Monitoring and statistical modelling of sedimentation in gully pots.

Gully pots are essential assets designed to relief the downstream system by trapping solids and attached pollutants suspended in runoff. This study applied a methodology to develop a quantitative gully pot sedimentation and blockage model. To this end, sediment bed level time series from 300 gully pots, spanning 15 months, were collected. A generalised linear mixed modelling (GLMM) approach was applied to model and quantify the accumulation of solids in gully pots and to identify relevant physical and catchment properties that influence the complex trapping processes. Results show that the retaining efficiency decreases as sediment bed levels increase. Two typical silting evolutions were identified. Approximately 5% of all gully pots experienced progressive silting, eventually resulting in a blockage. The other gully pots show stabilising sediment bed levels. The depth of the sand trap, elapsed time since cleaning and the road type were identified to be the main properties discriminating progressive accumulation from stabilising sediment bed levels. Furthermore, sediment bed levels exhibit no residual spatial correlation, indicating that the vulnerability to a blockage is reduced as adjacent gully pots provide a form of redundancy. The findings may aid to improve maintenance strategies in order to safeguard the performance of gully pots.

Selection of monitoring locations for storm water quality assessment.

Storm water runoff is a major contributor to the pollution of receiving waters. Storm water characteristics may vary significantly between locations and events. Hence, for each given location, this necessitates a well-designed monitoring campaign prior to selection of an appropriate storm water management strategy. The challenge for the design of a monitoring campaign with a given budget is to balance detailed monitoring at a limited number of locations versus less detailed monitoring at a large number of locations. This paper proposes a methodology for the selection of monitoring locations for storm water quality monitoring, based on (pre-)screening, a quick scan monitoring campaign, and final selection of locations and design of the monitoring setup. The main advantage of the method is the ability to prevent the selection of monitoring locations that turn out to be inappropriate. In addition, in this study, the quick scan resulted in a first useful dataset on storm water quality and a strong indication of illicit connections at one of the monitoring locations.

Comparison of core sampling and visual inspection for assessment of concrete sewer pipe condition.

Sewer systems are costly to construct and even more costly to replace, requiring proper asset management. Sewer asset management relies to a large extent on available information. In sewer systems where pipe corrosion is the dominant failure mechanism, visual inspection by closed circuit television (CCTV) and core sampling are among the methods mostly applied to assess sewer pipe condition. This paper compares visual inspection and drill core analysis in order to enhance further understanding of the limitations and potentials of both methods. Both methods have been applied on a selected sewer reach in the city of The Hague, which was reportedly subject to pipe corrosion. Results show that both methods, visual inspection and core sampling, are associated with large uncertainties and that there is no obvious correlation between results of visual inspection and results of drill core analysis.

Settlement as a driver for sewer rehabilitation.

This paper assesses the influence of (differential) settlement on sewer system functioning. Based on historical data of the vertical position of sewer invert levels, tilt measurements and in-sewer inspection videos, settlement and settlement related influences are analyzed for a case study area in Amsterdam. The average settlement rate of this system was 4 mm/year. Given this settlement rate, it is shown that settlement significantly influences sewer system functioning within the lifetime of a sewer (system).

Assessing characteristic time and space scales of in-sewer processes by analysis of one year of continuous in-sewer monitoring data.

Long-term and high-frequency in-sewer monitoring opens up a broad range of possibilities to study (influences on) water quantity and quality variations. Using data from the Eindhoven wastewater system in The Netherlands both dry weather flow and wet weather flow situations have been studied. For approximately 160 dry weather days mean diurnal variations of flow and pollutant concentrations have been derived. For wet weather situations (≈ 40 storm events) peak load factors have been studied. Generally, peak load factors for all considered pollutant parameters are larger than one. Peak load factors for particulate matter are larger than for dissolved constituents. Also, the smallest catchment area consistently shows the largest mean peak factors and vice versa.

Uncertainties of stormwater characteristics and removal rates of stormwater treatment facilities: implications for stormwater handling.

