Fractionation of Macro and Trace Metals Due to Off-Time Interrupted Electrodewatering

Abstract

Electrodewatering with interrupted voltage was set up to investigate the effects of long off-time interruption on solid content in the final sludge cake and the fractionation of macro and trace elements in the sludge matrix. In comparison to continuous direct current (DC) electrodewatering, long off-time interruption had a negative effect on water removal, resulting in a high water content in sludge at anode and the final sludge cake. However, long off-time interrupted electrodewatering significantly increased dry solid (DS) content in the final sludge cake in comparison to control experiments. Removal of Na⁺ and K⁺ from sludge was affected by long off-time interruption. The long off-time interruption also negatively influenced the dissolution and migration of macro (Ca, Mg, and Fe) and trace (Ni, Mn, and Zn) metals in sludge cake matrix. The long off-time interrupted voltage application did not have any effect on the chromium concentrations in sludge at the anode; however, the chromium concentrations in the removed water at the anode significantly depended on off-time interruption.

Keywords:

• Electrodewatering
• Electroosmosis
• Metal fraction
• Off-time interruption
• Sludge

ACKNOWLEDGMENTS

The authors thank Eveliina Repo for her assistance with the ICP metal analysis. Anshy Oonnittan is thanked for language revision of the manuscript. The authors gratefully acknowledge the financial support from Maa-ja Vesitekniikan tuki ry, EU, and City of Mikkeli.

Notes

6 M KOH and HCl solutions were used for pH adjustment.

^a Shaking was applied at 30 rpm.

^b Extraction of the residual fraction in the microwave oven was used the same method as the pseudo-total extraction.