The content of the water-soluble vitamins thiamine, riboflavin and folic acid was determined in the dry solids and the water phase of activated sludge and digested sludge respectively, in municipal and industrial wastewater treatment plants. Thiamine and riboflavin were determined by fluorimetric detection. Folic acid was determined by means of microbiological assays. Dry solids of activated sludge from municipal wastewater treatment plants contained 1.1-6.6 mg kg-1thiamine, 17.6-43.2 mg kg-1riboflavin and 10-13 mg kg-1folic acid with 1-6 μg l-1thiamine and 9-25 μg l-1riboflavin in the water phase. Dry digested sludge matter contained 0.9-6.0 mg kg-1thiamine with a content of the water phase after filtration of 18-386 μg l-1, riboflavin was 3.2-10.8 mg kg-1and 6-116 μg l-1, respectively, folic acid was 0.25-0.62 mg kg-1in the dry solid matter, none was found in the water phase. Dry solids of activated sludge from industrial sewage treatment plants contained 1.9-29.1 mg kg-1thiamine, the water phase after filtration contained 3-14 μg l-1, riboflavin was 21.3-41 mg kg-1with 1-26 μg l-1in the water phase, folic acid was 2 mg kg-1in the dry solids of activated sludge. The vitamin content varies in different sludge fractions. The requirements of heterotrophic saprophytes for thiamine and riboflavin should usually be met by the vitamin content in the sludge. Before dosing the vitamin content should be monitored. © 1994.
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