Enhanced purification of hospital wastewater by a novel ferrate(VI) flocs recycling process

Traditional Fe(VI) treatment process does not fully utilize the fresh iron flocs. This study proposed a novel Fe(VI) flocs recycling process. The flocs were recycled into the front-end reactor and the flocculation effluent further reacted with Fe(VI). Compared with Fe(VI) alone, the CODCr of the secondary effluent of hospital wastewater decreased from 74.9 to 59.4 mg/L and TP decreased from 0.36 to 0.10 mg/L at the dosage of 20 mg/L Fe(VI). However, the enhanced removal of NH3-N and TOC by the flocs recycling process is limited. The Fe(VI) flocs recycling process also strengthened the removal of luminescent bacterial acute toxicity, from 0.52 +/- 0.01 in secondary effluent to 0.17 +/- 0.01 mg-ZnSO4/L. Compared with polymeric ferric chloride and ferric chloride (FeCl3), Fe(VI) showed the best performance on purifying wastewater in the flocs recycling process. Compared with FeCl3, the C--O bond contents in flocs from Fe(VI) changed more obviously. Flocs from Fe(VI) have a smaller average particle size than those from FeCl3, which may result in better adsorption capacity of Fe(VI) flocs. In conclusion, the flocs recycling process not only taken full use of the Fe(III) flocs and reduced the iron sludge, but also strengthened the purification of the wastewater without additional Fe(VI) dosing.