| Summary: | 碩士 === 國立臺北科技大學 === 環境規劃與管理研究所 === 93 === The objective of this study was to eliminate nitrate contamination from a groundwater source with 30mg/L NO3--N in Nantou County by zero-valent iron/quartz sand packed columns. In the pure ZVI packed columns, nitrate reduction by ZVI was accompanied by with pH increase and ORP decrease. When nitrate removal was efficient, the pHs were around 10.5 and ORP were around -250 mV. Therefore, both pH and ORP are excellent indicator for nitrate removal. Increasing flux leads to reduce nitrate removal. After the reaction, ZVI was oxidized to Fe2O3 and Fe3O4. The dissolved iron was very few about from 0.2 to 0.4 mg/L, and most of nitrate was converted to the ammonia nitrogen.
In the columns mixed with ZVI and quartz sand, the porosity was increased due to stuffing with the quartz sand but the contact area between ZVI and water wasl reduced. S/V is physical factor, representing iron surface per porosity volume. Increase of S/V increases the nitrate removal. S/Q is physical factors, representing iron surface per porosity volume in the operation time. Taking 212μm iron as an example, when S/Q > 7 m2-day/L , nitrate removal rate was over 80%. If S/Q < 7 m2-day/L, columns have to increase the ZVI to fill the quantity.
The result also indicated the nitrate removal ratio can be simulated by the pseudo first-order equation. The Kobs of the ZVI columns were from 8.23 to 12.47 hr-1, quartz filling or increases of HRT also reduced the Kobs. Nitrate reduction by ZVI were from 1.78 to 2.89 mg NO/g ZVI. Comparing to the proposed stoichiometry, used ZVI was only 3.25% of the theoretical value. Therefore, the used iron can be reused again by pretreatment of ZVI.
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