How is the wastewater from Sulphur Black 1 production typically treated?

How is the wastewater from Sulphur Black 1 production typically treated?
Sulphur Black 1 manufacturing generates wastewater containing sodium thiosulfate, sodium chloride, and sodium sulfate. A typical treatment scheme for a 300-tonne-per-day production line involves activated carbon decolorization, plate-and-frame filtration, MVR evaporation, followed by double-effect evaporation to separate sodium chloride and sodium sulfate salts. The remaining liquor undergoes continuous crystallization to recover sodium thiosulfate as a saleable byproduct. For solid waste streams containing sodium thiosulfate and sodium sulfate, a high-temperature filtration step removes sodium sulfate first, then cooling crystallization yields sodium thiosulfate. Key process controls include maintaining feed concentration around 52-55 Baume, managing cooling water temperature at 35°C, and carefully controlling cooling rates to avoid excessive supersaturation, which would generate fine crystals rather than large, filterable ones. This integrated approach enables near-zero liquid discharge while recovering value from byproducts.