ADVANCED NITROGEN REMOVAL: 80 MGD AS-PROCESS MODIFICATION TO MLE-PROCESS AND FUTURE INTEGRATION TO POST-DENITRIFICATION FILTERS, CITY OF HELSINKI, VIIKINMÄKI WWTP

Viikinmäki wastewater treatment plant is the largest WWTP in Finland. All the wastewater from Helsinki and the neighboring areas flows through it. The plant is excavated underground and it has been in operation since 1994. The process started as a plug flow carbon removal activated sludge process. In 1998 the process was upgraded into a single-sludge MLE-process because the requirements for nitrogen removal had increased. The new process was implemented into the existing aeration tanks. From the beginning of the year 2000 the target of nitrogen removal was set to 70 %. As a response to the new requirements, the plant is now under enlargement. Tertiary treatment unit is being built with biological post-denitrification filters, which will be operational in 2003.Nutrient removal improvements in Viikinmäki WWTP will be accomplished through three enhancements: additional treatment lines, biological post-denitrification filters and separate handling of the bypass water. Pilot test runs were arranged with biological filters for the postdenitrification and with a pilot container for the bypass water treatment to ensure these extension projects will improve the treatment efficiency. All the projects will be completed in 2005.