Treatment of Tanning Wastewater with Flyash-Based Coagulant

PBS (flyash-based coagulant) made by fly ash in coal-fired thermal power plants and blast furnace iron sludge extracted with a dilute H₂SO₄ was used as coagulant in the treatment of tanning wastewater. The influence of pH value, coagulant dosage and temperature on coagulation effect was investigated. The results showed that this coagulant had satisfactory results to treat tanning wastewater under the pH value ranging from 6 to 9, combined with polysilicate aluminium(PSA) flocculant. The removal rate of SS, S^2-, Cr³⁺, CODCr and colority in tanning wastewater was 93.1%, 92.8%, 87.6%, 83.3% and 90.8% respectively in the condition where temperature was normal, pH value was 7.0 and coagulant dosage was 70mg/L. The temperature had little impact on the removal rate of CODcr. In comparison with the conventional coagulants, such as PAC (polyaluminium chloride) and PFS (polyferric sulfate), the coagulation performance of PBS coagulant was obviously superior to conventional coagulants. The coagulation mechanism of PBS coagulant in the treatment of tanning wastewater was also discussed.