On-line batch production of ferrate with an chemical method and its potential application for greywater recycling with Al(Ⅲ) salt

Ferrate(Ⅵ ) salt is an oxidant and coagulant for water and wastewater treatment. It is considered as a possible alternative method in greywater treatment. However, challenges have existed in putting ferrate(Ⅵ ) technology into full-scale practice in water and wastewater treatment due to the instability of ferrate solution and high production cost of solid ferrate products. This study demonstrated a new approach of greywater treatment with on-line batch production of Fe(Ⅵ ) to which Fe(Ⅲ ) salt was oxidized at a weak acidity solution. A series of experiments were conducted to investigate the effect of Fe(Ⅵ ) on light greywater(total organic carbon(TOC) = 19.5 mg/L) and dark greywater(TOC = 55 mg/L)treatment under different conditions with varying p H and Fe(Ⅵ ) doses. In addition, the combination use of Fe(Ⅵ ) and Al(Ⅲ ) salts was proved to be more efficient than using the Fe(Ⅵ ) salts alone at greywater recycling. The optimum dosage of Fe(Ⅵ )/Al(Ⅲ ) salts was 25/25 mg/L for light greywater, 90/60 mg/L for dark greywater, respectively. The TOC values of both light greywater and dark greywater were reduced to less than 3 mg/L with the dosages.The cost for treating greywater was 0.06–0.2 $/ton at ferrate(Ⅵ ) dosage of 25–90 mg/L and0.008–0.024 $/ton at AlCldosage of 25–60 mg/L. The full operating cost needs further assessment before the Fe(Ⅵ )/Al(Ⅲ ) technology could be implemented in greywater treatment.