Valorization of Post-Coagulation Water Treatment Sludge via Microwave and Ultrasonic Disintegration: Evaluation of Leaching Behavior and Sustainable Reuse Potential

Leachability studies of selected contaminants from water treatment sludge subjected to ultrasonic and microwave disintegration under various process conditions were conducted. The risk of contaminant migration into the environment is important in the context of sustainable sludge management and responsible resource stewardship, in line with circular economy principles. Changes in organic matter, total nitrogen (Ntot), total phosphorus (Ptot), aluminum, and selected metals were evaluated. In a water extract from non-disintegrated sludge, the COD, TOC, and Ntot values were 115, 36.5, and 13.1 mg/L, respectively. The aluminum concentration was 0.02 mg/L, while the Ptot and iron concentrations were less than 0.05 mg/L. Increasing the power of both disintegration processes resulted in increases in COD, TOC, Ptot, Ntot, and aluminum in the water extract. Following ultrasonic disintegration, the COD increased from 157 to 170 mg/L, the TOC increased from 37.6 to 50.5 mg/L, the Ptot concentration increased from 0.06 to 0.07 mg/L, the Ntot concentration increased from 14.3 to 17.7 mg/L, and the Al concentration increased from 0.02 to 0.05 mg/L. After microwave disintegration, the COD concentration increased from 155 to 176 mg/L, the TOC increased from 40.3 to 51.6 mg/L, the Ptot concentration increased from 0.11 to 0.47 mg/L, the Ntot concentration increased from 14.0 to 18.1 mg/L, and the Al concentration increased from 0.06 to 0.98 mg/L. Depending on the disintegration method used, the concentrations of metals reached 0.04 and 0.09 mg/L for Zn, 0.04 mg/L for Cu, and 0.03 mg/L for Ni. These results demonstrate that both the method and the parameters of sludge disintegration influence contaminant leachability.