Biological Wastewater Treatment

Purac AB has successfully delivered a turnkey contract including a completely new biological treatment plant for Värö Bruk. The total contract value was approx. MSEK 40.

Värö Bruk is a TCF (Totally Chlorine Free) pulp mill, and the wastewater treatment plant treats mainly bleaching effl uents rich in COD from the mill. Also a small portion of water from the debarking station and landfill leachate is fed to the plant. The process includes cooling, biological treatment in three steps and final clarification. The produced sludge is pumped 700 m to the evaporation building where it is dewatered in a centrifuge, evaporated and finally burnt in a recovery boiler. The biological process is a modified Biofilm Activated Sludge process (BAS) consisting of two biofilm steps prior to an activated sludge treatment step. The biological process is very compact and needs less space than a traditional activated sludge process. The operation principles in the modified BAS process are to add a very low dosage of nutrients, which will starve the micro-organisms. The result is lower sludge production and better sludge-settling properties compared to a conventional activated sludge process. With this process, it is also possible to fulfill the very exacting requirements for outlet of phosphorus and nitrogen.

Technical data

Inlet Wastewater
Design flow: 1 125 m3/h
Maximum flow (duration 2 h): 1 300 m3/h 
CODin, monthly average: 35 t/d
CODin, daily max: 50 t/d
N-total: 15 mg/l 
P-total: 2.5 mg/l

Effluent quality
> 70 % reduction at z90-pulp
> 60 % reduction at z85-pulp
N-total reduction > 50 % 
P-total reduction > 50 % 
SSGF/A < 30 mg/l
EDTA reduction > 80 %