The aim of this paper is to present current work to develop a system of performance indicators (PI) for wastewater services undertaken under the auspices of IWA and coordinated by LNEC. Present day wastewater utilities manage their services and systems in an increasingly demanding and complex way. For this reason, it is important to support their work and decision processes with the best available tools in order to deliver services with the most effective and efficient performance. The paper focuses on proposed performance indicators (PIs) for wastewater services and on the main aspects of PI assessment. These are based on data related to: environmental, operational, personnel, physical, quality of service and economic and financial performance. Data are mostly made available through the various common-use information systems in the utilities. This IWA forum has been important not only for the dissemination of the work already developed but also as promotion of a wider discussion to enhance the final draft version of the IWA Manual of Best Practice due for publication in 2003.
Published by IWA Publishing. 2003. ISBN 1-900222-90-6; xii + 174pp; hardback; price €52.50 to IWA Members, €70.00 to non-members.This publication is the third in a series of Manuals of Best Practice dealing with performance indicators and process benchmarking. The aim of the manual is to provide a set of indicators which describe the characteristics and performance of individual features of wastewater systems which are precisely defined and capable of being understood generally and accepted internationally.The publication comprises the text and a CD-ROM with the SIGMA Lite WW software, developed by lnstituto Tecnologico del Agua (ITA), Valencia Polytechnic University, Spain. The software is for use once the selection of the set of performance indicators (to be evaluated) has been made.The manual covers the structure of the wastewater performance indicator system and data reporting based upon a confidence grading scheme. The indicators rely upon a concept of 'Context Information' considered in terms of profiles for (a) the wastewater utility, (b) the systems managed, and (c) the geographical context in which the wastewater utility operates. A total of 182 indicators are included, ranging in number from 12 physical to 56 operations indicators.A set of three comprehensive appendices cover a glossaly of technical terms, specifications of each parameter required to assess the performance indicators, and an introduction to the software with tips for use and an example of application.The level of detail of the performance indicators is preciseperhaps too precise in some instances. One clue which demonstrates that the manual will be understood generally and accepted internationally is the claim in the introduction regarding the contribution of this manual and the water services manual to ISO/TC224 -Service activities relating to drinking water supply and wastewater systemsquality criteria of service and performance indicators. The claim that the IWA manuals are contributing to the work of the IS0 committee can be verified by your reviewer who leads the UK delegation to this IS0 TC.Brian Spark (Water Engineering and Standards Solutions)
Solids at the water-sediment interface in combined sewers are known to be important for pollution potential during storm washout via CSOs. They have been investigated in several studies, but nonetheless, little is known about the origins, build-up, transport and nature of these solids. From a review of current knowledge it is apparent that whilst there is general agreement that these solids are largely organic and have high polluting potential, their modes of transport and definition are not generally agreed upon. It is possible that there may be several "types" of these solids, defined as either: "near bed solids" or "fluid sediments/dense undercurrents", possibly representing transport modes in flows with different ranges of ambient (dry weather) velocities and with differing sewerage layouts. Current knowledge is presented and new ideas for resolving the uncertainties regarding the nature, movement and effects of this material are outlined.
The development of ASM2 has created a complex model for biological phosphorus removal. Most of the published work on calibrating this model has focused on the design of experiments to maximise information with which to calibrate the model, or the use of hourly data collected around and within an aeration tank. But many sewage works do not collect such data, nor have such instrumentation. The application of ASM2 with sparse data collected at a low frequency, and mostly only input-output, is considered in this paper, based on data collected at a Swedish sewage works. This paper shows that ASM2 can be calibrated with such measurements. This paper also looks at a modification to ASM2d to better handle heterotrophic usage of volatile fatty acids, and the use of this model to study the effects of large increases in in-sewer storage on sewage treatment works. Concern about the generation of large quantities of VFAs, and their effect on the sewage treatment processes, was unfounded.
This paper provides an overview and some preliminary results of a collaborative project recently completed at WL Delft Hydraulics. It describes tests in an annular flume, in which sediment deposits were formed under carefully controlled and monitored environmental conditions. The deposits were then subjected to a series of time steps in which the rotational speed of the flume's top and bottom plates was increased, progressively increasing the bed shear stress. The sediment deposits were formed using three different types of sediment. An artificial organic sediment, together with a uniformly sized sand were selected as surrogate sewer sediments. The deposits in the remaining experiments were real in-sewer sediments, from catchments in the UK (Dundee) and The Netherlands (Loenen). During the erosion test, total and volatile suspended solids concentration, particle size distribution of the eroded sediment, and COD and DO levels were recorded. The bed surface topography was also measured so that the influence of the deposit formation condition on bedforms could also be examined. Where bed consolidation times were least 24 hours a biologically active surficial layer was observed to develop at the sediment/water interface. The initial deposit conditions (temperature and deposit duration) were both found to have a significant impact on the subsequent erosion of the deposit.
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