DIKA, Driftstörningar i kommunala avloppsreningsverk - en studie av ...

8flow rate, COD and conductivity. With more frequent sampling, like during theintensive sampling days, the model improved. With on-line measurement the model canbe used to regulate the pre-precipitation.Data from weekly sampling also showed that floc properties and the presence of certainfilament forming organisms were connected to specific conditions concerning sludgeload and sludge age.The instrumentation at Borlänge sewage plant was supplemented with on-linemeasurement of TOC in untreated and treated water, conductivity, sludge concentrationin several positions and microbial activity based upon the amount of NADH. Data fromthese sensors and variables like flow rate, pH, dissolved oxygen and temperature wereused for a multivariate description of the process. The operator can at any time in agraph see if the process is normal or not. If it is upset, the model points out the deviatingparameters, and the model can also be used to suggest a suitable countermeasure. Thesystem can be expanded into an automatic regulating system.The project has shown that:• Surfactants and fatty acids in the sewage decrease the oxygen transfer rate.• The problems can be minimized by lowering the sludge load (increasing the sludgeconcentration) and/or by adsorbing a fraction of the incoming fatty acids on theexcess sludge.• Microscopical study of the biosludge and measuring the separation properties givevaluable information about the state of the process.• It is possible to control and regulate the process in real-time, based on signals fromsome extra sensors and multivariate models. One example is modelling of theconcentration of total phosphorus in untreated sewage, calculated from othervariables.The project has led to an increased interest and knowledge among the sewage plantpersonnel. Process disturbances are now less frequent than at the beginning of theproject, hopefully partly as a result of this project.