[Biotransformation and safety of cotton stalk alkaline peroxide mechanical pulping waste liquor].

Objective: We studied the conditions of culturing Bacillus subtilis SY1 to treat cotton stalk alkaline peroxide mechanical pulping waste water, and evaluated afterwards the safety of its release to plants and animals.
Methods: The culture conditions were optimized through single factor tests, including temperature, initial pH, oxygen, and inoculation size. We used rats and big ear rabbits to test the safety of treated waste water.
Results: The optimal condition was as follows: initial pH7.0, hydraulic retention time 30 h, temperature 30 degrees C, filling rate of aeration 16 L/h, the dosage of Bacillus subtilis SY1 0.8 g a liter water, and the stuffing volume accounting for 30% of the effective volume of the reactor. Under these culture conditions, the live spore number of Bacillus subtilis SY1 reached 6.27 x 10(9) CFU/mL. The removal rate of COD reached 70.4%. Results of the acute dermal toxicity test, dermal irritation test, eye irritation test and skin sensitization test after treated by the fermentation showed no clinical signs or changes conditions, and no deaths during the test period of 21 days. Animal body weight had a tendency to increase and had no abnormalities in the major organs, the Lethal Dose 50 (Abbreviated LD50) values was equal or greater than 10.5 g/(kg body weight) in acute dermal toxicity experiments. LD50 values were equal or greater than 2500 mg/(kg body weight) in dermal irritation experiments. No rabbits exhibited chemosis eye at any time during the test period. The results of skin sensitization test showed no erythema or edema. The skin sensitization value was less than 0.5.
Conclusion: Pulping waste water of APMP cotton stalk fermented by Bacillus subtilis SY1 had reduced COD and no obvious toxicity to animals.