Stormwater runoff is a major contributor to the pollution of receiving waters. This study focuses at characterising stormwater in order to be able to determine the impact of stormwater on receiving waters and to be able to select the most appropriate stormwater handling strategy. The stormwater characterisation is based on determining site mean concentrations (SMCs) and their uncertainties as well as the treatability of stormwater by monitoring specific pollutants concentration levels (TSS, COD, BOD, TKN, TP, Pb, Cu, Zn, E.coli) at three full scale stormwater treatment facilities in Arnhem, the Netherlands. This has resulted in 106 storm events being monitored at the lamella settler, 59 at the high rate sand filter and 132 at the soil filter during the 2 year monitoring period. The stormwater characteristics in Arnhem in terms of SMCs for main pollutants TSS and COD and settling velocities differ from international data. This implies that decisions for stormwater handling made on international literature data will very likely be wrong due to assuming too high concentrations of pollutants and misjudgement of the treatability of stormwater. The removal rates monitored at the full scale treatment facilities are within the expected range, with the soil filter and the sand filter having higher removal rates than the lamella settler. The full scale pilots revealed the importance of incorporating gross solids removal in the design of stormwater treatment facilities, as the gross solids determine operation and maintenance requirements.

Monitoring the performance of a storm water separating manifold with distributed temperature sensing.

Storm water separating manifolds in house connections have been introduced as a cost effective solution to disconnect impervious areas from combined sewers. Such manifolds have been applied by the municipality of Breda, the Netherlands. In order to investigate the performance of the manifolds, a monitoring technique (distributed temperature sensing or DTS) using fiber optic cables has been applied in the sewer system of Breda. This paper describes the application of DTS as a research tool in sewer systems. DTS proves to be a powerful tool to monitor the performance of (parts of) a sewer system in time and space. The research project showed that DTS is capable of monitoring the performance of house connections and identifying locations of inflow of both sewage and storm runoff. The research results show that the performance of storm water separating manifolds varies over time, thus making them unreliable.

An integrated approach for urban water quality assessment.

This paper introduces an integrated approach for the assessment of receiving water quality and the relative contribution of the urban drainage system to perceived receiving water quality problems. The approach combines mass balances with relatively simple receiving water impact models. The research project has learned that the urban drainage system is only one of the determining factors with respect to receiving urban water quality problems. The morphology of the receiving waters and the non-sewer sources of pollution, such as waterbirds, dogs, or inflow of external surface water might be equally important. This conclusion underlines the necessity to changes today's emission based approach and adopt an integral and immission based approach. The integrated approach is illustrated on a case study in Arnhem, where the receiving water quality remained unsatisfactory even after retrofitting a combined sewer system into a separated sewer system.

Advection-dispersion modelling tools: what about numerical dispersion?

In general the transport of dissolved substances and fine suspended particles is governed by the one-dimensional advection-dispersion equation. In order to model the transport of dissolved substances and fine suspended particles, the advection-dispersion equation is incorporated into commonly used urban drainage modelling tools such as InfoWorks CS (Wallingford Software, United Kingdom) and MOUSE (DHI Software, Denmark). Two examples show the use of InfoWorks CS and MOUSE using standard model settings. Modelling results using tracer experiments show that numerical model parameters need to be altered in order to calibrate the model. Using tracer experiments as a model calibration tool, it is shown that a non-negligible amount of dispersion is generated by InfoWorks CS and MOUSE and that it is in fact the numerical dispersion that is calibrated.

Suspended solids transport: an analysis based on turbidity measurements and event based fully calibrated hydrodynamic models.

