Kildesporing af miljøfremmede stoffer i kloaknet English SummaryThe project "Source Identification of Pollutants in Public Sewerage Systems" which is being reported here, is the last of a series of projects under the Danish EPA's "Framework Programme on Reduction of Environmentally Harmful Chemical Substances in Waste, Residual Products and Recyclable Materials". Objectives Discharges of environmentally hazardous chemical substances to public sewerage systems result in emission of substances to the water environment as well as quality problems with the sewage sludge generated. Based on experience, it is very difficult to identify the cause or origin of the problem in the sewerage catchment. Therefore, this project has aimed at developing a universally applicable concept and some tools to identify sources of specified chemical loads in public sewerage systems while methods for identification of unknown substances are not covered by the project. Experience collecting The first activity of the project was to collect and evaluate experience from previous source identification projects in selected municipalities in Denmark and use them to develop a preliminary source identification concept. It turned out that the municipalities interviewed, in general, regarded source identification as an activity which rarely met the expectations. Most of the municipalities stated that they lacked access to and overview of general knowledge about the substances, their use and potential sources. They recommended more focus on 'desk surveys' than on in situ tests and analyses which they found very resource demanding. Source identification concept The developed source identification concept is therefore based on a sequential procedure where Phase 0 is a preliminary assessment/screening with the objective of determining whether the problem in question requires source identification to be carried out or if other types of action are more adequate. The source identification procedure itself is divided into two main phases: Phase 1: "Dry" source identification (desk surveys) Phase 2: "Wet" source identification (in situ) "Dry" source identification In the project, the emphasis has been put on the dry source identification. This is mainly due to the fact that the dry source identification in itself can lead to locating the source (rendering the in situ tracing unnecessary), but also that it makes little sense to carry out the very resource demanding wet source identification without prior maximal use of existing information. The dry source identification is based on gathering and working up existing knowledge within two main groups:
Information on 17 substances Gathering information on the general features of a substance and its use can be very extensive. In the report, procedures and sources of information to use if new or updated information search is necessary, are described. For a number of substances, the municipalities do not need to gather the general information described above as such information on the following 17 substances has already been collected and categorised during the project:
General knowledge The project report contains general knowledge on the mentioned substances which can be used both electronically and manually. The major part of the accessible knowledge deals with the use of chemical substances in the industry and, hence, the collected data are presently especially useful for identification of industrial point sources. But the database also contains information on potential sources of chemical substances in the service sector, public institutions, private households and urban runoff. The database enables answering of a number of typical and central questions in a source identification process, e.g.:
Local information Further development of the database should be made locally based on existing information in the local administrations to make possible, in connection with the project database, the answering of questions like:
PC-based database The above mentioned general data and other information have been entered into a PC-based relational database. This provides the possibility of having a fast overview of the existing knowledge and combining different parameters. To further strengthen these possibilities and to visualise the spatial dimension, the database was linked to a Geographical Information System (GIS). "Wet" source identification The "wet" part of the source identification consists of a number of elements including choice of overall strategy, choice of monitoring points, types of samples and analytical methods and procedures depending on the substance properties and the specific conditions. The report describes the considerations to be made and gives an assessment of the results to be expected. Strategy The choice of source identification strategy primarily depends on how far the dry source identification can be taken. If the load of a substance on the system immediately can be traced to a single or a few isolated sources, the choice of strategy should be different from the situation where the source identification starts with many possible sources spread out in a large catchment area. Sampling methods The choice of sampling method for source identification of different types of substances should be adjusted according to type of source (industry, household, urban runoff), the likely discharge pattern, most adequate sample matrix (water, suspended matter, biofilm on the surface of pipes) etc. in view of the properties of the substance in question including the possible transformation of the substance. Substance properties that are particularly important to know are e.g. the water solubility, lipofilicity and partitioning (including sorption), the microbial and chemical degradability, and whether the "substance" is actually a group of substances which may differ in exact composition depending on the specific field of use (LAS, PAH and NPE are examples of such group designations). Case studies Wet and dry source identification have been carried out in two Danish municipalities (Århus and Roskilde) to test the overall source identification concept. Four main model substances were selected for this purpose, namely PAH, LAS, NPE and DEHP, which are the four xenobiotics for which Danish quality standards have been defined for sewage sludge to be used in agriculture. In the municipality of Århus, the northern catchment area of the Marselisborg wastewater treatment plant was selected for the case study. In this area, the main problem is to comply with the sludge quality standard for LAS. In the municipality of Roskilde, where a sub-catchment area in the southern part of the town was chosen, NPE is the main concern. The dry source identification was based on the existing lists of registered industrial enterprises in each municipality supplemented by an additional registration of major institutions and other possible, significant non-industrial sources in the selected catchment areas. These data were combined with the general knowledge on each model substance to identify the location of possible local sources. The list of likely sources was later compared with the results of the wet source identification. Wet source identification was carried out during six days with continuous collection of suspended matter in the waste water at selected monitoring points reflecting the outputs from the sub-catchment areas identified as most relevant by the dry source identification. The concentration of the model substances combined with information on the water flow in the sewerage system was used to point out the main contributors. A good correlation was found between the sub-catchment areas and potential sources identified by the dry source identification, and the actual concentrations of the model substances found in the samples collected from those areas. An alternative collection method for environmentally harmful substances dissolved in the wastewater (the so-called SPMD) was tested, and it proved fast and reproducible. Options for further actions The report points out a number of possibilities for local action against polluting activities depending on the outcome of an actual source identification. Which type of action to choose depends, apart from that, on the local conditions including the political situation and priorities. Therefore it is difficult to give a universal formula for the action phase. Conclusion It is concluded that the collected general knowledge advantageously can be stored and handled by a pc-based database and be combined with local information on industrial and other potentially polluting activities to encircle the possible sources of a specific substance in a selected part of a specific public sewerage system. With a limited effort the municipalities can extend the already registered local data to make their source identification more comprehensive.
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