High rate anaerobic effluent treatment for AS Estonian Cell Pulp mill in Kunda, Estonia

AS Estonian Cell is the main pulp mill in Estonia. Due to investment in a brand new pulp dryer the owners decided at the same time to invest in a new anaerobic effluent treatment plant for the COD-rich effluent prior to the existing activated sludge waste water treatment plant. The produced biogas replaces fossil natural gas as the main energy source for the dryer. The new high loaded anaerobic plant has a capacity of 8 000 m3/day and a load of 100 ton COD/day. Purac was contracted in the beginning of 2013 to design and supply the new plant.

The plant was ready for commissioning early 2014 and at present the new anaerobic plant installed by Purac is running with excellent performance such as a COD reduction more than 75 %, low operating costs, low sludge production and high-yield biogas production. The anaerobic process is a high rate expanded granular sludge bed consisting of a neutralization tank, one anaerobic ECSB-reactor with a bottom distribution system and two threephase separators. Prior to the anaerobic process an extensive pre-treatment comprising of coarse screen, fine screens and dissolved air flotation is installed. After the anaerobic pre-treatment the effluent is led to the existing aerobic treatment plant before it is discharged to the Baltic Sea. The produced biogas is dried and transported in a gas pipe to a boiler where the biogas partly will replace natural gas as fuel, giving economic and environmental benefits.

Teknisk data

Inlet data

  • Hydraulic flow 8 000 m3/day
  • COD-load 100 tons/day
  • TSS 4 000 mg/l

Performance data

  • COD-reduction >75 %
  • Biogas production 30 000 Nm3/day
  • Methane content in biogas >75 %