Modelling suspended solids transport is a key issue for predicting the pollution load discharged by CSOs. Nonetheless, there is still much debate on the main drivers for suspended solids transport and on the modelling approach to be adopted. Current sewer models provide suspended solids transport models. These models, however, rely upon erosion-deposition criteria developed in fluvial environments, therewith oversimplifying the sewer sediment characteristics. Consequently, the performance of these models is poor from a theoretical point of view. To get an improved understanding of the temporal and spatial variations in suspended solids transport, a measuring network was installed in the sewer system of Loenen in conjunction with a hydraulic measuring network from June through December 2001. During the measuring period, 15 storm events rendered high-quality data on both the hydraulics and the turbidity. For each storm event, a hydrodynamic model was calibrated using the Clemens' method. The conclusion of the paper is that modelling of suspended solids transport has been and will be one of the challenges in the field of urban drainage modelling. A direct relation of either shear stress or flow velocity with turbidity could not be found, likely because of the time varying characteristics of the suspended solids.

Wastewater planning in Djenné, Mali. A pilot project for the local infiltration of domestic wastewater.

The city of Djenné (Mali) is famous for its mosque which is the world's largest adobe building. Djenné is considered to be one of the most interesting cities in Western Africa from an architectural point of view. Since 1988, Djenné is listed as a UNESCO World Heritage Site. In the 1990s, a drinking water supply network was provided by foreign development organisations. However, no facilities were provided for the disposal of wastewater, resulting in an increase of waterborne diseases. This paper describes the urban drainage problem in Djenné and discusses the systematic evaluation of possible solutions and the subsequent pilot project for the local infiltration of sullage. The infiltration of sullage proved to be an appropriate technology for solving the urban drainage problem in Djenné.

Interactions within the wastewater system: requirements for sewer processes modelling.

Today's focus on wastewater system optimisation necessitates the development of knowledge on the interactions between sewer systems and wastewater treatment, since these interactions have often been neglected in the past. In this paper the question is discussed to what extent it is favourable and possible to include dynamic changes of wastewater quality in wastewater system optimisation studies. The sensitivity of the wastewater treatment works to influent fluctuations proved to be the key issue in determining which sewer processes are involved in the dynamic interactions between sewer systems and treatment works. The preliminary results show the importance of a good description of the transport processes involving the double and suspended fractions.

Increasing wastewater system performance--the importance of interactions between sewerage and wastewater treatment.

The necessity to assess sewer systems and wastewater treatment plants (WWTPs) as integral parts of the wastewater system has been well known for several years and discussed in many conferences. Until recently, sewer systems and WWTPs were improved (or optimised) separately or independently, which resulted in suboptimal solutions. Nowadays, in The Netherlands as well as in other European countries, a trend can be recognised towards more integral solutions. Nevertheless, due to a lack of knowledge on the interactions between the sewer systems and the WWTPs the implementation of this way of thinking in practice takes a long time. This paper describes the results of two cases in which the interactions between sewerage and wastewater treatment are incorporated within the optimisation of a wastewater system. The first case illustrates the importance of taking the interactions into account, while the second case shows how to deal with the interactions within a wastewater system optimisation study. It is concluded that the combination of total wastewater system analysis, incorporating the interactions within the wastewater system, with efficient search algorithms is expected to be very valuable in future wastewater system optimisation studies.

Isolation of sequences from a random-sequence expression library that mimic viral epitopes.

We describe the use of random peptide sequences for the mapping of antigenic determinants. An oligonucleotide with a completely degenerate sequence of 17 or 23 nucleotides was inserted into a bacterial expression vector. This resulted in an expression library producing random hexa- or octapeptides attached to a beta-galactosidase hybrid protein. Mimotopes, or antigenic sequences that mimic an epitope, were selected by immunoscreening of colonies with monoclonal antibodies, which were specific for antigenic sites on the spike protein of the coronavirus transmissible gastroenteritis virus. We report one mimotope for antigenic site II, eight for site III and one for site IV. The site III and site IV mimotopes were closely similar to the corresponding linear epitopes, localized previously in the amino acid sequence of the S protein. An alignment of the site II mimotope and the sequence of the S protein around Trp97, which is substituted in escape mutants, suggests that this mimotope mimics a conformational epitope located around residues 97-103. Applications of mimotopes to epitope mapping, serodiagnosis and vaccine development are discussed.