Influence of H2O2 Advanced Oxidation Processes on Phosphorus Recovery from Waste Activated Sludge

Various studies have proposed using plasma treatment prior to anaerobic digestion to enhance the degradation of organic dry residue (oDR) and increase biogas production. This disintegration process also significantly affects phosphorus release by disrupting cell walls. Several studies show that the driving disintegration process through plasma implementation occurs due to the production of hydrogen peroxide. Since targeted plasma treatment is still technically demanding, this study proposes to estimate the related P release by applying defined hydrogen peroxide dosage to the test medium. Here, the approach was implemented on washed activated sludge (WWAS) in batch tests using H₂O₂ at two different temperatures: 20 °C and 60 °C. Results show only heating treatment mobilised approximately 23% P as PO₄-P, while only 9% P was mobilised by applying 3.4 g H₂O₂ / g DR at 20 °C. The reason behind this scenario is the low reactivity of H₂O₂ as catalase is active at ambient temperature, which also caused only 3% COD solubilisation. However, complete COD solubilisation was achieved by applying similar dosage of H₂O₂ at 60 °C. In this treatment condition, dissolved P mobilisation increased to 40% while PO₄-P mobilisation reduced by 11%. The reduction of PO₄-P can be occurred by parallel formation of P related precipitants, since metal ions like Ca and Mg released in this study. Additionally, the oxidation of ammonia to nitrate is also observed, resulting in lower pH (4.41). Also, the oxidation of Fe²⁺ to Fe³⁺ could cause FePO₄ precipitation. These observed effects are probably transferrable to activated sludge from other wastewater treatment plants (WWTPs). Summarizing these effects, high temperature developed in intense wet plasma treatment can prevent the intended P recovery from the wet sludge phase or sludge liquor.