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208 



1 EUGENE P. HAYDU 



2 to be very satisfactory. 



3 Recent studies have shown that a substan- 



4 tial portion of pulp mill wastes, including the toxic 



5 components, are very susceptible to microbial degradation 

 g and destruction. In one study kraft mill wastes were 



7 found to be nontoxic to oysters at a dilution of 1 to 20 

 g when the BOD of the wastes were reduced by 80 percent. 

 9 ! In another study, the toxicity of kraft waste to silver 

 salmon was found to diminish in approximate proportion 

 jj to the degree of BOD reduction. 

 12 Results of the most recent investigations 



by scientists of the International Pacific Salmon Commission 

 indicate a fairly close relationship between the degree of 

 BOD reduction and decrease in the toxicity of kraft wastes. 

 They found no apparent toxicity to salmon when the BOD 

 was reduced by 65 percent. While similar studies have not 

 been made with sulfite liquor, the available evidence indi- 

 cates that the toxic components of this waste are also 



20 degraiable. The toxicity of fresh sulfite waste liquor at a 



21 PBI concentration of 50 ppm would be much greater, there- 



22 fore, than of biodegraded sulfite waste liquor at the same 



23 PBI concentration. 



24 The composition and the toxic characteris- 



25 tics of sulfite waste liquor in receiving waters would vary, 



13 

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