School of Chemical Technology Degree Programme of Chemical Technology Laura Rossi ENHANCING PHOSPHORUS REMOVAL BY DISC FILTRATION – A CASE STUDY FROM VIIKINMÄKI WASTEWATER TREATMENT PLANT Master’s thesis for the degree of Master of Science in Technology

Phosphorus is an essential nutrient for all living organisms. However, high concentrations in a water body accelerates eutrophication. Discharge limits for phosphorus are getting tighter for wastewater treatment plants, thus new tertiary treatments for removal have to be considered. In addition, hygienization of wastewater may become mandatory. At Viikinmäki wastewater treatment plant, the phosphorus discharge limit can tighten from 0.3 mg/l to 0.1–0.2 mg/l. New limit is not possible to achieve with the current process. The aim of this study was to investigate the feasibility of a discfilter in the removal of phosphorus and suspended solids at the Viikinmäki wastewater treatment plant. The goal was to achieve total phosphorus concentrations below 0.1 mg/l in the effluent. In addition, the ability to treat bypass waters and hygienization was studied. Before pilot scale studies, suitable chemical combinations were determined by jar tests. Pilot runs proved that mechanical removal is insufficient thus chemical addition is mandatory. Two aluminium based and one iron based coagulant were tested with cationic polymer. Aluminum based coagulants performed better and the optimum dose was 0.5–1.0 mg/l with polymer concentration 1.0 mg/l. However, the quality of the pilot influent affected greatly to the chemical doses. Nevertheless, with the discfilter it was possible to achieve consistently effluent with under 0.1 mg/l total phosphorus concentration. Furthermore, discfilter was able to reduce the bacteria amount and removal was enhanced by chemical addition and smaller pore size. However, the discfilter is more suitable in removing suspended solids before more efficient hygienization process such as UV-hygienization or ultraor nanofiltration. Bypass water tests proved that phosphorus concentrations can be decreased from 1.6 mg/l to 0.51 mg/l. Based on pilot runs, it can be concluded that the discfilter can be an alternative tertiary treatment step for phosphorus and suspended solid removal at Viikinmäki WWTP