Rening av metallhaltigt avloppsvatten
En teknisk/ekonomisk utvärdering av reningsmetoder för metallhaltigt avloppsvatten
This Master?s Thesis aims to investigate and assess the methods used to decrease the discharge ofmetals, primarily copper, from the water purification plant at Assa Industries plating factory inEskilstuna.Literature studies of the purification methods precipitation, ion exchange, evaporation, reverseosmosis and electrolysis has been done to appraise the adequacy of the technique. Thesetechniques are commonly used for purification of industrial waste water.Assa has four plating lines: the Trumline, the big Zinkline, the new Zinkline and the Decorativeline. The new Zinkline is the most modern of the four lines and purification is done byrecirculation over an ion exchange unit. The demand for fresh water is thereby heavily reduced.The Trumline, the big Zinkline and the Decorative line all use older techniques. No ion exchangetakes place in these three and many of the rinses are two step rinses which causes a large waterdemand. When the parts are dipped into the process bath, drag containing metal will follow intothe rinse water. This causes various impurities of metals and complexing agents to appear in therinse water.A number of measurements have been done to establish the metal concentration in the differentparts of the purification plant. The metal concentration is therefore known to some extent. It wasestablished that the concentration in to the purification plant varied significantly but at the end ofthe purification process, the metal concentrations were stable at low levels. Laboratory tests weredone to examine if sulphur based precipitation chemicals, as an extra purification step, wouldaffect the results.Cost calculations using annuity tables [3] have been carried out to examine the capital andproduction costs which, put together, are the total costs. The remaining equipment value has notbeen taken into consideration because it is very much affected by decisions not controlled by thecompany itself, for example municipal regulations.The conclusion after literature studies and cost calculations is that ion exchange is the besttechnology. The costs are fairly low and the purification results are very good. I also think thatthis technology has improvement potential.