Abstract
The effects of cobalt sulphate and sodium fluoride on the vitamin B_<12> content in activated sludge and on the efficiency of sewage treatment were investigated. The addition of cobalt sulphate within the range of 0.002 to 40 p.p.m. to the sewage going to be aerated for the purpose of increasing the vitamini B_<12> content in activated sludge has been found not to affect both the vitamin B_<12> content and the efficiency of sewage treatment. The presence in the sludge of sodium fluoride, which was added to the city water up to 1 p.p.m. for preventing tooth decay, was found to show no unfavorable effect on the vitamin B_<12> amount and the efficiency of sewage treatment.
