Long-term performance of enhanced-zero valent iron for drinking water treatment: A lab-scale study

- Enhanced-ZVI bed become passivated after 10,000-bed volumes operation.
- The passivated enhanced-ZVI bed could be regenerated with sulfuric acid.
- Enhanced-ZVI could improve the performance of subsequent biofiltration.
- A novel water treatment train incorporating enhanced-ZVI was proposed.

Former studies have shown that enhanced-zero valent iron (ZVI) could effectively remove various contaminants. The present study evaluates for the first time the long-term performance of enhanced-ZVI to remove natural organic matter (NOM), an important water quality parameter in drinking water. Lab-scale flow-through experiments showed that averagely 7-14% dissolved organic carbon (DOC) and 6-15% ultraviolet absorbance at 254 nm (UV254) reduction could be achieved by enhanced-ZVI in the first 10,000 bed volumes filtration when a 0.36 or 1.8 mins empty bed contact time (EBCT) was applied. After 10,000-bed volumes, the enhanced-ZVI bed became passivated. However, sulphuric acid was able to regenerate the passivated enhanced-ZVI bed, recover the capacity of enhanced-ZVI in removing NOM, and hence make the best use of the available ZVI. The acidic rinsing solution containing dissolved iron was suitable as a supplemental source of iron for coagulation. In addition, during the long-term experiments, the biofilters following enhanced-ZVI (1.8 min EBCT) removed more NOM than biofilters without any pre-treatment. This could be explained by the formation of biodegradable organic matter (BDOC) during the enhanced-ZVI process and the precipitation of iron in the biofilters. Based on these findings, a novel water treatment train, incorporating enhanced-ZVI with periodical regeneration, biofiltration, and coagulation, was proposed and evaluated.

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