Sludge reduction and volatile fatty acid recovery using microwave advanced oxidation process

Sewage sludge was subjected to the combined microwave-hydrogen peroxide-sulfuric acid enhanced advanced oxidation process (MW-H₂O₂-H⁺-AOP) to evaluate the potential of reducing suspended solids in sludge. The soluble chemical oxygen demand (SCOD) and acetic acid produced were dependent on the amounts of H₂O₂ and acid used in the process. For sewage sludge, a higher volume of H₂O₂ addition not only favored the destruction of sludge solids, but also conserved the carbon content in the medium. Volatile fatty acid (VFA) concentrations also increased with the amount of inorganic acid in the solution. For the soluble fraction of solutions derived from microwave-treated sludge, over 96% of the total COD was in the soluble form, and up to 25% of this soluble COD was acetic acid. The presence of an inorganic acid was a stability factor in retaining the SCOD in solution, instead of the formation of carbon dioxide, resulting in reduced total COD in the solutions. By controlling the amounts of H₂O₂ and acid addition, the MW-H₂O₂-H⁺-AOP could solubilize and/or reduce the sludge mass.

Keywords:

• Advanced oxidation process
• microwave
• hydrogen peroxide
• acid
• sludge solubilization
• volatile fatty acids.

Acknowledgments

The authors wish to acknowledge the research funding of a Discovery Grant by the Natural Science and Engineering Research Council of Canada.

Notes

∗30 wt%.

∗In Phase 2, the initial COD is the soluble COD from Phase 1.