Abstract
The nitrate pollution of waters and groundwaters is an important environmental and health concern. An interesting method to remove the oxidized forms of nitrogen from waters and wastewaters is chemical denitrification by means of metallic iron (Fe0). Particularly advantageous is the use of nanoscopic zero-valent iron particles due to the elevated surface area, which allows reaching extremely high reaction rates. In the present paper, the efficiency of nitrate reduction by means of nanoscopic Fe0 has been investigated under several operating conditions. The iron nanoparticles were synthesized by the chemical reduction of ferric ions with sodium borohydride. The effects of Fe0 dosage, initial N–NO3− concentration and pH on chemical denitrification were identified. In particular, the results of the tests carried out showed that it is possible to reach an almost complete nitrate reduction in treating solutions with a nitrate nitrogen concentration higher than 50 mg/L. Moreover, the process performance was satisfactory also under uncontrolled pH. By means of the trends detected during the experiments, the kinetic-type reaction was identified. Furthermore, a relation between the kinetic constant and the process parameters was defined.
Highlights
Nitrate pollution is a serious environmental problem, because it causes eutrophication phenomena and may lead to diseases when drinking water sources are contaminated
In treating solutions with an initial N–NO3− concentration of about 50 mg/L, at pH = 3 and with the lower amount of nanoparticles, an abatement close to 56% was obtained, reaching a residual concentration of about 23 mg/L (Figure 1a). This yield rapidly increased up to an almost complete nitrate abatement using a concentration of nanoparticles equal to 2 g/L. (Figure 1a)
The experiments conducted for this work allowed investigating the effects of operating conditions on nitrate reduction in wastewaters by means of nanoscopic zero-valent iron particles
Summary
Nitrate pollution is a serious environmental problem, because it causes eutrophication phenomena and may lead to diseases when drinking water sources are contaminated. Many physicochemical and biological processes, such as ion exchange, reverse osmosis and biological denitrification, have been used to remove nitrate from waters and wastewaters. Ion exchange and reverse osmosis may be expensive, because they require frequent regeneration of the media and generate secondary waste [1]. Biological denitrification, the most widely-used method, produces excessive biomass and soluble microbial products that require further expensive treatment for use in drinking water supplies. The N–NO3− chemical reduction to ammonia by means of microscopic zero-valent iron has been widely studied, because this metal is abundant, inexpensive and readily available and because its reduction process requires little maintenance [1,2,3,4,5,6,7,8,9,10,11,12]
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