Ferrate is believed to have a dual role in water treatment, both as oxidant and coagulant. Few studies have considered the coagulation effect in detail, mainly because of the difficulty of separating the oxidation and coagulation effects. This study aims to evaluate the coagulation performance of ferrate together with its oxidation effect in water and wastewater treatment processes, as it has not been studied thoroughly in previous work. The study involves laboratory-based experiments that investigate the coagulation reaction dynamically via a PDA instrument, between ferrate and a suspension of kaolin powder, and humic acid solution at different doses and pH values, and comparing the observation with the use of ferric chloride. The PDA output gives a comparative measure of the rate of floc growth and the magnitude of floc formation. The results of the tests with kaolin suspension show some similarities and significant differences in the pattern of behaviour between ferrate and ferric chloride. Ferrate demonstrated very similar coagulation characteristics to ferric chloride with regard to the influence of pH and Fe dose. However, the magnitude of floc formation with ferrate was always inferior to that with ferric chloride. The rate of floc growth with ferrate was slower and sometimes less extensive than that with ferric chloride in most cases. It was discovered that the reason for the inferior performance of ferrate was the slow formation of Fe(III) species at neutral to high pH owing to the low degradation rate of ferrate in aqueous solution at these pH values. The interaction between HA and ferrate was extensively investigated in comparison to ferric chloride in this study. The results reveal that ferrate achieved comparable or better floc formation to ferric chloride over a much broader Fe dose range. However, the degree of organics removal (DOC) was lower than ferric chloride (~5%). The results obtained from model waters containing HA were consistent with those for samples of a natural upland coloured water. Ferrate oxidation appears to increase the hydrophilic and electronegative nature of the HA leading to an extended region of charge neutralization and a consequent slightly lower HA removal compared to ferric chloride.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:556517 |
| Date | January 2012 |
| Creators | Tran Tien, Khoi |
| Contributors | Graham, Nigel |
| Publisher | Imperial College London |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/10044/1/9642 |
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