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RESEARCH PRODUCT

Optimalisering av driften ved Saulekilen Renseanlegg i Arendal kommune med hensyn på kjemisk felling og slamavvanning

subject

description

The wastewater contains a lot of nutrients that can be harmful to nature, such as phosphorus. Therefore, to avoid negative consequences caused by these nutrients, it is desirable to minimize them before discharge. The chemical purification step consists of several processes, chemical precipitation, coagulation, flocculation, and separation. The main goal of these processes is to form large enough flocks of the precipitated particles so that they become large enough to be able to separate it from the wastewater by separation methods. The separated particles are passed on in the form of sludge where it is treated and thickened and centrifuged to dewater it. Arendal municipality doses based on the dosing table to reach a precipitation pH of 5,9 and in winter the plant struggles to thicken the sludge. This master thesis is about optimizing the operation of the Saulekilen treatment plant in Arendal municipality, about chemical precipitation and sludge dewatering. It also investigates whether the plant’s dosing table corresponds with results from the laboratory and which precipitation pH gives better results about phosphorus concentration in the outlet. Moreover, it explains the relationship between incoming wastewater and phosphorus concentration in the inlet and outlet, by analyzing the operation data. And whether road salt has any effect on the sludge’s drainage properties. Through analyzing the results from the laboratory, it shows that Arendal municipality overdoses chemicals to reach a precipitation pH of 5,9 when the water volume is above 60 l/s. Examination of Arendal municipality’s plant data shows that the larger the amount of water that enters, the lower the phosphorus concentration in the wastewater. The same applies to outlets. The sludge tests show that adding saline solution destroys the polymer bonds, makes the sludge more liquid and decreases the dewatering effect.