Freezing-Activated Oxidation with Nitrite and H₂O₂ for Efficient Waste Activated Sludge Solubilization and...

Area of Science:

• Environmental Engineering
• Water Treatment Technologies
• Biotechnology

Background:

• Waste activated sludge (WAS) treatment presents challenges in solubilization and dewatering.
• Nitrite-based pretreatment is known to enhance WAS solubilization.
• Effective sludge pretreatment is crucial for efficient wastewater treatment and resource recovery.

Purpose of the Study:

• To investigate a novel freezing-activated oxidation method using nitrite and hydrogen peroxide (H₂O₂) for WAS pretreatment.
• To optimize the nitrite-to-H₂O₂ ratio for enhanced sludge solubilization.
• To evaluate the impact of this method on sludge filterability and organic matter release.

Main Methods:

• A freezing-activated oxidation process combining nitrite and H₂O₂ was applied to WAS.
• Experiments were conducted at varying nitrite and H₂O₂ concentrations and molar ratios.
• Sludge solubilization was assessed by measuring dissolved organic carbon (DOC) release.
• Sludge filterability was evaluated using capillary suction time (CST) and particle size analysis.

Main Results:

• The optimal nitrite-to-H₂O₂ molar ratio of 1:1 significantly enhanced dissolved organic carbon (DOC) release, reaching 67.6 mg C g⁻¹ VS.
• Compared to freezing alone (32.2 mg DOC g⁻¹ VS), the combined treatment showed superior performance.
• Sludge filterability improved markedly, with CST reduced by over 80% and median particle size increased sevenfold.
• Low molecular weight (LMW) fractions, particularly LMW acids, increased by 4.5-fold.

Conclusions:

• Freezing-activated oxidation with nitrite and H₂O₂ is a highly effective method for WAS solubilization and improving dewaterability.
• The process likely involves the in-situ formation of peroxynitrous acid (HOONO) and reactive intermediates.
• This method offers a promising strategy for sludge treatment and resource recovery, especially in cold climates.