Vitamin content of four sludge fractions in the activated sludge wastewater treatment process

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 −1 thiamine, 17.6–43.2 mg kg −1 riboflavin and 10–13 mg kg −1 folic acid with 1–6 μg l −1 thiamine and 9–25 μg l −1 riboflavin in the water phase. Dry digested sludge matter contained 0.9–6.0 mg kg −1 thiamine with a content of the water phase after filtration of 18–386 μg l −1, riboflavin was 3.2–10.8 mg kg −1 and 6–116 μg l −1, respectively, folic acid was 0.25–0.62 mg kg −1 in 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 −1 thiamine, the water phase after filtration contained 3–14 μg l −1, riboflavin was 21.3–41 mg kg −1 with 1–26 μg l −1 in the water phase, folic acid was 2 mg kg −1 in 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.