Improve acid production of excess sludge anaerobic digestion using potassium ferrate or ferrate anode solution

Potassium ferrate (K2FeO4) has been widely applied as a pretreatment agent for residual sludge digestion, but the complete synthesis of its solid form is costly. In this study, the use of ferrate anode solution (FAS) was examined as a more economical alternative. FAS is generated as an intermediate byproduct during the electrolytic production of solid K2FeO4. The performance of FAS was compared with that of conventional solid K2FeO4 to assess their respective effects on anaerobic acid production and sludge dewatering. The results indicate that sludge soluble chemical oxygen demand (SCOD) was increased to 3807 mg/L at the low dosage of 10 mL/L, and the production of short-chain fatty acids (SCFAs) reached 2142 mg COD/L. At this dosage, higher efficiencies in protein and polysaccharide release were achieved compared with high-dose K2FeO4 (0.5 g/g TSS). Sludge settling and dewatering properties were also improved, and reductions of 9.1% in sedimentation ratio and 9.7% in cake moisture content were achieved during pretreatment. These findings suggest that FAS, as an intermediate byproduct, can replace solid K2FeO4 for sludge pretreatment because of its high efficiency at low dosages and its distinct enhancement of dewatering performance. FAS may therefore serve as a more economical and effective option.