Study On Removal Of Nitrate From Groundwater By Zero-valent Iron Reduction Process

In recent years, with the high speed development of economy and society, bringing much serious pollution to groundwater resources. Nitrate is one of the pollutants which entering the underground water frequently most. Nitrate pollution in ground water has been an importantly environmental problem. During the technologies applied to remove nitrate in ground water, biological denitrification which based on nitrification and denitrification has more complex process operation and high management demand, except that it may lead to the existence of bacteria and organic compounds in water, it request further treatment. But lively metal reductive law because of the operation is simple and quick response affected by many scholars' attention. The zero-valent iron called internal electrolysis and less-biodegradable dates from 1970s, after the 1990s using iron powder as reductant purify water nitrate nitrogen studies are extensively. Many scholars found that the main product of nitrate reduction by zero-valent iron is the ammonium, and the wastewater disposed by zero-valent iron achieves good effects. Because of the iron powder which source wide, price cheap, it can be the ideal reductant, except that the zeolite has the good adsorbability to the ammonia nitrogen. Since that the nitrate can be removed from ground water by Fe⁰-zeolite and Fe⁰/C micro-electrolysis.This research tests on the basis of static test, by using dynamic continuous flow mode of operation research. It is the important that to determine the process operating conditions for example pH, NO₃^--N content and HRT etc of nitrate remove from groundwater by Fe⁰-zeolite and Fe⁰/C micro-electrolysis, and explore the mechanism and product analysis.This paper concluded that:â‘ The pH value has a lager influence on the remove nitrate in ground water by Fe⁰-zeolite and Fe⁰/C micro-electrolysis, and low pH is favorable for the denitrification of nitrate. Fe⁰-zeolit: the results show that when at the case of around 2.2 of pH value a 60% denitrification rate was achieved. The mix mixed structure of Fe/C bed: at the case of around 2.5 of pH value a 68% denitrification rate was achieved. The layer-lattice structure of Fe/C bed: at the case of around 2.5 of pH value a 68% denitrification rate was achieved.â‘¡The major product of the reaction is ammonium, only a little nitrate may be transformed to nitrite,the main of rest is nitrogen. The path way of nitrite transformation: Fe⁰+NO₃^-+2H+→Fe²⁺+H₂O+NO₂^-. The path way of ammonium transformation: Fe⁰+NO₃^-+10H⁺→4Fe²⁺+3H₂O+NH⁴⁺. The path way of nitrogen transformation: 10Fe⁰+6NO₃^-+3H₂O→5Fe₂O₃+3N₂+6OH^-. The zeolite has the good adsorbability to the ammonia nitrogen. The NO₃^-→NO₂^-→NH⁴⁺ is the key path way of chemical denitrification by Fe⁰.â‘¢The higher nitrate removal can be achieved by Fe⁰/C micro-electrolysis compare to Fe⁰-zeolite. In the research of nitrate remove from groundwater by Fe⁰/C micro-electrolysis,iron and carbon grain has two combinations. Compare to the mix mixed structure of Fe/C bed, it has lower denitrification rate by the layer-lattice structure of Fe/C bed, but it prevent the blocking up and harden of Fe/C and reducing scrap iron and carbon particles of change frequency, especially it avoided air rotating and Iron sludge pollution , reducing the costs.