Spent liquor from alkaline pulping and bleaching containing spent inorganic process chemicals and dissolved organic substances originating from the cellulosic raw material.

Toxicity to microorganisms

Description of key information

EC50 (15 min) values for V. fisheri were 1. ) ca.2156 mg/l (wwt.), 2.) 374 mg/l (wwt.) and 3.) 849 mg/l (wwt.).
The composition of the three tested samples are:
1. Mixed liquor (liquor from after the mixed liquor tank, after soap removal, with the extractive agens largely extracted, with a dry substance content of 20 %), 
2. Concentrated black liquor (from after the final concentrator) with a dry substance content of 65 % and 
3. Concentrated black liquor, which is a mixture of three weak black liquors (two from sulphate cooking and one from neutral sulphite cooking), with a dry substance content 68%. 

Key value for chemical safety assessment

EC50 for microorganisms:

374 mg/L

Additional information

There was only one study concerning toxicity to microorganisms. The EC50 (15 min) values for V. fisheri varied between about 374-2156 mg/l (wwt.). In general the toxicity of black liquor to micro-organisms is at low level.