COD平均为85．7mg／L，平均去除率为57．9％；对SS的去除率为82．7％。组合工艺对油、COD、BOD，和SS的总去除率分别为96．1％-96．9％、58．2％～75．1％、80．0％-93．1％和80．7％～87．1％。扫描电镜（SEM）观察结果显示：生物膜结构紧密，并且观察到裂口虫，生物相非常丰富。ABR-BAF工艺能够很好地处理采油废水，出水水质满足污水二级排放标准。     

The impact of combined sewer overflows on the dissolved oxygen concentration of a river

As described in the preceding paper by Harremoës (Harremoës, Water Res.16, 1093–1098, 1982) it is important to distinguish between removal and degradation of organic matter for non-steady-state discharges to rivers. These effects were investigated to determine the impact of combined sewer overflows on the dissolved oxygen concentration of a small river. Two different effects on the DO-concentration in the receiving river were observed during and after the passage of the bulk of combined sewage discharged at an existing outlet:

1. 1. An immediate effect caused mainly by degradation of the soluble BOD-fraction in the water body and by direct absorption and degradation of organic matter at the bottom.

2. 2. A delayed effect caused by degradation of adsorbed soluble, colloidal and fine particulate organic matter. After the passage of the bulk discharge a delayed effect on the DO-concentration in the river would be observed. This delayed effect lasted 12–24 hours after the discharge event.

Only 4% of the discharged organic matter was degraded during passage of the investigated stretch of the river, approx. 4 km. On the other hand about 35% of the discharged organic matter was removed by transfer to the bottom sediments. The rest was carried past the stretch of river investigated. This results in a rate of adsorption from the water phase of k = 9 m day⁻¹. The deposited organic matter was degraded with a first order reaction rate of K₄ = 0.75 day⁻¹.     

Cork industry wastewater partition by ultra/nanofiltration: a biodegradation and valorisation study

Wastewater from cork processing industry present high levels of organic and phenolic compounds, such as tannins, with a low biodegradability and a significant toxicity. These compounds are not readily removed by conventional municipal wastewater treatment, which is largely based on primary sedimentation followed by biological treatment. The purpose of this work is to study the biodegradability of different cork wastewater fractions, obtained through membrane separation, in order to assess its potential for biological treatment and having in view its valorisation through tannins recovery, which could be applied in other industries. Various ultrafiltration and nanofiltration membranes where used, with molecular weight cut-offs (MWCO) ranging from 0.125 to 91 kDa. The wastewater and the different permeated fractions were analyzed in terms of Total Organic Carbon (TOC), Chemical Oxygen Demand (COD), Biochemical Oxygen Demand (BOD), Total Phenols (TP), Tannins, Color, pH and Conductivity. Results for the wastewater shown that it is characterized by a high organic content (670.5-1056.8 mg TOC/L, 2285-2604 mg COD/L, 1000-1225 mg BOD/L), a relatively low biodegradability (0.35-0.38 for BOD₅/COD and 0.44-0.47 for BOD₂₀/COD) and a high content of phenols (360-410 mg tannic acid/L) and tannins (250-270 mg tannic acid/L). The results for the wastewater fractions shown a general decrease on the pollutant content of permeates, and an increase of its biodegradability, with the decrease of the membrane MWCO applied. Particularly, the permeated fraction from the membrane MWCO of 3.8 kDa, presented a favourable index of biodegradability (0.8) and a minimized phenols toxicity that enables it to undergo a biological treatment and so, to be treated in a municipal wastewater treatment plant. Also, within the perspective of valorisation, the rejected fraction obtained through this membrane MWCO may have a significant potential for tannins recovery. Permeated fractions from membranes with MWCO lower than 3.8 kDa, presented a particularly significant decline of organic matter and phenols, enabling this permeates to be reused in the cork processing and so, representing an interesting perspective of zero discharge for the cork industry, with evident environmental and economic advantages.     

味精废水好氧同步硝化反硝化的试验研究

采用SBR处理味精废水,考察了味精废水的可生化性、好氧条件下的同步硝化反硝化以及不同C/N下有机负荷和氨氮负荷的变化.结果表明,对COD的去除率为91.6%～97.2%,对BOD5的去除率>95%,味精废水的BOD5/COD为0.5,说明其可生化性较好,可为反硝化过程提供充足的碳源;试验中存在明显的同步硝化反硝化现象,对氨氮和总氮的去除率分别达到99%、96%;随着进水C/N的降低,有机负荷降低,氨氮负荷升高.     

Removal of organic matter in stormwater ponds: a plug-flow model generalisation from waste stabilisation ponds to shallow rivers

ABSTRACT

This study investigates the effect of flow conditions on the organic matter concentration, removal efficiency, and reaction kinetics in a stormwater pond in Fortaleza, Brazil. As a result of unauthorized sewage discharges, BOD and COD concentrations were similar to those of combined sewer systems. The concentrations remained roughly the same during the rainy season, which was attributed to sewage network overflow. Removal efficiencies ranged from 70–90%, similar to primary facultative ponds. Fitting different hydraulic models to the field data, it was possible to obtain BOD and COD removal rates that could be described as functions of the Reynolds number. The best fit was achieved considering the plug-flow assumption, and a general BOD model including data reported in the literature for waste stabilisation ponds, stormwater ponds and shallow rivers was derived. Lastly, simulations with this general model were performed to assess the impact of remediation measures on the studied pond.     

Trace element carriers in combined sewer during dry and wet weather: an electron microscope investigation

The nature of trace element carriers contained in sewage and combined sewer overflow (CSO) was investigated by TEM-EDX-Electron diffraction and SEM-EDX. During dry weather, chalcophile elements were found to accumulate in sewer sediments as early diagenetic sulfide phases. The sulfurization of some metal alloys was also evidenced. Other heavy metal carriers detected in sewage include metal alloys, some iron oxihydroxide phases and neoformed phosphate minerals such as anapaite. During rain events, the detailed characterization of individual mineral species allowed to differentiate the contributions from various specific sources. Metal plating particles, barite from automobile brake, or rare earth oxides from catalytic exhaust pipes, originate from road runoff, whereas PbSn alloys and lead carbonates are attributed to zinc-works from roofs and paint from building siding. Soil contribution can be traced by the presence of clay minerals, iron oxihydroxides, zircons and rare earth phosphates. However, the most abundant heavy metal carriers in CSO samples were the sulfide particles eroded from sewer sediments. The evolution of relative abundances of trace element carriers during a single storm event, suggests that the pollution due to the "first flush" effect principally results from the sewer stock of sulfides and previously deposited metal alloys, rather than from urban surface runoff.