THE ENHANCEMENT OF BENZOQUINONE ON CR (VI) REDUCTION BY EXCESS SLUDGE
Keywords:
Cr(VI) reduction, Excess sludge, Electron shuttle, BenzoquinoneAbstract
The excess sludge is rich in reducing substances, which can convert highly toxic hexavalent chromium (Cr(VI)) into less toxic trivalent chromium (Cr(III)). However, the process often suffers from low electron transfer efficiency. This study investigated the effect of the electron shuttle benzoquinone on the reduction of Cr(VI) by excess sludge. The results showed that, in a system containing 2 g/L of excess sludge and 5 mg/L of Cr(VI), after 30 minutes of reaction, the Cr(VI) removal efficiency increased from 43.2% to 76% as the benzoquinone concentration rose from 0 to 6 μM. However, when the benzoquinone concentration further increased to 10 μM, the removal efficiency decreased to 59.8%. Without benzoquinone, the Cr(VI) removal efficiencies within 30 minutes were 95.8%, 82.8%, 43.2%, 35.7%, and 23.6%, when the pH values were 3, 5, 7, 9, and 11, respectively. After adding benzoquinone, these values changed to 95.5% and 84.8% at pH 3 and 5, and increased to 76%, 54.2%, and 33.4% at pH 7, 9, and 11, respectively. These results indicate that benzoquinone can promote the reduction of Cr(VI) by excess sludge under neutral and alkaline conditions, while under acidic conditions or in the presence of bicarbonate, it has little effect on Cr(VI) reduction.References
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