Treatment of Chromium Removal Wastewater from Tanning by a New Coupling Technology

Abstract

In this study, the coupling process of flocculation and membrane separation was used to treat tannery chromium removal wastewater, and the experimental results of the different process operating conditions were investigated to optimize the entire process design. First, the wastewater was pretreated by flocculation ultrafiltration (UF), and the produced water could directly enter nanofiltration (NF) for concentration treatment. The removal rates of turbidity, chroma, and chemical oxygen demand (COD) of the pretreated wastewater were 96.5%, 53.7%, and 45.8%, respectively. Then, NF multistage treatment was used to control the freshwater recovery rate to 90%, where the salt content of the primary freshwater was 200–500 mg·L−1, and the salt content of the secondary freshwater was 800–1000 mg·L−1, which all met the reuse standards of the factory. The total dissolved solids (TDS) and COD of the concentrated wastewater were 44,000–46,000 mg·L−1 and 10,000–13,000 mg·L−1, respectively. Finally, electrodialysis (ED) was used to desalinate the wastewater, and the desalination rate after primary ED desalination was 52.2%. Subsequently, by increasing the temperature of the wastewater in the desalination chamber to 31 °C, the wastewater was subjected to two-stage ED to remove the sulfate in the wastewater for the second time, and the total desalination rate reached 61.9%. The results showed that this new coupling process could realize the efficient reuse of chromium removal from tannery wastewater.