Improvement of settleability and dewaterability of sludge by newly prepared alkaline ferrate solution

• NPAF enhanced sludge disintegration and improved the settling and dewatering property of sludge.
• The increase of ferrate stability leaded to the better performance of NPAF.
• The flocculation of ferric in situ formed also contributed to the sludge settling.
• The improvements of settleability and dewaterability attributed to the degradation polymeric matters.
• The effect of single Fe(VI) or alkali on sludge reduction was feeble.

Dewatering and settleability by alkaline hydrolysis and oxidation (e.g. ferrate) has been a key issue in waste activated sludge treatment. This study demonstrated that, the newly prepared newly prepared alkaline ferrate (NPAF), containing Fe(VI) and KOH, could effectively disrupt sludge structure and simultaneously improved the dewaterability. It was determined that, at 500 mg/l of NPAF dosage range, the sludge settleability and dewaterability were improved to 55.1% and 7%, respectively. At low dosage of NPAF (i.e. <150 mg/l), the dissolved organic matter in the medium was increased whereas, in higher concentration (i.e. 200–700 mg/l) free water content of sludge floc was released by degrading polymeric substances and other biological macromolecules. The disintegration and structural damages of sludge floc treated with different NPAF concentration and extent to which complete damage (400 mg/l) were determined by scanning electron microscope. Owing to the presence of alkali-KOH in NPAF, the stability of Fe(VI) was significantly improved by 4–6 times, which may resulted on the excellent performances of NPAF for the degradation of the macromolecules.

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