WASTEWATER TREATMENTIN LAHTI

There are 2 wastewater treatment plants in Lahti- Kariniemi- Ali-Juhakkala

In these slides we examine waste water treatment in Kariniemi, where the daily intake was 21 500 m3 (2011)

WASTEWATER TREATMENTIN LAHTI (Kariniemi)

•WWTP was built in 1975

•Biological treatment – activated sludge process

•WWTP is underground in a cave (volume = 120 000 m3)

•Sludge treatment on the ground

•Operation of the WWTP happens from control room

SCREENINGScreening removes big particles (e.g. paper) from

wastewater. Screenings are washed, dryed and transported to

a landfill.

GRIT REMOVALGrit is removed by sedimentation, which

means separation of solid, insoluable, particles into a concentrated slurry.

Grit is washed, dryed and transported to a landfill.

PRIMARY CLARIFICATIONIn primary clarification sludge is removed by

sedimentation.Settled sludge is pumped to a sludge treatment.Effluent goes to the aeration (biological

treatment).

AERATION

Aeration + secondary sedimentation = biological treatment

In aeration, the activated sludge concentration is 3 g/l.

Alltogether about 35000 kg of bacteria.

SECONDARY CLARIFICATIONIn secondary clarification the activated

sludge sinks down and is pumped back to aeration.

Effluent goes to the Nikula basin via tunnel, from which to river Porvoonjoki.

NIKULA BASINVolume of the basin is 50 000 – 60 000 m3

PROCESS RECAPWATER TREATMENTScreeningsGrit removalPrimary sedimentationAerationSecondary sedimentationTunnelNikula basinPorvoonjoki

SLUDGE TREATMENTThickeningAnaerobic digestionSludge dryed with

centrifugesComposting

PROCESS RECAPBIOGAS

Biogas is collected and used to heat wastewater treatment plant.

The surplus gas is sold to power company.

CAVE VENTILATION

Cave is ventilated by two blowers -> 20 m3 / second

Air is changed once per hour in the cave.

THAT’S ALL FOLKSTHANK YOU