Tungmetallsrening vid Sofielunds lakvattenreningsverk : Utvärdering av reningsprestandan och driftoptimering efter teknisk utbyggnad

Sammanfattning

Landfill leachate containing high concentrations of heavy metals poses a risk to human health and the environment if not treated properly. Sofielunds leachate treatment plant, located in Stockholm, treats landfill leachate and less polluted runoff from impervious surfaces used for handling waste. With regards to regulatory limits, Sofielunds leachate treatment plant is required to reduce As, Cd, Cr, Cu, Hg, Pb and Zn in the discharge effluent. Jar tests and full-scale tests were conducted using polyaluminiumklorid (PACl) and sodium hydroxide dosed within the ranges 5-45 g Me/m3 and 0-1 l/m3 respectively. A constant dose of polymer was used. Jar tests were used to evaluate the effect of chemical dosages on heavy metal removal in different mixtures of leachate and waste runoff. Full-scale tests were carried out to optimize chemical dosages for a constant mixture of leachate and waste runoff, with regards to the overall plant performance. An increased proportion of landfill leachate relative to waste runoff increased the water’s conductivity and achieved a more effective treatment. For the jar tests, the removal of Cd, Zn och Pb increased with higher dosages of sodium hydroxide, while the Cr and Cu reduction was more dependent on PACl dosages. The As reduction remained low regardless of chemical dosages. In full-scale higher dosages improved the efficiency of the chemical treatment but also put greater strain on subsequent treatment steps. To attain an adequate heavy metal removal, sodium hydroxide additions and PACl dosages over 10 g Me/m3 were necessary. The optimal dosage, for the conditions applied during the full-scale tests, was determined to be 20 g Me/m3 PACl and 0.5 l/m3 sodium hydroxide. Using these dosages, all analysed metals were reduced below regulated quantities.